Compositional analysis on the reverted austenite and tempered martensite in a Ti-stabilized supermartensitic stainless steel: Segregation, partitioning and carbide precipitation. (15th February 2018)

• Record Type: Journal Article
• Authors: Escobar, J.D.; Poplawsky, J.D.; Faria, G.A.; Rodriguez, J.; Oliveira, J.P.; Salvador, C.A.F.; Mei, P.R.; Babu, S.S.; Ramirez, A.J.
• Is Part Of: Materials & design. Volume 140(2018)
• Page Start: 95
• Page End: 105
• Publication Date: 2018-02-15
• Subjects: α ferrite in thermodynamic equilibrium -- α' tempered martensite -- γ austenite in thermodynamic equilibrium -- γr reverted austenite stabilized at room temperature -- APT atom probe tomography -- XEDS energy dispersive X-ray spectroscopy -- ICT inter-critical tempering -- MCN used to refer to titanium carbo-nitride precipitates -- SMSS supermartensitic stainless steels -- SXRD synchrotron X-ray diffraction; Atom probe tomography -- Austenite reversion -- Isothermal tempering treatments -- Synchrotron diffraction; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2017.11.055
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Controlling the amount of reverted austenite at room temperature allows for tailoring of mechanical properties in supermartensitic stainless steels. The austenite reversion and stabilization occurs during inter-critical tempering through partitioning of austenite-stabilizing elements. The degree of partitioning greatly depends on the reversion temperature, which dictates the local equilibrium conditions. Atom probe tomography and energy dispersive spectroscopy in transmission electron microscopy were used to study the austenite reversion mechanism in terms of the elemental distribution of austenite-stabilizing, ferrite-stabilizing and carbide forming elements. Synchrotron X-ray diffraction confirmed that the austenite equilibrium phase fraction was reached after 2.5 h of isothermal reversion at 625 °C, allowing for direct comparison with thermodynamic and kinetic calculations. However, such soaking time was not enough to produce compositional homogenization in the reverted austenite. The austenite reversion and stabilization mechanism was related mainly to strong partitioning of Ni. Negligible partitioning of Cr, Mo, Si and Ti were observed. Instead, these elements were strongly segregated at the reverted austenite/martensite interfaces. Carbon and Ti played a secondary role in the austenite stabilization through the precipitation of nano-sized Ti (C, N) with partial substitution of Ti by Mo. Virtually carbon-free austenite and martensite were observed away from the interfaces and precipitates. Graphical abstract: Image 1 Highlights: Austenite growth occurred by strong partitioning of Ni according to local equilibrium. Reverted austenite/martensite interface segregation of Cr, Mo, Si and Ti was evidenced. Virtually carbon-free reverted austenite and martensite were found after tempering due to precipitation of Ti (C, N).