Microstructure evolution and microhardness of thermal-simulated HAZ in Fe–Mn–Al–C steel

Abstract

The microstructure evolution and microhardness of Fe–Mn–Al–C steel heat-affected zone (HAZ) were investigated systematically using the weld thermal simulation technique. The results illustrated that the microstructure in HAZ with different peak temperatures (600, 800, 1000 and 1300°C) and heat inputs (10, 20 and 30 kJ cm–1) mainly consisted of ferrite and austenite. When the peak temperature was 1300°C, there are many high-angle grain boundaries which may inhibit crack propagation. With the increase in heat input, κappa carbide precipitation increased, the grain size became finer and microhardness increased. The microhardness was 438 HV when the peak temperature was 1300°C at 30 kJ cm–1. Highlights The welding of high carbon, high aluminium and low-density steel was simulated. The HAZ was composed of austenite and a small amount of high-temperature δ-ferrite. The proportion of high- and low-angle grain boundaries has a great influence on the mechanical properties. The welding heat input was 30 kJ cm–1, the grain size of the HAZ decreased and microhardness was the largest.

The Dominant Role of Recrystallization and Grain Growth Behaviors in the Simulated Welding Heat-Affected Zone of High-Mn Steel

“…High manganese austenitic steel for cryogenic application has a fully austenitic structure, and the austenite phase can remain stable during welding thermal cycling [7,8]. This leads to significant differences in the HAZ characteristics of high manganese austenitic steel compared with other steels and alloys such as high-strength low-alloy (HSLA) steels [9], austenitic stainless steels [10], high manganese low-density steels [11], nickel-based superalloys [12,13] and high-entropy alloys [14]. Due to the absence of γ −→ α phase transformation, the HAZ characteristic of high manganese austenitic steel is significantly different from that of HSLA steel [15].…”

“…For example, it is common for an inter-critical heat affected zone (ICHAZ) to exist in the HAZ of HSLA steel, but cannot be found in high Materials 2024, 17, 2218 2 of 13 manganese austenitic steel. Similarly, γ −→ δ phase transformation has been reported to lead to a deterioration in the mechanical properties of the HAZ in austenitic stainless steel [10] and high manganese low-density steel [11], however, it is difficult to find in high manganese austenitic steel. A common factor that deteriorates the HAZ of high manganese austenitic steel [16][17][18] and austenitic stainless steel [19] is the precipitation of a M 23 C 6 -type carbide caused by the macrosegregation and/or grain boundary segregation of C, Mn, and Cr elements.…”