Martensite–Void Interaction Arpan Das ⇑ Fatigue & Fracture Group, Materials Science & Technology Division, CSIR–National Metallurgical Laboratory (Council of Scientific & Industrial Research), Jamshedpur 831 007, India Received 14 September 2012; revised 29 November 2012; accepted 29 November 2012 Available online 12 December 2012 The interaction between deformation-induced martensite and voids has been quantitatively established during the tensile defor- mation of metastable austenitic stainless steel at various strain rates under ambient temperature where the initial inclusion volume fraction was kept constant. The inhomogeneous distribution of deformation-induced martensite under tension influences void nucle- ation and growth, and hence keeps imprint on dimple geometries on fracture surfaces. Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Deformation-induced martensite; Austenitic stainless steels; Strain rate; Void density fraction; Ductile fracture Analysis of ductile fracture process is central to a number of engineering problems where toughness and ductility are the most important mechanical properties. Damage is described as a volume representation of deg- radation phenomena, and it is based on constitutive equations coupling plasticity and damage, known as continuum damage mechanics [1]. According to Gurson [2] and Garrison and Moody [3], ductile fracture is ex- plained as a three-stage process. Voids are first nucle- ated at material defects (i.e., inclusions, second-phase particles, etc.) under the influence of favourable plastic strain and hydrostatic stress. Due to the large amount of plastic deformation, voids grow in situations where stress triaxiality is high, and when the voids are large en- ough they tend to coalesce to form microcracks and eventually a macroscopic crack, which leads to fracture. Many void-nucleating particles are generally containing Fe and Si (2024 aluminium alloy), elongated (X52 steel) or spherical (A508 steel) manganese sulphide (MnS), spherical CaS particles (X 100 steel) etc. [1]. Voids not only initiate and grow at inclusions; they can also nucle- ate at other sites, including precipitates, shear band intersections, grain boundary triple points, other sec- ond-phase particulate matter etc. [3]. An emphasis on the role of inclusions and particles in initiating ductile fracture is justified when one considers the range of deformation states and the variety of alloys in which it has been demonstrated, e.g., internally oxidized copper alloys, various maraging steels, quenched and tempered high-strength steels, low-strength steels, aluminium alloys etc. [3]. However, while the second-phase particles act as void nuclei in many systems where voids can be nucleated by other mechanisms [3]. These include the formation of voids at interfaces, as in a–b titanium alloys [4], at slip-band intersections [5], at ferrite–martensite inter- faces etc. [6,7]. The distribution, size, shape, type and coherency of these constituents of the microstructure play an important role in controlling void nucleation, growth and eventual fracture. For ductile alloys, the mechanical properties are determined by the interaction of stress and strain fields with the microstructural con- stituents (i.e., phases, defects, etc.) [3]. The contribution of deformation processes in the development of voids has been well established. While the growth mechanisms can vary, say, with the temperature of testing, their nucleation invariably occurs where inhomogeneous deformation takes place [3]. Recently, the present author has correlated fracture properties with the fracture sur- face features of AISI 304LN stainless steel and HSLA- 100 steels by varying the deformation paths and ageing treatment, respectively [8–10]. Deformation paths at various strain rates can control not only the mechanical behaviour of the material, but also the void nucleation and growth process. In certain grades of metastable austenitic stainless steels, formation of deformation- induced martensite (DIM) is reported, and it is conceiv- able that this could contribute to void nucleation and the manner in which further deformation takes place. 1359-6462/$ - see front matter Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.scriptamat.2012.11.039 ⇑ Tel.: +91 (0) 657 234 5192; fax: +91 (0) 657 234 5123; e-mail: dasarpan1@yahoo.co.in Available online at www.sciencedirect.com Scripta Materialia 68 (2013) 514–517 www.elsevier.com/locate/scriptamat