Estimation of the Cooling Time t8/5 and Thermal Factor of Weldments with Local Preheating.

Abstract

Preheating is performed to prevent cold cracking in steel constructions. Preheating produces a good effect on cooling times, which are t8/5 (cooling time from 800°C to 500°C) related to the maximum hardness at HAZ, or which are t200, t150, t100 (tθ : cooling time from the solidification to θ) connected with the thermal factor. In the welding field, a whole member can not be preheated uniformly, and then local preheating near the weld line is generally performed.This report deals with local preheating and welding procedures of a butt joint and a corner joint. Predicted values of cooling times have been compared with the experimental data. The predicted values have been obtained by theoretical formulae. The results are summarized as follows :(1) Relation between cooling time and thermal factor, (ΣD·Δt)100 has been investigated. The thermal factor is correlated most closely with cooling time t150.(2) The predicted values of cooling time t8/5 and thermal factor (ΣD·Δt)100 have given good agreement with the experimental values.