1990 年 41 巻 1 号 p. 62-66
Charpy impact tests were carried out in accordance with an experimental design on high-strength low alloy rolled structural steel with a grade of 785MPa, and on high-strength bolt steels with a grade of between 785 and 1177MPa such as low carbon boron steel. The following results were obtained.
(1) For the structural steel, impact values were not affected by the galvanizing conditions, but the impact values of the galvanized steel, under the restraint of plastic deformation by the cδ1 layer, which was harder than the steel, became lower by about 10 to 12% at the upper transition temperature curves.
(2) For bolt steels, when the hardness of the steel was less than the cδ1 layer, galvanizing decreased the impact values of the steels at room. For galvanized SNCM steel, these value decreased by about 12% after shot blasting and 20% after acid pickling. The decrease for galvanized LCB steel was about 9%. When, on the other hand, the steel was harder than the cδ1 layer, these effects were not observed.
The above results indicate that when the cδ1 layer is harder than the steel, impact values decrease under the restraint of plastic deformation by the cδ1 layer.