On the Relationship between the Chromium Concentration, the Z‐Phase Formation and the Creep Strength of Ferritic‐Martensitic Steels

Abstract

In this study, the long term creep strength behavior of commercial heat resistant martensitic/ferritic steels with Cr levels ranging from 1 to 15 wt% is analyzed by linking their computed equilibrium compositions to their creep properties. At lower Cr levels, the calculated strength due to precipitation hardening agrees well with the experimental results. At high chromium levels and longer exposure times, an accelerated strength loss due to the formation of Z-phase precipitates has been reported. The accelerated strength loss is computationally analyzed and a correlation between accelerated strength loss and Z-phase formation is confirmed. A study is made to explore the option of adjusting the chemical composition of existing high-chromium steels to reduce the driving force for Z-phase formation. However, no proper composition ranges are found which combine a high Cr concentration with a significantly lower driving force for Z-phase formation.

Creep strength breakdown and microstructure in a 9%Cr steel with high B and low N contents

“…The creep strength breakdown in 11%Cr steels of P122 type is associated with the replacement of nanoscale MX carbonitrides by coarse Z-phase particles (CrVN) [14,[18][19][20][21]. The Z-phase particles exhibit relatively high coarsening rate under creep at elevated temperatures as compared to other precipitates and, thus, are considered as undesirable from the standpoint of microstructural stability [23,24,34].…”

A Review of Self-healing Metals: Fundamentals, Design Principles and Performance

“…To realize commercial application, it is advised to incorporate self-healing agents in commercial creep-resistant steels, so that potential commercial benefits of extending safe lifetimes are gained due to self-healing together with the damage prevention ability guaranteed via the strengthening mechanism. To achieve synergistic effects, advanced computational methods are essential to design the optimal compositions and heat-treatment routes [83,84].…”