Root Cracking Modes in Restraint Cracking Test of High-Strength Steel Based on AE Technique and Fractography

Restraint cracking tests were applied against weldable high-strength steels HT80 and HY110. Shielded metal-arc welding was done in Y-, y- or single bevel groove in the test specimens, and AE linear source location technique along the weld line was started immediately after the welding and continued for 48 h. Cracked surface was studied in detail with SEM after the test. The combination of AE technique and fractography revealed that there is distinct difference in root cracking mode in relation to whether the cracking mainly passed through heat affected zone or weld metal. The root cracking which occurred in the heat affected zone has a tendency to grow along the weld line close to the bottom of weld bead instead of upward toward the surface of weld bead. On the other hand, root cracking which occurred in weld metal has a tendency to grow toward the surface of weld bead due to anisotropy of columnar crystal.9 refs.--AA