CHANGES IN MECHANICAL CHARACTERISTICS DURING THE STRAIN-AGING OF WIRE ROD MADE OF STEEL Sv-08G2S

摘要

The Moldavian Metallurgical Plant has made a study of dynamic strain aging by subjecting specimens of wire rod made of steel Sv-08G2S to tension. Some of the steel had been microalloyed with boron, while another portion was made without this element. A stable reduction in strength properties was seen nearly throughout this range (the only exceptions were the increases in σ_u and Δσ_u in the boron-free wire rod for a test temperature of 350°C). There were some differences in the temperature dependences of ψ of steel Sv-08G2S made with and without boron. For the boron-bearing steel, the high values of ψ (77-80%) in the temperature range 200-450°C - the range that poses the greatest danger from the standpoint of reducing process ductility in drawing - in fact give the rod excellent ductility for deformation. Relatively low values of ψ are seen for the boron-free steel in the range 200-450°C. Wire rod made of steel Sv-08G2S (with or without boron) is characterized by a multiphase structure, and its matrix contains not only polygonal ferrite grains but also evenly distributed colonies of pearlite, bainite, and martensite. The stable decrease in strength properties at 100-150°C is connected with redistribution of the stresses between the structural components of the steel. Additional studies will be needed to explain the relatively stable level of ψ of boron-bearing steel Sv-08G2S wire rod in the range 200-450°C.