Title of Invention	A PROCESS FOR NITRO-CARBURIZING AND OXIDIZING STEELS IN FLUIDIZED FURNACE, USING CO2/ CH4/ STEAM
Abstract	Conventional steel hardening processes are time consuming and agonizingly slow, requiring thereby larger capital outlay in plant machinery and equipment for a given output of hardened steels and higher overall costs of production. An improved process for gas-based nitro-carburizing of steels in fluidized bed furnace and for second-step-oxidation of the nitro-carburized components is disclosed. It significantly reduces production cycle time by 25% to 35%, allows optimization of fluidized bed furnace capacities and imparts additionally - as a part of the production cycle - chemical corrosion resistance properties to the nitro-carburized components. The process works by feeding in controlled quantities nitrogen or air, ammonia, a carbonaceous gas and steam.

Title of Invention

A PROCESS FOR NITRO-CARBURIZING AND OXIDIZING STEELS IN FLUIDIZED FURNACE, USING CO2/ CH4/ STEAM

Abstract

Conventional steel hardening processes are time consuming and agonizingly slow, requiring thereby larger capital outlay in plant machinery and equipment for a given output of hardened steels and higher overall costs of production. An improved process for gas-based nitro-carburizing of steels in fluidized bed furnace and for second-step-oxidation of the nitro-carburized components is disclosed. It significantly reduces production cycle time by 25% to 35%, allows optimization of fluidized bed furnace capacities and imparts additionally - as a part of the production cycle - chemical corrosion resistance properties to the nitro-carburized components. The process works by feeding in controlled quantities nitrogen or air, ammonia, a carbonaceous gas and steam.

Full Text	FORM 2 THE PATENT ACT 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10 and rule 13) 1. TITLE OF THE INVENTION : 'A gas-based process of nitro-carburizing and oxidation of steels in fluidized bed furnace' 2. APPLICANT (a) NAME: Nilesh Kashinath Pendharkar (b) NATIONALITY (c) ADDRESS: Indian 12 17, D-5, Royal Park Appartment, K.P. Kulkarni Road, Off. Apte Road, Near Gaurish Hotel, Pune - 411004, M.S. India 3. PREAMBLE TO THE DESCRIPTION COMPLETE SPECIFICATION The following specification particularly describes the invention and the manner in which it is to be performed ....2 1.0 Title of Invention A gas-based process of nitro-carburizing and oxidation of steels in fluidized bed furnace 2.0 Field of Invention: This invention relates to the metallurgical field, and more particularly to the field of hardening steel surfaces up to required depths in fluidized bed furnace and of performing in the same furnace the twin tasks of nitro-carburizing and oxidation of nitro-carburized steels by means of diffusion of ammonia, nitrogen or air, a carbonaceous gas and steam into steel surfaces. 3.0 Background of Invention 3.1 Since the invention of fluidized bed furnaces in late 1970s, no work has been reported on use of fluidized furnace for surface hardening of steels. Very few developments have taken place with regard to reducing long cycle times required of conventional furnaces from 8 hours for hardening surface of steel components/parts to a depth of 0.1 mm or of 46-50 hours for hardness depths of 0.5-0.6 mm. 3.2 There is no prior work of art in the field of steel nitro-carburizing in fluidized bed furnace. An earlier work of art in the Patent No. CN 2699302 by Arthur W. Whitaker pertains to only measuring ammonia decomposition rate and nitriding nitrogen potential in a conventional furnace. This earlier work is of different type, not covering therein fluidized bed furnace for nitro-carburizing of steels. 4.0 Object of the Invention 2 4.1 The primary object of this invention is to reduce substantially and by as much as 35% the conventionally required nitriding cycle time for high quality case hardening of steel components/parts, in a fluidized bed furnace, which facilitates efficient transmission of heat from heating source to steel surfaces. 4.2 Another important object of the present invention is to devise a process of nitro-carburizing steel components and the subsequent v oxidation using nitrogen/air, ammonia gas, a carbonaceous gas and for oxidation stream instead of using solid or liquid reactants. 4.3 Another significant object of the present invention is to additionally impart to the hardened steel surfaces corrosion resistance properties in the same fluidized bed furnace at a fraction of overall cost of production. 4.4 Another object of this invention is to strictly meet hardness specifications of end users in terms of core hardness, surface hardness and depth of compound and diffusion layer. 5.0 Summary of Invention This invention is a substantial improvement over the conventional nitriding furnaces and accomplishes the stated objects as illustrated in the ensuing complete specification and in the claims following the said complete specification. Not only are the hardness specifications strictly adhered to by the present invention in the reduced-time production cycle, the invention imparts to steels chemical corrosion resistance equivalent to withstanding exposure to salt spray for 100 to 500 hours at 5% Sodium Chloride Solution strength. 3 6.0 Description of Drawings Drawing # 1 illustrates cross sectional view of a fluidized bed Furnace. Drawing # 2 illustrates a cross sectional view of a superheated Steam boiler Drawing # 3 illustrates equipment and twin furnaces layout Drawing # 4 illustrates cross sectional and isometric views of a diffuser plate (11). 7.0 Description of the Invention 7.1 This invention relates to an improved gas-based nitro-carburizing process which is carried out in a fluidized bed furnace, as illustrated in the accompanying drawing # 1/4. 7.2 Fluidized bed furnace (10) is a cylindrical shell (15), with a circular cross section for its entire length. The said shell (15) is centrally fitted for entire length thereof with a retort (13). A metal diffuser plate (11) - as illustrated in the accompanying drawing # 4/4 - is lowered or raised to its operational position by means of a check nut (12) fixed to bottom end of the said diffuser plate (11). 7.3 The cylindrical retort (13) constructed of stainless steel 310 or of inconeP600 steel - which can withstand high temperatures and high thermal stresses resulting from sudden temperature fall and rise - is supported at its bottom end on the said diffuser plate (11). 4 The said retort (13) is made of a semi-circular dome (14) at its top end that is supported on the said shell (15). The said dome (14) has a central opening (16), which is connected to a vertical exhaust flue (17) to vent out unused feed gases and production waste gases. Coarse alumina (aluminium oxide) particles of 30 to 40 greet (19-A) are spread out in the form of a loose bed on the said diffuser plate (11), up to a level of 100 mm and above that fine alumina of 90 greet is spread as it is a good conductor of heat and efficiently serves as a heat transfer medium in conduction and convection of heat to feed gases and to steel components to be nitro-carburized. The said furnace charge is heated to temperature of 500°C -600°C by means of electrical coiled or strip heaters (18) that are fixed on the entire cylindrical surface of the said retort (13), covering thereby almost 3A height of the said submerged, lower region of the said retort (13) upward of the said diffuser plate (11). The said coarse alumina bed (19-A) supports a bed of 90 greet alumina (19), comprising of comparatively finer alumina particles that ensure efficient transfer of heat to the said feed gases and the said steel components. The said steel components lie supported on the said bed of coarse alumina (l*?^) while being completely submerged in the fluidized state of the said finer particles of 90 greet alumina (19). The central core - that is made of the said retort (13) and the said serial electrical heaters (18) - is insulated from the said shell (15) by a thick flexible layer of fiber glass insulation (20) to reduce heat losses by radiation to a minimum. 5 7.7 The furnace is dually supported from ground level by means of 4 no. floor mountings (21) and from production-platform level by means of 4 no. structural arms (22), secured to the said production shop floor level by means of fastners. 7.8 A bank of ammonia gas cylinders (25) is connected through ammonia gas pressure regulating valve (26) to feed low-pressure ammonia gas through ammonia feed pipe (27) to ammonia gas rotameter (28), as illustrated in the accompanying drawingJ 3/4. 7.9 A bank of LPG cylinder (30) is connected through LPG gas pressure regulator valve (31) to feed low-pressure LPG gas through feed pipe (32) to LPG gas rotameter (33), as shown in the accompanying drawing # 31 A. 7.10 A bank of compressed nitrogen gas cylinders (40) is connected through nitrogen gas pressure regulating valve (41) to feed low-pressure nitrogen gas through nitrogen gas feed pipe (42) to nitrogen gas rotameter (43). 7.11 The gas mixture of measured quantities of ammonia, carbonaceous gas (carbon dioxide or LPG or methane vapour) and nitrogen is led from gas mixer (80) through gas mixture feed pipe (45) and a non-return valve (46) while keeping a non return valve (47) closed - thereby bypassing boiler(50) - and is fed to the diffuser plate (11) of the furnace (10). For introducing steam, non-return valve (47) is opened. Line heaters (45, 45-A) are provided for pre-heating gas feed, if required. 6 7.12 The boiler (50) is a simple, low-pressure boiler that works on heating water by means of LPG gas stove (55), placed under cylindrical vertical shell (52) of the boiler or it can be heated electrically also (50). The boiler is filled to its 2/3"1 depth with waterAA thermo well (53) and water-level indicator (54) measure respectively temperature and level of the said water. The boiler (50) has at its top end a pressure indicator (56), a pressure release valve (57) and superheated steam laden nitrogen gas outlet pipe (58), as illustrated in the accompanying drawing # 2/ 7.13 The outlet pipe (58) of the boiler (50) feeds the said water vapour-saturated gas mixture through a non-return valve (59) to the retort (13) through the diffuser plate (11). 7.14 Alternatively, in place of compressed pressurised nitrogen gas from the said nitrogen cylinders liquid nitrogen from liquid nitrogen tank (60) through vaporizer is de-pressurized through pressure regulating valve (61), is led through a non-return valve (62), is again de-pressurized through pressure regulating valve (63) and is fed as low pressure nitrogen gas into the said nitrogen gas feed pipe (41), as illustrated in the accompanying drawing # 2/3. 7.15 An oil quenching tank or polymer quenching (64) is provided for cooling of hot components, removed from the said fluidized bed furnace (10) after nitro-carburizing and oxidation. 7.16 Alternatively, in place of the said low pressure nitrogen gas, low-pressure compressed air from compressor's (70) storage tank (71) is fed to the said gas mixer (80). 7 7.17 The diffuser plate (11) is comprised of a cylindrical shell (11-1), having a circular cross section, constructed of a stainless steel 310 plate of 8 mm thickness or higher into outer diameter of 430 mm and lateral length of 50 mm, as illustrated in the accompanying drawing # 4/4. The said shell (11-1) is closed at both ends by a welded plate (11-2) each for top and bottom ends. The said bottom welded plate of the shell (11-1) has centrally a hole of 100 mm diameter to which a 100 mm diameter stainless steel 310 pipe (11-3) of 450 mm length is welded vertically. The said pipe (11-3) is externally threaded for its entire length, has a hole of 50 mm diameter (11-4) at its bottom end, which is connected as gas inlet line to the outlet pipe (58) to introduce into the said retort (13) mixed gas feed for fluidizing fine alumina bed. A check nut (1% T) facilitates opening or closing of the retort (13). The shell (11-1) is fitted centrally with a stopper plate (11-6) of 120 mm diameter and of 6 mm thickness that is elevated on a pair of vertical supports (11-7, 11-8) to 40 mm vertical height from bottom end of the shell (11-1). The stopper plate (11-6) serves to divert flow of fluidizing gases equally to periphery of the diffuser plate (11). The top welded plate (11-2) has 10 no. holes (11-9) along the periphery of the said top plate (11-2) and 4 no. holes (11-10) along periphery of an inner concentric circle of 150 mm diameter, each hole being of 30 mm diameter and fitted by fasteners with a 150 mesh stainless steel 310 screen (11-11) of 3mm-4mm thickness to ensure plug-free entry of fluidizing mixed gases into alumina bed. The top welded plate (11-2) has a hook (11-12) centrally welded for lifting the said diffuser plate (11). 8 8.0 Operation of Invention 8.1 The present invention is operated by loading the said fluidized bed furnace (10) with 30-40 greet coarse alumina (19-A) that corresponds to a vertical height 100 mm of the said retort (13) over and above the 75 mm height of the said diffuser plate (11). 8.2 90 greet fine alumina (19) in a quantity that corresponds to a vertical height of 1275 mm approximately of the said retort (13) and weighing about 300 kg is charged together with components to be nitro-carburized and oxidized. Simultaneous charging of the two ensures that the components are completely submerged into the said fine alumina bed. 8.3 Electrical heaters of the rated output of 30-36 KW, after the said charging is complete, are switched on to heat the charge, whose temperature is continuously measured and indicated on the control panel (100). 8.4 The specific purpose of this invention is to diffuse nitrogen and carbon atoms so that the diffused atoms are filled in the interstitial spaces at the grain boundary matrix structure of the steel being hardened. As the static bed together with the charge of the steel components is heated to the minimum process temperature of 500°C - 630°C, a mixture of ammonia and nitrogen gases at the ambient temperature and in volumetric ratio of 35-65% to 65-35% respectively is introduced into the said fluidized bed furnace (10) from the bottom end in the overall volumetric flow rate of 7-10 normal cubic meters per hour by simultaneously opening the valve (26) for ammonia gas and the valve (63) for nitrogen gas till the respective measured quantity of each gas corresponds to the volumetric percentage for that gas in the mixture, as stated herein 9 above. The stabilized flow condition is maintained for the time period of the first 1- 8 hours from the time temperature of 500°C to 600°C is reached for a case nitro-carburizing depth of 0.1- 0.6 mm. Electrical heating is continued till the fluidized bed is heated to a temperature of 500°C to 600°C for the said nitro-carburizing case depth and maintained thereafter for the entire ammonia boosting or purging period of 1 to 8 hours. Under the volumetric conditions of the gas mixture and the bed temperature of 500 - 630°C, the bed of 90 greet alumina is fluidized around the charge of steel components such that each individual particle of 90 greet fine alumina randomly moves around the said charge of steel components within the circumferential confines of the steel retort, of the coarse alumina at bottom end and of the void at the upper end of the retort (13) of the furnace. The volumetric flow of the gas mixture is not allowed to exceed the stated value so as to prevent 'boiling over' of the fluidized bed. At the end of the said ammonia boosting period, the said gas mixture feed is altered to include a carbonaceous gas in the form of carbon dioxide or carbon monoxide or methanol vapor or methane gas or LPG gas or a combination of two or more than two of the said gases such that the volumetric percentage of the said carbonaceous gas is 5-10% of the resulting altered gas mixture at the ambient temperature without altering the stated operating volumetric ratio of the ammonia to nitrogen gases. The carbonaceous gas is introduced for a minimum time period of 4 hours. The end of the 4 hours period marks the end of the nitro- 10 carburizing cycle. Ammonia and LPG gas supplies are switched off by shutting respectively valves (26) and (31). Nitrogen gas alone is passed through the non-return valves (46) and (47) through the boiler (50) and is led out from the outlet pipe (58) and the non-return valve (59) into the furnace (10). Nitrogen gas exiting the boiler (50) carries superheated steam to the fluidized bed furnace at bed temperature 450°C to 600°C. 8.8 The said nitro-carburized steel components are oxidized by introducing nitrogen gas laden with superheated steam into the fluidized bed for maximum 2-20 minutes, after the production cycle has ended, as explained in paragraph 7.7 herein above. 8.9 The diffuser plate (11) is opened, after the charge of steel components is emptied out from the retort (13), the hot steel components are cooled by dipping them into the oil quenching tank (64) or in polymer quenching tank or in air and coarse alumina (19-A), fine alumina (19) are emptied out from the retort (13) on to the floor after cooling to ambient temperature, is sieved from the fine alumina (19) and both are readied for re-use, unless the said alumina is found to be contaminated by any foreign particles or steel oxide particles. 9.0 Best Method of Operation of Invention 9.1 The cylindrical shell (15) is constructed of 1350 mm diameter and 1750 mm height. The retort (13) is constructed of 450 mm diameter and 1800 mm height. 9.2 Electrical load in Kilowatt is computed by using the heat conduction formula as given below: {[(CW + [ FW) x 0.16] x (T1-T2) x 4 } / 3415 Where, CW =charge weight, kgs 11 FW = fixture weight, kgs Tl = charge temperature required, °C T2 = room temperature, °C 0.16 is the specific heat of steel 9.3 Ammonia boosting period is of maximum 8 hours for case depth of 0.1 mm 9.4 Carbonaceous gas is approximately 10% maximum of the volume of overall altered gas mixture and is passed for minimum of 4 hours. Nilesh Kasbtnatn Pendharkar Applicant 9.5 Operating temperature is 500°C to 600°C 9.6 Carbonaceous gas is LPG or methanol vapour or carbon dioxide or a combination of the three in the volumetric ratio of 1:1:1 12 9.0 Claims: I claim 1. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace, comprised of a bed of coarse alumina supporting a bed of fine alumina, the said bed of finer alumina capable of being fluidized by passage of gases having at ambient temperature a volumetric flow rate of 5-25 cubic meters per hour, the said process initially comprised of ammonia boosting at 500-600°C furnace temperature by passing a gas mixture of ammonia and nitrogen gases for 1-10 hours, followed by altering the said gas mixture composition by introducing at ambient temperature a carbonaceous gas for nitro-carburizing steel components for additional 4-30 hours and thereafter introducing for maximum 20 minutes superheated steam to the said altered gas mixture for oxidation of nitro-carburized steel and bringing to end production cycle of the said process, the said bed of finer alumina and of coarse alumina heated in static as well as in fluidized conditions by electrical heaters, the charge of the case hardened steel components after ending the said production cycle emptied together with the said coarse and fine alumina from bottom of the said fluidized bed furnace by opening a diffuser plate (11) by means of a check nut (12), the charge of the said steel components separately cooled to ambient temperature by quenching in an oil or in polymer or in air, the said emptied but coarse alumina and finer alumina after cooling to ambient temperature separated by sieving for re-use if found contaminated by oxide particles or foreign materials. 13 2. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1 wherein, the said gas mixture for the said ammonia boosting has at ambient temperature a volumetric composition of ammonia 35-65% and nitrogen 65-35%; 3. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 2 wherein, the said carbonaceous gas is carbon dioxide or liquefied propane gas (LPG) or methanol vapour or methane gas or a mixture of any two or more than two of the said constituents; 4. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1, 2 and 3 wherein, the volumetric percentage of the said carbonaceous gas at ambient temperature is 5-10% of the said altered gas mixture; 5. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein nitriding of steel components for case depths of 0.1 mm, 0.3 mm and 0.5-0.6 mm is carried out with the said altered gas mixture of ammonia, nitrogen and carbon dioxide/LPG/methanol vapour gases at the furnace temperature of 525-600 +/- 5°C for 4 hours, of 500-600 +/- 5°C for 12-15 hours and of 520-600 +/- 5°C for 24-30 hours respectively; or 530 to 590°C with similar process as above. 6. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein nitro-carburizing of steel components for case depth of 14 0.1-0.5 mm is carried out in presence of the said altered gas mixture of ammonia, nitrogen and LPG/carbon dioxide/methanol vapour gases at the furnace temperature of 530-630 degree C for 4-20 hours; 7. A process for ntriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 6 wherein, the said oxidation of the said nitro-carburized steel components is carried out at the furnace temperature of 430-570°C by introducing for maximum of 20 minutes superheated steam-laden nitrogen gas leaving the said boiler outlet pipe (58) and the said non-return valve (59) into the said fluidized bed furnace (10); 8. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 8, wherein only nitrogen gas, after shutting off supplies of ammonia and LPG gases, is led into steam boiler (50) through the said water-submerged line (51) to bubble through boiling water, to carry superheated steam therewith through the outlet pipe (58) and is fed to the fluidized bed furnace (10) for carrying out oxidation of the nitro-carburized cases of steel components; 9. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein pinion shaft and helical gears of AISI 4140 steel are nitrided by ammonia boosting for first 8 hours at the furnace temperature of 515-600 +/- 5 degree C with volumetric flow of nitrogen being 2.7-4.1 cubic metres/hour and of ammonia being 3.9-4.8 cubic metres/hour, then nitrided at the same temperature for the next additional 18 hours with the said altered 15 gas mixture of ammonia, nitrogen and carbon dioxide/LPG/methanol vapour mixture with carbonaceous gas volumetric flow rate being 0.5-0.7 cubic metres/hour and finally air- or oil-quenched to yield compound layer of 20-25 microns depth, diffusion of up to 0.56 mm depth, 32-34 HRC core hardness and surface hardness of 88-92 HR 15 N; then the surface is micro finished by adding lapping operation and material removal of 4 to 10 microns radically. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein gear components of EN 19 steel construction are nitrided by ammonia boosting for 1 hour at the furnace temperature of 500-600 +/- 5 degree C in presence of gases volumetrically having flow rate of nitrogen being 2-4 cubic metres/hour and ammonia being 3-4.5 cubic metres/hour and nitrided at the same temperature for the additional 13 hours with the said altered gas mixture of ammonia, nitrogen and the said carbonaceous gas with the said carbonaceous gas volumetrically measuring 0.5-0.7 cubic metres/hour to yield compound layer of 12-15 microns, diffusion up to 0.35-0.42 mm depth, core hardness of 30-33 HRC and surface hardness of 83-88 HR15N; A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein break pistons of EN9/AISI 4141/ AISI 1144 steel construction are nitro-carburized by firstly carrying out nitriding for first 2 hours at furnace temperature of 535-600 +/- 5 degree C, with the said gas mixture of ammonia, nitrogen being respectively 16 of volumetric flow rates of 3.9-4.8 cubic metres/hour and 2.7-4.1 cubic metres/hour, followed by nitro-carburizing for additional 14 hours in presence of the said flow rates of ammonia and nitrogen gases and of carbonaceous gas in volumetric flow rate of 0.5-0.7 cubic metres/hour, polymer or air- or oil-quenching the charge and micro finish the surface by introducing lapping operation, lastly oxidation for 20 minutes in presence of 1-3 cubic metres of nitrogen gas laden with superheated steam at the furnace temperature of 470 - 530 °C to yield compound layer depth of 15-22 microns, diffusion layer depth of 0.4-0.5 mm, core hardness 28-35 HRC, surface hardness 600 HV 0.2 kg load and oxidation layer of 1-3 microns depth; A process for nitnding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein sheet metal components of mild steel or CRCA or FE 410 or IS 226 construction is nitro-carburized by ammonia purging at furnace temperature of 580-630 degree C for 1 hour, followed by nitnding at the said temperature with 3.9-4.8 cubic metres/hour of ammonia and 2.7-4.1 cubic metres/hour of nitrogen gas for 1 hour, followed by nitro-carburizing at the same temperature in presence of the said gas mixture of ammonia, nitrogen and the said carbonaceous gas for 3-5 hours and oxidation thereof with superheated steam for 20 minutes and nitrogen flow rate of 1-3 cubic metres/hour at the furnace temperature of 470-530 degree C to yield compound layer of 24-34 microns, surface hardness of 400-700 HV 0.2 kg load and oxidation layer depth of 1-3 microns; 17 A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein idler shafts, pins, valve guides, pots, chambers and machine parts made of mild steel, EN 32B, EN 1A, EN 8, EN 9, CK 45, EN 19, EN 4IB, EN 24, SGI casting, SS 300 series construction are nitro-carburized by ammonia purging for 1 hour at furnace temperature of 525-610 degree C, followed by nitriding at the same temperature in presence of 3.9-4.8 cubic metres/hour of ammonia gas and 2.7-4.1 cubic metres/hour of nitrogen gas for 1 hour, followed by nitro-carburization at the same temperature in presence of the said ammonia, nitrogen flow rates and the said carbonaceous gas of volumetric flow rate of 0.5-0.7 cubic metres/hour for additional 3-14 hours and polymer or air- or oil-quenching to yield white layer of depth of 15-25 microns, diffusion layer of 0.1-0.5 mm depth, core hardness 28-35 HRC, surface hardness 300-1000 HV 0.2 kg load; A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace substantially described herein above and illustrated in the accompanying drawings # 1 to 4. Date : 29th November, 2006 Nilesh Kashinath Pendharkar Applicant 18 Abstract Drawings: 4 A gas-based process of nitro-carburizing and oxidation of steels in fluidized bed furnace Conventional steel hardening processes are time consuming and agonizingly slow, requiring thereby larger capital outlay in plant machinery and equipment for a given output of hardened steels and higher overall costs of production. An improved process for gas-based nitro-carburizing of steels in fluidized bed furnace and for second-step-oxidation of the nitro-carburized components is disclosed. It significantly reduces production cycle time by 25% to 35%, allows optimization of fluidized bed furnace capacities and imparts additionally - as a part of the production cycle - chemical corrosion resistance properties to the nitro-carburized components. The process works by feeding in controlled quantities nitrogen or air, ammonia, a carbonaceous gas and steam. Nilesh Kashinath Pendharkar Applicant 23

Full Text

FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. TITLE OF THE INVENTION :

'A gas-based process of nitro-carburizing and oxidation of steels in fluidized bed furnace'

2. APPLICANT

(a) NAME:

Nilesh Kashinath Pendharkar

(b) NATIONALITY
(c) ADDRESS:

Indian
12 17, D-5, Royal Park Appartment, K.P. Kulkarni Road, Off. Apte Road, Near Gaurish Hotel, Pune - 411004, M.S. India

3. PREAMBLE TO THE DESCRIPTION
COMPLETE SPECIFICATION The following specification
particularly describes the invention
and the manner in which it is to be
performed
....2

1.0 Title of Invention
A gas-based process of nitro-carburizing and oxidation of steels in
fluidized bed furnace
2.0 Field of Invention:
This invention relates to the metallurgical field, and more particularly to the field of hardening steel surfaces up to required depths in fluidized bed furnace and of performing in the same furnace the twin tasks of nitro-carburizing and oxidation of nitro-carburized steels by means of diffusion of ammonia, nitrogen or air, a carbonaceous gas and steam into steel surfaces.
3.0 Background of Invention
3.1 Since the invention of fluidized bed furnaces in late 1970s, no work has been reported on use of fluidized furnace for surface hardening of steels. Very few developments have taken place with regard to reducing long cycle times required of conventional furnaces from 8 hours for hardening surface of steel components/parts to a depth of 0.1 mm or of 46-50 hours for hardness depths of 0.5-0.6 mm.
3.2 There is no prior work of art in the field of steel nitro-carburizing in fluidized bed furnace. An earlier work of art in the Patent No. CN 2699302 by Arthur W. Whitaker pertains to only measuring ammonia decomposition rate and nitriding nitrogen potential in a conventional furnace. This earlier work is of different type, not covering therein fluidized bed furnace for nitro-carburizing of steels.
4.0 Object of the Invention
2

4.1 The primary object of this invention is to reduce substantially and by as much as 35% the conventionally required nitriding cycle time for high quality case hardening of steel components/parts, in a fluidized bed furnace, which facilitates efficient transmission of heat from heating source to steel surfaces.
4.2 Another important object of the present invention is to devise a process of nitro-carburizing steel components and the subsequent
v
oxidation using nitrogen/air, ammonia gas, a carbonaceous gas and for oxidation stream instead of using solid or liquid reactants.
4.3 Another significant object of the present invention is to additionally impart to the hardened steel surfaces corrosion resistance properties in the same fluidized bed furnace at a fraction of overall cost of production.
4.4 Another object of this invention is to strictly meet hardness specifications of end users in terms of core hardness, surface hardness and depth of compound and diffusion layer.
5.0 Summary of Invention
This invention is a substantial improvement over the conventional nitriding furnaces and accomplishes the stated objects as illustrated in the ensuing complete specification and in the claims following the said complete specification. Not only are the hardness specifications strictly adhered to by the present invention in the reduced-time production cycle, the invention imparts to steels chemical corrosion resistance equivalent to withstanding exposure to salt spray for 100 to 500 hours at 5% Sodium Chloride Solution strength.
3

6.0 Description of Drawings
Drawing # 1 illustrates cross sectional view of a fluidized bed
Furnace. Drawing # 2 illustrates a cross sectional view of a superheated
Steam boiler Drawing # 3 illustrates equipment and twin furnaces layout Drawing # 4 illustrates cross sectional and isometric views of a
diffuser plate (11).
7.0 Description of the Invention
7.1 This invention relates to an improved gas-based nitro-carburizing process which is carried out in a fluidized bed furnace, as illustrated in the accompanying drawing # 1/4.
7.2 Fluidized bed furnace (10) is a cylindrical shell (15), with a circular cross section for its entire length. The said shell (15) is centrally fitted for entire length thereof with a retort (13). A metal diffuser plate (11) - as illustrated in the accompanying drawing # 4/4 - is lowered or raised to its operational position by means of a check nut (12) fixed to bottom end of the said diffuser plate (11).
7.3 The cylindrical retort (13) constructed of stainless steel 310 or of inconeP600 steel - which can withstand high temperatures and high thermal stresses resulting from sudden temperature fall and rise - is supported at its bottom end on the said diffuser plate (11).
4

The said retort (13) is made of a semi-circular dome (14) at its top end that is supported on the said shell (15). The said dome (14) has a central opening (16), which is connected to a vertical exhaust flue (17) to vent out unused feed gases and production waste gases.
Coarse alumina (aluminium oxide) particles of 30 to 40 greet (19-A) are spread out in the form of a loose bed on the said diffuser plate (11), up to a level of 100 mm and above that fine alumina of 90 greet is spread as it is a good conductor of heat and efficiently serves as a heat transfer medium in conduction and convection of heat to feed gases and to steel components to be nitro-carburized. The said furnace charge is heated to temperature of 500°C -600°C by means of electrical coiled or strip heaters (18) that are fixed on the entire cylindrical surface of the said retort (13), covering thereby almost 3A height of the said submerged, lower region of the said retort (13) upward of the said diffuser plate (11).
The said coarse alumina bed (19-A) supports a bed of 90 greet alumina (19), comprising of comparatively finer alumina particles that ensure efficient transfer of heat to the said feed gases and the said steel components. The said steel components lie supported on the said bed of coarse alumina (l*?^) while being completely submerged in the fluidized state of the said finer particles of 90 greet alumina (19).
The central core - that is made of the said retort (13) and the said serial electrical heaters (18) - is insulated from the said shell (15) by a thick flexible layer of fiber glass insulation (20) to reduce heat losses by radiation to a minimum.
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7.7 The furnace is dually supported from ground level by means of 4 no. floor mountings (21) and from production-platform level by means of 4 no. structural arms (22), secured to the said production shop floor level by means of fastners.
7.8 A bank of ammonia gas cylinders (25) is connected through ammonia gas pressure regulating valve (26) to feed low-pressure ammonia gas through ammonia feed pipe (27) to ammonia gas rotameter (28), as illustrated in the accompanying drawingJ 3/4.
7.9 A bank of LPG cylinder (30) is connected through LPG gas pressure regulator valve (31) to feed low-pressure LPG gas through feed pipe (32) to LPG gas rotameter (33), as shown in the accompanying drawing # 31 A.
7.10 A bank of compressed nitrogen gas cylinders (40) is connected through nitrogen gas pressure regulating valve (41) to feed low-pressure nitrogen gas through nitrogen gas feed pipe (42) to nitrogen gas rotameter (43).
7.11 The gas mixture of measured quantities of ammonia, carbonaceous gas (carbon dioxide or LPG or methane vapour) and nitrogen is led from gas mixer (80) through gas mixture feed pipe (45) and a non-return valve (46) while keeping a non return valve (47) closed - thereby bypassing boiler(50) - and is fed to the diffuser plate (11) of the furnace (10). For introducing steam, non-return valve (47) is opened. Line heaters (45, 45-A) are provided for pre-heating gas feed, if required.
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7.12 The boiler (50) is a simple, low-pressure boiler that works on heating water by means of LPG gas stove (55), placed under cylindrical vertical shell (52) of the boiler or it can be heated electrically also (50). The boiler is filled to its 2/3"1 depth with waterAA thermo well (53) and water-level indicator (54) measure respectively temperature and level of the said water. The boiler (50) has at its top end a pressure indicator (56), a pressure release valve (57) and superheated steam laden nitrogen gas outlet pipe (58), as illustrated in the accompanying drawing # 2/ 7.13 The outlet pipe (58) of the boiler (50) feeds the said water vapour-saturated gas mixture through a non-return valve (59) to the retort (13) through the diffuser plate (11).
7.14 Alternatively, in place of compressed pressurised nitrogen gas from the said nitrogen cylinders liquid nitrogen from liquid nitrogen tank (60) through vaporizer is de-pressurized through pressure regulating valve (61), is led through a non-return valve (62), is again de-pressurized through pressure regulating valve (63) and is fed as low pressure nitrogen gas into the said nitrogen gas feed pipe (41), as illustrated in the accompanying drawing # 2/3.
7.15 An oil quenching tank or polymer quenching (64) is provided for cooling of hot components, removed from the said fluidized bed furnace (10) after nitro-carburizing and oxidation.
7.16 Alternatively, in place of the said low pressure nitrogen gas, low-pressure compressed air from compressor's (70) storage tank (71) is fed to the said gas mixer (80).
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7.17 The diffuser plate (11) is comprised of a cylindrical shell (11-1), having a circular cross section, constructed of a stainless steel 310 plate of 8 mm thickness or higher into outer diameter of 430 mm and lateral length of 50 mm, as illustrated in the accompanying drawing # 4/4. The said shell (11-1) is closed at both ends by a welded plate (11-2) each for top and bottom ends. The said bottom welded plate of the shell (11-1) has centrally a hole of 100 mm diameter to which a 100 mm diameter stainless steel 310 pipe (11-3) of 450 mm length is welded vertically. The said pipe (11-3) is externally threaded for its entire length, has a hole of 50 mm diameter (11-4) at its bottom end, which is connected as gas inlet line to the outlet pipe (58) to introduce into the said retort (13) mixed gas feed for fluidizing fine alumina bed. A check nut (1% T) facilitates opening or closing of the retort (13). The shell (11-1) is fitted centrally with a stopper plate (11-6) of 120 mm diameter and of 6 mm thickness that is elevated on a pair of vertical supports (11-7, 11-8) to 40 mm vertical height from bottom end of the shell (11-1). The stopper plate (11-6) serves to divert flow of fluidizing gases equally to periphery of the diffuser plate (11). The top welded plate (11-2) has 10 no. holes (11-9) along the periphery of the said top plate (11-2) and 4 no. holes (11-10) along periphery of an inner concentric circle of 150 mm diameter, each hole being of 30 mm diameter and fitted by fasteners with a 150 mesh stainless steel 310 screen (11-11) of 3mm-4mm thickness to ensure plug-free entry of fluidizing mixed gases into alumina bed. The top welded plate (11-2) has a hook (11-12) centrally welded for lifting the said diffuser plate (11).
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8.0 Operation of Invention
8.1 The present invention is operated by loading the said fluidized bed furnace (10) with 30-40 greet coarse alumina (19-A) that corresponds to a vertical height 100 mm of the said retort (13) over and above the 75 mm height of the said diffuser plate (11).
8.2 90 greet fine alumina (19) in a quantity that corresponds to a vertical height of 1275 mm approximately of the said retort (13) and weighing about 300 kg is charged together with components to be nitro-carburized and oxidized. Simultaneous charging of the two ensures that the components are completely submerged into the said fine alumina bed.
8.3 Electrical heaters of the rated output of 30-36 KW, after the said
charging is complete, are switched on to heat the charge, whose temperature is continuously measured and indicated on the control panel (100).
8.4 The specific purpose of this invention is to diffuse nitrogen and
carbon atoms so that the diffused atoms are filled in the interstitial
spaces at the grain boundary matrix structure of the steel being
hardened. As the static bed together with the charge of the steel
components is heated to the minimum process temperature of
500°C - 630°C, a mixture of ammonia and nitrogen gases at the
ambient temperature and in volumetric ratio of 35-65% to 65-35%
respectively is introduced into the said fluidized bed furnace (10)
from the bottom end in the overall volumetric flow rate of 7-10
normal cubic meters per hour by simultaneously opening the
valve (26) for ammonia gas and the valve (63) for nitrogen gas till
the respective measured quantity of each gas corresponds to the
volumetric percentage for that gas in the mixture, as stated herein
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above. The stabilized flow condition is maintained for the time period of the first 1- 8 hours from the time temperature of 500°C to 600°C is reached for a case nitro-carburizing depth of 0.1- 0.6 mm.
Electrical heating is continued till the fluidized bed is heated to a temperature of 500°C to 600°C for the said nitro-carburizing case depth and maintained thereafter for the entire ammonia boosting or purging period of 1 to 8 hours.
Under the volumetric conditions of the gas mixture and the bed temperature of 500 - 630°C, the bed of 90 greet alumina is fluidized around the charge of steel components such that each individual particle of 90 greet fine alumina randomly moves around the said charge of steel components within the circumferential confines of the steel retort, of the coarse alumina at bottom end and of the void at the upper end of the retort (13) of the furnace. The volumetric flow of the gas mixture is not allowed to exceed the stated value so as to prevent 'boiling over' of the fluidized bed.
At the end of the said ammonia boosting period, the said gas mixture feed is altered to include a carbonaceous gas in the form of carbon dioxide or carbon monoxide or methanol vapor or methane gas or LPG gas or a combination of two or more than two of the said gases such that the volumetric percentage of the said carbonaceous gas is 5-10% of the resulting altered gas mixture at the ambient temperature without altering the stated operating volumetric ratio of the ammonia to nitrogen gases. The carbonaceous gas is introduced for a minimum time period of 4 hours. The end of the 4 hours period marks the end of the nitro-
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carburizing cycle. Ammonia and LPG gas supplies are switched off by shutting respectively valves (26) and (31). Nitrogen gas alone is passed through the non-return valves (46) and (47) through the boiler (50) and is led out from the outlet pipe (58) and the non-return valve (59) into the furnace (10). Nitrogen gas exiting the boiler (50) carries superheated steam to the fluidized bed furnace at bed temperature 450°C to 600°C.
8.8 The said nitro-carburized steel components are oxidized by introducing nitrogen gas laden with superheated steam into the fluidized bed for maximum 2-20 minutes, after the production cycle has ended, as explained in paragraph 7.7 herein above.
8.9 The diffuser plate (11) is opened, after the charge of steel components is emptied out from the retort (13), the hot steel components are cooled by dipping them into the oil quenching tank (64) or in polymer quenching tank or in air and coarse alumina (19-A), fine alumina (19) are emptied out from the retort (13) on to the floor after cooling to ambient temperature, is sieved from the fine alumina (19) and both are readied for re-use, unless the said alumina is found to be contaminated by any foreign particles or steel oxide particles.

9.0 Best Method of Operation of Invention
9.1 The cylindrical shell (15) is constructed of 1350 mm diameter and 1750 mm height. The retort (13) is constructed of 450 mm diameter and 1800 mm height.
9.2 Electrical load in Kilowatt is computed by using the heat conduction formula as given below:
{[(CW + [ FW) x 0.16] x (T1-T2) x 4 } / 3415 Where, CW =charge weight, kgs
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FW = fixture weight, kgs Tl = charge temperature required, °C T2 = room temperature, °C 0.16 is the specific heat of steel
9.3 Ammonia boosting period is of maximum 8 hours for case depth of 0.1 mm
9.4 Carbonaceous gas is approximately 10% maximum of the volume of overall altered gas mixture and is passed for minimum of 4 hours.
Nilesh Kasbtnatn Pendharkar Applicant
9.5 Operating temperature is 500°C to 600°C
9.6 Carbonaceous gas is LPG or methanol vapour or carbon dioxide or a combination of the three in the volumetric ratio of 1:1:1
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9.0 Claims:
I claim
1. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace, comprised of a bed of coarse alumina supporting a bed of fine alumina, the said bed of finer alumina capable of being fluidized by passage of gases having at ambient temperature a volumetric flow rate of 5-25 cubic meters per hour, the said process initially comprised of ammonia boosting at 500-600°C furnace temperature by passing a gas mixture of ammonia and nitrogen gases for 1-10 hours, followed by altering the said gas mixture composition by introducing at ambient temperature a carbonaceous gas for nitro-carburizing steel components for additional 4-30 hours and thereafter introducing for maximum 20 minutes superheated steam to the said altered gas mixture for oxidation of nitro-carburized steel and bringing to end production cycle of the said process, the said bed of finer alumina and of coarse alumina heated in static as well as in fluidized conditions by electrical heaters, the charge of the case hardened steel components after ending the said production cycle emptied together with the said coarse and fine alumina from bottom of the said fluidized bed furnace by opening a diffuser plate (11) by means of a check nut (12), the charge of the said steel components separately cooled to ambient temperature by quenching in an oil or in polymer or in air, the said emptied but coarse alumina and finer alumina after cooling to ambient temperature separated by sieving for re-use if found contaminated by oxide particles or foreign materials.
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2. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1 wherein, the said gas mixture for the said ammonia boosting has at ambient temperature a volumetric composition of ammonia 35-65% and nitrogen 65-35%;
3. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 2 wherein, the said carbonaceous gas is carbon dioxide or liquefied propane gas (LPG) or methanol vapour or methane gas or a mixture of any two or more than two of the said constituents;
4. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1, 2 and 3 wherein, the volumetric percentage of the said carbonaceous gas at ambient temperature is 5-10% of the said altered gas mixture;
5. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein nitriding of steel components for case depths of 0.1 mm, 0.3 mm and 0.5-0.6 mm is carried out with the said altered gas mixture of ammonia, nitrogen and carbon dioxide/LPG/methanol vapour gases at the furnace temperature of 525-600 +/- 5°C for 4 hours, of 500-600 +/- 5°C for 12-15 hours and of 520-600 +/- 5°C for 24-30 hours respectively; or 530 to 590°C with similar process as above.
6. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein nitro-carburizing of steel components for case depth of
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0.1-0.5 mm is carried out in presence of the said altered gas mixture of ammonia, nitrogen and LPG/carbon dioxide/methanol vapour gases at the furnace temperature of 530-630 degree C for 4-20 hours;
7. A process for ntriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 6 wherein, the said oxidation of the said nitro-carburized steel components is carried out at the furnace temperature of 430-570°C by introducing for maximum of 20 minutes superheated steam-laden nitrogen gas leaving the said boiler outlet pipe (58) and the said non-return valve (59) into the said fluidized bed furnace (10);
8. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claims 1 and 8, wherein only nitrogen gas, after shutting off supplies of ammonia and LPG gases, is led into steam boiler (50) through the said water-submerged line (51) to bubble through boiling water, to carry superheated steam therewith through the outlet pipe (58) and is fed to the fluidized bed furnace (10) for carrying out oxidation of the nitro-carburized cases of steel components;
9. A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein pinion shaft and helical gears of AISI 4140 steel are nitrided by ammonia boosting for first 8 hours at the furnace temperature of 515-600 +/- 5 degree C with volumetric flow of nitrogen being 2.7-4.1 cubic metres/hour and of ammonia being 3.9-4.8 cubic metres/hour, then nitrided at the same temperature for the next additional 18 hours with the said altered
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gas mixture of ammonia, nitrogen and carbon dioxide/LPG/methanol vapour mixture with carbonaceous gas volumetric flow rate being 0.5-0.7 cubic metres/hour and finally air- or oil-quenched to yield compound layer of 20-25 microns depth, diffusion of up to 0.56 mm depth, 32-34 HRC core hardness and surface hardness of 88-92 HR 15 N; then the surface is micro finished by adding lapping operation and material removal of 4 to 10 microns radically.
A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein gear components of EN 19 steel construction are nitrided by ammonia boosting for 1 hour at the furnace temperature of 500-600 +/- 5 degree C in presence of gases volumetrically having flow rate of nitrogen being 2-4 cubic metres/hour and ammonia being 3-4.5 cubic metres/hour and nitrided at the same temperature for the additional 13 hours with the said altered gas mixture of ammonia, nitrogen and the said carbonaceous gas with the said carbonaceous gas volumetrically measuring 0.5-0.7 cubic metres/hour to yield compound layer of 12-15 microns, diffusion up to 0.35-0.42 mm depth, core hardness of 30-33 HRC and surface hardness of 83-88 HR15N;
A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein break pistons of EN9/AISI 4141/ AISI 1144 steel construction are nitro-carburized by firstly carrying out nitriding for first 2 hours at furnace temperature of 535-600 +/- 5 degree C, with the said gas mixture of ammonia, nitrogen being respectively
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of volumetric flow rates of 3.9-4.8 cubic metres/hour and 2.7-4.1 cubic metres/hour, followed by nitro-carburizing for additional 14 hours in presence of the said flow rates of ammonia and nitrogen gases and of carbonaceous gas in volumetric flow rate of 0.5-0.7 cubic metres/hour, polymer or air- or oil-quenching the charge and micro finish the surface by introducing lapping operation, lastly oxidation for 20 minutes in presence of 1-3 cubic metres of nitrogen gas laden with superheated steam at the furnace temperature of 470 - 530 °C to yield compound layer depth of 15-22 microns, diffusion layer depth of 0.4-0.5 mm, core hardness 28-35 HRC, surface hardness 600 HV 0.2 kg load and oxidation layer of 1-3 microns depth;
A process for nitnding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein sheet metal components of mild steel or CRCA or FE 410 or IS 226 construction is nitro-carburized by ammonia purging at furnace temperature of 580-630 degree C for 1 hour, followed by nitnding at the said temperature with 3.9-4.8 cubic metres/hour of ammonia and 2.7-4.1 cubic metres/hour of nitrogen gas for 1 hour, followed by nitro-carburizing at the same temperature in presence of the said gas mixture of ammonia, nitrogen and the said carbonaceous gas for 3-5 hours and oxidation thereof with superheated steam for 20 minutes and nitrogen flow rate of 1-3 cubic metres/hour at the furnace temperature of 470-530 degree C to yield compound layer of 24-34 microns, surface hardness of 400-700 HV 0.2 kg load and oxidation layer depth of 1-3 microns;
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A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace according to claim 1, wherein idler shafts, pins, valve guides, pots, chambers and machine parts made of mild steel, EN 32B, EN 1A, EN 8, EN 9, CK 45, EN 19, EN 4IB, EN 24, SGI casting, SS 300 series construction are nitro-carburized by ammonia purging for 1 hour at furnace temperature of 525-610 degree C, followed by nitriding at the same temperature in presence of 3.9-4.8 cubic metres/hour of ammonia gas and 2.7-4.1 cubic metres/hour of nitrogen gas for 1 hour, followed by nitro-carburization at the same temperature in presence of the said ammonia, nitrogen flow rates and the said carbonaceous gas of volumetric flow rate of 0.5-0.7 cubic metres/hour for additional 3-14 hours and polymer or air- or oil-quenching to yield white layer of depth of 15-25 microns, diffusion layer of 0.1-0.5 mm depth, core hardness 28-35 HRC, surface hardness 300-1000 HV 0.2 kg load;
A process for nitriding or nitro-carburizing and oxidation of nitro-carburized steels in a fluidized bed furnace substantially described herein above and illustrated in the accompanying drawings # 1 to 4.
Date : 29th November, 2006
Nilesh Kashinath Pendharkar Applicant
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Abstract
Drawings: 4
A gas-based process of nitro-carburizing and oxidation of steels in fluidized bed furnace

Conventional steel hardening processes are time consuming and agonizingly slow, requiring thereby larger capital outlay in plant machinery and equipment for a given output of hardened steels and higher overall costs of production. An improved process for gas-based nitro-carburizing of steels in fluidized bed furnace and for second-step-oxidation of the nitro-carburized components is disclosed. It significantly reduces production cycle time by 25% to 35%, allows optimization of fluidized bed furnace capacities and imparts additionally - as a part of the production cycle - chemical corrosion resistance properties to the nitro-carburized components. The process works by feeding in controlled quantities nitrogen or air, ammonia, a carbonaceous gas and steam.
Nilesh Kashinath Pendharkar Applicant
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A PROCESS FOR NITRO-CARBURIZING AND OXIDIZING STEELS IN FLUIDIZED FURNACE, USING CO2/ CH4/ STEAM

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PCT Conventions: