高温渗碳齿轮钢的晶粒粗化行为

  为了开发适合980 ℃高温渗碳的齿轮钢，利用伪渗碳方法，研究了铌质量分数为0、0.036%、0.060%和0.100%的18Cr2Ni2Mo渗碳齿轮钢在930和980 ℃的晶粒粗化行为。结果表明，由于析出NbC钉扎晶界，铌微合金化可以显著细化试验钢在930和980 ℃奥氏体化后的晶粒尺寸，且随着铌质量分数增加，铌微合金化明显抑制试验钢在980 ℃长时间奥氏体化晶粒粗化倾向。添加0.100%Nb的18Cr2Ni2Mo齿轮钢在980 ℃奥氏体化20 h后，平均晶粒尺寸仍然在26 μm左右，适合于980 ℃高温长时间渗碳。     

Nb微合金化对齿轮钢高温渗碳奥氏体晶粒度的影响

摘要：通过Nb微合金化提高渗碳温度是当前发展高端齿轮钢的重要思路。以20Cr钢为基准成分,通过实验室熔炼、锻造以及977~1134℃范围内高温伪渗碳实验,研究了0.02%、0.04%、0.06%、0.08%等不同Nb质量分数下渗碳后的奥氏体晶粒结构。在此基础上,依据热力学计算及析出颗粒熟化模型,对AlN、Nb(C,N)颗粒的钉扎强度进行估算并与晶粒尺寸建立联系,得到了适用于含Al、Nb齿轮钢的奥氏体晶粒度控制预测模型。最后,依据此模型分析了Nb含量对20Cr钢渗碳温度的影响,并基于高温渗碳目标提出了Nb微合金化的成分建议。     

微合金化渗碳齿轮钢的研究进展

通过添加Al、Nb、Tj、N和B等微合金化元素可细化渗碳齿轮钢的晶粒,提高切削性能和钢的疲劳性能;同时通过添加Nb、Ti等元素,可缩短渗碳时间,精简工序,降低成本。介绍了微合金化冷锻齿轮钢,高温渗碳齿轮钢,高强韧性齿轮钢的钢种、化学成分、生产工艺特点和研究进展。     

温锻和等温正火对20CrMnTiH3齿轮钢渗碳淬火后奥氏体晶粒度的影响

通过理化和原材料奥氏体晶粒度检验分析了温锻（880~930℃）加工工艺对20CrMnTiH3齿轮钢奥氏体晶粒长大的影响,得到温锻加工齿轮工序在后续890~920℃渗碳过程中该钢奥氏体容易异常长大,830℃渗碳淬火后转变为粗大马氏体组织。温锻后回火、普通正火工艺对渗碳淬火后20CrMnTiH3齿轮钢奥氏体晶粒粗大无改善效果,而通过950℃1 h空冷至650℃8h空冷的等温正火工艺可以避免渗碳淬火后粗大马氏体。     

20MnVB钢奥氏体晶粒度控制的探讨

一、前言20MnVB 钢作为东风载重汽车后桥大模数齿轮材料,承受着较大的载荷。齿轮加工中需经过940～960℃渗碳淬火处理,这就要求材料在高温状态下具有晶粒不粗化倾向。第二汽车制造厂,根据齿轮生产和使用的需要,对20MnVB 钢的奥氏体晶粒度提出了严格的技术要求,即在960℃加热,保温     

高温渗碳齿轮钢铝氮含量对奥氏体尺寸的影响

 轨道交通用高端齿轮钢往往要求长时间高温渗碳处理以提高其表面硬度与耐磨性,利用合适的铝、氮含量实现AlN粒子对奥氏体晶界的有效钉扎对保证齿轮的晶粒度、力学性能与尺寸精度至关重要。在通常的渗碳温度下,AlN已经发生了部分固溶,为了保证高温渗碳后奥氏体晶粒细小,齿轮钢中的酸溶铝质量分数一般需要保持在0.02%~0.055%以保证析出足量细小的AlN第二相粒子来钉扎晶界,且氮质量分数要求为0.01%~0.016%。这一元素含量范围较广,因此有必要研究钢在高温渗碳时所需要的恰当铝氮积与铝氮比,也就是钢中w(Al)与w(N)的乘积和比值的取值范围,还需要研究AlN粒子对于奥氏体的钉扎作用。针对不同含铝含氮轨道交通用齿轮钢进行了伪渗碳试验与AlN第二相粒子Ostwald熟化和Gladman钉扎模型计算研究,揭示了奥氏体晶粒不均匀性因子Z与加热温度T的定量关系式。研究了含铝含氮齿轮钢高温保温过程奥氏体晶粒半径R_A的变化规律,以及不同铝氮积和铝氮比对奥氏体晶粒生长的影响。结果表明,加热温度T在1 173~1 273 K范围内,此类微合金高强钢的奥氏体晶粒长大不均匀性因子服从线性规律Z=3.742 97-0.001 76T;保温时间t一定时,lnR_A与1/T大致呈二次多项式关系;加热温度T一定时,lnR_A与lnt呈线性关系,奥氏体生长时间指数为0.33;当钢中铝氮积大于4.77×10-4、对应奥氏体晶粒粗化温度T_C>1 263 K时,在T=T_C-10 K温度下保温6 h后,铝氮比为1.5~3.8的钢均可保证其奥氏体晶粒度达到7级以上;当铝氮积或T_C为定值时,同样在T=T_C-10 K加热温度下保温6 h后,钢的奥氏体晶粒大小与其铝氮比呈线性正相关;铝氮比在1.5~3.8范围内,其奥氏体晶粒度相差约在1级以内。     

渗碳齿轮钢晶粒度检验方法的研究

主要研究了晶粒度显示方法对18CrMnB渗碳齿轮钢奥氏体晶粒度测定结果的影响。研究结果表明：用渗碳法和晶粒边界腐蚀法测定其晶粒度差别很大;由于用渗碳法显示晶粒比较接近渗碳钢实际热处理条件,故对渗碳钢宜采用渗碳法测定晶粒度。     

N含量对22CrMoH齿轮钢伪渗碳条件下晶粒度的影响

采用热处理试验研究了不同N含量对22CrMoH齿轮钢在930和980℃伪渗碳条件下晶粒度的影响。结果表明,低N含量试验钢在930℃伪渗碳条件下保温10h后出现混晶现象,在980℃伪渗碳条件下保温大于等于1h即出现混晶现象;而高N含量22CrMoH齿轮钢在930和980℃伪渗碳条件下保温10h以内均未出现混晶现象。     

钛铌微合金化齿轮钢的奥氏体晶粒长大研究

 采用热模拟渗碳方法研究了Ti、Ti-Nb微合金化的20CrMnTi和20CrMnTiNb渗碳齿轮钢在930~1200℃的奥氏体晶粒长大规律。结果表明,添加0. 038%(质量分数,下同)的钛和0. 048%的铌的20CrMnTiNb钢中含有铌和钛的析出相,其粒子间距为0. 361μm;而含0. 054%的钛的20CrMnTi钢中仅含有较大尺寸的TiN析出相,粒子间距为0. 471μm,前者奥氏体晶粒粗化倾向明显低于后者。20CrMnTiNb钢经1000℃奥氏体化10h后奥氏体晶粒长大不明显,且无混晶现象,适合高温渗碳工艺。     

AlN和Zr微合金化对齿轮钢热塑性及渗碳处理晶粒度的影响

齿轮钢渗碳过程常采用AlN控制奥氏体晶粒长大，然而，AlN大量析出将恶化其热塑性和裂纹敏感性，且1 050℃高温渗碳时AlN回溶，钉扎作用减弱。通过设计不同AlN浓度积([%Al][%N])以及Zr微合金化的钢种，研究AlN和Zr微合金化对于20Cr系齿轮钢热塑性和渗碳处理奥氏体晶粒长大行为的影响，结果表明：对于20Cr系齿轮钢，提高AlN浓度积会使其热塑性恶化，塑性低谷(750～900℃)向高温区移动。而渗碳过程钢中AlN浓度积较低或Ostwald熟化现象，均会减弱AlN的钉扎晶界效果。因此，将钢中的[%Al][%N]控制在2.9×10^-4～5.1×10^-4之间偏下限控制较为合适。此外，齿轮钢中的Zr在凝固过程中会优先析出粗大的Zr(C,N)，而造成AlN析出量减少，削弱钉扎晶界的效果。故需要对N元素含量进行控制，避免粗大高温析出相的出现对AlN造成影响。     

Microstructure and Mechanical Properties of Gear Steels After High Temperature Carburization

High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity. However, the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening. The gear steel 20CrMnTiNb, which is microalloyed with 0. 048% Nb and 0. 038% Ti, has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000 °C for 4 h and mechanical properties after carburizing and pseudo-carburizing. The results indicate that the fine austenite grains exist in the carburized case of 20CrMnTiNb steel, while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn. The average prior austenite grain sizes are 19.5 and 34.2 μm for the steels 20CrMnTiNb and 20CrMn, respectively. In addition, the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel. In particular, the HV hardness of the former is higher than that of the latter by about 40–70 in the range of less than 0.7 mm in depth. Therefore, the steel 20CrMnTiNb is suitable for high temperature carburization.     

Microalloyed Steels for Heat Treating Applications at Higher Process Temperatures

The potential is considered for use of microalloyed bar steels,in conjunction with thermomechanical processing,to enhance the properties of steels heat treated at higher process temperatures than have been used historically.Two examples are highlighted:microalloyed spring steels with enhanced resistance to tempering and Nb-modified gear steels for high temperature vacuum carburizing,e.g.on the order of 1050℃ versus 930℃ for a typical gas carburizing operation.In the spring steel example,the Nb+V steel results in significantly finer prior austenite grain sizes than the other steels considered,enhanced fatigue performance,and improved toughness.In the Nb-modified carburizing steel,Nb additions up to 0.1 wt pct to a Ti-modified 8620 steel,in conjunction with thermomechanical processing to control initial precipitate distributions prior to carburizing,are shown to lead to materials with improved resistance to abnormal austenitic grain growth at the higher process temperatures.Alloy content and heating rate to the carburizing temperature were shown to be important variables and suppression of abnormal grain growth was correlated with the development of a critical distribution of fine NbC precipitates,stable at the austenitizing temperature leading to improved fatigue performance in steels with fine and uniform grain structures.Opportunities for extending the results of this study to alloy design and controlled rolling in bar mills are assessed.     

高强度汽车渗碳齿轮钢的发展及应用

渗碳齿轮钢是汽车用主要结构钢之一，国内主要汽车生产厂家的高强度齿轮钢材料一直使用不同国家多个牌号的渗碳钢。随着技术和应用的发展有必要开发新品种的高强度齿轮钢。分析了高强度汽车渗碳齿轮钢在国内外的发展及应用现状，并根据我国合金材料的特点展望了其发展趋势。     

Development of microalloyed steels for high temperature carburizing

The potential for use of microalloy additions to suppress abnormal austenite grain growth and produce steels with enhanced bending fatigue resistance after high temperature vacuum carburizing was investigated in a series of Ti-modified SAE 8620 steels with w(niobium) additions up to 0.1%.Results are considered from a series of papers at the Advanced Steel Processing and Products Research Center on the effects of Nb content,heating rate, rolling history,and processing temperature on the evolution of austenite grain structures in carburizing steels. Emphasis is placed on understanding the effects of alloying and processing on each stage in the annealing process including the as received laboratory rolled conditions,during the onset of carburizing after annealing at different heating rates,and after annealing for various times at carburizing temperatures up to 1 100℃.Heating rate to the carburizing temperature was shown to be an influential variable and suppression of abnormal grain growth was dependent on the development of a critical distribution of fine NbC precipitates,stable at the austenitizing temperature.The importance to industrial carburizing practice of heating rate effects on precipitates and austenite grain size evolution are discussed and correlated to selected data on fatigue performance.     

Numerical Simulation on Carburizing and Quenching of Gear Ring

 The carburizing process of the gear ring was simulated by taking into account the practical carburizing and quenching techniques of the gear ring and by solving the diffusion equation. The carbon content distribution in the carburized layer was obtained. Based on the results, the quenching process of the gear ring was then simulated using the metallic thermodynamics and FEM; it was found that the carburization remarkably affects the quenching process. Microstructures and stress distributions of the gear ring in the quenching process were simulated, and the results are confirmed by experiments.