地铁用U型头的开裂原因分析

地铁用U型头服役多年后在其表面发现多条裂纹,通过宏观分析、化学成分分析、非金属夹杂物评定、扫描电镜形貌分析和能谱分析以及金相检验对U型头开裂的原因进行了分析.结果 表明:U型头为302奥氏体不锈钢,在晶界析出碳化物,导致晶界周围贫铬,产生晶间腐蚀,随着零件运行时间的延长,被腐蚀的晶界作为裂纹源,在Cl-和外力的作用下,...     

奥氏体-铁素体双相不锈钢晶间腐蚀试验方法

奥氏体-铁素体双相不锈钢在300～1000℃范围内会在晶界、相界及其周边区域析出σ相、χ相、R相、碳化物及氮化物等第二相,并导致晶界或析出相周边形成贫铬区,在特定环境下具有一定的晶间腐蚀敏感性,需在试验室进行准确测定.概述了奥氏体-铁素体双相不锈钢的试验室晶间腐蚀试验方法,包括化学浸泡法和电化学方法,并提出了试验中需要...     

铁素体不锈钢餐具铬离子析出量超标的原因分析

某430铁素体不锈钢餐具在进行重金属迁移量检验时,发现铬离子析出量严重超标。通过电化学动电位再活化法测试该430铁素体不锈钢试样的腐蚀敏感性,利用光学显微镜、扫描电镜、能谱仪对试样的腐蚀形貌、显微组织和表面碳、铬元素分布情况进行分析。结果表明:在430铁素体不锈钢餐具的生产过程中,由于热处理工艺不当导致杂质碳化物的偏析以及马氏体残余,进而在腐蚀介质中发生原电池腐蚀反应,最终导致铬离子析出量超标。     

铸造双相不锈钢点腐蚀行为研究

采用化学浸泡腐蚀试验及微观组织和化学成分分析研究了5种铸造双相不锈钢在6%Fe Cl3溶液中的点腐蚀行为,并与316L奥氏体不锈钢进行了对比。结果表明,铸造双相不锈钢的抗点腐蚀性能均优于316L的,腐蚀速率和点腐蚀深度均小于316L奥氏体不锈钢的;双相不锈钢主要耐点蚀能力合金元素在奥氏体和铁素体相内分布不均匀,铬、钼更多地分配于铁素体相内,而镍、氮则更多地分配于奥氏体相内,铁素体相的耐点蚀指数PRE(Cr%+3.3Mo%+16N%)大于奥氏体相;双相不锈钢的耐点腐蚀性能与化学成分有关,随着PRE的增加,双相不锈钢的耐点腐蚀性能提高,铜元素在铁素体内析出的富铜相导致点蚀优先在铁素体内发生和发展。     

正三棱锥形夹杂物诱导晶内铁素体形核模型研究

通过建立晶内铁素体形核模型,结合数学推导发现,基底相为不规则形状的夹杂物比基底相为球形夹杂物形核功小,易诱导铁素体形核。根据数学模型分析球形夹杂物诱导晶内铁素体形核的影响因素。结果表明:夹杂物尺寸过小时不利于诱导晶内铁素体形核,其尺寸增加到0.15μm后,对铁素体的形核影响反而不大;夹杂物与钢液的润湿角越小,越易诱导铁素体形核;夹杂物与钢液的润湿角为70°~90°时,球形夹杂物易诱导正三棱锥形铁素体析出,而润湿角小于70°时,易诱导球形铁素体析出;析出相为正三棱锥形铁素体形核模型的形核率比析出相为球形铁素体模型的形核率高。通过实验验证了不规则夹杂物可以诱导铁素体形核,且夹杂物尺寸大于0.15μm后,对铁素体的形核影响不大。     

乙二醇不锈钢蒸发器开裂原因分析

采用金相分析、断口微观分析以及腐蚀产物能谱分析等方法，对某石化公司乙二醇不锈钢蒸发器开裂原因进行了分析和研究。结果表明，由于材料在焊接过程中，焊接热影响区的组织受到敏化，铬的碳化物沿晶界呈网状析出，造成该区域贫铬，从而在应力与腐蚀介质的共同作用下，导致设备发生了晶问应力腐蚀开裂。     

高温时效后的310不锈钢高温硫腐蚀研究

研究了310不锈钢在气氛总压为10^-5Pa,于2.3％SO2－S2－8.8％N2气氛中600℃下的高温硫腐蚀行为。利用金相、能谱及X射线衍射等分析手段对其腐蚀形貌、成分及结构进行了分析。结果表明：310不锈钢于700℃,10000h时效在其晶界大量析出σ相,造成晶界附近贫Cr,从而降低了晶界抗硫腐蚀性能,使高温时效处理后的310不锈钢6抗硫腐蚀能力明显降低,未时效处理的310不锈钢以均匀腐蚀为主,时效处理后的则以晶界腐蚀为主,并伴随有均匀腐蚀。     

国外某些特种钢和特种合金的发展动向

不锈钢的发展趋势在不锈钢方面,铬仍保持较高的比例。由于铁素体不锈钢所需的合金元素含量低,成本低,所以发展的趋势是用铁素体不锈钢代替奥氏体不锈钢。铁素体不锈钢具有它独特的使用性能。如抗氯化物应力腐蚀裂纹、在氧化性水介质中的耐蚀性、高温抗氧化性和在氯化物介质中抗锈斑和腐蚀裂纹等。而且这种钢的塑性好,便于成形和焊接。     

粉末冶金多孔高氮奥氏体不锈钢的制备及性能

采用粉末冶金方法制备了多孔高氮奥氏体不锈钢并研究其力学性能和耐腐蚀性能。结果表明,高温气固渗氮能促进双相不锈钢向奥氏体不锈钢的转变,在其显微组织中出现了细条状和颗粒状CrN相析出物。随着造孔剂含量的提高孔隙率随之提高,而力学性能和耐腐蚀性能降低。与普通的多孔不锈钢相比,这种多孔高氮奥氏体不锈钢的力学性能更加优越,源于N的固溶强化和CrN等析出物的强化机制。随着孔隙率的提高多孔高氮奥氏体不锈钢的腐蚀倾向和腐蚀速率逐渐增大,造孔剂含量(质量分数)为10%的试样具有最佳的耐腐蚀性能。提高烧结温度有利于烧结块体的致密化,使腐蚀速率明显下降。     

不锈钢Cr17Ni2高温气体氰化

Cr17Ni2是航空工业应用较多的铁素体马氏体型高强度不锈钢,不仅要求良好的抗腐蚀性,有时还要求表面具有高的硬度和耐磨性。六十年代,国外已对不锈钢进行渗氮和渗碳的表面硬化工艺。不锈钢氮化,国内已应用于生产,对不锈钢渗碳则介绍甚少,国外虽有报道,但资料不详。本文将叙述不锈钢的高温氰化,抛砖引玉,供大家参考。     

The effect of TiN inclusions and deformation-induced martensite on the corrosion properties of AISI 321 stainless steel

Stainless steel of type 321 is commonly used for the production of exhaust systems because of its temperature resistance and welding properties, which are better than those of AISI 304 or similar steels. AISI 321 is a titanium stabilized austenitic stainless steel, where this element is added to form carbides in order to avoid chromium impoverishment due to chromium carbide formation. Cold shaping can, in the case of austenitic stainless steel, cause the formation of deformation induced martensite, which can improve its mechanical properties, but unfortunately can also spoil its good resistance to corrosion. Titanium nitride inclusions are cathodic with respect to steels, and therefore cause their anodic dissolution. Martensite is, however, more susceptible to the corrosion than austenite in steels. The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.     

含Cu抗菌不锈钢的工艺与耐蚀性能

与普通0Cr17铁素体不锈钢和0Cr18Ni9奥氏体不锈钢相比，含铜铁素体和奥氏体抗菌不锈钢均具有良好的冷热加工性能和焊接性能．通过提高浇铸温度，抗菌不锈钢能保持良好的铸造性能．奥氏体抗菌不锈钢的抗应力腐蚀性能比0Cr18Ni9不锈钢有很大的提高，而铁素体抗菌不锈钢比0Cr17有明显的下降．与相应的普通不锈钢相比，两种类型抗菌不锈钢的耐点蚀性能均略有下降．     

Mechanisch-technologische Eigenschaften nickelhaltiger Superferrite

Mechanical and Technological Properties of Nickel Containing Superferrites High chromium ferritic stainless steels with molybdenum and nickel additions, containing low amounts of interstitials, show remarkably good mechanical properties besides their excellent corrosion behaviour. Yield strengths of these materials can be more than the twofold, compared with that of austenitic stainless steels. In contrary to commercial ferritic stainless chromium steels, the Superferrites exhibit remarkable notch impact toughness also at temperatures below 0 °C. These properties as well as their permanent toughness after a welding process permit a good technological workability and, because of the high strength properties, the application of thinner dimensions in construction.     

Cyclic oxidation resistance of ferritic stainless steels used in mufflers of automobiles

This work investigates the cyclic oxidation resistance of AISI 439 and AISI 441 ferritic stainless steels (FSS) at a typical temperature of muffler (300 °C). This temperature is characteristic of the cold exhaust of an automobile. The oxidation testing of steels was performed in synthetic air in a tube furnace under two different conditions: after immersing in the synthetic condensed (TOC) for 10 h and without immersion in the synthetic condensed (TOP). The mass gain of AISI 439 steel without previous immersion in condensate was the half of the mass gain of AISI 439 steel oxidized after immersion in condensate. In all samples, the Fe₂O₃ was only identified in the oxide layer on samples that oxidized after immersion in a condensate solution. The corrosion perforation of mufflers is mostly attributed to the cyclic and synergetic effect of oxidation and condensation processes of hot moisture-bearing exhaust gas.     

Evolution of the metal–oxide interface during the initial stage of the high temperature oxidation of ferritic stainless steels

Abstract

Two grades of ferritic stainless steel, a bi-stabilised Ti, Nb (AISI 441) and a stabilised Ti (AISI 439), were oxidised at 1060°C under the simulated process atmosphere for durations between 45 and 1800 s. Focused ion beam coupled with field emission gun and scanning electron microscopy was carried out to investigate the cross-section morphology of the oxide growing on ferritic stainless steels. Matrix protrusions localised at the metal – chromia interface through the silica layer are observed and the following mechanism for their formation is proposed. During the first step of oxidation, interface undulation, induced by growth stresses, in combination with silica precipitation at the metal – oxide interface lead to the formation of matrix protrusions in the chromia layer. For an increased oxidation time, due to the laterally silica growth matrix protrusions are trapped into the Cr₂O₃ layer as matrix inclusions.     

Stabilisation of ferritic stainless steels with Zr and Ti additions

Abstract

Traditional 11·5 wt-%Cr ferritic stainless steels are single stabilised with Ti or dual stabilised with Ti–Nb additions. A dual-stabilised ferritic stainless steel 409 with Zr–Ti additions was studied, which was selected through thermodynamic and kinetics analysis. The alloy was subjected to thermomechanical processing using both hot and cold rolling and annealing. The intergranular corrosion resistance and microstructure of this alloy was evaluated. Of particular interest was to study the stabilisation behaviour of this alloy under all processing conditions. The results showed that the precipitation of Cr_xC_y was effectively prevented; hence, the alloy used in this investigation had an excellent resistance to intergranular corrosion.     

Sintering and characterization of YAG dispersed ferritic stainless steels

The present study investigates the effect of yttrium aluminium garnet (YAG) addition on the densification, mechanical, tribological and corrosion behaviour of ferritic (434L) stainless steels. The composites were sintered at both solid-state (1200 °C) and supersolidus (1400 °C) sintering conditions. Supersolidus sintering results in superior densification, hardness and corrosion resistance of both straight 434L stainless steel as well as YAG reinforced 434L stainless steels. The addition of YAG to 434L stainless steels at supersolidus sintered conditions improves the strength and wear resistance of 434L stainless steels without significantly degrading the corrosion performance.     

钨含量对新型高铬锰氮双相不锈钢Cr29Mn12Ni2N0.6Wx组织和性能的影响

研究了钨含量对新型高铬锰氮双相不锈钢Cr29Mn12Ni2N0.6Wx(x=1,2,3)显微组织、力学性能和耐腐蚀性能的影响。结果表明:Cr29Mn12Ni2N0.6Wx不锈钢固溶处理后具有典型的铁素体+奥氏体双相组织,铁素体含量在45%~60%范围内;随着钨含量的增加,合金中σ相的析出倾向增强,铁素体含量增加,合金的耐腐蚀性能降低,屈服强度和抗拉强度升高;经1 050℃固溶处理30 min后,该系列双相不锈钢中不再有σ相析出,其屈服强度大于650 MPa,抗拉强度大于900 MPa,断后伸长率大于30%,作为高强度资源节约型超级双相不锈钢具有潜在应用前景。     

A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献