Effect of Tensile Axis on .ALPHA.' Martensitic Formation of SUS304 Stainless Steel Single Crystals

We have studied the effect of tensile axis on strain induced martensitic formation in SUS304 steel. Single crystal specimens having various tensile axes were deformed by the Instron type testing machine at 293 K. After deformation, quantitative analysis of alpha ' martensite formed in specimens were carried out by using a newly developed apparatus. This apparatus estimates an amount of a martensite with measuring the magnetic force between a specimen and a permanent magnet, of which force was calibrated by standard samples. The formation of alpha ' martensite appeared to be classified into 3 groups. In case of < 001 > specimen, no martensite was found without necking down part. In < 111 > specimen, relatively small amount of martensite formation was found. In specimen with the other tensile axes, large amount of martensite was formed. This classification agrees with previously reported hydrogen induced fracture.