Process of Contraction During First-Pass Welding and Cooling (Part 1)

Theoretical analysis of contraction process by welding heat flow

Abstract

As a part of the research project on weld cracking of mild and high strength steels under hindered contraction, analytical attack was undertaken on the contraction process of weld joint during first-pass welding and cooling. Considerations on the heat flow in first-pass welding of heavy, steel plate show that contraction during cooling is proceeded by both weld metal contraction and decrease in thermal, expansion of mother plates. The latter is rather predominate. Contraction as the results of the decrease in thermal expansion of mother plate consists of two parts. The one is as the results of the decrease in temperature difference along thickness direction, and it is increased with increase of plate thickness (h). The other is as the results of overall heat loss from a part of the plate in a gauge length (l) over which contraction is measured. It is increased with decrease of heat capacity or thickness of plate, and is delayed with increase of gauge length even for a given thickness. As the results contraction is proceeded with different process as affected by thickness and gauge length. Some examples calculated for a usual arc-welding condition of mild steel are shown in Figs. 9, 10, 13 and 14.