Temper-treatment development to decompose detrimental martensite–austenite and its effect on linepipe welds

Abstract

A tempering cycle was developed via heat treatment to study the decomposition of detrimental martensite–austenite (MA). The heat treatment cycle was found to preferentially decompose hard MA with a critical size of ≥1 µm, which decreases the hardness of these microconstituents after tempering at 300°C for 10 min. The dislocation density inside the MA and in the surrounding matrix was also decreased. Tempering of the X80 weldments containing MA reveals a similar decomposition behaviour. During transverse weld tensile testing of welds, a fracture occurred in the heat-affected zone due to void formation at the MA/ferrite interfaces. However, a fracture occurred in base metal with improved strength and ductility after tempering, in comparison to the fracture in the heat-affected zone of as-welded samples.

Microstructural and Mechanical Characterization of Low-Alloy Fire- and Seismic-Resistant H-Section Steel

“…This tempered MA structure is characterized by the presence of some carbides within the grains, a morphology similar to that observed in previous studies [21,23]. The decrease in nano-hardness within the MA constituents, attributed to the decomposition of MA, aligns with previously reported findings [27]. Figure 9f illustrates the overall distribution of nano-hardness across the thickness of the steel after thermal exposure.…”

Kinetics of Martensite/Austenite Decomposition during Tempering of Ultrafine Nano-Bainitic Steels

“…Bulky M/A can decompose more quickly with the right heat treatment. According to recent research by Huda et al [20], a significant amount of coarse M/A can be broken down by tempering it for 10 min at 300 • C. At higher temperatures, M/A tends to break Materials 2024, 17, 2690 2 of 14 down into ferrite and carbide. Significant decomposition of residual austenite occurs within the temperature range of 550 to 600 • C [21].…”

“…Bulky M/A can decompose more quickly with the right heat treatment. According to recent research by Huda et al [ 20 ], a significant amount of coarse M/A can be broken down by tempering it for 10 min at 300 °C. At higher temperatures, M/A tends to break down into ferrite and carbide.…”