机械能助渗的基本规律及其发展前景

根据以往的试验结果，归纳出机械能助渗的一般规律。机械能助渗遵循化学热处理的基本规律，是一个分解、吸附及扩散过程。但是，由于运动粒子动能激活表面点阵原子，形成空位等点阵缺陷，将纯热扩散的点阵扩散变为点阵缺陷扩散，使扩渗温度大幅度降低，扩渗时间显著缩短，这是机械能助渗的特殊规律。机械能助渗节能效果十分显著，热处理畸变量小，产品质量高，设备投资少，可实现渗金属、渗碳、渗氮等几乎全部化学热处理，可能成为21世纪化学热处理的主要工艺。     

Study of active screen plasma processing conditions for carburising and nitriding austenitic stainless steel

Active screen (AS) is an advanced technology for plasma surface engineering, which offers some advantages over conventional direct current (DC) plasma treatments. Such surface defects and process instabilities as arcing, edge and hollow cathode effects can be minimised or completely eliminated by the AS technique, with consequent improvements in surface quality and material properties. However, the lack of information and thorough understanding of the process mechanisms generate scepticism in industrial practitioners.In this project, AISI 316 specimens were plasma carburised and plasma nitrided at low temperature in AS and DC furnaces, and the treated samples were comparatively analysed. Two diagnostic techniques were used to study the plasma: optical fibre assisted optical emission spectroscopy, and a planar electrostatic probe. Optimum windows of treatment conditions for AS plasma nitriding and AS plasma carburising of austenitic stainless steel were identified and some evidence was obtained on the working principles of AS furnaces. These include the sputtering of material from the cathodic mesh and its deposition on the worktable, the generation of additional active species, and the electrostatic confinement of the plasma within the operative volume of the furnace.     

Solid Solution Nitriding Technology of 15Cr-7.5Mn-2.6Mo Duplex Stainless Steel

NEW DEVELOPMENT of stainless steel mainlyoccurs in area of nitrogen-containing austenitic steeland austenitic-ferritic duplex steel.It has been proposedthat a nitrogen-alloyed steel can be considered as anhigh nitrogen steel(HNSs),when the nitrogenconcentration is higher than0.4wt%in austenitic steelsand higher than0.08wt%in martensitic steels'M1.Butthis concept has been developed for the newmanufacturing technologies of HNS,such as pressureor powder metallurgy.In addition,the chemical…     

Study of the Active Screen Plasma Nitriding

Active screen plasma nitriding (ASPN) is a novel nitriding process, which overcomes many of the practical problems associated with the conventional DC plasma nitriding (DCPN). Experimental results showed that the metallurgical characteristics and hardening effect of 722M24 steel nitrided by ASPN at both floating potential and anodic (zero) potential were similar to those nitrided by DCPN. XRD and high-resolution SEM analysis indicated that iron nitride particles with sizes in sub-micron scale were deposited on the specimen surface in AS plasma nitriding. These indicate that the neutral iron nitride particles, which are sputtered from the active screen and transferred through plasma to specimen surface, are considered to be the dominant nitrogen carder in ASPN. The OES results show that NH could not be a critical species in plasma nitriding.     

工具钢渗氮后的韧性和抗弯性能

最近，对经渗氮和未渗氮的AISI H13、AISI D2、K340、AISI D6和AISI M2等工具钢进行了详细的研究。采用了不同的渗氮工艺，包括气体渗氮、液体渗氮以及液体渗氮＋扩散处理，并进行了对比。对这些钢进行了弯曲试验和冲击试验，以评定其性能。用光学金相技术表征其显微组织。渗氮处理会降低无缺口冲击试样的断裂模数和冲击吸收功。由于扩散层较深，导致经气体渗氮处理的试样的力学性能下降。通过扩散处理来减薄液体渗氮试样的白亮层厚度并不会影响试样的力学性能。试验结果表明，渗氮对工具钢的最有害的影响是使冲击试验的冲击吸收功降低。     

钛气体渗氮的数值模拟

根据修正的Fick第二定律,对钛渗氮工艺进行数值模拟,研究氮气压、渗氮温度和氮化时间因素对渗氮工艺的影响,得到了不同工艺参数下渗层深度和氮的浓度分布曲线,为渗氮工艺参数的优化设计和渗氮过程的自动控制提供参考.     

预氧化+稀土铈对42CrMo钢离子渗氮的影响

针对离子渗氮渗层浅及生产周期长等技术难题,采用预氧化与稀土复合催渗对工程常用结构钢42CrMo进行了离子渗氮。利用显微硬度计、光学显微镜(OM)、扫描电镜(SEM)等对渗氮速率、渗氮层组织、表面形貌等进行了系统的研究。结果表明,经400 ℃×1 h氧化+0.6 cm²/kg(铈表面积/装炉量)稀土的复合催渗工艺具有最佳催渗效果;与无催渗试样相比,优化后的复合催渗不仅提高了渗氮效率,同时减少了脉状氮化物,且降低了渗氮层的硬度梯度。     

(Fe)-C-N合金经沉淀硬化后的疲劳强度

为了寻求新的方法促进渗氮工艺在重型机械零件中的应用，渗氮层的硬化及通过对基体和心部进行进一步奥氏体化并快冷使其硬化的可能性引起了注意。本文给出了渗氮后的45钢(C-0．45％；Mn-0．65％)经沉淀硬化处理后的疲劳强度试验结果。试验结果表明经沉淀硬化后其近表层获得了不同的组织，可发现形态上与不同沉淀分散程度的贝氏体组织相似的纯马氏体区。渗氮后沉淀硬化有利于碳钢及其抗疲劳强度。本文还讨论了渗氮后沉淀硬化处理可替代渗碳或感应淬火。     

Thermochemical treatment of tools for hot forging

The possibilities of the use of power-saving processes of cyaniding and boronizing instead of the traditional gas nitriding without deterioration of the service stability of the tools are described. The nitriding process is shown to be intensified by treatment in a vibrofluidized bed. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 10–13, July, 2000.     

Investigations on the Corrosion Behaviour and Structural Characteristics of Low Temperature Nitrided and Carburised Austenitic Stainless Steel

The wear resistance of austenitic stainless steels can be improved by thermo-chemical surface treatment with nitrogen and carbon. However, it is possible that the corrosion resistance will be impaired by the precipitation of chromiumnitrid or -carbide. The present contribution deals with investigations of the corrosion behaviour and structural characteristics of a low temperature nitrided and carburised austenitic stainless steel.The material investigated was AISI 316L (X2CrNiMol7-12-2) austenitic stainless steel. A commercial plasma-nitriding unit (pulsed dc) was used for the nitriding and carburising process. Additional samples were treated by the gasoxinitriding process for a comparison between plasma- and gasoxinitriding. The nitrided and carburised layer of austenitic stainless steel consists of the nitrogen or carbon S-phase (expanded austenite), respectively. X-ray diffraction investigations show the typical shift of the peaks to lower angles, indicating expansion of the fcc lattice. Also the X-ray diffraction technique was employed to study the residual stresses in the nitrogen and carbon S-phase. The corrosion behaviour of surface engineered samples was investigated with electrochemical methods. Anodic potentiodynamic polarisation curves were recorded for testing the resistance against general corrosion (in H2SO4) and pitting corrosion (in NaCl).     

渗扩时间比对AISI 316不锈钢渗氮层组织与性能的影响

采用真空两段渗氮工艺,在不同的强渗、扩散时间下对AISI 316不锈钢进行渗氮处理,通过X射线衍射(XRD)、扫描电镜(SEM)、光学显微镜(OM)、显微硬度测试和摩擦磨损试验等分析了渗氮层的组织和性能。结果表明,经过12 h的真空渗氮后,AISI 316不锈钢表面形成了一层由γ′-Fe₄N、ε-Fe_2-3N和CrN等相组成的渗氮层,其表面硬度和耐磨性能相较于基体均有明显的提高。其中,渗扩时间比为1∶1(强渗6 h、扩散6 h)时的渗层厚度约为96 μm,表面硬度约为1069 HV0.5,是基体表面硬度的4.5倍,在20 N载荷下的磨损量约为基体的1/3;渗扩时间比为1∶2(强渗4 h、扩散8 h)时的渗层厚度约为120 μm,ε-Fe_2-3N相衍射峰增强,在20 N载荷下的磨损量约为基体的1/30。延长扩散时间能增加渗氮层厚度,改善表面形貌,进一步提高不锈钢的耐磨性。     

Study on the active screen plasma nitriding and its nitriding mechanism

The active screen plasma and DC plasma nitriding of the low alloy steel 722M24 are investigated. Experimental results showed that the metallurgical characteristics and hardening effect on 722M24 steel nitrided by AS plasma nitriding at both floating potential and grounded potential were similar to those nitrided by DC plasma nitriding. Particles sputtered from the active screen and deposited on the specimen surface play the role of the nitrogen carrier in AS plasma nitriding. XRD and high-resolution SEM analysis indicated that the particles with sizes in sub-micron scale were Fe_xN (x > 2). Based on metallurgical analysis and Optical Emission Spectrometer (OES) experimental results, an AS plasma nitriding model has been proposed considering that AS plasma nitriding is a multi-stage process, involving sputtering, physical adsorption, desorption, diffusion and deposition.     

常压等离子体渗氮工艺的研究

利用介质阻挡放电原理，在自行研制的设备上进行了常压非平衡等离子体渗氮。研究表明，在等离子环境中，试样表面能迅速获得很深的渗层和白亮层，而电场外试样几乎无渗层。说明电场内气体电离率高，活性粒子浓度高。整个工艺过程操作简便，是一种很有发展前景的新工艺。     

氮化-氧化复合工艺研究进展

综述了各种氮化一氧化复合工艺的研究进展，讨论了含氧气氛的添加对渗层组织和性能的影响。含氧气氛的添加方式不同，所起的作用不同：在渗氮前添加可加速渗氮；渗氮后添加可提高氮化层的耐磨性、耐蚀性；在渗氮过程中添加形成氧氮化，在加速渗氮的同时还可提高渗氮层的表面性能。其中，离子氮化后氧化一直是国外研究的重点。     

Progress in sensor controlled nitriding and nitrocarburising

Abstract

The measurement of oxygen partial pressure in nitriding and nitrocarburising atmospheres by using the oxygen probe on the basis of solid state electrolytes has been approved for the in situ determination of the process parameters such as nitriding, oxidising and carburising potentials respectively. The oxygen can be used as a reactant as well as an indicator for the control of the parameters for nitriding and nitrocarburising processes. Process control on the basis of in situ probes provides a more precise and flexible approach to meet the demands made on surface layers. It can prevent disturbances caused by uncontrolled external oxygen and facilitates a rational gas regime, thus contributing to process and product optimisation as well as quality.     

A Hybrid Low Temperature Surface Alloying Process for Austenitic Stainless Steels

This paper describes a novel, hybrid process developed to engineer the surfaces of austenitic stainless steels at temperatures below 450℃ for the improvement in wear and corrosion resistance. The process is carried out in the plasma of a glow discharge containing both nitrogen and carbon reactive species, and facilitates the incorporation of both nitrogen and carbon into the austenite surface to form a dual-layer structure comprising a nitrogen-rich layer on top of a carbon-rich layer.Both layers can be precipitation-free at sufficiently low processing temperatures, and contain nitrogen and carbon respectively in supersaturated fcc austenite solid solutions. The resultant hybrid structure offers several advantages over the conventional low temperature nitriding and the newly developed carburizing processes in terms of mechanical and chemical properties, including higher surface hardness, a hardness gradient from the surface towards the layer-core interface, uniform layer thickness, and much enhanced corrosion resistance. This paper discusses the main features of this hybrid process and the various structural and properties characteristics of the resultant engineered surfaces.     

稀土化学热处理进展

综述了哈尔滨工业大学稀土化学热处理研究和应用成果。包括稀土渗碳及碳氮共渗、稀土渗氮及氮碳共渗、等离子体稀土渗氮、稀土渗硼及硼铝共渗、稀土多元共渗、稀土渗金属工艺技术，稀土的催化和微合金化机制，渗层组织和性能的改善，稀土化学热处理在生产中的应用及其过程的数学模型与计算机仿真等。     

短应力线轧机拉杆离子渗氮畸变控制

为探明杆状工件离子渗氮畸变的影响因素,对短应力线轧机拉杆的加工残余应力、装卡方式、多次升温和降温等因素进行了研究。结果发现,影响拉杆渗氮畸变的最大因素是拉杆的加工应力,所以对于长杆状工件,在精加工和渗氮之前加入合理的去应力工序可以有效控制渗氮畸变;另外,缓慢升温、降温及垂直悬吊的装卡方式也可以在一定程度上减小渗氮畸变。需多次渗氮才能满足图纸技术要求的长杆状工件,在每渗氮一次之后,把工件旋转180°,可以有效控制渗氮畸变。     

Low pressure carburising and high pressure gas quenching

Abstract

The traditional technology of heat treatment for gear components is the combination of atmospheric gas carburising with oil quenching. This technology is proven to deliver reliable results. However, the need of modern production is to react fast according to changing processes and production volumes. The highest technical requirements in combination with economical production methods must be met to ensure the highest quality standards and to establish environmental friendly production. Low pressure carburising and high pressure gas quenching is a reliable method that is used more and more in Asia, Europe and North America. This technology is an answer to the above described needs. Major car and gear makers have proven this process and implemented it into the mass production of gears components. With low pressure carburising and high pressure gas quenching it is possible to have real high production volumes and to react very flexible to different production scenarios.     

Influence of plasma peening on oxidation of H13 hot work steel in water vapor

The surface oxidation films on H13 steel samples, obtained by different oxidation processes were observed by optical microscope. It is shown that the oxidation speed of H13 steel is increased remarkably due to the surface modification of plasma peening. Further researches were made by XRD, SEM and EDS. The activation of H13 surface caused by plasma peening and the subsequent higher oxygen diffusion rate into the steel seem to be the main reasons of higher oxidation speed. The nitride layer, generally formed on the steel surface under plasma nitriding process, can be substituted by oxide in subsequent oxidation process, which can reduce the risk of heat cracking in some hot work applications. Therefore, the plasma nitriding plus oxidation process is a proper choice for some hot work dies, which demands high hardness to avoid indentation as well as high toughness to avoid cracks.