SURFACE HARDENING OF STEEL PARTS

Abstract

Surface hardening is a generic term covering a number of processes used to improvethe wear resistance of ferrous parts without affecting the more soft, tough interior of thepart. The combination of a hard surface and softer interior, made possible, for example,by case hardening methods, is of inestimable value in modern engineering practice. Bythe use of high-quality alloy steels, great strength and toughness in the core can be com-bined with extreme surface hardness, resulting in a composite structure capable of with-standing certain kinds of stress to a high degree. For less exacting requirements, thereare many applications where low or moderate core properties, together with a highdegree of surface hardness, can be obtained with cheaply fabricated, low-priced carbonsteel.Three of the major types of treatments that are conventionally used to enhance sur-face wear resistance are classified as thermochemical, thermal, and coating or plating.Examples of thermochemical treatments include carburizing, nitriding, and carboni-triding (case hardening methods). Examples of thermal or applied energy treatmentsinclude flame and induction hardening. Coating or plating processes include hardchromium plating, electroless nickel plating, and various hardfacing methods. Theselong established surface hardening technologies are continually being improved andremain among the most widely used. However, today completely different surface hard-ening technologies are being applied to and developed for steels. The objective remainsthe same, that is, enhanced surface performance, but technologies that incorporate high-energy beams, plasmas, magnetic and electrical fields, and vacuums are being applied.Some of these technologies have been used for some time in the electronics industry tofabricate thin film devices and circuits and therefore cannot be considered new tech-nologies. Their application to steel, however, is relatively new, and they elevate thelevel of sophistication and control of surface hardening.Surface Hardening of Steels: Understanding the Basics is a practical selection guideto help engineers and technicians choose the optimum surface hardening treatment fora given application from an ever increasing number of options. Emphasis is placed oncharacteristics such as processing temperature, case/coating thickness, bond strength,and hardness level obtained. The advantages and limitations of the various surface mod-ification technologies are compared. Recent developments in the understanding of therelationships between microstructure and fatigue and wear performance are reviewed,as are more recently introduced surface hardening processes such as vacuum/plasma-related technologies, laser processing, chemical vapor deposition/physical vapor depo-sition, and ion implantation. Methods for evaluating hardness patterns and depths ofhardness for quality control and failure analysis are described. Metallurgical compar-isons are made between those processes that offer rapid heating and rapid cooling (self-quenching) characteristics—for example, induction hardening—and conventional fur-nace hardening. Metallurgical characteristics and properties obtained by atmosphereand vacuum carburizing are also compared. Wear and corrosion data are also providedto demonstrate the benefits of each process. MLA 8th Edition (Modern Language Assoc.) Davis, J. R. Surface Hardening of Steels : Understanding the Basics. ASM International, 2002. APA 7th Edition (American Psychological Assoc.) Davis, J. R. (2002). Surface Hardening of Steels : Understanding the Basics. ASM International.