FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION
Hardened Plain carbon Steel with Micro alloying and manufacturing by
control cooling
APPLICANT
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Raghavendra G., Deodatta Shende
All Indian national
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
Hardened Plain carbon Steel with Micro alloying and manufacturing by control cooling
FIELD OF INVENTION:
This invention is related to Hardened Plain carbon Steel with Micro alloying and manufacturing by control cooling more particularly to using micro alloying elements like boron, molybdenum, Titanium, Vanadium and Nitrogen; and using control cooling of the alloy.
The typical cycle for manufacturing includes forging and control cooling to use forging heat and avoid heat treatment to save cost and get desired properties.
BACKGROUND OF THE INVENTION:
Presently various grades of steel are used for varying application of products from low carbon to high carbon steel or spring steel. The typical cycle for manufacturing of forging parts includes forging - normalizing and heat treatment. This grade of steel is developed for cost reduction purpose.
40Cr4 provides adequate material property for desired application. However it is expensive due to the addition of Chromium as the alloying element. Chromium is added for hardenability. To make full use of potential of this material and get adequate material property, 40Cr4 needs to be hardened and tempered. Hardening and tempering is done after forging, which requires more heat energy because of reheating and do the necessary heat treatment. Hence a lot of heat energy is wasted and also detrimental to environment due to pollution caused for reheating. Because of above reasons it is not economic and require more time to manufacture.
SAE1541 material is more economic and but the required mechanical properties are not met. So, SAE1541 is not a suitable material for use in desired application.
Brief Description of Drawings:
Figure 1 and 2 Shows Pearlite grain boundary ferrite (-5%) with grain size 5-6.

THE OBJECT OF THIS INVENTION:
The main object of this invention is to obviate the above drawbacks.
Another object of this invention is to decrease the cost of the alloy.
Yet another object is to avoid heat treatment process like annealing and hardening.
SUMMARY OF THIS INVENTION:
Hardened Plain carbon Steel with Micro alloying elements comprising forged SAE 1541 grade which is a plain medium carbon steel and alloying elements and micro-alloying elements wherein nitrogen is added as an alloying element by purging during steel making and micro-alloying elements like boron, molybdenum, titanium, and vanadium and is manufactured by control cooling.
Nitrogen combines with carbon to form carbon-nitrides to impart desired strength. Presence of nitrogen in the alloy is 70 to 80 ppm. The micro-alloying elements are added 0.010% max individually or in combination. The alloy is forged and cooled in a controlled manner in a variable frequency belt conveyer having blowers. The rate of cooling is adjustable by changing the belt speed. The rate of cooling rate is 63-66 deg/minute from 850 °C to 550 °C. The hot forging temperature is 1230 °C -1250 °C. The finish forging temperature is 950 °C -1050 °C.
DETAILED DESCRIPTION OF THIS INVENTION:
In the instant invention SAE 1541 is used as a base material and more alloying elements are added to get the desired properties like Tensile strength; Yield strength, % Elongation, % area of c/s. Hardness BHN. Microstructure etc.. The cost reduction is achieved by using steels with not using alloying elements like Chromium etc.. Though Nitrogen is considered as gaseous impurity in the instant invention Nitrogen is added as alloying element which in turn combines with carbon and forms carbonitrides resulting in higher strength of material. As the heat treatment processes like Normalizing and hardening etc are expensive involving heat, fuel/electricity cost, in the instant invention the forging heat is utilized for the treatment and the process is termed as controlled cooling. The micro-alloying elements are preferably boron, molybdenum, Titanium, Vanadium and Nitrogen in a fixed range to achieve the desired property. Boron is added to steel preferably 0.0005

to 0.003 % to improve hardenability. Molybdenum is added to increase hardness and increase toughness. It helps to resist softening at high temperature and assures high creep strength. Titanium helps to improve machinability. Titanium is also used to achieve improvements in inclusion characteristics. Titanium causes sulfide inclusions to be globular rather than elongated thus improving toughness and ductility in transverse bending. Vanadium retards grain growth and resists better shock, so help in manufacturing process described below. It also increases the yield strength and the tensile strength of carbon steel. The addition of small amounts of Vanadium can significantly increase the strength of steels. Vanadium is one of the primary contributors to precipitation strengthening in micro alloyed steels. When thermo mechanical processing is properly controlled the ferrite grain size is refined and there is a corresponding increase in toughness. The impact transition temperature also increases when vanadium is added. Nitrogen though on its own supposed to be as impurity in Ferrite phase. However in the instant invention when it is combined with carbon it forms carbonitrides which acts as alloying element to enhance microalloying effect. The presence of nitrogen is limited to 70 to 80ppm, The same can be enhanced further by addition of Vanadium, Niobium and Titanium etc. For given grade of steel above elements namely boron, molybdenum, Titanium and Vanadium are added 0.010% max individual or in combination to get required properties.
To achieve the desired property and to avoid subsequent heat treatment control cooling is done which involves the cooling of hot forged component with proper cooling rate to get desired properties. In this, forgings are cooled in a controlled manner with specific entry and exit temperature of forgings in the cooling belt with specific belt travel time. Said specific entry temperature is preferably 947± 5° C and exit temperature 595 ± 5° C of forgings in the cooling belt with specific belt travel time also termed as residence time is preferably 6 to 10 minutes according to the requirement of desired property.
Presently for Carbon- Mn steel SAE / AISI 1541 steel parts need to be uniformly fast air cooled (control cooled) from temp, range 1000 °C up to 500 °C on conveyor / gravity chute followed by transferring into storage bins. In the instant invention heat treatment processes like quenching and tempering can be eliminated. In the instant invention Hot Forging temperature is maintained at 1230-1250 °C and Finish forging temperature is

maintained at 950-1050 °C and subsequently Cooling rate is maintained at 63-66 deg/min from 850 to 550 °C taking a time of 6-7 minutes approximately for cooling.
The alloy steel with controlled cooling can have many applications as for example control cooled stub axle can be used for all passenger cars. Through control cooling process for SAE 1541 material, heat treatment operation can be eliminated for various forged components like shifter shafts, Rear axle shaft, differential case and cover.
As heat treatment process will not be required because of control cooling, so carbon footprint of the components will decrease apart from decrease in cost and time of production. So. environment friendly products having wide requirement in automobiles with better mechanical properties can be manufactured at less cost.
Preferred example and its Metallurgical Parameters
I) Chemical Composition:

c Si Mn P S Al N2
0.35-0.45 0.15-0.35 1.25-1.75 0.035 max 0.035 max 0.0.20-0.060 70-80 ppm
II) Inclusion rating
Max. permissible inclusion rating when measured as per IS 4163 J K chart no 2 for secondary refined steel is as follows

A ' B C D
Thin series 2.5 2 2 2
Thick series 1.0 - - -
III) Reduction ratio
For Concast route min 6:1 For ingot route min 8:1

IV) Grain Size
ASTM grain size: 7/8
V) Gas content

Oxygen Nitrogen Hydrogen
15 ppmmax. 100 ppm max 2 ppm max
VI) Hardenability

J (mm) 1.5 5.0 8
HRC 60-53 57-43 52-32
Comparison of New Hardened Plain carbon Steel with Micro alloying and manufacturing by control cooling vis a vis SAE 1541 and 40Cr4 Other material qualities are as per SS: 4027
Property Comparison for micro alloyed SAE 1541 control cooled with 40Cr4 and SAE 1541 material

Property SAE1541 40Cr4 Hardened Plain
Hardened tempered Hardened tempered carbon Steel with Micro alloying and manufacturing by control cooling
Tensile strength 85-100 91.77
Yield strength 70 min 74.74
% Elongation 12 min 15.20
% area of c/s 50% min 61.57
Hardness BHN 260-300 286 min
Microstructure Tempered Coarse grain of
rnartensite pearlite in grain boundaries ferrite with 6-7% bainitic

structure
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Claims;
We Claim
1. Hardened Plain carbon Steel with Micro alloying elements comprising:
forged SAE 1541 grade which is a plain medium carbon steel and alloying elements and micro-alloying elements wherein nitrogen is added as an alloying element by purging during steel making and micro-alloying elements like boron, molybdenum, titanium, and vanadium and is manufactured by control cooling.
2. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1, wherein Nitrogen combines with carbon to form carbon-nitrides to impart desired strength.
3. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1, wherein presence of nitrogen in the alloy is 70 to 80 ppm.
4. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1, wherein said micro-alloying elements are added 0.010% max individually or in combination.
5. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1, wherein said alloy is forged and cooled in a controlled manner in a variable frequency belt conveyer having blowers.
6. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 5 wherein rate of cooling is adjustable by changing the belt speed.
7. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 5 wherein said rate of cooling rate is 63-66 deg/minute from 850 °C to 550 °C.
8. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1 wherein hot forging temperature is 1230 °C -1250 °C.
9. Hardened Plain carbon Steel with Micro alloying elements as claimed in claim 1 wherein finish forging temperature is 950 °C -1050 °C.

10. Hardened Plain carbon Steel with Micro alloying elements and manufacturing by control cooling as herein above described and as illustrated in accompanying drawings.