The Phenomenon of High Hardness Values on the S-Phase Layer of Austenitic Stainless Steel via Screen Plasma Nitriding Process

The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect;that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).

Plasma Nitriding of Austenitic Stainless Steel with Severe Surface Deformation Layer

The dc glow discharge plasma nitriding of austenite stainless steel with severe surface deformation layer is used to produce much thicker surface modified layer. This kind of layers has useful properties such as a high surface hardness of about 1500 Hv 0.1 and high resistance to frictional wear. This paper presents the structures and properties of low temperature plasma nitrided austenitic stainless steel with severe surface deformation layer.

GROWTH PROCESS OF LOW-TEMPERATURE PLASMA-NITRIDING LAYER ON AUSTENITIC STAINLESS STEEL

The growth process of low-temperaturs plasma-nitriding layer was investigated by scan-ning electron microscopy (SEM) and X-ray diffraction (XRD). The layer is composedof expanded fcc phase (γN), whose lattice parameter of the layer increases with processtime resulting from increasing the nitrogen content. The layer hardness increases grad-ually with nitrogen content. The high slip band density on the layer surface observedin situ by SEM shows that the surface yield occurs when supersaturated nitrogen con-tent in the layer attains to some value, which is also responsible for the increase inlayer hardness.

Glow Discharge Plasma Nitriding of AISI 304 Stainless Steel

Glow discharge plasma nitriding of AISI 304 austenitic stainless steel has been carried out for different processing time under optimum discharge conditions established by spectroscopic analysis. The treated samples were analysed by X-ray diffraction （XRD） to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of an expanded austenite phase （TN） owing to incorporation of nitrogen as an interstitial solid solution in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of indentation depth （μm）. The results showed clear evidence of surface changes with substantial increase in surface hardness.

The Study of Plasma Nitriding of AISI304 Stainless Steel

This paper presents results on the plasma nitriding of AISI 304 stainless steel at different temperatures in NH 3 gas. The working pressure was 100-200 Pa and the discharge voltage was 700-800V. The phase of nitrided layer formed on the surface was confirmed by X-ray diffraction. The hardness of the samples was measured by using a Vickers microhardness tester with the load of 50g. After nitriding at about 400 °C for two hours a nitrided layer consisting of single YN phase with thickness of 5um was obtained. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 950 HV (for nitrided samples at temperature of 420°C). The phase composition, the thickness, the microstructure and the surface topography of the nitrided layer as well as its properties depend essentially on the process parameters.

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 fee 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).

Optimization Study of Pulsed DC Nitrogen-Hydrogen Plasma in the Presence of an Active Screen Cage

A glow discharge plasma nitriding reactor in the presence of an active screen cage is optimized in terms of current density,filling pressure and hydrogen concentrations using optical emission spectroscopy（OES）.The samples of AISI 304 are nitrided for different treatment times under optimum conditions.The treated samples were analyzed by X-ray diffraction（XRD） to explore the changes induced in the crystallographic structure.The XRD pattern confirmed the formation of iron and chromium nitrides arising from incorporation of nitrogen as an interstitial solid solution in the iron lattice.A Vickers microhardness tester was used to evaluate the surface hardness as a function of treatment time（h）.The results showed clear evidence of improved surface hardness and a substantial amount of decrease in the treatment time compared with the previous work.

钛催渗低温离子渗氮对304不锈钢组织性能的影响

目的 在保障304奥氏体不锈钢良好耐蚀性前提下,研发显著改善表层硬度及耐磨性的低温高效离子渗氮技术。方法 低温离子渗氮时,在试样周围均匀放置微量海绵钛,研发304奥氏体不锈钢创新钛催渗低温离子渗氮技术。采用光学显微镜、扫描电子显微镜、能谱分析仪、X射线粉末衍射仪、显微维氏硬度计、摩擦磨损测试仪,以及电化学工作站等设备分别对试样截面显微组织、物相及成分、截面显微硬度、渗层耐磨性能、耐蚀性能等渗层组织性能进行测试与分析。结果 304奥氏体不锈钢在420℃/4h钛催渗离子渗氮处理后,不仅保持了良好耐蚀性,且渗层耐蚀性比常规低温离子渗氮略有提升,同时,表面硬度与耐磨性大幅提高,表面硬度由常规离子渗氮的978HV0.025提升至1350HV0.025。磨损率由20.9μg/(N·m)降低至7.4μg/(N·m),下降了约2/3。特别有价值的是,钛催渗低温离子渗氮效率比传统离子渗氮显著提升,渗氮层厚度由常规离子渗氮的11.37μm增厚到48.32μm,即渗氮效率提高到常规离子渗氮的4倍以上。结论 本研究研发的钛催渗低温离子渗氮技术在保障304奥氏体不锈钢优良耐蚀性的同时,能够大幅度提升不锈钢表面硬度及耐磨性能,且具有显著的催渗效果。

高效离子氮化奥氏体不锈钢及助渗方法的研究进展

等离子体辅助氮化技术因具有氮化速率较快、渗层氮含量高、工艺绿色环保等优点成为研究的焦点。本文综述了活性屏等离子体辅助氮化、低压电弧等离子体辅助氮化和热丝增强等离子辅助氮化的新型等离子氮化技术。同时,发现通过添加稀土元素、增加预处理、后氧化等复合氮化处理可以进一步增强氮化效果。

奥氏体不锈钢低温渗氮层的组织与耐磨性

利用低压等离子体弧离子源在350～450℃之间对奥氏体不锈钢进行快速渗氮表面强化,在适当的工艺条件下,处理90min即可得到厚度10μm左右的高硬度的氮过饱和奥氏体固溶体强化层.采用X射线衍射、电子探针及俄歇谱仪等对渗层进行结构分析表明,在处理温度低于450℃时,渗层为单相氮过饱和奥氏体固溶体层,表面氮可以达到15%,显微硬度达到1200HV,与原基体材料相比。

奥氏体不锈钢低温低压等离子体渗氮

利用低压等离子体弧源离子渗氮技术在低压（４×１０^(－１)Ｐａ）、低温 （３５０～４００℃）条件下进行奥氏体不锈钢表面渗氮处理，可在奥氏体不锈钢表面形成硬度高、耐蚀性好，厚度１０μｍ左右的氮在奥氏体中的过饱和固溶体氨化层，最高表面氮浓度达到４５％左右。

奥氏体不锈钢表面改性层耐蚀性实验研究 Ⅰ.孔蚀和均匀腐蚀性能

用等离子体源离子渗氮技术在380℃处理1Cr18Ni9Ti奥氏体不锈钢，获得了高氮面心相（γN）表面改性层，γN相层在0.5％─6％NaCl溶液中具有显著优于原始不锈钢的耐孔蚀性能；在0．5mol／LH2SO4溶液中具有相当于原始不锈钢的耐均匀腐蚀性能。γN相的氮浓度影响其耐孔蚀性能，但对其耐均匀腐蚀性能则没有明显影响、γN相的室温浸泡与电化学测试取得了规律相同的实验结果．

气压对304奥氏体不锈钢低温离子渗氮组织与性能影响

在400℃、8 h、不同气压(80~400 Pa)条件下对304奥氏体不锈钢进行离子渗氮处理。采用扫描电镜(SEM)、X射线衍射仪、显微硬度计及万能摩擦试验机对表面改性后的304奥氏体不锈钢渗层组织、相结构、渗层硬度以及耐磨性进行了测试和分析。结果表明,400℃离子渗氮处理后304奥氏体不锈钢形成了明显的白亮层,即单相S相层;低压对304奥氏体不锈钢离子氮化具有良好的催渗效果,即渗层厚度随气压的减小而增加,在100 Pa条件下,渗层厚度达到最大值51.7μm;渗氮后试样表面硬度达到最大值1100 HV0.01;低温低压离子渗氮能够提高304奥氏体不锈钢耐磨性,80 Pa和100 Pa是提高304奥氏体不锈钢耐磨性的最佳气压。

处理温度对1Cr18Ni9Ti钢脉冲直流等离子渗氮的影响

利用脉冲直流辉光等离子技术，在不同的温度下对1Cr18Ni9Ti奥氏体不锈钢进行了渗氮处理。利用光学显微镜、显微硬度计、XRD以及电化学工作站对渗氮层进行了分析。结果表明，处理温度显著影响1Cr18Ni9Ti钢渗氮层的结构与性能。处理温度≤440℃时，渗层为纯S相结构；处理温度在460～540℃之间时，为S相＋CrN＋Fe4N的混合组织；处理温度≥560℃时，为CrN＋Fe4N的化合物层。可在较宽的温度范围内对该钢进行脉冲直流等离子渗氮，获得表面硬度高于基底5～6倍的渗氮层。渗氮层的厚度随处理温度的升高而增加，而抗腐蚀性能随着处理温度的升高呈下降趋势。

等离子体源离子渗氮 1Cr18Ni9Ti 奥氏体不锈钢磨损特性的试验研究

用等离子体源离子渗氮，即低能（１～３ｋｅＶ）、超大剂量（１０１９～１０２０ｉｏｎｓ／ｃｍ２量级）Ｎ＋注入－同步扩散改性技术，在２８０℃和３８０℃下处理１Ｃｒ１８Ｎｉ９Ｔｉ奥氏体不锈钢，获得了最大深度分别为１．６μｍ和１０．６μｍ，固溶Ｎ的最高原子浓度均约为２５％的Ｎ过饱和面心立方相（γＮ）改性层．销－盘磨损试验表明：在２ｍ／ｓ和较宽负荷范围（等效正应力０．２～２．８ＭＰａ）条件下，高硬度（ＨＫ０．１Ｎ２２００）的γＮ相改性层具有较高的承载能力和较长的耐磨寿命．高度过饱和Ｎ在母相奥氏体中的固溶强化作用，是使等离子体源离子渗氮奥氏体不锈钢耐磨性提高的主要原因．

奥氏体不锈钢高频高压低温等离子体渗氮

利用浸没式高频高压等离子体渗氮（ＩＨＨＰＮ）技术对ＳＳ３０４奥氏体不锈钢进行了低温渗氮处理。在３００℃×２５ｈ处理条件下获得了０３μｍ厚的高氮层。表面显微硬度较未处理的样品明显提高。ＸＲＤ分析表明，改性层内形成了膨胀奥氏体。

AISI304奥氏体不锈钢阳极渗氮层的组织与摩擦磨损性能

为避免传统直流离子渗氮存在的表面打弧和边缘效应等弊端,采用活性屏阳极渗氮法对AISI 304奥氏体不锈钢进行表面处理。将样品放置于阳极电位,在440~520℃范围内,渗氮处理8 h。分析了渗氮层的微观组织结构与形貌,并考察了渗氮前后的摩擦磨损性能。结果表明:在低温440℃下,在表面制备了高硬度的S相强化层。XRD与TEM表明S相为面心立方结构,且无Cr N相析出。高温520℃渗氮表面硬度值(1100 HV0.1)是基体的5倍,但Cr N相明显析出。在干摩擦条件下,渗氮处理后的摩擦系数在0.8左右,相对渗氮前降低约0.2,特别是磨损率只有渗氮前的十分之一量级。磨损机制从原始基体的严重粘着转变为轻微的氧化和磨粒磨损。

等离子体源渗氮304L奥氏体不锈钢改性层的耐蚀性能

采用等离子体源渗氮技术经450℃×6 h在304L奥氏体不锈钢表面获得了厚度约为15μm、峰值氮浓度高达25 at%的单一面心结构的γΝ相改性层。研究了γΝ相改性层在3.5%NaCl溶液中的耐腐蚀性能,分析了其钝化膜的化学组成,并与原始304L不锈钢相比较。结果表明:γΝ相改性层的阳极极化曲线未发生明显的点蚀击穿,自腐蚀电位比原始不锈钢提高了323 m V(SCE),维钝电流密度低一个数量级。γΝ相钝化膜的EIS与原始不锈钢钝化膜相比,其容抗弧直径增大,相位角平台变宽,采用等效电路Rs-(Rct//CPE)拟合的电荷转移电阻Rct由原始不锈钢3.05×10~4Ω·cm^2增至1.98×105Ω·cm2,计算的双电层电容Cdl由313μF/cm^2降低至70.3μF/cm^2。γΝ相钝化膜具有双层结构,外层是Fe、Cr氢氧化物和氧化物构成,内层以Cr_2O_3为主,N主要以离子键类型的Fe Nx和Cr Nx形式存在。与原始奥氏体不锈钢相比,γΝ相钝化膜更加致密,具有保护性的Cr_2O_3阻碍层增厚,增强了γΝ相改性层的耐蚀性能。

奥氏体不锈钢循环离子氮氧共渗工艺研究

对0Cr18Ni9奥氏体不锈钢进行氮氧共渗循环离子渗氮试验,并和常规离子渗氮进行对比。利用光学显微镜、显微硬度计、XRD及磨损仪对渗氮层进行分析。结果表明,氮氧共渗循环离子渗氮比常规离子渗氮的渗氮速度快,渗层比常规离子渗氮厚;表面硬度为920 HV0.05(比常规离子渗氮高20 HV0.05),硬度梯度平缓;渗层中的ε相减少,γ′相增多;且渗层中的微量Fe3O4降低了表面摩擦系数,使工件经氮氧共渗循环离子渗氮后获得更高耐磨性。

直流等离子氮化工艺对316L不锈钢组织和磨损的影响

应用高压直流辉光放电等离子技术，改变氮化工艺参数，对316L奥氏体不锈钢进行表面渗氮处理。利用XRD衍射仪分析渗氮层的相组成，SEM观察氮化层厚度和结构，表面显微硬度计检测渗层的表面硬度，结果表明：当氮化温度T为400℃时，氮化层为单一的S-phase；当420℃≤T〈480℃时，氮化层为CrN＋S—phase两相混合；当温度为480℃时，S—phase衍射峰消失，仅出现CrN相；渗层厚度约为5～9μm，渗层深度随着温度和气压的升高而增加；表面显微硬度随着温度和气压的增加而增加，最高的表面显微硬度可达839Hv0.1。在MM200磨损实验机上用环块式的方法评价磨损性能，结果表明等离子氮化显著提高了不锈钢表面的耐磨性能；用SEM观察磨损表面形貌，表明未氮化的不锈钢的磨损机制主要是粘着磨损、氧化磨损和磨粒磨损；等离子氮化试样的磨损机制主要是氧化磨损。