Optimized Design of Ultra-High Strength Stainless Steel Based on Thermo-Calc Calculation

Abstract:

The thermodynamic calculation software Thermo-Calc was used to study the influences of alloy elements Cr, Co, and Mo on the precipitated phases of a S280 ultrahigh strength stainless steel at the temperatures ranging from 400 °C to 1200 °C. The results showed that the precipitated phases in the steel were mainly composed of M₂₃C₆ carbide, M₆C carbide, intermetallic compound of Laves phase and σ phase. The temperature and the content change of alloying elements Cr, Co and Mo have little effect on the precipitation of M₂₃C₆ carbide, while have great effect on the precipitation of Laves phase and σ phase. By lowering the element content and adjusting the heat treatment temperature, the precipitation of σ phase in the alloy can be reduced．According to the results of thermodynamic simulation, after optimizing the chemical composition, the Ф300mm bar was trial-produced. The chemical composition, microstructure and mechanical properties of the alloy were analyzed and tested. The results show that, after tempering at 550 °C, the main precipitated phases in the S280 alloy were M₂₃C₆ carbide and intermetallic compound of Laves phase. The characterized nano-precipitates have good agreement with simulation results. The optimized design of S280 steel reached a tensile strength over 1930 MPa and a fracture toughness of 90 MPa•m^1/2.

• Periodical: Materials Science Forum (Volume 993)
• Pages: 585-591
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.993.585
• Online since: May 2020
• Authors: Mu Tong Liu*, Ping Zhong, Wei Sheng, Zhen Ye Zhao
• Keywords: Laves Phase, M₂₃C₆ Carbide, Thermo-Calc, Ultra-High Strength Stainless Steel

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