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This work focuses on finding the residual stress distribution in post carburized steels. Initially, three different steel specimens (EN 3, 20MnCr5 and EN 353) were carburized with gas carburizing technique. For post carburizing treatment, one set of the samples was air-cooled (normalizing treatment) and others were quenched in water (hardening treatment). Scanning electron microscope (SEM) was used to study the microstructure of post carburized steels. The normalized steels displayed pearlite and bainite structures and hardened steels displayed low and high carbon martensite along with retained austenite. In few samples, the residual stresses were measured with the X-ray stress analyzer. A Finite Element Analysis (FEA) model was established using the varied material properties and thermophysical parameters of different steels. Later the measured and experimental data from the FEA were compared, there were in a good fit and the FEA model was validated. It was observed that the residual stress in normalized and hardened steels were dependent on the carbon gradient as well as the temperature difference from the core (center) to the case (surface) of the steels. The formation of martensite and retained austenite in the hardened steels led them to attain high magnitude stresses than normalized steels

Carbo-austempered steels with a nanobainitic microstructure in the case are established as an exciting alternative in applications demanding high stability and reliability against wear and fatigue. In this work, the effect of heat treatment conditions, i.e. austenitizing and isothermal transformation temperatures, on the wear behavior under rolling/sliding conditions of a carburized cast steel with a nanobainitic structure in the surface was examined. The results show that wear damage is mainly due to contact fatigue, with a small extent of oxidative wear, abrasion and adhesion. The results were compared with the conventional tempered martensite plus retained austenite microstructure obtained by means of carburizing followed by quenching and tempering. The nanobainitic microstructures show a better wear resistance than the quenched and tempered microstructures. Also, the specific wear rate in carbo-austempered steels was lower as the isothermal heat treatment temperature decreased. Results are explained in terms of the microstructural differences, hardening behavior and plasticity of the materials under study., The authors want to thank the CODI-Universidad de Antioquia for the financial support for the development of this research through the project PRG2017-15869, the National Center for Metallurgical Research - CENIM - and the Tribology and Surfaces Laboratory at the Universidad Nacional de Colombia, Medellin, for the support provided for the experimental development of this work.

In this paper, modelling of a low pressure carburizing furnace is developed. Acetylene is chosen as the reactive gas and its pyrolysis, described by a detailed kinetic mechanism is studied in a perfectly stirred tank reactor. Special attention is paid to the fluid-solid interactions; adsorption is described using a Langmuir approach and a first order surface reaction in acetylene is assumed. The diffusion of carbon in the steel is modelled by means of Fick’s second law and solved numerically using a finite volume method. All the simulations are performed using MATLAB environment. The numerical results provide the composition of the gas phase in the reactor as well as the spatio-temporal carbon profile in the steel, and are consistent with the experimental observations.

It is unable to strengthen molybdenum (Mo) through solid-state phase transformation, while exploring the effect of carbon (C) on microstructures and properties of fusion zone (FZ) of laser beam welding (LBW) joints of Mo alloy with serious grain boundary embrittlement is significant. An analysis was made on changes of bonding strength of grain boundary and precipitates on the grain boundary surface in the FZ of Mo carburized welded joints, and the existing form and strengthening mechanism of carbon. At first, solid carburizing (SC) can achieve the goal of adding the C to welded joints and C mainly appeared as C atoms and Mo2C in Mo alloy. Afterwards, C could increase the grain boundary strength and the plasticity of grains in the FZ. Therefore, the compatibility of deformation at grain boundary and grain interior was improved. Finally, Mo2C distributing at the grain boundary can inhibit the crack propagation during the deformation. As a result, the tensile strength of carburized weld joints rose by 426% compared with that of uncarburized weld joints, meanwhile the above results provide a new idea for the method for strengthening the Mo fusion weld joints. Keywords: Molybdenum, Carbon, Laser beam welding, Grain boundary embrittlement

Functionally graded cemented carbides (FGCCs) usually have a coarse-grained surface layer. In order to refine the grain size of WC and to improve the mechanical properties, VC and NbC as grain growth inhibitors, were added to WC–6Co FGCCs. The grain growth kinetics of WC was investigated, and both the room temperature and high temperature mechanical properties were tested. The results show that the additions of NbC and VC reduce the thickness of the gradient layer in FGCCs. The addition of VC reduces the thickness of the gradient layer by half, while that of NbC is less effective. The additions of NbC and VC refine the grain size by suppressing the adsorption/desorption processes of WC grains in Co phase during the pre-sintering and the carburizing processes, and VC is more effective than NbC. The addition of NbC increases the transverse rupture strength of FGCCs, because of the fine microstructure, and the solution strengthening in Co phase. Both the additions of NbC and VC increase the high temperature hardness of FGCCs due to improved oxidation resistance, more homogeneous and finer microstructures. Keywords: Functionally graded cemented carbides, Gradient layer, Grain growth, Transverse rupture strength, High temperature hardness

Surface engineering is the process of modifying or coating the surface of a component to enhance its properties, and has an important role to play in tribology. This chapter reviews a large number of surface engineering processes in a logical manner, moving from processes that modify the surface with no change in composition, to those involving compositional change, and then to the application of coatings. In each case the physical and chemical principles of the process are explained, practical examples of its implementation are provided and the properties of the resulting surface and its tribological applications are discussed. Examples of the processes included range from transformation hardening and surface texturing, through carburizing, nitriding and anodizing, to electroplating, weld hardfacing, thermal spraying and physical vapour deposition (PVD). A very wide range of materials is covered.

The service condition of many machine parts of steel such as gears, shafts, cams, pinions, and piston pins demands very hard and wear-resistant case but with tough and shock-resistant core. This can be achieved by case hardening of low carbon steel. Carburizing is the most satisfactory and widely used method of case hardening of low carbon steel. In this chapter the three general methods of carburization such as solid or pack carburization, liquid carburization, and gas carburization with the theory of carburization are described in detail. The carburized machine parts are subjected to heat treatment (hardening and tempering) to develop the desired microstructure and properties. Different heat treatment (hardening) techniques for carburized steels with their resultant microstructures are described. This chapter also deals with the carburization of different alloy steels. Lastly the problems during carburization and their probable remedies and recommended processing sequence for carburized components are addressed.

Different steel alloys of tool steel and alloy steel were heat treated with different heat treatment processes such as hardening, gas carburizing, and gas nitriding. The electrochemical behavior, especially corrosion characteristics, of the different steel grades were evaluated using different electrochemical techniques in 0.1 M sodium chloride solutions at different values of solution pH. Potentiodynamic scans indicated similar corrosion behavior between the different heat treatment processes. However, the nitriding process added extra corrosion resistance to certain steel alloys which included strong nitride forming elements. Also, the electrochemical impedance spectroscopy and salt spray tests confirmed the same and indicated an increase in corrosion resistance after the nitriding process. Keywords: Heat treatment, Corrosion, Nitriding, Carburizing, EIS

Cold plasma technology has enabled the development of a new generation of low-temperature (450°C or less) thermochemical surface treatments for stainless steels. This chapter describes how the technology is used. By varying the process parameters, it is possible to synthesize a variety of layered structures, and, in particular, to produce hard, precipitate-free layers based on the expanded austenite lattice. The diffusion elements can be nitrogen, carbon, or nitrogen and carbon. In this chapter, we examine the different metallurgical structures and their main characteristics in terms of wear and corrosion resistance.

Fatigue behavior is an important property in the technical application of steels. Carburizing and nitriding enhance the fatigue strength because the local resistance to crack initiation is increased by hardness profiles and compressive residual stresses in the heat treated case. The influences of the carburized or nitrided microstructures on the fatigue strength are described as well as the statistical character of the fatigue behavior.

This chapter discusses the benefits of nitriding on the mechanical properties of steels. The generation of a compressive residual stress using nitriding can have beneficial impacts on such characteristics as hardness and fatigue life. These effects are explained in terms of the effect of nitrogen diffusion on the microstructure of the steels and a model presented for calculation of the residual stresses induced, and volume changes associated with the process.

Nitriding and carburizing by laser irradiation in combination with a process gas is a common method to enhance the surface properties of various materials. This chapter discusses the different aspects of the process starting from fundamental mechanism up to engineering applicability. It will introduce and classify the method followed by a brief but detailed summary on the basic physical and chemical mechanisms involved. Further, the most common materials, their suitability and upcoming opportunities will be discussed. A major goal is to offer an insight into the issues at the model system titanium (Ti-alloys) comprising laser radiation and time aspects. Carburizing will be the central focus in another section. Surface treatments of steel and nonferrous materials will be explained and examined from different sides. As well, nitrocarburizing as a kind of hybrid process will be introduced. The chapter closes with referring to future developments and trends.

A major purpose of thermochemical diffusion processes is to alleviate surface degradation. Wear resistance is not a simple property. There are many wear mechanisms. We show nitrided/nitrocarburized steels have good functionality in mildly oxidational environments at elevated temperature (up to 400°C); outperforming untreated, carburized and carbonitrided steels. e -Fe 2-3 N layers formed via nitrocarburizing, have specific advantage under lubricated high pressure (> 1GPa) rolling contact conditions. Borided steels exhibit anisotropic fracture behaviour and are too brittle being only suited to low contact pressures (< 100MPa). Conversely, vanadized steels (via the TD process) have sufficient hardness to resist abrasion by the hardest of abrasives and can best be exploited on very tough and very strong steel substrates. They maintain these properties up to 450°C.

Carburizing, usually followed by subsequent quenching and frequently also by tempering, the total process being called case-hardening, is the dominant heat treatment technology for improving hardness, strength, wear resistance, load carrying capability and fatigue strength of components made of metals and especially steels. The chapter explains the theory of carbon transfer, carbon diffusion, process control, the various processes used for carburizing and quenching as well as the improvement of properties achieved and the furnaces used for industrial case-hardening.

Low-temperature surface hardening of stainless steels through plasma or gaseous processes improves the performance of various industrial components subjected to a combination of wear and corrosion resistance. This chapter describes typical industrial applications in the nuclear, mechanical, chemical and food industries.

The standard carburizing steel 18CrNiMo7-6 is often used when high hardenability is required. Because of its highly fluctuating price, there has always been an incentive to develop Ni-free steel grades. The 23MnCrMo5-5-2 or Jomasco 23mod has been developed for this purpose. To ensure smooth substitution within existing production lines, a number of points have to be addressed: first, checking the response to carburizing treatments, second, having similar mechanical properties with identical tooth root bending performance on gears. The latter is the purpose of this paper.

Carburizing is used to enhance fatigue resistance and toughness properties of dynamically loaded components. By carbon enrichment in gas atmospheres, carbon profiles are established and transferred by quenching into hardness profiles based on microstructures of plate martensite and retained austenite in the outer case and lath martensite in the interior core of carburized low carbon steels. In addition, the martensitic transformation results in a beneficial surface compressive residual stress distribution. Both hardness profile and residual stresses enhance the fatigue strength, which is also affected by parameters such as the main parameters such as the relation of case to component size, the surface hardness and the amount of retained austenite. The relation of case to component size is also the parameter dominating the toughness, which can also be increased by alloying with nickel.

Hardening and depth of hardening of steel parts are critically important material and process design parameters. Hardenability is the composition-dependent property of a steel that describes its ability to harden by martensite formation and is related to parameters such as austenitizing temperature, cooling rates after austenitizing, and part size and geometry. A selective overview of the experimental and predictive procedures to determine hardenability is presented. This discussion covers the breadth of steel hardenabilities, including those of shallow-hardening, low-carbon steels, plain-carbon and low-alloy medium-carbon steels, air-hardening tool steels, and carburizing steels. Sufficient detail and references are provided to enable the reader to adequately understand and practice the methods discussed.

Expanded austenite can be generated on austenitic stainless steels either by ion carburizing or ion nitriding. In both cases the resulting fcc crystal structure, supersaturated with nitrogen or carbon, is strongly hardened with improved wear-resistance, while maintaining the original resistance to corrosion. In this work, we have studied the stability of expanded austenite, generated by ion nitriding and ion carburizing on AISI 316L SS with N and C, under: a—high temperature (225 °C – 504 °C), and b—under irradiation with high energy (30 keV – 500 keV), high fluence (~ 1015 cm− 2), short duration (~ 400 ns) light (deuterium and helium) ion beams. It was found that expanded austenite is stable below 325 °C. Between 325 °C and 504 °C expanded austenite lattice parameter presents gradual reduction with increasing temperature. We observed microstructural changes related only to the temperature treatment. We did not observe any microstructure change due to the duration of the heat treatment. Over 504 °C, the lattice parameter returns to the material's austenite original parameter. On the other hand, when irradiated with pulsed ion beams, a gradual reduction of the lattice parameter corresponding to the expanded austenite with the number of pulses was observed. This behavior can be explained through the thermal shock induced on the surface by each beam, consisting in fast heating followed by fast cooling that induces the gradual exo-diffusion of N (or C). Nevertheless, after 20 ion pulses, a final lattice parameter slightly higher than the corresponding to the original austenite was found as stable limit. This residual expansion can be attributed to partial amorphization of the first few micrometers that induces stresses on the crystals of austenite which are closer to the surface layers. Fil: García Molleja, J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina Fil: Milanese, Maria Magdalena. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil; Argentina Fil: Piccoli, M.. Università Roma Tre. Dipartimento di Ingegneria Meccanica e Industriale; Italia Fil: Moroso, Roberto Luis. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil; Argentina Fil: Niedbalski, Jorge Julio. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil; Argentina Fil: Nosei, L.. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura. Instituto de Mecánica Aplicada y Estructuras; Argentina Fil: Burgi, Juan Mauel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina Fil: Benporad, E.. Università Roma Tre. Dipartimento di Ingegneria Meccanica e Industriale; Italia Fil: Feugeas, Jorge Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina

Low temperature plasma carburizing is a plasma surface engineering technique developed for austenitic stainless steels to achieve combined improvements in tribological and corrosion resistant properties. However, until recently very little work has been conducted to study the response of carburized stainless steel to combined actions by wear and electrochemical corrosion. In this paper, the tribocorrosion behavior of low temperature plasma carburized AISI 316L stainless steel under unidirectional sliding in 1 M H2SO4 and 0.5 M NaCl solutions is compared. It is found that in both test solutions, the carburized layer exhibits much better resistance to material removal than the untreated specimen at anodic potentials, but its effectiveness in improving wear resistance at open circuit and cathodic potentials is less significant. Particularly, in the pitting environment containing 0.5 M NaCl, numerous corrosion pits are formed inside the wear track on the untreated specimen at potentials much lower than the pitting potential, while no corrosion pits are observed inside the wear track on the carburized specimen at anodic potentials as high as 1000 mV(SCE). Further experiments conducted in 1 M H2SO4 solution at various contact loads and frequencies reveal that the carburized layer has a much better ability to repassivate than the untreated specimen. The much improved tribocorrosion behavior of the carburized layer can thus be attributed to its high hardness, good corrosion resistance and excellent repassivation ability.

Low temperature plasma carburizing is a surface engineering technique developed for austenitic stainless steels to achieve combined improvements in tribological and corrosion resistant properties. However, very little work has been conducted to study the response of carburized stainless steel to combined actions by wear and electrochemical corrosion. In the present work, experiments have been conducted to study the tribocorrosion behavior of low temperature plasma carburized AISI 316L stainless steel, under unidirectional sliding in 1 M H2SO4 solution, using a pin-on-disk tribometer integrated with a potentiostat for electrochemical control. Sliding wear tests were conducted under potentiodynamic and potentiostatic conditions at a wide range of applied potentials. It is found that the carburized layer exhibits much better tribocorrosion resistance than the untreated specimen at anodic potentials, but is not effective in improving wear resistance at cathodic potentials. The results are discussed in terms of the accumulation of the third body wear particles, material transfer and the contribution of mechanical wear and chemical wear to overall material removal by tribocorrosion.

The understanding of high temperature corrosion phenomena requires detailed knowledge of the specific environment in which exposure has taken place. While focus upon the effects of temperature and gaseous environment comprises much of the breadth of the knowledge of high temperature corrosion, factors such as pressure, gas velocity, condensate composition, and stress state are important considerations as well. This article provides an up-to-date review of high temperature corrosion environments encountered in industry. Major discussion topics include oxidizing, nitriding, carburizing, and sulfidizing environments, as well as halide-containing environments. Coal-fired and oil-fired boiler corrosion considerations, as well as applications encountering molten metal and molten salt corrosion are reviewed.

The response of a cast 316 type austenitic stainless steel to the novel low temperature plasma carburizing process has been investigated in this work. The cast steel has a dendritic structure with a mix of austenite, ferrite and carbide phases. The results show that such a complex structure responds well to the carburizing process, and the inter-dendrite regions containing ferrite and carbides can be transformed to expanded austenite to form a continuous and uniform layer supersaturated with carbon. Such a layer is precipitation free and possesses a high hardness and good corrosion resistance.

Samples of Al-MCM-41 (Si/Al=20) and Si-MCM-41 molecular sieves were impregnated with ammonium heptamolybdate solutions using the incipient wetness method in order to have a MoO 3 loading of 21wt%. β-Mo 2 C supported on Al-MCM-41 and Si-MCM-41 was obtained by carburizing the oxide samples using the Temperature-Programmed Carburization (TPC) methodology with a 20%(v/v) CH 4 /H 2 mixture. The carburized samples were tested as hydrotreating (HDT) catalysts employing the hydrodesulfurization (HDS) of thiophene at different temperatures as model reaction. The activity results obtained at atmospheric pressure show that Al incorporation to the MCM-41 framework led to a twofold increase in the catalytic activity. For the experiments at high pressure (3 MPa) the results reveal that while β-Mo 2 C supported on Si-MCM-41 presented a decrease in activity with time on stream, the β-Mo 2 C supported on Al-MCM-41 was quite stable along twenty hours on stream.

A study is made of the use of a steel-making by-product (rolling mill scale) as a material for removing Cu2+ ions from aqueous solutions. The influence of contact time, initial copper ion concentration and temperature on removal capability is considered. The removal of Cu2+ ions from an aqueous solution involves two processes: on the one hand, the adsorption of Cu2+ ions on the surface of mill scale due to the iron oxides present in the latter; and on the other hand, the cementation of Cu2+ onto metallic iron contained in the mill scale. Rolling mill scale is seen to be an effective material for the removal of copper ions from aqueous

The tungsten carbides on FSM-16 were prepared in carburizing of WO 3 /FSM-16 with 20% CH 4 /H 2 and characterized using nitrogen adsorption, XRD, TEM, and NMR. The relationship between the surface properties and the catalytic activity of tungsten carbides on FSM-16 in cyclohexene hydrogenolysis at 250°C was discussed.

Publisher Summary This chapter discusses the preparation of tungsten carbide supported on aluminium (Al-)FSM-16 along with its catalytic activity. The tungsten carbides on FSM-16 are prepared in the carburizing of WO3/FSM-16 with 20% methane/hydrogen (CH4/H2) and characterized using nitrogen adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and nuclear magnetic resonance (NMR). The relationship between the surface properties and the catalytic activity of tungsten carbides on FSM-16 in cyclohexene hydrogenolysis at 250°C are also discussed.

This chapter discusses elastoplasticity coupled with phase changes. The transformation-induced plasticity (TRIP) term as an additional strain rate term to the “classical” plastic strain rate term is valid for ductile metals like steel under diffusional or displacive phase transformations subjected to a monotonic loading path. The transformation kinetics described in this chapter is valid for many technically relevant metals subjected to nearly any paths of heating or cooling. The selection of mechanical material data is typical of heat treatment simulations, welding simulations, or surface treatment simulations by induction hardening, carburizing, and nitriding. The model consists of two more or less connected parts: the transformation process itself and the deformation process described as the deformation process. In practice, a picture on the transformation kinetics is reflected by the time-temperature-transformation diagram continuous cooling diagram, cooling transformation diagram, and continuous cooling transformation diagram.

Chemical vapor deposition (CVD) coatings are useful in applications requiring resistance to wear and corrosion over a wide range of temperature. Wear and corrosion protection can be provided by the techniques of hard-facing and plating or by surface modification processes such as boriding, nitriding, carburizing, and ion implantation. The protection these processes provide is adequate in most environments but fail over a period of time if the conditions are too severe. Another useful technique is plasma spraying. It has a drawback of requiring thick deposits to insure adequate protection. It often requires extensive grinding and polishing. Other techniques, such as sputtering, provide excellent protection. CVD suffers limitations to a lesser degree and so it is being used in many industrial applications, particularly those operating in extreme conditions. It is the best solution to severe problems of erosion, friction, or hot corrosion. The number of CVD coating materials for wear and corrosion resistance is relatively small. The most important are—titanium carbide, titanium carbonitride, and chromium carbide.

This chapter explores the effects of deposition conditions on diamond nucleation. Deposition conditions, such as substrate temperature, gas pressure, and gas composition, critically influence diamond nucleation density and rate. It has been noted that ideal growth conditions may not be optimal for nucleation. The characterization of diamond deposits using micro Raman spectroscopy, scanning electron microscopy (SEM) and optical microscopy (OM) revealed that the maximum nucleation density of diamond particles on the unscratched Si substrate occurred at a pressure of 5 torr. The pressure dependence of the nucleation density was explained by the competition effect between β-SiC formation, which increases the diamond nucleation density, and atomic-hydrogen etching, which decreases the number of nucleation sites. On the basis of this finding, a new fabrication approach for high-quality diamond films without any substrate pretreatment was proposed, i.e., diamond nucleation at a lower pressure (5 torr) and growth at a higher pressure (30 torr). An in situ treatment with an optimum combination of deposition conditions has been proposed to reduce the nucleation delay and enhance the nucleation density on MO substrates to promote diamond nucleation by carburizing the substrate surface and enhancing the surface.

When one examines parts having worked under strongly loaded contact situations, irreversible marks can be seen; they are the results of a dissipative process: contact plasticity. Residual stresses measurements can confirm this plastic evolution. Often, for hard materials having a quite brittle response, tensile tests classically used to identify the characteristics for plastic behaviour give very uncertain results. Contact tests, such as indentations, coupled with a numerical model, allow a much better knowledge of this plastic behaviour using an inverse method. For components on which a thermo-mechanical treatment has been performed, such as carburizing or induction quenching, the surface layers have quite distinct elastic-plastic properties compared with the bulk material, and do not exist freely. From our indentation test and associated code, the behaviour of these surface layers can be determined. The knowledge of the surface layers' behaviour will then allow the prediction of the evolution of treated industrial components. It will be quite appropriate especially for contact purposes such as those which are encountered in rolling bearings or gears.

Creep fatigue behavior of SUS304 stainless steel in carburized sodium at 550°C was investigated. Test duration was up to 6000 hours and the maximum carbon concentration at the surface of the specimen was 0. 46%. It was made clear that creep fatigue lives under the heavy carburizing condition showed no life reduction compared with those in air environment. It was implied that creep fatigue lives at low strain ragnes were governed by creep cavity nucleation and growth inside the material rather than environmental effect which was restricted to the surface reagion of the material. Evaluation of creep fatigue life in carburized sodium was shown to be possible based on the linear damage summation rule using the material properties obtained in air environment.

In the present work a model of the carburizing and carbonitriding atmospheres has been derived that will give the expected values of the carbon and nitrogen contents in a foil in equilibrium with the atmosphere as well as potential values and activities for carbon and nitrogen. In the model all the reactions of importance in the carburizing and carbonitriding atmospheres are considered simultanously, each with its individual activity value and reaction rate. As a second step the model is used as a base in a model where the diffusion profiles obtained after a given heat treating cycle cen be predicted. Then non constant values for the surface contents of carbon and nitrogen are used, dependent on the net reaction rate for each component. The diffusion coefficients for carbon and nitrogen are concentration dependent. Mathematically finite difference approximations are employed for the solution of the differential equations. Comparisons with experimental data show very encouraging agreement for carbon and nitrogen potentials as well as for carbon and nitrogen profiles in steel.

Thermal treatments discussed in this paper are induction and laser hardening of steel and thermochemical treatments are carburizing, nitriding, nitrocarburizing and boriding of steel. The principles for the methods are briefly described and experimental data on residual stresses are reviewed. The mechanisms for the residual stress generat is then discussed in some detail supported by computer models. The effect of varying the process parameters on the residual stress is analysed.

The tribological characteristics of steel 20Cr2Ni4 after carburizing and carburize-sullfurizing was studied. It was shown that an excellent resistance against adhesive wear may be obtained by a complex thermochemical treatment. The coefficient of friction and the wear rate values on the surface of wearing pairs of carburize-sulfurized steel were reduced in pin-ring tests. Together with other experimental data, the carburize-sulfurizing treatment is shown to be a prospective method for improving the tribological properties of various machine parts.

Publisher Summary This chapter presents the research background of the thermalloy grades of chromium–nickel–iron heat-resisting alloys. It explains how the thermalloys differ in some respect from common wrought and other cast alloys. The corrosion grades have used such suffixes for years; but in that case, the numbers designate maximum carbon contents. The function of the various alloying elements differs; for instance, chromium increases oxidation resistance and corrosion by hot gases. Manganese and silicon are added for steel-making purposes, but silicon does influence carburizing resistance. In addition, it has benefited from many unbudgeted contributions of material and services.