WO2022148492A1 - 一种乘用车万向节叉冷锻用钢及其制造方法 - Google Patents

一种乘用车万向节叉冷锻用钢及其制造方法 Download PDF

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WO2022148492A1
WO2022148492A1 PCT/CN2022/076389 CN2022076389W WO2022148492A1 WO 2022148492 A1 WO2022148492 A1 WO 2022148492A1 CN 2022076389 W CN2022076389 W CN 2022076389W WO 2022148492 A1 WO2022148492 A1 WO 2022148492A1
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steel
manufacturing
molten
furnace
continuous casting
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PCT/CN2022/076389
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English (en)
French (fr)
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张磊
白云
罗元东
吴小林
李冰
汤敏浩
孙艺凡
顾畔
朱和平
刘雯
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江阴兴澄特种钢铁有限公司
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Definitions

  • the invention belongs to the technical field of iron-based alloys, and in particular relates to a steel suitable for cold forging and a manufacturing method thereof.
  • Universal joint fork is a key component used in the steering system of passenger cars.
  • 1 casting 2 hot forging
  • 3 cold forging Castings are prone to blisters, easy to break and unsafe, have great quality defects, and are not easy to detect.
  • the disadvantage of hot forging is mainly that the dimensional accuracy of the formed part is low, and subsequent processing is required, which destroys the fibers inside the metal.
  • Cold forging refers to the direct production of products close to the final shape of the part at room temperature, or even to provide qualified finished parts.
  • the cold forging material should have high deformation capacity and small deformation resistance, that is, the yield strength and hardness of the cold forging material should be as low as possible, and the elongation and section shrinkage should be as high as possible. Cold deformation properties; the lower the work hardening sensitivity of the material, the better.
  • Step for cold forging and its manufacturing method disclosed in Patent Document 1 Application No. CN201680089645, the chemical components in mass % contain C: 0.05-0.30%, Si: 0.05-0.45%, Mn: 0.40-2.00%, S: 0.008 % or more and less than 0.040%, Cr: 0.01 to 3.00%, Al: 0.010 to 0.100%, Bi: 0.0001 to 0.0050%, Mo: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 0.30%, B : 0 to 0.0200%, Mg: 0 to 0.0035%, Ti: 0 to 0.060%, and Nb: 0 to 0.080%, and the balance includes Fe and impurities.
  • Casting process of cold forged steel casting billets (including continuous casting billets or die-casting ingots); hot working process (including hot forging and hot rolling), hot-working the billets to obtain steel materials; and annealing process , annealing the steel.
  • Patent Document 2 Application No. CN201910035191, discloses "A Method for Smelting Low-Carbon Steel", the components involve C: 0.01-0.04%, Si: 0.15-0.35%, Mn: 0.50-0.70%, P ⁇ 0.010%, S ⁇ 0.006 %, Al: 0.020 to 0.040%, and the rest are Fe and inevitable impurities.
  • the method includes converter primary refining, vacuum residual oxygen decarburization, LF refining, VD vacuum treatment, and continuous casting processes; in the converter primary refining process, the carbon content at the end point is controlled to be less than or equal to 0.08%; the vacuum residual oxygen decarburization process, VD
  • the seat bag is evacuated, the degree of vacuum is ⁇ 500Pa, the vacuum is maintained for 4-6min, and the carbon in the steel is removed to ⁇ 0.02%.
  • the purpose of the present invention is to obtain a kind of raw material steel with high deformation ability and small deformation resistance, which is suitable for cold forging to manufacture universal joint forks with complex structure by designing chemical components and combining production methods.
  • the main manufacturing object of the present invention is steel for cold forging of universal joint forks for passenger vehicles.
  • the specific specifications of the steel are ⁇ 20mm- ⁇ 40mm bars, surface hardness ⁇ 110HV30; Rp0.2 ⁇ 280MPa, Rm ⁇ 360MPa, elongation rate A5 ⁇ 40%, section shrinkage rate Z ⁇ 75%, spheroidization rate is the carbide spheroidized particles in pearlite, which are point-like under the microscope, spherical under high magnification, accounting for ⁇ 80% of pearlite, even ⁇ 85% %, or even ⁇ 90%, the steel exhibits excellent plasticity and low deformation resistance, and is an ideal cold forging steel.
  • the inventors of the present application preferably design the chemical composition to have a low-carbon composition as much as possible, and increase the annealing treatment in the production method, and the obtained microstructure is ferrite and pearlite spheres (spheroidization rate ⁇ 80%).
  • the specific technical scheme of the present invention a steel for cold forging of universal joint forks for passenger cars, the chemical composition of the steel contains C: 0.04-0.10%, Si: 0.01%-0.12%, Mn: 0.40-0.60% by mass. %, P: ⁇ 0.015%, S: 0.020 ⁇ 0.035%, Cr: ⁇ 0.10%, Ni: ⁇ 0.10%, Cu: ⁇ 0.10%, Mo: ⁇ 0.02%, Al: 0.020% ⁇ 0.050%, N: 0.007 % ⁇ 0.009%, the balance is Fe and inevitable impurity elements; the structure of the steel is ferrite and pearlite, and the spheroidization rate of pearlite is ⁇ 80%.
  • the delivery state of the steel is the annealed state, preferably the annealed wagon material.
  • C content is the main element of mechanical properties. With the increase of carbon content, the strength increases, the plasticity decreases, and the cold forging performance decreases. The C content fluctuates greatly and has a great influence on the cold forging performance.
  • the universal joint fork has low requirements on the strength of the steel and high requirements on the plasticity.
  • Si can improve the strength and hardness of cold forged steel, and reduce the plasticity and toughness. Too high Si content will lead to the increase and aggregation of SiO2 -containing C-type and D-type inclusions, which easily lead to cold forging cracking. From the perspective of cold forging, the lower the Si content, the better, to improve the plasticity and toughness of the steel.
  • the ladle, the refractory material and the refining slag all contain Si materials. During deoxidation, a small amount of Si elements are reduced to the molten steel, and Si cannot be 0 in the molten steel. Based on the aforementioned smelting conditions, the present invention uses Si The content is controlled at 0.01% to 0.12%.
  • Mn dissolves in ferrite and cementite, increasing strength and reducing plasticity.
  • the Mn content of low carbon cold forging steel should not exceed 0.6%, otherwise it will cause difficulties in the cold forging process. Therefore, the present invention controls Mn to be 0.40% to 0.60%.
  • P can strengthen the ferrite and increase the strength, but at the same time it will reduce the plasticity and cause cold brittleness.
  • P promotes the delayed fracture and shrinkage rate of the steel, and the present invention is designed to control P ⁇ 0.015%.
  • the steel with high plasticity and toughness requires a large cutting force, and the resulting cutting temperature is also high. In addition, it is prone to bonding, large cutting deformation, severe tool wear, poor surface quality after cutting, and low carbon annealing.
  • Steel has high plasticity and toughness, and poor machinability.
  • a certain amount of S is added to the steel, and the combination of S and Mn in the steel forms MnS, which is less harmful to the performance of the steel, reducing or inhibiting the production of FeS, which can improve or improve the cutting performance. Too much will not only lead to poor plasticity of the steel, but also produce more serious segregation in the steel, which will have a harmful effect on the continuous casting and rolling of the steel. Therefore, the present invention controls S at 0.020-0.035%.
  • Al is added as a deoxidizing element in the steel.
  • Al and N form dispersed fine AlN particles to refine the grains. Inclusions, reduce the purity of molten steel. Therefore, the present invention controls the content of Al at 0.020-0.050%.
  • the N in the steel combines with the Al element to form a nitride refined grain, and the fine grain is beneficial to improve the plasticity, toughness and strength, and improve the overall performance of the steel.
  • too high N content is unfavorable to continuous casting production, and it is easy to form surface cracks and poor surface quality of continuous casting. Therefore, the present invention controls the N content to be 0.007% to 0.009%.
  • Al/N ⁇ 3 should be controlled, too low Al/N can not achieve obvious grain refinement effect, which is not conducive to improving plasticity and toughness.
  • Cr, Ni, Cu, Mo are non-special added elements, they can exist as residual elements, or as some non-essential added elements.
  • Cr, Ni, Cu, Mo and other elements will inevitably exist along with the raw materials.
  • Cr , Ni, Cu, and Mo with high content will increase the strength and deteriorate the plasticity and toughness of the steel, so the application limits the upper limit of their content, requiring Cr: ⁇ 0.10%, Ni: ⁇ 0.10%, Cu: ⁇ 0.10%, Mo: ⁇ 0.02%.
  • the present application requires that the round steel after hot rolling and forming needs to be annealed, and the annealing is used to make pearlite spheroidized to further improve the toughness and plasticity of the steel, and to improve the cold forging performance to satisfy the production of complex parts.
  • Another object of the present invention is to provide a manufacturing method of steel for cold forging of a universal joint fork of a passenger car, which mainly includes step 1, molten steel smelting; step 2, casting billet; step 3, hot forming; step 4, sawing Cut and stack to cool; step five to anneal.
  • the specific requirements and implementation methods of the main processes are as follows:
  • the molten steel smelting in step 1 involves: molten iron pretreatment, primary smelting in a converter, and refining, wherein
  • the hot metal pretreatment removing impurities such as S, P, Si, Ti and other elements in the molten iron, reducing the amount of slag and improving the metal yield during initial smelting in the converter, pouring refractory (corundum) and baking the cross-shaped stirring head , immersed in the molten iron ladle pool, and generates a vortex by its rotation.
  • the weighed alloy raw material is added to the surface of the molten iron by the feeder, and is swept into the molten iron by the vortex so that the raw material and the molten iron are fully contacted and reacted, and the molten iron is removed while melting.
  • S, Si, Ti impurity elements is to improve the productivity of steelmaking and the purity of molten steel.
  • the primary smelting of the converter the raw materials fed into the furnace are loaded into the primary smelting furnace, and the pretreated molten iron in the raw materials into the furnace accounts for more than 75%, and the rest is scrap steel.
  • the scrap steel is baked before entering the furnace, and Cr, Mo, Ni, Scrap with low Cu content.
  • the initial smelting of the converter adopts a high carbon pulling operation to improve the high carbon pulling rate at the end of the initial smelting of the converter, control the carbon content at the end of the smelting to be below 0.04%, and the tapping temperature is 1540-1580 °C.
  • the molten steel is slag-retained to prevent the oxidation of slag.
  • the content of C and O in molten steel has a dynamic relationship.
  • the probability of the O content is high. Therefore, the corresponding Al block and O content are used in the tapping process.
  • Al particles strongly deoxidize molten steel and perform partial alloying of Mn and Al elements to prevent molten steel from overoxidizing.
  • the refining process adopts argon stirring, adjusting the chemical argon stirring intensity so that the molten steel is not exposed, using aluminum powder, aluminum particles, carbon powder for diffusion deoxidation, using Al wire for precipitation deoxidation, through precipitation deoxidation and diffusion deoxidation, Significantly reduce the content of non-metallic inclusions in the molten steel.
  • the adjusted components are all within the specified content requirements; the N content in the molten steel is sampled and analyzed, and the Al/Mn content in the molten steel is controlled by supplementing nitrogen and manganese lines. N ratio ⁇ 3, in order to play the role of AlN to refine grains.
  • the molten steel does not need vacuum degassing, but directly to the argon blowing station to blow argon softly, the purpose is to reduce the temperature of the hanging bag and avoid the reduction of N content caused by vacuum degassing.
  • Soft blowing argon for more than 15 minutes can fully float the inclusions and ensure the purity of the steel.
  • Casting the billet in the second step involves manufacturing the molten steel into a billet by continuous casting, or first casting the billet into a billet through an ingot casting method and then hot working the billet into the billet.
  • continuous casting has more advantages than ingot casting.
  • the continuous casting process is the key to the entire smelting process.
  • the risk of nodules in molten steel is high. Dead water inlets create waste.
  • the molten steel from the large ladle to the tundish to the mold is all sealed and poured to isolate the molten steel from the air and control the secondary oxidation of the molten steel;
  • the continuous casting process adopts low superheat pouring, and the pouring superheat degree is 10 °C ⁇ 20°C, and equipped with a suitable pulling speed of 0.8 ⁇ 1.3m/min to improve the internal quality;
  • the obtained continuous casting billet needs to be cooled slowly in the pit, the slow cooling temperature should be above 400°C, and the slow cooling time should be more than 12 hours to prevent casting.
  • the blank is cracked.
  • Hot forming in step 3 heating the billet to 1050-1080°C and keeping the temperature for 3-4 hours. After the continuous casting billet is released from the furnace, it is descaled by high-pressure water and rolled with a continuous rolling mill, and hot-rolled to the required specifications, and the rolling temperature is 950-900°C. 1020°C, the final rolling temperature is 780 ⁇ 820°C, the rolling is controlled in the two-phase region, the average pass reduction ratio is 1.1 ⁇ 1.2, the rolling is 10 ⁇ 15 passes, and the ferrite and pearlite are obtained by slow cooling after rolling Organised round bars.
  • the annealing in step 5 is to spheroidize the steel whose structure is ferrite + pearlite based on the above chemical composition.
  • the furnace temperature rises to 700-715°C after the steel enters the furnace.
  • the holding time h in the annealing process is preferably 10-18 hours; the cooling rate S is preferably 0.32-0.52°C/min.
  • the steel for cold forging of the present application adopts a low-C design.
  • the low-carbon steel has few carbides and a large diffusion distance of carbon atoms during spheroidization, which makes spheroidization difficult.
  • technicians can use the Gleeble3800 thermal simulation testing machine to measure the phase transition point AC 1 first , and then design the spheroidizing annealing temperature according to the phase transition point.
  • the main purpose is to evaluate the spheroidization. rate and surface hardness in order to obtain the appropriate spheroidizing annealing temperature.
  • the determination process of the annealing process of the present application is as follows:
  • Test 1 Complete annealing: complete annealing at 20°C-30°C (ie, 758°C-768°C) above AC 1 , and keep for 10-18 hours. min cooling, the surface hardness is 135HV30; the spheroidization rate is 70%.
  • Test 2 Isothermal annealing: at 20°C-30°C above AC1 (ie 758°C-768°C), hold for 3-5 hours, then rapidly cool to 680°C-710°C with the furnace, then hold for 7-13 hours, and then keep the temperature for 7-13 hours. Furnace air cooling, surface hardness 130HV30, spheroidization rate 60%.
  • Test 3 Low temperature annealing: set the annealing temperature to 500-600°C (significantly lower than AC 1 ), keep for more than 10 hours, the surface hardness is 140HV30, and there is no spherical structure.
  • Test 4 Annealing at 20°C-50°C (ie 690°C-720°C) below AC1 (as shown in Figure 4), the surface hardness is about 105HV30, and the spheroidization rate is about 85% (the microstructure is shown in Figure 5). And the surface hardness reaches the ideal, to meet the performance design requirements.
  • An annealing process suitable for this application is designed on the basis of the test data, which is different from complete annealing, isothermal annealing and low temperature annealing, and has specificity and pertinence.
  • the manufacturing method of the present application also includes step 6.
  • Car body the steel used for cold forging has strict requirements on the size of the steel, and generally requires no defects in the surface quality.
  • the dimensional tolerance of the pre-designed round steel is 0/-0.05mm, and the dimensional accuracy and The surface is free of defects.
  • a plastic ferrule is added per meter of the steel behind the car skin to prevent the round steel from being scratched and bumped during the hoisting and transfer process.
  • Low-temperature rolling is adopted for hot forming, and the controlled deformation is completed in the two-phase region, which is 80-100 °C lower than the traditional rolling temperature.
  • the grain size of low-temperature rolling is 1-1.5 grades higher than that of conventional low-temperature rolling. Further thinning to improve toughness and plasticity. And the structure of ferrite + pearlite is obtained after rolling.
  • Annealing is based on the setting of the round steel after hot forming, and the annealing process is set for the purpose of increasing the spheroidization rate and reducing the surface hardness, which is an optimization of the existing annealing process.
  • the holding time and cooling rate of annealing have fully considered the specifications of the round steel, so as to reduce the influence of product specifications on the annealing results, in order to obtain the optimal plasticity and toughness after annealing within the specifications.
  • the toughness and plasticity of the steel of the present application are better, but it is prone to bonding, large cutting deformation, and large tool wear when the car is turned. Without changing the toughness and plasticity, adding a certain amount of S can improve the cutting performance, Improve the rear surface quality and dimensional accuracy of the wagon.
  • Fig. 1 is the part diagram of the universal joint fork of passenger car made of cold forged steel of the application;
  • Fig. 2 is the typical metallographic structure diagram of the steel for cold forging of the application
  • Fig. 3 adopts Gleeble3800 thermal simulation testing machine to measure the phase transition temperature curve of the steel for cold forging of the present application
  • Fig. 4 is the annealing process curve corresponding to annealing test four;
  • Figure 5 is the microstructure diagram of annealing test 4 after annealing, and the spheroidization rate is about 85%.
  • Production method of steel bars for cold forging of universal joints for passenger cars production process route with manufacturing specifications of ⁇ 20mm— ⁇ 40mm: molten iron pretreatment—converter primary refining—refining—continuous casting—continuous casting billet cooling — continuous casting billet heating — Rolling - cooling - spheroidizing annealing - wagon - finishing - inspection - finished product storage. details as follows:
  • the steel specifications of Examples 1 and 2 are ⁇ 20 mm, and the cumulative rolling ratio is 183.4.
  • Hot metal pretreatment The cross-shaped stirring head, which is poured with refractory material (corundum) and baked, is immersed in a certain depth below the liquid level of the molten iron ladle. The surface of molten iron is swept into the molten iron by the vortex to make the raw material and molten iron fully contact and react.
  • refractory material corundum
  • the loading capacity of the converter is 100 tons, including 75 tons of molten iron and 25 tons of scrap steel.
  • oxygen blowing is used for slagging, high carbon drawing operation, the tapping temperature is 1542 ° C, and the end point carbon is 0.03%.
  • tapping add ferromanganese, ferroaluminum, lime, and refining slag; hoist the bales to the LF furnace.
  • the LF furnace seat is powered, and after the slag is formed, aluminum powder, aluminum particles, and carbon powder are added in batches for diffusion deoxidation, and Al wire is fed for precipitation and deoxidation. Control the Al/N ratio ⁇ 3, ensure that the white slag time is 15 minutes, and the temperature of the LF furnace is 1585 °C.
  • the whole process of continuous casting protects the pouring and isolates the molten steel from the air.
  • the temperature of the tundish is 1548 °C
  • the superheat is 10-20 °C
  • the continuous casting speed is set to 0.8m/min.
  • the obtained continuous casting slab was slowly cooled in a pit at 600°C for 13 hours.
  • the continuous casting billet is heated to 1055°C and kept for 3 hours.
  • the rolling temperature is 980-1020°C and the final rolling temperature is 780-820°C.
  • the continuous casting billet is rolled into round steel in the two-phase region. cold.
  • roller hearth type continuous annealing furnace annealing the steel is heated up to 690 °C after entering the furnace and incorporated into the holding section for 10 hours.
  • Wagon A plastic ferrule is added every one meter to the steel behind the wagon, which is convenient for hoisting and transportation.
  • Embodiment 3-4 involves the specification of steel ⁇ 40mm, the rolling ratio is 91.7
  • the charging capacity of the converter is 100 tons, including 90 tons of molten iron and 10 tons of scrap steel.
  • oxygen is blown to make slag
  • the tapping temperature is 1550°C
  • the carbon at the end point is 0.02%.
  • the seat of the LF furnace is powered, and the refining process uses argon stirring. It is advisable to adjust the chemical argon stirring intensity so that the molten steel is not exposed.
  • aluminum powder, aluminum particles, and carbon powder are added in batches for diffusion deoxidation, and Al wire is fed for precipitation and deoxidation.
  • the white slag retention time is 12 minutes
  • the temperature of the LF furnace is 1580 ° C
  • the element composition of the molten steel is adjusted by adding baked alloy blocks during the refining process
  • the molten steel is sampled to analyze the N content, and the nitrogen and manganese lines are accurately controlled according to the N content. Al/N ratio.
  • the argon was blown on the argon stage softly for 15 minutes, and the temperature of the hanging bag was 1570 °C.
  • the whole process of continuous casting adopts protective pouring and isolation of air.
  • the temperature of the tundish is 1543°C
  • the pulling speed is 1.2m/min
  • the superheat degree is controlled at 10-20°C.
  • the continuous casting billet was slowly cooled in the pit at 650°C for 15 hours.
  • the continuous casting billet is heated at 1080°C and kept for 4 hours.
  • the rolling temperature is 1000°C and the final rolling temperature is 820°C. After the rolling is completed, it is cooled slowly.
  • Roller hearth type continuous annealing furnace was used for spheroidizing annealing. After the steel was put into the furnace, the furnace temperature was raised to 715°C, and it was incorporated into the heat preservation section for 18 hours.
  • Example A fine A thick B fine B thick C fine C thick D fine D thick 1 1.5 0.5 0.5 0.5 0 0 0 2 1.5 0.5 0.5 0 0 0 0.5 0.5 3 2.0 0.5 0.5 0 0 0 0.5 4 2.0 0.5 0.5 0.5 0 0 0.5 0.5
  • the tensile strength, hardness and spheroidization rate of the above-mentioned embodiments were directly detected after annealing, the tensile strength was detected according to the EN ISO 6892-1 standard, and the hardness was detected according to the EN ISO 6507-1 standard.
  • the spheroidization rate is the proportion of spheroidized tissue under microscope observation, as shown in Table 3.
  • the metallographic structure of the product is ferrite and pearlite spheres, the grain size after annealing is 6-8, the spheroidization rate is ⁇ 85%, generally ⁇ 90%, the plasticity and toughness are good, and the hardness is low and can be used for cold forging complex parts.
  • the present invention also includes other embodiments, and all technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the claims of the present invention.

Abstract

一种乘用车万向节叉冷锻用钢及其制造方法，钢的化学成分按质量％计含有C：0.04～0.10％，Si：0.01％～0.12％，Mn：0.40～0.60％，P：≤0.015％，S：0.020～0.035％，Cr：≤0.10％，Ni：≤0.10％，Cu：≤0.10％，Mo：≤0.02％，Al：0.020％～0.050％，N：0.007％～0.009％，余量为Fe及不可避免的杂质元素；钢的组织为铁素体和珠光体，其中珠光体的球化率≥85％。生产工艺路线：铁水预处理—转炉初炼—精炼—连铸—连铸坯冷却—连铸坯加热—轧制—冷却—球化退火—车皮。以Φ20mm‑Φ40mm的棒材为例，表面硬度≤110HV30；Rp0.2≤280MPa、Rm≤360MPa、延伸率A5≥40％、断面收缩率Z≥75％、产品具有优异的塑性和低变形抗力，是一种性能理想的冷锻用钢。

Description

一种乘用车万向节叉冷锻用钢及其制造方法 技术领域
本发明属于铁基合金技术领域，尤其涉及一种适用于冷锻加工的钢材及其制造方法。
背景技术
万向节叉是应用在乘用车转向系统上的关键零部件，目前主要有3种制作方式：①铸件；②热锻件；③冷锻件。铸件容易产生砂眼，易断不安全，存在很大的质量缺陷，且不易被检测。热锻件缺点主要在于成形件尺寸精度低，需要后续加工，破坏了金属内部的纤维。冷锻件是指在室温下通过直接生产接近零件最终形状的产品，甚至是提供合格的成品零件。
冷锻件特点：①改善组织和性能，晶粒组织变细，致密度提高，微观缺陷少；晶粒细化及金属流线合理分布；②零件强度高，寿命长；③可加工形状复杂的零件(材料利用率高)；④生产效率高；⑤产品尺寸一致性好，精度高。
冷锻材料要具有较高的变形能力和较小的变形抗力，即对冷锻材料的屈服强度和硬度要求要尽可能的低，延伸率和断面收缩率尽可能的高，材料具有较好的冷变形性能；材料的加工硬化敏感性越低越好。
专利文献1申请号CN201680089645公开的《冷锻用钢及其制造方法》，化学成分以质量％计含有C：0.05～0.30％、Si：0.05～0.45％、Mn：0.40～2.00％、S：0.008％以上且小于0.040％、Cr：0.01～3.00％、Al：0.010～0.100％、Bi：0.0001～0.0050％、Mo：0～1.00％、Ni：0～1.00％、V：0～0.30％、B：0～0.0200％、Mg：0～0.0035％、Ti：0～0.060％、和Nb：0～0.080％，余量包含Fe和杂质。冷锻钢的铸造工序：铸造铸坯(包括连铸铸坯或模铸钢锭)；热加工工序(含热锻、热轧)，对所述铸坯进行热加工从而得到钢材；和退火工序，对所述钢材进行退火。
专利文献2申请号CN201910035191公开的《一种低碳钢的冶炼方法》，成分涉及C：0.01～0.04％、Si：0.15～0.35％、Mn：0.50～0.70％、P≤0.010％、S≤0.006％、Al：0.020～0.040％，其余为Fe和不可避免的杂质。所述方法包括转炉初炼、真空残氧脱碳、 LF精炼、VD真空处理、连铸工序；所述转炉初炼工序，控制终点碳含量≤0.08％；所述真空残氧脱碳工序，VD座包抽真空，真空度≤500Pa，真空保持4～6min，将钢中碳脱至≤0.02％。
发明内容
本发明的目的是要通过设计化学成分并结合生产方法，获得一种具有较高变形能力和较小的变形抗力，适用于冷锻成形制造万向节叉这类结构复杂的原料钢材。
本发明的主要制造对象为乘用车用万向节叉冷锻用钢，所述钢的具体规格为Φ20mm-Φ40mm棒材，表面硬度≤110HV30；Rp0.2≤280MPa、Rm≤360MPa、延伸率A5≥40％、断面收缩率Z≥75％、球化率即珠光体中碳化物球化颗粒，在显微镜下呈点状，高倍观察为球状，占珠光体的比例≥80％，甚至≥85％，更甚至≥90％，钢材表现出优异的塑性和低变形抗力，是一种性能理想的冷锻用钢。
为了满足上述要求，本申请发明人设计化学成分时优选尽可能低碳组成，并且在生产方法中要增加退火处理，获得的组织为铁素体和珠光体球(球化率≥80％)。
本发明的具体技术方案：一种乘用车万向节叉冷锻用钢，钢的化学成分按质量％计含有C：0.04～0.10％，Si：0.01％～0.12％，Mn：0.40～0.60％，P：≤0.015％，S：0.020～0.035％，Cr：≤0.10％，Ni：≤0.10％，Cu：≤0.10％，Mo：≤0.02％，Al：0.020％～0.050％，N：0.007％～0.009％，余量为Fe及不可避免的杂质元素；所述钢的组织为铁素体和珠光体，其中珠光体的球化率≥80％。钢的交货态为退火态，优选退火车皮材。
本发明合金成分的主要作用原理和含量设置的具体说明如下：
C含量要求
C含量作为机械性能的主要元素，随着碳含量增加则强度提高，塑性降低，冷锻性能下降。C含量波动大，对冷锻性能影响较大，万向节叉对钢材强度要求低、而对塑性要求高，本申请优选较低含量的C，本发明控制C含量0.05％～0.10％。
Si含量要求
Si能提高冷锻钢的强度和硬度，降低塑性和韧性。Si含量过高会导致含SiO 2的C类和D类夹杂物增加和聚集，容易导致冷锻开裂。从冷锻加工角度来评价，Si含量要求是越低越好，以提高钢材的塑性和韧性。但是在钢水冶炼过程中钢包、耐火材料和精 炼渣都有含Si材料，脱氧时有一小部分Si元素被还原到钢水中，Si在钢水中不可能为0，基于前述冶炼状况，本发明将Si含量控制在0.01％～0.12％。
Mn含量要求
Mn溶于铁素体和渗碳体，提高强度和降低塑性。低碳冷锻用钢Mn含量不能超过0.6％，否则会造成冷锻过程困难。因此本发明控制Mn在0.40％～0.60％。
P含量要求
P能强化铁素体提高强度，但是同时会导致塑性降低，引起冷脆。对于冷锻用钢来说，P促进钢的延迟断裂和收缩率，本发明设计控制P≤0.015％。
S含量要求
在钢的强度相同时，塑性和韧性大的钢材所需的切削力大，产生的切削温度也高，另外容易发生粘结、切削变形大，刀具磨损厉害，切削后表面质量差，低碳退火钢材塑性和韧性大，切削性差。为了改善切削性能，在钢添加一定量的S，S与钢中的Mn结合形成对钢的性能危害较小的MnS，减少或抑制FeS的产生，能够改善或提高切削加工性能，但S添加过多不但会导致钢的塑性变差，而且还会在钢中产生较严重的偏析从而对钢的连铸和轧制产生有害影响。因此本发明控制S在0.020～0.035％。
Al、N含量要求
Al作为钢中脱氧元素加入，除为了降低钢水中溶解氧之外，Al与N形成弥散细小AlN颗粒可以细化晶粒，但Al含量过大，钢水熔炼过程中易形成Al 2O 3等脆性夹杂物，降低钢水纯净度。因此本发明控制Al的含量在0.020～0.050％。
钢中的N与Al元素结合，形成氮化物细化晶粒，细小的晶粒有利于提高塑性、韧性和强度，改善钢综合性能。但是过高的N含量对连铸生产不利，易形成连铸表面裂纹、表面质量差。因此本发明控制N含量在0.007％～0.009％。为了达到细化晶粒目的，应控制Al/N≥3，过低Al/N起不到明显的细化晶粒作用，不利于提高塑性、韧性。
Cr、Ni、Cu、Mo含量
Cr、Ni、Cu、Mo为非特别添加元素，他们可作为残余元素存在，或者作为一些非必要添加元素，钢水冶炼过程中随着原料不可避免会存在Cr、Ni、Cu、Mo等元素，Cr、Ni、Cu、Mo含量较高时会提高强度，而恶化钢的塑性和韧性，因此本申请对它们的含量上限进行了限定，要求Cr：≤0.10％，Ni：≤0.10％，Cu：≤0.10％，Mo：≤0.02％。
本申请要求热轧成型后的圆钢需要进行退火处理，利用退火使珠光体球化进一步提 高钢材的韧性和塑性，提高冷锻性能来满足制作复杂的零件。
本发明的另一目的是要提供一种乘用车万向节叉冷锻用钢的制造方法，主要包括步骤一、钢水冶炼；步骤二、铸造钢坯；步骤三、热成型；步骤四、锯切和堆冷；步骤五退火。主要工序的具体要求和实施方法如下：
步骤一的钢水冶炼涉及：铁水预处理、转炉初炼、精炼，其中
所述铁水预处理：去除铁水中S、P、Si、Ti等杂质元素，减少转炉初炼时渣量和提高金属收得率，将浇注耐火材料(刚玉)并经过烘烤的十字形搅拌头，浸入铁水包熔池，借其旋转产生漩涡，经过称量的合金原料由给料器加入到铁水表面，并被旋涡卷入铁水中使原料与铁水充分接触反应，一边熔解一边达到去除铁水中S、Si、Ti杂质元素的目的，提高炼钢生产率、钢水纯净度。
所述转炉初炼：将入炉原料装入初炼炉，入炉原料中经预处理的铁水占75％以上，其余为废钢，废钢入炉前进行烘烤，并且选取Cr、Mo、Ni、Cu含量低的废钢。转炉初炼采用高拉碳操作，提高转炉初炼终点高拉碳率，控制熔炼终点碳含量在0.04％以下，出钢温度为1540～1580℃。出钢过程对钢水进行档渣，防止下氧化渣。另外，由于出钢时碳含量较低，钢水中C和O的含量存在动力学关系，当C含量较低时O的含量较高的概率极大，因此相应的在出钢过程采用Al块和或Al粒对钢水强脱氧和进行部分Mn、Al元素合金化，防止钢水过氧化。
所述精炼：精炼过程采用氩气搅拌，调整化学氩气搅拌强度以不裸露钢水为宜，使用铝粉、铝粒、碳粉扩散脱氧，使用Al线进行沉淀脱氧，通过沉淀脱氧和扩散脱氧，显著降低钢水中的非金属夹杂含量，通过使用烘烤后的合金，调整成分是全部进入规定的含量要求；取样分析钢水中的N含量，通过补喂氮锰线的方式控制钢水中的Al/N比≥3，以发挥AlN细化晶粒的作用。
精炼结束后，钢水不需要真空脱气，直接到吹氩台软吹氩，目的是降低吊包温度，避免采用真空脱气导致N含量降低。软吹氩15分钟以上，实现夹杂物充分上浮，保证钢材纯净度。
步骤二的铸造钢坯涉及将钢水通过连铸法制造为连铸坯，或者通过铸锭法先浇注成钢锭然后将钢锭热加工为钢坯。从提高生产效率和节省成本考虑，连铸法较铸锭法更有优势。连铸工序是整个冶炼过程的关键，鉴于本发明[Al]含量高、[Si]含量低，钢水结瘤风险较高，对连铸工艺参数若控制不当，铸坯表面就会产生开裂或结死水口造成废品。连铸法的具体措施：钢水从大包到中间包再到结晶器，均采用密封保护浇注让钢水与空 气隔绝，控制钢水的二次氧化；连铸过程采用低过热度浇注，浇注过热度10℃～20℃，并配备合适的拉速0.8～1.3m/min，改善内部质量；获得的连铸坯需要下坑缓冷，缓冷温度400℃以上，缓冷时间应大于12小时，防止铸坯开裂。
步骤三的热成型：将钢坯加热至1050～1080℃，并保温3～4小时，连铸坯出炉后经高压水除鳞采用连轧机轧制，热轧成所需规格，开轧温度950～1020℃，终轧温度780～820℃，控制在两相区进行轧制，平均道次压缩比1.1～1.2，轧制10～15道次，轧制后缓冷，获得铁素体和珠光体组织的圆钢。
步骤五的退火是对基于上述化学成分的组织为铁素体+珠光体的钢进行球化退火，退火温度在AC 1以下20℃-50℃即690-720℃，在此基础上再优化退火温度至700-715℃，钢材入炉后炉温升到700～715℃，在保温段保温，可参照保温时间h＝2+0.4D，式中D为圆钢直径，单位mm，h为保温时间，单位hour，保温结束后参照冷却速度S＝0.72-0.01D随炉冷却，式中S的单位为℃/min，D为圆钢直径，单位mm。
一般地，退火工序中所述的保温时间h为10～18小时为宜；所述的冷却速度S为0.32～0.52℃/min为宜。
本申请冷锻用钢采用低C设计，低碳钢在球化退火时因碳化物少，球化时碳原子扩散距离大，球化困难。实际在确定退火保温温度时，技术人员可采用Gleeble3800热模拟试验机先测得相变点AC 1，再根据相变点设计球化退火温度，在对退火温度进行优化时，主要是评估球化率和表面硬度这两个因素，以获得适当的球化退火温度。
本申请退火工艺的确定过程如下：
试验一、完全退火：在高于AC 1以上20℃-30℃(即758℃-768℃)完全退火，保温10—18小时，奥氏体化保温结束后以0.32℃/min～0.52℃/min冷却，表面硬度135HV30；球化率为70％。
试验二、等温退火：在高于AC1以上20℃-30℃(即758℃-768℃)，保温3-5小时，随炉速冷到680℃～710℃，再保温7-13小时，随炉空冷，表面硬度130HV30，球化率为60％。
试验三、低温退火：设置退火温度500-600℃(显著低于AC 1)，保温10小时以上，表面硬度140HV30，无球状组织。
试验四、在AC1以下20℃-50℃(即690℃-720℃)退火(如图4)，表面硬度约105HV30，球化率约85％(微观组织如图5所示)，球化率和表面硬度达到最理想，满足性能设计要求。
上述四种试验显示，低碳钢的球化率、表面硬度受退火工艺的影响较大，且影响关系较复杂，无法用简单的规律概括，本申请的发明人凭借生产经验和理论，在基于试验数据的基础上设计了适于本申请的退火工艺，它不同于完全退火、等温退火、低温退火，具有特殊性和针对性。
本申请的制造方法还包括步骤六、车皮：冷锻用钢对钢材尺寸要求严格，一般也要求表面质量无缺陷，预设计圆钢的尺寸公差：0/-0.05mm，通过车皮保证尺寸精度和表面无缺陷。另外，由于钢材表面硬度低，车皮后钢材每米增加一个塑料套圈，防止圆钢在吊装、转运过程中出现擦伤、磕碰伤。
与现有技术相比，本发明的优点或特点在于：
(1)通过化学成分设计，保证钢材塑性、韧性和切削性能完全能够达到乘用车万向节叉的设计要求：表面硬度≤110HV30；Rp0.2≤280MPa、Rm≤360MPa、A5≥40％、Z≥75％、球化率≥80％。
(2)化学成分中对提高强度的元素进行了限制，通过控制Al和N以及Al/N比≥3来达到细化晶粒，晶粒度控制在5级以上，提高钢材的韧性、塑性。
(3)热成型采用低温轧制，控制变形在两相区完成，比传统轧制温度低80～100℃,低温轧制的晶粒度比常规低温轧制要高1～1.5级，晶粒进一步变细，提高韧性、塑性。并在轧后获得铁素体+珠光体的组织。
(4)退火是基于热成型后的圆钢设置，退火工艺是以提高球化率和降低表面硬度为目的设置的，是对现有退火工艺的一种优化。退火的保温时间、冷却速度都充分考虑了圆钢的规格，以减小因产品规格对退火结果的影响，以期在规格范围内都能获得最优的退火后的塑性、韧性。
(5)本申请钢的韧性、塑性都更好，但车皮时容易发生粘结、切削变形大，刀具磨损大，在不改变韧性、塑性条件下，通过添加一定量S，改善切削加工性能，提高车皮后表面质量和尺寸精度。
(6)钢水精炼时，设计采用沉淀脱氧和扩散脱氧，其目的是降低非金属夹杂含量，让夹杂物水平达到：A类≤2.5级、B类≤1.5级、C类≤0.5级、D类≤1.5级。精炼结束后调控N含量在0.004％～0.006％，通过补喂微量氮锰线，节省氮锰线喂入量和减少外来夹杂物；使用的合金和废钢都要求进行烘烤，确保H含量≤2ppm；通过前述一系列措施，省去真空脱气，尤其N含量的波动，实现涉及元素成分的精确调整，节约生产成本。
附图说明
图1为本申请钢冷锻成的乘用车万向节叉的零件图；
图2为本申请冷锻用钢的典型金相组织图；
图3为采用Gleeble3800热模拟试验机测得本申请冷锻用钢的相变温度曲线；
图4为退火试验四对应的退火工艺曲线；
图5为退火试验四退火后的组织图，球化率约85％。
具体实施方式
以下结合实施例对本发明作进一步详细描述，所述实施例是示例性的，旨在用于解释本发明，而不能理解为对本发明的限制。
乘用车万向节冷锻用钢棒材的制作方法：制造规格为Φ20mm—Φ40mm的生产工艺路线：铁水预处理—转炉初炼—精炼—连铸—连铸坯冷却—连铸坯加热—轧制—冷却—球化退火—车皮—精整—检验—成品入库。具体如下：
实施例1和2的钢材规格Φ20mm，累计轧制比183.4。
铁水预处理：将浇注耐火材料(刚玉)并经过烘烤的十字形搅拌头，浸入铁水包熔池液面以下一定深度，借其旋转产生的漩涡，经过称量的原料由给料器加入到铁水表面，并被旋涡卷入铁水中使原料与铁水充分接触反应。
转炉装炉量100吨，其中铁水装入量75吨，废钢装入量25吨，转炉冶炼过程中，吹氧造渣，高拉碳操作，出钢温度1542℃，终点碳0.03％。出钢时加入锰铁、铝铁、石灰、精炼渣；吊包至LF炉。
LF炉座位送电，炉渣化好后分批加入铝粉、铝粒、碳粉扩散脱氧，喂入Al线沉淀脱氧，同时继续调整化学成分使进入规格要求，尤其是通过喂入氮锰线精确控制Al/N比≥3，保证白渣时间15分钟，出LF炉温度1585℃。
精炼结束后，上吹氩台软吹氩20分钟，吊包温度1578℃。
连铸全程保护浇注，让钢水和空气隔绝，中间包温度1548℃，过热度在10-20℃，设置连铸拉速0.8m/min。获得的连铸坯600℃入坑缓冷13小时。
将连铸坯加热1055℃，保温3小时，开轧温度在980～1020℃，终轧温度780～820℃，在两相区将连铸坯轧成圆钢，轧制后圆钢要进行缓冷。
辊底式连续退火炉退火，钢材入炉后升温到690℃并入保温段10小时，保温结束后以0.52℃/min速度随炉冷却。
车皮：车皮后钢材每隔一米加一个塑料套圈，方便吊装和转运。
实施例3-4涉及钢材的规格Φ40mm，轧制比91.7
转炉装入量100吨，其中铁水装入量90吨，废钢装入量10吨，转炉冶炼过程中，吹氧造渣，出钢温度1550℃，终点碳0.02％。出钢加入锰铁、铝铁、石灰、精炼渣；吊包至LF炉精炼。
LF炉座位送电，精炼过程采用氩气搅拌，调整化学氩气搅拌强度以不裸露钢水为宜，炉渣化好后分批加入铝粉、铝粒、碳粉扩散脱氧，喂入Al线沉淀脱氧，白渣保持时间12分钟，出LF炉温度为1580℃，精炼过程中添加烘烤过的合金块对钢水的元素成分调整，对钢水取样分析N含量，根据N含量补喂氮锰线精确控制Al/N比。
精炼结束后上吹氩台软吹氩15分钟，吊包温度1570℃。
连铸全程采用保护浇注，隔绝空气，中间包温度1543℃，拉速1.2m/min，过热度控制在10-20℃。连铸坯650℃入坑缓冷15小时。
连铸坯加热1080℃，保温4小时，开轧温度1000℃，终轧温度820℃，轧制完成后缓冷。
采用辊底式连续退火炉进行球化退火，钢材入炉后炉温升温到715℃并入保温段保温18小时，保温结束后以0.32℃/min速度随炉冷却。
上述各实施例涉及钢的化学成分如表1
表1化学成分(％)
实施例 C Si Mn P S Cu Ni Cr Mo Al N
1 0.05 0.05 0.58 0.010 0.021 0.02 0.01 0.06 0.01 0.035 0.008
2 0.06 0.08 0.48 0.012 0.025 0.02 0.02 0.06 0.01 0.025 0.0075
3 0.07 0.09 0.47 0.008 0.030 0.02 0.02 0.09 0.02 0.040 0.009
4 0.09 0.1 0.55 0.005 0.032 0.02 0.02 0.10 0.01 0.045 0.0085
上述各实施例非金属夹杂物按ASTM E45检验如下表2
表2非金属夹杂物水平
实施例 A细 A粗 B细 B粗 C细 C粗 D细 D粗
1 1.5 0.5 0.5 0.5 0 0 0 0
2 1.5 0.5 0.5 0 0 0 0.5 0.5
3 2.0 0.5 0.5 0 0 0 0 0.5
4 2.0 0.5 0.5 0.5 0 0 0.5 0.5
上述各实施例退火后直接检测拉伸、硬度、球化率，拉伸按照EN ISO 6892-1标准检测，硬度按照EN ISO 6507-1标准检测。球化率是在显微镜观测下球化组织所占的比例，如表3。
表3拉伸、硬度、组织
检测状态 Rp0.2(MPa) Rm(MPa) A5(％) Z(％) 表面硬度HV30 球化率
热轧态 287 427 39 70 157 /
热轧态 285 427 38 70 159 /
退火态 218 332 50 83 100 95％
退火态 228 336 49 83 102 90％
退火态 229 336 49 82 102 90％
退火态 232 334 48 82 102 95％
实施例产品金相组织为铁素体和珠光体球，退火后晶粒度6～8级，球化率≥85％，普遍≥90％，塑性和韧性好，硬度低可用冷锻复杂零件。
除上述实施例外，本发明还包括有其他实施方式，凡采用等同变换或者等效替换方式形成的技术方案，均应落入本发明权利要求的保护范围之内。

Claims (7)

  1. 一种乘用车万向节叉冷锻用钢的制造方法，其特征在于：所述钢的化学成分按质量％计含有C：0.04～0.10％，Si：0.01％～0.12％，Mn：0.40～0.60％，P：≤0.015％，S：0.020～0.035％，Cr：≤0.10％，Ni：≤0.10％，Cu：≤0.10％，Mo：≤0.02％，Al：0.020％～0.050％，N：0.007％～0.009％，余量为Fe及不可避免的杂质元素；所述钢的组织为铁素体和珠光体，其中珠光体的球化率≥85％；
    所述制造方法包括：
    步骤一、钢水冶炼：涉及精炼，精炼过程采用氩气搅拌，调整化学氩气搅拌强度以不裸露钢水为宜，使用铝粉、铝粒、碳粉扩散脱氧，并且使用Al线进行沉淀脱氧，通过沉淀脱氧和扩散脱氧，使用烘烤后的合金，调整合金使全部进入规定的含量要求；取样分析钢水中的N含量，通过补喂氮锰线控制钢水中的Al/N比≥3，细化晶粒；
    步骤二、铸造钢坯；
    步骤三：热成型：将钢坯加热至1050～1080℃，并保温3～4小时，连铸坯出炉后经高压水除鳞采用连轧机轧制，热轧制成所需规格，开轧温度950～1020℃，终轧温度780～820℃，控制在两相区进行，平均道次压缩比1.1～1.2，轧制10～15道次，轧制后缓冷，获得铁素体和珠光体组织的圆钢；
    步骤四：堆冷；
    步骤五：退火：对组织为铁素体+珠光体的钢进行球化退火，退火温度在AC1以下20℃-50℃即690-720℃，在此基础上再优化退火温度至700-715℃，钢材入炉后炉温升到700～715℃并入保温段保温，保温时间h＝2+0.4D，式中D为圆钢直径，单位mm，h为保温时间，单位hour，保温结束后以冷却速度S＝0.72-0.01D随炉冷却，式中S的单位为℃/min，D为圆钢直径，单位mm。
  2. 根据权利要求1所述的制造方法，其特征在于：步骤一钢水冶炼涉及：铁水预处理、转炉初炼、精炼，其中
    所述铁水预处理：去除铁水中S、P、Si、Ti杂质元素，将浇注耐火材料并经过烘烤的十字形搅拌头，浸入铁水包熔池，借其旋转产生漩涡，经过称量的合金原料由给料器加入到铁水表面，并被旋涡卷入铁水中使原料与铁水充分接触反应；
    所述转炉初炼：将入炉原料装入初炼炉，入炉原料中经预处理的铁水占75％以上， 其余为废钢；转炉初炼采用高拉碳操作，提高转炉初炼终点高拉碳率，控制熔炼终点碳含量在0.04％以下，出钢温度为1540～1580℃上，出钢过程对钢水进行档渣防止下氧化渣，出钢过程采用Al块和或Al粒对钢水强脱氧和部分Mn、Al合金化，防止钢水过氧化；
    精炼结束后，钢水不需要真空脱气，直接到吹氩台软吹氩，软吹氩15分钟以上，实现夹杂物充分上浮。
  3. 根据权利要求2所述的制造方法，其特征在于：所述转炉初炼工序中，废钢入炉前进行烘烤，并且选取Cr、Mo、Ni、Cu含量低的废钢。
  4. 根据权利要求1所述的制造方法，其特征在于：步骤二铸造钢坯涉及将钢水通过连铸法制造为连铸坯，或者通过铸锭法先浇注成钢锭然后将钢锭热加工为钢坯；其中，连铸法的具体措施：钢水从大包到中间包再到结晶器，均采用密封保护浇注让钢水与空气隔绝，控制钢水二次氧化；连铸过程采用低过热度浇注，浇注过热度10℃～20℃，并配备合适的拉速0.8～1.3m/min，改善内部质量；获得的连铸坯下坑缓冷，缓冷温度400℃以上，缓冷时间大于12小时。
  5. 根据权利要求1所述的制造方法，其特征在于：所述的保温时间h为10～18小时；所述的冷却速度S为0.32℃/min～0.52℃/min。
  6. 根据权利要求1所述的制造方法，其特征在于：所述钢的交货态为退火态。
  7. 根据权利要求1所述的制造方法，其特征在于：所述钢的表面硬度≤110HV30；Rp0.2≤280MPa、Rm≤360MPa、延伸率A5≥40％、断面收缩率Z≥75％、珠光体球化率≥80％。
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CN116103573A (zh) * 2023-04-17 2023-05-12 宁波钢铁有限公司 适用于直热装生产的汽车结构用热轧钢带及其制备方法

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