1993 年 11 巻 4 号 p. 550-555
Residual stresses and angular distorsions are very important probrems in welding design and fabrication. In the previous reports it was shown that the materials with a martensitic transformation at low temperature were effective to the reduce residual stress and anguler distorsion in welding.
In this report the effects of transformation on prevention against crack in welding were examined by use of restraint thermal cycle test and constraint crack test. The results are shown as follows;
(1) The materials with transformation at low temperature were effective to reduce residual stresses in stress concetration area and to prevent cracks in welding.
(2) As the result of the stress consentration test (mild steel was broken in the midst of cooling by this test method), it was possible to prevent a crack or a failure at the stress concentration area by use of the materials with the transformation at low temperature. In this case, the transformation superplasticity was more effecive than transformation expansion to release the stress concentration.
(3) The Ms temperature of the materials with the transformation at low temperature (there was no crack by use of these materials in this test) was less than 200°C. But a dilution from a base metal raised the transformation temperature and the free thermal contraction curve changed. Therefore in welding practices, the change of transformation temperature by the dilution from base metal is also important.