Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels(HNSS) were investigated by electrochemical and immersion testing methods in chloride solution,respectively.The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum(XPS).HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel.With increasing the nitrogen content in steels,pitting potentials and critical ...     

Intergranular corrosion behavior of high nitrogen austenitic stainless steel

The intergranular corrosion (IGC) behavior of high nitrogen austenitic stainless steel(HNSS) sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation(DL-EPR) method.The effects of the electrolytes,scan rate,sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addition of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2_SO_4+1 mol/L NaCl+0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr_2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.     

Microstructural evolution and mechanical properties of aging high nitrogen austenitic stainless steels

The microstructural evolution of 18Cr18Mn2Mo0.77N high nitrogen austenitic stainless steel in aging treatment was investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm and body-centered cubic intermetallic χ phase with a=0.892 nm precipitate gradually in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular Cr2N pre...     

氮对新型无镍高氮奥氏体不锈钢塑性流变行为的影响

利用Ludw igson模型研究了两种氮含量不同的无镍奥氏体不锈钢18Cr-12Mn-0.55N（质量分数/%）和18Cr-18Mn-0.63N在室温快速拉伸时的塑性流变行为.结果表明,由于N含量的增大,实验钢18Cr-18Mn-0.63N的加工硬化能力明显强于实验钢18Cr-12Mn-0.55N.N促进CrMnN奥氏体不锈钢中的短程有序,使位错在更高的应变水平进行单系滑移和平面滑移,推迟位错的多系滑移和交滑移,因而提高CrMnN奥氏体不锈钢的加工硬化能力.     

Influence of chemical composition and cold deformation on aging precipitation behavior of high nitrogen austenitic stainless steels

The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr~2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.     

应变速率对18Cr-12Mn-0.55N高氮奥氏体不锈钢塑性流变行为的影响

研究了拉伸应变速率对高氮奥氏体不锈钢18Cr-12Mn-0.55N（质量分数/%）室温力学性能和塑性流变行为的影响.结果表明,随应变速率的升高,实验钢的屈服强度R0.2增大,断后延伸率A减小,抗拉强度Rm略有降低,断面收缩率Z变化不大;在各应变速率下,实验钢的塑性流变行为均可用Ludwigson模型进行描述;随应变速率的升高,实验钢的加工硬化能力和发生屈服时第一根位错开动所需的短程作用力降低;增大应变速率促进多系滑移和交滑移,降低瞬变应变,使实验钢的塑性流变行为在更低的应变水平符合Ludwik模型.     

高氮钢的熔炼及试生产技术

综述了各种制备高氮钢的方法及途径,认为实现高氮钢大生产的最优方案是高氮气压下等离子熔炼＋ 高氮气压下雾化＋ 多重粉末锻轧     

双相不锈钢表面奥氏体高氮层的制备技术

高温渗氮是在奥氏体/铁素体双相不锈钢表面形成奥氏体高氮层的一种有效方法.为了获得氮含量高、组织均匀且适合于后续加工的表面高氮不锈钢层，必须确定合理的高温渗氮工艺.通过优化高温渗氮工艺参数，研究了双相不锈钢高温渗氮过程中加热温度、保温时间、氮气压力等对渗氮效果的影响.结果表明，通过高温高压渗氮可使不锈钢表面形成高氮氮化层，可使双相不锈钢通过渗氮发生表面奥氏体转变，获得组织梯度变化的多相复合不锈钢材料.     

Preparation of high nitrogen and nickel-free austenitic stainless steel by powder injection molding

High nitrogen and nickel-free austenitic stainless steel has received much recognition worldwide because it can solve the problem of "nickel-allergy" and has outstanding mechanical and physical properties. In this article, 0Cr17Mn11Mo3N was prepared by powder injection molding (PIM) technique accompanied with solid-nitriding. The results show that the critical solid loading can achieve up to 64vol% by use of gas-atomized powders with the average size of 17.4 μm. The optimized sintering conditions are de-termined to be 1300°C, 2 h in flowing nitrogen atmosphere, at which the relative density reaches to 99% and the N content is as high as 0.78wt%. After solution annealing at 1150°C for 90 min and water quench, the 0.2% yield strength, ultimate tensile strength (UTS), elongation, reduction in area, and hardness can reach as high as 580 MPa, 885 MPa, 26.0%, 29.1%, and Hv 222, respectively.     

316L不锈钢应力腐蚀敏感性指数计算与回归分析

通过慢应变速率拉伸腐蚀试验(SSRT),计算了316L不锈钢在湿硫化氢环境中的应力腐蚀敏感性指数.在环境因素中,主要考虑了H2S浓度、Cl-浓度、温度和pH值等介质参数单独或交互作用对应力腐蚀敏感性的影响.通过试验数据的逐步回归分析,得到了应力腐蚀敏感性指数随介质参数变化的数学模型,并指出了各介质参数影响的显著性.     

镍对07Cr17Ni12Mo2N奥氏体不锈钢组织和高温拉伸性能的影响

利用Gleeble-1500D热模拟机对07Cr17Ni12Mo2N奥氏体不锈钢试样分别在950,1000,1 050,1 100℃以0.05 s-1的应变速率进行了高温拉伸试验,通过分析试验钢组织、断面收缩率曲线、抗拉强度曲线、断口形貌,研究镍对试验钢高温拉伸性能的影响.结果表明：降镍后试验钢仍为单一的奥氏体组织;热塑性有所降低,断面收缩率平均下降了18.87％;抗拉强度平均提高了12.39％.     

Antibacterial and corrosive properties of copper implanted austenitic stainless steel

Copper ions were implanted into austenitic stainless steel (SS) by metal vapor vacuum arc with a energy of 100 keV and an ions dose range of (0.5-8.0)×1017 cm-2. The Cu-implanted SS was annealed in an Ar atmosphere furnace. Glancing X-ray diffrac-tion (GXRD), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) were used to reveal the phase compositions, microstructures, and concentration profiles of copper ions in the implanted layer. The results show that the antibacterial property...     

点蚀孔腐蚀钢构件力学性能劣化简化分析方法

点蚀是一种局部和剧烈的腐蚀形态,导致钢结构构件力学性能退化,突然之间发生事故,对结构整体造成安全隐患.本文针对具有点蚀孔腐蚀特征的钢构件,提出一种通过等效弹性模量定量评价其力学性能劣化程度的简化分析方法.依据周期喷雾复合试验数据,以锈蚀率和最大点蚀深度为基础,对点蚀孔深度、直径及分布情况作出适当假定;考虑涂层寿命的影响,以锈蚀率相等为原则建立人工加速腐蚀试验和海洋大气条件下Q235钢构件腐蚀情况的转换关系.建立考虑点蚀影响的有限元构件模型,通过轴向均布力作用下的构件变形确定海洋大气环境不同暴露时间下点蚀构件的等效弹性模量,提出点蚀构件力学性能劣化分析的实用计算方法.数值算例验证了上述采用等效弹性模量分析腐蚀构件受力性能方法的正确性;计算结果表明,在相同锈蚀率条件下,点蚀构件的等效弹性模量低于均匀腐蚀构件.     

真空感应炉近常压气氛保护熔炼高氮马氏体不锈钢

研究了在真空感应炉近常压气氛保护熔炼条件下氮在马氏体不锈钢0Cr16Ni5Mo中的溶解度,探讨了炉内保护气体种类、氮化铬铁加入量对钢中氮含量的影响.结果表明,炉内保护气体种类对钢中氮的溶解度有较大影响,氮化铬铁合金加入量对钢氮含量的影响因保护气体种类不同而异.     

316L不锈钢的高压增氮与脱氧研究

采用真空/高压感应炉在0.1~1.0 MPa高纯氮气氛下熔炼316L不锈钢,分析了氮的溶解度与氮分压之间的关系。氮在316L不锈钢中的溶解服从Sievert定律。采用热力学数据预测了不同氮分压下316L不锈钢中氮的溶解度,计算结果表明,预测值与实验值相吻合。采用铝、硅钙以及二者混合进行脱氧,总氧含量可以达到20×10-4%以下,提出了制备低氧高氮316L不锈钢的实验条件。     

Effects of pre-precipitation of Cr2N on microstructures and properties of high nitrogen stainless steel

Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively. The mechanisms of precipitation and solid solution of high nitrogen austenitic stainless steel were studied using the scanning electron microscopy, transmission electron microscopy, electron probe micro analysis and mechanical testing. The results show that, Cr₂N is the primary precipitate in the tested stainless steels instead of Cr₂₃C₆. Cr₂N nucleates at austenitic grain boundaries and grows towards inner grains with a lamellar morphology. By means of pre-precipitation of Cr₂N at 800 °C, the microstructure of the steels at solid solution state can be refined, thus improving the strength and plasticity. After the proposed treatment, the tensile strength, the proof strength and the elongation of the tested steel reach 881 MPa, 542 MPa and 54%, respectively.     

氮含量和环境温度对316L不锈钢耐腐蚀性的影响

研究低温条件下腐蚀溶液温度以及钢中氮含量对316L奥氏体不锈钢耐腐蚀性能的影响,在1mol／L H2SO4＋0．5mol／L NaCl的腐蚀液中,对氮含量为0．0095％～0．5575％的316L奥氏体不锈钢进行阳极极化曲线及电化学阻抗测量。结果表明,提高氮含量,316L奥氏体不锈钢耐蚀性增强;腐蚀液温度升高,316L奥氏体不锈钢耐蚀性减弱。     

Corrosion behavior of ferritic stainless steel with 15wt% chromium for the automobile exhaust system

The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400- 900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb（C,N） and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb（C,N） and NbC precipitates and Cr segregation adjacent to the precipitates.     

节镍奥氏体不锈钢Cr18Mn6Ni4N的组织及性能

为节约镍资源,研究了不同成分17.8~19.1%Cr,3.93~6.05%Mn,3.58~4.62%Ni,0.32~0.42%N节镍型奥氏体不锈钢固溶后的力学性能和耐蚀性能,以期获得可替代304不锈钢的新钢种。结果表明:Cr18.4Mn5.98Ni4.62N0.42不锈钢的力学性能和耐蚀性能与304不锈钢相当。分析了该成分不锈钢时效处理后的组织演变规律、冷变形过程中奥氏体稳定性及形变诱发马氏体相变过程。结果表明:800℃是Cr2N相析出的鼻尖温度,随着时效时间的增加,析出相首先以颗粒状形貌沿晶界析出,而后以胞状析出方式向晶内生长。冷轧压下率18.5%时尚未发现形变诱发马氏体组织,随着变形量增大,片层状ε'马氏体含量先增加后减少至消失,而板条状α'马氏体含量逐渐增多,相对磁导率增加,但其奥氏体稳定性远高于304不锈钢。可见,Cr18.4Mn5.98Ni4.62N0.42不锈钢可替代304不锈钢。