Abstract
In this paper, the effects of various factors on the brittle fracture strength of the gas pressure welded joints of the reinforcing steel bars at low temperatures have been investigated by design of experiments. Further the brittle fracture initiation characteristics of the steel bars with surface flaws have been investigated by the tensile tests of surface notched round bars at low temperatures. The results are summarized as follows; (1) The surface flaws on the steel bars caused in process of the gas pressure welding have a bad effect on the strength of the joints at low temperatures. (2) A wedge type bar clamp used in welding does not almost cause the surface flaws on the bars, then has a good effect on the strength of the joints. (3) The round bars notched by press work don't bring about the low stress brittle fractures at the region from room temperature to about-190℃. (4) Severity of the surface notch of the round bars is more than that of the surface flaws on the bars caused by the bar clamps in gas pressure welding. (5) It is guessed the reinforcing steel bars with the surface flaws caused by the clamps don't bring about the low stress brittle fractures at low temperatures. (6) There is strong correlation between the critical temperatures that the requirement of elongation is garranteed for the surface notched round bars and the crystality transition temperatures of charpy impact tests. Finally the evaluation method of material for the steel bars considering deformation at low temperatures is proposed in this report.
