Low-carbon-equivalent high-toughness NM450 steel and production process thereof

Abstract

The invention discloses NM450 steel with low carbon equivalent and high toughness and a production process thereof, and relates to the technical field of steel production, and the NM450 steel comprises the following chemical components in percentage by mass: 0.15%-0.20% of C, 0.15%-0.35% of Si, 0.30%-0.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.0020% of S, 0.65%-0.85% of Cr, 0.25%-0.50% of Mo / Ni, 0.002%-0.006% of Ti, 0.050%-0.080% of Nb, 0.020%-0.050% of V, 0.0010%-0.0030% of B, 0.070%-0.090% of Alt, less than or equal to 0.0050% of N, less than or equal to 0.0003% of H, less than or equal to 0.55% According to the steel plate, the yield strength is larger than or equal to 1100 MPa, the tensile strength is larger than or equal to 1400 MPa, the ductility is larger than or equal to 12%, the surface Brinell hardness is larger than 430 HB, the core Brinell hardness is larger than 400 HB, the low-temperature impact energy at the temperature of-40 DEG C is larger than or equal to 60 J, and the welding performance is good.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a low-carbon equivalent high-toughness NM450 steel and a production process thereof. Background Art

[0002] Wear-resistant steel has become the most widely used wear-resistant material due to its excellent comprehensive mechanical properties. It is widely used in mining, machinery, metallurgy, military and other industries. With the development of the field of engineering machinery, the working environment of dump trucks and loaders is becoming more and more harsh, and the requirements for wear-resistant steel are getting higher and higher. Not only good hardness and wear resistance are required, but also good low-temperature toughness is required to resist low-temperature impact. Low-alloy wear-resistant steel usually has low impact toughness due to its high hardness, which makes the steel plate easy to be cracked under extremely cold conditions, affecting the service life of the steel plate. Usually, alloys are added to improve the impact toughness of the steel plate, but this will increase costs and make it difficult to promote.

[0003] The patent with publication number CN 102666897 A discloses a high-toughness wear-resistant steel plate with good processability and manufacturing conditions that are not easily affected by the characteristics and its manufacturing method. It has a low carbon equivalent and excellent low-temperature impact toughness, but the hardness of the thickness section is not evaluated. In addition to the surface hardness, some engineering machinery equipment also has requirements for the hardness of the thickness section, and generally requires the core hardness to be no less than 85% of the surface hardness. The test was completed in the laboratory, and the cooling rate was slightly high, which cannot be achieved in normal industrial production.

[0004] The patent with publication number CN 110205557 B discloses a 350-380 HBW hardness grade thick specification high toughness wear-resistant steel plate and a preparation method thereof, wherein the impact energy at -40°C is greater than 60J and the hardness is only 350-380 HBW. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the disadvantages of the prior art and provide a low-carbon equivalent high-toughness NM450 steel and a production process thereof.

[0006] In order to solve the above technical problems, the technical solution of the present invention is as follows: A low carbon equivalent high toughness NM450 steel, the chemical composition and mass percentage of which are as follows: C: 0.15%-0.20%, Si: 0.15%-0.35%, Mn: 0.30%-0.60%, P≤0.015%, S≤0.0020%, Cr: 0.65%-0.85%, Mo: / , Ni: 0.25%-0.50%, Ti: 0.002%-0.006%, Nb: 0.050-0.080%, V: 0.020-0.050%, B: 0.0010%-0.0030%, Alt: 0.070%-0.090%, N≤0.0050%, H≤0.0003%, Ceq≤0.55, and the rest are Fe and unavoidable impurities.

[0007] As a preferred embodiment of the low carbon equivalent high toughness NM450 steel described in the present invention, its chemical composition and mass percentage are as follows: C: 0.17%-0.18%, Si: 0.20%-0.30%, Mn: 0.40%-0.50%, P≤0.012%, S≤0.0010%, Cr: 0.70%-0.80%, Mo: / , Ni: 0.25%-0.35%, Ti: 0.003%-0.004%, Nb: 0.070-0.080%, V: 0.030-0.040%, B: 0.0010%-0.0020%, Alt: 0.075%-0.085%, N≤0.0050%, H≤0.0003%, Ceq≤0.55, and the rest are Fe and unavoidable impurities.

[0008] The present invention also provides a production process of low-carbon equivalent high-toughness NM450 steel, which comprises in sequence: molten iron desulfurization pretreatment - converter smelting - LF+RH refining - continuous casting - ingot stack cooling - ingot acceptance - ingot heating - dephosphorization - rolling - air cooling - flaw detection - shot blasting - quenching - tempering - straightening - cutting, sampling - printing identification - inspection - warehousing.

[0009] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, wherein: in the continuous casting process, the thickness of the continuous casting billet is 150-260mm, the heating time of the continuous casting billet in the furnace is 150-390min, the soaking time is ≥30min, and the steel tapping temperature is 1190-1240℃.

[0010] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, wherein: in the rolling process, the final rolling temperature is 800-850°C, and the watering red-returning temperature after rolling is 550-750°C.

[0011] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, wherein: in the rolling process, the final rolling thickness is 4-40 mm.

[0012] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, in the quenching process, a roller bottom heat treatment furnace is used for quenching, the quenching temperature is 900-920°C, the heating rate is 2.2±0.1min / mm, and the holding time is 17-42min.

[0013] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, in the quenching process, the quenching machine roller speed is set to 0.05-0.55 m / s.

[0014] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, wherein: in the tempering process, the tempering temperature is 200-220°C, the heating rate is 4.5min / mm, the holding time is 45-100min, and the steel is air-cooled after tempering.

[0015] As a preferred solution of the production process of the low carbon equivalent high toughness NM450 steel described in the present invention, the microstructure of the prepared low carbon equivalent high toughness NM450 steel is tempered martensite.

[0016] The beneficial effects of the present invention are: (1) The mechanical properties of the steel plate of the present invention reach the following levels: yield strength ≥1100MPa, tensile strength ≥1400MPa, elongation ≥12%, surface Brinell hardness greater than 430HB, core Brinell hardness greater than 400HB, -40°C low-temperature impact energy ≥60J, and good welding performance.

[0017] (2) Under the condition of low carbon equivalent, the present invention realizes that the core hardness of the wear-resistant steel plate is not less than 90% of the surface hardness through reasonable composition design and rolling-heat treatment process optimization, while having good low-temperature impact toughness and good welding performance. DETAILED DESCRIPTION

[0018] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation methods.

[0019] An embodiment of the present application provides a low carbon equivalent, high toughness, wear-resistant steel plate, whose chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.25%, Mn: 0.45%, P: 0.008%, S: 0.0010%, Cr: 0.80%, Mo: 0.002%, Ni: 0.22%, Ti: 0.004%, Nb: 0.070%, V: 0.040%, B: 0.0015%, Alt: 0.080%, N≤0.0040%, H≤0.0002%, and the rest are Fe and unavoidable impurities.

[0020] The manufacturing method includes the following processes: hot metal desulfurization pretreatment - converter smelting - LF+RH refining - continuous casting - ingot stack cooling - ingot acceptance - ingot heating - dephosphorization - rolling - air cooling - flaw detection - shot blasting - quenching - tempering - straightening - cutting, sampling - printing mark - inspection - warehousing, specifically: The molten steel smelted according to the required proportions is subjected to RH vacuum treatment and then continuously cast, with a continuous casting billet thickness of 150mm; The continuous casting billet was heated, the furnace time was 155min, the soaking time was 35min, the tapping temperature was 1211℃, and weak controlled rolling was performed after heating. The second stage rolling temperature was 940℃, the final rolling temperature was 844℃, the final rolling thickness was 15mm, and the watering temperature after rolling was 740℃. After rolling, offline heat treatment is carried out, the quenching temperature is 910℃, the heating rate is 2.2min / mm, the holding time is 20min, the quenching machine roller speed is set to 0.17m / s, and the total water volume of the high-pressure section of the quenching machine is ≥3000m3 / h; the quenched steel plate is tempered in a car-bottom heat treatment furnace, the tempering temperature is 210℃, and the holding time is 50min.

[0021] The mechanical properties of the steel plate in the embodiment were tested, wherein the strength was measured according to the room temperature tensile test method for metal materials in GB / T228-2002, the low temperature impact toughness was measured according to the metal Charpy V-notch impact test method in GB / T 229-2007, and the hardness was measured according to the GB / T231.1-2009 method. The performance test results are shown in Table 1.

[0022]

[0023] Table 1 It can be seen from Table 1 that the wear-resistant steel of the present invention has a yield strength of ≥1100MPa, a tensile strength of ≥1400MPa, an elongation of ≥12%, a surface Brinell hardness of greater than 430HB, a core Brinell hardness of greater than 400HB, and a -40°C low-temperature impact energy of ≥60J. It can be seen that the wear-resistant steel of the present invention has good wear resistance and also has good low-temperature impact toughness.

[0024] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A low carbon equivalent high toughness NM450 steel, characterized by: Its chemical composition and mass percentage are as follows: C: 0.15%~0.20%, Si: 0.15%~0.35%, Mn: 0.30%~0.60%, P≤0.015%, S≤0.0020%, Cr: 0.65%~0.85%, Mo: / , Ni: 0.25%~0.50%, Ti: 0.002%~0.006%, Nb: 0.050~0.080%, V: 0.020~0.050%, B: 0.0010%~0.0030%, Alt: 0.070%~0.090%, N≤0.0050%, H≤0.0003%, Ceq≤0.55, and the rest are Fe and unavoidable impurities.

2. The low carbon equivalent high toughness NM450 steel according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.17%~0.18%, Si: 0.20%~0.30%, Mn: 0.40%~0.50%, P≤0.012%, S≤0.0010%, Cr: 0.70%~0.80%, Mo: / , Ni: 0.25%~0.35%, Ti: 0.003%~0.004%, Nb: 0.070~0.080%, V: 0.030~0.040%, B: 0.0010%~0.0020%, Alt: 0.075%~0.085%, N≤0.0050%, H≤0.0003%, Ceq≤0.55, and the rest are Fe and unavoidable impurities.

3. A production process of low carbon equivalent high toughness NM450 steel according to claim 1 or 2, characterized in that: Including in order: Hot metal desulfurization pretreatment - converter smelting - LF+RH refining - continuous casting - ingot cooling - ingot acceptance - ingot heating - dephosphorization - rolling - air cooling - flaw detection - shot blasting - quenching - tempering - straightening - cutting, sampling - printing identification - inspection - warehousing.

4. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the continuous casting process, the thickness of the continuous casting billet is 150-260 mm, the heating time of the continuous casting billet in the furnace is 150-390 min, the soaking time is ≥30 min, and the tapping temperature is 1190-1240°C.

5. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the rolling process, the final rolling temperature is 800-850°C, and the watering red-returning temperature after rolling is 550-750°C.

6. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the rolling process, the final rolling thickness is 4-40 mm.

7. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the quenching process, a roller-bottom heat treatment furnace is used for quenching, the quenching temperature is 900-920° C., the heating rate is 2.2±0.1 min / mm, and the holding time is 17-42 min.

8. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the quenching process, the quenching machine roller speed is set to 0.05-0.55 m / s.

9. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: In the tempering process, the tempering temperature is 200-220° C., the heating rate is 4.5 min / mm, the holding time is 45-100 min, and the steel is air-cooled after being taken out of the furnace.

10. The production process of low carbon equivalent high toughness NM450 steel according to claim 3, characterized in that: The microstructure of the prepared low carbon equivalent and high toughness NM450 steel is tempered martensite.

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