Evolution of Residual Stress and Microstructure during Annealing of 30SiMn2MoVA High-Strength Alloy Steel Tube Processed by Cold Radial Forging

30SiMn2MoVA is a high-strength alloy steel used for barrels. Cold radial forging can greatly improve the performance of axles, barrels and other shaft parts. However, residual stresses will greatly affect the dimensional stability and service life of the products. This work focused on the effects of different annealing temperatures on the residual stress, microhardness, dislocation density, grain boundary and grain size of radial forged tubes. The results show that the residual stresses are gradually eliminated with the deformed grains transform into equiaxed and the reduction in dislocation density. The residual stress relaxation caused by the creep process conforms to the Zener-Wert-Avrami equation. As the dislocation density and low-angle grain boundary decrease, the microhardness also decreases gradually. The best annealing temperature for radial forged 30SiMn2MoVA high-strength steel tube is 500 °C. After annealing at 500 °C, the microhardness decreases by 5%, the axial and hoop residual stress on the outer surface are close to 0 MPa, and the residual stress near the inner surface are less than 200 MPa. When the annealing temperature is higher than 500 °C, there is no significant change in residual stress relaxation rate. Nevertheless, the grain size and the low angle boundary decreased significantly. Partial recrystallization occurred, and the microhardness decreased by more than 10%.