Influence of Normalization on Impact Fracture Behavior of Friction-Welded Joints. Examination with 0.46%C Carbon Steel.

Abstract

The impact transition characteristics and fracture behavior were investigated in friction-welded joints with softened structure and grain refinement by normalization treatment. After manufacture using 0.46%C hot-rolled bar steel, friction-welded joints tested in this study were kept at 850°C for 1 h in a vacuum furnace and then cooled with N2 gas. The impact specimens were machined from the central portion of the bar joint, and a V-notch was made along the weld interface of the joint. The impact tests were carried out at various temperatures using the instrumented Charpy impact machine. The testing temperature was controlled using liquid nitrogen and heating oil. The main results obtained are as follows. (1)The absorption energy of the normalized joint was very much larger in all regions than the absorbed energy of the as-welded joint and was restored to the same level as that of the hot-rolled base metal, with the exception of the upper shelf energy. (2)The energy transition temperature was about 24°C in the normalized joint, which agreed closely with the temperature estimated from the fracture surface. These transition temperatures were lower in comparison to those of both the as-welded joint and the hot-rolled base metal. (3)In the case of the normalized joint in the transition region, the crack propagation resistance was more markedly increased than that of the as-welded joint. (4)The impact bending strength of the normalized joint after friction welding was almost equal to that of the hot-rolled base metal. The value, however, was somewhat lower than that of the as-welded joint.