Assessment of the Heat Input Effect on the Distribution of Temperature Cycles in the HAZ of S460MC Welds in MAG Welding

Jaromír Moravec,Martin Švec,Jiří Sobotka,Šárka Bukovská

doi:10.3390/met11121954

Abstract

Temperature cycles generated during welding have a significant effect on the changes in the HAZ of welds, regardless of whether these are changes in structure or mechanical properties; however, it is problematic to obtain temperature cycles with sufficient accuracy across the entire HAZ so that they can be generally taken and used in welding simulations and for real experiments of processes occurring in HAZ. In particular, for a study in a specific location, it is important to know the maximum temperature of the cycle and the cooling rate defined mainly by the parameter t8/5. No studies in which anybody tries to find a mathematical description defining the basic parameters of temperature cycles in the HAZ could be found in the performed research. Therefore, the study presented in this paper results in a mathematical description defining the dependence of achieved maximum temperature on the distance from the fusion line in the HAZ of S460MC welds and with heat input values in the interval from 8 to 14 kJ·cm−1. Moreover, this paper presents the influence of heat input value on the weld pool geometry, including the effect of heat input value on grain coarsening in the highly heated HAZ.

Highlights

In recent years, research teams have dealt with the issue of changes occurring in the HAZ of welds from high-strength fine-grained steels, including HSLA steels and steels hardened by quenching and tempering (Q-type), or steels for which normalizing rolling is essential (N-type)
For heat input within the range 8–14 kJ·cm−1, high geometric stability was achieved in the steady-state welding zone with deviations from the mean value lower than 5%. (2) For correct mapping of the temperature distribution in HAZ, it is necessary to use S-type thermocouples
Even a very small deviation in measuring such distance can significantly affect the predicted temperature distribution in a highly heated HAZ. (3) Equations (1) and (2) can be used to describe the temperature distribution in HAZ of welds made by the MAG method on steel S460MC for heat input values 8 and 14 kJ·cm−1

Summary

Introduction

Research teams have dealt with the issue of changes occurring in the HAZ of welds from high-strength fine-grained steels, including HSLA steels and steels hardened by quenching and tempering (Q-type), or steels for which normalizing rolling is essential (N-type) These are mainly studies where temperature cycles are applied to the testing sample using a thermal-mechanical simulators or other similar equipment; the basic approaches used in these studies are quite different. Lan et al [1] used the socalled Rykalin mathematical model to determine the microstructure in HAZ They generated a temperature cycle with a heating rate of 130 ◦C·s−1 to 1350 ◦C, holding for 2 s and cooling with t8/5 times of 30, 50, and 120 s. Despite the very interesting results obtained, it is not easy to relate these results to a specific area of HAZ for the chosen process parameters and welding method

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Conclusion