Abnormail Grain Growth Properties of Steel Material with a Complex Strain History

When steel is heated to high temperatures, abnormal grain growth occurs in which the prior austenite grain size locally increases. When abnormal grain growth occurs, the strength of the metal, especially the toughness value, decreases. For this reason, it is important to heat and heat treat steel materials under a process design that prevents abnormal grain growth. Previous research has shown that crystal grains become coarser when strain, especially shear strain, is applied to a material. On the other hand, in actually manufactured parts, a large amount of strain applied in the pre-heat treatment process does not necessarily result in a larger grain size. In this study, we confirmed that not only the maximum strain but also the strain history that the material has followed acts on dislocations inside the material, and that coarse grains grow from these as starting points. This confirmed that the strain history in the previous process affected the prior austenite grain size in the finished product.