Controlled generation of ferromagnetic martensite from paramagnetic austenite in AISI 316L austenitic stainless steel
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. Sorta) Institucio´ Catalana de Recerca i Estudis Avanc¸ats (ICREA) and Departament de Fı´sica, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
M.O. Liedke and J. Fassbender Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany
S. Surin˜ach and M.D. Baro´ Departament de Fı´sica, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
J. Nogue´s Institucio´ Catalana de Recerca i Estudis Avanc¸ats (ICREA) and Institut Catala` de Nanotecnologia, Edifici CM7, Campus Universitat Auto`noma de Barcelona, 08193 Bellaterra, Spain (Received 30 May 2008; accepted 8 December 2008)
The strain-induced austenite (g) to martensite (a0 ) transformation in AISI 316L austenitic stainless steel, either in powders or bulk specimens, has been investigated. The phase transformation is accomplished using either ball-milling processes (in powders)— dynamic approach—or by uniaxial compression procedures (in bulk specimens)—quasistatic approach. Remarkably, an increase in the loading rate causes opposite effects in each case: (i) it increases the amount of transformed a0 in ball-milling procedures, but (ii) it decreases the amount of a0 in pressed samples. Both the microstructural changes (e.g., crystallite size refinement, microstrains, or type of stacking faults) in the parent g phase and the role of the concomitant temperature rise during deformation seem to be responsible for these opposite trends. Furthermore, the results show the correlation between the g ! a0 phase transformation and the development of magnetism and enhanced hardness.
I. INTRODUCTION
Austenitic stainless steels (ASSs) are extensively used in widespread industrial and technological domains, such as nuclear power plants, alimentation, or biomedical applications, due to their good ductility, weldability, and, especially, outstanding resistance to corrosion and oxidation, even at high temperatures.1 It is well known that because of mechanical stress, a phase transformation from the face-centered cubic (fcc) austenite (g), which is paramagnetic at room temperature, to the body-centered cubic (bcc) martensite (a0 ) phase— ferromagnetic—can occur in these ferrous alloys.2–4 The control of this transformation is critically important for the safe operation of steel-based applications since it can lead to cracks caused by either the brittle nature of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0067 J. Mater. Res., Vol. 24, No. 2, Feb 2009
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the martensite phase5,6 or the decohesion phenomena that can take place at the g–a0 interfaces.7 In fact, the magnetic properties of the induced martensite are being exploited to develop nondestructive methods to assess the degradation of austenitic steels, since the magnetic properties are sensitive to microstructural changes,8,9 or even to generate magnetic information.4,10 However, these austenitic steels are rather soft, resulting in poor wear resista
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