WO2023077838A1 - 一种中等强度钢轨及其生产方法 - Google Patents

一种中等强度钢轨及其生产方法 Download PDF

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WO2023077838A1
WO2023077838A1 PCT/CN2022/102696 CN2022102696W WO2023077838A1 WO 2023077838 A1 WO2023077838 A1 WO 2023077838A1 CN 2022102696 W CN2022102696 W CN 2022102696W WO 2023077838 A1 WO2023077838 A1 WO 2023077838A1
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medium
strength steel
steel rail
rail
strength
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PCT/CN2022/102696
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English (en)
French (fr)
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袁俊
邓勇
陈崇木
汪渊
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攀钢集团攀枝花钢铁研究院有限公司
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Priority to US17/996,603 priority Critical patent/US20240068063A1/en
Priority to AU2022215194A priority patent/AU2022215194A1/en
Publication of WO2023077838A1 publication Critical patent/WO2023077838A1/zh

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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
    • B21B1/085—Rail sections
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • 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
    • C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/22—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
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
    • E01B5/00—Rails; Guard rails; Distance-keeping means for them
    • E01B5/02—Rails
    • 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
    • C21D2221/00—Treating localised areas of an article

Definitions

  • the invention relates to the field of heat treatment of metal materials, in particular to a medium-strength steel rail and a production method thereof.
  • the object of the present invention is to provide a medium-strength steel rail and its production method, which can improve the toughness of the steel rail while ensuring the strength of the steel rail, and the production unit weight is ⁇ 60kg/m, and the strength level is H350-H370 grade rails.
  • a medium-strength steel rail the weight percentage of the chemical composition of the medium-strength steel rail is: carbon 0.70-0.90%, silicon 0.08-0.65%, manganese 0.69-1.31%, chromium 0.10-0.25%, phosphorus ⁇ 0.020%, sulfur ⁇ 0.020% , and iron 96.85-98.41%.
  • the sum of the percentages by weight of silicon, manganese and chromium is less than or equal to 1.9%.
  • the hardness of the medium-strength steel rail is 350-370HB.
  • the wear amount of the medium-strength steel rail is ⁇ 0.40g.
  • a method for producing medium-strength steel rails comprising the steps of:
  • Step 1 smelting and casting the steel billet of the above-mentioned medium-strength steel rail;
  • Step 2 the steel billet is heated, and the medium-strength steel rail is rolled;
  • Step 3 heat-treating the medium-strength steel rail by using the waste heat from rolling;
  • Step 4 applying accelerated cooling to the entire section of the heat-treated medium-strength steel rail.
  • step 2 the steel billet is heated at a temperature of 1200-1250° C., and the holding time of the soaking section is 150-240 minutes.
  • step 3 the rolling waste heat temperature is 620-780°C.
  • step 3 a cooling intensity of 1-4° C./s is applied to the tread width of the head tread of the medium-strength steel rail of 50-60 mm.
  • step 3 a cooling intensity of 2-6° C./s is applied to the width of both sides of the head of the medium-strength steel rail of 20-30 mm.
  • step 4 1-3°C/s accelerated cooling is applied to the entire cross-section of the medium-strength steel rail.
  • the elements commonly used in rails are carbon, silicon, manganese, phosphorus, sulfur, and chromium. Among them, carbon is the most influential element and also the most economical element. Chromium can increase the depth of the hardened layer of the rail and ensure the good performance of the rail.
  • Carbon is the most important alloying element in steel, and its content and distribution form have an important impact on the microstructure and mechanical properties of steel. Carbon is a stable element of austenite. With the increase of carbon content, the stability of supercooled austenite increases, the position of C curve moves to the right, the critical start temperature of martensitic transformation decreases, and the growth of bainite period becomes longer. Carbon is also a strong interstitial solid solution strengthening element, which can strongly increase the strength of steel.
  • Phosphorus (P) In general, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance.
  • Sulfur is also a harmful element in general. It causes hot brittleness of steel, reduces the ductility and toughness of steel, and causes cracks during forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance.
  • Chromium can increase the austenite transformation temperature and delay the high-temperature phase transformation reaction.
  • the specific effects of chromium on phase transformation are as follows: chromium is a ferrite stable element, which can reduce the austenite zone and increase the phase transformation temperature of austenite; chromium can reduce the diffusion rate of carbon atoms in austenite. The diffusion rate of chromium in austenite is 3-5 orders of magnitude lower than that of carbon.
  • chromium It can improve the activation energy of self-diffusing iron atoms and reduce the coordination of iron atom diffusion, so it can delay the high-temperature phase transformation of ultra-fast cold austenite; chromium is a strong carbide-forming element, and chromium atoms have a strong tendency to combine with carbon atoms. It is more difficult to move the coherent phase boundary forward, thus delaying the transformation process of bainite.
  • the composition of the medium-strength steel rail of the present invention is 0.70-0.90% carbon, 0.08-0.65% silicon, 0.69-1.31% manganese, 0.10-0.25% chromium, ⁇ 0.020% Phosphorus, ⁇ 0.020% sulfur, and 98.41-96.85% iron by weight.
  • the medium-strength steel rail and its production method of the present invention propose low-cost component design and high-efficiency long-gauge rail production.
  • the use of rolling waste heat for heat treatment, while improving the performance of the rail, combined with the operating conditions of the line reduces the hardness of the tread, ensures the uniformity of cooling of the rail head tread and rail bottom, and reduces the residual stress of the rail to meet the requirements of low-cost and high-performance rails.
  • the rail hardness of the medium-strength rail of the present invention is 350-370HB, the wear amount is ⁇ 0.40g, the contact fatigue life is ⁇ 50,000 times, and the 610mm long rail waist opening is ⁇ 3.0mm/400mm. It is a low-cost, maintenance-free, long-life railway. Use rails.
  • Medium-strength steel rails are mainly used in passenger-dedicated lines or passenger-cargo mixed railways, which meet the needs of most international railway lines.
  • the medium-strength steel rails produced by the method of the present invention are especially suitable for the annual transportation volume of 20-50 million tons.
  • the low-cost and high-artificial steel rails for remote railway lines have good economic benefits and market prospects.
  • Fig. 1 shows the schematic diagram of the heat treatment position of medium-strength steel rail of the present invention
  • Figure 2 shows a schematic diagram of the balance between wear and contact fatigue crack growth rate
  • Figure 3 shows a schematic diagram of the sampling location of rolling contact fatigue samples
  • Figure 4A shows a cross-sectional view of the rolling contact fatigue specimen dimensions
  • Figure 4B shows a top view of the rolling contact fatigue specimen dimensions.
  • the medium-strength steel rail provided by the invention, wherein the weight percent of the chemical composition of the medium-strength steel rail is: carbon 0.70-0.90%, silicon 0.08-0.65%, manganese 0.69-1.31%, chromium 0.10-0.25%, phosphorus ⁇ 0.020%, sulfur ⁇ 0.020%, and iron 96.85-98.41%.
  • the sum of the percentages by weight of silicon, manganese and chromium is less than or equal to 1.9%.
  • the hardness of the medium-strength steel rail of the present invention is 350-370HB, the wear amount is ⁇ 0.40g, the contact fatigue life is ⁇ 50000 times, and the rail waist opening of the 610mm long rail is ⁇ 3.0mm/400mm. It is especially suitable for low-cost and high-artificial remote railway lines with an annual transportation volume of 20-40 million tons.
  • the medium-strength steel rail production method provided by the invention comprises the following steps:
  • Step 1 smelting and casting the billet of the medium-strength steel rail of the present invention
  • the weight percentage of the chemical composition of the medium-strength steel rail is: carbon 0.70-0.90%, silicon 0.08-0.65%, manganese 0.69-1.31%, chromium 0.10-0.25%, phosphorus ⁇ 0.020%, sulfur ⁇ 0.020%, and iron 96.85-98.41%;
  • Step 2 the steel billet is heated, the steel billet heating temperature is 1200-1250°C, the soaking section holding time is 150-240min, and the medium-strength steel rail is rolled;
  • Step 3 heat-treat medium-strength steel rails with rolling waste heat, wherein the rolling waste heat temperature is 620-780°C, apply 1-4°C/s cooling strength to medium-strength steel rails with a rail head tread width of 50-60mm, and apply 1-4°C/s cooling strength to medium-strength steel rails
  • the width on both sides of the rail head is 20-30mm, and the cooling intensity is 2-6°C/s;
  • Step 4 applying accelerated cooling to the entire section of the medium-strength steel rail after heat treatment, and applying 1-3° C./s accelerated cooling to the entire section of the medium-strength steel rail.
  • Hardness is directly related to wear, which interacts with contact fatigue performance.
  • the wear rate should be controlled at the ideal position of point "B" in Figure 2. To achieve this purpose, the rail strength should be properly designed.
  • Embodiments of the medium-strength rail production method of the present invention are described below.
  • the chemical compositions and weight percentages of the medium-strength steel rails of the examples and the steel rails of the comparative examples are shown in Table 1.
  • the weight percent of chemical composition in the embodiment is: carbon 0.70-0.90%, silicon 0.08-0.65%, manganese 0.69-1.30%, chromium 0.10-0.25%, phosphorus 0.013-0.017%, sulfur 0.008-0.012%, the rest is iron, silicon
  • the sum of the weight percentages of manganese and chromium is 0.87-1.90%, and the steel alloy cost per ton is 42-92 yuan/ton.
  • the weight percent of chemical composition in the comparative example is: carbon 0.76%, silicon 0.5-0.8%, manganese 0.9-1.1%, chromium 0.05-0.30%, phosphorus 0.012-0.018%, sulfur 0.010-0.011%, and the rest are iron, silicon and manganese
  • the sum of weight percentages of chromium and chromium is 1.55-2.15%, and the cost of steel alloy per ton is 74-104 yuan/ton.
  • the medium-strength steel rails of the examples and the steel rails of the comparative example were smelted and cast into billets according to the chemical composition and weight percentage in Table 1. After the steel billet is heated, the steel billet heating temperature is 1200-1250°C, the soaking section holding time is 150-240min, and rolled into a medium-strength steel rail. After rolling, the medium-strength steel rails are heat-treated with different heat treatment processes using the waste heat from rolling. The heat treatment processes are shown in Table 2.
  • Example The final cooling temperature of medium-strength steel rails is 620-780°C, the width of the rail head tread is 50-60mm, the cooling rate of the rail head tread is 1-4°C/s, and the width of both sides of the rail head is 20-30mm.
  • the cooling rate on both sides of the head is 2-6°C/s, as shown in Figure 1;
  • the final cooling temperature of the rail rolling in the comparative example is 600-800°C
  • the width of the rail head tread is 40-70mm
  • the cooling speed of the rail head tread is 0.9 -5°C/s
  • the width on both sides of the rail head is 15-35mm
  • the cooling rate on both sides of the rail head is 1.5-6.5°C/s.
  • the oxygen content and nitrogen content of the medium-strength steel rails of the examples and the steel rails of the comparative examples were tested, as shown in Table 1.
  • the oxygen content in the medium-strength steel rail of the embodiment is 7-12ppm
  • the nitrogen content is 30-51ppm
  • the oxygen content in the steel rail of the comparative example is 6-15ppm
  • the nitrogen content is 34-42ppm.
  • the medium-strength steel rail of the embodiment and the steel rail sample of the comparative example are used in the MM-200 wear testing machine, and the double discs are used for grinding, and the test rotation speed is 200 rpm.
  • the U75V hot-rolled rail sample is used as the opposite grinding sample, which is located on the driving shaft, to simulate the wheel;
  • the medium-strength rail samples of the embodiment and the comparative rail sample are used as the normal grinding sample, which is located on the driven shaft, to simulate the rail.
  • Both the diameter of the opposite grinding sample and the normal grinding sample are 36mm. Under the condition of a relative slip of 10%, wear tests with different loads and different revolutions were carried out, as shown in Table 3, where P in Table 3 represents pearlite and M represents martensite.
  • the medium-strength steel rail wear load of the embodiment is 980N, the number of revolutions is 100,000 times, the wear amount is 0.37-0.40g, and the contact fatigue life is 42123-72314 times;
  • the comparison example rail wear load is 980N, the number of revolutions is 100,000 times, The amount is 0.28-0.50g, and the contact fatigue life is 22124-81254 times.
  • the contact fatigue test is processed in the rail, and the sample is processed according to Figure 4A and 4B.
  • the U75V hot-rolled rail sample is used as the grinding sample, the contact stress is 1400Mpa, the speed is 400rpm, the slip is 1%, and the dry grinding method is adopted.
  • the fatigue life judgment is based on the vibration signal 3mm/s.
  • the invention adopts low-cost chromium micro-alloying component smelting, steel billet heating and rolling, utilizes rolling waste heat for heat treatment, adopts carbon-chromium-cooling rate relationship, and systematically grasps the critical cooling rate of the rail as 6°C/s.
  • heat treatment cooling position and width the strength of the rail head can be improved to ensure the operation requirements of the line.
  • the hardness of the top surface of the rail head is reduced to ensure that the rails have a good wheel-rail matching relationship.
  • it can ensure the consistency of the rail cooling bending deformation during the heat treatment process of the rail, reduce the residual stress of the rail, and ensure the safe operation of the rail.
  • the invention designs the best strength index H350-H370 grades of the steel rails, and designs the chemical composition of the steel rails and the corresponding heat treatment process. Through the heat treatment process, the strength of the rail is improved, the residual stress and flatness of the rail are reduced, and the safety and smoothness of the line operation are guaranteed.

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Abstract

一种中等强度钢轨，中等强度钢轨的化学成分的重量百分比为：碳0.70-0.90％、硅0.08-0.65％、锰0.69-1.31％、铬0.10-0.25％、磷≤0.020％、硫≤0.020％、以及铁96.85-98.41％。本发明的中等强度钢轨生产方法，生产的中等强度钢轨的钢轨硬度350-370HB，磨损量≤0.40g，接触疲劳寿命≥50000次，610mm长钢轨轨腰张开度≤3.0mm/400mm。

Description

一种中等强度钢轨及其生产方法 技术领域
本发明涉及金属材料热处理领域，特别是涉及一种中等强度钢轨及其生产方法。
背景技术
随着国内外铁路运量的增加、轴重的加大、速度的提高，对钢轨质量或是性能的要求越来越高。同时，随着国内外钢轨厂家产能的扩大，技术的革新，钢轨供大于求局面进一步扩大，低成本高性能钢轨成为主流铁路的首选。
铁路依据运输条件分为客运专线铁路、货运专线铁路和客货混运铁路。国内外铁路以客运专线和客货混运线路为主流线路，占比达到90％以上。客运专线线路和客货混运铁路用钢轨需综合考虑钢轨强度级别、运量和成本经济性等方面。通过提高钢轨性能，降低钢轨单重，缩减钢轨使用量成为经济高效钢轨发展趋势。通常，客运专线线路和客货混运铁路用钢轨单重≤60kg/m。通过国内外钢轨服役跟踪，钢轨强度级别选择H350-H370级完全能满足客运专线和客货混运线路用钢轨使用要求。
发明内容
针对现有技术中存在的不足，本发明的目的在于提供一种中等强度钢轨及其生产方法，在保证钢轨强度的同时提高钢轨的韧性，生产单重≤60kg/m、强度级别为H350-H370级钢轨。
为了实现上述目的，本发明提供的技术方案是：
一种中等强度钢轨，中等强度钢轨的化学成分的重量百分比为：碳 0.70-0.90％、硅0.08-0.65％、锰0.69-1.31％、铬0.10-0.25％、磷≤0.020％、硫≤0.020％、以及铁96.85-98.41％。
进一步地，在中等强度钢轨中，硅和锰和铬的重量百分比的和小于等于1.9％。
进一步地，中等强度钢轨硬度为350-370HB。
进一步地，中等强度钢轨磨损量为≤0.40g。
一种中等强度钢轨生产方法，包括以下步骤：
步骤1，冶炼浇铸上述中等强度钢轨的钢坯；
步骤2，钢坯经过加热，轧制中等强度钢轨；
步骤3，利用轧制余热对中等强度钢轨进行热处理；
步骤4，对热处理后的中等强度钢轨全断面施加加速冷却。
进一步地，在步骤2中，钢坯加热温度为1200-1250℃，均热段保温时间为150-240min。
进一步地，在步骤3中，轧制余热温度为620-780℃。
进一步地，在步骤3中，对中等强度钢轨轨头踏面宽度50-60mm施加1-4℃/s冷却强度。
进一步地，在步骤3中，对中等强度钢轨轨头两侧宽度20-30mm施加2-6℃/s冷却强度。
进一步地，在步骤4中，对中等强度钢轨全断面施加1-3℃/s加速冷却。
钢轨中常用的元素为碳、硅、锰、磷、硫、铬。其中，碳为影响最大元素，也是最经济的元素，铬能提高钢轨的淬硬层深度，保证钢轨良好的使用性能。
碳(C)：碳是钢中最重要的合金元素，其含量、分布形态对钢的显微组织和力学性能具有重要影响。碳元素是奥氏体稳定元素，随着碳含量的増加，过冷奥氏体稳定性增大，C曲线的位置向右移动，马氏体相变的临界开始温度降低，贝氏体的孕育期变长。碳还是很强的间隙固溶强化元素， 能强烈提高钢的强度。
硅(Si)：在炼钢过程中加硅作为还原剂和脱氧剂，硅置换固溶体形式存在于铁素体或高温奥氏体中，缩小奥氏体相区，硅的添加减缓碳原子的扩散，阻碍碳化物的析出。提高铁素体和奥氏体的硬度和强度，较锰、镍、铬、钨、铝和钒更强，显著提高钢的弹性极限、屈服强度和屈强比，并提高疲劳性能。
锰(Mn)：在炼钢过程中，锰是良好的脱氧剂和脱硫剂，锰能够提高钢的淬透性，改善其热加工性能。锰作为弱碳化物形成元素和奥氏体稳定元素，虽然在基体中对碳化物的扩散阻碍能力较弱，但是其强烈的溶质“类拖曳”作用会阻碍富碳奥氏体的进一步分解。
磷(P)：在一般情况下，磷是钢中有害元素，增加钢的冷脆性，使焊接性能变坏，降低塑性，使冷弯性能变坏。
硫(S)：硫在通常情况下也是有害元素。使钢产生热脆性，降低钢的延展性和韧性，在锻造和轧制时造成裂纹。硫对焊接性能也不利，降低耐腐蚀性。
铬(Cr)：铬能够提高奥氏体相变温度，推迟高温相变反应。铬对相变的具体影响如下：铬是铁素体稳定元素，能够缩小奥氏体区，提高奥氏体的相变温度；铬能够降低碳原子在奥氏体中的扩散速率。铬在奥氏体中的扩散速率比碳低3-5个数量级。在较高温度下进行的贝氏体转变过程中合金元素的重新分配，因为铬与碳的扩散速度差异，使过冷奥氏体向受扩散机制控制的贝氏体相变过程被推迟；铬能够提高自主扩散铁原子的激活能，降低铁原子扩散的协调性，因此能够推迟超快冷奥氏体的高温相变；铬是强碳化物形成元素，铬原子和碳原子结合倾向强烈，这使连贯相界向前推移的难度增大，因此推迟了贝氏体的转变过程。
因此，通过成分和性能数据回归分析，本发明的中等强度钢轨成分为0.70-0.90％的碳，0.08-0.65％的硅，0.69-1.31％的锰，0.10-0.25％的铬，≤0.020％的磷，≤0.020％的硫，以及98.41-96.85％重量的铁。
本发明的有益效果为：
本发明的中等强度钢轨及其生产方法，提出了低成本成分设计和高效长尺钢轨生产。同时，利用轧制余热进行热处理，在提高钢轨性能的同时，结合线路使用条件，降低踏面硬度，保证轨头踏面和轨底冷却统一性，降低钢轨残余应力，以满足低成本高性能钢轨使用要求。本发明的中等强度钢轨的钢轨硬度350-370HB，磨损量≤0.40g，接触疲劳寿命≥50000次，610mm长钢轨轨腰张开度≤3.0mm/400mm，是一种低成本、免维护、长寿命铁路用钢轨。
中等强度钢轨主要应用于客运专线或是客货混运铁路，解决了国际绝大部分铁路线路需求，采用本发明方法生产的中等强度钢轨，特别适宜年运量介于2000-5000万吨运量的低成本高人工偏僻铁路线路用钢轨，具有良好的经济效益和市场前景。
中等强度因其强度适中，耐磨性和疲劳性能优异，成本低廉，未来必将在北美、南美及澳洲等国家铺设使用，也是攀钢未来出口钢轨主力产品，具有良好的经济效益和市场前景。根据国贸公司2020年12月统计数据，钢轨边际效益达1000元/吨，以成功推广后年产3万吨计算，可至少新增经济效益3000万元以上。同时，将带动攀钢钢轨全系列产品的推广和应用。
附图说明
图1显示本发明的中等强度钢轨的热处理位置的示意图；
图2显示磨耗与接触疲劳裂纹扩展速率平衡示意图；
图3显示滚动接触疲劳试样取样位置示意图；
图4A显示滚动接触疲劳试样尺寸的截面图；
图4B显示滚动接触疲劳试样尺寸的俯视图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，下面结合实施 例及附图，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅用以解释本发明，并不用于限定本发明。
本发明提供的中等强度钢轨，其中中等强度钢轨的化学成分的重量百分比为：碳0.70-0.90％、硅0.08-0.65％、锰0.69-1.31％、铬0.10-0.25％、磷≤0.020％、硫≤0.020％、以及铁96.85-98.41％。在中等强度钢轨中，硅和锰和铬的重量百分比的和小于等于1.9％。
本发明的中等强度钢轨硬度为350-370HB，磨损量≤0.40g，接触疲劳寿命≥50000次，610mm长钢轨轨腰张开度≤3.0mm/400mm。特别适宜年运量介于2000-4000万吨运量的低成本高人工偏僻铁路线路用钢轨。
本发明提供的中等强度钢轨生产方法，包括以下步骤：
步骤1，冶炼浇铸本发明的中等强度钢轨的钢坯，中等强度钢轨的化学成分的重量百分比为：碳0.70-0.90％、硅0.08-0.65％、锰0.69-1.31％、铬0.10-0.25％、磷≤0.020％、硫≤0.020％、以及铁96.85-98.41％；
步骤2，钢坯经过加热，钢坯加热温度为1200-1250℃，均热段保温时间为150-240min，轧制中等强度钢轨；
步骤3，利用轧制余热对中等强度钢轨进行热处理，其中轧制余热温度为620-780℃，对中等强度钢轨轨头踏面宽度50-60mm施加1-4℃/s冷却强度，对中等强度钢轨轨头两侧宽度20-30mm施加2-6℃/s冷却强度；
步骤4，对热处理后的中等强度钢轨全断面施加加速冷却，对中等强度钢轨全断面施加1-3℃/s加速冷却。
硬度与磨耗直接相关，磨耗与接触疲劳性能成交互作用。通过合理设计钢轨轨头踏面硬度区间，合理设计钢轨磨耗，匹配良好的接触疲劳性能，促进钢轨综合的服役性能。
钢轨强度较低时，磨损量提高，耐磨性不足。当钢轨强度较高时，耐磨性提高，轨面表层不能被及时磨掉，在接触应力的反复作用下，塑性耗竭，导致产生裂纹并扩展。要使磨损寿命与接触疲劳寿命有一综合的良好匹配，就应将磨耗速率控制在图2中点“B”这一理想位置。要达到此目的， 就应该合适设计钢轨强度。
在下面描述本发明的中等强度钢轨生产方法的实施例。
实施例中等强度钢轨和对比例钢轨的化学成分及重量百分比如表1所示。实施例中化学成分重量百分比为：碳0.70-0.90％、硅0.08-0.65％、锰0.69-1.30％、铬0.10-0.25％、磷0.013-0.017％、硫0.008-0.012％、其余为铁，硅和锰和铬的重量百分比的和为0.87-1.90％，吨钢合金成本为42-92元/吨。对比例中化学成分重量百分比为：碳0.76％、硅0.5-0.8％、锰0.9-1.1％、铬0.05-0.30％、磷0.012-0.018％、硫0.010-0.011％、其余为铁，硅和锰和铬的重量百分比的和为1.55-2.15％，吨钢合金成本为74-104元/吨。
表1化学成分
Figure PCTCN2022102696-appb-000001
Figure PCTCN2022102696-appb-000002
实施例中等强度钢轨和对比例钢轨按照表1的化学成分及重量百分比经冶炼浇铸为钢坯。钢坯经过加热，钢坯加热温度为1200-1250℃，均热段保温时间为150-240min，轧制为中等强度钢轨。轧制后的中等强度钢轨，利用轧制余热采用不同的热处理工艺进行热处理，热处理工艺在表2中显示。
表2热处理工艺
Figure PCTCN2022102696-appb-000003
Figure PCTCN2022102696-appb-000004
实施例中等强度钢轨中轧制终冷温度为620-780℃，轨头踏面宽度为50-60mm，轨头踏面冷速为1-4℃/s，轨头两侧宽度为20-30mm，轨头两侧冷速为2-6℃/s，如图1所示；对比例中钢轨轧制终冷温度为600-800℃，轨头踏面宽度为40-70mm，轨头踏面冷速为0.9-5℃/s，轨头两侧宽度为15-35mm，轨头两侧冷速为1.5-6.5℃/s。
检测实施例中等强度钢轨和对比例钢轨的氧含量和氮含量，如表1中所显示。实施例中等强度钢轨中氧含量为7-12ppm，氮含量为30-51ppm，对比例钢轨中氧含量为6-15ppm，氮含量为34-42ppm。
按照TB/T 2344-2012标准，对实施例和对比例钢轨轨头踏面位置进行HBW10/3000布氏硬度检验。检验结果如表3所示。实施例中等强度钢轨中踏面硬度平均值为350.4-369.2HBW10/3000；对比例钢轨中踏面硬度平均值为330.8-383.8HBW10/3000。
对实施例中等强度钢轨和对比例钢轨试样在MM-200磨损试验机，采用双盘对磨，试验转数为200转/分。以U75V热轧轨试样为对磨样，位于主动轴上，模拟车轮；对实施例中等强度钢轨和对比例钢轨试样为正磨样，位于从动轴上，模拟钢轨。对磨样和正磨样直径均为36mm。在相对滑差为10％的条件下，开展不同载荷、不同转数的磨损试验，如表3，其中表3中的P代表珠光体、M代表马氏体。实施例中等强度钢轨磨损负荷为980N，转数为10万次，磨损量为0.37-0.40g，接触疲劳寿命为42123-72314次；对比例钢轨磨损负荷为980N，转数为10万次，磨损量为0.28-0.50g，接触疲劳寿命为22124-81254次。
按图3在钢轨中加工接触疲劳试验，按图4A和4B进行试样加工。在TIME M8123滚动接触疲劳磨损试验机上，对磨样采用U75V热轧钢轨试样，接触应力为1400Mpa，转速为400rpm，滑差为1％，采用干磨方式。疲劳 寿命判定依据振动信号3mm/s。
表3踏面硬度、残余应力、平直度以及磨损和接触疲劳
Figure PCTCN2022102696-appb-000005
本发明通过低成本铬微合金化成分冶炼、钢坯加热及轧制，利用轧制 余热进行热处理，采用碳-铬-冷速关系，系统掌握钢轨临界冷速为6℃/s。通过热处理冷却位置和宽度，提高钢轨轨头强度，保证线路运行要求。结合客运专线铁路和客货混运铁路运行特点，降低轨头顶面硬度，保证钢轨具备良好的轮轨匹配关系。通过轨头顶面和轨低中心相同的冷却方式，保证钢轨热处理过程中，钢轨冷却弯曲变形的一致性，降低钢轨残余应力，保障钢轨安全运行。
本发明按照客运专线和客货混运铁路用钢轨线路条件，结合磨损和接触疲劳关系特点，设计了钢轨最佳强度指标H350-H370级，并设计了钢轨化学成分和相对应的热处理工艺。通过热处理工艺，提高钢轨强度、降低了钢轨残余应力和平直度，保障了线路运行的安全性和平顺性。
以上所述实施例仅表达了本发明的实施方式，其描述较为具体和详细，但并不能因此而理解为对本发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。

Claims (10)

  1. 一种中等强度钢轨，其特征在于，所述中等强度钢轨的化学成分的重量百分比为：碳0.70-0.90％、硅0.08-0.65％、锰0.69-1.31％、铬0.10-0.25％、磷≤0.020％、硫≤0.020％、以及铁96.85-98.41％。
  2. 根据权利要求1所述的中等强度钢轨，其特征在于，在所述中等强度钢轨中，所述硅和锰和铬的重量百分比的和小于等于1.9％。
  3. 根据权利要求2所述的中等强度钢轨，其特征在于，所述中等强度钢轨硬度为350-370HB。
  4. 根据权利要求3所述的中等强度钢轨，其特征在于，所述中等强度钢轨磨损量为≤0.40g。
  5. 一种中等强度钢轨生产方法，其特征在于，包括以下步骤：
    步骤1，冶炼浇铸权利要求1-4中任一项所述的中等强度钢轨的钢坯；
    步骤2，所述钢坯经过加热，轧制中等强度钢轨；
    步骤3，利用轧制余热对所述中等强度钢轨进行热处理；
    步骤4，对热处理后的所述中等强度钢轨全断面施加加速冷却。
  6. 根据权利要求5所述的中等强度钢轨生产方法，其特征在于，在所述步骤2中，所述钢坯加热温度为1200-1250℃，均热段保温时间为150-240min。
  7. 根据权利要求6所述的中等强度钢轨生产方法，其特征在于，在所述步骤3中，所述轧制余热温度为620-780℃。
  8. 根据权利要求7所述的中等强度钢轨生产方法，其特征在于，在所述步骤3中，对所述中等强度钢轨轨头踏面宽度50-60mm施加1-4℃/s冷却强度。
  9. 根据权利要求8所述的中等强度钢轨生产方法，其特征在于，在所述步骤3中，对所述中等强度钢轨轨头两侧宽度20-30mm施加2-6℃/s冷却强度。
  10. 根据权利要求9所述的中等强度钢轨生产方法，其特征在于，在所述步骤4中，对所述中等强度钢轨全断面施加1-3℃/s加速冷却。
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