关键词: 焊接接头;超高周疲劳;裂纹萌生;气孔;夹杂物

Abstract: Conventional fatigue test is conducted in 25Cr2Ni2MoV steel welded joint specimen at room temperature. The fatigue failure mechanism in welded joint is investigated by fatigue test and microscopic analyses. Results show that the stress-fatigue life relationship presented a stepwise shape. In high cycle fatigue(HCF) regime, base metal is preferential fracture sites, which are originated at surface or subsurface inclusions. Whereas in the very high cycle fatigue(VHCF) regime, fatigue cracks are always initiated at pores in the weld metal. The fatigue life will be longer in the condition of small surface defect size or interior defect as fatigue crack initiation. Small surface defect with large interior defect has similar potential for crack initiation. Stress distribution of fatigue specimen at micro-defects are performed by finite element analyses, and it shows that the stress concentration around pore and inclusion in the weld metal are larger than inclusion in base metal. It is found that large quantities of granular particles disperse inclusions in base metal will form bigger defects and these defects are easier to initial fatigue crack than inclusions in the weld metal.

Key words: welded joint;very high cycle fatigue;crack initiation;pore;inclusion