High-carbon-chromium bearing steel is often annealed in a sealed pot with a small amount of charcoal without physically contacting it. The charcoal is supposed to provide non-contact protection by simultaneously preventing oxidation and decarburisation during spheroidising. However, the actual effects of charcoal have not been thoroughly studied previously. In this paper, the effect of the non-contact charcoal protection is investigated. It remarkably reduces oxidation, but significantly increases decarburisation, compared with ambient air annealing. The oxide and decarburised layers with the non-contact charcoal protection are thicker than those after annealing in a sealed pot without charcoal protection and in ambient air. Experimental results have been analysed based on thermodynamics, and an improved spheroidising process for the bearing steel is suggested.
The common test for assessing hardenability is the standardised Jominy end-quench test according to ASTM-A255 or DIN-EN 50191. This test is applied essentially for non-alloyed and low alloyed structural steels, when quenched in liquid quenchants, but it is not applicable for high alloyed (air hardening) steels, because the cooling rate at the opposite end of the Jominy specimen is higher than the critical cooling rate of those steels. Today there is no a standardised method to test and evaluate the hardenability of high alloyed steels. Nowadays, not only high alloyed steels, but also some low alloyed structural steels are quenched by high pressure gas quenching (HPGQ) in vacuum furnaces. Obviously there is need from one side to develop a standardised method for testing and evaluation of hardenability for high alloyed steels when they are gas quenched, and from the other side to establish a database for hardenability of low-alloyed structural steels when they are quenched in vacuum furnaces by HPGQ, i.e. at different high pressures and different flow velocities. Corresponding equipment that can be used to satisfy both requirements is discussed.
Problems with ensuring the quality of large tools have led to the creation of several processing standards the most widely applied of which is from NADCA. The basis of this standard is briefly described along with the vacuum furnace equipment capable of achieving it. Results of experimental validation show that this equipment can easily meet the current and future needs of the tooling industry.
In this paper, the carburising process of steel foil was simulated by numerical method and the carbon transfer coefficient β at the workpiece surface was calculated with the conventional formula for the steel foil carburising test. The results indicated that foil thickness, carburising time and carbon diffusion coefficient in foil apparently affect the calculated carbon transfer coefficient, which always has a smaller value than the preset β value (the true value) and decreases with decreasing carbon diffusion coefficient. This paper suggests that the conventional formula is applicable only when carbon diffusion coefficient in foil is close to infinity; otherwise, the calculated β has obvious error and consequently, gives false information about the influences of other test factors. We propose a new calculation method based on the analytical solution of the diffusion equation during steel foil carburising and a supplementary test, with which the calculated β coefficient is close to the true value, and the carbon diffusion coefficient can be obtained simultaneously.
The paper briefly describes the origins of the heat treatment sector in Turkey and its historical development. The current status, and problems and predictions for the future, are covered in some detail.
AbstractA novel active screen plasma nitriding (ASPN) process provided excellent temperature homogeneity in the load and showed further progress in the control of nitriding potential. In addition to a variation of the nitrogen partial pressure in the process gas commonly used in the conventional plasma nitriding, the applied bias power strongly impacted the nitriding results. In the present work, an application of both methods for the control of nitriding potential in the ASPN process was systematically investigated for a wide range of process parameters to meet the treatment requirements for different types of engineering steel. A two-stage technique based on proper choice of process temperature and required nitriding potential in each stage has been applied in the ASPN process to avoid unnecessary compromises between sufficient thickness of the compound layer, the maximum case hardness and the acceptable nitriding hardness depth.
A plain medium carbon steel was borided by alternating current field enhanced pack boriding (ACFEPB). Diffusion kinetics and case characteristics of the borided steel were investigated to understand effects of an alternating current field (ACF) on pack boriding. Conventional pack boriding (CPB) was also employed for comparison. A series of boriding were conducted at temperatures of 873, 973, 1073 and 1173 K for 1, 2, 4 and 6 h, respectively, with a fixed current of 4 A. The morphology and types of borides formed in the steel were investigated by optical microscopy and X-ray diffraction, respectively. Boride growth kinetics was analysed by measuring the average thickness of the boriding case as a function of time and temperature. The growth rate of the ACFEPB case versus time showed the same parabolic character as CPB. The parameters of the boron diffusion kinetics, D = D0exp(−QR−1T −1), have been determined. The results showed that the ACF enhanced inter-diffusion of boron in the substrate. The value of D, diffusion coefficient, in ACFEPB was more than 4 times of that in the CPB. The activation energy Q (44·45 kJ mol−1) of the borided steel in the ACFEPB was less than 1/4 of that (180·6 kJ mol−1) in the CPB.
exploration, which is heavily dependent on heat treatment and surface engineering. The paper has clearly demonstrated with statistical data how stabilising and improving product quality as the result of the improvement of scientific, technical and management level of HT during the last decade in the petroleum machinery manufacturing industry in China has raised the equipment utilisation rate and reduced the energy consumption. We hope it may trigger a series of studies on various important industrial branches. In general, any scientific achievements in materials science in HT and SE, as well as technical innovations and upgrading in process efficiency, energy efficiency, furnace design and construction, measurement and process control, etc. contribute to the solution of energy-environment problems. In this relatively ‘old’ field of HT, many interesting and practically important effects still need to be reinvestigated and clarified, such as those presented in the paper by Dong and Zhu 2 . Energy and environment are, from the optimistic viewpoint, the external driving forces for the future of HT and SE. No doubt, clean energy generation and supply systems require not only upgrading of conventional HT and SE, but also new materials and methods for their processes. The energy transition may not be realised without innovation of new types of steels and highly developed steel processing. For example, the offshore wind power station demands high corrosion resistant steels for its foundations and towers. The efficiency of thermal power plant may be much improved when its pressure and temperature are raised, which may only be possible with new high-performance alloys. Recently the 2 nd International Conference on Energy and the Future of Heat Treatment and Surface Engineering 3 organised by Chinese Heat Treatment Society (CHTS) took place in Beijing. Following its predecessors the conference addresses the main themes of energy management in HT and SE and the HT and SE in the manufacture of clean energy generation and supply systems. In the coming IHTSE issues we will introduce selectively most interesting papers to our readers.
Titanium alloys are among the most important and frequently used class of biomaterials. In addition to biocompatibility, it is important that an implant material present satisfactory mechanical properties that allow long term use in the body. To improve such properties, different heat treatments are used, as well as doping with oxygen. The presence of interstitial oxygen in the crystal lattice causes deformation, increases the hardness, and causes modifications in anelasticity, thereby decreasing the elastic modulus. In this study, an alloy was prepared by arc melting precursor metals, heat and mechanically treated, and doped with oxygen, resulting in samples with different processing conditions. In each condition, the alloy was characterised in terms of amount of oxygen, X-ray diffraction, and optical microscopy. In addition, properties of the alloy, such as hardness and elastic modulus, were analysed.
Kobasko et al. have primarily shown that rapid water quenching can create compressive residual stresses near the surface and thereby a significant increase in the fatigue-limit (Intensive Quenching). Such processes result in an increase in hardness. Depending on steel grade, dimensions of the component and quenching intensity through hardening or only shell hardening will result. In this work, shell hardening processes were investigated in a more detailed manner for cylinders made of two different unalloyed steels. The goal of the work was discovering the general requirements to reach, on the one hand, a sufficient surface hardness paired with a non-through hardened hardening profile. On the other hand, compressive residual stresses in the near surface area should be as high as possible to achieve huge lifetime cycles for the heat treated work pieces. The experiments were carried out with a device that was especially developed for high speed quenching. As a quenching medium only tap water or water with 10% salt were used. It was shown that with this equipment very high heat transfer coefficients up to 50 000 W m−2 K−1 can be reached. Within the experimental design, cylinder made out of C35 and C56E2 with diameters between 25 and 43 mm were quenched with heat transfer coefficients in the range of 20 000 to 50 000 W m−2 K−1. The quenching results were characterised by measuring the microstructure, the hardness and the residual stresses. The experiments show that compressive stresses in the near surface area of 1200 MPa can be achieved.
Originating from discussions held in Rio de Janeiro in July 2010 and in Glasgow 2011, a proposal was made to International Federation for Heat Treatment and Surface Engineering (IFHTSE) that an int...
Oxidation ceramic coatings were prepared by MAO (microarc oxidation) technology in sodium phosphate electrolyte on Ti6Al4V titanium alloy. The morphology of the coating surface and the interface, and the phase composition were studied by OM, SEM, XRD respectively. The thermal cycling oxidation experiment at 700°C was carried out to evaluate the oxidation resistance property. The result showed that the ceramic coatings made by MAO technology on titanium alloy were composed of a porous layer and a dense layer which was regarded as a transition layer bonding the substrate and the porous layer. The coating was mainly consisted of rutile and anatase TiO2. The thermal cycling oxidation experiment showed that the coating had an excellent oxidation resistance at 700°C. The oxidation reaction constants and the reaction index of Ti6Al4V substrate and coated sample were determined through fitting oxidation kinetics data by linear regression equation.
he real time control of furnaces for low pressure carburizing requires rugged sensors and systems, which provide a signal correlated to the momentary carbon transfer into raw materials. A coulometric solid electrolyte sensor based on stabilized zirconia was developed and tested for this purpose, which enables the continuous titration of an aliquot of the exhaust low with oxygen. Investigations in the laboratory as well as on a single chamber furnace proof that the response time of the measuring system is signiicantly shorter than that of a H-2 thermal conductivity detector and that an on-site calibration enables the interpretation of the coulometric signal as a direct measure for momentary carbon transfer. he comparison of the online measured integral transferred carbon mass with the oline analysed carbon proiles of the treated work pieces shows good agreement related to the achievable precision.
Active screen plasma nitriding (ASPN) is a novel nitriding method, which has been demonstrating its growing commercial recognition for many years now. A characteristic feature of the ASPN process is a repositioning of the plasma source from the component surface towards a screen surrounding the batch. Application of independent bias power to the metal substrate provides an additional control of the flux of energetically active species directed to the components' surface. The advanced plasma technology overcomes a number of limitations of the conventional DC diode plasma nitriding. Both plasma assisted nitriding methods are very comparable regarding the equipment, which makes the ASPN method highly commercially competitive. Owing to the large number of independent process parameters in the ASPN process the structure of the nitrided layer with defined case characteristics can be effectively controlled to fulfil the application requirements. Process gas composition, working pressure and bias activation are the important process parameters. Controlled plasma nitriding and plasma nitrocarburising with the active screen provides a unique possibility to produce the whole spectrum of the nitrided layers beginning from the compound layer free surface, through the γ′- and ϵ-phase layer, up to the ϵ-carbonitrided layer.
Microstructural evolution of a dual phase steel sheet at different heating rates and temperatures was investigated by scanning electron microscopy (SEM). Texture, grain size distribution and grain boundary characteristic of ferrite phase in the dual phase steel were analysed by the electron backscattered diffraction (EBSD) technique. EBSD results show that the sample had obvious {111}//ND (normal direction) and {001} //ND texture at the heating rate of 50 and 250 K s−1 respectively, and that the grain size may be refined by rapid annealing. However, the effect of the heating rate on microstructure decreases as the heating temperature reaches 1173 K. It was found that grain size distribution and grain boundary characteristics of dual phase steel have been significantly affected by heating rate and temperature.
The work of the Collaborative Research Centre ‘Distortion Engineering’, begun at the University of Bremen in 2001, comes to a formal end in 2011. This note briefly describes the background to the project and the body of open information it has yielded
This paper discloses the findings of an XRD investigation of microstructural characteristics and calculations of their contribution to hardening of carbonitrided 20Cr3MoVW steel subjected to three heat treatment conditions. A method for evaluation of the total yield strength using X-ray diffraction data is proposed herein. It is based on a model of the steel strengthening being linearly affected by several microstructure strengthening mechanisms. Analysis of changes in depth profiles of the estimated yield strength with heat treatment is given together with comparison against microhardness distribution in the hardened case.
The Navy C-ring has been one of the most common types of specimen used for observing the dimensional changes (distortion) after heat treatment. The dimensional changes in the Navy C-rings are generally assumed to be comparable to those in an actual heat treated component. In this paper, we first review the various types of C-rings that have been used, and the results obtained for size and shape distortions for steels that have been carburised or nitrocarburised. An overview is then presented of the parameters that are included in simulation models to predict internal stresses and distortion. Finally, we present our own experimental and modelling results for the distortion in 1010 steel C-ring samples (three thicknesses) and an automotive component (torque converter piston) subjected to a gas ferritic nitrocarburising treatment. The predictions, on the basis of the nitrocarburised layer, and measured distortions were in better agreement for the thinner C-rings where the thickness was comparable to the thickness of the actual component. Hence, the distortion of C-rings with smaller bulk volume to nitrocarburised volume (V/VN) ratio compares favourably with the simulated values.
New phosphate black coatings for the improvement of mechanical properties on metallic objects have been developed to extend life time of machinery. The performance of phosphate black coatings was evaluated by weight gain studies, micro hardness studies, abrasive wear resistance and corrosion resistant measurement by electrochemical methods. The surface morphology of the coatings was assessed by XRD, SEM and XPS. The absorption coefficient of the coatings was evaluated by UV-visible spectrometer. Salt spray analysis was carried out to follow up the corrosion and get an idea about the performance of black coatings in automobile parts. The mechanical properties were very much improved after heat treatment of coatings at 200°C.
