Title of Invention | A PROCESS FOR MANUFACTURE OF HIGH STRENGTH (MORE THAN 1500 MPA) AUSTEMPERED DUCTILE IRON |
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Abstract | A high strength (more than 1500 MPa) austempered ductile iron, also known as ADI, suitable for manufacture of various high performance components in steel plants/rolling mills for different service conditions and also at high temperatures, due to its excellent combination of superior mechanical and metallurgical properties. Such properties are obtained through a process of heat treatment cycles to which the as cast ductile iron is subjected, with controlled process parameters comprising austenitizing and the austempering at preferred temperatures and durations, favoring achieving desired microstructure with selective alloy chemistry. The tensile strength was achieved upto a maximum of 3 times higher than existing to about 152 kg/mm2 and elongation of about 4.5%. An alternative heat treatment process with selective alloy chemistry was used to achieve high ductility of 11% and a moderate tensile strength of 105 kg/mm2 in the resulting ductile iron. ADI can be easily cast to suit any application and is an economic alternative material for a variety of industrial applications. |
Full Text | FIELD OF INVENTION: Present invention relates to development of a high strength (more than 1500 MPa) austempered ductile iron, also known as ADI, suitable for manufacture of various high performance components in steel plants /rolling mills for different service conditions and also at high temperatures, due to its excellent combination of superior mechanical and metallurgical properties. Such properties are obtained through a selective process of heat treatment cycles to which the as cast ductile iron is subjected, with controlled process parameters comprising austenitizing and the austempering at preferred temperatures and durations, favoring achieving desired microstructure with selective alloy chemistry. The tensile strength was achieved upto a maximum of 3 times higher than existing to about 152 kg/mm2 and elongation of about 4.5%. The invention is also directed to an alternative heat treatment process with selective alloy chemistry to achieve high ductility of 11% and a moderate tensile strength of 105 kg/mm2 in the resulting ductile iron. This material (ADI) has a potential for replacement of high value forged and heat-treated components of steel and non-ferrous material. ADI is 10% less dense than steel and an ADI component consumes 50% less energy than a steel casting and almost 80% less energy than a steel forging. Traditional cast irons often cannot meet these stringent demands and designers have been forced to specify expensive forging in place of castings. The trend toward reduced size and power output in the present design has placed great demands on component materials. ADI can be used as an alternative to steel, alloyed and white irons, bronze and other non-ferrous materials. The advantage of this material is that it is made through casting process and thus can be tailor-made to suit any particular application. The ADI is therefore a cost effective material consuming less energy compared to the forged steel and other materials, making it an economic alternative material for a variety of industrial applications. BACKGROUND ART: Use of austempered ductile iron has emerged as a new class of engineering materials in the recent past. ADI, as it is alternatively known, refers to a family of ductile irons whose properties can be varied over a wide range by the correct choice of heat-treatment variables corresponding to the selective alloy chemistry used. It has excellent combination of properties making it suitable for manufacturing of various high performance components. It is well known in the art of making ductile iron and as the name suggests, the as cast microstructure of ductile iron consists of nodular graphite in ferritic matrix and thus giving a relatively low tensile strength but high % elongation/ductility. Thus there had been an increased demand and newer use of austempered ductile iron, necessitated for inducing higher strength for making it suitable for applications in mechanical components like connecting rods, crankshafts and gears, screen plates, chain sprockets, bushes, slide bearings, wear guides, digger teeth, brake blocks to be made from this material. Conventional as cast ductile iron fails to provide these properties and meet the application specific requirements, there by forcing the designers to select more expensive alloy steel forgings as an alternative material. In our earlier granted Indian Patent 199279 there was disclosed a process for producing ADI having strength properties upto about less than 1500 MPa. However, there is a continuing need in the art to achieve further strength properties beyond 1500 MPa for variety of other end use and applications involving superior mechanical and metallurgical properties in the end product. Present invention is thus directed to developing a process of selectively using heat treatment parameters with selective design of alloy chemistry, of the as cast ductile iron such as to obtain preferred microstructure induce the required mechanical strength and ductility properties to suit various applications as said exceeding those provided by the existing variety of ADI the range of mechanical properties such as 95-140 kg/mm2 coupled with 3-10% elongation. OBJECTS OF THE INVENTION: The basic object of the present invention is thus directed to obtaining a high strength (> 1500 MPa) austempered ductile iron(ADI) and preferably 152 kg/mm2 with moderate ductility such as 4.5 % elongation for desired variety of use of the ADI for high performance components in different engineering applications. A further object of the present invention is directed to obtaining ADI by the use of selective alloy chemistry favoring obtaining said desired mechanical properties in the resulting austempered ductile iron, by providing selective chemistry. A further object of the present invention is directed to obtaining a high strength (>1500MPa) austempered ductile iron (ADI) and favorable ductility for different engineering applications has an alternative process by altering the parameters such as the properties obtained in the end product is having a moderate tensile strength of 105kg/mm2 and ductility in the range of about 11%. A further object of the present invention is directed to obtaining a high strength (>1500 MPa) austempered ductile iron (ADI) and favorable ductility for different engineering applications, said desired properties of the ADI were obtained while tested at room temperature and also the testing of the material conducted at elevated temperature viz at about 300°C and the said desired properties maintained at satisfactory levels. A further object of the present invention is directed to obtaining a high strength (>1500 MPa) austempered ductile iron (ADI) and favorable ductility for different engineering applications, such that a low cost alternative material is obtained at lower energy consumption, to substitute expensive alloy steel forgings wherever used for the purpose of higher strength properties, hardness or ductility in specific applications. SUMMARY OF THE INVENTION: Thus according to the basic aspect of the present invention there is provided a process for the manufacture of high strength more than 1500 Mpa ductile iron comprising: i) providing a selective composition comprising: C- 3.5 to 3.7 by wt; Mn.- 0.15 to 0.20 by wt; Si-3.00 to 3.20 by wt; S-0.01 to 0.012 by wt; P-0.01-0.03 by wt; Mg- 0.02 to 0.06 by wt;and Iron- balance. ii) subjecting to selective austenitizing within the desired temperature range and for desired duration of time and austemperaing treatment within the desired temperature range and for a desired duration of time followed by selective cooling to achieve synergistically improved high strength with eleongation. The said heat treatment (Austanitization) is carried out in a bed of cast iron chips to minimize decarburisation. This ensures that no significant decarburisation takes place during the heat treatment. Austempering is carried out preferably in salt bath furnaces for better homogenization of the process A further aspect of the present invention directed to said process for the manufacture of high strength more than 1500 MPa ductile iron comprising: i) providing a selective composition comprising: C- 3.5 to 3.7 by wt.; Mn.- 0.15 to 0.20 by wt.; Si-3.00 to 3.20 by wt.; S-0.01 to 0.012 by wt; P-0.01-0.03 by wt; Mg- 0.02 to 0.06 by wt;and Iron- balance. ii) subjecting to selective austenizing at a temperature of 900°C and for selective duration of one hour and austempering treatment at temperature of 280°C for a selective duration of two hours followed by selective furnace cooling to achieve synergistically improved high strength with elongation. A still further aspect of the present invention directed to said process for the manufacture of high strength more than 1500 MPa ductile iron the tensile strength is surprisingly improved from 48Kg/mm2 to 152 kg/mm2 with 4.5 % elongation. A further aspect of the present invention directed to a process for the manufacture of high strength more than 1500 MPa ductile iron wherein the Hardness achieved is 404- 406 (BHN). According to a further important aspect of the present invention is directed to said process for the manufacture of high ductility and moderate strength ductile iron for industrial application comprising: i) providing a selective composition comprising: C- 3.5 to 3.7 by wt; Mn.- 0.15 to 0.20 by wt; Si- 3.00 to 3.20 by wt; S- 0.01 to 0.012 by wt; P-0.01-0.03 by wt; Mg- 0.02 to 0.06 by wt.; and Iron- balance. ii) subjecting to selective austenizing at a temperature of 880°C and for selective duration of one hr and austempering treatment at temperature of 400°C for a selective duration of two hrs followed by selective air cooling to achieve synergistically improved high ductility with moderate tensile strength. A further aspect of the present invention directed to a process for the manufacture of high ductility and moderate strength ductile iron for industrial application such as to obtain high ductility 11% and moderate tensile strength 105kg/mm2. A further aspect of the present invention directed to said process for the manufacture of high ductility and moderate strength ductile iron for industrial application wherein the hardness achived is in the range of 270-276 BHN. BRIEF DESCRIPTION OF THE FIGURE: Figure 1: is the illustration of the process chart for the production of austempered ductile iron (ADI) of high strength (>1500 MPa). Figure 2 & 3: is the illustration of micrographs of typical heat treated ADI sample of the present invention obtained following austenitisation at 900°C for 1 hr and austempering at 280°C for 2 hrs is shown in accompanying figure 2 and figure 3, with 200x and 800x magnifications respectively. DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING EXAMPLES AND ILLUSTRATIONS: Austempered ductile iron (ADI) are used for various engineering applications in any integrated steel plant and rolling mills because of its high strength and toughness, moderate hardness and favorable ductility with superior microstructure/metallurgical properties, suitable for different service conditions and also at high temperature. ADI has the potential for replacement of high value forged and heat treated component of steel and non-ferrous materials. The material can be advantageously obtained in the form of casting as tailor- made to suit any application. Moreover, it is cost effective and also consumes low energy compared to forged steel and other materials. EXAMPLE: Investigation work was carried out to develop austempered ductile iron of the present invention. The selection of process variables for heat treatment such as heat-treating temperature (austenisation temperature and austempering temperature), time duration and alloy composition were found to play a very important role on achieving the mechanical and metallurgical properties. The selective composition of the as cast grade of the ductile iron identified as given in the following Table I: The effect of heat treatment parameters was studied in detail for various alternatives. The design of experiments for such study comprised: (i) design of heat treatment cycle- austenizing and austempering, (ii) design of alloy chemistry for the ductile iron and (iii) development of the desired high-strength(greater than 1500 MPa) austempered ductile iron. The tensile strength, hardness and other mechanical properties of various samples were evaluated. The accompanying figure 1 representing the flow process chart for the production stages for the processes for ductile iron making and its subsequent heat treatment and pouring into test bars to study the results obtained in terms of mechanical and metallurgical properties of the ADI. It is well known that the as cast micro-structure of ductile iron is nodular graphite in ferritic matrix so as to instill in it the soft yet tough and ductile behaviour. However to improve upon the strength and hardness properties, the micro-structure of austempered ductile iron is processed to consist of bainitic ferrite, retained austenite, nodular graphite and carbide in desired proportions/distribution. During the experimentation and trials, a number of heat treatment cycles were studied to find out the effect of heat treatment parameters on the mechanical properties. It has been observed that austenitizing at 900°C for one hour and austempering at 280°C preferably for two hours followed by air cooling, is suitable for high strength application. The micrographs of typical heat treated ADI sample following austenitisation at 900°C for 1 hr and austempering at 280°C for 2 hrs is shown in accompanying figure 2 and figure 3 with varied magnification. For the present invention, the tensile strength has remarkably improved by about three times from 48 kg/mm2 for as cast value to about 152 kg/mm2 with 4.5% elongation in the ADI obtained. High temperature tensile test was also carried out with the same material at about 300°C. And the test results obtained were satisfactory and improvement over the existing grades of ADI earlier developed. Austanisation at 880°C for one hour and subsequent austempering at 400°C for two hours followed by air cooling can also be successfully used such that high ductility viz 11% elongation and moderate tensile strength of about 105kg/mm2 was achieved for suitable industrial application. Properties of as cast and austempered ductile iron tested at room temperature and also for high temperature test data, following the protocol as follows: i) The room temp, tensile testing has been carried out in Instron-1135 with attachment for measuring elongation. This is a ISO certified testing machine which is being used world wide. ii) The hardness measurement has been carried out in vickers testing machine which is also ISO certified and calibrated. iii) The high temperature tensile testing at 300° C has been carried out in MTS-8110 mechanical testing system. MTS dynamic testing machine MTS-810 which is also used world wide and ISO certified. The room temperature and also for high temperature test data are presented in the accompanying Table II below. It is thus possible by way of the present invention, obtaining a high strength and preferably UTS greater than 1500 MPa with moderate hardness and ductility so as to favor austempered ductile iron (ADI) obtained by following the controlled parameters of the austenitizing and austempering process of the present invention, with micro-structure comprising bainitic ferrite, retained austenite, nodular graphite and carbide in preferred proportions and distribution suitable for use of the material for high performance components in various engineering applications in steel plants, rolling mills and the like, because of having excellent combination of properties in said ADI according to the invention. We Claim: 1. A process for the manufacture of austempered ductile iron temperature dependent induced microstructure adapted for generation of high strength more than 1500 MPa ductile iron or high ductility and moderate strength ductile iron comprising: i) providing a selective composition comprising: C-3.5 to 3.7 by wt; Mn.-0.15 to 0.20 by wt.; Si- 3.00 to 3.20 by wt.; S- 0.01 to 0.012 by wt.; P-0.01-0.03 by wt.; Mg-0.02 to 0.06 by wt.;and Iron- balance. ii) subjecting to selective austenitizing within the temperature range of 880° to 900° and fora duration of time of approximately 1 hour and austempering treatment within the temperature range of 280° to 400°C for desired duration of approximately 2 hours followed by cooling in ambient air to room temperature to achieve synergistically improved high strength with elongation. 2. A process for the manufacture of high strength more than 1500 MPa austempered ductile iron as claimed in claim 1 comprising: i) providing a selective composition comprising: C-3.5 to 3.7 by wt.; Mn.-0.15 to 0.20 by wt.; Si-3.00 to 3.20 by wt; S- 0.01 to 0.012 by wt.; P-0.01-0.03 by wt.; Mg- 0.02 to 0.06 by wt.; and Iron- balance. ii) subjecting to selective austenitizing at a temperature of 900°C and for selective duration of one hour and austempering treatment at temperature of 280°C for a selective duration of two hrs followed by selective furnace cooling to achieve synergistically improved high strength with elongation. 3. A process for the manufacture of high strength more than 1500 MPa austempered ductile iron as claimed in anyone of claims 1 or 2 the tensile strength is surprisingly improved from 48Kg/mm2 to 152 kg/mm2 with 4.5 % elongation. 4. A process for the manufacture of high strength more than 1500 MPa austempered ductile iron as claimed in anyone of claims 1 to 3 wherein the Hardness achieved is 404-406 (BHN). 5. A process for the manufacture of high ductility and moderate strength austempered ductile iron as claimed in claim 1 for industrial application comprising: i) providing a selective composition comprising: C-3.5 to 3.7 by wt.; Mn.- 0.15 to 0.20 by wt.; Si-3.00 to 3.20 by wt.; S- 0.01 to 0.012 by wt.; P-0.01-0.03 by wt.; Mg- 0.02 to 0.06 by wt; and Iron- balance. ii) subjecting to selective austenitizing at a temperature of 880°C and for selective duration of one hr and austempering treatment at temperature of 400°C for a selective duration of two hrs followed by selective air cooling to achieve synergistically improved high ductility with moderate tensile strength. 6. A process for the manufacture of high ductility and moderate strength austempered ductile iron for industrial application as claimed in claim 5 such as to obtain high ductility 11% and moderate tensile strength 105kg/mm2. 7. A process for the manufacture of high ductility and moderate strength austempered ductile iron for industrial application as claimed in anyone of claims 5 or 6 wherein the hardness achieved is in the range of 270-276 BHN. ABSTRACT A PROCESS FOR MANUFACTURE OF HIGH STRENGTH (MORE THAN 1500 MPa) AUSTEMPERED DUCTILE IRON. A high strength (more than 1500 MPa) austempered ductile iron, also known as ADI, suitable for manufacture of various high performance components in steel plants/rolling mills for different service conditions and also at high temperatures, due to its excellent combination of superior mechanical and metallurgical properties. Such properties are obtained through a process of heat treatment cycles to which the as cast ductile iron is subjected, with controlled process parameters comprising austenitizing and the austempering at preferred temperatures and durations, favoring achieving desired microstructure with selective alloy chemistry. The tensile strength was achieved upto a maximum of 3 times higher than existing to about 152 kg/mm2 and elongation of about 4.5%. An alternative heat treatment process with selective alloy chemistry was used to achieve high ductility of 11% and a moderate tensile strength of 105 kg/mm2 in the resulting ductile iron. ADI can be easily cast to suit any application and is an economic alternative material for a variety of industrial applications. |
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00289-kol-2007-correspondence-1.1.pdf
0289-kol-2007-correspondence others.pdf
0289-kol-2007-description (complete).pdf
289-KOL-2007-(16-09-2013)-CLAIMS.pdf
289-KOL-2007-(16-09-2013)-CORRESPONDENCE.pdf
289-KOL-2007-(16-09-2013)-OTHERS.pdf
289-KOL-2007-(22-04-2013)-CLAIMS.pdf
289-KOL-2007-(22-04-2013)-CORRESPONDENCE.pdf
289-KOL-2007-(22-04-2013)-OTHERS.pdf
289-KOL-2007-CORRESPONDENCE.pdf
289-KOL-2007-EXAMINATION REPORT.pdf
289-KOL-2007-GRANTED-ABSTRACT.pdf
289-KOL-2007-GRANTED-CLAIMS.pdf
289-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf
289-KOL-2007-GRANTED-DRAWINGS.pdf
289-KOL-2007-GRANTED-FORM 1.pdf
289-KOL-2007-GRANTED-FORM 2.pdf
289-KOL-2007-GRANTED-FORM 3.pdf
289-KOL-2007-GRANTED-SPECIFICATION-COMPLETE.pdf
289-KOL-2007-REPLY TO EXAMINATION REPORT.pdf
Patent Number | 257368 | |||||||||
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Indian Patent Application Number | 289/KOL/2007 | |||||||||
PG Journal Number | 40/2013 | |||||||||
Publication Date | 04-Oct-2013 | |||||||||
Grant Date | 27-Sep-2013 | |||||||||
Date of Filing | 26-Feb-2007 | |||||||||
Name of Patentee | STEEL AUTHORITY OF INDIA LIMITED | |||||||||
Applicant Address | RESEARCH & DEVELOPEMENT CENTER FOR IRON & STEEL DORANDA,RANCHI-834002 | |||||||||
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PCT International Classification Number | C21D 10/00 | |||||||||
PCT International Application Number | N/A | |||||||||
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