Claims:WE CLAIM:

1. A composition of high strength wear resistant steel comprising in wt % C 0.15-

0.20, Mn 1.20-1.60, S 0.01max., P 0.025 max. Si 0.40-0.60, Al 0.02-0.06, Cr 0.30-

0.60, Ni 0.20-0.24, Mo 0.10-0.20, V 0.03-0.05 and the rest iron (Fe).

2. A composition as claimed in claim 1, wherein the steel has the hardness of 370

HBW (minimum), UTS 1370 MPa (minimum), elongation 11% (minimum), and

CIE 30J at -40o C (minimum).

3. A process for the manufacture of high strength wear resistant steel as claimed in claims 1 and 2, wherein the process steps comprising heat treatment by the route of Basic Oxygen Furnace (BOF) through Vacuum Arc Refining (VAR) / Vacuum Oxygen Refining (VOR), Ladle Heating Furnace (LHF), Continuous Casting Machine (CCM), Plate Mill (PM), Special Plate Plant (SPP) (quenching).

4. A process as claimed in claim 3 wherein the heat treatment of steel is made by austenitizing at 930o C and then water quenching for 10-15 minutes to achieve a minimum value of mechanical properties as follow : hardness - 370 HBW, UTS -
1370 MPa, elongation of 11% and CIE - 30J at -40o C.

5. The said steel has potential application in earth movers for construction and agricultural equipment and mostly fabricated as excavator sharp bucket teeth, dozer blades and other similar equipments due to its unique combination of properties easily serve the purpose for required ground penetration, enabling excavator to dig with the least possible effort, and hence the longer life.

Dated: this 16th day of March, 2017

(N. K. Gupta)
Patent Agent
Of NICHE
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:COMPOSITION OF HIGH STRENGTH WEAR RESISTANT STEEL AND A PROCESS FOR MANUFACTURING THE SAID STEEL

FIELD OF THE INVENTION

This invention relates to a composition of high strength wear resistant steel and a process for manufacturing the said steel.

BACKGROUND ART

High strength steel plates with excellent combination of high strength, toughness and wear resistance are used for load carrying structures & wear resistant applications in rail road cars, hoppers and feeders, dumper bodies, dump trucks, buckets, barges etc. These applications are such that the material needs higher wear resistance for longer life. This particular property can be attributed by higher hardness of surface as well as through thickness of the material.

Quenching is most commonly used to harden steel by introducing martensite, in which the steel must be rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. This process prevents undesired low-temperature processes, such as phase transformation from occurring by reducing the window of time during which these undesired reactions are both thermodynamically favourable, and kinetically accessible. In steel alloyed with metals such as Mn, Ni, the eutectoid temperature becomes much lower, but the kinetic barrier to phase transformation remains the same. On the other hand, steel alloyed with metals such as Cr, Mo, and V has reverse effect on eutectoid temperature. So, austentizing temperature for a high strength steel(micro alloyed with Cr, Mo, V to enable certain desirable properties) should be such that all pearlite is transformed into austenite before its quenching in suitable media to enable homogeneity in properties especially, hardness determined by surface hardening or through hardening varying on the rate at which the material is cooled.

OBJECT OF THE INVENTION

The object of the invention is to provide for a composition of high strength wear resistant steel.

The other object of the invention is to provide for a process technology for development of high strength wear resistant steel.

Another object of the invention is to provide details of probable equipment/application which can be made from said steel. The said equipment by way of example, can be earth movers for construction, agricultural equipments and those mostly fabricated as excavator sharp bucket teeth, dozer blades and similar equipments.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

Fig. 1 shows the martensitic microstructure of the invented steel (a) surface (b) mid surface.

DESCRIPTION OF THE INVENTION

According to this invention there is provided a composition of high strength wear resistant steel which comprises in wt % C 0.15-0.20, Mn 1.20-1.60, S 0.01max., P
0.025 max., Si 0.40-0.60, Al 0.02-0.06, Cr 0.30-0.60, Ni 0.20-0.24, Mo 0.10-0.20, V

0.03-0.05 and the rest iron (Fe).

The invented steel has the hardness of 370 HBW (min.), UTS 1370 MPa (min.), elongation 11% (min.) and CIE 30J at -40o C (min.).

The invention includes a process for the manufacture of high strength wear resistant steel which comprises a route of Basic Oxygen Furnace (BOF) through Vacuum Arc Refining (VAR) / Vacuum Oxygen Refining (VOR) - Ladle Heating Furnace (LHF) – Continuous Casting Machine (CCM) – Plate Mill (PM) - Special Plate Plant (SPP)(quenching). The heat treatment of steel is made by austenitizing at 930o C and then water quenching for 10-15 minutes to achieve a minimum value of mechanical
properties as follow: hardness 370 HBW, UTS 1370 MPa, elongation 11% and CIE

30J at -40o C.

The invention also includes probable equipment/application details of the said steel. The said equipment by way of example, can be as earth movers for construction and agricultural equipments and those mostly fabricated as excavator sharp bucket teeth, dozer blades and other similar equipments. Having unique combination of properties

the invented steel can easily serve the purpose for required ground penetration enabling excavator to dig with the least possible effort and hence the longer life.

According to the invention industrial heat treatment of steel is made in steel melting shop using Basic Oxygen Furnace (BOF) and processed through Vacuum Arc Refining (VAR)/Vacuum Oxygen Refining (VOR) - Ladle Heating Furnace (LHF) - Continuous Casting Machine (CCM) route. Alloy chemistry (Wt. %) is given in Table 1 as follows:

Table 1: Alloy chemistry

C Mn S P Si Al Cr Ni Mo V
0.15-

0.20 1.20-

1.60 0.01

max 0.025

max 0.40-

0.60 0.02-

0.06 0.30-

0.60 0.20-

0.24 0.10-

0.20 0.03-

0.05

Slabs having dimensions 210mm x 1150mm x 2690mm are rolled into Plates having dimensions 20mm x 220mm x 3600mm. Finishing temperature is maintained in the range of 905–9100 C. Draft per pass is 10-12 mm. Hardness in the range of 215-220
BHN is achieved in as rolled condition. Plates are then heat treated by austenitizing at

9300 C and then water quenched for 10-15 minutes at Special Plate Plant (SPP). Mechanical properties achieved after heat treatment are shown in Table 2.

Table 2: Properties of quenched steel after heat treatment

Hardness

(HBW) UTS, MPa % El

(50 mm GL) CIE, J

(at -400C)
370-415 1370 - 1415 11-13 30-36

Innovative alloy design and processing has resulted into excellent combination of properties in terms of high tensile strength, high hardness along-with higher chary impact energy (CIE) values at -400 C. Microstructure analysis of quenched plates has also been done to check the extent of martensite transformation which is shown in Fig.1 of the accompanying drawing. Fully martensitic microstructures are observed in the surface and mid thickness.

Present invention has significant implication in integrated steel plant plate mills/plate mills having heat treatment facilities for producing high strength wear resistant

steel. The alloy design and performed process route facilitates formation of fully martensitic structure enabling higher hardness which can be exploited for load bearing and wear resistant applications.

? Salient Features of The Invention

? Special steel grade has been developed with excellent combination of wear- resistant properties through Basic Oxygen Furnace (BOF) and processed through Vacuum Arc Refining (VAR) / Vacuum Oxygen Refining (VOR) - Ladle Heating Furnace (LHF) – Continuous Casting Machine (CCM) – Plate Mill (PM) – Special Plate Plant (quenching) route.

? Heat treatment of plates by austenitizing at 9300 C and then water quenching for 10-15 minutes led to achieve a minimum value of mechanical properties as follows; hardness - 370 HBW.

From the above disclosure of the invention it is apparent that several additional embodiments beyond those disclosed herein are possible which can be carried out by a person skilled in the art. The same are included within the broad ambit of the invention claimed hereinafter.