Abstract
A high strength chain is manufactured by bending steel bars, flash welding and subsequent heat treatment. The welded zone is generally softer than the base steel. The cause of the softening is clarified in the present report. The method for reducing the softening and improving Charpy impact value of the weld is investigated.
1) The softening takes place because the amounts of C, Mn, Ni, and Cr reduce during welding and consequently the hardenability of the welded zone decreases.
2) When a chain is heat-treated at low austenitizing temperatures, the softening of the welded zone is remarkable.
3) The hardness of the welded zone increases with raising the austenitizing temperature. At 1 050°C of austenitizing temperature the softening is not recognized. This is because the hardnability increases owing to the recovery of carbon concentration by diffusion and the austenite grain growth.
4) The impact value of the welded zone is low when the softening of the welded zone is large. Therefore, it improves with increasing the austenitizing temperature up to 1 000°C, above which the grain growth prevents the improvement of the impact value.
