薄层真空碳氮共渗技术及应用

介绍了薄层真空碳氮共渗技术的进展和难点.试验采用同一真空碳氮共渗工艺处理10、20和45碳素钢以及20Cr和20CrMo合金钢后测试和观察了渗层深度、硬度和显微组织,分析了温度和时间对渗层性能的影响.举例说明了3种关键零件真空碳氮共渗后的渗层深度、硬度、畸变量等技术要求及达标情况.     

柴油机45钢齿轮的气体氮碳共渗

本文综述了柴油机 45钢齿轮经气体氮碳共渗工艺处理后的组织性能。结果表明 ,用5 70℃× 2 .5h的气体氮碳共渗 ,可使齿轮获得 0 .2 5mm的化合物层和扩散层 ,表面硬度可达5 0 0HV0 .1,且畸变量小、寿命高。     

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.     

18Cr2Ni4WA钢真空碳氮共渗工艺试验

制定了一种18Cr2Ni4WA钢的真空碳氮共渗的热处理工艺,研究了该真空碳氮共渗工艺对18Cr2Ni4WA钢的微观组织和性能的影响。结果表明,18Cr2Ni4WA钢经真空碳氮共渗、高压气体淬火、深冷与低温回火后,表层微观组织为细针状马氏体,心部为板条状回火马氏体;表面残留奥氏体含量为9.19%(Vol.);试样表面硬度达到了901 HV0.2,有效渗碳层深度达到了1.3 mm。     

真空脉冲氮碳共渗在模具中的应用

选用二氧化碳加氨气为渗剂，对各种模具材料及H13钢模具进行了真空脉冲低温氮碳共渗试验。试验表明，真空脉冲氮碳共渗具有白亮层少，渗速快，又能比普通气体氮碳共渗获得更深渗层的优点，并能承受重负荷和冲击载荷。     

稀土碳共渗碳的扩散系数研究

本文对20钢进行了气体渗碳和稀土碳共渗,在满足碳势控制精度条件下测定了稀土碳共渗过程中碳在奥氏体中的扩散系数。 1 试验材料和试验方法试验材料为20钢,加工成15×10×5mm的金相试样。在碳势控制精度为±0.05％的井式气体渗碳炉中随炉进行气体渗碳和稀土碳共渗处理,湿度分別为880、900和920℃。稀土加入量为能够获得最大层深吋的克数,将稀土溶入甲醇中滴入炉内。 2 试验结果及分析     

真空氮碳共渗工艺对不同钢种组织与性能的影响

采用光学显微分析、XRD衍射分析、氮化层深和硬度测试等检测方法,研究了真空氮碳共渗温度、时间对氮化后不同钢试样性能的影响规律。结果表明:为了保证真空氮化后零部件的最佳使用性能,真空氮化的氮碳共渗温度应控制在550℃左右,保温时间在3～5 h为宜。NH3流量应控制在3.8～4.8 m3/h,可根据装炉量、氮化阶段及实测的氨分解率量进行适当调整。     

非重载齿轮硫氮碳共渗层组织与抗胶合、承载特性

较系统的理化检测与抗胶合台架试验结果表明,经硫氮碳共渗的35CrMoV齿轮的抗胶合、承载能力高于20CrMo浅层渗碳(层深0.8～1.0mm)淬火、回火齿轮。测量了共渗后齿面的磨损趋势,并对磨损机理进行了研究,指出用中碳或中碳合金钢调质加硫氮碳共渗取代低碳系列钢浅层渗碳(≤1mm)或碳氮共渗工艺制造非重载齿轮,既可保证质量、减小变形,又能减少工序、大幅度节约能源和降低成本。     

碳氮共渗的特点

<正>同时有氮原子渗入的渗碳称为碳氮共渗,和渗碳相比,碳氮共渗有下列特点:1)氮使钢的A1和A3下降,碳氮共渗温度比渗碳温度低,因而渗碳过程中奥氏体晶粒较细小,不使用本质细晶粒钢也可以进行直接淬火。不但可使工序简化,能耗降低,而且工件形状畸变可显著减轻。2)氮使过冷奥氏体TTT曲线右移,因而碳氮共渗渗层淬透性较高,有些碳素钢零件碳氮共渗后可在油中淬火。3)氮使Ms点下降,因而碳氮共渗渗层中残留奥氏体量较多,表面酸度稍低于渗碳,但工件接触疲劳强度可能较高。     

Q235钢氨气加二氧化碳气体氮碳共渗工艺的研究

研究了Q2 35钢用NH3 CO2 进行气体氮碳共渗工艺 ,找到了最佳工艺参数。同时与NH3 CH3 OH气体氮碳共渗进行对比 ,表明NH3 CO2 气体氮碳共渗比NH3 CH3 OH气体氮碳共渗的渗层质量好。     

Rheology Feature of Simple Metal Melt

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 k Hz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more {110}116 grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, {110}116 can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of {110}116 grains and therefore enhance the sharpness of Goss texture.     

Laser Cladded TiCN Coatings on the Surface of Titanium

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80?滋m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

Microstructure,Mechanical Properties and Corrosion Behavior of Extruded Mg–Zn–Ag Alloys with Single-Phase Structure

Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag(wt%,x=0.2,0.5 and0.8)alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.     

Growth Morphologies of a Binary Alloy with Low Anisotropy in Directional Solidification

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.