Effect of Steplike Plastic Deformation on the Mechanical Properties and the Fracture of the Bimetal Produced by Exposition Welding

The mechanical properties and the structure of the 08Kh18N10T steel/grade 10 steel bimetallic welded joint formed by explosion welding after step-by-step rolling at a reduction of ~10% per pass are studied. There is a zone of increased microhardness ~0.4 mm wide in the bimetallic weld region. An increase in the number of rolling passes decreases the width of this zone and the wave relief of the weld. First rolling passes result in nonuniform deformation of the bimetallic layers. Grade 10 steel, whose deformation resistance is lower in the initial state than that of the 08Kh18N10T steel, experiences the greatest deformation. Both bimetal layers deform uniformly during strain hardening the grade 10 steel. The mechanical properties of the bimetal, grade 10 steel, and 08Kh18N10T steel after the same plastic deformation are compared. The bimetal in the initial state has greater strength than its individual components. However, the 08Kh18N10T steel is hardened during rolling more intensely than the bimetal due to the formation of strain-induced martensite; therefore, the strength of the 08Kh18N10T steel significantly exceeds the strength of the bimetal as a whole at a total reduction of ~20% or higher. The initial stage of fracture along the bimetallic weld during rolling is shown to be associated with shear of the layers due to more intense spreading of the grade 10 steel layer. The curvature of the side surface of the bimetal strip increases as the strain increases, which generates tensile stresses in the direction of the strip height. This fact and the rolling-induced tensile longitudinal stresses result in a network of cracks in the bimetal layers along the maximum shears.