New ecological fluid bed nitrocarburising technology for improvement of properties in X160CrMoV121 steel

Abstract

New technologies for fluidised bed nitrocarburising are described that employ either a chemically active bed or a chemically inert bed, plus additional activation of the fluid bed with mechanical vibration (alone or accompanied by the flow of a gas medium). Investigations were performed on X160CrMoV121 tool steel, with three methods of nitrocarburisation, at 580°C for 2 and 4 h. The nitrocarburised layers produced were investigated via surface hardness tests and microhardness distribution examination, metallography and X-ray spectrometry. Wear results are also reported. The new processes are reported to reduce gas consumption and to provide better case properties under optimised process conditions.     

The Optimization of Interlamellar Spacing in a Nanopearlitic Lead-Patented Hypoeutectoid Steel Wire

In this study, in order to optimize the interlamellar spacing prior to drawing operation in a nanopearlitic lead patented hypoeutectoid steel wire, a model based on finite element method is presented to predict the optimum immersion time in a lead bath. A typical suitable immersion time for the wire with 1.8 mm diameter is about 10 s. The austenitizing and quenching temperature for a wire with diameter of 1.8 mm and composition of 0.72% C, to obtain the lowest interlamellar spacing (i.e., 29 nm), are 910 and 510 °C, respectively. The hardness and the yield strength of the steel wire followed a linear relationship with the inverse square root of the interlamellar spacing (S ^−1/2). Pearlite interlamellar spacing obtained after patenting treatment, was decreased by increasing the amount of prior deformation.     

Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420–230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m²·K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160–170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.     

Effects of fluidised bed quenching on heat treating characteristics of cast Al–Si–Mg and Al–Si–Mg–Cu alloys

Abstract

The quench sensitivity of Al–Si–Mg (D357 unmodified and Sr modified), and Al–Si–Mg–-Cu (354 and 319 Sr modified) cast alloys was investigated using a fluidised bed (FB). The average cooling rate of castings in the fluidised bed is lower than those quenched in water; the cooling rate first increases to a certain maximum and then decreases during quenching. The change in the cooling rate during quenching in water was more drastic, where the cooling rate varied from 0 to ?80 K s^?1 in less than 8 s, as compared with those quenched in FB, where the cooling rate varied from 0 to ?14 K s^?1 in 18 s. The FB quenching resulted in the formation of several metastable phases in Al–Si–Mg–Cu alloys; in contrast, no such transformation was observed during water quenching. The T4 yield strength of the FB quenched alloys was greater than water quenched alloys owing to the formation of a greater volume fraction of metastable phases in the FB quenched alloys. The tensile properties of T6 treated alloys show that Al–Si–Mg alloys (both unmodified and Sr modified) are more quench sensitive than Al–Si–Mg–Cu alloys. The high quench sensitivity of the Al–Si–Mg alloys is because GP zones are not formed, whereas GP zones are formed during quenching of the Al–Si–Mg–Cu alloys as predicted by time temperature transformation and continuous cooling transformation) diagrams.     

Two-stage quenching of steel Kh12M

Conclusions  

Microstructure evolution,fracture and hardening mechanisms of quenched and tempered steel for large sized bearing rings at elevated quenching temperatures

Based on 42CrMo steel, a steel with a higher C and Ni content is developed for use in large sized bearing rings. The impact energy and hardness of the quenched and tempered steel increase with the quenching temperature, but then decrease when the temperature is above 925 °C. When the temperature is below 925 °C, some larger M₂₃C₆-type carbides (with average diameters of 255.6 μm) exist in the quenched and tempered microstructure. The number of carbides is reduced as the quenching temperature increases. At the same time, the fracture modes change from microvoid coalescence and quasi-cleavage to microvoid coalescence. The number of round quasi-cleavage fractures, which are formed around the carbides, decrease as the number of carbides decrease. The existence of larger M₂₃C₆-type carbides leads to round quasi-cleavage fractures and decrease the impact energy. The precipitation strengthening of M₂₃C₆-type carbides increases the hardness at a quenching temperature of 925 °C.     

Shell hardening of unalloyed steel cylinders by high speed quenching

Abstract

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.     

Critical quenching rate for high hardness and good exfoliation corrosion resistance of Al-Zn-Mg-Cu alloy plate

By means of the end-quenching technique, we investigated the relationship between quenching rate and hardness as well as exfoliation corrosion rating for Al-2.21 Zn-3.59 Mg-0.45 Cu-0.038 Zr (at%) alloy plate. In order to achieve an exfoliation corrosion rating of P or EA, the quenching rate must be greater than approximately 460 °C/min and 300 °C/min, respectively, and the drop degree in hardness should simultaneously be lower than approximately 2.0% and 3.5%, respectively. The results of microstructural and microchemical examination using a scanning transmission electron microscope indicate that a lower quenching rate leads to a higher content of Zn, Mg, and Cu in the grain-boundary particles and a greater width of precipitate-free zones near grain boundaries; therefore, grain-boundary particles with Zn and Mg contents less than approximately 13.39% and 10.23% (at%), respectively, and precipitate-free zones near grain boundaries with widths less than about 107 nm can contribute to an exfoliation corrosion rating better than EA. The amount of quench-induced η-phase particles, which lead to lower hardness, increases with decreasing quenching rate, and the area fraction of these particles is approximately 2.9% at a quenching rate of 300 °C/min.     

Antifriction coatings of Pb–Sn–Cu alloy electro-deposited from methanesulphonate bath

Abstract

Electrodeposition of antifriction Pb–Sn–Cu coatings from a bath based on methanesulphonic acid (MSA) has been investigated. The bath contains two specially selected organic additives which modify both the structure and the appearance of deposits, prevent the oxidisation of Sn(II) ions and allow the increase of tin content in deposits. The antifriction lead (～90%)–tin (～8%)–copper (～2%) films are deposited from the MSA-electrolyte at a current density of 4 A dm^?2 and a bath temperature of about 20–25°C. Inhibition of the Sn²⁺ ions discharge reaction is observed when the ternary alloy is deposited on the cathode. The Cu²⁺ ions discharge proceeds at a diffusion limiting current. Simultaneous co-deposition of copper has no effect on the kinetics of both lead and tin electrodeposition. Wear characteristics of the deposits from the methanesulphonate bath do not differ from those obtained from the usual fluoroborate bath.     

Effect of quenching temperature on structure and properties of titanium alloy: Structure and phase composition

X-ray diffraction analysis and transmission and scanning electron microscopy have been used to study regularities of the formation of structure and phase composition of a VT16 alloy during its quenching. The formation of an athermal ω phase in the VT16 alloy with the initial (α + β) structure during quenching of the alloy from 800°C was found to be possible. Quenching temperatures (T _q) at which various metastable phase compositions, such as the metastable β solid solution, β + α″ + ω, β + α″, and α″ martensite, are formed have been determined to be 750, 800, 750–850, and ≤850°C, respectively. Dependences of variations in the volume fractions of phases were plotted. It has been shown that, at quenching temperatures close to the β-transus, the active growth of β-phase grains takes place at the expense of a decrease in the α-phase volume fraction.     

快速获得7055铝合金淬火敏感温度区间的新方法及机理（英文）

采用一种省时、节约资源的变温热处理(ATHT)新方法，基于硬度与电导率，获得喷射沉积7055铝合金的淬火敏感温度区间。此外，通过透射电子显微镜(TEM)表征ATHT期间的显微组织演变。研究表明，7055合金的ATHT是一个溶质原子随着温度的升高而析出和再溶解的过程。当温度达到200℃时，合金的硬度急剧增加，电导率适当增加。随着温度升高到400℃以上，电导率从峰值迅速下降，表明溶质原子回溶加速，同时，在基体内η’强化相逐渐转变成η平衡相。通过对硬度曲线和电导率曲线的分析，得出当前合金淬火敏感性温度范围为200～400℃，这与传统分级保温法测得的结果一致。     

Effect of temperature on failure of gas cylinders

A number of ammonia cylinders burst during open storage in a field in the month of June. The cause of failure was studied. No flaws in the cylinder material were detected. Under normal conditions, the tangential stress (5.4 kg/mm ² )in the cylinder is well below the yield strength (49 kg/mm ² ). The tangential stress increases with the rise of temperature of the ammonia. As long as some vapor exists inside the cylinder, the liquid remains in equilibrium with the vapor, the cylinder pressure is equal to the vapor pressure of ammonia at that temperature, and the rise in tangential stress is insignificant (0.14 kg/mm ² /°C). However, as the temperature increases, the specific volume of the liquid ammonia inside the cylinder also increases. The cylinder is completely filled with liquid under certain conditions in accordance with the bulk thermal expansion of the liquid; under these conditions, the cylinder pressure rises sharply with increased temperature, causing a large rise in tangential stress (4.76 kg/mm ² /°C). Thus, an approximate 10 °C temperature rise in a cylinder filled with liquid ammonia can lead to failure.     

Precipitation behavior in Al-Zn-Mg-Cu alloy after direct quenching

The precipitation behavior in an Al-6.8Zn-1.9Mg-1.0Cu-0.12Zr alloy after direct quenching from solution heat treatment temperature of 470 °C to 205–355 °C was investigated by means of hardness tests, electrical conductivity tests, and transmission electron microscopy. At temperatures below 265 °C, the hardness increased gradually to a peak value and then decreased rapidly with time. At 265 °C, the hardness was almost unchanged within the initial 2000 s and then decreased gradually. At higher temperatures, the hardness decreased slowly with time. The electrical conductivity started to increase after a certain period of time and then tended to maintain a constant value at all temperatures. Microstructure examination indicated heterogeneous precipitation of the η phase at grain boundaries and inside grains during holding at 205 °C and 325 °C. Based on the electrical conductivity data, the precipitation kinetics could be described quite well by the Johnson-Mehl-Avrami-Komolgorov relationship with a n value varying between 0.78 and 1.33. The activation energy was estimated to be about 44.9 kJ/mol, which is close to that expected for a dislocation diffusion mechanism. Time-temperature-transformation diagrams were constructed and the nose temperature ranged from 295 °C to 325 °C.     

Effect of Aluminum on Microstructure and Properties of Martensitic Wear-Resistant and Heat-Resistant Steel

The effect of aluminum on microstructure and properties of martensitic wear-resistant and heat-resistant steels was investigated. The results indicate that as-cast microstructure of the specimens is composed of ferrite, pearlite and carbides. After quenching at 1,000 °C and tempering at 600 °C, the microstructure of the specimens consists of tempered sorbite and Fe–Cr–Al intermetallic compounds which distribute directionally in the matrix and increase with increase in Al content. The additions of Al enhance the ambient tensile strength which reaches the peak at 1,230 MPa when the specimens contain 1.97 % Al. Oxidation notably decreases with the increase of Al and the average oxidation rates reduce to 0.0095 g m^?2 h^?1 at 650 °C and 0.0285 g m^?2 h^?1 at 800 °C, respectively. Wear resistance of the specimens containing Al obviously increased when compared to the Al-free specimens.     

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

Eventhough 9–12% Cr steels are mechanically designed for power plant applications up to 650 °C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic‐martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe₂Al₅ or FeAl phases were thus developed for deposition temperatures between 650 and 715 °C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe₂Al₅ coatings at 550 °C. Furthermore, Si or codiffusion Al‐Si coatings were developed at temperatures as low as 550 °C.     

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract

Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool, are essential to increase the maximum welding speed. These conditions can be obtained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4–4·5 m min^?1 is achieved by setting the current ratio to a value ranging from 0·31 to 0·5.     

Accumulation and diffusion of radiogenic helium in beryllium

Accumulation of radiogenic helium isotope ⁴He, its diffusion characteristics, and microstructure of beryllium have been studied after irradiation at 70 and 200°C by neutrons with an energy of E > 0.1 MeV to fluences of (1.0–13.3) × 10²² cm^?2. Experimental results concerning the concentration of radiogenic helium in beryllium after irradiation and subsequent isothermal annealings for 1 h in a temperature range of 700–1200°C have been obtained. The accumulation of helium corresponds to a linear dependence up to a neutron fluence of ～6 × 10²² cm^?2 (E > 0.1 MeV); at fluences from 6 × 10²² to 13 × 10²² cm^?2 (E > 0.1 MeV), a deviation from the linear dependence toward the decrease in the rate of accumulation is observed. The diffusion of radiogenic helium in beryllium at annealing temperatures of 70–200°C is low; intense diffusion and degassing of helium from beryllium start at an annealing temperature of 700°C. At annealing temperatures of 1100–1200°C, virtually all helium escapes from the irradiated beryllium.     

Effect of low-temperature quenching on the microstructure and capacity for corrosion cracking of steel 03Kh11N10M2T-VD

Conclusions Low-temperature quenching (from 800°C) of steel 03Kh11N10M2T-VD promotes a noticeable increase in the ultimate rupture strength and the resistance to corrosion cracking after aging at 520°C. We established a tendency toward an increase in the resistance to corrosion cracking after quenching from 800°C and a provoking aging at 500°C. This behavior of the steel seems to be connected with the formation of a finer martensite with a disperse intermetallic phase with uniformly distributed grain size after low-temperature quenching. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 8–11, February, 2000.     

Electrochemical impedance spectroscopy evaluation of behaviour of Pb–Ag anodes for zinc electrowinning

Abstract

Pb–0·5–0·7Ag anodes are widely used in the industry of zinc electrowinning. Two commercial lead anodes containing 0·56 and 0·69%Ag were studied by electrochemical impedance spectroscopy to evaluate their electrochemical activity. An industrial acid zinc sulphate electrolyte containing glue and chloride ion, but without manganese addition, was considered. In this study, 5 h of electrolysis at a density of 50 mA cm^?2 (currently used in practice) and also 6 h of potential decay were made to represent electrowinning periods of maintenance both at 38°C. During the 5 h polarisation, the average double layer capacity of Pb–0·56Ag alloy was higher (～9%) than that of Pb–0·69Ag alloy. During the first hour of potential decay, the Warburg impedance controls the electrochemical reaction. For the period from the second to sixth hour, the double layer capacity decreased with immersion time, and the charge transfer resistance increased with time. During the potential decay, the average charge transfer resistance of Pb–0·69Ag anode was higher (～52%) than that of Pb–0·56Ag anode.     

Thermomechanical processing of 42CrMoS4 steel

Abstract

Billets of 42CrMoS4 steel were subjected to a programme including forging and rolling to different reduction ratios, followed by quenching and tempering to simulate online thermomechanical treatment (TMT) during rolling. The mechanical properties obtained were compared with those obtained by conventional heat treatment (CHT) (quenching from 860°C and tempering). It was found that increasing the hot reduction ratio from 18 to 60%, accompanied by a decrease in the finish rolling temperature from 900 to 750°C, enhances strength only at the expense of elongation, while rapid quenching instead of air cooling from the same finish rolling temperature yields improvements in both strength and ductility. It was also found that CHT provides higher hardness, whereas TMT provides higher impact toughness. TMT will confer major economic savings since the heat treatment is achieved online.