Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

ABSTRACT

The metadynamic softening behaviour and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950–1150°C was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5–300 s after achieving a strain of 0.3. Based on the experimental results, a model was established for estimation of a softening fraction at different deformation parameters, and the softening fraction was compared with a recrystallised fraction. A major deviation was observed at the beginning of interpass time denoting a significant contribution of recovery to the fractional softening (FS). However, by increasing the time and temperature, the difference between the FS and recrystallised fraction is reduced. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of 53 µm decreased down to 32 and 19 µm at the deformation temperatures of 1020 and 940°C, respectively. The austenite grains have considerable growth at a temperature higher than 1020°C, while the grain coarsening is negligible at lower deformation temperatures.

RÉSUMÉ

On a examiné le comportement d’adoucissement métadynamique et l’affinement de la taille de grain de l’acier inoxydable martensitique AISI 422 dans la gamme de température de 950 à 1150°C au moyen d’essais de compression interrompue. On a maintenu les échantillons déformés à la température de déformation, avec décalages de 5 à 300 s après avoir obtenu une déformation de 0.3. Basé sur les résultats expérimentaux, on a établi un modèle pour l’estimation de la fraction d’adoucissement à différents paramètres de déformation, et l’on a comparé la fraction d’adoucissement à la fraction recristallisée. On a observé une déviation majeure au début de l’intervalle de temps, dénotant une contribution importante de la restauration à l’adoucissement fractionnel. Cependant, avec l’augmentation de la durée et de la température, la différence entre l’adoucissement fractionnel et la fraction recristallisée était réduite. On a obtenu la taille de grain la plus fine au moyen d’un grain antécédent plus fin de pré-austénite et d’une température plus basse de déformation secondaire. La taille de grain initiale de 53 μm diminuait à 32 μm et à 19 μm aux températures de déformation de 1020°C et de 940°C, respectivement. Les grains d’austénite ont une croissance importante à des températures au-delà de 1020°C, alors que le grossissement du grain est négligeable aux températures inférieures de déformation.

KEYWORDS:

• AISI 422 stainless steel
• softening fraction
• grain size
• hot deformation
• grain growth
• EBSD analysis

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Reza Mohammadi Ahmadabadi is a PhD Student at Amirkabir University of Technology He is currently working on his thesis project, “Investigation of the Thermochemical Properties of Martensite Stainless Steel A982 for Optimization of Microstructure”.

Malek Naderi holds a Ph.D. degree (2004–2008) in Materials Engineering, Metal Forming – Thermomechanical behavior of materials, from RWTH Aachen University. His doctoral dissertation is entitled “Hot stamping of ultra-high-strength steels. In addition, he earned his Master’s degree (1998–2001) in Materials Engineering – Materials Characterization and Selection. His Master’s dissertation is entitled “Evaluation of temper embrittlement on fracture toughness of Chromium – Molybdenum steels”. He also holds a bachelor’s degree (1993–1998) in Materials Engineering – Extractive Metallurgy. His bachelor’s dissertation is entitled “Evaluation of investment casting of austenitic stainless steels in vacuum induction furnaces Master of Science, Materials Engineering – Materials Characterization and Selection”.

Jamshid Aghazadeh Mohandesi served as Deputy Head of department in Research Affairs, AUT, 1995–2002; Head of Metallurgical Engineering Group, AUT, 1996–1998; Deputy Head of department in Administration, AUT, 2002-2003; and Head of Mechanical Metallurgy Laboratory, Since 1995.

Jose Maria Cabrera served as Professor (Full) at the Department of Materials Science and Metallurgy (CMEM), Polytechnic University of Catalonia, Spain, in 1996–2017. Previously, he is Director of Materials Forming Area Fundació CTM Centre Tecnològic Spain, Manresa, Catalonia, in 2001–2016.

Additional information

Funding

This work was supported by Isfahan Steel Alloy Company.