Effects of Heat Input Conditions on the Local Thermophysical Properties of Super Duplex Stainless Steels

Abstract

The thermal properties of the super duplex stainless steels are strongly affected by the thermal history when welding procedure are applied leading to substantial changes on the mechanical properties of the welding region. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this research a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure is developed. The model was verified by measured temperature profile and used to predict local properties such as grain size evolution, hardness and mechanical strength. An inverse method was implemented to obtain the parameters fitting for the grain growth evolution, hardness and yielding strength compatible with the final microstructure and grain size measured using SEM images and stereological techniques.

Influence of the Interpass Welding Temperature on Microstructure and Corrosion Resistance of Superduplex Stainless Steel SAF 2507

“…According to Ramirez et al 14 , intragranular austenite is obtained due to the thicker grains formed in this region. The explanation follows the classical mechanism confirmed by previous results 11, [18][19][20][21][22][23][24][25][26][27] .…”

“…The EDS analysis did not show significant changes in the distribution of the alloying elements for the FZ and HAZ zones, regardless of the interpass temperature. Still, the Cr in the ferrite phase was consistently higher than in the BM, as expected due to its effect as a stabilizer of the ferrite phase [26][27][28][29][30] . XRD analysis for the severest welding condition of this study is presented in Figure 7.…”

“…Therefore, the phase balance represented by their volume fractions and spatial distributions besides their morphological characteristics is mainly related to their specific grain boundary area and the local cooling rates. These main key parameters strongly relate to the growth kinetics of the phases developed during the welding procedures, which in turn, are defined by the welding parameters and the local thermophysical properties of the material [11][12][13][14][15][16][18][19][20][21][22][23][24][25][26][27] . Consequently, larger regions in the center of the ferrite grains will be available for the nucleation and growth of austenite due to the resulting supersaturation with austenitizing elements of the ferrite phase.…”

“…Thus, the final grain structure is achieved for a particular region of the joint following its own path. Therefore, the final grain spatial distribution is a function of the materials properties such as thermal conductivity, specific heat capacity, heat fusion, and heat input distribution [26][27][28][29][30] . Therefore, the grain size and phase volume fractions distribution are coupled phenomena affected by the volumetric heat source shape [25][26][27] , which are dynamically developed during the welding schedule designed to achieve balanced phases and hence welded joints with controlled properties, mainly its mechanical and corrosion resistance.…”

“…This model has been applied by Castro et al 26,27 , where the authors propose a model capable of predicting the thermal history of a superduplex stainless steel and its mechanical properties developed after welding, adjusting the thermophysical parameters based on data measured in their work. Using Equation 1 for the cooling rates obtained from the thermocouples measurements, Table 5 was obtained.…”