Effect of Strain-Induced Precipitation on the Austenite Non-recrystallization (Tnr) Behavior of a High Niobium Microalloyed Steel

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 50; no. 12; pp. 5816 - 5838
• Main Authors: Rajinikanth, V., Kumar, Tipu, Mahato, B., Ghosh Chowdhury, Sandip, Sangal, Sandeep
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2019; Springer Nature B.V
• Subjects: Austenite; Characterization and Evaluation of Materials; Chemistry and Materials Science; Compression tests; Evolution; High strength low alloy steels; Materials Science; Metallic Materials; Microalloying; Nanotechnology; Niobium carbonitride; Nucleation; Plane strain; Recrystallization; Softening; Structural Materials; Surfaces and Interfaces; Tensile properties; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-019-05488-3

The non-recrystallization temperature ( T nr ) of high niobium microalloyed steel was determined from both multihit and double-hit compression tests obtained under plane strain condition. The T nr was determined to be in the range of 985 °C to 1010 °C for multihit conditions. The double-hit tests carried out at an interpass time of 5 seconds gave very low T nr in the range of 860 °C to 900 °C. In order to understand this, double-hit experiments were carried out for different interpass times (2, 15, 100 seconds) at three different temperatures (950 °C, 1050 °C, and 1150 °C). The negative softening behavior was observed at 950 °C for higher interpass times of 15 and 100 seconds. This implies that the T nr of this steel is well above 950 °C. This was due to the high amount of strain-induced precipitation of niobium carbonitrides at higher interpass times as revealed from TEM investigation. The precipitate size evolution considering the Dutta and Sellars nucleation condition in TC-PRISMA agrees well with the experimentally observed precipitate sizes. However, the evolution of Zener pinning forces considering TC-PRISMA nucleation condition is similar to both reported and experimentally determined values. The evolution of tensile properties also correlates well with the observed austenite recrystallization softening behavior. Therefore, a minimum interpass time of 15 seconds is required during double-hit compression tests to effectively precipitate Nb(C, N) and delay the static recrystallization softening behavior of this steel. This lead to the determination of comparable T nr values between double-hit and multihit methods.