Influence of Microstructural Morphology and Prestraining on Short Fatigue Crack Propagation in Dual-phase Steels

• Published in: ISIJ International Vol. 41; no. 3; pp. 298 - 305
• Main Authors: Nakajima, Katsumi, Urabe, Toshiaki, Hosoya, Yoshihiro, Kamiishi, Susumu, Miyata, Takashi, Takeda, Nobuo
• Format: Journal Article
• Language: English
• Published: Tokyo The Iron and Steel Institute of Japan 01.01.2001; Iron and Steel Institute of Japan
• Subjects: Applied sciences; crack closure; crack initiation; crack propagation; Cross-disciplinary physics: materials science; rheology; dual phase steel; Exact sciences and technology; fatigue; Fatigue, corrosion fatigue, embrittlement, cracking, fracture and failure; Fatigue, embrittlement, and fracture; heat treatment; in-situ observation; Materials science; Metals. Metallurgy; microstructural morphology; Physics; prestraining; short crack; Treatment of materials and its effects on microstructure and properties; Crack formation; Fracture mechanics; Predeformation; Carbon steels; Mechanical properties; Experimental study; Heat treatments; Crack propagation; Crack opening displacement; Morphology; Dual-phase steels; Crack length; Property structure relationship; Steels; Microstructure; Fatigue cracks
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.41.298

The ferrite–martensite dual phase (DP) steels offer a better combination of strength and ductility than other conventional steels with equivalent static strength which are generally used in the automobile industry. The continuous martensite phase in DP steels seems to play an important role in determining fatigue properties and be a key factor to gain a higher resistance to fatigue. Additionally it is very important from a practical point of view to improve the fatigue properties after prestraining or cold working. The effects of microstructural morphology and prestraining on the propagation behavior of short fatigue cracks in DP steels were investigated by the in-situ observation in a scanning electron microscope. The material with martensites continuously surrounding individual ferrites exhibited a higher fatigue strength and longer fatigue life than those of the material with martensite phase dispersed in the ferrite matrix. Cold rolling prior to fatigue testing resulted in a decrease of fatigue life for both materials, especially an extreme decrease for the martensite-dispersed material. It was found that the fatigue crack propagation was sensitive to microstructural morphology and prestraining only in the small crack within a range of approximately 250μm and the propagation life of this region governed the total fatigue life.