In-situ observation of dark phase precipitation during heating and soaking process of a high nickel steel

Abstract

In-situ observation of microstructural evolution during heating and soaking process was carried out for a high nickel steel using HTCLSM. Dark phases were observed when soaking at 900 °C. Results showed that the number of the dark phases culminated in about 50 s during soaking at 900 °C. With the increase of soaking time the area proportion of the dark phases increased and reached the maximum value in about 3 min. When temperature rose from 900 °C, the dark phases remained steady initially, but started to dissolve into the matrix at about 1 060 °C and completely disappeared at 1 132 °C. When the specimen soaked at 900 °C was cooled down to room temperature (RT), the dark phases kept stable. Energy spectrum analysis results showed that the dark phases contained much more Cr and Mn elements than the matrix and were also rich in V. Tensile test results showed that the dark phase strengthened the steel with the maximum tensile strength obtained after soaking at 900 °C for 3 minutes.