CN110894584B - Non-quenched and tempered steel and manufacturing method thereof - Google Patents
Non-quenched and tempered steel and manufacturing method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 118
- 239000010959 steel Substances 0.000 title claims abstract description 118
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 24
- 238000009749 continuous casting Methods 0.000 claims abstract description 58
- 238000007670 refining Methods 0.000 claims abstract description 46
- 238000005096 rolling process Methods 0.000 claims abstract description 45
- 238000003723 Smelting Methods 0.000 claims abstract description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 7
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- 238000009489 vacuum treatment Methods 0.000 claims abstract description 7
- 239000000126 substance Substances 0.000 claims abstract description 4
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 55
- 150000003568 thioethers Chemical class 0.000 claims description 42
- 238000000034 method Methods 0.000 claims description 40
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- 230000008569 process Effects 0.000 claims description 35
- 238000003756 stirring Methods 0.000 claims description 31
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 19
- 229910052593 corundum Inorganic materials 0.000 claims description 19
- 238000010079 rubber tapping Methods 0.000 claims description 19
- 229910001845 yogo sapphire Inorganic materials 0.000 claims description 19
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 17
- 238000010583 slow cooling Methods 0.000 claims description 15
- 239000000498 cooling water Substances 0.000 claims description 10
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- 238000007711 solidification Methods 0.000 claims description 10
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- 235000011941 Tilia x europaea Nutrition 0.000 claims description 5
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- 229910052681 coesite Inorganic materials 0.000 claims 1
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- 229910052682 stishovite Inorganic materials 0.000 claims 1
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- 238000009826 distribution Methods 0.000 description 9
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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Abstract
The invention discloses non-quenched and tempered steel and a manufacturing method thereof, wherein the manufacturing method comprises the following production steps: electric furnace smelting, LF refining, VD vacuum treatment, continuous casting and rolling; the chemical components of the non-quenched and tempered steel are C: 0.37-0.39%; si: 0.56-0.62%; mn: 1.45-1.50%; p is less than or equal to 0.020%; s: 0.030-0.045%; cr: 0.15-0.20%; ni is less than or equal to 0.15 percent; cu is less than or equal to 0.20 percent; al is less than or equal to 0.010 percent; mo is less than or equal to 0.05 percent; n: 0.013-0.017%; v: 0.010-0.020%; ti: 0.010-0.020%; nb: 0.010-0.020%; the balance of Fe and inevitable impurities; the carbon equivalent Ceq is C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, and Ceq is 0.65-0.69.
Description
Technical Field
The invention relates to the field of metal materials and manufacturing thereof, in particular to non-quenched and tempered steel and a manufacturing method of the non-quenched and tempered steel.
Background
The application of the non-quenched and tempered steel can reduce the energy consumption of the automobile industry in the processes of part production and heat treatment. The application of the non-quenched and tempered steel can reduce the weight of the automobile body and help to realize the light weight of the automobile. The weight can be reduced by 14% by using the front cantilever made of non-quenched and tempered steel, and the weight can be reduced by 10% by using the fractured connecting rod made of non-quenched and tempered steel. Research shows that the reduction of the vehicle body mass can reduce the energy consumed by the vehicle in the driving process and save the fuel consumption. Meanwhile, the running resistance of the automobile and the mass of the automobile body are in a linear relation, the mass of the passenger car is reduced by 100kg, and the automobile runs 1km more per liter of oil. Therefore, the research and development of the non-quenched and tempered steel can accelerate the progress of the automobile industry in the aspects of energy conservation and emission reduction, and the development trend of the current society is met.
The requirements of the modern society on automobile products are higher and higher, the requirements on the environmental protection and safety of automobile engines are higher, and the high efficiency and energy conservation are also needed. Therefore, higher requirements are provided for automobile crankshaft materials, the crankshaft steel is required to be energy-saving, consumption-reducing and manufacturing cost-reducing, and better comprehensive mechanical properties are required to meet the requirements of high-performance automobile engine crankshaft materials. The non-quenched and tempered steel has the characteristics of grain refinement, structural state improvement, strength and plasticity improvement in a certain range, and is widely applied to machining of automobile crankshaft materials.
The existence of sulfide in the non-quenched and tempered steel enables the steel to generate stress concentration in the cutting process, and the processing performance of cutting, namely the automatic chip breaking and chip removal performance, is improved. High sulfur in non-heat-treated steel can improve the machinability of steel, but simple sulfides in steel tend to form elongated sulfides extending in the rolling direction during rolling, resulting in anisotropy of mechanical properties of steel and differences in mechanical properties. Research shows that the spherical and spindle-shaped composite sulfide can improve the anisotropy of the transverse performance of steel more than the strip-shaped simple sulfide. At present, domestic non-quenched and tempered steel production enterprises have low control level on sulfides in steel, and the quantity, form, size and distribution of the sulfides in the steel are not ideal, so that the cutting processability of the non-quenched and tempered steel is restricted. At present, the alkalinity of furnace slag in the common carbon steel smelting is controlled within the range of 3.0-4.0; the initial rolling temperature control range of common carbon steel rolling is 960-1000 ℃, and the final rolling temperature control range is 920-960 ℃; in order to obtain better sulfide control form and mechanical property, smelting and rolling parameters of the sulfur-containing non-quenched and tempered steel need to be further optimized to meet production requirements.
Disclosure of Invention
The invention provides non-quenched and tempered steel and a manufacturing method thereof, aiming at solving the problem of high sulfur content in the non-quenched and tempered steel and solving the problem of sulfide control in the production process of the non-quenched and tempered steel. According to the invention, the refined low-alkalinity slag is adopted to increase the adsorption of fine oxides in steel, so that sulfide inclusions form a spherical composite sulfide inclusion form which takes the oxides as cores and is wrapped with sulfide in the solidification process; by increasing the cooling water amount of continuous casting, the temperature of the continuous casting billet is controlled to rise again, the growth rate of sulfides in the continuous casting billet is reduced, and the size of sulfides is reduced; through three-stage electromagnetic stirring of the continuous casting crystallizer, the aggregation phenomenon of sulfides is improved, the sulfides are crushed, and the size of the sulfides is reduced; by setting the proper heating temperature and the proper heat preservation time of the continuous casting billet, sulfides at different parts in the continuous casting billet are crushed due to atomic diffusion caused by different diameters, and the average size is reduced; by reducing the rolling initial temperature, the sulfide plastic deformation is reduced, and more spherical or spindle-shaped sulfides are generated. The sulfide in the non-quenched and tempered steel produced by the method of the invention appears in a spherical or spindle-shaped complex sulfide form, the grade of sulfide inclusion is less than 1.5 grade, the sulfide control quality requirement of the non-quenched and tempered steel is completely met, and the cutting processing requirement of the non-quenched and tempered steel is more favorably met.
The invention provides a non-quenched and tempered steel on the one hand, which is characterized in that the chemical components of the non-quenched and tempered steel are C in percentage by weight: 0.37-0.39%; si: 0.56-0.62%; mn: 1.45-1.50%; p is less than or equal to 0.020%; s: 0.030-0.045%; cr: 0.15-0.20%; ni is less than or equal to 0.15 percent; cu is less than or equal to 0.20 percent; al is less than or equal to 0.010 percent; mo is less than or equal to 0.05 percent; n: 0.013-0.017%; v: 0.010-0.020%; ti: 0.010-0.020%; nb: 0.010-0.020%; the balance of Fe and inevitable impurities; wherein the carbon equivalent Ceq is C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, and Ceq is 0.65-0.69. The sulfide in the non-quenched and tempered steel is in a spherical or spindle-shaped complex sulfide metallographic structure, and the grade of sulfide inclusion is less than or equal to 1.5. The non-quenched and tempered steel has a tensile strength of 751-843 MPa, a yield strength of 462-511 MPa, and an elongation after fracture of 18-22%.
Another aspect of the invention provides a method for producing a non-heat treated steel, in particular a non-heat treated steel with an ideal sulphide morphology and distribution, comprising the following steps: electric furnace smelting, LF refining, VD vacuum treatment, continuous casting and rolling; the LF refining comprises a slagging process of refining alkalinity slag; the continuous casting comprises three-stage electromagnetic stirring and a continuous casting billet air-water mist cooling process; the rolling comprises the processes of billet heating, low-temperature rolling and slow cooling.
Further, in the electric furnace step, the composition of the molten steel end point of the electric furnace is controlled as follows: c: 0.10-0.32%; p is less than or equal to 0.012 percent; tapping temperature is 1610 to 1660 ℃; adding auxiliary materials during electric furnace tapping: 490-510 kg of lime per furnace, 290-310 kg of cleaning agent per furnace and 70-100 kg of aluminum block per furnace.
Further, in the LF refining step, the tapping requirement of the LF furnace is as follows: c: 0.26 to 0.34%, Si: 0.45-0.55%, Mn: 1.12-1.27%, Cr: 0.10-0.16% of steel tapping temperature, 1530-1550 ℃; and deoxidizing in the whole LF refining process. Adding a slagging agent for slagging during LF refining, wherein the alkalinity of LF refining slag after slagging is 3.2-3.7; the refining slag comprises the following components: CaO: 48-51%; SiO 22：13～16％；FeO：0.29～0.41％；Al2O3：20～23％；MgO：7.6～9.7％。
Adding 150-160 Kg of silica sand per furnace before LF hoisting; refining slag after slaggingThe component range is as follows: CaO: 41-44%; SiO 22：19～23％；FeO：0.70～1.10％；Al2O3: 19-21%; MgO: 7.3-11.0%; the alkalinity range of the refining slag is 1.9-2.0; LF ladle temperature: 1620-1640 ℃.
Further, the VD vacuum process includes: the vacuum degree is less than or equal to 67Pa, and the vacuum maintaining time is 10-20 minutes; VD vacuum ladle temperature: 1554-1569 ℃; the alkalinity range of VD vacuum slag is 1.9-2.0; the VD vacuum slag comprises the following components: CaO: 33 to 42 percent; SiO 22：17～22％；FeO：0.39～0.60％；Al2O3：18～21％；MgO：8～16％。
In the LF refining and VD vacuum treatment processes, the principle that the low-alkalinity refining slag adsorbs fine oxides in steel is utilized, so that spherical composite sulfide inclusions with the oxides as cores and wrapped with sulfides are formed in the solidification process of sulfides in the molten steel, the relative plasticity of the sulfide inclusions is reduced, the sulfide inclusions are not easy to deform in the rolling process, and a foundation is laid for obtaining an ideal sulfide form.
Further, in the continuous casting process, the superheat degree of a continuous casting furnace is 18-30 ℃; the continuous casting speed is 0.65-0.67 m/min; a gas water mist cooling mode is adopted, and the cooling water quantity is 3200-3300 m/min; three-stage electromagnetic stirring is adopted for continuous casting, wherein the electromagnetic stirring (M-EMS) parameter in the crystallizer is 250A of current and 2Hz of frequency; the parameters of the second cold section electromagnetic stirring (S-EMS) are current 180A and frequency 8 Hz; the solidification end electromagnetic stirring (F-EMS) parameters were current 1100A, frequency 8 Hz. In the continuous casting step, the temperature of the continuous casting billet is controlled to rise again through large continuous casting cooling water quantity, so that the growth rate of sulfide is reduced, and the size of the sulfide is reduced; meanwhile, continuous casting three-stage electromagnetic stirring is adopted, so that the aggregation phenomenon of sulfides is improved, the size of the sulfides is smaller, spherical or spindle-shaped composite sulfides are gradually formed, the anisotropy of the transverse performance of steel can be improved compared with the strip-shaped simple sulfides in the prior art, and the mechanical performance of the steel is improved.
Further, in the rolling step, the continuously cast steel billet is heated by a heating furnace, and the control range of the heating temperature is as follows: the temperature of the preheating section is 880-920 ℃, and the heating time is 0.75-1.0 h; heating for the first time at 900-1100 ℃ for 0.75-1.0 h; heating 1180-1280 ℃ at the second section, heating 1200-1260 ℃ at the third section, and adding the heating time of the second section and the third section for 2.5-3 hours; low-temperature rolling is adopted, the initial rolling temperature is 850-930 ℃, and the final rolling temperature is less than or equal to 900 ℃; the slow cooling process is that the temperature of the lower cooling bed of the rolled steel is as follows: 380-420 ℃; slowly cooling in a slow cooling pit for more than or equal to 36h, and discharging the steel from the slow cooling pit at a temperature of less than or equal to 200 ℃.
In the rolling process, the continuous casting billet is reasonably heated and kept warm for a long time, so that sulfides at different positions in the billet are subjected to atomic diffusion due to different diameters, the sulfides are crushed into multiple sections, and the average size is reduced; meanwhile, by reducing the rolling initial rolling temperature, the plastic deformation of the sulfide compound is reduced, more spherical or spindle-shaped sulfides are generated, the cutting processing performance of the non-quenched and tempered steel is more excellent, and meanwhile, various performances such as the tensile strength of the non-quenched and tempered steel are improved.
Drawings
FIG. 1 is a sulfide distribution diagram of a general non-quenched and tempered steel on the market;
FIG. 2 is a sulfide distribution diagram of a conventional C38+ N2 non-quenched and tempered steel;
FIG. 3 is a sulfide distribution diagram of a non-quenched and tempered steel according to the present invention;
FIG. 4 is a sulfide distribution diagram of a C38+ N2 non-quenched and tempered steel of the present invention.
Detailed Description
The following exemplary examples illustrate specific embodiments of the present invention in detail. The present invention may be variously modified and may include various embodiments.
Other features and advantages of the present invention will be described in the following detailed description of the invention which refers to the accompanying drawings.
Referring to the attached figures 3 and 4, the invention utilizes the principle that low-alkalinity slag increases the adsorption of fine oxides in steel, so that sulfides in molten steel form spherical composite sulfide inclusion which takes oxides as cores and is wrapped by sulfides in the outside in the solidification process, and an ideal sulfide form is obtained; controlling the temperature of the continuous casting billet to rise again through large continuous casting cooling water amount in the continuous casting step, reducing the growth rate of sulfide and reducing the size of the sulfide; continuous casting three-stage electromagnetic stirring is adopted, so that the aggregation phenomenon of sulfides is improved, and the size of the sulfides is reduced; in the rolling process, the billet steel is heated and kept for a reasonable time, so that sulfides at different positions in the billet steel are subjected to atomic diffusion due to different diameters, the sulfides are crushed into multiple sections, and the average size is reduced; by reducing the rolling initial temperature, the plastic deformation of the sulfide composite is reduced, and more spherical or spindle-shaped sulfides are generated. The invention adopts a plurality of means to control the shape and distribution of sulfides in steel, the high-sulfur non-quenched and tempered steel produced by the method has uniform sulfide distribution, the sulfide shape conforms to the spherical shape or the spindle shape, the sulfide inclusion grade is less than 1.5 grade, the cutting processing performance of the non-quenched and tempered steel is improved, and the sulfide control quality requirement of the non-quenched and tempered steel is completely met and better.
Referring to the attached figures 3 and 4, the chemical composition of the non-quenched and tempered steel of the present invention is, in weight percent, C: 0.37-0.39%; si: 0.56-0.62%; mn: 1.45-1.50%; p is less than or equal to 0.020%; s: 0.030-0.045%; cr: 0.15-0.20%; ni is less than or equal to 0.15 percent; cu is less than or equal to 0.20 percent; al is less than or equal to 0.010 percent; mo is less than or equal to 0.05 percent; n: 0.013-0.017%; v: 0.010-0.020%; ti: 0.010-0.020%; nb: 0.010-0.020%; the balance of Fe and inevitable impurities; wherein the carbon equivalent Ceq is C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, and the Ceq is 0.65-0.69; the sulfide in the non-quenched and tempered steel is in a spherical or spindle-shaped complex sulfide metallographic structure, and the grade of sulfide inclusion is less than or equal to 1.5. The non-quenched and tempered steel has a tensile strength of 751-843 MPa, a yield strength of 462-511 MPa, and an elongation after fracture of 18-22%.
The degree of superheat of the continuous casting furnace refers to the number of times from the second furnace for casting and the temperature higher than the liquidus temperature.
The electromagnetic stirring can improve the solidification structure of a casting blank, increase the isometric crystal rate, reduce center segregation, strengthen the flowing of liquid during the pouring and solidification, promote the falling of crystals and branches of a solidified layer, cause stronger temperature fluctuation, strengthen the value-added action after the crystals fall, obtain fine isometric crystals and improve the comprehensive mechanical property of steel.
Example 1
Referring to fig. 3, example 1 relates to a non-quenched and tempered steel comprising, by weight: c: 0.37 percent; si: 0.56 percent; mn: 1.45 percent; p: 0.010%; s: 0.030%; cr: 0.15 percent; ni: 0.10 percent; cu: 0.10 percent; al: 0.008 percent; mo: 0.02 percent; n: 0.013%; v: 0.010%; ti: 0.010%; nb: 0.010%; the balance of Fe and inevitable impurities; carbon equivalent Ceq ═ C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, Ceq ═ 0.66.
In the smelting step of the electric furnace, the end point components and weight percentages of the molten steel of the electric furnace are as follows: c: 0.10 percent; p: 0.08 percent; the tapping temperature of molten steel in an electric furnace is 1610 ℃; adding auxiliary materials when tapping from an electric furnace: 490kg lime, cleaning accelerator (CaO 53.5%, SiO)23.5％，Al2O334.3 percent of MgO 8.5 percent) and 290kg of aluminum blocks and 70kg of aluminum blocks.
In the LF refining step, the molten steel tapping end point of an LF furnace comprises the following components: c: 0.26%, Si: 0.45%, Mn: 1.12%, Cr: 0.10 percent and the tapping temperature is 1540 ℃; and deoxidizing in the whole process of LF refining.
Adding a slagging agent for slagging in the LF refining process, and melting slag after slagging to ensure that the alkalinity of the LF refining slag is 3.7; the refining slag comprises the following components in percentage by weight: CaO: 51 percent; SiO 22：13％；FeO：0.30％；Al2O3：22％；MgO：7.9％；
Further, 150Kg of silica sand per furnace is added before the ladle of the LF furnace is hung; the refining slag after slagging comprises the following components in percentage by weight: CaO: 43 percent; SiO 22：19％；FeO：0.70％；Al2O3: 19 percent; MgO: 7.5 percent; the alkalinity of the refining slag is 2.0; LF ladle temperature: 1620 ℃.
In the VD vacuum processing step of this embodiment: the vacuum degree is 67Pa, and the holding time is 10 minutes; VD ladle temperature: 1555 deg.C; the alkalinity of VD vacuum slag is 2.0; VD vacuum slag components and weight percentages are as follows: CaO: 41 percent; SiO 22：18％；FeO：0.39％；Al2O3：19％；MgO：10％。
In the LF refining and VD vacuum treatment process, the low-alkalinity slag is utilized to increase the adsorption of fine oxides in steel, so that spherical composite sulfide inclusions with the oxides as cores and the sulfides as outsourcing are formed in molten steel in the solidification process, and the sulfide forms enable the produced non-quenched and tempered steel to have better cutting performance and consistency of mechanical properties.
In the continuous casting process, the superheat degree of a continuous casting furnace is 19 ℃; the continuous casting speed is 0.65 m/min; the continuous casting blank adopts a gas water mist cooling mode, and the cooling water quantity is 3200/min; three-stage electromagnetic stirring is adopted during continuous casting, namely electromagnetic stirring (M-EMS) current in a crystallizer is 250A, and the frequency is 2 Hz; the current of the second cooling section electromagnetic stirring (S-EMS) is 180A, and the frequency is 8 Hz; coagulation end electromagnetic stirring (F-EMS) Current 1100A, frequency 8 Hz. In the continuous casting step, the temperature of the continuous casting billet is controlled to rise again through large continuous casting cooling water quantity, the growth rate of sulfides is reduced, and the size of the sulfides is reduced; meanwhile, because continuous casting three-stage electromagnetic stirring is adopted, the aggregation phenomenon of sulfides is improved, and the size of the sulfides is reduced.
In the rolling process, the continuous casting billet is heated by the stepping heating furnace, and the heating control range is as follows: the temperature of the preheating section is 890 ℃, and the heating time is 1.0 h; heating for the first time at 900 ℃ for 1.0 h; heating at 1180 ℃ in the second section and 1200 ℃ in the third section, and heating the second section and the third section for 3 hours; rolling at the beginning temperature of 930 ℃ at a low temperature, and rolling at the finishing temperature of 900 ℃; and (3) slowly cooling the rolled steel bar, wherein the temperature of a cooling bed below the steel bar is 420 ℃, the slow cooling time is 40h, and the temperature of the steel bar leaving a slow cooling pit is 180 ℃. In the rolling process, the billet is heated by a reasonable heating furnace and is kept warm for a long time, so that sulfides at different positions in the billet are subjected to atomic diffusion due to different diameters, the sulfides are crushed into multiple sections, and the average size is reduced; meanwhile, by reducing the rolling initial rolling temperature, the plastic deformation of the sulfide compound is reduced, more spherical or spindle-shaped sulfides are generated, and the metallographic structure micrograph shown in figure 3 is obviously compared with the sulfide forms shown in figures 1 and 2. Meanwhile, the non-quenched and tempered steel bar is slowly cooled for a long time after being rolled, so that the generation of thermal stress cracks is reduced, and a better surface form is obtained.
In the embodiment, the refining low-alkalinity slag is adopted to adsorb inclusions in steel in the production process, so that spherical composite sulfide inclusions which are wrapped by sulfide and take oxides as cores are formed in the solidification process of the sulfide inclusions, the relative plasticity of the sulfide inclusions is reduced, and the sulfide inclusions are not easy to deform in the rolling process; by increasing the amount of cooling water for continuous casting, the temperature of the continuous casting billet is controlled to rise again, the growth rate of sulfide is reduced, and the size of the sulfide is reduced; through three-stage electromagnetic stirring of the continuous casting crystallizer, the aggregation phenomenon of sulfides is improved, and the size of the sulfides is reduced; through proper three-section heating and heat preservation of continuous casting billets, sulfides at different parts are crushed into multiple sections due to atomic diffusion caused by different diameters, and the average size is reduced; by reducing the rolling initial temperature, the plastic deformation of the sulfide compound is reduced, and more spherical or spindle-shaped sulfides are generated. The purpose of controlling the form and distribution of sulfides in the non-quenched and tempered steel is achieved by various means in the embodiment, as shown in fig. 3. The non-quenched and tempered steel bar produced by the embodiment has the tensile strength of 751MPa, the yield strength of 472MPa, the elongation after fracture of more than 21.5 percent and the grade of sulfide non-metallic inclusion of 1.5, and completely meets and is superior to the sulfide and mechanical property control requirements of non-quenched and tempered steel. The invention produces non-quenched and tempered steel through smelting, continuous casting and rolling, and reduces production cost due to the fact that the quenching and tempering technology is reduced in production. By normalizing the steel material and performing a cutting experiment, the automatic chip breaking and chip removal performance of the steel material is remarkably improved, and the data also show that the performance index of the produced non-quenched and tempered steel is remarkably improved.
Example 2
Example 2 relates to the production of C38+ N2 non quenched and tempered steel as shown in fig. 4. The non-quenched and tempered steel comprises the following components in percentage by weight: c: 0.38 percent; si: 0.60 percent; mn: 1.47%; p: 0.018; s: 0.035%; cr: 0.17 percent; ni: 0.10 percent; cu: 0.15 percent; al: 0.010%; mo: 0.03 percent; n: 0.015 percent; v: 0.015 percent; ti: 0.015 percent; nb: 0.015 percent; the balance of Fe and inevitable impurities; carbon equivalent Ceq ═ C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, Ceq ═ 0.68.
In the present example, in the electric furnace smelting step, the composition of the end point of the molten steel in the electric furnace is as follows: c: 0.20 percent; p: 0.010%;the tapping temperature is 1630 ℃; adding auxiliary materials during electric furnace tapping: lime 500 kg/furnace, cleaning promoter (CaO 52.5%, SiO)2 4.5％，Al2O334.3%, MgO 8.7%) 300 kg/furnace, and aluminum block 80 kg/furnace.
In the LF refining process, the molten steel end point of the LF furnace comprises the following components in percentage by weight: c: 0.29%, Si: 0.50%, Mn: 1.20%, Cr: 0.13 percent and the tapping temperature is 1540 ℃; and deoxidizing in the whole process of LF refining.
Adding a slagging agent in the LF refining process for slagging, wherein the alkalinity of LF refining slag after slagging is 3.4; the refining slag comprises the following components in percentage by weight: CaO: 50 percent; SiO 22：15％；FeO：0.35％；Al2O3：21％；MgO：9.0％；
Further, 155Kg of silica sand is added before LF lifting ladle; the refining slag after slagging comprises the following components in percentage by weight: CaO: 42%; SiO 22：20％；FeO：0.80％；Al2O3: 20 percent; MgO: 9.0 percent; the alkalinity of the refining slag is 1.92; LF ladle temperature: 1630 deg.C.
In the VD vacuum processing step of this embodiment: the vacuum degree is 66Pa, and the vacuum holding time is 15 minutes; the VD ladle temperature is 1560 ℃; the alkalinity of VD vacuum slag is 1.95; the VD vacuum slag comprises the following components in percentage by weight: CaO: 38 percent; SiO 22：20％；FeO：0.50％；Al2O3：19％；MgO：11％。
In the continuous casting step, the superheat degree of a continuous casting furnace is 20 ℃; the continuous casting speed is 0.66 m/min; the continuous casting billet adopts a gas water mist cooling mode, and the cooling water amount is 3250/min; three-level electromagnetic stirring is adopted for continuous casting, namely electromagnetic stirring (M-EMS) current in a crystallizer is 250A, and the frequency is 2 Hz; the current of the second cooling section electromagnetic stirring (S-EMS) is 180A, and the frequency is 8 Hz; coagulation end electromagnetic stirring (F-EMS) Current 1100A, frequency 8 Hz.
In the rolling process, the continuous casting billet is heated by the stepping heating furnace, and the heating control range is as follows: the temperature of the preheating section is 900 ℃, and the heating time is 0.90 h; heating for 0.90h at 980 ℃ for the first time; heating at the second stage of 1200 ℃, heating at the third stage of 1230 ℃, and heating at the second stage and the third stage for 2.7 hours; the initial rolling temperature adopts low temperature of 920 ℃ for rolling, and the final rolling temperature is 880 ℃. And (3) slowly cooling the rolled steel bar, wherein the temperature of a cooling bed below the steel bar is 400 ℃, slowly cooling the steel bar in a slow cooling pit for 40h, and the temperature of the steel bar out of the slow cooling pit is 160 ℃.
The C38+ N2 non-quenched and tempered steel bar produced in the embodiment has the tensile strength of 779MPa, the yield strength of 467MPa, the elongation after fracture of 21% and the grade of sulfide non-metallic inclusion of 1.5, and completely meets the sulfide control requirement and the mechanical property control requirement of the C38+ N2 non-quenched and tempered steel.
Example 3
Example 3 non-quenched and tempered steel comprising the following components in percentage by weight: c: 0.39 percent; si: 0.62 percent; mn: 1.50 percent; p: 0.008; s: 0.045%; cr: 0.18 percent; ni: 0.15 percent; cu: 0.10 percent; al: 0.010%; mo: 0.04 percent; n: 0.013%; v: 0.015 percent; ti: 0.020%; nb: 0.020%; the balance of Fe and inevitable impurities; carbon equivalent Ceq ═ C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, Ceq ═ 0.69.
In the smelting step of the electric furnace, the end point components and weight percentages of the molten steel of the electric furnace are as follows: c: 0.32 percent; p: 0.007%; the tapping temperature of the molten steel is 1660 ℃; adding auxiliary materials when tapping from an electric furnace: lime 510 kg/furnace, cleaning promoter (CaO 55%, SiO)23.5％，Al2O333%, MgO 8.5%) 310 kg/furnace, 100 kg/furnace of aluminum block.
In the LF refining process, the molten steel tapping end point of an LF furnace comprises the following components: c: 0.30%, Si: 0.55%, Mn: 1.27%, Cr: 0.16 percent and the tapping temperature is 1550 ℃; and performing whole-course deoxidation in the LF refining process.
Adding a slagging agent to carry out slagging in the LF refining process, and melting slag after slagging to ensure that the alkalinity of the LF refining slag is 3.2; the refining slag comprises the following components in percentage by weight: CaO: 48 percent; SiO 22：16％；FeO：0.40％；Al2O3：22％；MgO：9.7％；
Further, 160Kg of silica sand is added into the LF furnace before the ladle is hung; the refining slag after slagging comprises the following components in percentage by weight: CaO: 41 percent; SiO 22：23％；FeO：1.10％；Al2O3: 21 percent; 11.0 percent of MgO; the alkalinity of the refining slag is 1.9; LF ladle temperature: 1640 ℃.
The true bookIn the VD vacuum treatment step of the example: the vacuum degree is 65Pa, and the holding time is 20 minutes; the VD ladle temperature is as follows: 1569 deg.C; the alkalinity of VD vacuum slag is 1.9; the VD vacuum slag comprises the following components in percentage by weight: CaO: 34 percent; SiO 22：22％；FeO：0.60％；Al2O3：21％；MgO：16％。
In the continuous casting process, the superheat degree of a continuous casting furnace is 30 ℃; the continuous casting speed is 0.67 m/min; the continuous casting billet adopts a gas water mist cooling mode, and the cooling water amount is 3300/min; three-level electromagnetic stirring is adopted for continuous casting, namely electromagnetic stirring (M-EMS) current in a crystallizer is 250A, and the frequency is 2 Hz; the current of the second cooling section electromagnetic stirring (S-EMS) is 180A, and the frequency is 8 Hz; coagulation end electromagnetic stirring (F-EMS) Current 1100A, frequency 8 Hz.
In the rolling process, the continuous casting billet is heated by the stepping heating furnace, and the heating control range is as follows: the temperature of the preheating section is 920 ℃, and the heating time is 0.8 h; heating for a period of time of 0.8h at 1100 ℃; heating at 1280 ℃ for the second section, heating at 1260 ℃ for the third section, and heating at the second section and the third section for 2.5 hours; the initial rolling temperature adopts low temperature of 880 ℃ for rolling, and the final rolling temperature is 860 ℃. And (3) slowly cooling the rolled steel bar, wherein the temperature of a cooling bed below the steel bar is 380 ℃, the slow cooling time is 40h, and the temperature of the steel bar leaving a slow cooling pit is 150 ℃.
As shown in FIG. 3, the non-quenched and tempered steel bar produced in the embodiment has a tensile strength range of 823MPa, a yield strength range of 502MPa, an elongation after fracture of 18.5% and a sulfide non-metallic inclusion grade of 1.5, and completely meets the sulfide control requirement and the mechanical property control requirement of the non-quenched and tempered steel.
The above are only preferred embodiments of the present invention. It will be apparent to those skilled in the art that various modifications can be made without departing from the principles of the invention. Such modifications are also to be considered as within the scope of the invention.
Claims (7)
1. A non-quenched and tempered steel is characterized in that the chemical components of the non-quenched and tempered steel in percentage by weight are C: 0.37-0.39%; si: 0.56-0.62%; mn: 1.45-1.50%; p is less than or equal to 0.020%; s: 0.030-0.045%; cr: 0.15-0.20%; ni is less than or equal to 0.15 percent; cu is less than or equal to 0.20 percent; al is less than or equal to 0.010 percent; mo is less than or equal to 0.05 percent; n: 0.013-0.017%; v: 0.010-0.020%; ti: 0.010-0.020%; nb: 0.010-0.020%; the balance of Fe and inevitable impurities; wherein the carbon equivalent Ceq is C +1/6Mn + (Cr + Mo + V)/5+ (Ni + Cu)/15, and the Ceq is 0.65-0.69; the sulfide in the non-quenched and tempered steel is in a spherical or spindle-shaped complex sulfide metallographic structure, and the grade of sulfide inclusion is less than or equal to 1.5;
the non-quenched and tempered steel has a tensile strength of 751-843 MPa, a yield strength of 462-511 MPa, and an elongation after fracture of 18-22%.
2. A method for manufacturing non-quenched and tempered steel is characterized by comprising the following production steps:
electric furnace smelting, LF refining, VD vacuum treatment, continuous casting and rolling; wherein the LF refining comprises a slagging process of refining alkaline slag; the continuous casting comprises three-stage electromagnetic stirring and a continuous casting billet air-water mist cooling process; the rolling comprises the processes of billet heating, low-temperature rolling and slow cooling; wherein,
in the electric furnace smelting process, the end point composition of the molten steel of the electric furnace is as follows: c: 0.10-0.32%; p is less than or equal to 0.012 percent; the tapping temperature of molten steel is 1610 to 1660 ℃; adding the following auxiliary materials into electric furnace tapping: 490-510 kg of lime per furnace, 290-310 kg of cleaning agent per furnace and 70-100 kg of aluminum block per furnace;
in the continuous casting process, the superheat degree of a continuous casting furnace is 18-30 ℃; the continuous casting speed is 0.65-0.67 m/min; wherein the cooling water amount of the air water mist is 3200-3300/min; the three-stage electromagnetic stirring comprises electromagnetic stirring (M-EMS) in a crystallizer, electromagnetic stirring (S-EMS) in a second cooling section and electromagnetic stirring (F-EMS) at a solidification tail end;
in the rolling process, the control range of the continuous casting billet heating is as follows: the temperature of the preheating section is 880-920 ℃, and the heating time is 0.75-1.0 h; heating for the first time at 900-1100 ℃ for 0.75-1.0 h; heating 1180-1280 ℃ at the second section, heating 1200-1260 ℃ at the third section, and heating the second section and the third section for 2.5-3 hours;
the low-temperature rolling is carried out at the initial rolling temperature of 850-930 ℃ and the final rolling temperature of less than or equal to 900 ℃;
the slow cooling process comprises the following steps: the temperature of the lower cooling bed of the steel is as follows: 380-420 ℃, the slow cooling time of the slow cooling pit is more than or equal to 36h, and the temperature of the steel discharged from the slow cooling pit is less than or equal to 200 ℃.
3. The method for manufacturing non-quenched and tempered steel according to claim 2, wherein in the LF refining process, the tapping requirement of an LF furnace is as follows: c: 0.26 to 0.34%, Si: 0.45-0.55%, Mn: 1.12-1.27%, Cr: 0.10-0.16%; the tapping temperature is 1530-1550 ℃; deoxidizing in the whole LF refining process;
adding a slagging agent for slagging in the LF refining process, wherein the alkalinity of LF refining slag after slagging is 3.2-3.7; the refining slag comprises the following components: CaO: 48-51%; SiO 22：13～16％；FeO：0.29～0.41％；Al2O3：20～23％；MgO：7.6～9.7％；
Adding 150-160 Kg of silica sand per furnace before LF hoisting; the refining slag after slagging comprises the following components: CaO: 41-44%; SiO 22：19～23％；FeO：0.70～1.10％；Al2O3: 19-21%; MgO: 7.3-11.0%; the alkalinity of the refining slag is 1.9-2.0; LF ladle temperature: 1620-1640 ℃.
4. The method for producing a non-quenched and tempered steel according to claim 2, wherein the VD vacuum treatment comprises: the vacuum degree is less than or equal to 67Pa, and the vacuum maintaining time is 10-20 minutes; the temperature of the VD vacuum crane ladle is 1554-1569 ℃; the alkalinity of VD vacuum slag is 1.9-2.0; the VD vacuum slag comprises the following components: CaO: 33 to 42 percent; SiO 22：17～22％；FeO：0.39～0.60％；Al2O3：18～21％；MgO：8～16％。
5. A method for producing non-heat-treated steel according to claim 2, wherein the cleaning accelerator is CaO: 50-55% of SiO2：1.5～5.5％，Al2O3：28.5～35.5％，MgO：5～9％。
6. A method of manufacturing non-quenched and tempered steel according to claim 2, wherein electromagnetic stirring (M-EMS) parameters in the mold are: current 250A, frequency 2 Hz; the parameters of the second cold section electromagnetic stirring (S-EMS) are as follows: current 180A, frequency 8 Hz; the solidification end electromagnetic stirring (F-EMS) parameters were: current 1100A, frequency 8 Hz.
7. A method of producing a non-heat-treated steel according to any one of claims 2 to 6, wherein the sulfides in the non-heat-treated steel have a spherical or spindle-shaped complex sulfide metallographic structure and a sulfide inclusion grade of 1.5 or less;
the non-quenched and tempered steel has a tensile strength of 751-843 MPa, a yield strength of 462-511 MPa, and an elongation after fracture of 18-22%.
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