2007 Volume 25 Issue 4 Pages 560-568
In order to improve fatigue strength in welded joints, low transformation-temperature welding wire has been developed in which residual tensile stress can be reduced. In application of the low transformation-temperature welding wire, the prevention of cold cracking without pre-heating in high strength steel welded joints is expected and examined from the control of residual tensile stress. However, it is expected that residual stress distribution in welded joint can be suggested by numerical analysis, because the residual stress cannot be measured simply and non-distractively.
In this report, martensite transformation behavior such as Ms point, transformation expansion and so on is measured firstly by Formaster test.
And temperature dependence of several mechanical properties was measured in full-austenite and full martensite microstructures, and temperature dependence of mechanical properties was estimated in dual phase microstructure of austenite and martensite.
By these data, numerical analysis was carried out and martensite transformation behavior was compared with measured and calculated results in side rigid model test. From the comparison, it was suggested that transformation superplasticity had to be considered in numerical analysis.
Next, the increase of Ms point due to transformation induced plasticity was guessed from the comparison with measured data by laser speckle measurement and calculated data under transformation superplasticity consideration.
From the all results, it was found that the measured transformation behavior and residual stress had the good agreement with the calculated results under transformation superplasticity and transformation induced plasticity considerations.
