抄録
The grain growth of austenite in a heat-affected-zone (HAZ) has been generally described by the following equation, Dn-D0n=k0t exp(-Q/RT), where D is average grain diameter, D0 is initial grain size, n and k0 are material constants, t is annealing time, Q is experimental activation energy for grain growth, R is gas constant, and T is absolute temperature.
The above material constants are obtained by the isothermal annealing experiment on heating processes, but thermal cycle of welding is composed of heating and cooling process. Therefore, it is necessary to consider the grain growth in cooling process.
In this paper, the material constants in heating and cooling processes were examined by isothermal annealing experiment, respectively. Then, the grain growth in the HAZ was separated into heating and cooling processes, and the relation between grain growth and welded thermal cycle were examined.
Main conclusions obtained in this report are summarized as follows;
(1) The difference of grain growth between heating and cooling processes in the HAZ did not show. The material constants obtained,
(a)In the case of n=2
k0=2.408×104mm2/s, Q=51100cal/g·atom
(b)In the case of n=4
k0=2.208×108mm4/s, Q=89200cal/g·atom
(2)The average grain size in the HAZ could be estimated by using n=2 and material constants of (1).
