Enhancing mechanical properties and avoiding cracks by simulation of quenching connecting rods

If the service load onto a part is heavy, e.g. for the connecting rods of high-power diesel engine, high mechanical properties are critically required. When quenched in oil, it cannot meet the requirements. While quenching it in aqueous polymer quenchant or water, the mechanical properties could be higher than that required but cracking would occasionally happen. In order to obtain the expected mechanical properties and avoid cracking by quenching and tempering, the heat transfer coefficients of quenchants were measured and calculated, and the quenching process of connecting rods was simulated by using finite element method so that its processing parameters were determined. The results show that the mechanical properties of the treated rods have been enhanced and cracks were avoided.     

JY6607 PAG淬火介质应用研究

介绍了JY6607PAG淬火介质特性,测定了不同浓度了JY6607PAG冷却特性曲线。选择不同浓度的JY6607PAG淬火介质及传统水或油淬火介质对45钢、30CrMo和1Cr13试棒进行淬火,分析了拉伸性能、淬透性、淬火硬度均匀性及淬火开裂倾向。结果表明,45钢采用5％--10％JY6607PAG淬火、30CrMo钢采用10％--15％JY6607PAG淬火可以获得比传统淬火介质水或油更好的综合性能。试验所采用的所有浓度的JY6607PAG淬火介质都能淬透1Cr13不锈钢,但是,浓度低于20％时,出现了淬火开裂。因此,使用时建议采用高于30％的浓度。     

Effect of Poly-Alkylene-Glycol Quenchant on the Distortion,Hardness, and Microstructure of 65Mn Steel

Currently, the 65Mn steel is quenched mainly by oil media. Even though the lower cooling rate of oil compared to water reduces the hardness of steel post quenching, the deforming and cracking of parts are often minimized. On the other hand, the oil media also has the disadvantage of being flammable, creating smoke that adversely affects the media. The poly alkylene glycol (PAG) polymer quenchant is commonly used for quenching a variety of steels based on its advantages such as non-flammability and flexible cooling rate subjected to varying concentration and stirring speed. This article examines the effect of PAG polymer quenching solution (with concentrations of 10% and 20%) on deformation, hardness, and microstructure of C-ring samples made of 65Mn steel. Furthermore, the performance of PAG polymer quenchant is also compared with those of two common quenching solutions: Water and oil. When cooling in water, the C-ring samples had the largest deformation and 2 times higher than the results obtained when a 10% PAG solution was used. In particular, similar levels of deformation on the C-ring samples were observed in both cases of 20% PAG solution and oil as the primary quenching media. Furthermore, the hardness level measured between the sampled parts quenched in the 20% PAG solution appeared to be more uniform than that obtained from the oil-quenched sample. The study of the microscopic structure of steel by optical microscopy combined with X-ray diffraction showed that the water hardened sample exhibited cracks and comprised of two phases, martensite and retained austenite. According to the results of Electron Back Scattering Diffraction (EBSD) analysis and backscattering electronic image (BSE), the content of austenite residue in the sample when the sample was cooled in PAG 10 and 20% solution was 3.21% and 4.73%, respectively and smaller than the measurements obtained from oil quenching solution. Thus, the 65Mn steel is cooled in 20% PAG solution for high hardness and more evenly distributed than when it is quenched in oil while still ensuring a small level of deformation. Therefore, the PAG 20% solution can completely replace oil as the main media used to quench the 65Mn steel.     

A comparative analysis of outcome of carbide-tool holder quenching in various liquids upon induction brazing

The paper provides some results of prediction of hardness and hardened layer thickness of a 35KhGSA steel holder of carbide tool upon quenching in aqueous solution of salts and bases, in water, and in oils at various quenchant temperatures. Thermokinetic cooling paths of the holder surface points are shown to differ quantitatively and qualitatively between the first two quenchants and oils at room temperature. Numerical investigation of quenching in water at 100°C has revealed an abrupt increase, by a factor of 2–3, in the holder surface cooling rate as soon as the cooling curve enters the austenite-to-bainite phase transformation region. For the case of quenching in an aqueous solution of salts and bases a functional relation has been found between the thickness of the holder surface layer quenched to maximum hardness and the quenchant temperature.     

Comparison of the mechanical and microstructural properties of heat‐treated boron steel in different cooling media

This paper focuses on the effects of heat treatment parameters on the microstructural and mechanical properties of quenchable 30MnB5 steel. Heat treatment parameters, such as different cooling media and different heating times at the same temperature, were investigated and compared. Tensile and hardness tests were performed at room temperature, and then the microstructures of the specimens were studied using optical microscopy and the results were compared. The results showed that boron steel heat treated using a water quenching process exhibited the best mechanical properties because of the formation of a martensitic microstructure.     

Effect of bath and specimen temperature on the thermal stress resistance of brittle ceramics subjected to thermal quenching

The effect of specimen and bath temperature on the failure of brittle ceramics in a thermal quench experiment was studied by quenching glass and alumina rods in water and silicon oil baths at different temperatures. The results were discussed in terms of the variation of heat transfer coefficient of the quenching media and the change in material properties as a function of temperature. It was found that the usual assumption of constant heat transfer coefficient and material properties may lead to considerable errors in the quantitative interpretation of the results of thermal quench experiments. Effective values for the film coefficient of heat transfer for water and oil baths were estimated as a function of film temperature from thermal quench data. Recommendations were made for the selection of quenching media and for the procedure to be followed in reporting the results.     

硼对刃具钢组织与性能的影响

为研制开发适合水淬的新型刃具钢,采用显微组织观察、力学性能测试、热处理试验和磨粒磨损试验等技术手段,对比研究了含硼中碳钢与不含硼的65Mn钢热轧后与热处理后的显微组织和应用性能.结果表明:热轧态中碳含硼钢中存在较多铁素体相,强硬性更低,韧塑性更好;中碳含硼钢水淬回火后组织为回火马氏体,硬度可达50 HRC以上,高于油淬回火的65Mn钢,韧塑性和耐磨性也明显好于65Mn钢.中碳含硼钢完全适合水淬工艺,减少了工业污染,符合环保要求.     

Distortion Behaviour and Mechanical Properties of AlCu4Mg1 Sheet Components after High‐Pressure Gas Quenching in Comparison to Liquid Quenching

The quenching process after solution annealing of age hardenable aluminium alloys is necessary for an improvement of the mechanical properties, but also tends to result in distortion, especially in thin or complex shaped parts, and requires a costly reworking. High‐pressure gas quenching can reduce distortion compared to liquid quenching, because of the better temperature uniformity during quenching. A determination of the distortion behaviour of different serial parts of the aluminium wrought alloy 2024cl (AlCu4Mg1,clad) points out, that high‐pressure gas quenching offers predominantly excellent values regarding the dimensional accuracy after quenching compared to liquid quenchants. In comparison to the conventional heat treatment, similar values in strength, hardness and electrical conductivity have been determined after gas quenching and aging of different aluminium alloys (2024, 6013, and 7075), Furthermore, the residual stresses have been investigated and could be clearly reduced after gas quenching.     

Design of Quenching Process for Large-sized AISI P20 SteelBlock Used as Plastic Die

For large-sized AISI P20 steel block used as plastic die with a thickness of more than 200 mm, appropriate quenching processes are the key to obtain much thick hardened layer. In this paper, different quenching processes of AISI P20 steel block such as oil quenching, direct water quenching, water quenching with pre-cooling and water quenching with pre-cooling and self-tempering were numerically investigated by computer simulation based on the detailed discussion on the mathematical models of quenching processes including partial differential equations of heat transfer, thermal physical properties, latent heat, heat transfer coefficient and calculation of phase transformation, The results show that the water quenching with pre-cooling and self-tempering process can not only effectively avoid quenching cracks, but also obtain deeper harden depth than oil quenching.     

Mechanical properties enhancement in Ti–29Nb–13Ta–4.6Zr alloy via heat treatment with no detrimental effect on its biocompatibility

The present investigation deals with the microstructural evolution and mechanical properties optimization of a new titanium based TNTZ (Ti–29Nb–13Ta–4.6Zr) alloy through applying a proper heat treatment strategy. The TNTZ alloy was subjected to solution treatment and cooling procedure via different medias including liquid nitrogen, water, oil, static air and vacuum furnace. The slow cooling in vacuum furnace and static air resulted in precipitation of ω phase. The formation of this phase secures an increase in the strength and hardness value, however stands detrimental to the ductility. The α″ martensite is formed due to accelerated cooling in liquid nitrogen, water and oil. This phase remains neutral to the ductility of the alloy, while its excessive formation increases the hardness and shear strength. This study proposes the liquid nitrogen quenching as a process that optimizes the mechanical properties by rendering the highest strength while preserving the ductility.     

An investigation on the microstructure and mechanical properties of direct-quenched and tempered AISI 4140 steel

Direct quenching (DQ) process is an appropriate method in steels heat treatment field. This method enhances production rate, reduces energy consumption and decreases environment contamination. In this study hot-rolled AISI 4140 steel billets with different diameters (75, 80, 85, 100, 105 and 115 mm) and 20 m length were quenched directly in a water tank. Also some samples with similar size and composition were provided by conventional reheating, quenching and tempering (RQ) heat treatment process. The quenched samples were tempered at the temperature of 630 °C for 2 h. Mechanical properties of heat treated samples including tensile strength, yield strength, elongation, hardness and impact toughness were measured. Also, the microstructure and harden-ability of this steel were investigated under various conditions and the results were compared to RQ heat treated products. The results showed that direct quenching and tempering processes (DQ–T) is due to enhance of mechanical properties such as tensile strength and harden-ability of AISI 4140 and it is affected by various parameters such as steel temperature before quenching, water temperature, quenching time and also billet size.     

Comparative experimental study on the modification of microstructural and mechanical properties of friction stir welded and gas metal arc welded EN AW‐6061 O aluminum alloys by post‐weld heat treatment

In this paper, the effects of post‐weld heat treatment on modification of microstructures and mechanical properties of friction stir welded and gas metal arc welded AA6061‐O plates were compared with each other. Gas metal arc welding and friction stir welding were used as the applicable welding processes for AA6061‐O alloys. The applied post‐weld heat treatment consisted of solution heat treatment, followed by water quenching and finally artificial aging. The samples were classified as post‐weld heat treated and as‐welded joints. The microstructural evolution, tensile properties, hardness features and fracture surfaces of both as‐welded and post‐weld heat treated samples were reported. The results clearly showed that friction stir welding process demonstrated better and more consistent mechanical properties by comparison with the gas metal arc welding process. The weld region of as‐welded samples exhibited a higher hardness value of 80 HV0.1 compared to the base material. In addition, the feasibility of post‐weld heat treatment in order to enhance the mechanical properties and to obtain more homogeneous microstructure of 6061‐O aluminum alloys was evaluated.     

Computer modeling of the formation of a differential of mechanical properties on the holder surface of carbide-tipped tool bit through quenching upon induction brazing

A scheme of intensive cooling of a portion of the steel holder of a carbide-tipped tool bit during its quenching after induction brazing is put forward. The scheme implies that the cooling of various portions of the holder working surface is carried out in such a way that they should have different martensite content, resulting in a differential of mechanical properties. The scheme is illustrated by some examples of computer modeling of the mechanical properties differential for a 35KhGSA steel holder of a carbide-tipped tool bit in the cases of quenching in aqueous solutions of Na-KMTs polymer and in quenching oil I-20. It is demonstrated that by choosing an appropriate quenchant and cooling scheme one can impart high hardness to the major-wear portion of the holder and high impact toughness to the zone of the tool bit fixing in a milling cutter.     

Effect of a post-weld heat treatment on the mechanical and microstructure properties of AA6061 joints welded by the gas metal arc welding cold metal transfer method

This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using the gas metal arc welding (GMAW) cold metal transfer (CMT) method. The CMT method was used because the method provides spatter-free welding, outstanding gap bridging properties, low heat input and a high degree of process flexibility. The welded samples were divided into as-welded and PWHT samples. The PWHTs used on the samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the GMAW CMT method.     

The effect of single and double quenching and tempering heat treatments on the microstructure and mechanical properties of AISI 4140 steel

This investigation is concerned to evaluate the effect of double quenching and tempering (DQT) with conventional quenching and tempering (CQT) heat treatment processes on microstructure and mechanical behavior of a commercially developed hot rolled AISI 4140 type steel. Comparison of microstructure and mechanical properties of DQT and CQT heat treated specimens have been established in details. Optical and scanning electron microscopies have been used to follow impurity concentration and microstructural changes, and their relation to the associated mechanical properties. The results indicate that the improvement of mechanical properties particularly impact toughness of DQT heat treated specimens is much higher than that of the CQT condition, and this observation is rationalized in terms of finer austenite grain size developed in the DQT condition providing much finer martensitic packets within the grains and a lower level of impurity concentration of sulfur (S) and phosphorus (P) near the prior austenite grain boundaries as well.     

热处理保温时间对25Mn2钢力学性能和显微组织的影响

对25Mn2钢进行了不同工艺的热处理,研究了淬火保温时间和回火保温时间对其力学性能和显微组织的影响,以探讨优化其热处理工艺的可能性。结果表明：回火保温时问对力学性能的影响是显著的,而淬火保温时间对力学性能的影响并不显著;在淬火温度为900℃,回火温度为615℃的条件下,回火保温20min是必要且足够的;经优化后工艺热处理25Mn2钢的力学性能能较好地满足API5CT标准要求。     

Effect of Heat Treatment on Prior Grain Size and Mechanical Property of a Maraging Stainless Steel

Effect of the heat treatment, including solution treatment (ST) and aging treatment (AT), on the prior austenite grain (PAG) size, microstructure and mechanical properties of a precipitation hardening maraging stainless steel was investigated. The results indicate that the relations between PAG size and yield strength (σy) under both ST and AT conditions obey the Hall-Petch relationship. Furthermore, after ST at 1050℃for 1 h cryogenic treated (CT) at -70℃ for 8 h AT at 535℃ for 4 h, the tested steel showed its ultimate tensile strength (σb) and σy over 1900 MPa and 1750 MPa, respectively.     

Effect of environmental factors on thermal shock behaviour of polycrystalline alumina ceramics

The effect of the environmental factors on thermal shock behaviour of polycrystalline alumina ceramics was studied by quenching the alumina specimens into various quenching media. The environment factors of quenching media were controlled by changing the temperature of water and changing the concentration of the propylene glycol/water solution. The convection heat transfer coefficient and thermal stress increased as the temperature of cooling water increased and decreased as the concentration of the propylene glycol in water increased. The critical thermal stress which makes the cracks grow catastrophically was found to be generated by the critical cooling rate, and the critical cooling rate of alumina ceramics was found to be a certain value (550 °C/s) and same for all cooling liquids. Therefore, cooling rate was found to be the most influential of the environmental factors in thermal shock.     

Thermal proof testing of ceramics

The possibility of thermal proof testing with thermal stress induced by quenching was examined. For this purpose, the bending strength and the critical temperature difference for quenching into water and quench oil for soda-lime-silica glass were measured before and after proof testing by quenching the specimens into water, ethyl alcohol, silicon oil and quench oil. Proof testing by water, ethyl alcohol and silicon oil quenching modified the distribution of the critical temperature difference as expected, but not that of the bending strength at all. It is suggested that proof testing by rapid quenching is a useful method for truncating the critical temperature difference distribution of ceramic components of heat engines and so on.     

Quenching-rate determination for standard steel tensile specimens

A vertical tube furnace and a four-channel digital storage oscilloscope have been used to determine quench rates for standard tensile specimens of a martensitic stainless steel. The quenching media examined were air, oil and water. Theoretical calculations were made, based on convection heat-transfer approaches, which quantify the heat flow from the specimen surfaces during cooling. Experimental data are in reasonable agreement with predicted values.