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

1.通过组织控制改善马氏体时效钢的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，断口上出现大量裂纹和沿晶裂纹。湿度对裂纹的萌生和裂纹的早期扩展都有促进作用，特别是对裂纹的萌生影响较大。2.表面处理对疲劳性能的改善经氮化和喷丸处理后，疲劳强度显著提高。这主要是由于两种表面处理的表面硬化和残余压应力的形成造成的。在低应力水平下，破裂发生在地下，而在高应力水平下，破裂发生在地表。Co ...更多信息 结果表明，S-N曲线呈双阶段性。渗氮对疲劳强度的影响取决于渗氮条件。即在欠时效状态下进行渗氮处理，疲劳强度提高幅度较大，而在过时效状态下，疲劳强度提高幅度较小。3.喷丸强化与组织控制相结合提高疲劳性能对一种马氏体时效钢进行了旋转弯曲疲劳试验，研究了回复奥氏体对喷丸强化后马氏体时效钢内部断裂的影响。在长寿命区，断裂起源于内部夹杂物，而与回复奥氏体的形成无关，而在短寿命区，断裂起源于试样的粗糙表面。虽然疲劳强度下降时，表面断裂发生，而内部断裂的增加，相反，通过形成回复奥氏体。在没有回复奥氏体的情况下，夹杂物周围形成扁平小平面后产生许多沿晶裂纹，然后通过表面裂纹的扩展而断裂，而回复奥氏体的形成抑制了沿晶裂纹的扩展，并在沿晶裂纹之后出现内部裂纹的扩展过程。因此，在内部裂纹和表面裂纹的扩展之间的边界处形成了清晰的轨道轨迹。少

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