Cooling Time and Crack in the Heat-Affected Zone of Various Steels

Abstract

The CTS cracking test of 50kg/mm² high tensile steel KT and 55kg/mm² high tensile steel YC and the special cracking test of 60kg/mm² high tensile steels YF and YG were performed. The results are as follows ;
(1) The cooling of weld thermal cycles in the case of bithermal and trithermal of CTS cracking test, are generally slower than those in the case of bead on a large plate and T-butt weld joint, respectively.
(2) In the case of deposition on a CTS specimen of the steels KT and YC with ilmenite Type electrodes, cracks tend to occur in the heat-affected zone, when the cooling times are shorter than about C_f' critical cooling time.
(3) In the case that low hydrogen type electrodes are used, the cracking tendency is still small, even if the cooling times are shorter than about C_f'.
(4) In the case of the special CTS tests in which the CTS specimens were quenched in water during natural cooling after welding, the cracking tendency was large, when the specimen was quenched in water from the temperature at the neighbourhood of fusion line at the center of bead-length, being higher than about 350°C.
(5) The cracking tendency in the heat-affected zone may be predicted to some degree by the continuous cooling transformation diagram of the steel used, and the C_f' critical cooling time and the temperature-range of martensite transformation are especially concering to the cracking heat-affected zone.