50t电炉-LF-VD流程生产SAE8620H齿轮钢淬透性的控制

对影响采用50 t电炉-LF-VD工艺生产SAE8620H齿轮钢的淬透性的冶金因素进行分析;重点关注生产过程中化学成分C含量的变化规律,分析工艺过程对化学成分C含量的控制精度的影响因素并进行研究优化。通过实施设计子钢号化学成分、缩窄化学成分控制范围、对工艺关键位置加强全过程控制等措施后,钢中Mn、Cr、Ni均控制在较窄的范围内,w(C)波动控制在0.03%以内,从而较好地控制了SAE8620H齿轮钢淬透性和淬透性带宽。     

美标SAE8620H齿轮钢的研制

莱钢特钢厂通过采取精料、电炉冶炼全程泡沫渣、LF精炼和VD真空脱气等措施,生产出的SAE8620H钢具有淬透性带窄、纯净度高、晶粒细小均匀、表面质量优良等优点,完全能够满足高性能汽车齿轮的需要.     

热处理工艺对SAE8620H低碳齿轮钢带状组织的影响

试验了由300mm×340mm连铸坯生产的SAE8620H齿轮钢(%:0.19C、0.48Cr、0.48Ni、0.18Mo、0.032Al)φ100mm轧材在热轧、完全退火(930℃1 h炉冷至650℃1 h空冷)以及等温退火(930℃1 h出炉快冷至650℃1 h空冷)3种状态下的的带状组织。结果表明,完全退火后轧材带状级别较热轧态高;因930～650℃快冷抑制先共析铁素体的析出,等温退火轧材带状级别较热轧态低1.0～1.5,显著改善了钢的带状组织。     

齿轮钢SAE8620H高温变形行为及热加工图

通过高温压缩试验研究齿轮钢SAE8620H在950~1100℃、应变速率0.01~10 s^-1条件下的高温变形行为.该合金钢的流动应力符合稳态流变特征,流变应力随变形温度升高以及应变速率降低而减小,其本构方程可以采用双曲正弦方程来描述.基于峰值应力、应变速率和温度相关数据推导出SAE8620H高温变形激活能Q=280359.9 J·mol^-1.根据变形量40%和60%下应力构建该齿轮钢的热加工图,通过热加工图中耗散值及流变失稳区确定其热变形工艺参数范围.SAE8620H钢在在变形程度较小时宜选取低的应变速率进行成形,而在变形程度大时则要选取低温低应变速率或者高温高应变速率.     

常用齿轮钢渗碳层淬透性的计算方法

用20CrMnTi、20MnVB及20CrNiMo 3种常用齿轮钢作试验,在研究3种相关淬透性组织判据(D_I(90%M)、D_I(99.9%M)和D_I(50%M))的基础上,以90%马氏体透性的组织判据,建立了含有元素交互作用项、能连续计算渗层淬透性值JD(90%)(端淬试为渗层淬样上自水冷端到90%马氏体区的J距离)的多项式回归方程。利用该方程对上述3种钢所作的相应计算,结果与实测值符合得很好。     

钒对高温渗碳SCM420H齿轮钢组织和淬透性的影响

对高温渗碳SCM420H齿轮钢进行了钒微合金化处理,并对钢中组织及淬透性进行了研究。结果表明：SCM420H齿轮钢中V含量和N含量应控制范围分别在0.03%～0.05%和0.012%～0.018%。MN(M=Ti,V)在966℃时析出并在559℃时向M(C,N)发生转化,常温时的M(C,N)质量百分数约为0.049%。将加热温度控制在1 200℃±20℃,在预热段（室温升至850℃左右）加热时间控制在120 min内,在940～980℃高温渗碳保温6 h后,圆钢的带状组织控制在1.5～2级,奥氏体晶粒稳定在7.5～8级,M(C,N)主要为能起到钉扎晶界、细化奥氏体晶粒的纳米级球状V(C,N)。将连铸结晶器电磁搅拌强度参数调整为150 A,2.5 Hz,铸坯拉速为0.85 m/min,浇铸过热度为15～30℃,碳含量偏差值可控制在0.01%,碳含量的均匀化有利于淬透性的窄带化控制,钒微合金化后,试样的淬透性硬度值（HRC）最高为37,最低为35,淬透性带宽硬度值（HRC）≤3。     

微量元素对20CrMnB齿轮钢淬透性的影响

本文讨论了微量元素钛、氮、铝对渗碳齿轮钢20CrMnB淬透性的影响,并采用径迹显微分析技术对钢中的硼分布形态进行了分析,探讨了生产淬透性高且稳定的钢的可能方式。     

齿轮渗碳热处理变形及对策

本文对渗碳热处理的变形规律与变形原因进行了详细的介绍,对零件热处理变形的有关原因进行了全面的总结,把整个齿轮制造过程的因素较全面的进行考虑,在变形的因素中从材料因素到工艺因素等方面进行分析,在对策方面从预热处理到淬火介质及工装夹具进行考虑,并有针对性地提出了解决对策。     

冶金因素对齿轮钢淬透性的影响

论述冶炼工艺流程对齿轮钢淬透性的影响，指出炉外精炼，真空脱气和连铸技术是提高齿轮钢产品质量和５生产窄淬透性钢的最有效方法。     

Rolling Contact Fatigue Properties of SAE 8620 Steel after Case Carburizing

Rolling contact fatigue(RCF)properties of SAE 8620 steel after case carburizing have been investigated under two contact stresses of 4.0and 5.5GPa.Results show that the RCF life ranges from 2.5×10~6 to 3×10~7 cycles under the contact stress of 5.5GPa,while it can be more than 1×10~8 cycles under the contact stress of 4.0GPa.The rated fatigue life L_(10)(lives with the 10%failure)is also drastically shortened from 9.8×10~6 to 5.4×10~5 cycles when the contact stress is increased from 4.0to 5.5GPa.Theoretical calculations and fractographs show that the maximum shear stress and the contact area increase with increasing the contact stress,making RCF tend to occur earlier.     

20CrMnTi齿轮钢中TiN析出相对淬透性的影响

为了研究20CrMnTi齿轮钢中TiN析出相对淬透性的影响,以实际生产中两种具有不同淬透性特性的20CrMnTi端淬试样为基础,对试样的外围硬度进行测试,用金相显微镜观察室温组织和原奥氏体晶粒组织,用扫描电镜观察分析钢中TiN颗粒的特征,以及利用Thermo-Calc软件分析TiN的析出过程.研究结果表明,奥氏体晶粒度...     

齿轮钢窄淬透性带控制技术

 为提高齿轮钢淬透性带控制精度,优化了齿轮钢成分控制目标及精度要求,建立合金加料计算机控制模型和成分调整规则库,开发基于增量神经网络的齿轮钢淬透性预报模型,形成一套完整的齿轮钢窄淬透性带宽控制技术,并将该技术应用于20CrMnTiH齿轮钢。研究结果表明,可实现窄淬透性带控制,J9和J15淬透性带宽不大于4HRC的比例分别达到93.3%和89.2%,不大于6HRC的比例分别达到99.3%和98.4%。     

含硫齿轮钢SAE8620H热轧棒材夹杂物

 以EAF电炉—LF精炼炉—VD真空精炼炉—LF精炼炉—CC连铸工艺流程生产含硫齿轮钢SAE8620H热轧棒材,利用光学显微镜、扫描电镜和能谱仪分别对棒材横纵截面的边缘部位、1/2半径处和中心部位的夹杂物进行了检测,综合分析了夹杂物的尺寸、数量、分布以及形貌和成分。结果表明：含硫齿轮钢SAE8620H热轧棒材中的夹杂物主要有单独硫化锰和核心主要是Al2O3和MgO-Al2O3,外围是MnS或者（Ca、Mn）S的氧硫复合夹杂物;从边缘到中心,夹杂物总数递增,氧硫复合夹杂物比例递减;棒材横截面上夹杂物大部分小于2μm,长宽比小于3;棒材纵截面上夹杂物平均长度为11μm,边缘部位夹杂物平均长度较中心部位短3μm,纺锤状夹杂物的比例占30%。     

铌微合金化对高铁车轴钢淬透性的影响

 为了研究铌对DZ2高铁车轴钢淬透性的影响规律和机理,通过末端淬透性试验和物理化学相分析等方法,研究了铌质量分数分别为0、0.026%和0.039%的DZ2钢的微观组织、析出相和淬透性。结果表明,距淬火端20 mm以内,铌微合金化车轴钢硬度均高于对比钢,不同铌含量试验钢的淬透性曲线拐点位置均在距淬火端25～30 mm处,总体来看,3种试验钢淬透性相当;随着铌质量分数的增加,奥氏体晶粒尺寸越小,降低了钢的淬透性;铌微合金化抑制了M₃C相的析出,增加了奥氏体中碳、锰、铬固溶量,从而提高了钢的淬透性,弥补了晶粒细化造成的淬透性下降,综合作用下淬透性基本保持不变。     

Computational Thermodynamic Study of Inclusions Formation in the Continuous Casting of SAE 8620 Steel

The general purpose of this work is a thermodynamic study of non‐metallic inclusions in the CC tundish for SAE 8620 steel. Specific purposes are: (1) Obtaining the phases formed and their composition in inclusions by applying computational thermodynamics for SAE 8620 steel; (2) Establishing conditions of steel composition for the improvement of SAE 8620 castability, including the plant validation in terms of the castability index. Thermodynamic studies were performed with the commercial software FactSage and databases. Simulations were carried out by the global chemical composition of SAE 8620 steel in the CC tundish, resulting in both steel composition and non‐metallic inclusions (oxides and sulphides) at the desired temperature. Furthermore, results showed both different solid oxides and liquid phase formation in inclusions by varying calcium content in the steel. Thus, it was possible to determine the inclusion composition as a function of aluminium and calcium content of SAE 8620 steel, and moreover, to establish a range of calcium content in which the inclusions are predominantly formed by liquid phase. In addition, the percentages of liquid and solid phase in inclusions, as well as, oxide compositions could be calculated.     

Computational Thermodynamics Application on the Calcium Inclusion Treatment of SAE 8620 Steel

A thermodynamic study was carried out to evaluate the contents of Al, Ca, S and O at which liquid or partially liquid inclusions are formed to optimize the castability of SAE 8620 steel. Samples of steel secondary treatment (Ladle) and continuous‐casting billets (Tundish) were obtained from an electric steel mill. Entry data for this study were obtained in heats carried out in the steel plant. Furthermore, analyses were performed with a Scanning Electron Microscope (SEM) and an Energy‐Dispersive Spectrometer (EDS), as well as chemical analysis of both steel and total oxygen. In the Ladle sample, after calcium addition, inclusions had concentrations between 30 and 45% CaO and consisted mainly of calcium‐aluminates with MgO content of 10%. In the Tundish sample, inclusions contained a high percentage of alumina. Combining the characterization of inclusions with a computational thermodynamics model, the obtained results showed that the ideal range of calcium may vary between 10 and 14 ppm to form liquid inclusions with a minimum CaS content for the O, S and Al levels from SAE 8620 in this process stage. An analysis of Mg influence on the formation of calcium‐aluminates was also carried out. For contents of Mg found in aluminium‐killed steels treated with Ca, Mg does not significantly influence the formation of calcium‐aluminates inclusions. Higher calcium contents can be taken into account, depending on both the process type in steel production and the demanded product properties. The present study shows that the combined application of both inclusions characterization techniques and computational thermodynamics can drastically reduce the empiricism regarding the development of processes for the control of non‐metallic inclusions in steels. Thus, this research can contribute to increase the efficiency of manufacturing processes, improve the quality of existent products and make possible the economic development of new ones.     

Quenching distortion induced by ingot segregation in gear steel

The influence of ingot segregation on quenching distortion of gear steel was investigated in this paper.The results show that the shape of ingot segregation of rod steel depends on the shape of continuous casting (CC) molds,and that the distortion of gear steel with square ingot segregation is uniform,while that of gear steel with rectangular ingot segregation is anisotropic.After quenching,the outer circle of the ring sample with a large rectangular segregation area is distorted into an oval shape.No obvious element segregation has been found in the rod steel produced through the rectangular CC mold.Obvious difference in density has been detected at the cross section of rod steel.It suggests that center porosity may be the main reason for the strong impact of segregation on heat treatment distortion of gear steel.