CN108531816B - 500 MPa-grade steel for engineering machinery and manufacturing method thereof - Google Patents

500 MPa-grade steel for engineering machinery and manufacturing method thereof Download PDF

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CN108531816B
CN108531816B CN201810513565.8A CN201810513565A CN108531816B CN 108531816 B CN108531816 B CN 108531816B CN 201810513565 A CN201810513565 A CN 201810513565A CN 108531816 B CN108531816 B CN 108531816B
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steel
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molten steel
steel plate
rolling
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CN108531816A (en
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冯勇
吴俊平
谯明亮
李明
霍松波
刘继宏
翟冬雨
潘中德
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Nanjing Iron and Steel Co Ltd
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
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    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18Hardening; Quenching with or without subsequent tempering
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    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
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    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/08Ferrous alloys, e.g. steel alloys containing nickel
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/12Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/14Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/16Ferrous alloys, e.g. steel alloys containing copper
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    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/32Ferrous alloys, e.g. steel alloys containing chromium with boron
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    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Abstract

the invention discloses 500 MPa-grade steel for engineering machinery and a manufacturing method thereof, wherein the steel comprises the following components in percentage by mass: c: 0.12 to 0.23%, Si: 0.10 to 0.60%, Mn: 0.80-1.90%, P: < 0.018%, S: less than 0.010 percent; and is selected from Cr: 0-0.50%, Ni: 0-0.60%, Mo: 0-0.45%, Cu: 0-0.40%, Nb: 0 to 0.060%, V: 0-0.15%, Ti: 0-0.12%, B: 0-0.0030%, Al: 0.010-0.050% of one or more; the balance being Fe and unavoidable impurities. The metallographic structure of the alloy is a uniform and fine martensite high-temperature tempering structure, so that the alloy has good mechanical property and fatigue property. The fatigue life of the steel is obviously prolonged compared with the prior engineering machinery steel.

Description

500 MPa-grade steel for engineering machinery and manufacturing method thereof
Technical Field
the invention relates to an alloy steel technology, in particular to steel for 500MPa engineering machinery and a manufacturing method thereof.
background
At present, two types of steels for construction machinery, such as Q235B and SS400, are used as the steel, for example, a boom arm of an excavator, a loader boom, and the like. The yield strength is 235MPa, the normal temperature impact performance is met, and the service life is within 30000 h. The yield strength and fatigue life are both significantly insufficient.
the Chinese patent with the application number of 201310289099.7 and the name of 500 MPa-grade superfine crystal steel for engineering machinery and a manufacturing method discloses steel for engineering machinery with the yield strength of more than 500MPa, wherein the content of C is 0.04-0.08%, and the steel is not beneficial to formation of quenched martensite. The steel plate has the problems of high alloy cost, poor plate shape, unstable performance, large blanking deformation and the like.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides 500 MPa-grade steel for engineering machinery, and the steel has yield strength of over 500MPa and higher fatigue life.
another object of the present invention is to provide a method for producing a steel for 500 MPa-grade engineering machinery, which can produce a steel for 500 MPa-grade engineering machinery having a high fatigue life.
the technical scheme is as follows: the invention relates to 500 MPa-grade steel for engineering machinery, which comprises the following components in percentage by mass: c: 0.12 to 0.23 percent,
Si:0.10~0.60%、
Mn:0.80~1.90%、
P:<0.018%、
S:<0.010%;
And is selected from Cr: 0-0.50%, Ni: 0-0.60%, Mo: 0-0.45%, Cu: 0-0.40%, Nb: 0 to 0.060%, V: 0-0.15%, Ti: 0-0.12%, B: 0-0.0030%, Al: 0.010-0.050% of one or more;
The balance being Fe and unavoidable impurities.
The metallographic structure of the steel for the 500 MPa-grade engineering machinery is a uniform and fine martensite high-temperature tempering structure.
The reason for limiting the mass percentage of each chemical component in the 500MPa grade steel for engineering machinery is as follows:
The C element can obviously increase the strength of the matrix through solid solution strengthening, and the content of the C element is too low to be beneficial to the formation of quenched martensite, but the content of the C element is too high to be beneficial to the welding performance of the material. Therefore, the content of C is controlled to be 0.12-0.23%.
Si is a deoxidizing element in the steelmaking process, proper amount of Si can inhibit segregation of Mn and P, the toughness is damaged by the segregation of Mn and P due to too high content of O, in addition, the Si can generate solid solution strengthening, and proper amount of Si is beneficial to stable improvement of the tempering structure performance. However, an excessively high Si content may form inclusions. The invention controls Si to be 0.10-0.60%.
mn is a ferrite strengthening element as a main alloy element of the steel plate, and the steel plate cannot perform alloying and quenching effects when the content is too low, but is very unfavorable for welding performance and is not economical when the content is too high. Therefore, Mn is controlled to 0.80 to 1.90%.
P, S belong to harmful elements in molten steel, and too much P, S may be harmful to the toughness of steel, may affect the welding performance, and may easily form cracks. Theoretically, the smaller the two elements, the better, the P is controlled to be less than 0.018 percent, and the S is controlled to be less than 0.010 percent;
The elements of Cr, Ni, Mo, Cu, Nb, V, Ti, B, Al and the like are all non-leading elements in the steel grade, wherein the elements of Cr, Ni, Mo and the like are added in small amount to be beneficial to alloying and quenching of the steel grade, and the hardenability can be improved by properly adding Ti, B, Al and the like. However, excessive addition of these elements is not economical on the one hand, and on the other hand, unnecessary non-metallic inclusions are formed. Therefore, the design can be met according to the matching of the alloy action, and the alloy welding machine is more favorable for saving alloy resources and improving the processing performances such as welding bending and the like. The invention limits C, Si, Mn, P and S, and according to the alloy action, the alloy is prepared from Cr: 0-0.50%, Ni: 0-0.60%, Mo: 0-0.45%, Cu: 0-0.40%, Nb: 0 to 0.060%, V: 0-0.15%, Ti: 0-0.12%, B: 0-0.0030%, Al: one or more elements of 0.010-0.050% and the like are selected and reasonably matched.
The invention relates to a manufacturing method of 500 MPa-grade steel for engineering machinery, which adopts the technical scheme that the manufacturing method comprises the following steps:
(1) Smelting molten steel: preparing molten steel according with the composition;
(2) casting to form a blank: feeding the molten steel into a continuous casting machine for argon protection pouring in the whole process, and meanwhile electromagnetically stirring at a pulling speed of 0.75-1.2 m/min to obtain a casting blank;
(3) heating a casting blank: uniformly heating the casting blank at 1100-1220 ℃ for 3.5-4.5 hours;
(4) rolling: rolling by a four-roller reversible rolling mill in two stages, wherein the rolling reduction rate of rough rolling is more than 60%, the initial rolling temperature of rough rolling is 1070-1180 ℃, the initial rolling temperature of two stages is 890-950 ℃, and the final rolling temperature is 820-900 ℃ to obtain a steel plate;
(5) And (3) controlling cooling: after the residual water at the outlet of the accelerated cooling zone is purged completely, measuring the anti-red temperature of the steel plate at 650-690 ℃;
(6) straightening: straightening the steel plate, and controlling the straightening unevenness to be 3-6 mm/m;
(7) Shot blasting: removing iron oxide scales on the surface of the steel plate;
(8) And (4) carrying out heat treatment on the steel plate with the scale removed to obtain the steel plate.
The molten steel with the composition meeting the requirements is prepared in the step (1), and the method comprises the following steps:
(1.1) pretreating molten iron so that S in the molten iron: less than 0.010 percent;
(1.2) adding the pretreated molten iron into a converter, smelting by adopting a BOF method, and carrying out deoxidation alloying, wherein the added alloy is 90% of the alloy addition amount in the designed molten steel components;
(1.3) refining in an LF furnace for 15-30 min, finely adjusting alloy components to enable the alloy components to meet requirements, and raising the temperature of molten steel;
(1.4) carrying out RH vacuum degassing treatment for 15-30 minutes, reasonably stirring and floating by RH bottom argon blowing to remove nonmetallic inclusions, and reducing the content of nitrogen, hydrogen and oxygen;
(1.5) feeding a calcium wire to purify the molten steel, so that the strip-shaped MnS non-metallic inclusions become dispersed, shortened and spheroidized, thus obtaining the MnS non-metallic inclusion-containing steel.
The heat treatment in the step (8) is to heat the steel plate to 880-920 ℃ by adopting a nitrogen protection non-oxidation roller hearth furnace; then carrying out roll-pressing type water jet quenching on the steel plate; and then tempering at 550-660 ℃.
has the advantages that: the steel for the 500 MPa-grade engineering machinery is designed by reasonable components, secondarily refined outside a furnace and unique manufacturing process, so that the steel is clean, crystal grains are refined, and the toughness is improved. The metallographic structure of the steel grade is a uniform and fine martensite high-temperature tempering structure, so that good mechanical property and fatigue property are obtained, the yield strength of the steel grade reaches more than 500MPa, and the tensile strength reaches more than 600 MPa. And the alloy elements of the steel grade can be selected or rejected according to the alloy action, so that the production cost of the steel grade is effectively controlled.
Detailed Description
The present invention will be described in further detail with reference to examples.
In order to upgrade the existing steel for engineering machinery from Q235B with the yield strength of 235MPa to a new generation of fatigue-resistant engineering machinery material with the yield strength exceeding 500MPa, the invention provides the steel for the engineering machinery with the 500MPa grade, and the steel comprises the following components in percentage by mass: 0.12 to 0.23%, Si: 0.10 to 0.60%, Mn: 0.80-1.90%, P: < 0.018%, S: less than 0.010 percent; and is selected from Cr: 0-0.50%, Ni: 0-0.60%, Mo: 0-0.45%, Cu: 0-0.40%, Nb: 0 to 0.060%, V: 0-0.15%, Ti: 0-0.12%, B: 0-0.0030%, Al: 0.010-0.050% of one or more; the balance being Fe and unavoidable impurities. Through a special manufacturing process, the metallographic structure of the steel is a uniform and fine martensite high-temperature tempering structure, so that good mechanical property and fatigue property are obtained.
the invention relates to a manufacturing method of 500MPa grade steel for engineering machinery, which adopts the technical scheme that the manufacturing method comprises the following steps:
(1) Firstly, smelting molten steel according with the composition by adopting the following steps: firstly, carrying out pretreatment on molten iron to ensure that S in the molten iron is: less than 0.010 percent, then adding the pretreated molten iron into a converter, smelting by adopting a BOF method and carrying out deoxidation alloying, wherein the added alloy is 90 percent of the alloy addition amount in the designed molten steel components; then, feeding the molten steel into an LF furnace for refining for 15-30 min, deoxidizing, finely adjusting alloy components to enable the alloy components to meet requirements, and raising the temperature of the molten steel according to the process; sending the molten steel into an RH refining furnace for vacuum degassing treatment for 15-30 minutes, reasonably stirring by RH bottom blowing argon and floating to remove nonmetallic inclusions, reducing the content of nitrogen, hydrogen and oxygen, and controlling the content of nitrogen in the molten steel to be not higher than 38ppm, the content of hydrogen to be not higher than 1.5ppm and the content of oxygen to be not higher than 20 ppm; then feeding calcium wire to purify the molten steel, so that the strip-shaped MnS non-metallic inclusion becomes dispersed, shortened and spheroidized, and the molten steel meeting the requirements is obtained.
(2) Casting to form a blank: feeding molten steel into a continuous casting machine for argon protection pouring in the whole process, simultaneously electromagnetically stirring to reduce low-power segregation, and controlling the continuous casting drawing speed to be 0.75-1.2 m/min to obtain a casting blank;
(3) Heating a casting blank: uniformly heating the casting blank at 1100-1220 ℃ for 3.5-4.5 hours, preventing the center of the casting blank from being heated and not being thoroughly due to too short heating time, and meanwhile, reasonably controlling the rolling time under the condition of proper rolling and preventing the energy waste due to too long heating time;
(4) Rolling: rolling by a four-roller reversible rolling mill in two stages, wherein the rolling reduction rate of rough rolling is more than 60%, the initial rolling temperature of rough rolling is 1070-1180 ℃, the initial rolling temperature of two stages is 890-950 ℃, and the final rolling temperature is 820-900 ℃ to obtain a steel plate;
(5) and (3) controlling cooling: after the residual water at the outlet of the accelerated cooling zone is purged completely, measuring the anti-red temperature of the steel plate at 650-690 ℃;
(6) Straightening: straightening the steel plate, and controlling the straightening unevenness to be 3-6 mm/m;
(7) shot blasting: removing iron oxide scales on the surface of the steel plate;
(8) Carrying out heat treatment on the steel plate with the scale removed, specifically, heating the steel plate to 880-920 ℃ by adopting a nitrogen protection non-oxidation roller hearth furnace; then carrying out roll-pressing type water jet quenching on the steel plate; and then tempering at the high temperature of 550-660 ℃ to obtain the product.
in the first embodiment, the 75mm specification Q500E steel plate comprises the following components in percentage by mass: 0.18%, Si: 0.27%, Mn: 1.53%, P: 0.011%, S: 0.006%, Cr: 0.25%, V: 0.035%, Ti: 0.019%, B: 0.0009% and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 25 minutes, RH vacuum refining is carried out for 30 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 0.75 m/min; reheating for 3.8h to ensure that the central temperature of the casting blank reaches 1170 ℃, the initial rolling temperature is 1120 ℃, the second-stage rolling is 890 ℃, the final rolling temperature is 830 ℃, and the reduction rate is 61%; the temperature of the steel plate returning to red is 650 ℃; straightening by 3 mm/m; the quenching temperature is 890 ℃ and the tempering temperature is 650 ℃. Mechanical properties of 530MPa of yield strength, 620MPa of tensile strength and 21 percent of elongation, and-40 ℃ impact energy of 186J,191J and 197J (10 x 10 mm).
Example two, a 10mm specification Q500E steel plate, comprising the following component C by mass percent: 0.15%, Si: 0.23%, Mn: 1.49%, P: 0.013%, S: 0.005%, Cr: 0.17%, V: 0.033%, Ti: 0.016%, B: 0.0011%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 30 minutes, RH vacuum refining is carried out for 25 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively enabled to be not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.2 m/min; heating for 4.0 hours again to ensure that the central temperature of the casting blank reaches 1180 ℃, the initial rolling temperature is 1140 ℃, the second-stage rolling temperature is 900 ℃, the final rolling temperature is 850 ℃ and the reduction rate is 65 percent; the temperature of the steel plate returning to red is 680 ℃; straightening by 5 mm/m; the quenching temperature is 900 ℃, and the tempering temperature is 650 ℃. The mechanical properties of the product are 545MPa of yield strength, 650MPa of tensile strength, 20% of elongation, 97J,99J and 93J (5 x 10mm) of impact energy at-40 ℃.
Example three, 22mm specification Q500E, comprising the following component C by mass percent: 0.16%, Si: 0.20%, Mn: 1.33%, P: 0.013%, S: 0.005%, Ni: 0.20%, Nb: 0.026%, Ti: 0.016%, B: 0.0011%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 26 minutes, and RH vacuum refining degassing is carried out for 29 minutes, so that the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.2 m/min; heating for 4.2 hours to ensure that the central temperature of the casting blank reaches 1190 ℃, the initial rolling temperature is 1140 ℃, the second-stage rolling temperature is 950 ℃, the final rolling temperature is 850 ℃ and the reduction rate is 65 percent; the steel plate reddening temperature is 690 ℃; straightening by 6 mm/m; the quenching temperature is 900 ℃, and the tempering temperature is 640 ℃. Mechanical properties of 530MPa of yield strength, 645MPa of tensile strength and 22 percent of elongation, and-40 ℃ impact energy of 192J,190J and 192J (10 x 10 mm).
example four, 8mm specification Q500E, comprising the following component C by mass percent: 0.15%, Si: 0.23%, Mn: 1.26%, P: 0.013%, S: 0.005%, Mo: 0.17%, Al: 0.027%, the balance being Fe and unavoidable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 28 minutes, and RH vacuum refining degassing is carried out for 28 minutes, so that the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.0 m/min; heating for 4.0 hours again to ensure that the central temperature of the casting blank reaches 1175 ℃, the initial rolling temperature is 1130 ℃, the second-stage rolling is 920 ℃, the final rolling temperature is 870 ℃, and the reduction rate is 76%; the steel plate reddening temperature is 690 ℃; straightening by 6 mm/m; the quenching temperature is 910 ℃, and the tempering temperature is 640 ℃. Mechanical properties of 540MPa of yield strength, 660MPa of tensile strength, 19 percent of elongation, and 86J,86J and 83J (5 x 10mm) of impact energy at-40 ℃.
Example five, 18mm specification Q500E, comprising the following component C by mass percent: 0.17%, Si: 0.26%, Mn: 1.50%, P: 0.012%, S: 0.003%, Cr: 0.15%, Cu: 0.016%, Al: 0.027%, Ti: 0.022%, B: 0.0015%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 26 minutes, RH vacuum refining is carried out for 15 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.0 m/min; heating for 4.0 hours again to ensure that the central temperature of the casting blank reaches 1180 ℃, the initial rolling temperature is 1135 ℃, the second-stage rolling temperature is 920 ℃, the final rolling temperature is 870 ℃, and the reduction rate is 73%; the steel plate reddening temperature is 690 ℃; straightening by 6 mm/m; the quenching temperature is 910 ℃, and the tempering temperature is 630 ℃. The mechanical properties of yield strength 543MPa, tensile strength 659MPa, elongation 21%, impact energy 126J at-40 ℃,123J and 129J (10 x 10 mm).
example six, a 50mm specification Q500E steel sheet comprising the following composition in mass percent C: 0.12%, Si: 0.6%, Mn: 0.8%, P: 0.017%, S: 0.006%, Cr: 0.50%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 15 minutes, RH vacuum refining is carried out for 30 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 0.75 m/min; reheating for 3.5h to ensure that the central temperature of the casting blank reaches 1100 ℃, the initial rolling temperature is 1070 ℃, the second-stage rolling temperature is 890 ℃, the final rolling temperature is 820 ℃ and the reduction rate is 75 percent; the temperature of the steel plate returning to red is 650 ℃; straightening by 4 mm/m; the quenching temperature is 880 ℃, and the tempering temperature is 620 ℃. Mechanical properties of 542MPa of yield strength, 629MPa of tensile strength and 21 percent of elongation, and-40 ℃ impact energy of 132J,139J and 130J (10 x 10 mm).
example seven, a 10mm specification Q500E steel sheet comprising the following composition in mass percent C: 0.23%, Si: 0.10%, Mn: 1.9%, P: 0.013%, S: 0.009%, V: 0.15%, Ti: 0.025 wt.%, B: 0.003 wt.%, the balance being Fe and unavoidable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 15 minutes, RH vacuum refining is carried out for 25 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively enabled to be not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 0.9 m/min; heating for 4.5 hours again to ensure that the central temperature of the casting blank reaches 1220 ℃, the initial rolling temperature is 1180 ℃, the second-stage rolling temperature is 950 ℃, the final rolling temperature is 900 ℃ and the reduction rate is 63 percent; the steel plate reddening temperature is 690 ℃; straightening by 5 mm/m; the quenching temperature is 920 ℃ and the tempering temperature is 660 ℃. Mechanical properties, yield strength 548MPa, tensile strength 646MPa, elongation 20%, and impact energy at-40 ℃ of 55J,69J and 78J (5 x 10 mm).
The eight embodiment, 22mm specification Q500E, includes the following composition C by mass percent: 0.12%, Si: 0.53%, Mn: 1.56%, P: 0.012%, S: 0.003%, Ni: 0.60%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 20 minutes, RH vacuum refining is carried out for 25 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.1 m/min; heating for 3.5 hours again to ensure that the central temperature of the casting blank reaches 1130 ℃, the initial rolling temperature is 1100 ℃, the second-stage rolling temperature is 910 ℃, the final rolling temperature is 820 ℃ and the reduction rate is 61 percent; the temperature of the steel plate returning to red is 650 ℃; straightening by 6 mm/m; the quenching temperature is 880 ℃, and the tempering temperature is 620 ℃. Mechanical properties of 539MPa of yield strength, 642MPa of tensile strength, 22 percent of elongation, 191J,195J and 193J (10 x 10mm) of impact energy at-40 ℃.
The nine embodiment, 8mm specification Q500E, includes the following composition C by mass percent: 0.16%, Si: 0.13%, Mn: 0.90%, P: 0.011%, S: 0.001%, Mo: 0.45%, Al: 0.05%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 26 minutes, and RH vacuum refining degassing is carried out for 28 minutes, so that the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 1.0 m/min; heating for 4.3 hours again to ensure that the central temperature of the casting blank reaches 1210 ℃, the initial rolling temperature is 1180 ℃, the second-stage rolling temperature is 940 ℃, the final rolling temperature is 900 ℃ and the reduction rate is 89%; the steel plate reddening temperature is 690 ℃; straightening by 3 mm/m; the quenching temperature is 910 ℃, and the tempering temperature is 640 ℃. The mechanical properties of the alloy are 556MPa of yield strength, 662MPa of tensile strength, 20 percent of elongation, 58J,47J and 48J (5 x 10mm) of impact energy at-40 ℃.
The tenth embodiment, the 30mm specification Q500E, comprises the following components by mass percent: 0.12%, Si: 0.17%, Mn: 1.21%, P: 0.010%, S: 0.003%, Cu: 0.40%, Al: 0.010% and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 21 minutes, RH vacuum refining is carried out for 25 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are respectively enabled to be not higher than 38ppm, 1.5ppm and 20 ppm; continuously casting the plate blank at the drawing speed of 0.85 m/min; heating for 4.0 hours again to ensure that the central temperature of the casting blank reaches 1150 ℃, the initial rolling temperature is 1130 ℃, the second-stage rolling temperature is 900 ℃, the final rolling temperature is 820 ℃ and the reduction rate is 61 percent; the temperature of the steel plate returning to red is 650 ℃; straightening by 3 mm/m; the quenching temperature is 920 ℃, and the tempering temperature is 620 ℃. Mechanical properties of yield strength 546MPa, tensile strength 655MPa, elongation 21%, impact energy 217J at-40 ℃,219J,221J (10 × 10 mm).
the eleven embodiment, 20mm specification Q500E steel plate comprises the following components by weight percent: 0.23%, Si: 0.46%, Mn: 0.95%, P: 0.016%, S: 0.009%, Nb: 0.06%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 30 minutes, RH vacuum refining and degassing are carried out for 30 minutes, so that the nitrogen content of molten steel is not higher than 38ppm, the hydrogen content is not higher than 1.5ppm, and the oxygen content is not higher than 20 ppm; continuously casting the plate blank at the drawing speed of 0.9 m/min; heating for 3.9 hours again to ensure that the central temperature of the casting blank reaches 1200 ℃, the initial rolling temperature is 1180 ℃, the second-stage rolling temperature is 950 ℃, the final rolling temperature is 900 ℃ and the reduction rate is 66%; the temperature of the steel plate returning to red is 680 ℃; straightening by 3 mm/m; the quenching temperature is 920 ℃, and the tempering temperature is 600 ℃. The mechanical properties of the alloy are 545MPa of yield strength, 636MPa of tensile strength, 21 percent of elongation, 188J,193J and 199J (10 x 10mm) of impact energy at-40 ℃.
the twelve-example 10mm specification Q500E steel plate comprises the following components in percentage by mass: 0.17%, Si: 0.10%, Mn: 1.10%, P: 0.013%, S: 0.003%, Ti: 0.12%, B: 0.0030%, and the balance of Fe and inevitable impurities. After alloying deoxidation in steelmaking, LF refining is carried out for 25 minutes, RH vacuum refining degassing is carried out for 25 minutes, and the nitrogen content, the hydrogen content and the oxygen content of the molten steel are enabled to be not higher than 38ppm, 1.5ppm and 20ppm respectively; continuously casting the plate blank at the drawing speed of 0.95 m/min; heating for 4.2 hours to ensure that the central temperature of the casting blank reaches 1210 ℃, the initial rolling temperature is 1170 ℃, the second-stage rolling temperature is 940 ℃, the final rolling temperature is 890 ℃, and the reduction rate is 64 percent; the steel plate reddening temperature is 690 ℃; straightening by 4 mm/m; the quenching temperature is 910 ℃, and the tempering temperature is 550 ℃. The mechanical properties of the alloy are 551MPa of yield strength, 643MPa of tensile strength, 20 percent of elongation, 57J,58J and 63J (5 x 10mm) of impact energy at-40 ℃.
Through the embodiment, the 500 MPa-grade steel for the engineering machinery has better mechanical property and fatigue property, can prolong the service life of the engineering machinery, and also meets the requirement of low-temperature toughness of the engineering machinery at 40 ℃ below zero. Q235B common material with the yield strength of only 235MPa can be perfectly replaced on the steel for the engineering machinery, and the upgrading and updating of the product quality in the metallurgy and engineering machinery industries are promoted.
the foregoing is only a preferred embodiment of the present invention, and it should be noted that several deductions or substitutions can be made without departing from the spirit of the present invention, and all such deductions or substitutions should be considered as the protection scope of the present invention.

Claims (1)

1. A manufacturing method of 500 MPa-grade steel for engineering machinery is characterized by comprising the following steps:
(1) Smelting molten steel: the preparation comprises the following components in percentage by mass: c: 0.15 to 0.18%, Si: 0.23-0.27%, Mn: 1.49-1.53%, P: less than or equal to 0.013%, S: less than or equal to 0.006 percent, Cr: 0.17-0.25%, V: 0.033 to 0.035%, Ti: 0.016-0.019%, B: 0.0009-0.0011% of molten steel, and the balance of Fe and inevitable impurities;
the method comprises the following steps: (1.1) pretreating molten iron so that S in the molten iron: less than 0.010 percent;
(1.2) adding the pretreated molten iron into a converter, smelting by adopting a BOF method, and carrying out deoxidation alloying, wherein the added alloy is 90% of the alloy addition amount in the designed molten steel components;
(1.3) refining for 15 ~ 30min in an LF furnace, finely adjusting alloy components to enable the alloy components to meet requirements, and raising the temperature of molten steel;
(1.4) carrying out RH vacuum degassing treatment for 15-30 minutes, reasonably stirring and floating by RH bottom blowing argon to remove nonmetallic inclusions, and controlling the nitrogen content of molten steel to be less than or equal to 38ppm, the hydrogen content to be less than or equal to 1.5ppm and the oxygen content to be less than or equal to 20 ppm;
(1.5) feeding a calcium wire to purify molten steel, so that strip-shaped MnS nonmetallic inclusions become dispersed, shortened and spheroidized to obtain the MnS nonmetallic inclusion compound;
(2) Casting and forming a blank, namely feeding the molten steel into a continuous casting machine for argon protection casting in the whole process, and meanwhile electromagnetically stirring at the drawing speed of 0.75 ~ 1.2.2 m/min to obtain a casting blank;
(3) Heating the casting blank, namely uniformly heating the casting blank at 1100 ~ 1220 ℃ for 1220 for 3.5 ~ 4.5.5 hours;
(4) rolling by a four-roller reversible rolling mill in two stages, wherein the rolling reduction rate of rough rolling is more than 60%, the initial rolling temperature of rough rolling is 1070 ~ 1180 ℃, the initial rolling temperature of the two stages is 890 ~ 950 ℃, and the final rolling temperature is 820 ~ 900 ℃ to obtain a steel plate;
(5) cooling control, namely, after the residual water at the outlet of the accelerated cooling zone is blown clean, measuring the red returning temperature of the steel plate to be 650 ~ 690 ℃;
(6) Straightening, namely straightening the steel plate, and controlling the straightening unevenness to be 3 ~ 6 mm/m;
(7) Shot blasting: removing iron oxide scales on the surface of the steel plate;
(8) The steel plate with the scale removed is heated to 880 ~ 920 ℃ by adopting a nitrogen protection non-oxidation roller hearth furnace, then is subjected to roller pressing type water jet quenching, and is subjected to high temperature tempering treatment at 550 ~ 660 ℃ to obtain the 500MPa grade steel for the engineering machinery, the metallographic structure of which is uniform and fine martensite high temperature tempering structure.
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