Metal Dusting of Alumina-Forming Creep-Resistant Austenitic Stainless Steels

Three developmental alumina-forming austenitic stainless steels were exposed to metal dusting conditions at 650?°C in a gas of 50%CO–49%H₂–1%H₂O (a _C: 36.7 and $ p_{{{\text{O}}_{2} }} $ : 2.83?×?10^?26?atm) under thermal cycling conditions. Metal wastage measurement showed initially slow kinetics followed by a fast weight loss. This observation is attributed to the formation of protective chromia/alumina oxide scales in the early stage of the reaction, followed by local oxide failure/spallation during cyclic reaction. Metal dusting initiated from these local defects, and pitting-type attack was observed after 131 cycles of reaction. After 352 cycles, severe dusting had developed, forming heavy and distinctive “tentacles” of superficial coke. This carbon deposit was composed of fine carbon filaments. Examination by TEM of the coke-metal reaction front showed direct surface metal disintegration, indicating that the dusting follows the classical mechanism for austenitic materials. Etching with aqua regia revealed a carburised zone formed in the alloy underneath the coke layer. Analysis by TEM of this zone revealed the formation of ultra-fine, needle-shaped chromium carbide precipitates within a chromium depleted austenite matrix.     

新型奥氏体不锈钢高温NaCl腐蚀行为研究

通过实验室模拟垃圾焚烧炉中水冷壁环境,研究了新型奥氏体不锈钢254SMo、904L和317L在750、850和950℃下NaCl盐中的热腐蚀行为,获得了腐蚀动力学曲线;利用SEM/EDS和XRD对3种材料腐蚀产物的形貌和组成进行了观察和分析,探讨了热腐蚀机理.结果 表明:3种不锈钢在热腐蚀过程中都表现为失重,并且随着温...     

Comparative Behaviour of Specialty Austenitic Stainless Steels in High Temperature Environments

Two different alloying strategies may be utilised to improve the high temperature performance of austenitic stainless steels: increasing the chromium content, sometimes in combination with a higher nickel level; and alloying with silicon, nitrogen and rare earth metals. The relative merits of the two approaches are explored by comparing the performance of commercial alloys in oxidation tests in air–water vapour, corrosion tests in an oxidising-sulphidising atmosphere and with applied deposits, and creep and fatigue testing. Significant increases in high temperature performance are achieved by selecting specialty heat-resisting austenitic stainless steels, and it will be shown that the choice of grade should be governed by the dominant operative degradation mechanisms.     

温度对高温水中奥氏体不锈钢应力腐蚀开裂速率的影响

温度是影响核电站材料在高温水冷却剂中应力腐蚀开裂的关键参数之一。测试和分析了温度对不同外加应力水平下不同屈服强度奥氏体不锈钢在高温纯水中应力腐蚀开裂速率的影响。发现在110℃~288℃温度范围内,冷加工316L不锈钢的应力腐蚀开裂扩展速率为热激活过程。应力腐蚀开裂速率的表观活化能与温度区间、应力强度因子大小和屈服强度有关。分析了试验结果与文献报道的温度影响奥氏体不锈钢应力腐蚀开裂的几种类型和相关联的因素。     

High Temperature Mechanical Properties of HK40-type Heat-resistant Cast Austenitic Stainless Steels

This work characterized HK40-type, cast austenitic stainless steel, as the W content was varied from 0 to 3.6 wt.%. Analysis of microstructure using optical and scanning electron microscopies showed that the alloys contained relatively large amount of Cr-carbide, Nb-compound, and MnS at the austenite grain boundary. The addition of W promoted the formation of Cr-carbide and affected the high-temperature mechanical properties. According to tension tests carried out at room temperature, 400, 600, and 800 °C, the alloys became significantly stronger and brittle as W content increased. The low-cycle fatigue tests showed that fatigue resistance was also increased with W addition, but an excessive amount of W decreased the fatigue resistance. The HK40-type alloys with 2.0 wt.% W exhibited best high-temperature mechanical performances.     

奥氏体不锈钢稀土催渗离子渗氮工艺研究

对304、316L奥氏体不锈钢采用不同氮一氢比的气氛,在不同温度和不同保温时间进行了离子渗氮和稀土催渗离子渗氮。结果表明,经580℃在氮一氢比为1：3的气氛中稀土催渗离子渗氮9h,304和316L钢的渗层深度分别为0．12mm和0．112mm,表面硬度达1000HV0．1左右,与常规离子渗氮工艺相比,渗氮时间缩短了1h。     

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.     

Temperature Dependence of Tensile Behaviors of Nitrogen-Alloyed Austenitic Stainless Steels

The temperature dependence of tensile behaviors of two nitrogen-alloyed austenitic stainless steels, an annealed 316LN steel and a high-nitrogen austenitic stainless steel (Fe-Cr-Mn-0.66% N), was investigated by tensile test at different temperatures from 293 K down to 77 K. It was found that strength of the two steels increased with decrease of temperature. With a decrease in temperature, the uniform elongation increased for the 316LN steel, whereas it increased followed by a decrease for the high-nitrogen steel. A three-stage hardening behavior occurred in the 316LN steel, but not in the high-nitrogen steel, with decrease of temperature. The strain-induced martensite transformation in the 316LN steel could retard void nucleation and increase the strain-hardening rate, resulting in much higher tensile stress and higher uniform elongation of 316LN steel. It was analyzed that stacking fault energy of the high-nitrogen steel decreased with decrease of temperature, which promoted the twinning and planar slipping in the steel, and resulted in brittle fracture at cryogenic temperatures.     

奥氏体不锈钢低温离子渗氮工艺研究

对304、316 L奥氏体不锈钢进行了不同温度、不同时间的离子渗氮。研究了渗层的显微组织和耐腐蚀性,测定了渗层的硬度。结果显示,随着渗氮温度的升高,两种钢渗层的表面硬度和深度都增加,而耐蚀性降低。渗氮温度≥400℃时,随着渗氮时间的延长,两种钢渗层的表面硬度变化不大,但深度明显增加,渗层的耐蚀性降低。当渗氮工艺相同时,316 L钢渗氮层的硬度、深度和耐蚀性均比304钢的渗氮层高。     

High Temperature Oxidation Behaviour of High Al Content Ferritic and Austenitic Stainless Steels With and Without Rare-Earth Element Addition

The oxidation behaviour of austenitic and ferritic alloys containing 4% Al and rare-earth element addition of (La?+?Ce) has been investigated, and comparisons made to an austenitic alloy with no such addition. The alloys were all found to exhibit good oxidation resistance; although, such resistance was highest when the alloy contained rare-earth elements. The addition led to a reduction in the amount of scale spalling. The scales formed after 10 and 100?h at 1,000?°C were examined using transmission electron microscopy and found to have bi-layered microstructures. The dislocation density and an amount of distortion in the scale were found to differ, depending on the absence or presence of (La?+?Ce) in the metal. It was observed that the outer-to-inner layer thickness ratio changed with time and the rare-earth element addition promoted growth of the inner layer relative to the outer layer. Analysis of the scale compositions demonstrated an apparent synergistic relationship between the effects of the rare-earth element addition and the degree to which iron is incorporated within the scales. The results are discussed in relation to the relative oxidation performance of the austenitic and ferritic alloys.     

Cr-Ni奥氏体不锈钢的研究进展

Cr-Ni奥氏体不锈钢凭借着优良的耐腐蚀性、力学性能和生物相容性,在众多领域得到了广泛的应用。综述了Cr-Ni奥氏体不锈钢的发展过程和制备工艺,着重分析了其耐腐蚀性能和表面改性。指出了制备过程和腐蚀性能研究中的问题,并提出了改进制备工艺和腐蚀防护的措施。讨论了利用表面改性得到性能优良Cr-Ni奥氏体不锈钢材料的应用前景。最后阐述了Cr-Ni奥氏体不锈钢未来的发展趋势。     

奥氏体不锈钢的铬氮复合渗

奥氏体不锈钢制零件经铬氮复合渗处理后,工件表面可获得较高的力学性能,在承受摩擦和夹持力的工况条件下,可有效地防止咬合、擦伤、磨损,具有良好的耐腐蚀性.目前已投产的工件总量达10 t.     

Controlling End-Grain Corrosion of Austenitic Stainless Steels

SS 304L is widely used as a structural material in applications handling nitric acid such as nuclear fuel processing plants and nuclear waste management facilities. Bar, wire, and tubular products of this material are especially susceptible to end-grain corrosion in nitric acid environment. Such an attack takes place on the tubular and forged surfaces that are perpendicular to the hot-working direction and occurs as localized pitting type attack. This study shows that the possible reasons for the directional nature of end-grain attack are the manganese sulfide inclusions aligned along the hot-working direction and/or segregation of chromium along the flow lines during the fabrication stage itself. It has been shown in this study that controlled solution annealing, laser surface remelting, and weld overlay can be used to avoid/minimize end-grain corrosion. Different annealing heat-treatments were carried out on two heats of SS 304L tube and susceptibility to corrosion was measured by ASTM A 262 practice C and electrochemical potentiokinetic reactivation (EPR) test. Solution annealing at 950 °C for 90 min has been shown to increase the resistance to end-grain corrosion. Laser surface remelting using continuous wave CO₂ laser under argon shield and weld deposition (overlay) using SS 308L material were done on the end faces of the tubes. These samples were completely resistant to end-grain corrosion in nitric acid environments.     

无镍高氮奥氏体不锈钢的脆韧转变

研究了无镍高氮奥氏体不锈钢的脆韧转变(BDT)。在176 K、273 K和336 K进行的落锤试验结果表明,尽管Fe-25Cr-1.1N(质量分数,%)是面心立方结构的奥氏体合金钢,但仍展现出显著的脆韧转变现象。对冲击试验试样的塑性变形观察表明,BDT是由于低温下差的延展性所致,这与铁素体钢的情况是一致的。为了测量BDT的激活能,利用4点弯曲试验研究了应变速率与BDT温度的关系。研究发现,BDT温度与应变速率之间的依赖关系不显著,且BDT温度对应变率的Arrhenius曲线表明Fe-25Cr-1.1N钢BDT的激活能比低碳铁素体钢的高得多。从滑移位错与溶质氮原子发生交互作用导致低温下位错可动性降低这一角度,本文探讨了高氮钢特有的BDT及其高激活能的本质原因。     

免固溶化处理精铸高性能奥氏体不锈钢研究

研究表明 ,CF8( 30 4 ) ,CF8M( 316)精铸奥氏体不锈钢加入免固剂处理后 ,其力学性能和耐腐蚀性能都达到固溶化处理的水平 ,耐点蚀性能提高 1.5倍以上     

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。认为大的有效电流密度是快速离子渗氮的关键