齿轮钢高温渗碳后的疲劳性能

利用旋转弯曲疲劳试验方法,研究了Nb和Ti微合金化20CrMn齿轮钢(20CrMnNb钢:w(Nb)0.077%;20CrMnTiNb钢:w(Nb)0.048%+w(Ti)0.038%)经1 000℃高温渗碳后的疲劳性能。结果表明,Nb-Ti复合微合金化的20CrMnTiNb钢中析出相尺寸小、数量多,其渗碳层原奥氏体晶粒平均尺寸明显低于Nb微合金化的20CrMnNb钢,因而20CrMnTiNb钢的疲劳极限高于20CrMnNb钢。疲劳断口观察发现,20CrMnNb和20CrMnTiNb钢主要以近表面基体方式起裂,渗碳层中疲劳裂纹沿晶界扩展,因而晶粒尺寸较细的20CrMnTiNb钢的疲劳性能较高。     

18CrMnB钢渗碳层奥氏体晶粒的长大倾向

本文主要研究了微量元素钛、铝、氮及预先热处理对18CrMnB钢渗碳层奥氏体晶粒长大倾向的影响。     

渗碳钢残余应力场在接触疲劳滚压过程中的行为

就汽车齿轮渗碳钢，经不同工艺渗碳与强力喷丸处理后，对试件在接触应力作用下滚压过程中残余压应力场动态变化行为和接触疲劳性能进行了研究，结果表明，喷丸可使接触劳动强度提高，喷丸所引入的残余压应力场在滚压过程前基本不发生变化，是喷丸延长接触疲劳寿命原因之一，喷丸过程和随后的接触疲劳滚压过程同属在赫兹应力作用下的循环弹塑性应变过程。     

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。     

晶粒尺寸对表面渗碳钢疲劳极限的影响

利用旋转弯曲疲劳试验方法,研究了渗碳钢的晶粒尺寸与其疲劳极限之间的定量关系。结果表明,晶粒尺寸越小,渗碳钢的疲劳极限越高,晶粒尺寸与疲劳极限之间存在类似Hall-Petch关系。疲劳试样断口观察发现,疲劳裂纹起源于渗碳层,并沿原奥氏体晶界扩展,细化渗碳层晶粒有利于提高疲劳裂纹扩展阻力,因此改善疲劳性能。     

钼对渗碳层性能的影响

在基体性能满足使用要求的前提下,渗层性能的好坏对齿轮使用寿命起决定作用。文中系统研究了钼含量(0～0.8％)对Cr-Mn钢渗层性能的影响。试验表明,Mo提高渗层的有效深度,并使碳浓度随层深的增加下降平缓,从而使渗层和心部得以良好的过渡。Mo的加入可提高渗层残余压应力,从而可提高疲劳强度,但是热处理变形度随钼含量的提高而增加。Mo的有益作用必须有一定量的Cr,Mn,Ni等合金元素配合,即保证一定淬透性时才能获得。综合看来,渗碳钢中加入0.2～0.4％的Mo从技术上和经济上考虑是最佳的。     

显微硬度法测定渗碳层深度的研究

一、前言 在机械制造工业中,常要求某些机器零件既能耐磨,又不易产生脆性断裂;既要求表面具有高硬度、耐磨、耐疲劳等,又要求其心部在保证足够强度的前提下,仍具有良好的韧性和塑性。要达到这些要求,可以借助于化学热处理方法。目前在工业生产中应     

X射线衍射法测定渗碳钢中残余奥氏体

用X射线衍射法测量低碳合金渗碳钢的渗碳层残余奥氏体含量，测量速度较快，结果精确，重现性好，优于传统的金相法测量。     

高氮18CrMnB钢渗碳层淬透性及晶粒度的研究

本文研究了微量元素铝，氮及预先预热处理对高氮１８ＣｒＭｎＢ钢渗碳层淬透性及奥氏体晶粒长大倾向的影响，结果表明，微量元素铝，氮对高氮１８ＣｒＭｎＢ钢心体淬透性影响很大，而对渗碳层淬透性，特别是对渗碳表层淬透性影响较小，预先热处理对高氮１８ＣｒＭｎＢ钢渗碳层奥氏体晶粒长大倾向影响很大，不同预先热处理状态的高氮１８ＣｒＭｎＢ钢渗碳层奥氏体晶粒粗化温度对钢中微量元素铝，氮含量变化的敏感程度不同。     

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。     

Effect of Prestrain on Microstructures and Properties of Si-Al-Mn TRIP Steel Sheet with Niobium

Paint baking treatment was carried out in a silicon oil bath at 170℃ for 20min for Si-Al-Mn TRIP Steel sheet with different prestrains,and effect of prestrain on microstructures and properties was studied before and after baking.The results show that with the increasing of prestrain amount during prestraining and baking,the volume fraction of retained austenite decreases,and the volume fraction of martensite and bainite increases as well as yield strength increases;as prestrain ranges from 0 to 4%,the baking-hardening(BH)value increases;while the prestrain ranges from 4% to 16%,the BH value decreases;when the prestrain amount is 4%,the highest BH value is about 70MPa for Si-Al-Mn TRIP steel sheet with niobium,which displays excellent baking-hardening behavior.     

Microstructure Characterization and Mechanical Properties of TRIP-aided Steel under Rapid Heating for Different Holding Time

In order to develop a comprehensive understanding about the effect of different holding time under rapid heating on the microstructural evolution and mechanical properties of transformation-induced plasticity (TRIP)steel, continuous annealing process simulations were performed using a thermal system with resistance heating method. The morphology and distribution of all phases present in the microstructure and the mechanical properties of TRIP steel were revealed.It appeared that the final tensile strength of the TRIP steel increased and retained austenite car-bon content decreased with increasing holding time.An overlap between ferrite recrystallization and austenitization was observed during intercritical holding.In addition,the work hardening of the samples was evaluated by calculat-ing the instantaneous n value as a function of the true strain.The difference in work hardening behavior corresponds to the rate of the retained austenite transformation during straining,which can be attributed to the carbon content and the morphology of the retained austenite.     

20CrMnMo渗碳淬火齿轮的接触疲劳强度

对齿面硬度HRC62的20CrMnMo渗碳淬火齿轮,进行了接触疲劳运转试验,获得33个试验数据。经过数据处理,绘制出R-S-N曲线,可靠度0.99,循环基数5×10⁷,其齿面接触疲劳极限应力为1571.6N/mm²。通过电镜等,对齿面损伤特性进行了宏观和微观的分析,获得一些有益的观点,提出一些有效的技术措施。     

H13改进型热作模具钢的组织与性能

 研究了高锰型马氏体热作模具钢SDH3-Mod的室温冲击韧性、回火稳定性和热疲劳性能,并结合透射电镜(TEM)分析了锰对其微观组织的影响。结果表明：SDH3-Mod钢回火组织中残余奥氏体以薄膜状存在于马氏体板条间,提高冲击韧性,延缓裂纹扩展;同时,锰在高温时阻碍碳化物粗化长大和延迟基体的回复再结晶,提高抗回火软化能力和热疲劳性能,使SDH3-Mod性能优于H13。     

HSLA-TRIP钢动态拉伸性能和残余奥氏体转变

对成分为 0 .11C- 0 .6 2 Si- 1.6 5 Mn的低硅 TRIP钢不同试验温度下的动态拉伸性能和残余奥氏体的转变行为进行了研究。试验结果表明 ,两相区热处理温度接近 Ac1 可以获得较多的铁素体和残余奥氏体 ,此类试样拉伸试验结果有较高的强塑性配合。 110℃下的抗拉强度较 2 0℃下的降低约 30 0 MPa;均匀伸长率在应变速率 10 0 0s- 1左右达到峰值 ,总伸长率随应变速率提高而单调增加。试验温度为 5 0℃和 75℃下的能量吸收值可达到 2 6 0 0 0MPa· %。试验温度越高 ,残余奥氏体稳定性越好 ,动态拉伸的绝热效应也抑制了残余奥氏体的形变诱发相变。     

Thermal Stability of Retained Austenite in TRIP Steel After Different Treatments

Thermal decomposition of retained austenite in TRIP steel was investigated by means of differential scanning calorimetry（DSC）.The decomposition curve was abnormal,and the decomposition temperature and the activation energy were measured by the Kissinger method,which were all higher than those in quenched steel.The thermal decomposition data of samples soaked in liquid nitrogen after TRIP treatment were all similar to those without additional low temperature treatment.It indicated that there is a high thermal stability in retained austenite of the TRIP steel at low temperature,which was also proved by XRD analysis.     

Mechanical Properties and Retained Austenite Transformation Mechanism of TRIP-Aided Polygonal Ferrite Matrix Seamless Steel Tube

 Through the comparison of microstructure for polygonal ferrite (PF) matrix transformation induced plasticity (TRIP) seamless steel tube at different positions before and after tensile rupture, the transformation behavior of retained austenite (RA) was studied. The results showed that there were no yield points in tensile process and the splendid elongation and tensile strength were contributed by the uniform ferrite/bainite grains and the transformation of RA. The stability of RA was to some extent in inverse proportion with the ability of transformation induced plasticity. The coarse retained austenite located in ferrite and ferrite/bainite laths were all transformed into martensite during the tensile process.     

Macro and Micro Behaviors of Low Alloyed TRIP780 Steel with Different Biaxial Proportional Loading

To investigate the macro and micro behaviors of TRIP(transformation induced plasticity)steel under biaxial loading,experiment and finite element simulation were carried out for TRIP780 steel under proportional biaxial tension with displacement ratio of 1∶1,2∶1,3∶1 and 4∶1,respectively.The results show that cruciform specimens of TRIP780 steel fractured under proportional biaxial stretching when effective strain was about 1.5%,and fracture was always generated on the cross arm or cross links.During biaxial tension,stress and strain components in xand ydirections of the center of the samples have the same nonlinear developing tendency,decreasing in one direction and increasing in another direction.Equal biaxial stretching stress state was helpful for retained austenitemartensite transformation than the other biaxial stress state.With increasing displacement ratio(DR)from 1∶1to 4∶1,corresponding stress distributed unevenly on the yield ellipse from 30° to 60° in the first quadrant of stress space and corresponding retained austenite volume fraction distributed symmetrically in bow tie format.