IMPROVEMENT OF MECHANICAL PROPERTIES OF MARTENSITIC STAINLESS STEEL BY PLASMA NITRIDING AT LOW TEMPERATURE

A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.

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).

Effect of processing temperatures on characteristics of surface layers of low temperature plasma nitrocarburized AISI 204Cu austenitic stainless steel

The influence of processing temperatures on the surface characteristics of AISI 204Cu austenitic stainless steel was investigated during a low temperature plasma nitrocarburizing.The resultant layer was a dual-layer structure,which comprises a N-enriched layer on the top of C-enriched layer.The surface hardness and the layer thickness increase up to about HV 0.05 1000 and 20μm with increasing temperature.The specimen treated at 400°C shows a much enhanced corrosion resistance compared to the untreated steel.A loss in corrosion resistance was observed for specimens treated at temperatures above 430°C due to the formation of Cr2N.

A PROBABILISTIC ASSESSMENT OF TEMPERATURE EFFECTSON THE LOW CYCLE FATIGUE BEHAVIOUR OF 1Cr_(18)Ni_9Ti STEEL WELD METAL

Based on the test results obtained from the single-step test and the incremental-step test at room temperature and 240℃, a probabilistic assessment of temperature effects on the cyclic stress-strum response and the fatigue life of 1Cr18Ni9Ti steel weld metal is performed. In orber to assess the temperature effect on cyclic stress amplitude where there is a scatter of the material cyclic constitution, a probabilistic assessment approach on the basis of probabilistic modified Ramberg-Osgood relations is introduced.The investigation shows that the cyclic stress amplitude and the scatter of cyclic stress amplitude data are decreased at 240℃. Similarly, from the consideration of the fatigue life scatter a probabilistic assessment of temperature effect on the fatigue life is suggested on the basis of probabilistic Langer S-N relations. The investigation shows that the crack initiation life is increased and the scatter of crack initiation life data is decreased at 240℃.

Low Temperature Characteristics of FBG Temperature Sensors with Small-size Packaging

Two small-size package methods, thin stainless steel tube based package method and plating gold based package method for fiber Bragg grating(FBG) temperature sensors, are designed. The characteristics of the FBG temperature sensors in the environment temperature between 203K and 243K are investigated. The wavelengths of the FBG temperature sensors as a function of the temperature are examined experimentally. The experiment results of the two different small-size package sensors in identical conditions are compared with each other. The transmission spectrum of the sensors is analyzed at the temperature of 273K and 213K. The temperature sensitive factors of the sensors are derived analytically and are verified by experiments. Linear fitting to the wavelength-temperature curve is carried out.

Effects of Rare Earth Elements on the Characteristics of Low Temperature Plasma Nitrocarburized Martensitic Stainless Steel

Low temperature plasma nitrocarburizing of 17-4PH martensitic stainless steel was conducted at 430 ℃ with and without rare earth （RE） addition. The microstructure, kinetics, microhardness, wear behavior as well as corrosion resistance of the modified layer were studied by optical microscopy, X-ray diffraction, Vickers microhardness tester, pin-on-disc tribometer and potentiodynamic polarization tests. The results show that the thickness of plasma RE nitrocarburized layer is much thicker than that formed by nitrocarburizing without RE addition. The incorporation of RE does not change the kind of the phases and the nitrocarburized layer consists mainly of nitrogen and carbon expanded martensite （aN）, γ-Fe4N and a-Fe with a trace of CrN phases. The surface microhardness of plasma nitrocarburized layer can be increased by 100 HV after RE addition. Wear resistance of the specimen can be apparently improved by low temperature plasma nitrocarburizing with and without RE addition and without sacrificing its corrosion resistance. Wear reduction effect of low temperature plasma nitrocarburizing with RE addition is better than that of the conventional one.

SIGMAPLUG—A NEW TEMPERATURE INDICATOR FOR REMAINING LIFE ASSESSMENT OF HIGH TEMPERATURE COMPONENTS

Improved life assessment techniques will enable engineering components to be replaced before failure, thereby reducing the risk of industrial accidents as well as minimizing financial loss due to unscheduled outages. For components operating at high temperatures, temperature measurement is very important. In many situations, the environmental conditions are too hostile for conventional techniques to be used. Researchers over the world have been looking for new techniques for temperature measurement and one such device, called Feroplug, has been developed previously by the and coworkers. The Feroplug has been patented in USA, UK and Europe by the British Technology Group. The underlying principle of the Feroplug is based on the transformation of ferrite in some specially designed duplex stainless steels. This paper describes a new invention called Sigmaplug which is a new development of the Feroplug but using an entirely different physical principle. It was discovered that the sigma phase in Fe

A damage-coupled multi-axial time-dependent low cycle fatigue failure model for SS304 stainless steel at high temperature

Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ？ C, and in the frame of unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.

焊接方法对奥氏体不锈钢焊接接头低温冲击性能的影响

为了研究奥氏体不锈钢焊接接头的低温冲击性能对低温压力容器的安全性影响,本文通过-196℃的低温冲击试验,对比研究了钨极气体保护焊(GTAW)、熔化极气体保护电弧焊(GMAW)、埋弧焊(SAW)3种焊接方法对S30408和S31608两种奥氏体不锈钢焊接接头低温冲击性能的影响。对于S30408焊接接头,热影响区的低温冲击性能小于母材与焊缝区,成为薄弱位置;3种焊接方法中,GTAW获得的焊接接头在热影响区的冲击性能处于最优水平。对于S31608焊接接头的低温冲击性能,焊缝、热影响区与母材的差异较小;3种焊接方法中,SAW获得的焊接接头在冲击吸收能量上与母材结果相近,能够获得焊接接头较好的综合冲击性能。通过对比不同焊接工艺下焊接接头断口形貌特征表明,焊接接头不同区域冲击断口形貌特征与低温冲击性能的结果相吻合。本文研究工作对于奥氏体不锈钢低温压力容器焊接工艺的选择具有参考意义。

温度和应变幅对亚稳奥氏体不锈钢S321低周疲劳行为的影响

在室温和650℃的环境下对S321、S321H不锈钢进行了0.5%、0.7%、0.9%应变幅下的低周疲劳试验,并在室温下对S321和S321H开展了多个寿命点的疲劳加载历史试验,结合X射线衍射定量分析测算形变诱发马氏体的含量。结果表明:形变诱发马氏体的生成会导致奥氏体钢持续循环硬化,室温下合金在初次硬化后继续二次硬化,而在650℃下没有形变诱发马氏体生成,合金在初次硬化后进入循环稳定阶段。循环过程中,碳含量越低,形变诱发马氏体含量越多,合金的循环硬化程度更高。两种温度下,两种材料的疲劳寿命在低应变幅下都相差不大,应变幅越大,两种材料的疲劳寿命相差越大,因此,可以考虑服役条件为低应变幅时使用S321不锈钢代替S321H不锈钢。

低温液体氧氮化对奥氏体不锈钢磨损行为的影响

[目的]奥氏体不锈钢被广泛用于制造各种航空电子装备零部件,但其硬度和耐磨性欠佳。[方法]采用低温液体氧氮化技术对304奥氏体不锈钢进行表面改性处理。采用扫描电子显微镜、透射电子显微镜、维氏硬度计等分析了所得复合改性层的微观组织和截面显微硬度分布,通过摩擦磨损试验探究了表面改性层的耐磨性。[结果]低温液体氧氮化表面改性层由外侧致密的Fe_(3)O_(4)相和内侧富氮S相构成。S相是含氮过饱和固溶体,含有大量位错、层错和孪晶,因此硬度较高。载荷和温度会影响不锈钢样品的磨损行为,温度升高和载荷增大都会使304奥氏体不锈钢样品和低温液体氧氮化样品的平均摩擦因数轻微下降,磨损体积损失增大。不过低温液体氧氮化处理能够缩短304奥氏体不锈钢样品初始磨损阶段的持续时间,使其在载荷10 N、温度200℃条件下的最大磨损体积损失由1.086 mm^(3)降至0.144 mm^(3)。[结论]低温液体氧氮化处理能够显著提高304奥氏体不锈钢的耐磨性。

干型黄酒大罐陈酿的研究

目前黄酒陈酿主要以陶坛为主,部分公司进行了大罐贮存陈酿试验,但均存在陈酿效果相对不明显、酸败风险高或能耗成本高等情况。本研究以实际大罐贮存陈酿为基础,研究了不同糖度干型黄酒的大罐常温陈酿效果、陈酿期间总酸与酒体温度关系及纯生干型黄酒的大罐常温陈酿效果.经扩大化试验得出总糖5 g/L以下的干型黄酒在大罐常温陈酿过程中酸度变化稳定,无需额外制冷冷却;通过自动化监控温度异常提示酸度风险,整体陈酿效果明显且节约经济成本。

基于液氢储运的超低温不锈钢微观组织演变与力学性能研究进展

针对不锈钢在低温服役过程中面临高强低韧、低耐磨以及氢脆等一系列问题,阐述3种典型的氢脆理论,并分析不锈钢超低温下材料化学成分、应变量和应变速率等参量对其力学性能的影响规律,从微观角度明晰不锈钢超低温下的组织演变机制,揭示位错组态、滑移带、机械孪晶、奥氏体相、马氏体相的变化与力学性能改变的内在联系,对改善加工工艺、调控材料化学成分比例以及减小晶粒尺寸3种强化手段进行机理分析。最后介绍不锈钢在氢能储运领域中的典型应用以及未来发展趋势。

TIG焊热输入对316LN奥氏体不锈钢焊接接头性能的影响

通过调整设置不同的焊接热输入条件,利用窄间隙TIG对316LN奥氏体不锈钢进行焊接,取试进行77K低温冲击韧性、常温力学性能、微观组织分析试验。将不同焊接热输入对试验结果进行对比,研究一定范围内热输入对TIG焊接接头强度、韧塑性性能以及金相组织的影响,为316LN奥氏体不锈钢批量焊接提供支撑。

22Cr High-Mn-N Low-Ni Economical Duplex Stainless Steels

A new family of economical duplex stainless steels in which N or Mn was substituted for Ni with composi- tion of 22Cr-8.0Mn-xNi-1.0Mo-0.7Cu-0.7W-0.3N （x = 0.5 -- 2.0） have been developed by examining the micro- structure, mechanical and corrosion properties of these alloys. The results show that these alloys have a balanced ferrite-austenite relation. In addition, the alloys are free of precipitation of sigma phase and Cr-nitride when solution- treated at 750 to 1300℃ for 30 min. The yield strength, tensile strength and fracture elongation values of experi- mental alloys solution-treated at 1050 ℃ for 30 min are about 500, 750 MPa and 40.0%, respectively. Low-temper- ature impact properties can be improved distinctly with the increase of nickel content. Among the designed DSS al- loys, the alloy with Ni of 2.0% is found to be an optimum alloy with proper phase proportion, better low-tempera- ture impact properties and higher pitting corrosion resistance compared with those o~ other alloys. The mechanical and corrosion properties and lower production cost of the designed DSSs are better than those of AISI 304.

焊接工艺对LNG储罐用高锰钢焊接接头组织和性能的影响

为了推动新型国产低温高锰钢及相应焊材在LNG储罐国产化中的应用,利用扫描电子显微镜、光学显微镜并通过常温拉伸、弯曲、低温冲击以及显微硬度等试验,研究了熔化极气体保护焊(GMAW),埋弧焊(SAW)和焊条电弧焊(SMAW)3种不同的焊接工艺对LNG储罐用低温高锰钢焊接接头组织和性能的影响。结果表明,3种焊接工艺的热影响区组织为奥氏体与少量夹杂物颗粒,熔合线附近晶粒粗大且狭长,焊缝组织为柱状晶。硬度最低值均位于焊缝中心,拉伸试验断裂位置均为焊缝部位。3种焊接工艺焊接接头抗拉强度分别为839.2,863.8,675.2 MPa,拉伸和弯曲性能均能满足要求。-196℃时的焊缝冲击吸收能量值分别为123,100,83.7 J,冲击断口均为韧性断裂。在焊接低温高锰钢时应严格控制热输入,从而保证低温高锰钢的焊接质量。

某油田核桃壳过滤器撬块内管线选材评价

为解决中东某油田核桃壳过滤器撬块内管线腐蚀穿孔严重的问题,通过文献调研优选出316L不锈钢、3Cr低合金钢、抗菌钢及耐高温聚乙烯(PE-RT II)等四种管材,进一步通过相容性、施工可行性及经济性进行选材评价。结果表明:在相容性评价试验后,PE-RT II管材表面无溶解、气泡、开裂及变形,参照静液压强度外推曲线可知PE-RT II管材在相应工况下服役周期应能超过20 a;316L不锈钢、3Cr低合金钢和抗菌钢表面呈均匀腐蚀形貌,其中316L不锈钢为轻微腐蚀、3Cr低合金钢和抗菌钢为中度腐蚀,三种管材在相应工况下服役周期均应能超过25 a;PE-RT II管材可通过热熔焊接和电熔焊接施工,316L不锈钢、3Cr低合金钢和抗菌钢可通过焊接施工,四种管材均能满足在核桃壳撬块内的安装施工要求;PE-RT II管材经济性最佳。综上,优选PE-RT II管材。

奥氏体不锈钢焊缝金属低温性能影响因素综述

随着低温系统向77 K以下应用发展,低温工程对奥氏体不锈钢焊接接头力学性能提出了更加苛刻的要求,焊缝金属的低温强度、低温冲击韧性及抗氢脆性成为低温工况安全运行的关键性能。因此,该文详细阐述低温对奥氏体不锈钢焊缝金属强度、冲击韧性的影响及不同温度导致的两种氢脆行为,并深入介绍了铁素体相、马氏体相变、氮含量对焊缝金属低温强度的提升作用及这些因素与析出相、夹杂物对低温冲击韧性进一步降低作用,然后着重论述了奥氏体相的高稳定性对焊缝金属抗氢脆性的积极作用及铁素体相的不利作用。在实际应用中焊缝金属的性能同时受多种因素地共同作用,因此对于相同因素对不同性能的研究将有助于提高低温下奥氏体不锈钢焊缝金属的使用安全性。

奥氏体不锈钢全奥氏体组织熔敷金属中Ni含量对力学性能影响

为了研究Ni含量对全奥氏体组织熔敷金属力学性能的影响,采用铬当量相近、Ni质量分数不同的6种E316LMn-15焊条,通过控制其它化学成分,避免金属间化合物的形成并减弱了热裂倾向。分别对SMAW施焊后熔敷金属进行光学金相组织观察、铁素体测量、室温拉伸试验和-196℃冲击试验。结果表明,熔敷金属均为以奥氏体模式凝固的全奥氏体组织,具有良好的室温拉伸性能,抗拉强度均在520 MPa以上,屈服强度均超过380 MPa,断后伸长率也都在35%以上;同时熔敷金属均具有较高的低温韧性,-196℃平均冲击吸收能量均超过60 J。Ni的质量分数在15.58%~16.04%范围内,-196℃平均冲击吸收能量提升幅度大于Ni质量分数在16.04%以上的熔敷金属,且Ni质量分数在16.27%以上的熔敷金属低温冲击吸收能量趋于稳定,Ni质量分数为16.85%的试样-196℃平均冲击吸收能量高达90.4 J。

焊接热输入量和保护气体成分对S32205双相不锈钢低温冲击韧性的影响

采用等离子弧焊(PAW)+钨极惰性气体保护焊(GTAW)对2205双相不锈钢进行焊接,研究了在GTAW焊接过程中,热输入量和保护气体这两个要素对材料焊接部位低温冲击韧性的影响,并通过金相和SEM等对微观组织结构进行分析研究。结果表明,采用GTAW焊接时,热输入量会影响晶粒组织中铁素体/奥氏体相比例和奥氏体形态,当热输入量为1.76 kJ/cm时,焊接部位的低温冲击性能(-46℃)最佳;在保护气体中添加N_(2),会影响奥氏体和铁素体比例以及氮化物(CrN/Cr_(2)N)析出相在铁素体中的析出数量,并且导致微气孔形成,当N_(2)添加量为1%左右时,焊接部位的低温冲击性能最佳。