爆炸冲击波压应力处理预防水轮机叶片裂纹的可行性

Probability of Preventing from Runner Bladés Cracking with Compressive Stress Induced by Explosive Shock Waves Treatment

大型混流式水轮机叶片的开裂属疲劳裂纹问题,主要与交变应力过大和残余应力过高有关。研究和应用表明,采用焊后600℃×8h的热处理只能消除少量残余应力,接近屈服强度的剩余拉应力严重降低材料的疲劳性能,加速疲劳裂纹的形成和扩展。在叶片易开裂部位进行压应力处理可大大提高疲劳寿命,爆炸冲击波处理用一次均匀微量塑性变形代替喷丸或锤击的多次不均匀变形实现压应力处理,可以避免表面粗化和微裂纹,其形成的压应力层厚度可提高10倍以上,还能起到治愈缺陷的作用。经爆炸处理的16Mn钢焊接接头疲劳强度提高60MPa,疲劳裂纹扩展速率降低10倍。在已获得的100多件大型水工结构爆炸处理满意结果的基础上,此法用于水轮机叶片的压应力处理,提高其疲劳寿命是完全可行的。

The cracking of large Francis turbine runner blades is mainly produced from fatigue process,which is related with great alternate stresses through forceful vibration and high value tensile residual stresses from the manufacturing processes.The research and application results show that the high values of residual stresses still remain after post-welded heat treatment with the process of 600℃×8h.The tensile residual stresses approaching to material＇s yield strength deteriorate greatly the fatigue properties of components;promote the formation and growth of fatigue cracks.The compressive stress treatment on the runner blades easy to cracking may increase obviously the fatigue life.Comparing with the traditional industrial peening technique,the explosive shock waves treatment not only may produce compressive stresses,but also improve the fatigue properties of materials themselves,cure the defects,avoid the surface coursing and microcracks.For 16 Mn low-alloy steel,the fatigue strength can be increased by 60 MPa,the fatigue crack growth rate reduced 10 times.On the base of over 100 components treated acceptably with explosive shock weaves,it should be probable for increasing the fatigue life of runner blades with the compressive stress treatment.