超高碳钢超级贝氏体转变及组织与性能

研究了碳含量1.26wt%的超高碳钢在等温淬火后的组织及其对拉伸力学性能的影响。结果表明,超高碳钢的等温淬火组织为超级贝氏体（Superbainite）+残留碳化物的复相组织。超级贝氏体的形成是因为超高碳钢中的高碳成分及铝元素的添加。由于原奥氏体晶粒细化,超级贝氏体的形核率增加,长大路径缩短,使转变速率加快。形貌观察表明,贝氏体铁素体片和残留奥氏体薄膜的厚度只随着等温温度的降低而减小;奥氏体化温度对贝氏体铁素体片厚度没有影响,但超级贝氏体组织的尺寸会随奥氏体化温度提高而增加。拉伸试验结果表明,随着等温时间的延长,抗拉强度逐渐升高,但断后伸长率却先增加后减小;等温温度或奥氏体化温度升高均会引起抗拉强度降低,但伸长率增加。     

超级贝氏体钢中残留奥氏体的行为

针对超级贝氏体钢中残留奥氏体组织对钢的强韧性贡献,设计了试验用钢60Mn2SiCr。通过对样品完全奥氏体化后不同温度和时间的等温处理,并通过SEM、TEM和MAUD软件分析了在超级贝氏体组织中残留奥氏体的存在、分布及数量。结果表明,残留奥氏体以薄膜状分布在贝氏体铁素体条束之间或针片内部;随等温温度的变化,其数量存在极值现象,在钢的Ms点稍上温度等温处理,可以获得残留奥氏体体积分数极大值为17.64%。此时,钢的强度为1930 MPa,伸长率7.44%,断面收缩率15.66%,具有良好的强韧性配合。     

75Si2Mn1.5CrB铸钢等温淬火组织及力学性能

对新型的高碳低合金75Si2Mn1.5CrB钢进行了在200℃等温淬火工艺组织和力学性能的研究。利用激光显微镜、透射电子显微镜(TEM)和X射线衍射仪(XRD)对等温淬火处理的试验用钢进行了观察和分析。结果表明,75Si2Mn1.5CrB钢经920℃奥氏体化快冷至200℃等温处理后,组织为带有奥氏体薄膜的贝氏体铁素体、马氏体和残留奥氏体。75Si2Mn1.5CrB钢在200℃等温22 h时,其综合力学性能良好。     

Effect of austenitising conditions on the impact properties of an alloyed austempered ductile iron of initially pearlitic matrix structure

This study sets out to investigate the effect of austenitising conditions on the microstructure and impact properties of an austempered ductile iron containing Copper and Nickel and having an initially fully pearlitic structure. Un-notched Izod impact test specimens were solution treated in the range 850–1000 °C for durations between 15 and 360 min. and then austempered at 360 °C for 180 min.

It was shown that increasing the austenitising temperature increases the amount of carbon taken in solution by the original austenite. This reduces the driving force controlling the transformation of the austenite to the ausferrite product, ferrite and austenite. As a result, the retained austenite volume in the final microstructure increases but simultaneously its stability falls. This places an upper limit on the austenitising temperature and the amount of retained austenite permissible. On the other hand, for optimum properties, the austenitising temperature and time must be high and long enough respectively to ensure complete austenitisation.

It was also shown that generally, in irons with an initially pearlitic structure, the impact properties increase steadily to a maximum value as the austenitising time increases to about 180 min. and remain constant as the soaking period extends further. Optimum properties are obtained following austenitising between 850 and 900 °C for durations of 120 to 180 min. and correspond to heat treatment cycles which saturate the initial austenite with carbon.     

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.     

Cr12MoV钢马氏体/贝氏体复相热处理工艺研究

研究了不同等温淬火工艺对Cr12MoV钢性能的影响。结果表明,Cr12MoV钢在1020℃奥氏体化后经280℃×3 h等温淬火,能够得到良好性能的M/B下复相组织,与常规淬火相比,在冲击性能不降低的情况下,耐磨性提高显著,其磨损量下降了56%。     

航空发动机16Ni3CrMoE钢制输出轴的热处理畸变控制

通过对航空发动机16Ni3CrMoE钢制输出轴渗碳淬火后出现轴向长度缩短、内花键畸变的原因进行分析与研究。结果表明,热处理畸变主要影响因素是零件在渗碳、淬火工序中产生的热应力和组织应力的综合作用,渗碳零件表面和心部的成分存在差异,使热处理过程中的应力分布变得更不均匀和复杂。通过改变渗碳装炉方式、降低渗碳冷却速度、静油等温淬火、渗碳前增加稳定化处理等工艺方法,将零件的热处理畸变控制在工艺要求范围内。     

等温淬火白口铸铁的耐磨性研究

在优选化学成分的基础上,研究了等温淬火白口铸铁的力学性能及抗磨性能,并与高涨各铸铁及高锰钢进行比较。结果表明,等温淬火白口铸铁兼有较高的硬度和韧性,是一种经济袂用的抗磨材料。     

非金属夹杂物对等温淬火高硅铸钢力学性能的影响

钢中非金属夹杂物对材料力学性能的影响十分显著。本文利用图像分析技术 ,系统研究了非金属夹杂物对等温淬火高硅铸钢力学性能的影响。试验结果表明 :高硅铸钢的夹杂物主要为Si、Cr、Fe的氧化物 ;夹杂物平均尺寸、夹杂物面积百分数、夹杂物平均间距等参数均影响材料的力学性能 ;夹杂物平均尺寸大于 15μm、夹杂物面积百分数大于1%、夹杂物平均间距小于 2 5μm时 ,就会极大地影响高硅铸钢的抗拉强度和冲击韧性。     

高硅铸钢的强韧化机理

采用X射线衍射，计算了高硅铸钢等温淬火热处理后的贝氏体铁素体含碳量，采用TEM分析了贝氏体铁素体中的错位，研究了贝氏体铁素体板条尺寸与高硅铸钢屈服强度、硬度间的关系。在此基础上分析了高硅铸钢的强化以及韧化机理，高硅铸钢的强化是固溶强化，位错强化和细晶强化综合作用的合理；而高硅铸钢的韧化是存在于贝氏体铁素体板条之间富碳的薄膜状残余奥氏体，细小的贝氏体铁素体板条共同作用的结果。合适的Si含量也是影响高硅铸钢韧性重要因素。