1/16 Tecnol Metal Mater Min. 2022;19:e2756 | https://doi.org/10.4322/2176-1523.20222756 Original Article – Special issue 75 th ABM Annual Congress 2176-1523 © 2022. Alves et al. Published by ABM. This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. a Abstract The deformation mechanism of lean duplex stainless steel (LDSS) is overly complex not only by their dual phase microstructure, but also due to metastable austenite, which can deform by different mechanisms and transform to martensite by strain. The purpose of this study was to investigate the mechanisms of deformation by tensile test on low deformed cold-rolled samples (4%-22%) of a 2304 LDSS. The microstructure was analyzed by X-ray diffraction, optical microscopy, electron backscattered diffraction and transmission electron microscopy. It was observed the formation of mechanical twinning, ε-martensite, and α’-martensite which evidenced the TRIP effect. The strain hardening rate was calculated and analyzed by Holomon and Crussard-Jaoul modeling together with instantaneous strain hardening exponent, and three operating mechanisms were observed: twinning, dislocations slipping, and strain induced martensite formation (SIM). Brass texture had compromised SIM transformation. The fractography analysis of tensile specimens showed quasi-cleavage occurrence, and dimples formation for this range of pre-deformation. Keywords: Lean-duplex stainless steel; TRIP effect; Twinning; Strain-hardening; Stacking fault energy. 1 Introduction Duplex stainless steels (DSS), which possess an excellent combination of corrosion resistance and mechanical properties, are widely applied to many industrial fields such as pollution control, oil and gas, petrochemical, and ocean engineering [1]. DSS have established themselves as a great alternative in aggressive environments in the chemical, petrochemical, and cellulose industrial sectors, as they have a good performance. They present a dual-phase microstructure, usually in the proportion of 50% of austenite and ferrite [2,3]. To obtain a lower cost, and thus a greater competitiveness in the market, as well as environmental issues, the concept of lean duplex stainless steel was developed, which has smaller amount of the elements nickel and molybdenum, being replaced by manganese and nitrogen [2]. The addition of these elements makes the austenite metastable, changing its stacking fault energy (SFE) value [4]. By presenting this dual-phase microstructure, the plastic deformation mechanisms of this steel become more complex than those of single-phase materials, such ferritic or austenitic stainless steels [1]. SFE will strongly influence the austenite deformation mechanisms. This can occur by slipping in crystalline planes due to dislocations movement, formation of deformation twins and strain-induced martensite (SIM). The latter mechanism being associated with the TRIP effect. The formation of martensite in this type of DSS can occur in two ways: (i) through the direct transformation of austenite to martensite γ → α’, or (ii) through the intermediate phase, the hexagonal ε-martensite, that is, γ → ε → α’. Some studies have observed these two transformation mechanisms in 2304 lean duplex stainless steel [5,6]. However, there is still a plenty of space to explore the phenomenon and how it acts on the work hardening behavior and which mechanisms are operating along the plastic deformation of this alloy, mainly during low deformation intensity, in present case by cold rolling processing. One important point to consider is the influence of ε-martensite on the strain hardening behavior of the alloy. 2 Materials and methods The material used in this study was a hot-rolled 2304 LDSS steel with the chemical composition according to Table 1. The material as-received (AR) was industrially hot- rolled to a thickness of 4.0 mm and then homogenized at 1050ºC for 180 s and water quenching. The samples (150x100x4 mm) were cold rolled with 4%, 12%, 17% and 22% of thickness reduction in successive passes on a laboratory rolling mill at room temperature (~25°C), and a speed of 6.25 m.min-1. These samples were called 4%-CR,12%-CR,17%-CR and 22%- CR. 1 Departamento de Engenharia Metalúrgica e de Materiais, Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG, Brasil. *Corresponding author: [email protected] Work hardening analysis in a lean duplex stainless Steel 2304 after low deformation by cold rolling Davi Silva Alves 1 Daniella Gomes Rodrigues 1 Dagoberto Brandão Santos 1*
Work hardening analysis in a lean duplex stainless Steel 2304 after low deformation by cold rolling
Jun 30, 2023
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