CLIAMS:We Claims:

1. Hot rolled medium carbon steel comprising:

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe;
having hardness values of - upto HRB 95.

2. Hot rolled medium carbon steel as claimed in claim 1 comprising of;
Yield Strength = 540-580 MPa;
UTS = 820-860 MPa;
% Elongation = 15-17
and having coarse pearlite micro-structure,
3. Hot rolled medium carbon steel as claimed in anyone of claims 1 or 2 which is in the form of coils having:
Coil thickness in the range of 2.3 – 6.0 mm;
Coil width in the range of 1000 -1250 mm.
4. Hot rolled medium carbon steel as claimed in anyone of claims 1 to 3 having hardness amd metallographic characteristics suitable for blanking forming, shearing and heat treatment operations.

5. A process for the manufacture of hot rolled medium carbon steel as claimed in anyone of claims 1 to 4 comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii) continuous slab casting;
(iii) subjecting to re-heating of slabs directly into a re-heating furnace ; and
(iv) controlled rolling to achieve desired hardness.

6. A process for the manufacture of hot rolled medium carbon steel as claimed in claim 5 wherein said step of controlled hot rolling comprises hot rolling maintaining:
Furnace Temperature (Soaking) in the range of 1220 – 1260 oC;
Finish Rolling Temperature in the range of 840 –880 oC; and
Coiling Temperature in the range of 620 – 660 oC.
7. A process for the manufacture of hot rolled medium carbon steel as claimed in anyone of claims 5 or 6 comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii)continuous slab casting;
(iii) hot charging directly into re-heating furnace;
(iv) re-heating the slabs followed by rough rolling such as to increase the austenite grain size and bring the chromium completely to solution and provide said coarse pearlitic structure under hot rolling;
(v) followed by Finish Rolling, ROT cooling and coiling.

8. A chain link comprising of hot rolled medium carbon steel having

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe
having hardened with central neck region and coarse pearlite micro-structure.

9. Chain link as claimed in claim 6 comprising two circular chain link openings connected by a central neck region wherein the connecting central neck region has a Hardness HRC in the region of 50 – 55 with the adjoining peripheral regions having hardness in the range of 55-60.

Dated this the 3rd day of January, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION

The present invention relates in general to hot rolled medium carbon steel and a process for its production. More particularly, the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability for chain link application in light and heavy earth moving equipments. Importantly, the present invention provides for the most economical way of increasing the hardenability of medium carbon steel by slightly increasing the re-heating temperature and adding small amount of chromium favouring lowering the rate of transformation of austenite there by having large austenite grains resulting in having better hardenability. The hot rolled medium carbon steel grade with improved hardenability according to the present invention is having combination of mechanical properties suitable specifically for application in producing chain links for light and heavy earth moving vehicles which ensure higher hardness in the neck portion combined with toughness of links thus reducing the rate of failure and favouring prospects of wide scale industrial application in such equipments.

BACK GROUND OF THE INVENTION

It is well known that chain links are one of the most important components for power transmission in any moving vehicles including automobiles. Chains are precision engineered and expected for excellent performance in terms of low wear and long life. Size of the chains and thickness of chain links vary with the applicable loads. Chain links for automobile applications are generally made from medium carbon steels. Hot rolled medium carbon steel sheets are subjected to operations like blanking, piercing & shaving, which are carried out on highly precision presses for making the chain links. Further links are hardened through heat treatment to avoid linear elongation & to get better strength. Blanked and stamped parts of chain links to be used for heavy earth moving equipments made from thicker
sheet metal. For these applications through thickness uniformity in mechanical properties after heat treatment (especially hardness) is must for rated life and safety of chain. In plain medium carbon steels there is inherent change in hardness along the thickness of the sheet or can be called to have low hardenability and therefore used in applications of thin sections only. The existing known methods of hot rolling medium and high carbon steel do not provide consistence suitable microstructure with desired hardenability for thicker chain link application particularly where the thickness is more than 2.5 mm and blank is about 20mm x 60mm. The heat treated chain links tend to fail at the neck region due to low hardness. The chain links generally use to get failed or cracked in the critical neck region due to variation in hardness. With increased size and thickness, innovative alloying combination and processing parameters are required to have good hardenability.

The two most important variables which influence hardenability are steel composition and austenite grain size.

There has been therefore a need in the art to developing new grades of steel at moderate cost with improved hardenability suitable for chain link application with reliable performance.
The present invention thus attempts to provide most economical way of increasing the hardenability of medium carbon steel.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to providing hot rolled medium carbon steel grade with improved hardenability and a cost effective process for its production for application of such steel in production of chain links for light and heavy earth moving vehicles.
A further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability by introducing the most economical way of increasing the hardenability of medium carbon steel is to slightly increase there heating temperature and add small amount of chromium.
A further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability by adding Chromium in lower percentages lowering the rate of transformation of austenite there by having large austenite grains resulting in having better hardenability.
A still further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability wherein chromium is used as a mild hardenability agent in precipitation hardening, a unique ability promoted at an optimum combination of chromium and carbon.
Yet another object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability wherein said grade ensure improved hardness at the neck region and through thickness uniformity of mechanical property of chain links produced from the steel grade preventing failure of link.
A further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability produced through a process wherein reheating furnace temperature is slightly increased(by 20°C) to increase the austenite grain size and bring the chromium completely to solution.

A still further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability which is having consistent and favourable mechanical properties suitable for blanking forming, shearing and induction heat treatment operations, required for producing component like chain links.

A still further object of the present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability through a process wherein usage of various ferroalloys are minimised, to keep the cost of production of the new grade steel at minimum.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to providing hot rolled medium carbon steel comprising:

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe,
having hardness values of - upto HRB 95.

A further aspect of the present invention is directed to hot rolled medium carbon steel comprising of;
Yield Strength = 540-580 MPa;
UTS = 820-860 MPa;
% Elongation = 15-17
and having coarse pearlite micro-structure,

A still further aspect of the present invention is directed to hot rolled medium carbon steel which is in the form of coils having:
Coil thickness in the range of 2.3 – 6.0 mm;
Coil width in the range of 1000 -1250 mm.

A still further aspect of the present invention is directed to hot rolled medium carbon steel having hardness and metallographic characteristics suitable for blanking forming, shearing and heat treatment operations.

Yet another aspect of the present invention is directed to a process for the manufacture of hot rolled medium carbon steel as described above comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii) continuous slab casting;
(iii) subjecting to re-heating of slabs directly into a re-heating furnace ; and
(iv) controlled rolling to achieve desired hardness.

A still further aspect of the present invention is directed to said process for the manufacture of hot rolled medium carbon steel wherein said step of controlled hot rolling comprises hot rolling maintaining:
Furnace Temperature (Soaking) in the range of 1220 – 1260 oC;
Finish Rolling Temperature in the range of 840 –880 oC; and
Coiling Temperature in the range of 620 – 660 oC.

Yet another aspect of the present invention is directed to said process for the manufacture of hot rolled medium carbon steel comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii)continuous slab casting;
(iii) hot charging directly into re-heating furnace;
(iv) re-heating the slabs followed by rough rolling such as to increase the austenite grain size and bring the chromium completely to solution and provide said coarse pearlitic structure under hot rolling;
(v) followed by Finish Rolling, ROT cooling and coiling.

A still further aspect of the present invention is directed to a chain link comprising of hot rolled medium carbon steel having

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe
having hardened with central neck region and coarse pearlite micro-structure.

A still further aspect of the present invention is directed to said Chain link comprising two circular chain link openings connected by a central neck region wherein the connecting central neck region has a Hardness HRC in the region of 50 – 55 with the adjoining peripheral regions having hardness in the range of 55-60.

The present invention thus provides most economical way of increasing the hardenability of medium carbon steel by slightly increasing there-heating temperature and adding small amount of chromium. Chromium in lower percentages has shown marked affect on lowering the rate of transformation of austenite there by having large austenite grains resulting in having better hardenability. Here, the hardenability, or austenite retention, should not be confused with austenite formation, which is the expansion of the austenite field at high temperature not promoted by chromium.

The objects and advantages of the present invention are described in greater details with reference to following non limiting illustrative drawing and embodiments.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

Figure 1: is the flow chart of the process for production of hot rolled medium carbon steel according to the present invention showing the steps involved in sequence.
Figure 2: shows the schematic view of chain link made of hot rolled medium carbon steel with circular portions marked A1, B1, A2, B2 & neck region marked C, where the hardness values are checked for uniformity to ensure reliable performance.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURE

The present invention relates to providing hot rolled medium carbon steel grade with improved hardenability and a cost effective process for its production for application of such steel in production of chain links for use in light and heavy earth moving vehicles.
In the present invention, the advancement establishes the most economical way of increasing the hardenability of medium carbon steel by slightly increasing the re-heating temperature and adding small amount of chromium.
Chromium in lower percentages has marked affect on lowering the rate of transformation of austenite there by having large austenite grains resulting in having better hardenability. Here, the hardenability, or austenite retention, should not be confused with austenite formation, which is the expansion of the austenite field at high temperature not promoted by chromium. In the present invention chromium is used as a mild hardenability agent by adding in the range of 0.15 – 0.35 % and preferably 0.25%, which resulted in precipitation hardening a unique ability promoted at an optimum combination of chromium and carbon. The chain links generally use to get failed or cracked in the critical neck region due to variation in hardness. Hardness at the neck region improved from 40 HRC to 53 HRC after chemistry modification.

The hardenability increases with increasing austenite grain size, because the grain boundary area is decreasing. This means that the sites for the nucleation of ferrite and pearlite are being reduced in number, with the result that these transformations are slowed down, and the hardenability is therefore increased. In the present invention, the process of re-heating was modified by changing the re-heating furnace temperature. Furnace temperature was increased by 20 oC from 1200 to 1220 oC. This was done to increase the austenite grain size and bring the chromium completely to solution.

The present invention thus relate to suitable chemistry selection, optimum rolling procedure to meet the required coarse pearlitic structure in the hot rolled state. This material is further suitable for little blanking forming, shearing and induction hardening to attain final requirement of chain link i.e. tough and strong.

This new steel grade is made through converter steel making and ladle heating furnace. It is further cast into slabs through continuous casting process. These slabs are processed through re-heating furnace and hot rolling followed by controlled cooling. The hot rolled coils are inspected manually. Samples are collected from the coils in longitudinal and transverse direction. These samples are tested in laboratory for cleanliness of steel and mechanical properties.

Thus according to the present invention, hot rolled medium carbon steel with improved hardenability has been produced comprising the steps of:
(v) selectively involving alloying elements in combination with chromium in steel making resulting in steel composition as presented in following Table I:
Table I:
%-C %-Mn %-S max %-P max %-Si %-Al %-N max %-Cr
0.50-0.58 0.50-0.90 0.020 0.025 0.15-0.35 0.010-0.040 0.0080 0.15-0.35

(vi) continuous slab casting;
(iii) hot charging directly into re-heating furnace;
(iv) re-heating the slabs followed by rough rolling such as to increase the austenite grain size and bring the chromium completely to solution such as to reach required coarse pearlitic structure under hot rolling;
(v) followed by Finish Rolling, ROT cooling and coiling.
Accompanying Figure 1 illustrates the flow chart of the process for production of hot rolled medium carbon steel according to the present invention showing the steps involved in sequence.

While deciding on the above alloy composition to achieve the desired properties in the resulting steel, following considerations were followed:
C: 0.5% or more and less than 0.65% by weight

Carbon is an element that improves the strength and hardness of steel. The carbon content needs to be 0.5% or more to ensure a required strength and hardness for the chain link application. At a C content of 0.65% or more, weldability and toughness are deteriorated. Accordingly, the C content is 0.5% or more and less than 0.65% and preferably in a range of 0.50 to 0.58% by weight.

Si: 0.10% or more and less than 0.40% by weight

Si acts to reinforce steel, and a necessary amount of Si is added to steel in accordance with the intended strength of the steel and needs to be contained in an amount of 0.10% or more. Incorporation of excess Si exceeding 0.4% significantly deteriorates toughness. Accordingly, the Si content is 0.10% or more and 0.40% or less and is preferably in a range of 0.15 to 0.35% by weight.

Mn: 0.50% or more and 0.90% or less by weight

Manganese is an element that improves the strength of steel material and 0.50% or more of Mn needs to be contained to ensure a required strength. In contrast, the hardenability is deteriorated if Mn is contained exceeding 0.90%. Accordingly, the Mn content is 0.5% or more and 0.90% or less and preferably in a range of 0.6 to 0.8% by weight.

P: 0.025% or less by weight

Phosphorus is an element that improves the atmospheric corrosion resistance of the structural steel material. However, adding too much P to steel in an amount of larger than 0.025 % by weight will have some negative influences on the hardenability of the steel. Accordingly, the P content is 0.025% or less and preferably less than 0.015% by weight.

S: 0.020% or less by weight

At a sulfur content exceeding 0.0200%, weldability and toughness is deteriorated. Accordingly, the S content is restricted to 0.020% or less and preferably less than 0.010% by weight.

Al: 0.010% or more and 0.050% or less by weight

Aluminum is added for deoxidization during steel making. The Al content needs to be 0.010% or more to achieve this effect. At an Al content exceeding 0.050%, however, weldability is adversely affected. Thus, the Al content is 0.010% or more and 0.050% or less and preferably in a range of 0.010 to 0.040% by weight.

Cr: more than 0.10% and 1.0% or Less

Chromium improves the hardenability of the steel by precipitation hardening. The Cr content needs to be more than 0.1% to fully bring this effect. At a Cr content exceeding 0.5%, the weldability is degraded. Thus, when Cr is to be contained, the Cr content is more than 0.1% and 0.5% or less and preferably in a range of 0.15 to 0.35% by weight.

N: not larger than 0.008 % by weight

More desirably, N is as smaller as possible for better mechanical properties of the steel. N in steel in an amount of not larger than 0.008 % by weight, would not have any significant negative influences on the hardenability and other properties of the steel. Therefore, the N content of steel is defined to be not larger than 0.008 % by weight, but preferably smaller than 0.004 % by weight.

The balance is Fe and unavoidable impurities.

The effect of various proportions of the alloying elements used in various trials on hardness to arrive at the desired composition of the medium carbon hot rolled steel according to the present invention specifically involving selective use of chromium for improved hardenability of the steel by precipitation hardening is illustrated in the following table 2.

Table-2:
%-C %-Mn %-S max %-P max %-Si %-Al %-N max %-Cr Hardness after heat treatment (Periphery) Hardness after heat treatment (centre) Remarks
0.55 0.7 0.01 0.01 0.026 0.028 0.006 0.28 58 54 Invention
0.53 0.65 0.011 0.01 0.029 0.032 0.006 0.25 57 54 Invention
0.52 0.68 0.01 0.01 0.18 0.01 0.007 0.05 49 42 Comparison
0.51 0.7 0.007 0.012 0.21 0.006 0.0053 0.038 48 43 Comparison
0.5 0.7 0.004 0.01 0.19 0.012 0.0057 0.041 48 44 Comparison

The above stated process for producing the hot rolled medium carbon steel with improved hardenability was implemented following the route as below in sequence:
1. Steel making by LD Converter;
2. Secondary steel making : Ladle Heating Furnace;
3. Continuous slab casting;
4. Hot Charging;
5. Re-heating, Hot rolling, ROT cooling and Coiling with set optimum processing parameters;

In the above process Hot rolling parameters specified for processing of the medium carbon steel with improved hardenability are presented in following Table 3:
Table 3:
1 Furnace Temperature (Soaking) 1220 – 1260 oC
2 Finish Rolling Temperature 840 –880 oC
3 Coiling Temperature 620 – 660 oC

The Hot rolled medium carbon steel so produced is in the form of coils having:
Coil thickness in the range of 2.3 – 6.0 mm;
Coil width in the range of 1000 -1250 mm.
As already stated, the hot rolled coils are inspected manually. Samples are collected from the coils in longitudinal and transverse direction. These samples are tested in laboratory for cleanliness of steel and mechanical properties.

Mechanical tests and Metallography

The tensile properties (yield strength, ultimate tensile strength) are measured using test specimens with 50 mm gauge length, fitted with a class 1 extensometer on a universal testing machine. The tensile test was conducted as per JIS Z2241 with sample number 5 as per JIS Z2201. The strain rate was kept 5mm/sec up to yield point. All tests are performed at room temperature.

Hardness is measured in final blanked and heat treated sample to verify the suitability of the links for chain application. Hardness is measured using Rockwell Hardness testing machine. The determination of the Rockwell hardness of a material involves the application of a minor load followed by a major load, and then noting the depth of penetration, vis a vis, hardness value directly from a dial, in which a harder material gives a higher number. Hardness is reported in the most commonly used being the "B" and "C" scales. Both express hardness as an arbitrary dimensionless number.

Metallographic analysis is carried out to rate the cleanliness of steel. Metallographic samples prepared are polished and etched with 5% nital. A simple light optical microscope is used to record the size of the grains comprising the material.

The hot rolled medium carbon steel so produced is having coarse pearlitic microstructure.
The Hot rolled medium carbon steel produced following the process according to the present invention found to have the properties of;
Yield Strength = 540-580 MPa;
UTS = 820-860 MPa;
% Elongation = 15-17
Hardness- upto HRB 95.
Thus by judicious selection of alloying elements in combination with chromium helped achieve good hardenability of the steel without compromising the strength. Moreover, optimum chemistry of the steel resulted in consistent and favourable mechanical properties suitable for blanking forming, shearing and heat treatment operations, required for components like chain link for light and heavy earth moving vehicles.

The steel grade is most suitable for hot rolling with improved Hardenability. The steel produced can be used by automobile component manufacturers for chain link application in light and heavy earth moving equipments with suitable heat treatment.

Accompanying Figure 2 shows the schematic view of the chain link comprising two circular chain link openings connected by a neck region produced with the hot rolled medium carbon steel according to the present invention wherein the hardness in neck region wherein the connecting neck region comprises a Hardness HRC in the region of 50 – 55. The comparative hardness properties are shown in the following Table 4:

Table 4:
Hardness HRC (after heat treatment) Before Modification After
Modification
A1, B1, A2, B2 55 - 60 55 - 60
C 36 - 45 50 - 55

It is thus possible by way of the present invention to provide hot rolled medium carbon steel grade with improved hardenability suitable for cost effective and reliable application in chain link for light and heavy earth moving vehicles without failure of such chain links at neck region. The present invention is also ensuring the following advantageous features:

1. The new hot rolled medium carbon grade steel with chromium and optimised rolling parameters increased the hardenability.
2. The new hot rolled grade steel with chromium and coarse pearlite microstructure can be directly used for chain link application in light and heavy earth moving equipments.
3. The new hot rolled grade steel reduced the rejection during induction hardening.
4. The chain links generally use to get failed or cracked in the neck region due to variation in hardness along the centre line. Hardness around the neck region improved after modification.
5. Optimum chemistry of the steel resulted in consistent and favourable mechanical properties suitable for blanking forming, shearing and heat treatment operations.
6. Judicious selection of alloying elements in combination with chromium helped achieve good hardenability of the steel without compromising the strength.
7. Coarse pearlite microstructure of the newly developed steel helped achieve a favourable combination of mechanical properties.
8. Due to minimum usage of various ferroalloys, the cost of production of the new grade steel is kept minimum.

We Claims:

1. Hot rolled medium carbon steel comprising:

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe;
having hardness values of - upto HRB 95.

2. Hot rolled medium carbon steel as claimed in claim 1 comprising of;
Yield Strength = 540-580 MPa;
UTS = 820-860 MPa;
% Elongation = 15-17
and having coarse pearlite micro-structure,
3. Hot rolled medium carbon steel as claimed in anyone of claims 1 or 2 which is in the form of coils having:
Coil thickness in the range of 2.3 – 6.0 mm;
Coil width in the range of 1000 -1250 mm.
4. Hot rolled medium carbon steel as claimed in anyone of claims 1 to 3 having hardness amd metallographic characteristics suitable for blanking forming, shearing and heat treatment operations.

5. A process for the manufacture of hot rolled medium carbon steel as claimed in anyone of claims 1 to 4 comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii) continuous slab casting;
(iii) subjecting to re-heating of slabs directly into a re-heating furnace ; and
(iv) controlled rolling to achieve desired hardness.

6. A process for the manufacture of hot rolled medium carbon steel as claimed in claim 5 wherein said step of controlled hot rolling comprises hot rolling maintaining:
Furnace Temperature (Soaking) in the range of 1220 – 1260 oC;
Finish Rolling Temperature in the range of 840 –880 oC; and
Coiling Temperature in the range of 620 – 660 oC.
7. A process for the manufacture of hot rolled medium carbon steel as claimed in anyone of claims 5 or 6 comprising:
(i) selectively involving said alloying elements in combination with chromium in steel making;
(ii)continuous slab casting;
(iii) hot charging directly into re-heating furnace;
(iv) re-heating the slabs followed by rough rolling such as to increase the austenite grain size and bring the chromium completely to solution and provide said coarse pearlitic structure under hot rolling;
(v) followed by Finish Rolling, ROT cooling and coiling.

8. A chain link comprising of hot rolled medium carbon steel having

C- 0.50-0.58% by wt.;
Mn-0.50-0.90% by wt.;
S- Upto 0.020% by wt.;
P- Upto 0.025 % by wt.;
Si-0.15-0.35 % by wt;
Al-0.010-0.040 % by wt.;
N- Upto 0.0080 % by wt.;
Cr-0.15-0.35 % by wt.: and
balance being Fe
having hardened with central neck region and coarse pearlite micro-structure.

9. Chain link as claimed in claim 6 comprising two circular chain link openings connected by a central neck region wherein the connecting central neck region has a Hardness HRC in the region of 50 – 55 with the adjoining peripheral regions having hardness in the range of 55-60.

Dated this the 3rd day of January, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: HOT ROLLED MEDIUM CARBON STEEL WITH IMPROVED HARDENABILITY AND A PROCESS FOR ITS PRODUCTION.

The present invention is directed to providing hot rolled medium carbon steel grade with improved hardenability for chain link application in light and heavy earth moving equipments. Importantly, the present invention provides for the most economical way of increasing the hardenability of medium carbon steel by slightly increasing the re-heating temperature and adding small amount of chromium favouring lowering the rate of transformation of austenite there by having large austenite grains resulting in having better hardenability. The hot rolled medium carbon steel grade with improved hardenability according to the present invention is having coarse pearlitic structure produced through controlled hot rolling and coiling with selectively maintained furnace temperature and finishing and coiling temperatures to produce desired mechanical property specifically suitable for application in chain links for light and heavy earth moving vehicles with higher hardness in the neck portion of links thus reducing the rate of failure and favouring prospects of wide scale industrial application in such equipments.
(Figure 1)