Mechanical Properties on Electron Beam Welds of Constructional High Tension Steels (Report III)

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In this investigation, the authors aimed to make clear the weldability of electron-beam welds for some commercial constructional high tension steels. Then, the influence of weld heat input on the weld defects, the hardness distributions and the impact properties of the electron-beam welds was investigated in this report. The materials used were three grades of high tension steel HT50, HT60 and HT80 with 25mm thickness. The conventional low voltage type electron-beam welder, 30KV-500mA(15KW) in maximum was employed in this experiment. All of weld bead were performed with bead-on-plate type welding. The active beam parameter, a_b adopted was 1.0 through the experiment. The remarkable conclusions are as follows: (1) All of weld seam except unstable location of bead 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 weld heat input. In Vickers hardness distributions of HT50 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 weld metal usually showed the different two levels, lower and higher, at particular testing temperature due to the difference in the fracture mode for 2mm notched standard Charpy impact test specimen. Namely, when the fracture occurred straightly along the notched direction, the absorbed energy showed lower value, however, when the fracture occurred out of the notched direction, it showed higher value. (4) The particular testing temperature, at which the fracture mode differs, tended to be raised with an increase of the weld heat input. This seemed to be related with the bead width of fusion zone and 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 limited change for the weld heat input from 10KJ/cm through 40KJ/cm. (6) In case of the welds of HT50 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 HT60, 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 HT5O and 80 steels.
大阪大学の論文

Mechanical Properties on Electron Beam Welds of Constructional High Tension Steels (Report III)

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