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

Abstract

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 250 mm and the propagation life of this region governed the total fatigue life.

Low cycle fatigue behavior and failure mechanism of a dual-phase steel

“…Fatigue short cracks nucleation and propagation have been investigated by Stolarz and Foct [4]. The influence of microstructure morphology on short crack growth behavior has also been investigated by in situ observation [8]. It was found that fatigue crack propagation is sensitive to microstructural morphology.…”

Mechanical Properties, Formability, and Corrosion Behavior of Dual Phase Weathering Steels Developed by an Inter‐Critical Annealing Treatment

“…Dual phase (DP) steels are currently receiving a great importance in automotive industry and weight saving applications, due to their convenient combination of high strength and good formability . The term dual phase implies that the microstructure of DP steels mainly consists of randomly distributed hard martensite islands dispersed in a soft ferrite matrix .…”

Short Fatigue Crack Growth Behaviour in Ferrite–Bainite Dual-phase Steels

“…Behaviour The influence of microstructure on the rate of fatigue crack propagation has been examined by several investigators, 20,[42][43][44] but the co-relation between the segmental lengths of a crack and the specific microstructural feature (different phases/constituents or interfaces) through which it traverses, has been reported only by Ray and his co-workers. 19,23) These investigators have quantitatively examined such co-relation in ferrite-pearlite plain carbon steels and reported that the amount of crack length passing through a microstructural feature is approximately proportional to the volume fraction of the constituent.…”

“…A substantial amount of evidences, well supplemented by a large number of investigations, has been accumulated over the last few decades which unambiguously exhibit faster short crack growth at low stress intensity factor ranges. [17][18][19] Though some reports are available on the fatigue crack growth behaviour of ferrite-martensite dual phase steels, only Nakajima et al 20) have reported their short crack growth behaviour and Hussain et al 21) have attempted modeling this behaviour; but unfortunately no report is available on the fatigue characteristics of short cracks in FBDP steels. Attempt to fulfill this gap is the primary objective of this study.…”