Study On Welding Residual Stress Relieving Of Cast Iron By Hammer Peening

Peening is a very effective method to eliminate the welding stress and has its unique advantages. In this paper, the welding stress value in different locations around the workpiece was measured by hole-drilled method before and after the weld was peened, the effect of peening parameters on welding stress was investigated, Optical microscope, the microstructural of peening before and after workpiece was observed with optical microscope, through the experiment emphasize analyzed the influence of peening force and peening temperature on microhardness of Cast Iron, the mechanism of release of welding stress by peening was also discussed.In order to do peening experiment better, the subject design the electromagnetic hammer fixture based on predecessor's research foundation, this fixture has suitable stiffness.and strength, and also realize the accurate positioning.Drawing the below conclusion through the peening experiment:(1) Peening treatment is a kind of very good method to reduce welding stress, the residual stress was reduced obviously after peening, the peak of reducing value is in the welding seam, more far from welding seam, more small of reducing value of stress.(2) With the increasing of peening force, the reduced amplitude of residual stress become large, but the speed will be more and more slowly. (3) When the weld was peened at high temperature, its plastic deformation was greater, so the release of residual stress was better. When the weld was peened at low temperature, plastic of the weld was poorer, and crack was easily formed. Increasing peening frequency and peening time, the deformation of weld was great, It was better to the release of residual stress. (4) Grain was refined in the area of weld seam after peening, plastic deformation occurred and hardness increased near the surface of the peened weld.Peening is able to eliminate the welding stress of Cast Iron, because radial prolongation occurred in the weld after peening, this could counteract residual elastic deformation, so the residual stresses reduced.