EFFECT OF VACUUM HEAT TREATMENT ON OXIDATION BEHAVIOR OF SPUTTERED NiCrAlY COATING

A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputtered NiCrAlY coating has been investigated. The as-sputtered NiCrAlY coating consists of γ-Ni and b-NiAl phases. After vacuum heat treatment, the sputtered NiCrAlY coating mainly consists of γ'-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isothermal oxidation of sputtered NiCrAlY coating with and without vacuum heat treatment has been performed at 1000℃. It is shown that a-Al2O3 formed during vacuum heat treatment acts as nuclei for the formation of a-Al2O3, and the protective a-Al2O3 scale is formed more rapidly on the vacuum heat treated NiCrAlY coating than that formed on the untreated coating. Also the a-Al2O3 scale has a better adherence to the vacuum heat treated NiCrAlY coating. Therefore the vacuum heat treatment improves the oxidation     

The Integration of Vacuum Brazing into Heat Treatment - A Progressive Combined Process

The continuous constructive challenge to improve the functionality and efficiency of components always results in higher demands on production engineering, against the background of the generally increasing cost pressure. In many cases, you will just succeed in producing competitive and innovative products by combining and coupling of different procedures to an independent (hybrid) technology. The use of hybrid procedures for metal joining and heat treatment of metallic materials finds more and more industrial fields of application. Modern vacuum lines with integrated pressurized gas quenching are considered high-performance and flexible means of production for brazing and heat treatment tasks as well in the turbine industry as in the mould making and tool manufacturing industry. In doing so, the heat treatment is coupled with the brazing cycle in a combined process so that the brazing temperatures and soak times are adapted to the necessary temperatures and times for solution heat treatment and austeniting. This user-oriented article describes on the one hand examples of brazing of turbine components, but above all the practical experience from the plastics processing industry, where the requirement for a high-efficient cooling of injection moulding dies gains more and more importance.The combined procedure “Vacuum Brazing and Hardening” offers plenty of possibilities to produce mould inserts with an efficient tempering system in an economic way.     

Industrial Experience with Case Hardening of Stainless Steels by Solution Nitriding

SolNit^R is a novel heat treatment to case harden stainless steels with nitrogen instead of carbon. The calculated equilibrium pressure of N2 corresponds well with the nitrogen content in the steel surface. The process is carried out in vacuum furnaces with pressurized gas quenching. Numerous parts of different stainless steels have been successfully SolNit^R treated in industry leading to superior properties in respect to hardness/strength and corrosion resistance     

EFFECT OF VACUUM HEAT TREATMENT ON OXIDATION BEHAVIOR OF SPUTTERED NiCrA1Y COATING

A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputteredNiCrAlY coating has been investigated. The as-sputtered NiCrAlY coating consists ofγ-Ni and β-NiAl phases. After vacuum heat treatment, the sputtered NiCrAlY coatingmainly consists of γ-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isother-mal oxidation of sputtered NiCrAlY coating with and without vacuum heat treatmenthas been performed at 1000C. It is shown that α-Al2O3 formed during vacuum heattreatment acts as nuclei for the formation of α-Al2O3, and the protective α-Al2O3scale is formed more rapidly on the vacuum heat treated NiCrAlY coating than thatformed on the untreated coating. Also the α-Al2O3 scale has a better adherence to thevacuum heat treated NiCrAlY coating. Therefore the vacuum heat treatment improvesthe oxidation resistance of sputtered NiCrAlY coating.     

Effect of Microstructure on Tensile Behavior and Mechanical Stability of Retained Austenite in a Cold-Rolled Al-Containing TRIP Steel

In the present study, a quenching treatment prior to two-stage heat treatment was conducted on a Fe–0.28 C–1.55 Mn–2.06 Al transformation-induced plasticity steel to tailor the final microstructure. Compared with the microstructure of the ferrite, bainite and blocky retained austenite obtained by conventional two-stage heat treatment, the microstructure subjected to quenching plus two-stage heat treatment was composed of the ferrite, lath bainite and film-like retained austenite. The corresponding tensile behavior and mechanical stability of retained austenite were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the mechanical stability of blocky retained austenite grains is lower and most of them transform to martensite during the tensile deformation, which leads to higher ultimate tensile strength and instantaneous work hardening exponent. Film-like retained austenite has relatively higher stability, which could cause sustained work hardening and high ductility as well as product of strength and elongation.     

Reduced energy consumption by using streamlined gating systems

In foundries a lot of effort is done to minimize energy consumption in the production to reduce costs and hence increase the competitiveness. At the same time the foundries must live up to the increased demands for high quality castings. Traditional gating systems are known for a straight tapered down runner, a well base and 90° bends in the runner system. Previous work has shown that the traditional way of designing gating systems creates high inconsistency in flow patterns during filling. In the streamlined gating systems there are no sharp changes in direction and a large effort is done to confine and control the flow of the molten metal during mould filling. The main objective in the work presented here is to use the principles of the streamlined gating systems to reduce the weight of the gating system relative to the traditional layouts. By reducing the weight of gating system and thereby improving yield, the amount of molten iron needed is also reduced, hence reducing the energy consumption for melting. Experiments in real production lines have proven that it is possible to achieve a reduction in the poured weight by using the streamlined gating systems. In a layout for casting of three valve housings in a vertically parted mould the weight of the gating system was reduced by 1.1 kg changing from the traditional layouts to the streamlined gating systems. This weight reduction corresponds in this case to a 20% weight reduction for the gating system. Using streamlined gating systems with fan gates to give a beneficial heat distribution in the castings may be an efficient tool to eliminate the need for heat treatment. In the experiments the change in gating system from the traditional layout to the streamlined layout removed the need for heat treatment. This obviously means a huge energy saving in the foundry. The energy consumption for heat treatment of iron has been found to be 0.489 kWh/ kg. The valve housing in the experiments weighs 3 kg so when the need for heat treatment is removed, around 1.5 kWh     

Effect of vacuum on solidification process and microstructure of LFC magnesium alloy

Lost foam casting （LFC） is regarded as a cost-effective, environment-friendly vital option to the conventional casting process for production of near-net shape castings with high quality. Effect of vacuum on the solidification process and microstructure of LFC magnesium alloy were explored. The results indicate that vacuum plays a very important role in the heat transfer during mould filling and solidification periods, it increases the cooling rate of the filling melt, but greatly decreases the cooling rate of the casting during solidification period, and the solidification time of the casting is greater than that without vacuum. The microstructure of LFC magnesium alloy is rather coarse. Compared with that without vacuum, the microstructure of the LFC magnesium alloy under vacuum is more refined and has less precipitated β-phase, which is formed at the grain boundry and around the Al-Mn compound particle.     

Influence of heat treatment on fracture and magnetic properties of radially oriented Sm2Co17 permanent magnets

The quenching, fracture and aging treatment of radially oriented Sm2Co17 ring magnets were investigated. The results indicate that the ring magnets have obvious anisotropy of thermal expansion, which easily leads to the splits of the magnets during quenching. The fracture is brittle cleavage fracture. The difference （Aa） of the expansion coefficient reaches the maximum value at 800-850 ℃. So, various quenching processes at different steps are adopted in order to reduce the splits. When the magnets are aged, 1：5 phase precipitates from the 2：17 matrix phase and forms a cellular microstructure with 2：17 phase. BHmax and JHc reach the maximum value 226 kJ/m^3 and 2 170 kA/m after being aged at 850 ℃ for 4 h and 8 h, respectively. The aging treatment at 850 ℃ has little influence on remanence（Br）, which can always keep a high value （≥1.0 T）. Through appropriate heat treatment, the ring magnets have uniform cellular microstructure and excellent magnetic properties： Br ≥ 1.0T, JHc ≥2 100 kA/m, BHmax ≥ 220 kJ/m^3.     

Stress Dependence of Transformation Plastic Behavior

Transformation plasticity is known to play an important role in the course of heat treatment processes, and so affect the results of heat treatment simulations, which means that the transformation plasticity coefficient is necessary to be identifies. The authors developed a new method by use of four-point bending system of a beam to identify transformation plasticity coefficient taking advantage of its easiness and high accuracy compared with other conventional methods like tension test, etc., and identified the coefficient for four kinds of steels; plane carbon steel, Cr-steel, Cr-Mo steel and bearing steel. In this paper, further experimental data are presented for the steels if the coefficient Kp during pearlite transformation depend on the applied stress. Obtained results reveals that the stress dependence of Kp is rather trivial except for uncertain tendency detected in plane carbon steel. The relation between the Kp and carbon content included is discussed in comparison with other data referred from references.     

Effect of heat treatment on microstructure and properties of VG10 and 3Cr13 dissimilar welded joints

Through laser swing welding of dissimilar steels, the microstructure and properties of welded joints of dissimilar steels under different heat treatment processes were investigated. In the test, the equilibrium phase diagrams of the base materials 3 Cr13 and VG10 were calculated by JMATPro software. The microstructures of the different regions of the welded joints after the original and heat treatment were analyzed by XRD and SEM, and the changes of the microhardness were tested. The test results show that a martensite-like structure is generated at the base material on the 3 Cr13 side of the original welded joint, and a non-convective mixing zone exists in the fusion zone on the VG10 side. At this location, a block-like, island-like structure is embedded in the base material. There were lamellar carbide formation on this structure. After heat treatment, the amount of carbides in the welded joints is reduced, but the primary carbides in the VG10 base metal are difficult to eliminate by heat treatment. In addition, the lamellar carbides in the VG10 side fusion zone are polymerized to form network carbides. The hardness of the base metal near the fusion line on both sides of the original welded joint is relatively large, and the hardness of the heat affected zone gradually decreases with increasing distance from the center of the weld. After heat treatment, the overall hardness of the welded joint has increased significantly. Among them, the hardness increase is greatest at the quenching temperature of 1 050 °C, and VG10 can reach about 830 HV.     

塑料模具钢及真空碳氮共渗热处理

介绍了常用的塑料模具钢及其相应的热处理工艺,并试验了碳素钢及P20(3Cr2Mo)钢制塑料模具的真空碳氮共渗工艺.结果表明碳素钢及P20钢制塑料模具经真空碳氮共渗油淬火处理后,淬火硬度值可提高至62 HRC以上,耐磨性增加,有助于提高模具的使用寿命.     

Effect of cyclic heat treatment on the microstructure and mechanical properties of W-Ni-Co alloys

Current generation heavy alloys with enhanced static as well as high strain rate properties are based on W-Ni-Co alloys. These alloys are subjected to a cyclic heat treatment to obtain fine tungsten precipitates in the matrix and to realise superior mechanical properties. The present study is focused on processing 92W-5Ni-3Co alloy using a post-sintering cyclic heat treatment to obtain fine tungsten precipitates in the matrix. As-sintered alloys and cyclic heat treated (in vacuum) alloys are then subjected to (i) vacuum heat treatment with oil quenching and (ii) nitrogen heat treatment with water quenching. A comparison has been drawn based on microstructural features and mechanical properties, between the alloys processed (i) with and without cyclic heat treatment and (ii) with oil and water quenching. This study thus helps in understanding the effect of cyclic heat treatment and quenching medium on the microstructure and mechanical properties of W-Ni-Co alloys.     

齿轮的热处理和淬火

加热和淬火是齿轮加工中最关键的操作工序,经此处理后将赋予齿轮以满足抵抗高接触应力要求的机械性能和耐磨性能并具备高的使用寿命.但遗憾的是,在齿轮的制造中,热处理和淬火通常是被了解得最少的.由于热处理后的工件通常会产生变形并使工件失去光泽,往往会成为后续加工工艺的"瓶颈"而备受责难.本文之目的意在分析引起齿轮热处理和淬火变形的原因,并提出一些对性能进行调整的方法以便在淬火时得到合适的变形和高残余应力状态.     

真空热处理技术的新近进展及其发展趋势

近年来，国内外真空热处理设备和技术在迅速发展。国内研发了WZDGQ30型单室高压气淬真空炉、WZGQ型对流加热高压气淬真空炉和WZLQH型铝钎焊真空炉；国外研发了燃气真空炉，半连续和连续式真空炉，流态化真空炉，多用途真空炉，高温超高压真空炉，真空烧结炉和真空炉生产线等。本文简单介绍了上述设备，并提出了真空热处理技术的发展趋势。     

搞好模具热处理是模具升级必由之路

叙述了我国热处理的现状,分析了真空淬火热处理的劣势,提出了一种创新热处理新工艺—复合淬火工艺,阐述了复合淬火工艺的的多种优点,经过30多年的实践证明,复合淬火工艺具有独特的技术优势和广阔的应用前景.     

两种真空高压气淬炉淬火工艺的数值模拟及验证

对管道式和压入式真空高压气淬炉中实施的高压气淬工艺进行了数值模拟和实物验证试验。研究结果表明,在相同的冷却压力下,管道式真空高压气淬炉的冷却速度比压入式真空高压气淬炉快,小型工件更适宜在管道式真空高压气淬炉中进行淬火。     

Advantages of low pressure carburising and high pressure gas quenching technology in manufacturing

Abstract

Over the last decade, vacuum carburising in combination with high pressure gas quenching (HPGQ) has become a preferred technology in gear industry mainly in Europe and North America. Driven by cost savings in manufacturing of gears and shafts, the heat treatment process has gone into the focus of the manufacturers. The potential of savings in heat treatment is huge because the new technology allows the integration into the manufacturing chain of gears and shafts. With vacuum heat treatment furnaces is it possible to implement this integration into manufacturing. The advantages of vacuum technology are in particular: the absence of surface oxidation, the cold wall technology, the gas quenching technology, the reduced logistics, flexible reaction on the needs of production and the control of distortion. In parallel to the development of the new heat treat process, a second point came into the focus of manufacturers: the choice of material. The industry recognised that by choosing a slightly higher alloyed material, significant savings in the entire manufacturing chain can be realised: smaller grinding stock, faster carburising cycles, gas quenching with control of distortion, and ultimately the reduction/elimination of grinding- and straightening operations. Vacuum furnaces are flexible in their reaction to the production requirements. Only with these types of heat treatment furnaces is it possible to switch them off after use and save immediately energy and costs. This benefit was essential for the industry in 2008/09 during the world economic crisis. In the past, the automotive industry in Europe and North America mostly ran on conventional pusher type furnaces which must be kept on operating temperature even if only 50% of installed production capacity is needed. The vacuum furnace of type ModulTherm is a multi-chamber system and each chamber can be switched On or Off according to the production plan which finally saves a huge amount of cost for energy. This paper presents the advantages of the vacuum carburising technology with high pressure gas quenching. The author will demonstrate with examples and comparisons the benefits of vacuum technology and the successfully integration of heat treatment in the manufacturing chain.     

S390粉末高速钢真空气淬的显微组织及性能

研究了不同淬火温度、不同冷却方式对S390粉末高速钢进行真空热处理的显微组织及性能的影响。试验结果表明,经不同工艺淬火后,S390粉末高速钢的晶粒度在13级左右,其中的合金碳化物数量减少、尺寸变小,硬度均大于63.2 HRC。经真空气淬后的S390粉末高速钢试样中均可得到下贝氏体组织,且在下贝氏体片状组织中及残留合金碳化物周围有纳米椭圆(球)状合金碳化物析出。     

真空低压渗碳热处理在重载齿轮上的应用

研究了20CrMnTiH钢同步器齿毂经真空低压渗碳热处理后组织和性能的变化,并与气氛渗碳热处理工艺进行对比。结果表明,真空渗碳热处理后齿面位置处几乎无晶间氧化和非马氏体组织,在晶间氧化的控制上较大幅度优于气氛渗碳热处理工艺;高压气淬在齿毂类零件的热处理畸变控制方面优于油液淬火。     

60Si2MnA钢簧片失效分析及热处理工艺

对60S i2MnA钢簧片分别进行普通淬火、真空淬火、薄层渗碳复合热处理试验,采用回零试验检验零件弹性合格情况,并测试了力学性能和表面残余应力。结果表明,簧片经复合热处理后合格率最高,普通淬火由于表面脱碳零件合格率最低,真空淬火因为淬火强化效果降低合格率一般。簧片失效原因在于热处理表面质量差,加载后表面产生塑性变形。薄层渗碳复合热处理工艺能改善簧片表面质量及性能,特别是提高了表面残余压应力,有效地提高了产品合格率。