Study on Cooling Characteristic and Hardness in Locally Drying Under water Weld of Mild Steel and 50kgf/mm₂ H.T. Steel

Abstract

Authors have developed a new automatic welding system called "Locally Drying Underwater Welding" based on unique locallized dry environment by fluid curtain. For applying this process to steel structures, we have studied the cooling characteristic of this underwater weld to estimate the quality of a underwater welding joint.
The main conclusions obtained in this study are summerized as follows.
1. In case of high current and high speed welding, an underwater weld was quenched by water surrounding the welding torch.
But in case of low current and low speed welding, cooling characteristic was similar to that of an air weld.
2. In this method, the dependence of the maximum hardness of an underwater weld on the welding speed and heat input differed from that of an air weld. But the maximum hardness has good correspondence with cooling time from 800°C to 300°C.
3. Heat flow of underwater weld was investigated theoretically as the problem of heat conduction and heat transfer from an instantaneous plane heat source and results of experiments were explained clearly by this theory.