Acta Metallurgica Sinica (English Letters) ›› 1992, Vol. 5 ›› Issue (5): 385-389.

• Research paper • Previous Articles     Next Articles

MICROFRACTOGRAPHY OF NEAR-THRESHOLD FATIGUE CRACK PROPAGATION IN DUAL-PHASE STEELS

ZHENG Yesha WANG Zhongguang AI Suhua State Key Laboratory of Fatigue and Fracture for Materials,Institute of Metal Research,Academia Sinica,Shenyang,110015,China   

  • Received:1992-10-25 Revised:1992-10-25 Online:1992-10-25 Published:2009-10-10

Abstract: SEM microfractography of near-threshold fatigue crack propagation were carried out in the dual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m). All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main- ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character- ized by mixed modes including cyclic cleavage facets,two types of secondary cracks and striations,etc..The roughness-induced crack closure of fracture surface is attributed primarily to extreme high fatigue crack growth threshold values.

Key words: dual-phase steel, threshold value, fatigue crack growth, fractograph, near-threshold