Examining the Critical Transformation Temperatures in Martensitic Stainless Steel Castings

Abstract

Understanding the critical transformation temperatures (Ac1, Ac3, Ms, and Mf) is crucial for optimizing the heat treatment and mechanical properties of martensitic stainless steel. Achieving the desired mechanical properties requires precise control of heat treatment processes to develop the correct microstructures, which can be particularly challenging with these grades. This challenge is compounded by the fact that foundries often conduct temper treatment near the Ac1 to soften the steel enough to meet specifications. However, variations in compositions and furnace conditions raise concerns about the reliability of consistently maintaining temperatures around Ac1, which is suspected to contribute to inconsistent mechanical properties. This inconsistency is often attributed to variations in the actual critical temperatures and their impact on heat treatment outcomes. Incorrectly selected temperatures lead either to incomplete austenitizing or inadequate softening during tempering. The study aims to determine the influence of heating rates and composition on the shift of the transformation temperatures (Ac1 and Ac3) in two grades of martensitic stainless steels. It employs dilatometry to determine phase transformation temperatures on continuous heating at various rates (10 °C/s, 1 °C/s and 0.1 °C/s). The experimental data obtained were used to determine the austenite start and finish temperatures. Subsequent analysis revealed that these temperatures are composition dependent and increase with heating rates.

Department(s)

Materials Science and Engineering

Keywords and Phrases

Ac1; Ac3; CA6NM; Dilatometer; Mf; Ms; Martensitic; S41000; Stainless Steel

International Standard Book Number (ISBN)

978-093076737-2

International Standard Serial Number (ISSN)

1551-6997

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Association for Iron and Steel Technology, All rights reserved.

Publication Date

01 Jan 2025

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