摩擦溶接された炭素鋼の衝撃強さの低下原因に関する二,三の検討

抄録

In the other report, tensile, bending, fatigue, and impact strength are tested on S20C and S45C welded by friction welding, and the result is that, under the properly selected welding conditions, they were almost the same as those of base metal except impact strength. Only Charpy impact strength largely descreased. This report is published to make clear the cause of its decrease.
In the case of carbon steel as welded, the causes of its impact strength decrease are commonly considered as the grain growth of structure or the increase of hardness. In the normalized one, however, they have not been finally concluded though they can be supposed to be the faults in welds or to be the fiber structure. Seeing that under the properly selected conditions in the other mechanical tests the strength of welded steel is nearly the same as that of base metal, it is supposed that impact strength decrease was not due to the faults at welds, but has relations with the fiber structure of steel. Some tests are tried on this point.
The result is that, when the test pieces cut off at right angles to the rolling direction of steel plate are welded, and also when those of cast steel are welded, they have the same impact strength as that of base metal after the heat treatment. From this result one can see that decrease of Charpy impact strength in friction welding is due not to the faults in welding, but to the fact that the fiber structure is bended in welding. It being due to the fiber structure bended by the axial pressure on the course of welding, it is impossible to remarkably prevent its decrease by improving welding conditions, and one must be contented with getting only the same strength or so as is gotten in lateral flowing direction of steel.
As for tensile impact strength, it is considered that its change in friction welding due to flowing direction of steel. But as it is so little, the decrease of impact strength in this case is not so remarkable nor worthy to be discussed.