55SiCr弹簧钢中的残留奥氏体与碳化物

通过扫描电镜(SEM)、电子背散射衍射(EBSD)、透射电镜(TEM)、X射线衍射仪(XRD)、热膨胀仪、洛氏硬度计等手段研究了弹簧钢55SiCr的组织和相变点以及残留奥氏体和碳化物在热处理过程中的组织演变。结果表明:55SiCr弹簧钢淬火后残留奥氏体以块状分布在基体上;随回火温度的升高,残留奥氏体减少并呈粒状和薄膜状分布;C在残留奥氏体中富集,使其稳定性增强;Si抑制了碳化物的析出,提高了残留奥氏体的稳定性。低温回火时,Si延缓了渗碳体析出;高温回火时,C原子扩散速率提高,促进渗碳体析出,引起体积的收缩。慢速加热回火时,C有足够的时间扩散,从而促进渗碳体的形成,使渗碳体的形成温度提前;快速加热回火时,C来不及扩散,抑制了渗碳体的析出。回火加热速率一样时,试验钢的硬度随回火温度的提高而下降。当回火温度为400 ℃时,硬度值最大为51 HRC;当回火温度为650 ℃时,硬度值最小为37 HRC。当加热速率为0.1 ℃/s时,硬度值最小为33 HRC;当加热速率为200 ℃/s时,硬度值最大为40 HRC。     

基于07MnNiMoDR钢热处理工艺窗口的热处理工艺

研究了07MnNiMoDR钢淬火和回火制度与晶粒尺寸和多边形铁素体含量的关系,建立了淬火保温时奥氏体尺寸窗口和回火保温时多边形铁素体含量窗口,确定了更为精准的热处理工艺。结果表明:奥氏体晶粒尺寸随淬火温度的升高、保温时间的延长而变大,均匀性存在最佳区间,合理的淬火制度为加热温度(940±10) ℃保温(80±10) min;随回火温度升高,约650 ℃出现多边形铁素体,其含量随回火温度的升高、保温时间的延长而增加,合理的回火制度为:加热温度(665±5) ℃、保温时间(165±15) min。优选后最佳热处理工艺为940 ℃×80 min淬火和660 ℃×180 min回火,最终性能测试结果表明:伸长率、冲击吸收能量和屈服强度相比国标分别提升了40.88%、206.25%和12.1%。     

0Cr16Ni5Mo马氏体不锈钢δ-铁素体含量及奥氏体晶粒度的控制

检验中发现0Cr16Ni5Mo钢的δ-铁素体含量超出技术协议规定值,为降低δ-铁素体的含量同时控制奥氏体晶粒度以满足材料使用要求,通过理论计算和热力学模拟分析δ-铁素体形成原因,后续采用不同温度的淬火和高温扩散对0Cr16Ni5Mo钢组织和δ-铁素体含量变化进行对比研究,另外采用两种循环热处理方式对奥氏体晶粒度进行控制。结果表明,随着淬火温度的提高,0Cr16Ni5Mo钢的奥氏体晶粒度不断增大,而对δ-铁素体含量的减少作用相对有限。高温扩散能使δ-铁素体明显减少,但当扩散温度大于奥氏体向δ-铁素体转变温度时,会相对延缓铁素体的溶解。进行1130 ℃的高温扩散后,可以采用850 ℃和830 ℃的变温循环相变热处理,消除马氏体组织遗传,均匀细化奥氏体晶粒。     

高锰钢中奥氏体的加工硬化机理

对铸造型的高锰钢(ZGMnl3)，水韧处理获得单一奥氏体耐磨钢的应力应变和残体硬度作了分析讨论，说明高锰钢奥氏体具有相当高的加工硬化度，在室温下权限变形后，共硬度远未达到峰值，因此，奥氏体高锰钢的加工硬化特性是由奥氏体本身强化作用影响产生的。同时迁就高锰钢的主要化学成分对组织及性能的影响，大型高锰钢件的制造中的问题作了简要介绍。     

钛含量对20MnMoB钢奥氏体晶粒度及晶粒粗化温度的影响

研究了钛含量对２０ Ｍｎ Ｍｏ Ｂ钢奥氏体晶粒度及奥氏体晶粒粗化温度的影响。结果表明,有效钛（ Ｔｉｅ）是决定２０ Ｍｎ Ｍｏ Ｂ钢奥氏体晶粒度和晶粒粗化温度的主要参数。随（ Ｔｉｅ）含量增加,试验用钢的奥氏体晶粒尺寸减小,晶粒粗化温度提高。当 Ｔｉｅ 超过０．０３７％ 时,钢的奥氏体本质晶粒度可达７ 级以上,晶粒粗化温度提高到１ ０００℃以上。     

EH36高强度船板钢奥氏体连续冷却的转变行为

利用Gleeble2000型热模拟试验机对EH36船板钢连续冷却相变行为以及在增速冷却和减速冷却条件下的相变行为进行了研究。结果表明：在连续冷却条件下,在400-650℃范围内,冷却速率在4～16℃／s时,相变组织以贝氏体组织为主且随着冷速的增大贝氏体的体积分数增加;在冷却速率≥1℃／s时,先以一定速率冷却至600℃,然后将冷速减半时,其显微组织与半速恒速冷却组织相近;而先以一定速率冷却至600℃,然后将冷速加倍时,其显微组织与两倍速恒速冷却的显微组织相近。     

Studies of cryotreatment on the performance of integral diaphragm pressure transducers for space application

The integral diaphragm pressure transducers machined out of precipitation hardened martensite stainless steel (APX4) are widely used for propellant pressure measurements in space applications. These transducers are expected to exhibit dimensional stability and linearity for their entire useful life. These vital factors are very critical for the reliable performance and dependability of the pressure transducers. However, these transducers invariably develop internal stresses during various stages of machining. These stresses have an adverse effect on the performance of the transducers causing deviation from linearity. In order to eliminate these possibilities, it was planned to cryotreat the machined transducers to improve both the long-term linearity and dimensional stability. To study these effects, an experimental cryotreatment unit was designed and developed based on the concept of indirect cooling using the concept of cold nitrogen gas forced closed loop convection currents. The system has the capability of cryotreating large number of samples for varied rates of cooling, soaking and warm-up. After obtaining the initial levels of residual stress and retained austenite using X-ray diffraction techniques, the pressure transducers were cryotreated at 98 K for 36 h. Immediately after cryotreatment, the transducers were tempered at 510 °C for 3 h in vacuum furnace. Results after cryo treatment clearly indicated significant reduction in residual stress levels and conversion of retained austenite to martensite. These changes have brought in improvements in long term zero drift and dimensional stability. The cryotreated pressure transducers have been incorporated for actual space applications.     

Corrosion fatigue of a manganese–nitrogen stabilized austenitic stainless steel

Austenitic chromium–manganese–nitrogen stabilized stainless steels have been developed to replace chromium–nickel–nitrogen stainless steels in certain applications. In comparison, chromium–manganese–nitrogen steels have improved mechanical properties and acceptable corrosion resistance in hot, high chloride containing media. In this paper, corrosion fatigue investigations of a solution annealed and for practice more relevant 14% cold worked high alloyed chromium–manganese–nitrogen steel have been done. Inert glycerine was used as reference media and 62% calcium chloride solution as corrosive media, both aerated at a temperature of 120 °C. The stress ratio between upper and lower stress levels was 0.05 (tension–tension loading) to avoid the destruction of the fracture surfaces. As testing frequency for the dynamic experiments, 20 Hz was chosen considering possible application areas. Maximum stress versus number of cycles curves were recorded and representative specimens were investigated in a scanning electron microscope. In addition, electrochemical tests, exposure tests and constant load tests were done. This paper shows results on the corrosion fatigue of a manganese–nitrogen stabilized austenitic steel in a hot high chloride containing salt solution and helps to get a better understanding of occurring failure mechanisms.     

汽车拨叉热处理工艺研究

采用正交试验法，确定的汽车拨叉零件热处理工艺参数组合，满足使用要求；分析了该工艺形成的拨叉表层碳浓度情况和碳浓度梯度分布，获得浅层碳氮共渗碳浓度梯度分布对性能的影响，采用在升温阶段手动通入适量氨气的工艺调整方法，可以缩短均温时间，保证表面硬度达到技术要求，探索了合适氨气流量确保表层不出现过量残余奥氏体和黑色组织的机理，选用MT25656分级淬火油，可以满足零件变形要求。     

Effect of austenite microstructure and cooling rate on transformation characteristics in a low carbon Nb-V microalloyed steel

Deformation dilatometry has been used to simulate controlled hot rolling followed by cooling of a Nb-V low carbon steel, looking for conditions corresponding to wide austenite grain size distributions prior to transformation. Recrystallization and non-recrystallization deformation schedules were applied, followed by controlled cooling at rates from 0.1 °C/s to about 200 °C/s, and the corresponding continuous cooling transformation (CCT) diagrams were constructed. The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling rates to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformations, displacing the CCT curve to higher temperatures and shorter times. However, it was found that the accelerating effect of strain on bainite transformation weakened as the cooling rate diminished and the polygonal ferrite formation was enhanced. Moreover, it was found that plastic deformation had different effects on the refinement of the microstructure, depending on the cooling rate. An analysis of the microstructural heterogeneities that can impair toughness behavior has been done.