Effect of Repair Welding on Mechanical and Microstructural Behaviors of Heat Affected Zone in HY100 Steels

The mechanical properties and microstructural behaviors of multiple–repaired welds were investigated in the heat affected zone (HAZ) of HY100 steels. Test coupons were prepared from flux cored arc welds at the same location of weldments that had been repaired one, three and five times. The multiple–repaired welding caused continuous high temperature reheating of the HAZ. The effects of multiple–repaired welding to the HAZ on the fine–grained heat affected zone were investigated with respect to hardness, tensile strength and toughness. The peak temperature and cooling rate were obtained with quasi-stationary temperature distribution according to the modified Rosenthal equation. The prior austenite grains (PAG) that had been repeatedly reheated above AC3 temperature were observed to have recrystallization and grain growth, and the distributed precipitates were identified as M3C and M23C6. Martensite–austenite constituents were identified through EBSD and TEM analyses to have a measured fraction of less than 2%. The PAG size (PAGS) of the original weld and the weld repaired one time were ~3 μm, while those that had been repaired three and five times were ~6 μm. The grain size strengthening and precipitation strengthening were calculated to be 294 MPa, 265 MPa, respectively, for the one time repaired and 220 MPa, 297 MPa for the five times repaired, respectively, for a total difference of 42 MPa. The welds repaired five times exhibited reasonable strength and impact toughness with insignificant variation in their microstructural behaviors.