Title of Invention

A PROCESS FOR MANUFACTURE OF HIGH STRENGTH (MORE THAN 1500 MPA) AUSTEMPERED DUCTILE IRON

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.

Documents:

00289-kol-2007-correspondence-1.1.pdf

00289-kol-2007-p.a.pdf

0289-kol-2007-abstract.pdf

0289-kol-2007-claims.pdf

0289-kol-2007-correspondence others.pdf

0289-kol-2007-description (complete).pdf

0289-kol-2007-drawings.pdf

0289-kol-2007-form1.pdf

0289-kol-2007-form2.pdf

0289-kol-2007-form3.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-form 18.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-PA.pdf

289-KOL-2007-REPLY TO EXAMINATION REPORT.pdf


Patent Number 257368
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
Inventors:
# Inventor's Name Inventor's Address
1 BANDYOPADHYAY PRABIR KUMAR RESEARCH & DEVELOPEMENT CENTER FOR IRON & STEEL DORANDA,RANCHI-834002
2 SEN SUSIL KUMAR RESEARCH & DEVELOPEMENT CENTER FOR IRON & STEEL DORANDA,RANCHI-834002
PCT International Classification Number C21D 10/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA