Mechanical Properties and Magnetism: Stainless Steel Alloys from First-principles Theory
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Mechanical Properties and Magnetism: Stainless Steel Alloys from Firstprinciples Theory L. Vitos1,2,3, H. L. Zhang1, N. Al-Zoubi1, S. Lu1, J.-O. Nilsson4, S. Hertzman5, and B. Johansson1,2 1
Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of
Technology, SE-10044 Stockholm, Sweden 2
Division for Materials Theory, Department of Physics and Materials Science, Uppsala
University, S-75120 Uppsala, Sweden 3
Research Institute for Solid State Physics and Optics, P.O.Box 49, H-1525 Budapest, Hungary
4
AB Sandvik Materials Technology, SE-811 81 Sandviken, Sweden
5
Outokumpu Stainless Research Foundation, Royal Institute of Technology, Stockholm SE-100 44, Sweden ABSTRACT Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest sub-category of stainless steels having as the main building blocks the paramagnetic substitutional disordered Fe-Cr-Ni-based alloys. Because of that, austenitic steels represent the primary choice for non-magnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from first-principles theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact Muffin-Tin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Fe-based alloys. INTRODUCTION Steels are mainly composed of iron and carbon. Other alloying elements are introduced in order to achieve some specific properties. The stainless steels are alloy steels containing more than 12 percent Cr. Chromium forms a passive oxide film on the surface, which makes these alloys resistant against corrosion in various chemical environments [1]. Austenitic stainless steels, the largest sub-category of stainless steels, comprise a significant amount of substitutional Ni as well. At low temperatures, these alloys exhibit a rich variety of magnetic structures as a function of chemical composition, ranging from ferromagnetic phase to spin-glass and
antiferromagnetic alignments [2]. At ambient conditions, Ni changes the ferromagnetic α-Fe structure of Fe-Cr steel to the paramagnetic γ-Fe structure. Today austenitic stainless steels dominate the steel applications, where high corrosion resistance and excellent mechanical properties are required. The austenitic grades represent the primary choice also
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