Abstract
The purpose of this study is to clarify the effect of homogenization heat treatment on HAZ cracking susceptibility of cast alloy 718. Homogenization heat treatment was conducted at 1368 K and 1378 K with varying holding time. HAZ cracking susceptibility was evaluated using Longitudinal -Varestraint test at three different strain levels. The test results showed that the number and length of cracks decreased by homogenization heat treatment. HAZ cracking susceptibility was found to be most improved at the heat treatment condition of 1378 K×10.8 ks. According to the isothermal liqaution test, grain boundary liquation was suppressed in heat treated samples. Microscopic observation indicated that the number and size of Laves cluster on the grain boundary decreased by homogenization heat treatment. On the basis of these results, the improvement of HAZ cracking susceptibility by homogenization heat treatment was considered to be attributed to mainly the reduction of Laves cluster on the grain boundary.
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