Application of analytical methods for predicting the structures of steel phase transformations in welded joints

Abstract

Abstract. The paper presents the feasibility the prediction of phase structures of the medium carbon S355 steel under the transformations running in welding process by using analytical methods. The relationships proposed here allow to specify start and finish temperatures of phase transformations in the case of formation of bainite, ferrite, pearlite and martensite structures at various cooling rates v 8/5 (t 8/5 ) as well. Continuous-Cooling-Transformation (CCT) diagram and volumetric fractions of each steel phases possible to occur are determined in function of cooling rates. Analytically obtained values are compared with results obtained by dilatometric research. Correctness of applied analytical methods in this field has been verified when the structure compositions formed in the heat affected zone (HAZ) of electric arc butt-welded sheets made of the S355 steel were predicted.

Statistical Modeling for Prediction of CCT Diagrams of Steels Involving Interaction of Alloying Elements

“…Also the quadratic effect of individual alloying elements was assessed in connection with martensite transformation in medium carbon S355 steel covering both the modeling of the start temperature as well as the prediction of mechanical properties. [27,28] A two-way interaction, which incorporates either a single combination of two alloying elements or a quadratic effect of a single alloying element, or both, is added to the model in Eqs.…”

Theoretical and Experimental Investigation of Temperature and Phase Transformation during SAW Overlaying

“…In quantification, volumetric share changes of individual phases in steel during thermal welding cycle are defined by the JMAK (Johnson-Mehl-Avrami-Kolmogorov) law [46,47] in description of diffusive transformations and KM (Koistinen-Marburger) principle is used in description of non-diffusive (martensitic) transformation kinetics [48]. If, during the temperature rise in the thermal cycle, its value exceeds the critical temperature A 1 , the transformation of the initial structure into austenite begins.…”

“…These graphs allow one to determine not only the beginning of the transformation, but also the progress of the process based on the temperature of the process, as well as the type of the structure being created. Limit values of cooling phase transitions (also t 8/5 values) can be determined using analytical formulas dependent on the chemical composition of steel [48]. This is because from a practical point of view the use of dependence equation (19) can often be troublesome due to the necessity to determine the current transformation time, and in [49] the corrected equation was used, in which the time parameter was replaced by the current process temperature:…”

Analysis of thermal cycles and phase transformations during multi-pass arc weld surfacing of steel casts taking into account heat of the weld

“…In this diagram, the progress of the phase transformation depends on the process temperature and the cooling time t 8/5 (material time between 500°C and 800°C) or the cooling rate v 8/5 , which is the material cooling velocity between 500°C and 800°C (v 8/5 = (800-500)/t 8/5 ). The temperatures of the beginning and end of the austenite transformation into cooling structures, as well as the t 8/5 can also be determined by means of analytical dependiences [29]. Replacing the time t in the equation (7) by the new variable -the temperature T [30], the equation for volume share of constituent will be written as follows:…”