The effects of robot welding and manual welding on the low- and high-cycle fatigue lives of SM50A carbon steel weld zones

摘要

The purpose of this study is to analyze the differences between the effects of robot welding and manual welding on the low- and high-cycle fatigue lives of the weld zones for T-shaped weld structures fabricated from SM50A carbon steel using a CO 2 gas arc welding method. Fatigue tests were conducted using a three-point bending method, and the S-N curves of the manual welding and robot welding crossed each other at approximately 3 × 10 4 cycles. The robot welding weld zone had better high-cycle fatigue lives than the manual welding. The results are attributable to the fact that the more uniform and higher welding speed of the robot welding leads to smaller weld zone area (i.e. ~12% smaller than the manual welding) and also smaller grain size than the manual welding. Because a smaller grain size in the robot welding weld zone results in a higher hardness than the manual welding and material brittleness increases with increasing hardness, the robot welding weld zone shows better high-cycle fatigue lives but poorer low-cycle fatigue lives than the manual welding.