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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. 相似文献
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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. 相似文献
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Yoon-Jun Kim Dong-Geun Lee Hyeon Kyeong Jeong Yong-Tai Lee Ho Jang 《Journal of Materials Engineering and Performance》2010,19(5):700-704
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. 相似文献
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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。 相似文献
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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. 相似文献
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Wei Wang Wei Yan Ke Yang Yiyin Shan Zhouhua Jiang 《Journal of Materials Engineering and Performance》2010,19(8):1214-1219
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. 相似文献
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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. 相似文献
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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. 相似文献
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Kamlesh Chandra Vivekanand Kain Puppala Ganesh 《Journal of Materials Engineering and Performance》2008,17(1):115-122
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. 相似文献
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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。 相似文献
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免固溶化处理精铸高性能奥氏体不锈钢研究 总被引:1,自引:0,他引:1
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 相似文献
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奥氏体不锈钢高频高压低温等离子体渗氮 总被引:4,自引:1,他引:4
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℃×25h处理条件下获得了03μm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 相似文献
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