Effect of Heat Input on Cleavage Crack Initiation of Simulated Coarse Grain Heat-affected Zone in Microalloyed Offshore Platform Steel

The combined effects of martensite-austenite (MA) constituent and pearlite colony on cleavage crack initiation in the simulated coarse-grained heat-affected zone (CGHAZ) of V-N-Ti microalloyed offshore platform steel under different heat inputs were investigated. The results of welding simulation, instrumented impact test, and quantitative analysis indicated that the size of the MA constituent decreased with the increase in cooling time, and by contrast, the size of the pearlite colony increased. According to Griffith theory, the critical sizes of cleavage microcracks were calculated. With the increase of cooling time, the calculated microcrack size could be characterized by the size of the MA constituent first, and then fitted with the size of the pearlite colony. Moreover, the calculated microcrack size variation was opposite to the microcrack initiation energy. This phenomenon is probably due to the combined effects of the MA constituent and pearlite colony with increasing the cooling time of the specimen's temperature from 800 to 500 degrees C.