HEALING OF HYDROGEN ATTACK CRACK IN AUSTENITE STAINLESS STEEL UNDER HEAT TREATMENT

The specimens of 304 austenite stainless steel with the hydrogen attack bubbles or cracks were heat treated at 600℃ for 6h. The SEM and TEM observations on the specimens before and after the heat treatment showed that the bubbles or cracks could be healed completely by heat treatment. The healing of hydrogen attack bubbles or cracks is closely related to heat diffusion of Fe and C atoms in austenite. The driving force of crack healing results from the plastic deforming energy Es induced by the growth of hydrogen attack bubbles or cracks. The critical condition of healing of bubbles or cracks is Es≥2γ (where γ is the surface tension, r is the radius of bubbles or half length of crack). During healing of the hydrogen attack bubbles or cracks, the recovery, polygonization and recrystallization of the sub-grain also occured.     

电化学动电位再活化法评定不锈钢晶间腐蚀敏感性的研究

本文用电化学动电位再活化法(EPR法)研究了奥氏体不锈钢在H_2SO_4+Na_2S_4O_6溶液中钝化区回扫电位、扫描速度、溶液温度、溶液浓度等因素对测试灵敏度的影响,确定了AISI304、316系列奥氏体不锈钢在此溶液中的最佳实验条件。并进行了不同敏化状态的奥氏体不锈钢在此溶液中的EPR测试。研究结果表明:采用Na_2S_4O_6作为活化剂的EPR法同样是一种快速、定量、非破坏性的评价奥氏体不锈钢晶间腐蚀敏感性的方法。但在实际应用时,对于304系列不锈钢选用H_2SO_4+KSCN溶液比较灵敏,而对于316系列不锈钢则选用H_2SO_4+Na_2S_4O_6溶液更为灵敏。     

Behaviour in hot ammonia atmosphere of SiO2-coated stainless steels produced by a sol-gel procedure

AISI 304 stainless steel coated with silica films obtained by a sol-gel procedure was tested together with uncoated 304 and 316 samples in anhydrous ammonia at high temperature. The highest rate of attack was experienced by all uncoated samples; the ammonia attack develops a nitride scale that embrittles the metal. After 115 h of testing at 500°C uncoated samples were completely degraded, while the coated 304 samples were lightly attacked. The SiO₂ coating is a good barrier against ammonia corrosion. The multilayer coatings provide lower corrosion protection than single-layer coatings.     

重油催化氨精制塔塔底封头失效分析

分析了重油催化装置的氨精制塔塔底封头开裂原因,发现母材３０４不锈钢由于冷却加工（旋压）工体相变,在湿硫化氢的环境下,含形变马氏体的３０４不锈钢发生了湿硫化氢应力腐蚀开裂（ＳＳＣＣ）,文中提出了防护措施。     

敏化处理对不同状态304奥氏体不锈钢氢脆敏感性的影响

研究固溶态和冷轧态304奥氏体不锈钢分别在650 ℃敏化2 h和24 h后的氢脆敏感性。结果表明:冷轧态与固溶态相比,因产生了应变诱导马氏体,氢脆敏感性增加;敏化处理会增加固溶态试验钢的氢脆敏感性,敏化时间越长,氢脆敏感性越高;相反,冷轧态试验钢在高温敏化时马氏体部分逆相变成奥氏体,会在一定程度上降低试验钢的氢脆敏感性,敏化时间越长,氢脆敏感性越低。     

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。     

基于镀锡银钎料钎焊304不锈钢接头的腐蚀行为

为揭示304不锈钢钎焊接头的腐蚀行为,以BAg50CuZn钎料为基材,采用电镀扩散工艺制备AgCuZnSn钎料,对304不锈钢进行感应钎焊,在60 ℃,3.5% NaCl溶液中评价不锈钢接头的局部腐蚀性,借助扫描电镜对其腐蚀形貌进行分析. 结果表明,经NaCl溶液腐蚀后,钎缝与不锈钢界面出现较长的腐蚀沟;304不锈钢表面腐蚀较严重,存在大范围坑洞、裂纹等缺欠,而钎缝区几乎无腐蚀缺欠,优先被腐蚀的是富铜相. 随着腐蚀时间延长,钎缝和304不锈钢的腐蚀速率均呈现先升高后降低的趋势,钎缝腐蚀速率略低于母材;腐蚀2.5 h后,钎缝区和304不锈钢的平均腐蚀速率分别为0.098和0.104 g/(m2·h).     

热处理对选区激光熔化304L不锈钢组织和力学性能的影响

采用光学显微镜(OM),X射线衍射仪(XRD),扫描电镜(SEM),透射电镜(TEM)等研究了热处理工艺对选区激光熔化(SLM)制备的304L不锈钢微观组织结构与力学性能的影响。结果表明:SLM制备的304L不锈钢的组织结构细小,组织中存在高密度位错、δ铁素体与σ相析出物,其强度和塑性均远高于传统304L不锈钢。对SLM制备的304L不锈钢分别进行1050℃×30 min和1000℃×2 h固溶处理后,其微观组织结构发生了变化,观察到了晶内胞状亚晶组织的长大和析出相的固溶,强度和塑性均有所降低。SLM制备过程产生的大量纳米级胞状亚晶结构,是304L不锈钢具有高强高韧性能的主要原因,析出强化和加工硬化可进一步提高其强度。     

汽车SCR系统用不锈钢的冷凝液腐蚀行为研究

运用600 ℃废气氧化与80 ℃冷凝液浸泡方法研究了柴油机SCR系统用441和304两种不锈钢的冷凝液腐蚀行为。结果表明：经有/无尿素的废气氧化后,441不锈钢在冷凝液中的腐蚀均处于钝化状态,而304不锈钢的腐蚀均处于活化状态;阳极极化曲线测量后,441不锈钢表面形成了点蚀坑,304不锈钢部分表面区域有明显的晶间腐蚀特征,氧化环境中引入尿素对两种不锈钢的前述局部腐蚀都具有增强作用。     

Protecting stainless steel by glass coating during slab reheating

A glass coating was prepared onto AISI 304 stainless steel by a slurry-spraying technique and its effects on oxidation behavior of this steel was investigated at 1250 °C in air. Results were compared with those for bare specimens. The glass coating decreased the weight gain by 98% after oxidation for 9 h, and oxidation kinetics of 304 stainless steel was changed to linear behavior due to the coating. Steel loss of the coated specimens was reduced by 1-2 orders of magnitude. Hot stage microscopic, optical, XRD and SEM-EDX analyses revealed that the as-received coating melted at high temperature, to form self-healing, homogeneous glass coating which acted as a perfect oxygen diffusion barrier and prevented the breakaway oxidation of 304 stainless steel. During cooling, the glass coating spalled because of CTE mismatch between coating and the steel. This glass coating by low-cost and easy handling method is potentially applicable during slab reheating of stainless steel.     

用碱性抛光液化学机械抛光304不锈钢片研究

为提高化学机械抛光的加工效果,我们研究了pH值、氧化剂种类和氧化剂含量对材料去除率和表面粗糙度的影响。结果表明:不同氧化剂的抛光液在各自的最佳pH值时达到最大的材料去除率,分别为181 nm/min（H₂O₂抛光液,pH=9）,177 nm/min（Cr₂O₃抛光液,pH=11）,172 nm/min（Na₂Cr₂O₇抛光液,pH=11）和147 nm/min（NaClO抛光液,pH=13）;抛光液中氧化剂含量、pH值对抛光后不锈钢的表面粗糙度影响较小。其中,材料去除率较高的H₂O₂和Cr₂O₃可作为304不锈钢化学机械抛光碱性抛光液的氧化剂。      

Thermal spray and weld repair alloys for the repair of cavitation damage in turbines and pumps: A technical note

The cavitation and erosion resistance of 21 thermal spray coatings and four weld repair materials were investigated in the laboratory using cavitation jet and slurry erosion testing. Of the thermal spray coatings, Stellite® 6 deposited by the high velocity oxyfuel (HVOF) process had the lowest cavitation rate (11.7 mg/h). This was higher than the corresponding cavitation rate (3.2 mg/h) of 308 stainless steel weld metal currently used as a reference. In the slurry erosion testing, the volume loss of Stellite® 6 applied by the HVOF process was 5.33 cubic mm/h, much lower than the corresponding loss (11.17 cubic mm/h) in the currently used stainless steel 304 reference. Furthermore, the electrochemical potential difference between the carbon steel and HVOF sprayed Stellite 6 coating was 0.25 volts, half the potential difference between the 304 stainless steel carbon steel substrate, and will result in reduced galvanic corrosion of the substrate near the contact areas. Stellite 6 deposited by the HVOF process was recommended for repair of damage resulting from erosion and subsequent cavitation by caused by surface roughening.     

304奥氏体不锈钢氮离子注入层的组织与性能研究

对具有抗磁性的304奥氏体不锈钢进行离子渗氮处理,以提高其硬度和耐磨性.研究了奥氏体不锈钢渗氮前后的金相组织、显微硬度、耐磨性和耐腐蚀性等,并与常用高硬度、高耐磨性GCr15钢进行了对比.结果表明:304奥氏体不锈钢通过一定时间的离子渗氮后,依然具有很好的抗磁性能,且表层硬度约为基体硬度的6倍,耐磨性能大大提高,其性能...     

Depassivation-repassivation behavior of type-312L stainless steel in NaCl solution investigated by the micro-indentation

Repassivation behavior of type-312L stainless steel containing 6% of molybdenum was examined in NaCl solution using in situ micro-indentation technique, together with type-304 and 316L stainless steels. High stability of the passive film formed on the type-312L stainless steel was also examined by depth profiling analysis of passive films using glow discharge optical emission spectroscopy (GDOES). In 0.9 mol dm⁻³ NaCl solution at 296 K the type-304 and 316L stainless steels are passive only up to 0.3 V (SHE), above which pitting corrosion occurs. In contrast, no pitting corrosion occurs on type-312L stainless steel. Despite the significant difference of the pitting corrosion resistance, the repassivation kinetics of the three stainless steels, examined by micro-indentation at 0.3 V (SHE), is similar. The presence of molybdenum in the stainless steel does not influence the repassivation kinetics. The charge required to repassivate the ruptured type-312L stainless steel surface increases approximately linearly with the potential, even though the passivity-maintaining current increased markedly at potentials close to the transpassive region. Repassivation occurs without accompanying significant dissolution of steel, regardless of the stability of passive state. Depth profiling analyses of the passive films on the type-312L stainless steels formed at several potentials revealed that molybdenum species enrich in the outer layer of the passive film, below which chromium-enriched layer is present. The permeation of chloride ions may be impeded by the outer layer containing molybdate, enhancing the resistance against the localized corrosion of the type-312L stainless steel.     

氢对304不锈钢阳极行为的影响

<正> 虽然奥氏体不锈钢在42％MgCl_2沸腾溶液中的应力腐蚀并不是由氢致开裂引起的,但在应力腐蚀过程中生成的氢可以进入试样并可在裂纹前沿富集。为澄清进入试样的氢是否对阳极溶解过程产生促进作用,曾有人用失重法、晶间腐蚀和极化曲线变化等研究氢对阳极行为的影响,并得出氢促进阳极溶解的结论。应当指出,充氢试样的阳极电流包括了氢的氧化电流,因此充氢后阳极电流的增大并不证明氢促进了阳极溶解过程。虽然失重法能反映氢的促进作用,但只适用于腐蚀较为严重的情况。     

304不锈钢在人工海水环境中的腐蚀磨损行为研究

目的阐述304不锈钢在人工海水环境中的腐蚀磨损行为及其力-电化学耦合作用下的损伤机理,为海水服役环境中海洋装备的开发和利用提供理论支持。方法利用腐蚀磨损试验仪研究了304不锈钢在人工海水环境中的摩擦学性能和电化学性能及其交互作用下的腐蚀磨损行为,并利用扫描电镜、X射线衍射仪、激光共聚焦显微镜等仪器对磨痕表面进行表征与分析。结果在载荷作用下,304不锈钢的腐蚀电位从静态腐蚀的-0.310V变为-0.368V,腐蚀电流密度也增加了约1个数量级。阳极恒电位下,304不锈钢和Al_2O_3陶瓷球摩擦副的摩擦系数比阴极保护下的小。载荷为5N时,304不锈钢的腐蚀磨损率为0.195mm~3/d,其中,腐蚀加速磨损速率占68.7%;载荷为15N时,总磨损速率明显增加,其中,纯磨损率所占比例最大,为60.1%,此时腐蚀加速磨损速率占比为39.1%。结论 304不锈钢的腐蚀磨损行为是"机械去钝化-化学再钝化"的动态过程。腐蚀和磨损过程存在明显的交互作用。在磨损过程中,304不锈钢表面发生马氏体相变,通过电偶腐蚀进一步加强腐蚀作用;同时,腐蚀过程的反应产物使304不锈钢的耐磨性能下降。随着载荷的增加,对总腐蚀磨损速率贡献最大的由腐蚀加速磨损速率逐渐变为纯磨损率,载荷对304不锈钢的机械磨损影响更大。     

20G钢氢腐蚀的超声背散检测

选用20G低碳钢,经450℃和500℃,18MPa氢气中分别暴露240,480和720小时,使材料发生不同程度氢腐蚀,用背散法对氢蚀进行了超声波检测结果表明,背散法对氢蚀程度非常敏感,用杂草波平均高度与原始波高之比做为信噪比,能很好地反映氢蚀程度,论证了用背散法检测氢蚀程度的可能性.     

Investigation of the diffusion kinetics of borided stainless steels

In this study, the kinetics of borides formed on AISI 420, AISI 304 and AISI 304L stainless steels was investigated. Boronizing treatment was carried out using Ekabor-II powders at the processing temperatures of 1123, 1173 and 1223 K for 2, 4 and 6 h. The phases of the boride layers of borided AISI 420, AISI 304 and AISI 304L stainless steels were FeB, Fe₂B, CrB and NiB, respectively. The thickness of the boride layer formed on the borided steels ranged from 4.6 to 64 μm depending on the boriding temperature, boriding time and alloying elements of the stainless steels. Depending on the chemical composition, temperature and layer thickness, the activation energies of boron in AISI 420, AISI 304 and AISI 304L stainless steels were found to be 206.161, 234.641 and 222.818 kJ/mol, respectively. The kinetics of growth of the boride layers formed on the AISI 420, AISI 304 and AISI 304L stainless steels and the thickness of the boride layers were investigated.     

MAGNETIC ACOUSTIC EMISSION CHARACTERISTICS OF HYDROGEN ATTACKED LOW CARBON STEEL

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304不锈钢的高温单轴应变循环与棘轮行为

对３０４不锈钢分别进行了高温单轴奕变控制和应力控制下的系统循环试验,揭示和分析了循环应变幅值,应变幅值历史以及温度历史对循环特性的影响以及应力幅值,平均应力及其历史对循环蠕变（棘轮效应）的影响,研究表明,无论单轴应变循环特性还是非对称单侧应力下的棘轮效应不但依赖于当前温度和加载状态,而且依赖于其加载历史,得到３０４不锈钢高温单轴循环行为的一些有意义的结果。