抄録
The impact transition characteristics and fracture behavior were investigated on friction welded joints with structure softened and grain refined with annealing treatments. After manufactured from 0.46%C hot-rolled bar steel, the friction welded joints tested in this study were annealed at 800°C for 60 minutes in a vacuum furnace. The impact specimens were taken from the central portion of bar joint, and a V-notch was given 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 in liquid nitrogen and heating oil. The main results obtained are as follows;
(1) The absorption energy of the annealed joint was in all regions extremely larger than the absorbed energy of the as-welded joint and was restored in the same degree up to the level of the hot-rolled base metal with the exception of the upper shelf energy.
(2) The energy transition temperature was about 27°C in the annealed joint and agreed closely to the temperature estimated from fracture surface. This transition temperature was lower in comparison with those of both the as-welded joint and the hot-rolled base metal.
(3) In the case of the annealed joint in the transition region, the crack propagation resistance was raised more remarkably than that of the as-welded joint.
(4) The impact bending strength, which was calculated by the formula of beam subjected to three-point bending from the maximum impact load obtained in the instrumented tests, increased in the order of the as-welded joint, hot-rolled base metal and annealed joint. They became maximum around -20°C, where 100% brittle fracture occurred.
