Types Of High-strength Steels Research Articles

Vanadium/Nitrogen Modification of 1% Cr and Cr-Cb Rail Steels

Abstract The composition of two commercial rail steels (1% Cr and Cr-Cb) were modified by addition of vanadium and nitrogen. The microstructures and mechanical properties of the steels were determined. The results indicate that addition of 0.1% vanadium to the base compositions offers potential for a cost effective increase of YS at “normal” nitrogen contents, providing the tensile ductility, we1dability, and fracture toughness at − 50°C are proven acceptable by testing as-rolled rail sections. The results are compared with those for other types of high-strength steels intended for wear-resistant rail.Laboratory heats of the two base compositions were prepared with vanadium contents of 0.1 and 0.2 %, and a vanadium:nitrogen ratio of 10:1.Ingots were forged to 64 × 64 × 1200mm billets and were cooled at a rate that simulated commercial practice [1].The 0.1% vanadium addition increased the yield strength of both types of steel to 830MPa and increased the hardness to Rc 38 (from Rc 34). There was a correspon...

Physical Metallurgy of Automotive High-Strength Steels

This paper briefly reviews the various available types of high-strength steels — conventional, recovery-annealed, and dual-phase steels. A judgmental analysis of a large number of stamped automotive components shows that dual-phase steels, with their superior strength at a given elongation (formability), offer the best potential for weight savings. The rest of the paper concerns the physical metallurgy and mechanical response of dual-phase steels. It is shown that strength is a function of the percent martensite in the structure, although the strength is less than predicted by a simple rule of mixtures. The enhanced ductility of dual-phase steels is shown to be a consequence of the high s train-hardening rate observed in these steels, the reason for which is not well understood but probably reflects the properties of the ferrite matrix. The strain-rate sensitivity of dual-phase steels is found to be higher than that of conventional high-strength steels of comparable tensile strengths. Fatigue studies of dual-phase steels show them to be comparable to conventional high-strength steels in the notched condition; energy absorption during the axial collapse of tubes is shown to be solely a function of tensile strength. Also included are data on the temperature dependence of tensile strength in both the notched and unnotched conditions; high-strength dual-phase steels exhibit notch sensitivity even at room temperature. A study of formability (springback) shows that high-strength dual-phase steel is slightly worse than SAE 950X but much better than SAE 980X steel.