Influence of Second Phase Particle on Fatigue Crack Growth Behavior in Ferrite Matrix Steels

Abstract

Fatigue crack growth tests of two ferrite-pearlite and two ferrite-bainite steels with different size and spacing of particle, where pearlite/bainite (hard) particles were uniformly distributed in the ferrite matrix, were carried out to investigate effect of second phase particle on fatigue crack growth behavior in Paris regime. The fatigue crack growth curves for the four materials did not coincide each other, even when the crack growth curves were arranged by the effective stress intensity factor range. From the in-situ observations, crack tip stress shielding phenomena, such as interlocking, branching, etc were found on the crack wake, which enhanced fatigue crack growth resistance. Small size and spacing of pearlite/bainite particle seemed to induce small but frequent crack deflections, which resulted in crack closure phenomena. On the other hand, large size of pearlite/bainite particle seemed to induce stress shielding phenomena and then contribute to high crack growth resistance, which was the main reason for lower fatigue crack growth rate of the large size and spacing of hard particle compared the small size of hard particle.

Effect of Hardness of Second Phase Particle on Fatigue Crack Growth Behavior of Steels with Hard Second Phase Particle in Soft Ferrite Matrix

“…3(b), which would result from hardness of martensite particle in FM. Figures crack path and crack growth rates for FP and FB steels were displayed and described in previous work [9].…”

“…FCG tests at ∆K-constant in Paris regime was mentioned in the previous work [9] . Also was explained the measurement and determining the crack closure were indicated.…”