CLIAMS:We Claim:

1. A process for producing variable high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength of atleast 1000 MPa and even more than 1300 MPa ductile iron and high ductility and moderate ductility iron respectively involving a selective combination of alloy elements comprising:
i) providing said selective alloy element composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.22 by wt.;

Si- 2.80 to 3.22 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 said selective alloy elements to austenitizing within the temperature range of 8500C to 9500C preferably at 9300C and for a duration of time ½ hour to 1hour preferably about 1 hour ;and finally
iii) subjecting to austempering treatment to control the microstructure anyone of said high strength of atleast 1000 MPa or even more than 1300 MPa ductile iron and high ductility or moderate ductility iron respectively.

2. A process for producing high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in claim 1 comprising:
i) providing said selective composition comprising:
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at lower austempering temperature 2500C to 3000C preferably about temperature of 2800C for a selective duration of two hours followed by selective furnace cooling to impart synergistically improved high strength 1350 MPa with 2 % elongation in the austempered ductile iron.

3. A process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in claims 2 wherein the Hardness achieved is 394 BHN.
4. A process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in anyone of claims 1 to 3, providing for microstructure comprising very fine needle shaped ferrites having graphite nodules embedded in the matrix, formed at said lower austempering temperature for the heat treatment cycle.
5. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength as claimed in claim 1 for industrial application comprising:
i) providing said selective composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at higher temperature in the range of 3500C to 4000C preferably temperature of about 4000C for a selective duration of two hours followed by selective air cooling to impart synergistically improved high strength 1000 MPa with 13 % elongation in the austempered ductile iron.

6. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as claimed in claim 5 wherein the hardness achieved is in the range of 277 BHN.
7. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as claimed in claims 5 to 6 providing for microstructure comprising large amount of retained austenite and ferrite (rod shaped) having graphite nodules embedded in the matrix, at higher austempering temperature for the heat treatment cycle.
8. A process for producing high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength more than 1300 MPa ductile iron or high ductility and moderate strength ductile iron as claimed in anyone of claims 1 to 7 , which is carried out such that the presence of austenite phase in austempered ductile iron undergoes metallugical transformation to hard martensite phase as a result of work hardening during working thus enhancing the wear resistance of ADI.

9. A process for producing high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength more than 1300 MPa ductile iron or high ductility and moderate strength ductile iron as claimed in anyone of claims 1 to 8 wherein the ductile iron subjected to controlled heat cycle have more than 95% nodularity in as cast condition with nodule size in the range of 15 to 30 microns.
10. A high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and

a microstructure of high strength of atleast 1350 MPa and high ductility of 2 % eleongation which is obtained involving lower austempering temperature following the process as claimed in claim 2.
11. A high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and

a microstructure of high strength of atleast 1000 MPa and high ductility of 13 % eleongation which is obtained higher austempering temperature following of the process as claimed in claim 5.

Dated this the 30th day of July, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION

The present invention relates to development of Austempered Ductile Iron(ADI) with improved strength, ductility combination alongwith high wear resistance properties. More particularly the present invention is directed to provide high strength, high wear resistant ductile iron, and process for its production. The stated properties are obtained by involving a selective composition processed through a selective heat treatment cycles to which the as cast ductile iron with selective alloy chemistry is subjected, with varied controlled process parameters comprising austenitizing and austempering at selected temperatures and durations, favoring achieving desired microstructures in the resulting ADI. The ultimate tensile strength has been achieved upto about 1350 Mpa which is more than 2.5 times higher than existing ADI grade with a combination of elongation of about 2%. The process according to the present invention also provide an alternative heat treatment process with the same selective alloy chemistry to achieve high ductility of 13% and a moderate tensile strength of 1000 Mpa in the resulting ductile iron. This material has a potential for replacement of high value forged and heat treated components of steel and non-ferrous material, suitable for manufacture of various high performance components in steel plants/rolling mills made through casting route, for different service conditions due to its excellent combination of superior mechanical and metallurgical properties.

BACKGROUND OF THE INVENTION

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 the matrix and this results in ductility of the material and hence find wide application in engineering industries. The advantage of this material is that it is made through casting process and thus any intricate shape can be made to suit any particular application. This material is also a cost effective consuming less energy compared to the forged steel and other material, making it an economic alternative material for a variety of industrial applications.
However conventional ductile iron has some limitation for application for high strength and demanding service conditions. 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, thereby forcing the designers to select more expensive alloy steel forgings as an alternative material.

In our earlier granted Indian Patent 257368, there was disclosed a process for producing ADI having strength properties upto about 1500 MPa. However, there is a continuing need in the art to achieve a unique combination of strength and wear properties along with considerable ductility for a variety of other end use and applications demanding 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 inducing the required mechanical strength and ductility properties such as tensile strength in the range of 950-1400 MPa coupled with 3-10% elongation, to suit various applications as said exceeding those provided by the existing variety of ADI.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to provide high strength high wear resistant austempered ductile iron (ADI) with moderate ductility for desired variety of use of the ADI for high performance components in different engineering applications, and a process for its production.

A further object of the present invention is directed to provide high strength high wear resistant austempered ductile iron (ADI) by the use of selective alloy chemistry favoring obtaining desired mechanical properties in the resulting Austempered ductile iron.

A further object of the present invention is directed to provide high strength high wear resistant austempered ductile iron (ADI) having favourable high elongation with moderate tensile strength suitable for different engineering applications produced by altering the austenitizing and austempering parameters to ensure achieving desired properties in the end product.

A further object of the present invention is directed to provide high strength high wear resistant austempered ductile iron (ADI) with favorable ductility having wear resistance of this material almost three times than that of mild steel under same operating tests condition thus making it attractive for wear resistant applications.

A further object of the present invention is directed to provide high strength high wear resistant austempered ductile iron (ADI) with favourable 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

The basic aspect of the present invention is thus directed to a process for producing variable high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength of atleast 1000 MPa and even more than 1300 MPa ductile iron and high ductility and moderate ductility iron respectively involving a selective combination of alloy elements comprising:
i) providing said selective alloy element composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.22 by wt.;

Si- 2.80 to 3.22 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 said selective alloy elements to austenitizing within the temperature range of 8500C to 9500C preferably at 9300C and for a duration of time ½ hour to 1hour preferably about 1 hour ;and finally
iii) subjecting to austempering treatment to control the microstructure to obtain anyone of said high strength of atleast 1000 MPa or even more than 1300 MPa ductile iron and high ductility or moderate ductility iron respectively.

Another aspect of the present invention is directed to a process for producing high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as stated above comprising:
i) providing said selective composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at lower austempering temperature 2500C to 3000C preferably about temperature of 2800C for a selective duration of two hours followed by selective furnace cooling to impart synergistically improved high strength 1350 MPa with 2 % elongation in the austempered ductile iron.

A further aspect of the present invention is directed to a process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as stated above wherein the Hardness achieved is 394 BHN.
A still further aspect of the present invention is directed to a process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as described herein before, providing for microstructure comprising very fine needle shaped ferrites having graphite nodules embedded in the matrix, formed at said lower austempering temperature for the heat treatment cycle.
Yet another aspect of the present invention is directed to a process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength as stated above, for industrial application comprising:
i) providing said selective composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at higher temperature in the range of 3500C to 4000C preferably temperature of about 4000C for a selective duration of two hours followed by selective air cooling to to impart synergistically improved high strength 1000 MPa with 13 % elongation in the austempered ductile iron.

Importantly, by way of the above advancement in the process according to the present invention the same takes care of wear which is an important property for materials for tribological applications in steel plant and Engineering industries. This processed material in accordance with the present advancement is benefitted by the matrix structure as well as austempering heat treatment process and this not only increases the strength and hardness but also the wear resistance . The ADI obtained following the above processes by means of austempered matrix structure is highly wear resistant compared to conventional material such as mild steel , and nonferrous materials. Advantageously, the above process of the present invention exploits the work hardenable austenite phase whereby the wear resistance is further improved. Thus the process results in a unique material where a number of properties are achievable in a single material with hosts of variety of engineering applications and demanding service conditions.

A further aspect of the present invention is directed to a process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as stated above wherein the hardness achieved is in the range of 277 BHN.
A still further aspect of the present invention is directed to a process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as stated above providing for microstructure comprising large amount of retained austenite and ferrite (rod shaped) having graphite nodules embedded in the matrix, at higher austempering temperature for the heat treatment cycle.
A still further aspect of the present invention is directed to a process for producing high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength more than 1300 MPa ductile iron or high ductility and moderate strength ductile iron as described above, which is carried out such that the presence of austenite phase in austempered ductile iron undergoes metallugical transformation to hard martensite phase as a result of work hardening during working thus enhancing the wear resistance of ADI.

A further aspect of the present invention is directed to provide a high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and
a microstructure of high strength of atleast 1350 MPa and high ductility of 2 % eleongation which is obtained involving lower austempering temperature following the process as stated above.
A still further aspect of the present invention is directed to provide a high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and

a microstructure of high strength of at least 1000 MPa and high ductility of 13 % elongation which is obtained higher austempering temperature following the process as stated above.
The objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative figures and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 (a): is the illustration of the flow process chart for the production of Austempered ductile iron (ADI) according to the present invention;

Figure 1(b) : Shows the flow chart for heat Treatment of as cast ductile iron;

Figure 2: is the micrograph of as cast ductile iron showing graphite nodules black embedded in ferritic matrix (white) exhibiting bulls eye structure;

Figure 3: shows the image of Microstructure comprising very fine needle shaped ferrites formed at lower austempering temperature observed under Optical microscope for the heat treatment cycle (Tg=9300C; 1hr, TA =2800C;2hr);

Figure 4: shows the image of Microstructure comprising large amount of retained austenite and ferrite (rod shaped), graphite nodules embedded in the matrix at higher austempering temperature for the cycle ( Tg = 9300C; 1hr; TA = 4000C; 2hr);

Figure 5: shows the Wear profile of Mild Steel and ADI in Sliding Mode in Amsler Wear testing machine.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is thus directed to provide high strength high wear resistant austempered ductile iron (ADI) with moderate ductility obtained through controlled autenitizing and austempering of as cast DI for desired variety of use of the ADI for high performance components. The invention is also directed to provide high strength high wear resistant austempered ductile iron (ADI) having favourable high ductility/elongation with moderate tensile strength suitable for different engineering applications produced by altering the austenitizing and austempering parameters to ensure achieving desired properties in the end product.

The Austempered ductile iron (ADI) produced according to the present invention are suitable 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 four stand heat treated component of steel and non-ferrous materials. This material can be advantageously obtained in the form of casting of any intricate shape and can be tailored made to suit any application. Moreover, it is cost effective and also consumes low energy compared to forged steel and other materials.

The above stated properties of the ADI has been achieved through providing selective alloy composition in as cast DI and austenitizing and austempering with controlled parameters as determined through trials as illustrated through following example:

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 (austenitisation 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 :

Table I :

Alloy elements C Mn Si S P Mg
Content
(Wt. %) 3.5-3.8 0.15-
0.22 2.80-3.22 0.01 –
0.012 0.01 –
0.03 0.02-
0.06

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 – austenitizing and austempering (ii) design of alloy chemistry for the ductile iron and (iii) development of the desired high-strength (greater than 1300 MPa) Austempered ductile iron. The tensile strength, hardness and other mechanical properties of various samples were evaluated.

Reference is invited to accompanying Figure 1(a) representing the flow process chart for the production stages for the processes for ductile iron making and pouring into test bars. The different test samples viz tensile samples, Hardness samples, and samples for microstructure and metallurgical investigation are machined from the bottom surface of the test bars to get sound samples free from casting defects. As also represented in accompanying Figure 1(b), these samples are subsequently austenitized and Austempered based on the designed heat treatment cycle in selective furnaces having close temperature control to achieve excellent mechanical and metallurgical properties of the ADI.

Importantly, in accordance with the invention it is also ascertained that the ductile iron should have more than 95% nodularity in as cast condition with nodule size in the range of 15 to 30 microns preferably and heat treatment cycle judiciously followed. The temperature control is very important and austempering treatment is preferable in low temperature salt bath furnaces.

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. Accompanying Figure 2 is the micrograph of as cast ductile iron showing black graphite nodules embedded in ferritic matrix (white) exhibiting bulls eye structure.

However, to improve upon the strength and hardness properties, the microstructure of Austempered ductile iron is processed by controlling the heat treatment parameters to consist of acicular ferrite, retained austenite, nodular graphite 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 930OC for one hour and Austempering at 280OC preferably for two hours followed by furnace cooling, is suitable for high strength application. For the present invention, the tensile strength has remarkably improved by more than 2.5 times from 480 Mpa for as cast value to about 1350Mpa with 2% elongation in the ADI obtained. Accompanying Figure 3 shows the image of Microstructure comprising very fine needle shaped ferrites formed at lower austempering temperature observed under Optical microscope for the heat treatment cycle (Tg=9300C; 1hr, TA =2800C;2hr).

Further trial showed Austenitisation at 930OC for one hour and subsequent Austempering at 400OC for two hours followed by air cooling can also be successfully used such that high ductility viz. 13% elongation and moderate tensile strength of about 1000 Mpa was achieved for suitable industrial application. Accompanying Figure 4 shows the image of Microstructure comprising large amount of retained austenite and ferrite (rod shaped), graphite nodules embedded in the matrix at higher austempering temperature for the cycle ( Tg = 9300C; 1hr; TA = 4000C; 2hr).

Testing:

The test results obtained were satisfactory and confirmed improvement over the existing grades of ADI earlier developed. Properties of as cast and Austempered ductile iron tested at room temperature are given in the accompanying Table II below.

Table II:

Austempered Ductile iron Austempered Ductile iron
Sl No Parameters/
Properties As cast Ductile Iron Heat treated ADI
Ist H.T Cycle (930OC for 1 hr.
280OC for 2 hrs)
Heat treated ADI
2nd H.T Cycle
(930OC for 1 hr
. 400OC for 2 hrs)

A) UltimateTensile Strength (Mpa) 480 1350 1000
B) Elongation% 12 2 13
C) Hardness
(BHN) 173 394
277

Heat Treatment Cycles :

1st Heat Treatment Cycle (T?=930oC for 1hr, TA=280oC for 2hr),
2nd Heat Treatment Cycle (T?=930oC for 1hr, TA=280oC for 2hr),
(T?= Austenitization Temperature)
(TA= Austempering Temperature)
Wear resistance of the ADI samples were also tested and the Wear profile of ADI in Sliding Mode in Amsler Wear testing machine as compared to mild steel have been shown in accompanying Figure 5 confirming sufficiently high wear resistance of the ADI compared to MS.

The wear graph reveals that under same operating test condition, the developed ADI is much more wear resistant than conventional mild steel making it more attractive for as a material for tribological application. The presence of austenite phase in austempered ductile iron undergoes metallugical transformation of phases. The austenite gets transformed to martensite phase as a result of work hardening during working. This martensite is hard and it enhances the wear resistance of ADI.

It is thus possible by way of the present invention, to provide high strength, high wear resistance austempered ductile iron having UTS greater than 1300 MPa with moderate hardness and ductility or alternatively moderate strength of 1000MPa combined with favourable ductility/elongation of 13%, obtained by following the controlled parameters of the austenizing and Austempering process of the present invention, with microstructure comprising accicular ferrite, retained austenite, nodular graphite 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 producing variable high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength of atleast 1000 MPa and even more than 1300 MPa ductile iron and high ductility and moderate ductility iron respectively involving a selective combination of alloy elements comprising:
i) providing said selective alloy element composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.22 by wt.;

Si- 2.80 to 3.22 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 said selective alloy elements to austenitizing within the temperature range of 8500C to 9500C preferably at 9300C and for a duration of time ½ hour to 1hour preferably about 1 hour ;and finally
iii) subjecting to austempering treatment to control the microstructure anyone of said high strength of atleast 1000 MPa or even more than 1300 MPa ductile iron and high ductility or moderate ductility iron respectively.

2. A process for producing high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in claim 1 comprising:
i) providing said selective composition comprising:
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at lower austempering temperature 2500C to 3000C preferably about temperature of 2800C for a selective duration of two hours followed by selective furnace cooling to impart synergistically improved high strength 1350 MPa with 2 % elongation in the austempered ductile iron.

3. A process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in claims 2 wherein the Hardness achieved is 394 BHN.
4. A process for the manufacture of high strength high wear resistance austempered ductile iron having strength more than 1300 MPa as claimed in anyone of claims 1 to 3, providing for microstructure comprising very fine needle shaped ferrites having graphite nodules embedded in the matrix, formed at said lower austempering temperature for the heat treatment cycle.
5. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength as claimed in claim 1 for industrial application comprising:
i) providing said selective composition comprising:

C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 9300C and for selective duration of one hour and austempering treatment at higher temperature in the range of 3500C to 4000C preferably temperature of about 4000C for a selective duration of two hours followed by selective air cooling to impart synergistically improved high strength 1000 MPa with 13 % elongation in the austempered ductile iron.

6. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as claimed in claim 5 wherein the hardness achieved is in the range of 277 BHN.
7. A process for producing high strength high wear resistance austempered ductile iron having high ductility and moderate strength for industrial application as claimed in claims 5 to 6 providing for microstructure comprising large amount of retained austenite and ferrite (rod shaped) having graphite nodules embedded in the matrix, at higher austempering temperature for the heat treatment cycle.
8. A process for producing high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength more than 1300 MPa ductile iron or high ductility and moderate strength ductile iron as claimed in anyone of claims 1 to 7 , which is carried out such that the presence of austenite phase in austempered ductile iron undergoes metallugical transformation to hard martensite phase as a result of work hardening during working thus enhancing the wear resistance of ADI.

9. A process for producing high strength high wear resistance austempered ductile iron having microstructure adapted for generation of high strength more than 1300 MPa ductile iron or high ductility and moderate strength ductile iron as claimed in anyone of claims 1 to 8 wherein the ductile iron subjected to controlled heat cycle have more than 95% nodularity in as cast condition with nodule size in the range of 15 to 30 microns.
10. A high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and

a microstructure of high strength of atleast 1350 MPa and high ductility of 2 % eleongation which is obtained involving lower austempering temperature following the process as claimed in claim 2.
11. A high strength high wear resistance austempered ductile iron comprising
C- 3.5 to 3.8 by wt.;

Mn.- 0.15 to 0.20 by wt.;

Si- 2.80 to 3.22 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 and

a microstructure of high strength of atleast 1000 MPa and high ductility of 13 % eleongation which is obtained higher austempering temperature following of the process as claimed in claim 5.

Dated this the 30th day of July, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: HIGH STRENGTH HIGH WEAR RESISTANT AUSTEMPERED DUCTILE IRON(ADI) AND PROCESS FOR ITS PRODUCTION.

High strength, high wear resistant austempered ductile iron(ADI), and process for its production. The advancement includes a selective composition processed through a selective heat treatment cycles to which the as cast ductile iron with selective alloy chemistry is subjected controlled austenitizing and austempering at selected temperatures and durations, favoring achieving desired microstructures in the resulting ADI. The ultimate tensile strength has been achieved upto about 1350 Mpa with elongation of about 2%. The process also enables by selective alternative heat treatment process to achieve high ductility of 13% and a moderate tensile strength of 1000 Mpa in the resulting ADI with desired wear property and matrix structure for tribological applications in steel plant and Engineering industries with increased strength and hardness. The advancement would favour replacement of high value forged and heat treated components used in steel plants/rolling mills by excellent combination of superior mechanical and metallurgical properties.