Low-temperature surface hardening is mostly applied to austenitic stainless steels when a combination of excellent corrosion performance and wear performance is required. This article provides a brief history of low-temperature surface hardening of stainless steel, followed by a discussion on physical metallurgy, including crystallographic identity, thermal stability and decomposition, nitrogen and carbon solubility in expanded austenite, and diffusion kinetics of interstitials. It provides a description of low-temperature nitriding and nitrocarburizing processes for primarily austenitic and, to a lesser extent, other types of stainless steels along with practical examples and industrial applications of these steels.

Surface hardening improves the wear resistance of steel parts. This article focuses exclusively on the methods that involve surface and subsurface modification without any intentional buildup or increase in part dimensions. These include diffusion methods, such as carburizing, nitriding, carbonitriding, and austenitic and ferritic nitrocarburizing, as well as selective-hardening methods, such as laser transformation hardening, electron beam hardening, ion implantation, selective carburizing, and surface hardening with arc lamps. The article also discusses the factors affecting the choice of these surface-hardening methods.

Electron beam hardening (EBH), with some special characteristics in comparison to other heat treatment technologies, allows beam deflection frequencies of up to 100 kHz. This article illustrates the principles of different thermal electron beam technologies, including beam-deflection, continuous EB interaction, EB flash, as well as multifield EB-deflection and multiprocess techniques. It characterizes the technical and technological possibilities for EBH in comparison to other surface-layer hardening processes. The article also discusses the technical design of electron beam facilities and the applications of EBH.

The thermoreactive deposition and diffusion process is a heat-treatment-based method to form coatings with compacted layers of carbides, nitrides, or carbonitrides, onto some carbon/nitrogen-containing materials, including steels. The amount of active carbide forming elements/nitride forming elements, coating temperatures and time, and thickness of substrates influence the growth rate of coatings. This article lists carbide and nitride coatings that are formed on carbon/nitrogen-containing metallic materials, and describes the coating process and mechanism of coating reagents. It details the growth process and nucleation process of carbide and nitride coatings formed on the metal surface. The article discusses the advantages, disadvantages, and characteristics of the various coating processes, including high-temperature salt bath carbide coating, high-temperature fluidized-bed carbide coating, and low-temperature salt bath nitride coating.

This article commences with a description of the principles of induction heating followed by a discussion on the high temperature electrical, magnetic, and thermal properties of steel, which influence the performance of induction heaters. The importance of eddy current distribution in a workpiece is explained, with emphasis on the skin effect. The article discusses typical procedures for induction hardening of steel, namely, austenitizing and quenching to form martensite either on the surface (case hardening) or through the entire section (through hardening). It briefly describes induction heating parameters for surface hardening, through hardening, tempering, and some general heating operations in metalworking.

Laser surface hardening is a noncontact process that provides a chemically inert and clean environment as well as flexible integration with operating systems. This article provides a brief discussion on the various conventional surface-modification techniques to enhance the surface and mechanical properties of ferrous and nonferrous alloys. The techniques are physical vapor deposition, chemical vapor deposition, sputtering, ion plating, electroplating, electroless plating, and displacement plating. The article describes five categories of laser surface modification, namely, laser surface heat treatment, laser surface melting such as skin melting or glazing, laser direct metal deposition such as cladding, alloying, and hardfacing, laser physical vapor deposition, and laser shock peening. The article provides detailed information on absorptivity, laser scanning technology, and thermokinetic phase transformations. It also describes the influence of cooling rate on laser heat treatment and the effect of processing parameters on temperature, microstructure, and case depth hardness.