軟鋼板の高速引張試験における流動応力と転位組織に及ぼすひずみ時効の影響

抄録

Dynamic behaviors of ultra-low-carbon mild steels were experimentally examined in order to clarify the contribution of the pure ferrite phase on the strain rate sensitivities. In the experiments, two types of mild steels, namely type A steel with no solute carbon in which whole carbon was scavenged as titanium carbide and type B steel with interstitial solute carbon which causes the increase in yield strength due to the strain aging were employed, and dynamic tensile tests were performed on these steels before and after strain aging to clarify the influence of the strain aging on the strain rate sensitivity by comparing the mechanical behaviors of both steels. From the experimental results, strain aging seemed to increase flow stress, however its amount was getting smaller with increasing strain rate. Furthermore, from the TEM observation, it was found that static deformation formed the dislocation cell structure, on the other hand, the dynamic deformation did not. In the case of strain aged type B steel, however, the weak cell structure was observed after dynamic deformation. It seemed to consist of the immobile dislocations which were pinned with carbon atoms by strain aging. In the case of type A steel, any difference in dislocation structure due to the strain aging effect was not observed. In order to express the mechanical behavior of Type A and B steels, the Tanimura-Mimura model was employed, and it was found that by simply taking into account the increase in quasi-static flow stress due to strain aging, flow stresses of both steels during subsequent dynamic loading were successfully described.