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Improvement of fatigue and stress corrosion properties by surface treatment and microstructure control

通过表面处理和微观结构控制改善疲劳和应力腐蚀性能

基本信息

批准号：
15560077
负责人：
KAWAGOISHI Norio
金额：
$ 1.98万
依托单位：
Kagoshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

1.On improvement of fatigue and stress corrosion properties by microstructure controlRotating bending fatigue tests were carried out to investigate the effects of humidity and reverted austenite on a crack initiation and its propagation of a maraging steel. Many cracks were initiated and intergranular cracks were observed on the fracture surface, when humidity was high. Both of the crack initiation and the early stage of the crack propagation of were accelerated by humidity, especially the effect on the crack initiation was large. However, the effect of humidity was suppressed by the formation of reverted austenite.2.On improvement of fatigue properties by surface treatmentBy nitriding and shot peening, fatigue strength was markedly improved. This was mainly caused by the surface hardening and formation of compressive residual stress in both surface treatments. Under low stress levels, fracture occurred from subsurface, while under high stress levels, fracture occurred from surface. Co … More nsequently, S-N curves had double stage. The effect of nitriding on the fatigue strength depended by nitriding condition. That is, when nitriding was carried out under under-aged condition, the increase in fatigue strength was large, while the increase was small under the over-aged condition.3.On improvement of fatigue properties by combined treatment of microstructure control and shot peeningRotating bending fatigue tests were carried out for a shot peened maraging steel in order to investigate the influence of reverted austenite on the internal fracture. Fracture initiated from an internal inclusion regardless of the formation of reverted austenite in long life region, while fracture occurred from a rough surface of specimen in short life region. Although fatigue strength was decreased when surface fracture occurred, that for an internal fracture was increased conversely by the formation of reverted austenite. Many intergranular cracks generated after the formation of flat facets around an inclusion and then fractured by the growth of a surface crack in case of no reverted austenite, while by the formation of reverted austenite intergranular cracking was suppressed and the growth process of an internal crack presented after intergranular cracking. Consequently, an orbit trace was formed clearly at the boundary between the growth of an internal crack and that of a surface crack. Less

1.通过微观组织控制改善疲劳和应力腐蚀性能通过旋转弯曲疲劳试验，研究了湿度和回复奥氏体对马氏体时效钢裂纹萌生和扩展的影响。当湿度较高时，会引发许多裂纹，并在断口表面观察到晶间裂纹。无论是裂纹萌生还是裂纹扩展的早期阶段，湿度都会加速裂纹萌生，尤其是对裂纹萌生的影响较大。然而，湿度的影响被回复奥氏体的形成所抑制。2.通过表面处理提高疲劳性能通过氮化和喷丸处理，疲劳强度得到显着提高。这主要是由于两种表面处理中的表面硬化和压缩残余应力的形成造成的。在低应力水平下，断裂发生在地下，而在高应力水平下，断裂发生在表面。因此，S-N 曲线具有双阶段。氮化对疲劳强度的影响取决于氮化条件。即在欠时效条件下渗氮时，疲劳强度增加幅度较大，而在过时效条件下，疲劳强度增加幅度较小。3.组织控制与喷丸联合处理改善疲劳性能的研究对喷丸马氏体时效钢进行了旋转弯曲疲劳试验，探讨回复奥氏体对内部断裂的影响。在长寿命区域，无论是否形成回复奥氏体，断裂都是从内部夹杂物开始的，而在短寿命区域，断裂是从试样的粗糙表面开始的。尽管发生表面断裂时疲劳强度会降低，但内部断裂时由于回复奥氏体的形成，疲劳强度反而增加。在没有回复奥氏体的情况下，在夹杂物周围形成扁平面后产生许多晶间裂纹，然后通过表面裂纹的扩展而破裂，而通过回复奥氏体的形成抑制了晶间裂纹，并在晶间裂纹后出现了内部裂纹的扩展过程。结果，在内部裂纹的生长和表面裂纹的生长之间的边界处清晰地形成了轨道痕迹。较少的