Abstract
One of the factors that effect the strength characteristics of gas pressure welded joints of reinforcing steel bars at low temperatures is metallurgical brittleness of the welds. On the other hand, notches are formed at the bulge due to contraction of knot interval on the process of gas pressure welding, and then the brittle fractures are easy to occur by stress concentration at the notches. In this paper metallurgical properties at the heat affected zone by the thermal cycle have been investigatedfirstly. In the next place the brittle fracture initiation characteristics at the heat affected zone have been investigated by the tensile tests using the circumferentially notched specimens. As a result the effect of normalizing in order to improve the low temperature toughness has been confirmed. The results are summarized as follows; (1) Brittle fracture initiation temperature, Ti, of the circumferentially notched specimen normalized adequately is about 65℃ lower than that of the specimen as welded. (2) Adequate temperature that grain refining occurs at the welds is about 900℃. (3) Crystality transition temperature, v_T_<rs>, that correlates the brittle fracture initiation temperature of circumferentially notched specimen has a close correlation with the Vickers hardness, Hv, at every material. This correlation is available to confirm normalizing of the joints at the job sites.
