INFLUENCE OF SHOT-PEENING -INDUCED RESIDUAL STRESSES ON POST-NECKING BEHAVIOR OF TEMPERED ULTRAHIGH-STRENGTH LOW ALLOY 300M STEEL

The effect of the tempering temperature and shot peening time on the uniaxial post-necking behavior of 300M steel (silicon-modified AISI 4340 steel) was experimentally investigated in this study. Normalized specimens were divided into two groups: one tempered at 280 degrees C and the other tempered at 302 degrees C. The specimens were shot-peened for various durations to study the effect of the shot peening time on their mechanical properties. Experimental results showed that the shot-peening induced compressive residual stress in the specimens tempered at 302 degrees C was greater than that in the specimens tempered at 280 degrees C, and the optimum compressive residual stress was obtained by shot peening for 5 min. Although the tempering temperature and shot peening time did not influence the yield and ultimate strengths, the total and post-necking elongations of the specimens decreased with the shot peening time. The necking behavior in the specimens tempered at 302 degrees C was more apparent than that in the specimens tempered at 280 degrees C. In this paper, the influence of the shot peening time on the post necking behavior is elucidated on the basis of work hardening resulting from shot peening, and the effect of the tempering temperature on the necking behavior is interpreted in terms of the presence of residual stress.