構造用高張力鋼（５０，６０および８０キロ級）の電子ビーム溶接性に関する研究 Ｉ 衝撃特性におよぼす溶接入熱の影響

Abstract

In this investigation, the authors aimed to make clear the weldability of electron-beam welds for some commercial constructional high tension steels. Then, the influences of weld heat input on the. weld defects, hardness distributions and impact properties of the electron-beam welds were investigated in this report. The meterials used were three grades of high tension steel as HT-50, HT-60 and HT-80 with 25 mm thick-ness. The conventional low voltage type-electron-beam welder, 30 KV-500 mA (15 KW) in maximum was employed in this experiment. All of the weld bead were performed with bead-on-plate type welding. The active beam parameter, ab adopted was 1.0.The remarkable conclusions are as follows:(1)All of the welds except unstable beads have had no defect according to dye penetrant and X-ray inspections.(2)The hardness in weld metal was generally reduced with an increase of the weld heat input. In Vickers hardness distributions of HT:50 and 60 steels, the hardness in the HAZ near fusion boundary was harder than that in the weld metal. This is considered due to the vaporization of Mn element in weld metal.(3)The value of impact strength for the weld metal usually showed the two levels even at the same testing temperature due to the difference in the form of the fracture path in impact test specimen. Namely, when the fracture occurred straightly along the notched direction, the absorbed energy showed the low value, however, when the fracture occurred out of the notched direction, it showed the high value.(4)The testing temperature, at which the form of fracture path differs, tended to be raised with an increase of the weld heat input. This seemed to be related with the bead width or the hardness difference between base and weld metal.(5)As far as the fracture propagates along the notched direction, there is little variation in the absorbed energies of weld metal for respective material within a limit changed for the weld heat input from 10 KJ/cm through 40 KJ/cm.(6)In case of the welds of HT-50 and 80 steels, the absorbed energies of the weld metal, which show lower value than that of the base metal are usually exceeding the minimum absorbed energy required in.JIS or WES specification, even though the fracture occurs within weld metal. In case of HT-60, however, they are not always satisfied with the criteria of JIS specification.(7)Furthermore, the impact strength of electron-beam welds showed higher value than that of submerged arc welds for HT-50 and 80 steels.