在VDR渗氮炉中进行的真空脉冲渗氮

在VRD渗氮炉中对H13、Crl2MoV和45钢进行真空脉冲渗氮,采用氮气和氨气作渗剂,渗氮温度为540℃,渗氮零件有冲头、凹模、热锻模等。VRD真空脉冲渗氮炉配备有计算机控制系统、排气系统、特殊的搅拌风机和密封装置以及冷却系统。在VRD渗氮炉中进行真空脉冲渗氮具有渗速快、渗层均匀、渗层脆性小以及废气不污染环境等优点。     

模具氮化及软氮化白亮层的控制

介绍了钢的氮化及软氮化白亮层(化合物层)的相结构和性能特点,讨论分析了不同机械零件对氮化及软氮化白亮层要求侧重点,重点论述了不同模具对氮化及软氮化白亮层的要求,以及模具氮化及软氮化白亮层的控制要点。     

Controlled Nitriding

A nitriding process is governed by the chemical potential of the saturating medium, the kinetics of mass transfer, and the composition and structure of the surface layer of parts. Controlled nitriding involves control of thermodynamic and kinetic parameters and of surface activation. The chemical potential of nitrogen, carbon, and oxygen in the saturating medium can be characterized by the parameters K _N, K _C, and K _O. In order to control the quality and obtain a nitrided layer with specified structure, they should be monitored and regulated. The values of K _N, K _C, and K _O are determined in an in-situ mode using gas analyzers based on solid electrolyte cells. The recently developed hydrogen sensors supplement the range of gas analyzers. In-situ control of a nitriding process with the help of analyzers makes it possible to meet the requirements on the surface layer, prevent disturbance of the equilibrium due to uncontrolled arrival of oxygen, and ensure the requisite proportion of the gas phases, thus optimizing the structure of the layer and its quality.     

热循环离子渗氮及其强渗作用

用正交试验法研究了３８ＣｒＭｏＡｌＡ钢热循环离子渗氮的特点及其强渗作用。结果表明，渗氮过程受循环参数控制，渗层组织呈层状结构，渗层生长曲线存在长达６ｈ的亚速线性段；在强渗工艺下，该段斜率明显增大。这一动力学特性看来是由热循环催渗和离子轰击加速氮原子扩散的有利作用所致，从而使深层渗氮时间比恒温或分段渗氮缩短了２／３￣１／２。     

快速渗氮技术的可行性研究--液相等离子体电解渗氮

应用液相等离子体电解渗氮技术处理Q235钢，探索了在直流脉冲电源下、不同的无机盐与甲酰胺组成的电解液体系下短时间内实现渗氮的可能性，并研究了电解液体系的稳定性。结果表明：KF-CONH2电解液体系最稳定，但是渗入的效果不好；NaNO3-HCON2电解液体系不稳定，渗入效果也不好；KCl-HCONH2电解液体系比较稳定，而且在3～5min内可以实现渗入。     

特殊渗氮

气体渗氮渗速慢、成本高 ,离子渗氮、超声波渗氮设备价格昂贵 ,工艺复杂。为了提高气体渗氮速度 ,使工件表面进行预先氧化和活化 ,然后在ＮＨ3 ＣＯ2 气氛中渗氮 ,提高了渗氮速度 ,且工艺效果稳定。1　工艺确定预氧化渗氮工艺确定如下 :(1)清洗　用高标号汽油清洗零件。(2 )预     

Nitriding of Laser-Alloyed Steel

A combined process of hardening the surface of structural steels by laser alloying with nitride-forming elements and subsequent nitriding is suggested for ensuring an optimum level of hardening and high characteristics of wear resistance and crack resistance. The microstructure, the kind of distribution of alloying elements in the zone of laser alloying, the phase composition, the microhardness, the distribution of residual stresses, the wear resistance, and the crack resistance of the hardened steel are determined.     

Nitriding of drop-forging dies

Conclusions Data from production tests indicate that two-stage nitriding of dies is the most promising process. The first stage, regardless of the composition of the steel, is conducted at 520° for 4–36 h, the holding time increasing with the alloying of the steel, since alloying elements (tungsten, chromium, molybdenum, et al.) reduce the diffusion of nitorgen in phase [5]. The second stage is conducted at 550–580°. The lower the hardness of the steel or the more highly alloyed the steel, the higher the nitriding temperature in the second stage. It is 15–30° below the tempering temperature. The holding time in the second stage depends on the case depth required. It is not always desirable to obtain the maximum hardness [2], since the highest wear resistance does not coincide with the maximum hardness.The microstructure of the case may differ, but nevertheless the dies have a long service life. Furthermore, the presence of phase in the surface layer does not impair the dies, which can be used without any additional treatment, although it is known that the formation of brittle phase leads to a sharp reduction of strength [5].It should be noted that nitriding is still a very long process, and therefore nitriding of dies is still not used in some cases, even in well-equipped plants.Physicotechnical Institute, Academy of Sciences of the Belorussian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 49–52, June, 1978.     

Nitriding of restored crankshafts

Conclusion The following technology is recommended for restoration of steel crankshafts: facing with an Sv-08 electrode wire under an AN-348A flux with chromium and niobium introduced into the melt in accordance with the method used at automotive-repair plants and subsequent gas nitriding at (570±10)°C for 12 h.Design and Technology Office of the Automotive-Repair Industry, Saratov. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 35–36, February, 1984.     

Nitriding of titanium alloys

Conclusions Nitriding at pressures from 300 to 10^–2 mm Hg with the nitrogen inflow cut off and holding at low pressure is the best method of obtaining a case of substantial depth, with satisfactory mechanical properties of the base metal.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 72–74, June, 1973.     

用稀土渗氮缩短合金结构钢渗氮时间的研究

通过试验,确立了在稀土的作用下,提高渗氮温度的可能性.通过二段稀土渗氮法与常规渗氮的对比试验,表明稀土二段渗氮法工艺比常规渗氮的渗速快、金相组织好、硬度不降低、脆性小等优点.     

A Novel kind of Air Cooling Bainite Nitriding Steel and Plasma Nitriding Test

In order to avoid serious distortion and cracking that may occur with nitrided parts while quenching and tempering, a novel kind of air cooling bainite nitriding steel consisting of Cr, Mo, Mn and Si was developed. After normalized and high temperature tempered, the tested steel has satisfactory strength, toughness and microstructure as well as good nitriding properties.     

Nitriding in magnetic field

Conclusions Magnetic field accelerates gas nitriding in pure ammonia by a factor of 3–4, eliminates brittleness of the nitrided case, substantially increases the wear resistance and seizing resistance of the case, and increases the fatigue strength. The nitriding process is accelerated to the maximum with a magnetic field strength of 25–30 Oe.Scientific-Research Institute of Technology of the Automobile Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 37–41, March, 1978.     

Plasma-Assisted Nitriding of Aluminum-Alloy Parts

Plasma-assisted nitriding of aluminum alloys promises to become a suitable alternative to variants of thermochemical treatment used for raising the wear resistance of these materials especially from the standpoint of the environmental effect. Process performed in vacuum with the use of nitrogen and an argon-hydrogen mixture as the process gas provides for the formation of a layer of compounds (aluminum nitrides) with enhanced hardness on various aluminum alloys. However, until the present the process has been used only at the laboratory scale. No data can be found in the literature, for example, on the effect of the batch size on the uniformity of the thickness of the nitrided layer or on the wear resistance of parts from aluminum alloys. The present work is a study of plasma-assisted nitriding of commercially produced parts (pistons) fabricated from an aluminum alloy. The parameters of the process are chosen after the determining optimum conditions for preliminary sputtering treatment. Special attention is devoted to provision of temperature uniformity within a batch and the possibility of improving the surface quality by increasing the thickness of the compound layer. The topography of the surface and the thickness, chemical composition, and hardness of the compound layer are studied by the methods of scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), metallography, and measurement of ultramicrohardness. The performance characteristics of untreated, nitrided, and anodized pistons are evaluated with the help of vibration wear tests with a rider fabricated from a standard material. The results of the tests show that the wear resistance of some nitrided pistons is comparable to that of anodized parts.