WO2019080458A1 - 微合金化弹簧钢及其制备方法 - Google Patents

微合金化弹簧钢及其制备方法

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Publication number
WO2019080458A1
WO2019080458A1 PCT/CN2018/082190 CN2018082190W WO2019080458A1 WO 2019080458 A1 WO2019080458 A1 WO 2019080458A1 CN 2018082190 W CN2018082190 W CN 2018082190W WO 2019080458 A1 WO2019080458 A1 WO 2019080458A1
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Prior art keywords
spring steel
microalloyed
preparing
temperature
steel
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PCT/CN2018/082190
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English (en)
French (fr)
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冯以盛
王正红
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山东汽车弹簧厂淄博有限公司
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Publication of WO2019080458A1 publication Critical patent/WO2019080458A1/zh

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Classifications

    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
    • 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
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the invention relates to a spring steel, in particular to a microalloyed spring steel and a preparation method thereof.
  • Spring is a key basic component of the equipment manufacturing industry. It has a wide range of products and various varieties. It is used to control the movement of parts, mitigate shock or vibration, store energy, and measure the force. It is widely used in automobiles, railways, and construction machinery. , electronic appliances and other areas of the national economy. At present, China's high-performance spring manufacturing has insufficient support capability, and high-grade springs and high-loaded railways still need to be imported. With the light weight of automobiles, the large-scale technical equipment and the parameterization limit, the demand for advanced springs has increased rapidly. At the same time, the increasing demand for high-performance springs has placed increasing demands on the variety and performance of spring steel. At present, China's spring steel products still have a series of problems such as unstable process quality and quality control, high-end varieties and special varieties that need to rely on imports, and there is still a big gap with the international advanced level.
  • the object of the present invention is to provide a microalloyed spring steel which has the advantages of high mechanical strength, large elongation, high reduction in area, and good fatigue resistance; the present invention also provides a preparation method thereof. Scientific and reasonable, simple and easy.
  • microalloyed spring steel of the present invention comprises the following chemical composition of mass ratio:
  • Carbon improves the elastic strength, hardness and wear resistance of spring steel by solid solution strengthening, but reduces the plasticity, toughness and fatigue strength of spring steel, and controls C within 0.48-0.55wt.%, which is the same as other alloying elements. At the time, a combination of optimum strength, fatigue life and economic efficiency can be obtained.
  • the C content used in the invention is much smaller than that of the conventional spring steel, which can change the martensite structure and improve the toughness of the spring steel.
  • Silicon strengthens the ferrite by solid solution, improves the elasticity of the steel, but weakens the plasticity and toughness of the steel, and greatly increases the tendency of decarburization and graphitization, generates inclusions, and deteriorates the fatigue performance of the spring. Therefore, in the present invention, it is found that When the silicon content is controlled within 0.15-0.35wt.%, the effect on fatigue strength is the lowest.
  • the Si content used in the invention is much smaller than that of the conventional spring steel, which can reduce the repellency to carbon and reduce decarburization.
  • Mn can increase the strength of steel by solid solution and at the same time increase the hardenability of steel, but excessive Mn promotes temper brittleness. Therefore, it is necessary to control the content of Mn between 0.95-1.20 wt.%.
  • Chromium improves the strength of steel by solid solution, can improve the hardenability of steel, improve the tempering stability, and improve the performance and dispersion of spring steel.
  • excessive chromium tends to form chromium carbide, which reduces the plasticity and toughness of steel. Therefore, the content of Cr is controlled to be 1.0-1.25 wt.%.
  • Mo improves the strength of steel by solid solution, strongly improves the hardenability of steel, stabilizes carbon, and is beneficial to increase the strength of spring steel.
  • excessive Mo changes the quenching curve of steel and tends to form feathery bainite. It is not conducive to the fatigue strength of spring steel, so it is necessary to control the content of Mo to be 0.15-0.25 wt.%.
  • V and Nb V: 0.15-0.25%; Nb: 0.03-0.05%;
  • V and Nb form densely dispersed VC, NbC, VN or NbN in the steel, which strongly strengthens the matrix, and at the same time refines the grain boundaries and prevents the growth of crystal grains. Therefore, fine and high-strength structures can be obtained, which is greatly improved.
  • S and P are inevitable in steel.
  • S, P and alloying elements form inclusions, such as MnS, which not only offset the beneficial effects of alloying elements, but also cause segregation of S and P, weakening the toughness of steel. It becomes a source of fatigue cracks, which seriously reduces the fatigue strength of the spring. Therefore, the content of S and P should be strictly controlled within 0.02 wt.% in the steel.
  • the spring Since the spring is subjected to subsequent thermal processing, Cu will seriously reduce the thermoplasticity of the material, and it is easy to produce micro-cracks during forging, which seriously affects the strength of the spring. Therefore, it should be strictly controlled. Since the steel wire is contained in the scrap, the steel material should be strictly controlled. The amount of Cu used in the scrap is ⁇ 0.2 wt.%.
  • Nickel can increase the strength and toughness of steel, reduce the brittle transition temperature, especially improve the hardenability, but the price of nickel is extremely expensive, so try to use other alloys to meet the performance requirements.
  • the spring steel of the present invention has a thickness of 25-38 mm.
  • the microstructure of the spring steel is ferrite and pearlite, and only ferrite and pearlite structures, and no other tissues.
  • the preparation method of the microalloyed spring steel the spring steel raw material is sequentially smelted, refined, vacuum degassed, continuously cast and cooled into steel ingot, steel ingot peeling, heating continuous rolling, controlled cooling, quenching and tempering, Said spring steel product.
  • the spring steel raw material can use part of the scrap steel, but the scrap steel contains copper wire, etc. Therefore, the amount of scrap steel needs to be controlled within 20% of the total mass of the spring steel raw material.
  • the smelting temperature is 1630-1700 ° C, the time is 25-60 minutes; the refining temperature is 1500-1550 ° C, the time is 20-60 minutes, and the refining process uses electromagnetic stirring. Electromagnetic stirring can uniform the microstructure.
  • the vacuum degassing, the degree of vacuum is ⁇ 130Pa.
  • the continuous casting is cooled into a steel ingot, first cooled to below 1150 ° C at 25-35 ° C / min, and then naturally cooled to room temperature. Therefore, the inclusions are limited to the center line of the ingot as much as possible, and the damage to the performance of the product is minimized after the steel is rolled.
  • the steel ingot is peeled to a depth of at least 3.0 mm.
  • the reheating continuous rolling and rolling temperature is 900-1100 ° C, and the finishing rolling temperature is 850-900 ° C.
  • Rolling in the austenite zone gives the best deformation properties of the material and provides favorable conditions for subsequent cooling.
  • the controlled cooling is specifically: firstly, it is rapidly cooled to 600 ° C, and then the temperature is slowly cooled to room temperature; the rapid cooling rate is ⁇ 30 ° C / min, and the slow cooling speed is ⁇ 10 ° C / min. This prevents surface decarburization and maintains a lower hardness for subsequent shear processing.
  • the quenching method is oil quenching, the quenching temperature is 850-900 ° C, the holding time is 1.0-1.5 min / mm, and the tempering temperature is 400-500 ° C.
  • the preparation process of the microalloyed spring steel according to the present invention further, the raw material is placed in the converter, and the quality content of the scrap in the raw material is controlled within 20%.
  • electromagnetic stirring and vacuum degassing can be used.
  • the fiber structure is uniform, with less bubbles, less pores, dense structure, continuous casting after vacuum degassing, can form stable macroscopic structure, heating continuous rolling, can ensure uniform size structure; control cooling temperature, can reduce The decarburization layer ensures the shear hardness. After cooling to room temperature, it is quenched and tempered to obtain a finished product.
  • the present invention has the following beneficial effects:
  • microalloyed spring steel prepared by the present invention are as follows:
  • the hardness of raw materials is ⁇ HB330. After heat treatment, the tensile strength can reach 1650MPa, the yield strength can reach 1500MPa, the elongation is ⁇ 8%, the reduction of area is ⁇ 25%, and the fatigue week is more than 300,000 cycles.
  • the semi-decarburized layer of the spring steel is less than 0.20 mm, and there is no full decarburization layer.
  • the grain size is greater than ASTM 8.5.
  • the preparation method of the invention is scientific and reasonable, simple and easy, and electromagnetic stirring and vacuum degassing can reduce bubbles and pores, and the microstructure is more uniform and compact.
  • microalloyed spring steel is prepared as follows:
  • the molten iron is added to a 120-ton converter, smelted at 1680 ° C, and after 45 minutes, the steel is tapped, 18% scrap steel is added to adjust the temperature to 1650 ° C, and transferred to a refining furnace. Under electromagnetic stirring, ferrosilicon, ferromanganese, chromium are added.
  • Molybdenum iron, ferrovanadium and strontium iron after adjusting the chemical composition for 40 minutes at 1535 ⁇ 15°C, vacuum degassing (vacuum degree ⁇ 130Pa) and then continuous casting into 180 ⁇ 180 slab, at 28°C
  • vacuum degassing vacuum degree ⁇ 130Pa
  • the speed of /min is cooled to 1150 °C, air cooling to room temperature, stripping the casting blank, peeling off 3.2mm depth, heating to 1200 °C, and then rolling into 30*89mm spring strip, rolling temperature 1050 °C, the end
  • the rolling temperature was 890 ° C, and after cooling, it was rapidly cooled to 600 ° C at a rate of 37 ° C / min, and then the temperature was slowly cooled to room temperature at a rate of 8 ° C / min.
  • 30*89mm strip steel was obtained. After testing, its chemical composition is shown in Table 1. It is further processed into two leaf springs. After quenching at 880 °C and tempering at 460 °C, it is stretched according to GB/T228-2002. The sample processing and tensile test were carried out, and the yield strength, elongation and reduction of area were tested. The assembled leaf springs were subjected to fatigue test in accordance with GB/T228-2002. The results are shown in Table 2.
  • microalloyed spring steel is prepared as follows:
  • the molten iron is added to a 120-ton converter, smelted at 1630 ° C, and after 60 minutes, the steel is tapped, 18% scrap steel is added to adjust the temperature to 1650 ° C, and transferred to a refining furnace. Under electromagnetic stirring, ferrosilicon, ferromanganese, chromium are added.
  • Molybdenum iron, ferrovanadium, ferroniobium and manganese nitride after adjusting the chemical composition at 1515 ⁇ 15 °C for 60 minutes, vacuum degassing (vacuum degree ⁇ 130Pa) and then continuously casting into 180 ⁇ 180 slab
  • vacuum degassing vacuum degree ⁇ 130Pa
  • microalloyed spring steel is prepared as follows:
  • Standard steel 9260 the chemical composition of which is tested is shown in Table 1. Further processing into two leaf springs, after quenching at 900 °C and tempering at 500 °C, the tensile specimen processing and tensile test are carried out according to GB/T228-2002, and the assembled leaf springs are subjected to fatigue test according to GB/T228-2002. Further, the yield strength, elongation, and reduction in area were measured, and the results are shown in Table 2.
  • Standard steel 5160 the chemical composition of which is tested is shown in Table 1. Further processing into two leaf springs, after quenching at 900 °C and tempering at 500 °C, the tensile specimen processing and tensile test are carried out according to GB/T228-2002, and the assembled leaf springs are subjected to fatigue test according to GB/T228-2002. Further, the yield strength, elongation, and reduction in area were measured, and the results are shown in Table 2.
  • Standard steel 6150 the chemical composition of which is tested is shown in Table 1. Further processing into two leaf springs, after quenching at 900 °C and tempering at 500 °C, the tensile specimen processing and tensile test are carried out according to GB/T228-2002, and the assembled leaf springs are subjected to fatigue test according to GB/T228-2002. Further, the yield strength, elongation, and reduction in area were measured, and the results are shown in Table 2.
  • the strength of the spring steel of the present invention including the yield strength (Rp 0.2 ) and the tensile strength (Rm), are significantly improved under the conditions of similarity in plasticity, toughness, reduction in area Z, and elongation A.
  • the fatigue strength is increased by more than 400%, and is particularly suitable for the manufacture of a reduced weight leaf spring.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Springs (AREA)
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  • Heat Treatment Of Steel (AREA)

Abstract

一种微合金化弹簧钢及其制备方法。该弹簧钢化学成分为：C：0.48-0.55％；Si：0.15-0.35％；Mn：0.95-1.20％；Cr：1.00-1.25％；Mo：0.15-0.25％；V：0.15-0.25％；Nb：0.03-0.05％；Pb、Sn、Zn、Sb和Bi≤0.03％；O 2和H 2≤25ppm；S和P≤0.02％；Cu≤0.2％；Ni≤0.35％；余量为Fe。制备方法为：熔炼、精炼、真空脱气、连续浇注冷却成钢锭、钢锭剥皮，再加热连续轧制、控制冷却、淬火和回火，得弹簧钢产品。

Description

微合金化弹簧钢及其制备方法 技术领域
本发明涉及一种弹簧钢，具体涉及一种微合金化弹簧钢及其制备方法。
背景技术
弹簧是装备制造业的关键基础件，量大面广、品种繁杂，用以控制机件的运动、缓和冲击或震动、贮蓄能量、测量力的大小等，广泛应用于汽车、铁路、工程机械、电子电器等国民经济的各个领域。目前，我国高性能弹簧制造的保障能力不足，高档汽车、重载铁路等行业用高级弹簧仍需进口。随着汽车轻量化、重大技术装备大型化及参数极限化，高级弹簧的需求量快速增长。同时，高性能弹簧制造需求的日益增加，也对弹簧钢的品种和性能提出了越来越高的要求。目前，我国弹簧钢产品仍存在工艺水平及质量控制不稳定、高端品种和特殊品种需要依赖进口等一系列问题，与国际先进水平仍有较大差距。
未来，适应汽车轻量化需求，发展高强度、延伸率高、断面收缩率高和抗疲劳性能的弹簧钢，将是提高我国高端装备零部件自主配套能力、有效替代进口的必然趋势。
发明内容
针对现有技术的不足，本发明的目的是提供一种微合金化弹簧钢，具有机械强度高、延伸率大、断面收缩率高、抗疲劳性能好的优点；本发明同时提供其制备方法，科学合理，简单易行。
本发明所述的微合金化弹簧钢，包括如下质量比的化学成分：
C：0.48-0.55％；Si：0.15-0.35％；Mn：0.95-1.20％；Cr：1.00-1.25％；Mo：0.15-0.25％；V：0.15-0.25％；Nb：0.03-0.05％；Pb、Sn、Zn、Sb和Bi≤0.03％；O 2和H 2≤25ppm；S和P≤0.02％；Cu≤0.2％；Ni≤0.35％；余量为Fe。
各化学成分的用量标准和作用如下：
C：0.48-0.55％；
碳是通过固溶强化，提高弹簧钢的弹性强度、硬度和耐磨性，但降低弹簧钢的塑性、韧性和疲劳强度，将C控制在0.48-0.55wt.％之内，与其它合金元素同在时，可获得最佳强度，疲劳寿命与经济效益的组合。本发明采用的C含量远小于常规的弹簧钢，能够改变马氏体组织形态，提高弹簧钢的韧性。
Si：0.15-0.35wt.％；
硅通过固溶强化铁素体，提高钢的弹性，但弱化钢的塑性和韧性，并剧烈增加脱碳和石墨化的倾向，产生夹杂物，恶化弹簧的疲劳性能，故在本发明中，发现硅含量控制在 0.15-0.35wt.％内时，对疲劳强度的影响最低。本发明采用的Si含量远小于常规的弹簧钢，能降低对碳的排斥性，减少脱碳。
Mn：0.95-1.20wt.％；
Mn可以通过固溶提高钢的强度，同时，提高钢的淬透性，但过量的Mn会促进回火脆性，因此，需要将Mn的含量控制在0.95-1.20wt.％之间。
Cr：1.00-1.25wt.％；
铬通过固溶提高钢的强度，还能提高钢的淬透性，提高回火稳定性，有利于提高弹簧钢的性能与弥散沉淀，但过量的铬易形成碳化铬，降低钢的塑性，韧性，故将Cr的含量控制在1.0-1.25wt.％。
Mo：0.15-0.25wt.％；
Mo通过固溶提高钢的强度，强烈提高钢的淬透性，稳定碳元素，有益于提高弹簧钢的强度，但过量的Mo会改变钢的淬火曲线，倾向于羽毛状贝氏体的形成，不利于弹簧钢的疲劳强度，所以需要控制Mo的含量为0.15-0.25wt.％。
V与Nb，V：0.15-0.25％；Nb：0.03-0.05％；
V与Nb在钢中形成弥散细小的VC、NbC、VN或NbN，对基体剧烈强化，同时，细化晶界，阻止晶粒的长大，所以，可以得到细密高强度的组织，极大提高弹簧钢的强度与疲劳性能，但单一元素过量时，粒子易粗化，失去优异作用，故本发明采用两种元素的综合功能，经优化后，其最佳含量为V：0.15-0.25wt.％；Nb：0.03-0.05wt.％。
S和P≤0.02％；
钢中不可避免存在S、P等夹杂物，S、P与合金元素形成夹杂物，如MnS等，不仅抵消与合金元素的有益作用，而且S、P会产生偏聚，弱化钢的韧性，并成为疲劳裂纹源，严重降低了弹簧的疲劳强度，所以在该钢料中应严格控制S、P含量在0.02wt.％以内。
Cu≤0.2wt.％；
由于弹簧要经历后续热加工，Cu会严重降低材料的热塑性，在锻造中易产生微裂纹，严重影响弹簧的强度，所以应严格控制，由于废料中含有钢线，故该钢料中应严格控制废料的Cu使用量≤0.2wt.％。
Ni≤0.35％；
镍可提高钢的强度与韧性，降低脆性转变温度，尤其是提高淬透性，但镍的价格极贵，所以尽量采用其他合金来满足性能要求。
本发明所述的弹簧钢的厚度为25-38mm。
通过金相检测发现，所述的弹簧钢的微观组织为铁素体和珠光体组织，并且只有铁素体 和珠光体组织，不含其他组织。
所述的微合金化弹簧钢的制备方法，将弹簧钢原料依次进行熔炼、精炼、真空脱气、连续浇注冷却成钢锭、钢锭剥皮，再加热连续轧制、控制冷却、淬火和回火，得所述的弹簧钢产品。
其中，所述的弹簧钢原料能够采用部分废钢，但是废钢中含有铜线等，因此，废钢的用量需要控制在弹簧钢原料总质量的20％以内。
所述的熔炼温度为1630-1700℃，时间为25-60分钟；所述的精炼温度为1500-1550℃，时间为20-60分钟，精炼过程采用电磁搅拌。采用电磁搅拌能够均匀显微组织结构。
所述的真空脱气，真空度≤130Pa。
所述的连续浇注冷却成钢锭，先以25-35℃/min降温至1150℃以下，然后自然冷却至室温。从而使夹杂物尽量限制在钢锭的中心线上，轧钢成材后，对产品的性能的危害降至最低。
所述的钢锭剥皮的深度为至少3.0mm。
所述的再加热连续轧制开轧温度为900-1100℃，终轧温度为850-900℃。以在奥氏体区进行轧制，发挥材料的最佳形变性能，并为后续的冷却提供有利条件。
所述的控制冷却具体为：首先快冷到600℃，然后保温慢冷至室温；快冷速度≥30℃/min，保温慢冷速度≤10℃/min。这样可以防止表面脱碳，并维持较低硬度，以利于后续的剪切加工。
所述的淬火方式为油淬，淬火温度为850-900℃，保温时间为1.0-1.5分钟/mm，回火温度为400-500℃。
本发明所述的微合金化弹簧钢的制备工艺，更进一步的，在转炉中投放原料，原料中废钢质量含量控制在20％以内，为了控制杂质含量，采用电磁搅拌和真空脱气，能使纤维组织结构均匀，且少气泡，少气孔，组织致密，真空脱气结束后，进行连铸，能够形成稳定的宏观组织，加热连续轧制，能保证均匀的尺寸组织；控制冷却温度，能减少脱碳层，保证剪切硬度，冷却至室温后，进行淬火，回火，得到成品。
与现有技术相比，本发明具有以下有益效果：
(1)本发明制备的微合金化弹簧钢的性能如下：
原材料的硬度≤HB330，经热处理后抗拉强度能够达到1650MPa，屈服强度能够达到1500MPa，延伸率≥8％，断面收缩率≥25％，疲劳周次大于300,000周次。
(2)弹簧钢的半脱碳层小于0.20mm，无全脱碳层。
(3)经热处理后，晶粒度大于ASTM 8.5级。
(4)本发明所述的制备方法，科学合理，简单易行，采用电磁搅拌和真空脱气能够减少气泡、气孔，使得显微组织结构更加均匀致密。
具体实施方式
下面结合实施例对本发明做进一步说明。
实施例中用到的所有原料除特殊说明外，均为市购。
实施例1
所述的微合金化弹簧钢，制备方法如下：
将铁水加入到120吨转炉中，1680℃下进行熔炼，45分钟后出钢，加入18％废钢进行调温至1650℃，转入精炼炉，在电磁搅拌下，加入硅铁、锰铁、铬钼铁、钒铁和铌铁，在1535±15℃下，对化学成分进行调整40分钟后，进行真空脱气(真空度≤130Pa条件下)然后连铸成180×180铸坯，以28℃/min的速度冷至1150℃后，空冷至室温，进行铸坯剥皮，剥去3.2mm深度后，再加热到1200℃，然后连轧成30*89mm弹簧带钢，开轧温度1050℃，终轧温度890℃，轧后以37℃/min的速度快冷至600℃，然后温度以8℃/min的速度慢冷到室温。
按上述方法制得30*89mm带钢，经检验其化学成分如表1所示，进一步加工成二片板簧，经880℃淬火及460℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，并对屈服强度、延伸率和断面收缩率进行测试，组装成的板簧按照GB/T228-2002进行疲劳试验，其结果如表2所示。
实施例2
所述的微合金化弹簧钢，制备方法如下：
将铁水加入到120吨转炉中，1630℃下进行熔炼，60分钟后出钢，加入18％废钢进行调温至1650℃，转入精炼炉，在电磁搅拌下，加入硅铁、锰铁、铬钼铁、钒铁、铌铁和氮化锰，在1515±15℃下，对化学成分进行调整60分钟后，进行真空脱气(真空度≤130Pa条件下)然后连铸成180×180铸坯，以30℃/min的速度冷至1150℃后，空冷至室温，进行铸坯剥皮，剥去3.5mm深度后，再加热到1200℃，然后连轧成30*89mm弹簧带钢，开轧温度950℃，终轧温度850℃，轧后以35℃/min的速度快冷至600℃，然后温度以10℃/min的速度慢冷到室温。
按上述方法制得30*89mm带钢，经检验其化学成分如表1所示，进一步加工成二片板簧，经850℃淬火及480℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，并对屈服强度、延伸率和断面收缩率进行测试，组装成的板簧按照GB/T228-2002进行疲劳试验，其结果如表2所示。
实施例3
所述的微合金化弹簧钢，制备方法如下：
将铁水加入到120吨转炉中，1700℃下进行熔炼，25分钟后出钢，加入18％废钢进行调 温至1650℃，转入精炼炉，在电磁搅拌下，加入硅铁、锰铁、铬钼铁、钒铁、铌铁和氮化锰，在1535±15℃下，对化学成分进行调整20分钟后，进行真空脱气(真空度≤130Pa条件下)然后连铸成180×180铸坯，以35℃/min的速度冷至1150℃后，空冷至室温，进行铸坯剥皮，剥去3.0mm深度后，再加热到1200℃，然后连轧成30*89mm弹簧带钢，开轧温度900℃，终轧温度900℃，轧后以40℃/min的速度快冷至600℃，然后温度以9℃/min的速度慢冷到室温。
按上述方法制得30*89mm带钢，经检验其化学成分如表1所示，进一步加工成二片板簧，经900℃淬火及500℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，并对屈服强度、延伸率和断面收缩率进行测试，组装成的板簧按照GB/T228-2002进行疲劳试验，其结果如表2所示。
对比例1
标准钢9260，经检验其化学成分如表1所示。进一步加工成二片板簧，经900℃淬火及500℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，组装成的板簧按照GB/T228-2002进行疲劳试验，另外，检测其屈服强度、延伸率和断面收缩率，其结果如表2所示。
对比例2
标准钢5160，经检验其化学成分如表1所示。进一步加工成二片板簧，经900℃淬火及500℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，组装成的板簧按照GB/T228-2002进行疲劳试验，另外，检测其屈服强度、延伸率和断面收缩率，其结果如表2所示。
对比例3
标准钢6150，经检验其化学成分如表1所示。进一步加工成二片板簧，经900℃淬火及500℃回火后，按照GB/T228-2002进行拉伸试样加工与拉伸试验，组装成的板簧按照GB/T228-2002进行疲劳试验，另外，检测其屈服强度、延伸率和断面收缩率，其结果如表2所示。
表1 实施例1-3和对比例1-3的化学成分比较
Figure PCTCN2018082190-appb-000001
Figure PCTCN2018082190-appb-000002
表2 检测结果
Figure PCTCN2018082190-appb-000003
从结果来看，在塑性、韧性、断面收缩率Z、延伸率A类似的条件下，本发明的弹簧钢的强度，包括屈服强度(Rp 0.2)与拉伸强度(Rm)均有显著提高，尤其是疲劳强度提高400％以上，特别适用于减重少片簧的制造上。

Claims (10)

  1. 一种微合金化弹簧钢，其特征在于：包括如下质量比的化学成分：
    C：0.48-0.55％；Si：0.15-0.35％；Mn：0.95-1.20％；Cr：1.00-1.25％；Mo：0.15-0.25％；V：0.15-0.25％；Nb：0.03-0.05％；Pb、Sn、Zn、Sb和Bi≤0.03％；O 2和H 2≤25ppm；S和P≤0.02％；Cu≤0.2％；Ni≤0.35％；余量为Fe。
  2. 根据权利要求1所述的微合金化弹簧钢，其特征在于：所述的弹簧钢的微观组织为铁素体和珠光体组织。
  3. 一种权利要求1或2所述的微合金化弹簧钢的制备方法，其特征在于：将弹簧钢原料依次进行熔炼、精炼、真空脱气、连续浇注冷却成钢锭、钢锭剥皮，再加热连续轧制、控制冷却、淬火和回火，得所述的弹簧钢产品。
  4. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的熔炼温度为1630-1700℃，时间为25-60分钟；所述的精炼温度为1500-1550℃，时间为20-60分钟，精炼过程采用电磁搅拌。
  5. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的真空脱气，真空度≤130Pa。
  6. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的连续浇注冷却成钢锭，先以25-35℃/min降温至1150℃以下，然后自然冷却至室温。
  7. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的钢锭剥皮的深度为至少3.0mm。
  8. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的再加热连续轧制开轧温度为900-1100℃，终轧温度为850-900℃。
  9. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的控制冷却具体为：首先快冷到600℃，然后保温慢冷至室温；快冷速度≥30℃/min，保温慢冷速度≤10℃/min。
  10. 根据权利要求3所述的微合金化弹簧钢的制备方法，其特征在于：所述的淬火方式为油淬，淬火温度为850-900℃，保温时间为1.0-1.5分钟/mm，回火温度为400-500℃。
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