Effects of cooling rate on mechanical properties and corrosion resistance of vacuum sintered powder injection molded 316L stainless steel

This study presents the results of corrosion behavior of powder injection molded 316L stainless steel parts sintered in vacuum. The feedstocks of metal powder and plastic binder were prepared and their viscosity was measured. Green samples were injection molded and binder was removed from the green parts. Brown test parts were sintered at 1325 °C with heating rate of 5 °C/min and 10 °C/min for 2 h followed by the same cooling rate. Corrosion response of the sintered test samples was measured by weight loss method in Ringer's Solution of pH 7.4 for 15 days. The test samples using cooling rate 10 °C/min showed higher mechanical properties and improved corrosion resistance compared to those sintered at low heating and cooling rate. High cooling rate reduced the evaporation of Cr and developed passive chromium oxide layer on the test samples resulting improved corrosion resistance.     

Die steels for high-speed automatic hot die forging machines

Conclusions Steel 3Kh3M3F produced by ESR has the best combination of strength, hardness, and toughness, and also resistance to crazing. The life of punches made of this steel was double that of standard steel 3Kh2V8F and considerably higher than that of steels with a higher carbon content (0.4–0.5%).The life of 3Kh3M3F punches (ESR) was three to four thousand bearing races higher than that of the same steel melted in an open furnace.These data lead us to recommend that punches for high-speed water-cooled presses be manufactured from steel 3Kh3M3F (ESR) with the following chemical composition: 0.26–0.34% C, 2.8–3.3% Cr, 2.5–2.9% Mo, 0.40–0.60% V (ChMTU-1-963-70).The following heat treatment is recommended: preliminary heating in an electric furnace at 500–510°, salt bath at 850–860°, and salt bath at 1040±10°. The parts should be quenched in oil with a temperature of 120–150°. The first tempering after quenching should be conducted in a salt bath at 600° for 2 h, with cooling in air. The second tempering should be conducted in a salt bath at 560° for 2 h, with cooling in air. The hardness of the parts after heat treatment is HRC 49–51.All-Union Scientific-Research Institute of the Bearing Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 20–25, November, 1973.     

Effect of low-rate isothermal plastic deformation on the structure and properties of ZhS6KP nickel alloy

ZhS6KP alloy is used in commercial production of blades of aircraft engines pressed in Widin presses. Standard heat treatment that consists in air hardening from 1220°C (4 h) and aging at 950°C for 2 h with cooling in air does not always provide an optimum combination of long-term strength and fatigue resistance for the alloy at 900°C. In this connection, the possibility of improving the fatigue resistance and the long-term strength while preserving the high level of short-term mechanical properties by conducting low-rate plastic deformation before the heat treatment is considered.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 31 – 33, July, 1996.     

Improvement of the technological plasticity of KhN56VMTYu-VD alloy

Conclusions The maximum technological plasticity of the KhN56VMTYu-VD alloy in the two-phase state is achieved after heat treatment by the following method: hardening at 1120°C (2 h) in air+aging at 975°C (2 h) with cooling in water.Kulebaksk S. M. Kirov Metallurgical Plant. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 40–42, March, 1981.     

Low-temperature cyaniding of cylinder block sleeves

Conclusions We recommend the following heat treatment for the cylinder sleeves of certain tractor and automobile engines; it ensures a high wear resistance and does not induce warping: a) annealing for stress relief, with heating at 75–100 deg/h to 580–600°C, soaking, cooling at the rate of 40–50 deg/h to 200°C; final machining, including honing; b) gas cyaniding 6 h at 560–580°C in a medium of 70% carburizing gas and 30% ammonia.Bauman MVTU, Moscow Automobile Plant. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 60–62, July, 1967.     

Effects of cooling air temperature on cryogenic machining of Ti-6Al-4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti-6Al-4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti-6Al-4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip-tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.     

Influence of oxidation on the composition and structure of the surface layer of hot-pressed boron carbide

The oxidation of hot-pressed boron carbide under isothermal conditions and under conditions of programmed heating up to 1500°C was investigated. Oxidized samples were studied by secondary-ion mass spectrometry, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray microanalysis, X-ray diffraction, and other methods. It has been demonstrated that oxidation starts above 600°C and results in the formation of a thin transparent B₂O₃ film that is cracked after cooling. Up to 1200°C, the oxidation process is limited by the diffusion of reagents through the oxide layer; at higher temperatures, it is determined by the rate of chemical reaction of carbide with oxygen in the air. During boron carbide oxidation the etching of grain boundaries occurs, it results in strength degradation at higher temperatures.     

Properties of seams with electron-beam welding of tubing to tube sheets

Conclusions As the result of two heat treatments the structural heterogeneity, microhardness gradient in the seam and the base metal, and the residual internal stresses in weldments decreased considerably. The best properties were obtained after heat treatment 1: heating at a rate of 20 deg/h at 1050–1080°, holding 30 min, and furnace cooling to room temperature at a rate of 65 deg/h.Donets Physicotechnical Institute, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 60–63, March, 1978.     

Effects of heating temperature and duration on the microstructure and properties of the self-healing coatings

The present work investigates how the heating temperature and duration affect the properties of the self-healing coating on martensitic steels. The coating composed of TiC + mixture (TiC/Al₂O₃) + Al₂O₃ is fabricated by means of air plasma spraying. The thermal shock test is performed at 600 °C, 700 °C and 800 °C, respectively, to evaluate the thermal-mechanical stability of the coating. The cross-section morphology of the samples after 1 h, 9 h, 18 h and 30 h of heat treatment shows that the porosity of the coating decreases with the increase of heating duration. The evaluation of electrochemical performance by electrochemical impedance spectroscopy shows that the corrosion resistance of the coating after being heated for 18 h is much better than the other samples due to the process of the inner layer being compacted in the coating. The adhesive tensile strength test between coating and substrate shows that the adhesive strength of the coatings is higher than 9 MPa within 40 h of heat treatment at 600 °C. The residual stress reaches a minimum value after the coating was heated for 9 h at 600 °C, then increases with the heating duration after 9 h. Energy dispersive X-ray analysis at the Vickers indentation indicates that the oxygen content at the crack position increases significantly after being heated for 30 h at 600 °C. These experimental results suggest that this coating can meet the requirement of application under the actual temperature conditions.     

Formation and evolution of phosphorus-containing species during high-temperature oxidation of TiAl dipped in a low-concentrated phosphoric acid solution

TiAl samples were dipped in a low-concentrated phosphoric acid solution, air dried, then heated to 800 °C under argon gas before oxidation under reconstituted air at this temperature. At the end of the heating ramp, sample surfaces were covered by a titanium pyrophosphate (TiP₂O₇) layer, well adhered to the substrate. This pyrophosphate was shown to be detectable from 400 °C. Chemical reactions have been proposed for the formation of this compound. TiP₂O₇ coating strongly increased the oxidation resistance of TiAl at 800 °C for 100 h. After 100 h, a transition period occurred leading to the change of TiP₂O₇ into TiO₂, which was achieved after 230 h, total mass gain always remaining below that of raw substrate. This evolution was demonstrated not resulting from a thermal decomposition of pyrophosphate compound.     

Formation of WSi2 coating on tungsten and its short-term cyclic oxidation performance in air

Microstructural aspects of WSi₂ coating on pure W and its short-term oxidation performance under cyclic heating and cooling conditions in air at 1100 and 1300 °C have been studied. Cyclic oxidation performance of this coating has been compared with its performance under isothermal oxidation. The coating was applied by using a pack siliconization method. The as-formed coating consisted of an outer WSi₂ layer and an inner W₅Si₃ layer. The WSi₂ layer had a columnar structure and had several through-thickness cracks generated due to the mismatch of coefficient of thermal expansion between the coating and the substrate. Based on the coating microstructure, the mechanism of coating growth during siliconizing has been suggested. Weight change data obtained under cyclic oxidation in air at 1100 and 1300 °C suggested that the above coating can provide protection to W substrate against oxidation for about 2 h. The oxide scale that formed on the coating during oxidation exposure consisted of SiO₂ and WO₃ at 1100 °C and only SiO₂ at 1300 °C. The protective silica layer underwent spallation during thermal cycling, leading to a diminishing of the protective capability of the coating. More importantly, localized oxidation of the W substrate through discontinuities present in the coating at sharp corners caused severe damage to the coated samples. Isothermal oxidation exposure of the coating, in comparison, resulted in a much lower degree of damage and the coating provided protection for a much longer duration (up to 10 h) at the above temperatures. In this study, apart from reporting a hitherto unreported oxide scale morphology, the microstructural degradation of the coating during oxidation has been linked to the columnar structure of the WSi₂ layer.     

Microstructural evolution in damaged IN738LC alloy during various steps of rejuvenation heat treatments

IN738LC is one of the superior nickel base superalloys utilized at high temperatures in aggressive environments. However, experiencing high temperatures and stresses during service causes microstructure deterioration and degradation of mechanical properties in this alloy. To restore the microstructure and mechanical properties of the degraded alloy, rejuvenation heat treatments can be considered. In this study, the evolution of microstructural features in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles was investigated. During solution treatment stage, dissolution of coarsened γ′ precipitates, grain boundary films and transition zone around primary MC carbides took place. Solution treatment at high temperature led to lower volume fraction and smaller size of remnant γ′ precipitates and further dissolution of grain boundary films and caused MC carbides to be remained without the surrounding transition zone. In addition, fine γ′ precipitates formed during the subsequent cooling, namely cooling precipitates, were detected in higher contents after solutionizing at higher temperatures. It was found that slower cooling rates after solution treatment gave rise to coarser γ′ precipitates with higher volume fraction. Among all heat treatment cycles investigated, double solution treatment at 1190 °C/4 h/FC (furnace cooling) + 1120 °C/2 h/AC (air cooling) followed by aging at 845 °C/24 h/AC was successful to revert the microstructure back to its virgin state.     

大直径锻造耐磨钢球的热处理工艺

采用二次加热淬火和低温回火工艺改善?120 mm锻造耐磨钢球的使用性能,研究了二次加热淬火工艺中不同升温速率和淬火冷却时间对钢球硬度分布、冲击性能和显微组织的影响.得出钢球的最佳热处理工艺为:以2.8℃/min的速率升温至840℃并保温1 h,出炉空冷至800℃后淬入35℃水中冷却350～400 s,然后出水空冷至80...     

热加工和后处理对Ti-6Al-4V合金显微组织和拉伸性能的影响

研究了热压缩、热轧制和后续轧制退火处理对Ti-6Al-4V合金显微组织和拉伸性能的影响。热压缩实验在温度800~1075°C和应变速率0.001~1s-1下进行,得到了流变曲线与加工过程参数之间的关系。然后,样品在温度800~1070°C和恒应变速率2s-1下进行2道次热轧制,总变形量为75%。热轧后,样品分别在870°C和920°C下保温热处理2h,随后空冷。在β相区的热轧导致粗大的β相冷却时转变为马氏体相,而在α/β两相区的热轧会导致生成部分球化的α相组织。后续的热轧处理能使在两相区部分球化的α相得以完成球化,然而,在β相区轧制的样品会导致马氏体结构被破坏。拉伸实验表明,随着轧制温度从两相区升高到单相区,合金的强度及伸长率会显著降低。升高热处理温度会降低两相区轧制合金的强度性能,而在β相区轧制合金的强度会得到提高。     

Strengthening heat treatment of alloy VT16 in vacuum

Conclusions Alloy VT16 can be strengthened by heat treatment in vacuum under the following conditions: heating at 775–800° for 2 h, cooling in the container in water, and aging at 500° for 8 h.The alloy subjected to this treatment has the following properties; _b = 103–107 kgf/mm², =59–63%, ₅ = 15.1–16.1%.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 65–67, May, 1978.     

The cracking behavior of anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C

The cracking behavior of sealed anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C was studied and the effects of anodizing temperature, heating temperature and heating rate on cracking behavior were investigated. The results showed that before heating some micro-cracks were present in sealed anodic films on the aluminum alloy tested. After heating between 100 °C and 300 °C, the initial micro-cracks became wider and deeper, and new cracks also may be initiated in the film. As anodizing temperature increased, both the crack density and the crack width increased after heating, which was attributed to increase of the porosity of the anodic films formed at higher temperatures. At higher heating temperature, the cracks obviously got wider, but the crack density remained almost unchanged. Increased heating rate resulted in more cracks in the anodic film, indicating that higher strain rate may promote initiation of the micro-cracks, while cooling rate had little influence on cracking behavior.