Abstract
The transformation mechanism of reverted austenite and the amount of reverted austenite during the tempering process in supermartensitic stainless steel have been investigated by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and a high-temperature laser scanning confocal microscope (HTLSCM). The results indicate that the microstructure mainly consists of tempered martensite and reverted austenite. The reverted austenite nucleates uniformly at the sub-block boundary and prior grain austenite boundary. The amount of reverted austenite strongly relies on the tempering time, showing a positive correlation in the supermartensitic stainless steel. The crystallographic orientation relationship between reverted austenite and martensite meets the Kurdjumov-Sachs(K-S) relationship and the deviation angle is mainly concentrated at about 2 degrees. The mechanism of reverted austenite transformed from martensite is a diffusion mechanism. The growth kinetics of the reverted austenite are dominated by diffusion of the Ni element and there is no shear deformation of the martensite matrix in the in situ observation. It can be deduced that the reverted austenite is formed by nickel diffusion during tempering at 620 °C for different tempering times.
Highlights
Supermartensitic stainless steel has outstanding mechanical properties, including a high strength, good toughness, excellent corrosion resistance, and weldability [1,2,3,4,5]
The microstructure mainly consists of tempered martensite and reverted austenite in the supermartensitic stainless steel
The results suggest that the contents of reverted austenite have an effect on the mechanical properties; The reverted austenite nucleates uniformly and transforms at sub-block boundaries and prior grain austenite boundaries
Summary
Supermartensitic stainless steel has outstanding mechanical properties, including a high strength, good toughness, excellent corrosion resistance, and weldability [1,2,3,4,5]. It has such excellent mechanical properties that it is increasingly applied to the offshore oil and gas industry and other scopes of the Oil. Country Tubular Goods (OCTG) market [6]. The mechanical properties are usually controlled by chemical composition and thermo-mechanical treatments [9,10,11,12,13,14,15].
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