Analysis of Martensite Transformation Behavior in Welded Joint of Low Transformation-Temperature Materials

Abstract

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 preheating 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.

Determination of Parameters for Fitting the Dilatation Curve of Austenite–Martensite Transformation in Cr–Ni Steels

“…Following work by other researchers 3,4) shows that b is a material constant varying with chemical compositions. These results convincingly support Eq.…”

“…If their relations can be expressed in equations, f m can be deduced from the experimental data of dilatation. Based on this idea, Yamamoto et al 4) proposed a simple model to determine b and M s from the dilation curve schematically represented in a solid line in Fig. 1.…”

“…(2)- (4). We only have experimental data of E vs. T. Yamamoto et al 4) assumed that line AB as shown in Fig. 1 is single austenite region, and a g is the gradient of line AB.…”

Prediction of Martensite Volume Fraction in Fe–Cr–Ni Alloys

“…Four dilation curves of Fe-Cr-Ni stainless steel alloys [16][17][18] (labeled S1 to S4) that have different chemical compositions (as shown in Table 3) were selected to verify the analytical model proposed in the present study. Figure 2 shows the four dilation curve changes due to the martensite transformation below each martensite start (M s ) temperature.…”

“…The measured volume fraction of martensite was taken from literature. [16][17][18] Good agreement between the measured and calculated volumes of martensite was confirmed when the effect of the alloying element was considered (called the "AE" calculation). Similarly good correspondence has been observed in the previous models [2][3][4][5][6][7][8] used for heat-treatable low-alloy steels when the alloying elements are considered.…”