Used for cutlery, steam, and gas turbine blades and buckets, bushings, Addition of sulfur for machinability, used for screws, gears etc. It was presented that the treatment fetches to the formation of the softened subsurface layer with thickness of 100 Mm. Titanium and niobium stabilization was used to avoid detrimental carbide precipitates on welding, but in modern, low carbon Cr-Ni-Mo steels this is not necessary. Some grades are alloyed with nitrogen to improve their strength, or with sulfhur to improve machinability. The structure examination of subsurface layer and cross-section of 12Cr1MoV and 30CrMnSiNi2 steel specimens following the ion-beam irradiation was accomplished by Vlasov et al. Typical applications for austenitic stainless steels are in the food industry, catering and kitchen equipment, process industries, building, architecture and transport. There are also stabilized grades where titanium or niobium is added to increase the mechanical properties at high temperatures by the formation of hardening carbides. The surface of the specimen was mechanically polished by lapping and then mirror finished by electrolytic polishing. Martensitic grades are especially susceptible to hydrogen embrittlement in tempered conditions. (2015) have studied fatigue life improvement of 12Cr1MoV steel by irradiation with Zr+ ion beam. To improve their strength and hardenability they have a higher carbon content compared to other grades, and nitrogen (N)is sometimes added to further improve the strength. Typical applications for austenitic stainless steels are in the food industry, catering and kitchen equipment, process industries, building, architecture and transport. The first type comprises those which contain carbon and which are strengthened by iron carbide precipitation when tempered at low temperatures or by alloy carbide precipitation on tempering at higher temperatures (secondary hardening). These grades are sometimes referred to as 18-8 type of stainless steels, indicating the approximate chromium and nickel content. The high temperature austenitic grades are characterized by high chromium (17–25%) and high nickel (8–20%) content but containing no molybdenum. They will contain inclusions, as do all steels, fine second-phase particles inherited from the austenitizing temperature, and will largely consist of lath or dislocated martensite rather than plate martensite. Figure 3: Martensitic stainless steel microstructure The martensitic grades (see Figure 3) are the smallest group of stainless steels. Austenitic and dual phase stainless steels present compositions near the eutectic valley in the ternary Fe–Cr–Ni liquidus [57] and their equilibrium solidification path depends on the position of their representative points in relation to that valley. Silicon is added in some grades to increase their oxidation resistance. Chromium in the steel is in the range of 10.5–18 wt.% with a higher level of carbon than the ferritics; though, the chromium and carbon contents are balanced to ensure a martensitic structure after a complete cycle of heat treatment. X-ray diffraction analysis indicated that the hardened case consists of a mixture of expanded austenite and expanded martensite,4 while ε-carbonitride is present close to the surface. M. Iannuzzi, in Stress Corrosion Cracking, 2011. Because of their low carbon contents these materials should not be as susceptible to quench cracking as the carbon-containing martensitic stainless steels. Molybdenum (0.3–4%) and nitrogen are added to improve the corrosion resistance and balance the microstructure. Small amounts of nickel can be added to improve corrosion resistance in some media and to improve toughness. The hardness range obtainable from common martensitic stainless steel grades at different conditions of heat treatment is shown in Figure 2. Various TiN thin film layers 2 µm thick were formed on the specimen surfaces by the IVD process using nitrogen ion beam implantation and titanium vapor deposition. Some grades are alloyed with nitrogen to improve the strength, or with sulfur to improve machinability. There will be thin films of retained austenite between martensite laths, between martensite packets and at the former austenite grain boundaries if lath martensite is formed. The work hardening process will cause fracture. Martensitic stainless steels are used when corrosion resistance and/or oxidation resistance are required in combination with either high strength at low temperatures or creep resistance at elevated temperatures. Schematic diagram of the ion beam vapor deposition apparatus for TiN film formation. By definition, all steels, including stainless steels, are primarily made up of crystallised iron atoms with the addition of carbon. Maria Cristina Tanzi, ... Gabriele Candiani, in Foundations of Biomaterials Engineering, 2019. These are also ‘general purpose grades’, but with increased corrosion resistance owing to alloying with molybdenum (2–3%), and they are sometimes referred to as ‘acid-proof’ stainless steels. The low nickel content of the duplex grades makes them more price stable. The low chromium and low alloying element content of the martensitic stainless steels also makes them less costly than the other types. GarrisonJr, in Encyclopedia of Materials: Science and Technology, 2001. In this article, Outokumpu provides a brief overview of the four main categories of stainless steel: Ferritic, Martensitic, Austenitic and Duplex, and outlines their particular advantages and typical applications. Figure 1: ferritic stainless steel microstructure. Thus, they are broadly selected for mild ambient conditions requiring a combination of high strength and corrosion resistance. 22 | No.2 1. Hardness profiles were fitted assuming a sigmoidal function [37]. Copyright © 2020 Elsevier B.V. or its licensors or contributors. Crystalline Structure of Stainless Steels The vast majority of metals have a crystalline structure in their solid state, meaning that they are made up of crystallised lattice structures of atoms. Their corrosion resistance may be described as moderate (i.e., their corrosion performance is poorer than other stainless steels of the same chromium and alloy content). Development of other grades of martensitic stainless steel from the 410 grade (http://www.spiusa.com). Solidification may proceed by the precipitation of a small proportion of interdendritic δ-ferrite (vermicular δ-ferrite), favoured by the segregation of ferrite-stabilising elements to the interdendritic region. Somers, T.L. Titanium and niobium stabilization was also used to avoid detrimental carbide precipitates on welding, but for modern low-carbon Cr-Ni steels this is not necessary. Vilpas [63] observed that when solidification occurred in the primary austenite mode, the dendrite cores show the lowest pitting corrosion resistance, due to the segregation of Cr and Mo (ferrite stabilising elements) to the interdendritic region, while in steels with primary ferrite solidification mode, the lowest pitting corrosion resistance occurs in the austenite formed at the end of solidification or by solid-state reaction, near the δ/γ interface, where a sharp solute concentration gradient exists. The austenitic grades are non-magnetic in the solution annealed condition. A theoretical explanation for this behaviour was proposed by Fukumoto and Kurz [22] on the basis of an analysis of the δ and γ dendritic solidification kinetics. The cathodic protection sets the potential in a risk area, at low negative potentials, for hydrogen embrittlement to occur. GarrisonJr., M.O.H. Stainless steels are defined as iron base alloys that contain at least 10.5% chromium. 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