A Study on Hot Cracking by a Synthetic Test for Weld Thermal Cycle

Using a new apparatus which can restrict the expansion and contraction of a synthetic specimen at an arbitrary temperature during thermal cycles, the hot cracking tendency of weld HAZ was examined on three high strength steels. The main results are summarized as follows: (1) In a test steel Z(HY-130 class), hot cracks occurred in the condition that a synthetic specimen was heated to above 1, 350°C and was restrained within the temperature range of 1, 350 to 1, 380°C. (2) Hot cracks were found in grain boundaries extremely coarsened by weld thermal cycles, which showed mostly white, relatively broad networks, so-called "heavy boundaries". (3) By an electon-probe microanalysis, an enrichment with many elements was observed such as Ni, Cr, Si and P, and Mn and S locally on heavy boundaries.