Claims:We Claim:
1. A low alloyed thicker section abrasion resistant steel having superior strength, ductility and abrasion resistance combination comprising the following composition expressed in weight %:
Carbon (C): 0.1% - 0.2%,
Manganese (Mn): 1.0% - 1.5%,
Chromium (Cr): 0.4-0.6%,
Silicon (Si): 0.4%-0.6%,
Nickel (Ni): 0.4%-0.6%,
Aluminium (Al): 0.05-1.2%,
Molybdenum (Mo): 0.1%-0.3%, Vanadium: 0.05% to 0.15%, and the remaining being substantially iron and incidental impurities, wherein the low alloyed thicker section abrasion resistant steel comprises a microstructure of 90 – 97 vol.% martensite, up to 10 vol.% retained austenite, and remaining carbides, wherein the low alloyed thicker section abrasion resistant steel exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
2. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the low alloyed thicker section abrasion resistant steel has a hardness (HV 1 kg) ≥ 300 Hv.
3. The low alloyed thicker section abrasion resistant steel as claimed in the claim 2, wherein the low alloyed thicker section abrasion resistant steel has hardness (HV 1 kg) in the range of 300 - 500 Hv.
4. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the low alloyed thicker section abrasion resistant steel has a yield strength ≥ 550 MPa.
5. The low alloyed thicker section abrasion resistant steel as claimed in the claim 4, wherein the low alloyed thicker section abrasion resistant steel has the yield strength in the range of 550 MPa – 900 MPa.
6. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the low alloyed thicker section abrasion resistant steel has uniform elongation in range 5 to 11%.
7. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-20 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
8. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the Mn 1.0 to 1.5 wt.%, Ni 0.40 to 0.60 wt.% and Mo 0.10 to 0.30 wt.% of the low alloyed thicker section abrasion resistant steel is kept in these ranges respectively to avoid to bainite, ferrite and pearlite formation during quenching.
9. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the C content in the low alloyed thicker section abrasion resistant steel helps in improving hardenability, increases strength through interstitial solid solution strengthening, and helps in retaining austenite phase at room temperature.
10. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein low alloyed thicker section abrasion resistant steel is also alloyed with a balanced addition of Si and/or Al to prevent the carbide precipitation and therefore achieve higher austenite retention.
11. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein a small amount of Vanadium is added for precipitation strengthening and grain refinement, and also Vanadium also consumes Nitrogen, thereby eliminating the detrimental free N from the steel by forming its precipitates.
12. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities.
13. The low alloyed thicker section abrasion resistant steel as claimed in the claim 12, wherein the low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 325-368 Hv, the abrasive wear volume loss in the range of 284-466 mm3, a yield strength in the range of 575 -620 MPa, the ultimate tensile strength in the range of 780 – 820 MPa, a uniform elongation in the range of 7-10%, and the total elongation in the range of 20-25%.
14. The low alloyed thicker section abrasion resistant steel as claimed in the claim 13, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 24-38 J at room temperature, and 4-16 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
15. The low alloyed thicker section abrasion resistant steel as claimed in the claim 1, wherein the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities.
16. The low alloyed thicker section abrasion resistant steel as claimed in the claim 15, wherein the low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 395-475 Hv, the abrasive wear volume loss in the range of 268-423 mm3, a yield strength in the range of 650 -840 MPa, the ultimate tensile strength in the range of 870 – 1050 MPa, a uniform elongation in the range of 5-10%, and the total elongation in the range of 14-23%.
17. The low alloyed thicker section abrasion resistant steel as claimed in the claim 16, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-18 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
18. A method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet or strip or blank, the method (100) comprising:
casting molten steel having a composition expressed in weight %: 0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and the balance being Iron (Fe) and unavoidable impurities to obtain a steel slab;
homogenizing the steel slab for austenitizing in a reheating furnace to a homogenizing temp in the range of 1150 - 1250oC for homogenizing time of 100-120 minutes depending on the slab thickness;
hot rolling the homogenized steel slab to about 50% deformation to produce a steel sheet such that finish rolling is done at a temperature (TFRT), wherein TFRT varies in the range 900oC to 1000oC;
quenching the hot rolled steel in a salt bath furnace to a quenching temperature in the range of 250 - 350oC at a quenching rate in the range of 15oC/s - 25oC/s; and
cooling at a cooling rate in the range of 0.001oC/s – 0.007oC/s in a salt bath furnace atmosphere till a room temperature is reached to obtain the low alloyed thicker section abrasion resistant steel sheet, wherein the low alloyed thicker section abrasion resistant steel sheet comprises a microstructure of 90 – 97 vol.% martensite, up to 10 vol.% retained austenite, and remaining carbides, wherein the low alloyed thicker section abrasion resistant steel sheet exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
19. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 18, wherein the low alloyed thicker section abrasion resistant steel sheet exhibits a yield strength ≥ 550 MPa, uniform elongation in range 5 to 11% and a hardness (HV 1 kg) ≥ 300 Hv.
20. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 18, wherein homogenizing temperature is 1200oC for homogenizing time of 120 minutes, TFRT is 900oC, quenching rate 20oC/s; and cooling rate 0.003oC/s.
21. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 18 to 20, wherein the quenching temperature is 250oC.
22. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 21, wherein the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities and having 5.1% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 325-367 Hv, the abrasive wear volume loss in the range of 284-303 mm3, the yield strength in the range of 575 -625 MPa, the ultimate tensile strength in the range of 780 – 820 MPa, the uniform elongation in the range of 7-10%, and the total elongation in the range of 21-25%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 29-38 J at room temperature, and 4-16 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
23. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 18 to 20, wherein the quenching temperature is 270oC.
24. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 23, wherein the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1.0, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities and having 9.7% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 401-475 Hv, the abrasive wear volume loss in the range of 294-338 mm3, the yield strength in the range of 700 -840 MPa, the ultimate tensile strength in the range of 940 – 1050 MPa, the uniform elongation in the range of 5-9%, and the total elongation in the range of 14-22%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 32-40 J at room temperature, and 8-18 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
25. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 18 to 20, wherein the quenching temperature is 350oC.
26. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 25, wherein the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities and having 2.1% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 338-368 Hv, the abrasive wear volume loss in the range of 385-466 mm3, the yield strength in the range of 590 -620 MPa, the ultimate tensile strength in the range of 780 – 815 MPa, the uniform elongation in the range of 7-9%, and the total elongation in the range of 20-22%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 24-31 J at room temperature, and 6-10 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
27. The method (100) for manufacturing low alloyed thicker section abrasion resistant steel sheet as claimed in the claim 25, wherein the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1.0, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities and having 9.8% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 395-446 Hv, the abrasive wear volume loss in the range of 268-423 mm3, the yield strength in the range of 650 -700 MPa, the ultimate tensile strength in the range of 870 – 925 MPa, the uniform elongation in the range of 9-10%, and the total elongation in the range of 21-23%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-28 J at room temperature, and 2-4 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
28. The method (100) for manufacturing the low alloyed thicker section abrasion resistant steel sheet as claimed in the claims 18 to 28, wherein the thickness of the steel sheet is at least 18 mm.
29. A component produced from the low alloyed thicker section abrasion resistant steel as claimed in the claims 1 to 28, wherein in the component is used in structural as well as wear resistant applications of the L&E equipment, particularly used in mining and earthmoving applications.
, Description:FIELD OF INVENTION
[0001] The present invention relates to a low alloyed thicker section abrasion resistant steel, and more particularly to the low alloyed thicker section abrasion resistant steel having with superior strength, ductility, and abrasion resistance, and method of manufacturing the low alloyed thicker section abrasion resistant steel.

BACKGROUND
[0002] Steel is used worldwide for numerous applications due to its low cost, easy recyclability, capability of mass production, excellent strength-ductility combination, etc. Other than the iron and carbon, various alloying elements are also added to the steel to achieve the desired properties suitable for any particular application. Steel, which is used in sectors such as mining, excavation, earthmoving, etc. are required to resist the wear. Therefore, steel with high wear resistance are preferred for such applications.
[0003] The existing steel grades, which are used in such applications, mainly includes medium and high carbon steel with complete martensitic or tempered martensitic microstructure. The tempering process is generally performed for reducing the brittleness of martensite and, therefore, achieve high ductility and impact toughness. However, this tempering process requires additional facility for heat treatment, which leads to additional energy consumption, reduced productivity and added cost. Hence, it is required to produce these steel grades directly through hot rolling mill by altering the alloy composition and processing conditions to achieve the desired microstructure and mechanical properties.
[0004] The achievement of advanced high strength while retaining sufficient ductility requires identification of a suitable microstructure. In this regard, a multiphase microstructure mainly containing martensite/bainite, retained austenite and carbides can be effective to achieve good strength-ductility combination. The presence of some amount of metastable austenite phase is also beneficial for wear-resistant applications. The multiphase microstructure can be achieved through quenching and partitioning (Q&P) process, particularly in low alloy steels. The originally proposed Q&P process involves quenching between Ms and Mf to form some amount of martensite with remaining austenite, followed by isothermal holding for carbon partitioning from martensite to austenite, which helps in its retention to room temperature. This isothermal holding requires an additional furnace and interrupts the continuous process flow in a hot rolling mill.
[0005] Further, the thickness of steel used in wear-resistant applications depends on loading and service condition. For example, a thicker-section steel is used if the component is experiencing higher loads during the service. The steel with high thickness is likely to exhibit a variation in the microstructure at different section through thickness. These changes will lead to nonuniform mechanical properties and as a result may lead to failure from weak link corresponding to poor mechanical properties. One of the commonly adopted strategy to eliminate this nonuniformity is the addition of alloying elements is large amount. However, a higher alloying content in steel is associated with increasing cost, welding and fabrication issues, and challenges during industrial processing. Therefore, it is important to achieve a uniform microstructure in thicker section, particularly in low alloy steel.
[0006] The present disclosure is directed to overcome one or more limitations stated above or any other limitation associated with the prior arts.
OBJECTIVE OF INVENTION
[0007] It is an object of the invention to solve the problems of the prior art and to develop a low alloyed thicker section abrasion resistant steel having with superior strength, ductility, and abrasion resistance for L&E and mining applications.
[0008] Another objective of the present invention is to provide the low alloyed thicker section abrasion resistant steel sheet, having the following composition in weight%: 0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and balance being Iron and residual impurities and a microstructure consisting of martensite, retained austenite and carbides.
[0009] Another objective of present invention is to produce a method to manufacture the low alloyed thicker section abrasion resistant steel such that uniform microstructure and mechanical properties are achieved through out different sections (surface vs center) in thick plate of low alloy steel.
[0010] Another objective of present invention is to design the low alloyed thicker section abrasion resistant steel economically.
SUMMARY OF INVENTION
[0011] This summary is provided to introduce concepts related to a low alloyed thicker section abrasion resistant steel having superior strength, ductility, and abrasion resistance. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0012] In one aspect of the present invention, a low alloyed thicker section abrasion resistant steel having superior strength, ductility and abrasion resistance combination is provided. The low alloyed thicker section abrasion resistant steel comprises the following composition expressed in weight %: 0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and the balance being Iron (Fe) and unavoidable impurities. The low alloyed thicker section abrasion resistant steel comprises a microstructure of 90 – 97% martensite, up to 10 % retained austenite, and remaining carbides. The low alloyed thicker section abrasion resistant steel exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
[0013] In an embodiment, the low alloyed thicker section abrasion resistant steel has a hardness (HV 1 kg) ≥ 300 Hv. In an embodiment, the low alloyed thicker section abrasion resistant steel has hardness (HV 1 kg) in the range of 300 - 500 Hv.
[0014] In an embodiment, the low alloyed thicker section abrasion resistant steel has a yield strength ≥ 550 MPa. In an embodiment, the low alloyed thicker section abrasion resistant steel has the yield strength in the range of 550 MPa – 900 MPa.
[0015] In an embodiment, the low alloyed thicker section abrasion resistant steel has uniform elongation in range 5 to 11%.
[0016] In an embodiment, the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-20 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0017] In an embodiment, the Mn 1.0 to 1.5 wt.%, Ni 0.40 to 0.60 wt.% and Mo 0.10 to 0.30 wt.% of the low alloyed thicker section abrasion resistant steel is kept in these ranges respectively to avoid to bainite, ferrite and pearlite formation during quenching.
[0018] In an embodiment, the C content in the low alloyed thicker section abrasion resistant steel helps in improving hardenability, increases strength through interstitial solid solution strengthening, and helps in retaining austenite phase at room temperature.
[0019] In an embodiment, the low alloyed thicker section abrasion resistant steel is also alloyed with a balanced addition of Si and/or Al to prevent the carbide precipitation and therefore achieve higher austenite retention.
[0020] In an embodiment, a small amount of Vanadium is added for precipitation strengthening and grain refinement, and also Vanadium also consumes Nitrogen, thereby eliminating the detrimental free N from the steel by forming its precipitates.
[0021] In an embodiment, the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities.
[0022] In an embodiment, the low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 325-368 Hv, the abrasive wear volume loss in the range of 284-466 mm3, a yield strength in the range of 575 -620 MPa, the ultimate tensile strength in the range of 780 – 820 MPa, a uniform elongation in the range of 7-10%, and the total elongation in the range of 20-25%.
[0023] In an embodiment, the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 24-38 J at room temperature, and 4-16 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0024] In an embodiment, the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities.
[0025] In an embodiment, the low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 395-475 Hv, the abrasive wear volume loss in the range of 268-423 mm3, a yield strength in the range of 650 -840 MPa, the ultimate tensile strength in the range of 870 – 1050 MPa, a uniform elongation in the range of 5-10%, and the total elongation in the range of 14-23%.
[0026] In an embodiment, the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-18 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0027] In another aspect of the present invention, a method for manufacturing low alloyed thicker section abrasion resistant steel sheet or strip or blank is provided. The method comprises casting molten steel having a composition expressed in weight %: 0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and the balance being Iron (Fe) and unavoidable impurities to obtain a steel slab. The method also comprises homogenizing the steel slab for austenitizing in a reheating furnace to a homogenizing temp in the range of 1150 - 1250oC for homogenizing time of 100-120 minutes depending on the slab thickness. The method further comprises hot rolling the homogenized steel slab to about 50% deformation to produce a steel sheet such that finish rolling is done at a temperature (TFRT). TFRT varies in the range 900oC to 1000oC. The method comprises quenching the hot rolled steel in a salt bath furnace to a quenching temperature in the range of 250 - 350oC at a quenching rate in the range of 15oC /s - 25oC/s. The method also comprises cooling at a cooling rate in the range of 0.001oC/s – 0.007oC/s in a salt bath furnace atmosphere till a room temperature is reached to obtain the low alloyed thicker section abrasion resistant steel sheet. The low alloyed thicker section abrasion resistant steel sheet comprises a microstructure of 90 – 97 vol.% martensite, up to 10 vol.% retained austenite, and remaining carbides. The low alloyed thicker section abrasion resistant steel sheet exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
[0028] In an embodiment, the low alloyed thicker section abrasion resistant steel sheet exhibits a yield strength ≥ 550 MPa, uniform elongation in range 5 to 11% and a hardness (HV 1 kg) ≥ 300 Hv.
[0029] In an embodiment, the homogenizing temperature is 1200oC for homogenizing time of 120 minutes, TFRT is 900oC, quenching rate 20oC/s; and cooling rate 0.003oC /s.
[0030] In an embodiment, the quenching temperature is 250oC. In an embodiment, the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities and having 5.1% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 325-367 Hv, the abrasive wear volume loss in the range of 284-303 mm3, the yield strength in the range of 575 -625 MPa, the ultimate tensile strength in the range of 780 – 820 MPa, the uniform elongation in the range of 7-10%, and the total elongation in the range of 21-25%. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 29-38 J at room temperature, and 4-16 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0031] In an embodiment, the quenching temperature is 270oC. In an embodiment, the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1.0, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities and having 9.7% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 401-475 Hv, the abrasive wear volume loss in the range of 294-338 mm3, the yield strength in the range of 700 -840 MPa, the ultimate tensile strength in the range of 940 – 1050 MPa, the uniform elongation in the range of 5-9%, and the total elongation in the range of 14-22%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 32-40 J at room temperature, and 8-18 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0032] In an embodiment, the quenching temperature is 350oC. In an embodiment, the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities and having 2.1% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 338-368 Hv, the abrasive wear volume loss in the range of 385-466 mm3, the yield strength in the range of 590 -620 MPa, the ultimate tensile strength in the range of 780 – 815 MPa, the uniform elongation in the range of 7-9%, and the total elongation in the range of 20-22%. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 24-31 J at room temperature, and 6-10 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0033] In an embodiment, the low alloyed thicker section abrasion resistant steel comprising the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1.0, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities and having 9.8% retained austenite in the microstructure exhibits the hardness (HV 1kg) in the range of 395-446 Hv, the abrasive wear volume loss in the range of 268-423 mm3, the yield strength in the range of 650 -700 MPa, the ultimate tensile strength in the range of 870 – 925 MPa, the uniform elongation in the range of 9-10%, and the total elongation in the range of 21-23%, wherein the low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-28 J at room temperature, and 2-4 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0034] In an embodiment, the thickness of the steel sheet is at least 18 mm. In an embodiment, a component produced from the low alloyed thicker section abrasion resistant steel. In an embodiment, the component is used in structural as well as wear resistant applications of the L&E equipment, particularly used in mining and earthmoving applications.
[0035] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Figure 1 illustrates a flowchart of a method of manufacturing a low alloyed thicker section abrasion resistant steel sheet, according to an embodiment of the present invention;
[0037] Figure 2 illustrates a graphical representation of thermo-mechanical processing routes of the method of manufacturing the low alloyed thicker section abrasion resistant steel sheet, according to the embodiment of the present invention;
[0038] Figure 3 illustrates a graphical representation of results of X-ray Diffraction analysis carried out on different samples of the low alloyed thicker section abrasion resistant steel, according to the embodiment of the present invention;
[0039] Figure 4 illustrates SEM images of different samples of the low alloyed thicker section abrasion resistant steel, according to an embodiment of the present invention; and
[0040] Figure 5 illustrates a graphical representation of stress versus elongation, obtained during tensile test of different samples of the low alloyed thicker section abrasion resistant steel, according to the embodiments of present invention.
[0041] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.

DETAILED DESCRIPTION
[0042] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0043] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0045] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0046] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0047] The present disclosure relates to a low alloyed thicker section abrasion resistant steel having superior strength, ductility, and abrasion resistance combination. The low alloyed thicker section abrasion resistant steel is suitable for producing components to be used in structural as well as wear resistant applications of the Lifting & Excavating equipment, particularly used in mining and earthmoving applications.
[0048] The low alloyed thicker section abrasion resistant steel comprises the following composition expressed in weight %:0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and the balance being Iron (Fe) and unavoidable impurities. The low alloyed thicker section abrasion resistant steel comprises a microstructure of 90 – 97 vol.% martensite, up to 10 vol.% retained austenite, and remaining carbides. The low alloyed thicker section abrasion resistant steel exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
[0049] The low alloyed thicker section abrasion resistant steel has a hardness (HV 1 kg) ≥ 300 Hv. In the preferred embodiment, the low alloyed thicker section abrasion resistant steel has hardness (HV 1 kg) in the range of 300 - 500 Hv.
[0050] The low alloyed thicker section abrasion resistant steel has a yield strength ≥ 550 MPa. In preferred embodiment, the low alloyed thicker section abrasion resistant steel has the yield strength in the range of 550 MPa – 900 MPa.
[0051] The low alloyed thicker section abrasion resistant steel has uniform elongation in range 5 to 11%. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8J -40 J at room temperature, and 2 J -20 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0052] In one embodiment, the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, V – 0.1, Ni – 0.5, Al – 0.0, Mo – 0.2, P – 0.011, S - 0.009, N – 0.006, and the balance being Iron (Fe) and unavoidable impurities. The low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 325-368 Hv, the abrasive wear volume loss in the range of 284-466 mm3, a yield strength in the range of 575 -620 MPa, the ultimate tensile strength in the range of 780 – 820 MPa, a uniform elongation in the range of 7-10%, and the total elongation in the range of 20-25%. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 24-38 J at room temperature, and 4-16 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0053] In another embodiment, the low alloyed thicker section abrasion resistant steel comprises the composition expressed in weight %: C - 0.15, Mn – 1.2, Si - 0.5, Cr - 0.5, Al – 1, Ni – 0.5, Mo - 0.2, V – 0.1, P – 0.013, S - 0.012, N – 0.008, and the balance being Iron (Fe) and unavoidable impurities. The low alloyed thicker section abrasion resistant steel exhibits a hardness (HV 1kg) in the range of 395-475 Hv. The abrasive wear volume loss in the range of 268-423 mm3, a yield strength in the range of 650 -840 MPa, the ultimate tensile strength in the range of 870 – 1050 MPa, a uniform elongation in the range of 5-10%, and the total elongation in the range of 14-23%. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-18 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0054] Referring to Figures 1 and 2, the method (100) of manufacturing the low alloyed thicker section abrasion resistant steel sheet of the desired composition is illustrated. At step (102), the method (100) comprises casting molten steel having a composition expressed in weight %: 0.10 to 0.20 Carbon, 1.0 to 1.5 Manganese, 0.40 to 0.60 Silicon, 0.05 to 1.2 Aluminium, 0.40 to 0.60 Chromium, 0.10 to 0.30 Molybdenum, 0.40 to 0.60 Nickel, 0.05 to 0.15 Vanadium, and the balance being Iron (Fe) and unavoidable impurities to obtain a steel slab. The molten steel is cast in a casting apparatus to obtain steel slabs (cast ingots). In the illustrated example, the steel is cast either in a conventional continuous caster or thin-slab caster.
[0055] At step (104), the method (100) comprises homogenizing the steel slab for austenitizing in a reheating furnace to a homogenizing temperature in the range of 1150 - 1250oC for homogenizing time of 100-120 minutes depending on the slab thickness. In the preferred embodiment, the slab is homogenized to homogenizing temperature of 1200oC for time duration of 2 hours depending on the slab thickness. A reheating temperature greater than 1250oC is also undesirable because it may lead to excessive grain coarsening of austenite and/or scale loss.
[0056] At step (106), the method (100) comprises hot rolling the homogenized steel slab to about 50% deformation to produce a steel sheet such that finish rolling is done at a temperature (TFRT). In the illustrate example, the TFRT is varied in the range 900oC to 1000oC. The reduction of the thickness to the desired levels is to break the as cast dendritic structure. In a preferred embodiment, the initial thickness of the low alloy steel before rolling is 36 mm.
[0057] After the steel slab is cast in the specified composition and homogenized, it is hot rolled. The slabs of higher thicknesses are rough rolled in roughing stands in a conventional hot-rolling mill. The rough rolling is done above the recrystallization temperature. Then the finish rolling is carried out in a 6 or 7 stands tandem rolling mill. The rolling is finished at the finish rolling temperature, TFRT given by such that 900 ≤ TFRT ≤ 1000oC. The above range of the finish rolling temperature (TFRT) is chosen to finish the hot rolling in the austenitic range. Here the TFRT is kept below Tnr to exploit the thermo-mechanical controlled rolling. In preferred embodiment, TFRT is 900oC. In the preferred embodiment, the steel sheet is hot rolled to 18 mm from 36mm.
[0058] At step (108), the method (100) comprises quenching the hot rolled steel in a salt bath furnace to a quenching temperature in the range of 250 - 350oC at a quenching rate in the range of 15oC/s - 25oC/s. In an embodiment, the quenching temperature is 250oC. In another embodiment, the quenching temperature is 270oC. In yet another embodiment, the quenching temperature is 350oC. In a preferred embodiment, the quenching rate is kept 20oC/s; and cooling rate is kept 0.003oC/s. In an embodiment, the quenching medium is molten salt. Martensite and austenite is observed in the microstructure of the steel once the quenching operation is performed.
[0059] At step (110), the method (100) comprises cooling at a cooling rate in the range of 0.001oC/s – 0.007oC/s in a salt bath furnace atmosphere till a room temperature is reached to obtain the low alloyed thicker section abrasion resistant steel sheet having martensite, retained austenite and carbides within the microstructure. The cooling rate is kept between 0.001oC/s – 0.007oC/s so as to simulate the hot rolled coil cooling condition.
[0060] The steel is cooled to allow development of retained austenite and martensite in the final microstructure, which will give rise to the superior strength, ductility, and abrasion resistance combination. The obtained low alloyed thicker section abrasion resistant steel sheet comprises a microstructure of 90 – 97 vol.% martensite, up to 10 vol.% retained austenite, and remaining carbides. The low alloyed thicker section abrasion resistant steel sheet exhibits an abrasive wear volume loss in the range of 250-500 mm3, an ultimate tensile strength in the range of 780 MPa – 1100 MPa, and a total elongation in range 15 to 25%.
[0061] In the illustrated example, the low alloyed thicker section abrasion resistant steel sheet exhibits a yield strength ≥ 550 MPa, uniform elongation in range 5 to 11% and a hardness (HV 1 kg) ≥ 300 Hv. In the illustrated example, the thickness of the steel sheet is in the range of 18 mm. The low alloyed thicker section abrasion resistant steel exhibits a Charpy impact toughness of 8-40 J at room temperature, and 2-20 J at -40°C temperature for a sub size sample with 5×10 mm2 cross section.
[0062] According to the disclosed invention method (100), it is possible to manufacture the low alloyed thicker section abrasion resistant steel sheet which exhibits abrasive wear volume loss in the range of 250-500 mm3, ultimate tensile strength in the range of 780 MPa – 1100 MPa, and total elongation in range 15 to 25%. The low alloyed thicker section abrasion resistant steel sheet has improved superior strength, ductility, and abrasion resistance combination. Such a steel sheet is suited for producing components to be used in structural as well as wear resistant applications of the L&E equipment, particularly used in mining and earthmoving applications where good abrasive wear resistance and impact toughness is a requirement along with the high hardness.
[0063] Following portions of the present disclosure, provides details about the proportion of each element in a composition of the low alloyed thicker section abrasion resistant steel, and their role in enhancing properties.
[0064] C: 0.10-0.20%: The presence of carbon is inevitable in any commercial steel. Carbon is added to control the strength of the steel. Depending on the final requirement, the weight percentage of the carbon addition changes. The purpose of carbon addition is to improve hardenability, increase strength through interstitial solid solution strengthening and for retention of austenite phase at room temperature. However, carbon cannot be increased to a large extent in steel as it impairs the weldability of the steel. Thus, in the current steel carbon content is restricted between 0.10 – 0.20 wt.%.
[0065] Si: 0.4-0.6% & Aluminium 0.05 to 1.2%: The steel was also alloyed with a balanced addition of Si and/or Al to prevent the carbide precipitation and therefore achieve higher austenite retention.
[0066] Mn: 1.0-1.5%, Ni: 0.40 to 0.60% & Mo: 0.10 to 0.30%: These elements are added to eliminate bainite, ferrite and pearlite formation during quenching. However, banding in the microstructure could arise when Mn is added in higher amounts and higher Ni addition is associated with a higher cost. Therefore, only a small amount of Mn and Ni was added to the steel. The combined addition of Ni and Mo is done due to their beneficial effects on hardenability.
[0067] Cr: 0.4-0.6%: A small amount of Cr is added for solid solution strengthening.
[0068] V: 0.05 to 0.15% & Nitrogen: A small amount of Vanadium is added for precipitation strengthening and grain refinement. The V also consumes N, therefore, eliminates the detrimental free N from the steel by forming its precipitates.
[0069] Microstructure: The final set of desired properties in the low alloyed thicker section abrasion resistant steel is achieved by the presence of martensite, retained austenite and carbides. All the hot-rolling, controlled cooling and coiling conditions have significance in achieving the final microstructure and properties. The contribution of the each of the phases i.e., martensite, retained austenite, and carbides are described below.
[0070] Martensite: The final microstructure contains 90 – 97% martensite. The martensite provides strength to the final product.
[0071] Retained Austenite: A small amount of austenite (10% maximum) is observed in the final microstructure. The retained austenite improves impact toughness and ductility in the final product
[0072] Carbides: A small amount of carbides were observed in the final microstructure.
[0073] The martensite in the microstructure ensures the hardness of > 300 Hv is achieved in the final steel sheet.
Examples
[0074] Further embodiments of the present disclosure will be now described with examples of compositions of the low alloyed thicker section abrasion resistant steel sheet, which are illustrated in Table 1.
[0075] The chemical composition of the proposed alloys are shown in Table 1.
Element C Mn Si Al Cr Mo Ni V
Alloy-1 0.15 1.2 0.5 0 0.5 0.2 0.5 0.1
Alloy-2 0.15 1.2 0.5 1.0 0.5 0.2 0.5 0.1
Element P S N Fe
Alloy-1 0.011 0.009 0.006 bal.
Alloy-2 0.013 0.012 0.008 bal.

Table -1: Chemical compositions of Steels Alloy 1 & 2
[0076] Various experiments and tests were conducted on a laboratory scale in order to evaluate various conditions. Two different alloys were designed and cast at 40 kg scale which were subsequently hot forged. A sample of size 100 mm × 80 mm × 36 mm was cut from the as forged plate with composition as mentioned in Table 1 for first homogenization at 1150-1250°C for 100-120 min.
[0077] After that the plates was hot-rolled to 18 mm from 36 mm, followed by quenching to 250-350°C at a quenching rate of 15-25°C/s and thereafter cooled at a cooling rate of 0.001-0.007 °C/s to room temperature (27°C). In the actual industrial setup this can be achieved in the ROT section. The detailed hot rolling scheme is depicted in Figure 2.
[0078] Different samples of the low alloyed thicker section abrasion resistant steel were prepared by utilizing the compositions as mentioned in table 1 and by varying the quenching temperatures followed during the method (100). After cooling to room temperature, standard metallography techniques were followed to prepare the samples for different mechanical properties measurements. The hardness measurement was characterized in Vickers hardness testing machine at 1 kg scale with a dwell time of 10 s. The measured properties for the steel samples are depicted in Table 2.
Mechanical Properties Alloy 1 (250°C) Alloy 1 (350°C) Alloy 2
(270°C) Alloy 2 (350°C)
Hardness (HV 1 kg) 325-367 338-368 401-475 395-446
Retained austenite (%) 5.1 2.1 9.7 9.8
Abrasive Wear volume loss (mm3) 284-303 385-466 294-338 268-423
Charpy Impact toughness at room temperature (J)* 29-38 24-31 32-40 8-28
Charpy Impact toughness at -40°C (J)* 4-16 6-10 8-18 2-4
Yield Strength (MPa) 575-625 590-620 700-840 650-700
Ultimate Tensile Strength (MPa) 780-820 780-815 940-1050 870-925
Uniform elongation (%) 7 -10 7-9 5-9 9-10
Total elongation (%) 21-25 20-22 14-22 21-23
* - Measured on the sub-size sample with 10×5 mm2 cross-section

Table -2: Variation in mechanical properties with varying composition and quenching temperature.
[0079] Referring to Figure 3, a graphical representation of results of X-ray Diffraction analysis carried out on different samples of the low alloyed thicker section abrasion resistant steel is illustrated. The results show the presence of reflections corresponding to martensite. In addition, some reflections of retained austenite were also observed, the intensity of which indicates its content to be less than 10 vol.%.
[0080] Referring to Figure 4, SEM images of different samples of the low alloyed thicker section abrasion resistant steel are illustrated. The microstructures of different steels (shown in Figure 4) depicts the presence of martensite, retained austenite and carbides. Referring to Figure 5, a graphical representation of stress versus elongation, obtained during tensile test of the low alloyed thicker section abrasion resistant steel is illustrated.
[0081] This variation in the mechanical properties is attributed to the alloy composition and microstructural features i.e., their content, size, morphology, etc. Their content such as percentage presence of the retained austenite within different steels is varied with varying quenching temperatures during manufacturing.
[0082] The present invention provides the low alloyed thicker section abrasion resistant steel having superior strength, ductility, and abrasion resistance combination. The disclosed low alloyed thicker section abrasion resistant steel has uniform microstructure and mechanical properties in thick plate of low alloy steel. The disclosed steel is suitable for producing components to be used in structural as well as wear resistant applications of the L&E equipment, particularly used in mining and earthmoving applications.
[0083] The disclosed method of manufacture the low alloyed thicker section abrasion resistant steel eliminates isothermal holding as required in conventional austempering or tempering or quenching and isothermal partitioning processes. The method (100) performs non-isothermal partitioning on the steel produced during manufacturing by utilizing the waste heat of a hot rolled coil after quenching on the run-out table, thereby, making it an energy-efficient approach. As a result, the steel with multiphase microstructure can be produced economically and directly from hot rolling mill without any additional facilities. The process parameters followed during the method (100) and the composition of the steel is selected such that uniform microstructure and mechanical properties are achieved through out different sections (surface vs center) in thick plate of low alloy steel. The low alloyed thicker section abrasion resistant steel makes an important contribution towards durable, cost effective, futuristic, and strategic application of steel with greater factor of safety. Further the steel having high hardness and good wear resistance may be used in the sectors of engineering, mining, construction, agriculture, port, electric power, and metallurgy etc.
[0084] It should be understood that the experiments are carried out for particular compositions of the low alloyed thicker section abrasion resistant steel sheet and the results brought out in the previous paragraphs are for the composition shown in Table 1. However, this composition should not be construed as a limitation to the present disclosure as it could be extended to other compositions of the low alloyed thicker section abrasion resistant steel sheet, as well.
[0085] Furthermore, the terminology used herein is for describing embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0086] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0087] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.