Title of Invention

AN IMPROVED MICRO ALLOYED CAST STEEL RAIL WHEEL AND THE PROCESS OF MANUFACTURING THEREOF

Abstract

The present invention relates to an improved rail wheel alloy using micro-alloying with vanadium 0.10- 0.20% and molybdenum 0.05-0.20% in a medium carbon steel casting. The usage of the process is for the manufacture of wheels having better properties for locomotives, freight wagons and passenger carriages. Micro-alloying with vanadium and molybdenum vastly improves mechanical properties, provides adequate wear resistance and resistance to thermo mechanical cracking compared to plain carbon steel wheel castings. Hitherto, locomotives were using forged wheels since plain carbon cast wheels could not meet the requirement of rigorous properties. Micro alloyed cast steel with improved properties is able to meet the requirement of locomotive wheels and have been approved for use in the Indian Railways. Micro alloyed cast steel wheels would also be more cost effective as compared to forged wheels due to its inherent process. It eliminates costly operations of forged and rolled wheels like rolling, forging and machining.

Full Text

This invention relates to a railwheel alloy and process of manufacturing the same and in particular to a process of micro-alloying with vanadium and molybdenum for manufacturing an improved micro alloyed cast steel rail wheel. Railwheels are connected through an axle and are mounted as a wheel pair at opposite ends of the axle of railcars, railcoaches, railwagons or locomotives for movement over the rails. For the purpose of braking, brake shoes of cast iron or any other suitable material are fitted over the wheel tread which when pressed against the wheel, causes friction which absorbs the Kinetic energy , thereby bringing the vehicle to a halt. Both rolling load running over the rail as well as braking process generates heat and the life of the railwheel is determined by the frictional wear as well as the thermal fatigue cracks which are produced on the tread of the wheels. The present invention of railwheel produced by micro-alloying process improves both frictional wear properties as well as the properties to resist thermal crack and thus improve the life of the railwheel. The conventional method of manufacture of wheels is through forging route. The method consists of using rolled steel ingots, forging of wheels and then machining to the required finished shape with built up tyres. The present day technology seeks to overcome the disadvantages of built up tyres by replacing them with monoblock solid wheels. Even the monoblock solid wheels produced by forging or rolling have limitations of the process. The process is unable to produce all the contours as well as parabolic dish design in order to eliminate stress concentrations and provide better strength-to-weight ratio. Cast steel wheels overcome these disadvantages and are ideally suited for optimum design of rail wheels. Reference may be made to "Indian patent 1666/m 98-steel railway wheel" which describes the steel railway wheel produced by casting, forging or rolling from the design point of view and does not dwell upon the chemistry of the alloy, specially micro alloying, which Is the crux of the present invention. Further "237/m/2002 US Patent 2003/0190251" deals with high strength micro-alloy steel and process for making the same. US Patent 23,4576655 deals with wrought material and not cast material as in the present case. US Patent 2002 / 0048529 AL describes grain refined austenitic manganese steel casting having micro additions of vanadium and titanium and its method of manufacture. This is different from the present invention, which includes both vanadium and molybdenum as a micro alloying agent and the applications are different (giving different loading conditions) which results in more wear than rolling friction. US Patent No. US 200201812 (A1) deals with a steel alloy casting for railwheel using chromium and molybdenum. This is different from the present invention since it does not deal with addition of molybdenum and vanadium. US Patent No.420/104 deals with railwheel casting alloy using Nickel and Chromium as micro alloying elements. It is different from the present invention since it does not include molybdenum and vanadium. Other railwheel castings which are used in the railroad application such as the one manufactured at Railwheel Factory, Bangalore, India, are made of plain carbon steel and not micro-alloyed steel and therefore have the property which can meet the application of rail coaches or wagons but not those required for locomotives where the loading patterns are much higher. Present invention aims to develop such properties through micro alloying with vanadium and molybdenum in order to meet the requirements for locomotive applications. Summary of invention: Accordingly, present invention comprises of an improved micro alloyed cast steel rail wheel essentially comprising of composition in weight percentage of - C>0.50-0.60, Mn 0.70 - 0.80, Si 0.32-0.57 P 0.030(max) S 0.030(max), with balance essentially iron, wherein micro-alloying elements such as Mo 0.05 - 0.20 in order to improve hardenability and high temperature strength and V 0.10 - 0.20 in order to get grain refinement and higher wear resistance have been added. Another invention comprises of the process of manufacturing an improved micro alloyed cast steel rail wheel wherein Ferro Molybdenum and Ferro Vanadium are charged to the ladle at a specified temperature of 1690 -1700° C and subsequently casting and heat treatment process is effected. The main object of the invention is to produce an improved micro alloyed cast steel rail wheel which will have better properties such as yield stress, percentage elongation, reduction of area, hardness, impact property and fracture toughness, than the presently used plain carbon steel wheel. Another object of the invention is to produce an improved micro alloyed cast steel rail wheel which will have a better wear resistance and consequent longer life. Still another object of the invention is to produce an improved micro alloyed cast steel rail wheel which will have improved resistance to thermal cracks and thus improved reliability, safety and service life. Yet another object of the invention is to produce an improved micro alloyed cast steel rail wheel that will be able to meet the requirements of locomotives which presently use forged wheels. Accordingly the invention provides for an improved micro alloyed cast steel rail wheel comprising of composition in weight percentage of C:0.50-0.60, Mn:0.70-0.80,Si:0.32-0.57,P:0.030(max),S:0.030(max) wherein it comprises micro alloying elements such as Mo:0.05-0.20, V: 0.10- 0.20 with balance iron and incidental impurities. Accordingly the invention provides for the process of manufacturing of the improved micro alloyed cast steel rail wheel wherein ferro molybdenum and ferro vanadium are charged to the ladle containing molten steel at a specified temperature of 1690 - 1700 °C and subsequently the wheels are cast and heat treated. The process of this invention, the manufacturing of an improved miao alloyed cast steel rail wheel broadly comprises of the following steps: 1. Steel making Electric arc furnace is used for melting and refining of steel from a charge of selected return scrap. Tapping is done at 1690-1700°C. Killing and micro alloying are done in the ladle. Low sulphur calcined lime and graphite are used as flux and carbon raiser respectively. High purity ferrosilicon, ferromanganese and aluminium are used for killing while ferro-vanadium and ferro-molybdenum are used for micro alloying. Optical emission spectroscopy is used for control of chemistry. Micro alloyed wheel thus prepared comprises of incidental impurities of trace elements like copper( Casting Precision machined and fused silica coated graphite moulds are employed for casting. As known in art controlled pressure casting method is used for manufacturing the improved micro alloyed cast steel rail wheel. Ladle containing liquid steel is kept in a refractory- lined flask equipment, is covered airtight by a cover. The cover is fitted with a preheated ceramic cylindrical tube and immersed in the liquid metal. The graphite mould assembly, machined to form the wheel cavity is placed over the ceramic tube. Air pressure of 30 - 40 Psi is applied over the liquid steel in the ladle. This causes the molten metal to raise through the ceramic tube and fill the mould cavity at a controlled rate of 1.25 to 2.25 seconds / Psi. When the mould is filled, the pressure is released by the help of a sensor. Simultaneously the run back of the liquid metal in to the ladle is arrested by plunging down a clay graphite stopper. The mould is moved over the conveyor and allowed to solidify the wheel. The mould assembly is parted and the wheel is sent to a refractory lined tunnel for facilitating controlled cooling. 3. Heat Treatment Normalising, rim quenching and tempering are the heat treatment schedule taking care of the physical properties of the casting. Normalising is carried out in Rotary Hearth Furnace at 900 - 960o C for 90-120 minutes. The rim of the normalized wheel is water spray quenched above 800 - 850° C for 5-6 minutes cycle time to impart circumferential compressive stresses and required depth of hardness on the rim section. Rim quenching does not exceed the critical cooling rate due to mass effect. Wheels are subjected to tempering at 550 -600° C for 120-150 minutes and hub cooled with water spray for 90 to 120 seconds. Wheel castings are then air cooled. 4. Cleaning and Inspection Wheels are cleaned by shot blasting followed by non-destructive inspection for internal and surface defects. Samples are periodically cut up for mechanical tests like ultimate tensile strength, yield stress, hardness, reduction in area and metallurgical properties like microstructure, inclusions and grain size. Closure test for residual stress measurement is also carried out periodically. In another embodiment, melting and refining is in a vacuum induction furnace. In still another embodiment is different sizes of wheels for wagons, coaches and locomotives. In one more embodiment is casting in a bottom pouring system. In order to confirm the effect of invention the improved micro alloyed cast steel rail wheels thus produced were evaluated with following tests and the test results are appended herewith as examples. EXAMPLE 1 In order to establish the design validation of changed composition of the wheel, tests based on the Association of American Railroads (AAR) currently used standards S660 "Procedure for the Analytical Evaluation of Locomotive and Freight Car Wheel Designs" were carried out at the Transportation Technology Center Inc. (TTCI) USA, a subsidiary of the Association of American Railroads, Pueblo, Colorado, USA. TTCI have submitted their report P-02-015 dated 18 April 2002. Micro alloyed wheels were subjected to finite element analysis to prove the design adequacy, loading pattern and thermal stress distribution pattern. Finite element analysis revealed that the design is adequate for high speed and heavy load conditions. EXAMPLE 2 Table 1 shows a comparison of the metallurgical and mechanical properties viz., ultimate tensile strength (UTS), yield strength, elongation, Brinell's Hardness number (BHN), Fracture Toughness, Closure value, microstructure and ASTM grain size of improved micro alloyed and cast steel rail wheel as compared to those of wheels produced by conventional processes viz., plam carbon cast steel wheel and forged steel wheels. TABLE-I Micro-alloyed cast steel process compared to forging process shows comparable closure values, UTS and lower elongation but is superior in Critical parameters of BHN, fracture toughness (both in radial and axial directions) and grain size. Micro Alloyed cast steel process compared to plain carbon cast steel process shows comparable UTS, marginally higher closure values but has significantly higher property in critical parameters of BHN, elongation, ASTM grain size, yield strength and fracture toughness. A comparative test report of mechanical properties by Rail Wheel Factory, Bangalore is appended herewith. EXAMPLE 3 Experiments were conducted to assess the resistance to thermal damage using a dynamometer at TTCI, USA. Further, Drag Braking Test was conducted to determine stress reversal (compressive to tensile) using saw cut method. Results are given in TABLE 2. From the above results it can be observed that the thermal capacity of cast steel wheel is around 55 kw. Severest drag braking on Indian Railways is found in Castle Rock - Kulem section of South Western Railways, which has the steep sustained gradient of 1 in 37. A locomotive wheel having axles load of 211 will have to absorb maximum 20 kw braking load in this section if train speed is maintained at 25 kmph while coming down grade with dynamic brakes not working. Even at 40 kmph speed down the grade (which is unlikely), the drag braking load will be 31 kw. Both these values are much less than the expected thermal capacity of 55 kw at 1000 mm dia. This means that micro-alloyed cast wheels will be able to withstand any foreseeable drag braking condition in this section even at the condemnation diameter. Similarly, tests to determine resistance to thermal cracking were conducted using the dynamometer. Results are tabulated in TABLE 3, r Plain carbon cast wheel when subjected to similar tests with cast iron block developed thermal cracks after only 9 cycles. Therefore, micro-alloyed cast steel wheel is at least 5 to 6 times more resistant to the development of tread thermal cracks with cast iron blocks and 10-12 times more resistant to the development of tread thermal cracks with composition block as compared to wheels cast using conventional cast steel. The conclusion of the test report submitted by M/s TTCI USA is appended herewith in page No. 14. EXAMPLE 4 Indian Railways have conducted field trails over four years on Locomotives using plain carbon cast wheel, micro-alloyed cast wheel and forged rolled wheels to compare the wear pattern of the wheels and also to record any other adverse performance. It has been observed that micro-alloyed cast steel wheels have 20% less wear than plain carbon cast steel wheels but marginally higher wear than the rolled wheels. No untoward incident on micro-alloyed steel has been experienced in field trials of four years. Research, Design and Standards Organization (RDSO) of Indian Railways has cleared the micro-alloyed cast wheels for locomotive application. Vanadium 0.10 to 0.20% is added in order to refine the grain size and consequently to improve mechanical properties. Vanadium also improves high temperature mechanical properties of steel by fine dispersion of vanadium carbide and carbonitrides. For refinement of primary grain size in casting, dispersed vanadium carbides form large number of nucleation sites which lead to formation of fine grain castings. Fine grain size improves yield strength, % elongation and impact properties. Molybdenum 0.05 - 0.20%is added in order to improve the tensile strength and yield stress. Dispersed molybdenum carbide also improves the facture toughness. Like vanadium, molybdenum also improves high temperature properties and this reduces the fatigue crack formation at operating temperatures. Vanadium and molybdenum together improve mechanical properties; provide adequate wear resistance and also resistance to thermo mechanical cracking. In addition, due to the ability of vanadium and molybdenum to improve strength, carbon content of the steel can be kept at a lower limit, which further improves the thermal cracking property. Advantages 1. In the manufacturing of the improved micro alloyed cast steel rail locomotive wheels melting and casting of wheels can be done by recycling of condemned wheels and other railway scrap generated from various railway workshops, so that it contributes to conservation of resources. 2. Casting made as per parabolic shape wheel design will have the advantage of higher strength-to-weight ratio with better heat dissipation and less stress concentrations, there by increasing the service life. 3. Casting to design shape eliminates machining of wheel to its close dimensional tolerance. 4. Controlled pressure casting process permits mass production with consistent quality where as forged wheels are produced in batches . 5. The improved micro alloyed cast steel rail wheels are 6 to 6 times more resistant to the development of tread thermal cracks with cast iron brake blocks and 10 to 12 times more resistant to development of tread thermal cracks with composition brake blocks contributing to service safety. The terms and expressions in this specification are of description and not of limitation, there being no intention to exclude any equivalence of the features illustrated and described since various other embodiments of an improved micro alloyed cast steel rail wheel proposed herein are possible without departure from the scope and ambit of this invention. The conclusion report submitted by M/s . Transportation Technology Centre . Inc, a subsidiary of the Association of American Rail roadf Pueblo, Colorado .USA. for being tested for suitability Wheel and Axle Plant ( Rail Wheel Factory-now) A 1092-MM cast locomotive wheels for Indian railways P-02-015 is appended here with. l.The finite element analysis of Indian Railways' 1092- millimeter diameter wheel is accurate well within the variations of expected from different finite element software packages and analysts. 2. The 1092- millimeter diameter wheel design is considered adequate and dose not warrant profile changes. 3. Given the fact that the WAP wheels have a carbon content that is at a low range or below that of AAR Grade B specification , the excellent tensile properties of the WAP alloy will result in superior wear resistance. 4. The fracture toughness properties of the WAP steels are slightly superior to the equivalent AAR grade. 5. The compressive rim residual stresses in the circumferential direction of the wheels indicate that a proper heat-treating process is employed by WAP. 6. The WAP alloy wheels are is at least 5 to 6 times more resistant to the development of tread thermal cracks with cast iron blocks and 10 to 12 times more resistant to the development of tread thermal cracks with composition blocks. 7. The growth of shattered rim cracks is greatly accelerated by the action of lateral loads during curving and flanging, and accelerated a lesser extent by braking. 8. In general ,the WAP alloy produces a wheel of superior properties that will provide excellent serviceability in train operation We claim 1) An improved micro alloyed cast steel rail wheel comprising of composition in weight percentage of - C:0.50-0.60, Mn: 0.70 - 0.80, Si: 0.32-0.57, P: 0.030(max), S: 0.030(max), wherein it comprises of micro alloying elements such as Mo: 0.05 - 0.20, V: 0.10 - 0.20 with balance iron and incidental impurities. 2) The process of manufacturing of improved micro alloyed cast steel rail wheel as claimed in Claim 1, wherein Ferro Molybdenum and Ferro Vanadium are charged to the ladle containing molten steel at a specified temperature of 1690 - 1700°C and subsequently the wheels are cast and heat treated. 3) The process of manufacturing improved micro alloyed cast steel rail wheel, as claimed in Claim 2, wherein heat treatment process comprising of normalizing at a temperature range of 900 - 960°C for 90 -110 minutes. Rim-quenching at a temperature at 800 - 850° C for 5-6 minutes, tempering at a temperature range of 550-600° C for 120 -150 minutes and hub cooling with water spray for 90-120 seconds. 4) The improved micro alloyed cast steel rail wheel, as claimed in Claim 1, wherein the said wheels are capable of being assembled in railway wagons, carriages and locomotives. 5) The improved micro alloyed cast steel rail wheel substantially as herein described and exemplified. 6) The process of manufacturing of the improved micro alloyed cast steel rail wheel substantially as herein described and exemplified. Dated this 17*^ of February, 2004.

Documents:

119-che-2004-abstract.pdf

119-che-2004-claims duplicate.pdf

119-che-2004-claims original.pdf

119-che-2004-correspondnece-others.pdf

119-che-2004-correspondnece-po.pdf

119-che-2004-description(complete) duplicate.pdf

119-che-2004-description(complete) original.pdf

119-che-2004-form 1.pdf

119-che-2004-form 3.pdf

119-che-2004-other documents.pdf