In forging, die life is often a problem in mass production. Particularly in the hot forging of steel, die life is short owing to galling, wear, and heat cracks. In hot forging, the friction between a material and dies strongly affects the die life. We proposed a new friction test method in the previous report. The method applies a developed die set with a rotating die in the ring compression test. With a combination of the measured load and torque, friction coefficients can be monitored throughout the measurement process. In this study, friction coefficients were measured using four types of hot forging lubricant. The results revealed that the lubricant performance for hot forging is strongly affected by the initial billet temperature, die surface temperature, lubricant combustion temperature, and thickness of the oxide film of the billet surface.

Shot peening is applied to shafts and pipes to improve fatigue strength. In this study, the peening intensity and residual stress distributions on the cylindrical surface were investigated for shot peening. When fixing the cylinder, the peening intensity varied depending on the position of the cylinder, because the collision angle γ between the cylindrical surface and the shot was greatly affected by the position. The function approximation method for estimating the peening intensity distribution was studied. The peening intensity was proportional to sin γ, and the modified Gaussian distribution approximated the peening intensity on the cylindrical surface. The residual stress distribution on the surface was different from the peening intensity distribution, and the compressive residual stress was highest when the central angle α was around 45°. The maximum compressive stress was on the surface when αwas 45° and inside the cylinder when α was 0°. The rotation angle with uniform intensity was determined by the approximation method. When the cylinder was rotated at that angle, the compressive residual stress distribution on the cylinder surface became uniform. However, it was noted that the cylindrical surface had a history of peening at different collision angles γ.