Fatigue crack growth behavior of the simulated HAZ of 800MPa grade high-performance steel

▶ Fatigue crack resistances of HSB800 base steel and HAZs: Base steel>FGHAZ>CGHAZ>ICCGHAZ. ▶ In the case of ICCGHAZ, fatigue cracks are rapidly initiated and propagated through massive M–A constituents. ▶ Fatigue crack growth rate of CGHAZ was faster than that of FGHAZ, mainly due to the coarsened prior austenite grain and martensite packet. The present study focuses on the fatigue properties in the weld heat-affected zone (HAZ) of 800MPa grade high-performance steel, which is commonly used in bridges and buildings. Single- and multi-pass HAZs were simulated by the Gleeble system. Fatigue properties were estimated using a crack propagation test under a 0.3 stress ratio and 0.1 load frequencies. The microstructures and fracture surfaces were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results of the crack propagation test showed that the fatigue crack growth rate of coarse-grained HAZ (CGHAZ) was faster than fine-grained HAZ (FGHAZ), although both regions have identical fully martensite microstructures, because FGHAZ has smaller prior austenite grain and martensite packet sizes, which can act as effective barriers to crack propagation. The fatigue crack growth rate of intercritically reheated CGHAZ (ICCGHAZ) was the fastest among local zones in the HAZ, due to rapid crack initiation and propagation via the massive martensite–austenite (M–A) constituent.