Microstructure and corrosion resistance of 304 stainless steel electroslag strip cladding

The 304 stainless steel strips were deposited one layer on carbon steel base metal by electroslag strip cladding(ESC) and submerged arc cladding(SAC),respectively.The solidification microstructure of ESC metal was analyzed by the optical microscopy,scanning electron microscope and energy dispersive spectroscopy.The corrosion resistance studies of strip cladding metals were carried out in 10%oxalic acid electrolytic etching test.The results showed that the cladding metal obtained by ESC presented low content of C,high content of Cr and enough alloying element of Ni in the chemical composition.The transition zone of ESC with small width was almost parallel with the base metal,leading to a lower dilution.There are three types of solidification modes(A→AF→FA) occurred in the ESC metal due to the decrease of cooling rate and degree of dilution from the transition zone to the top of ESC metal.As a result,the microstructure of ESC metal exhibited mainly austenite with a small amount offerrite,contributing to achievement of better corrosion resistance.     

Rhodanine azosulpha drugs as corrosion inhibitors for corrosion of 304 stainless steel in hydrochloric acid solution

The effect of rhodanine azosulpha drugs on the corrosion behaviour of 304 stainless steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated using weight loss and potentiostatic polarization techniques. Some corrosion parameters such as anodic and cathodic Tafel slope, corrosion potential, corrosion current, exchange current densities, surface coverage and inhibition efficiency were calculated. The polarization measurements indicated that the inhibitors are of mixed type and inhibit corrosion by parallel adsorption on the surface of steel due to the presence of more than one active centre in the inhibitor molecule. The adsorption is obeyed Langmuir adsorption isotherm. The activation energy and thermodynamic parameters were calculated at different temperature.     

光亮退火处理304不锈钢在NaCl溶液中的耐蚀性

采用稳态阳极极化曲线、恒电位开路衰减响应曲线和电化学噪声等多种电化学测试技术研究了光亮退火处理的304不锈钢在0.01-0.6mol/L NaCl溶液中的耐蚀性能.研究结果表明,不锈钢的点蚀击穿电位Eb值与Cl-浓度的对数呈线性关系,在同一浓度下,光亮不锈钢的Eb值比普通不锈钢大约正400-600mV;在0.6mol/L NaCl溶液中不锈钢恒电位开路衰减及电流噪声的测量结果也表明,光亮退火处理使不锈钢在NaCl溶液中钝化膜的稳定性明显改善,耐点蚀能力显著提高.     

Cerium chemical conversion coatings for corrosion protection of stainless steels in hot seawater environments

In order to replace the hazardous chromate‐based surface treatment, a new cerium chemical conversion coating was developed on 316L stainless steel through a mixed solution of hydrated cerium nitrate, citric acid, and hydrogen peroxide. The chemical composition was characterized by energy‐dispersive spectroscopy, X‐ray photoelectron spectroscopy and atomic force microscope. The dense conversion coating is composed of CeO₂ with a small amount of Ce₂O₃ and has small grain size lower than 50 nm. Its thickness is about 47.4 nm as determined by spectroscopic ellipsometry analysis. Potentiodynamic polarization was used to study the corrosion behavior of the coatings in the concentrated artificial seawater at 72 °C. In comparison with the conventional nitric acid‐chromate passivated specimens, the cerium conversion coatings show much higher pitting potentials. It is suggested that the cerium conversion treatment is more effective than the nitric acid‐chromate passivation to improve the pitting resistance of 316L stainless steel used in the hot seawater environments.     

The effect of mechanical polishing and finishing on the corrosion resistance of AISI 304 stainless steel

The aim of the present work was to study the influence of surface finishing on the corrosion resistance of AISI 304 stainless steel samples. Samples were submitted to lathe-turning, milling, lapping and grinding. Roughness parameters were determined by confocal laser scanning microscopy (CLSM). The corrosion resistance was evaluated using potentiodynamic polarisation curves and the corrosion morphology was assessed using CLSM and scanning electron microscopy. The results showed that the surface state had a remarkable influence on the corrosion behaviour of the samples, especially surface imperfections, whereas the roughness parameters did not directly correlate with the corrosion resistance.     

NaCl溶液中304不锈钢腐蚀过程的声发射特征

采用声发射技术研究了304不锈钢在0.01和0.05 mol·L-1Na Cl溶液中的腐蚀过程,应用光学显微镜观察了腐蚀前后试样表面形貌。结果表明,0.01和0.05 mol·L-1浓度下,304不锈钢腐蚀产生的声发射起始幅度不同,随时间延长,声发射幅度阶跃,直至达到最终的稳定幅度,这说明随浸泡时间延长,试样腐蚀程度加深。浸泡初期,声发射相对能量较高,声发射相对能量随浸泡时间延长而降低,但仍具有比较明显的相对能量积聚区,0.05 mol·L-1浓度时更为明显,同时其振铃数聚类区多于0.01 mol·L-1。浸泡4 h后,试样表面发生了晶间腐蚀和点蚀。相比0.01 mol·L-1浓度,0.05 mol·L-1下试样表面点蚀数量增多、点蚀孔尺寸增大。     

不同涂层对304不锈钢高温防护效果的对比研究

采用溶胶凝胶法在304不锈钢表面上分别制备了SiO2、Al2O3、ZrO2防护涂层。通过X射线衍射(XRD)、扫描电镜(SEM)对不同氧化物涂层进行了结构和形貌的表征。对比了不同氧化物涂层保护样品的高温抗氧化性、抗热冲击性以及在3.5wt%NaCl溶液中的耐电化学腐蚀性。结果表明Al2O3涂层具有很好的高温抗氧化性和耐电化学腐蚀性,而ZrO2涂层具有良好的抗热冲击性能。     

黄铜与304不锈钢的电阻软钎焊封装工艺

针对某热量表的温度传感器中由于尼龙成分的存在导致其构成材料黄铜和304不锈钢不能在高温下焊接的问题,采用电阻软钎焊的低温连接方法进行焊接试验,以实现密封连接效果. 结果表明,在0.3 MPa的焊接压力下,当焊接电流设定为26 kA时,以双层Sn-Pb箔片为钎料的焊件进行的试验效果良好,达到了可靠的连接,且黄铜中心尼龙成分未受到焊接温度的影响而损坏. 在扫描电镜下观察到钎料与不锈钢和黄铜均发生了表面扩散. 将焊接后的样品置于水中进行密封性试验,结果显示焊缝区域实现了可靠地连接,达到了密封防水效果.     

表面喷丸压力对304不锈钢应力腐蚀敏感性的影响

采用3种表面喷丸压力对304不锈钢板状试样进行强化处理。通过扫描电子显微镜分析了强化层的厚度和晶粒细化程度,采用显微硬度计检测了表层显微硬度分布。通过5%NaCl溶液中慢应变速率拉伸试验,比较了0.25、0.30和0.40 MPa喷丸压力处理后试样的应力腐蚀敏感性。结果表明：表面喷丸强化处理可以细化试样表层晶粒,提高硬度;随着喷丸压力的升高,试样表层晶粒层厚度增大,表面硬度提高,应力腐蚀敏感性指数降低。     

The synergistic effect of seawater's parameters on the corrosion rate of the austenitic stainless steel 304

In this article the corrosion rate of the austenitic stainless steel type 304, under the synergistic effect of environmental factors has been assessed via potentiodynamic polarization scan. Salinity, velocity, pH and temperature are the factors which induce effects on the corrosion rate of the considered metal. Quantitative analysis is applied using the full two-level factorial experimental design method, which results in the contribution value of each parameter in changing the quantity of average corrosion rate in both individual and synergistic cases. Besides this quantitative analysis, qualitative analysis has been used to predict the variation direction. These two analyses show the important role of the synergistic action, which changes the variation direction of corrosion rate and the contribution percentage of each parameter in varying the value of corrosion rate. Applying both these analyses can show the magnitude and quality of each parameter’s effect, which is remarkably valuable in marine applications.     

304不锈钢表面激光熔覆NiMoSi层的组织与性能

为改善304不锈钢的摩擦学性能,分别以A熔覆层20%Ni-48%Mo-32%Si,B熔覆层30%Ni-42%Mo-28%Si(质量分数)混合粉末为原料,在304不锈钢表面利用激光熔覆技术制备复合熔覆层,分别利用XRD、SEM和摩擦磨损试验机分析了熔覆层的物相、显微组织结构及室温下的摩擦学性能。结果表明:复合熔覆层和基体冶金结合良好,仅存在部分裂纹。Mo₅Si₃、MoSi₂是复合熔覆层的主要物相,A熔覆层显微硬度(1060.1 HV0.5)和B熔覆层显微硬度(725.9 HV0.5)均明显高于基体(257.2 HV0.5),A复合熔覆层的磨损率和摩擦因数最低。     

Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel

This experimental work was aimed at investigating the ability of acoustic emission (AE) technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel. Crevice initiation, propagation and repassivation was controlled by additions of hydrogen peroxide and hydrochloric acid and by the extent of the applied torque of crevice assembly, in the presence of chloride ions. The simultaneous measurements of corrosion potential of the specimen and AE global activity during the test, as well as the characterization of acoustic parameters of AE signals, evidences a good correlation between potential and AE activity fluctuations, AE rate and amplitude of crevice damage in terms of weight loss and metallic surface affected, in each tested experimental condition. Moreover, the evolution of cumulative% of AE signals number versus selected acoustic parameters shows that rise time, counts number, duration and cumulative energy of AE signals are affected by crevice development. Finally, visualization of crevice initiation and propagation during the test allows to propose that bubbles formation from cathodic reactions within the crevice is the emissive mechanism.     

新型304不锈钢软钎焊用钎剂的研制

研究制备了以有机金属盐甲基磺酸亚锡为主要活性成分的新型304不锈钢软钎焊用H36钎剂,并配合Sn-Cu-Ni钎料比较了其与传统H3PO4-C2H5OH钎剂、ZnCl2-HCl钎剂和ZnCl2-NH4Cl钎剂在304不锈钢基板上的润湿铺展性能.结果表明,新研制的H36钎剂的铺展性能明显优于其它钎剂,其最大铺展面积达到109.56 mm2,相比H3PO4-C2H5OH钎剂和ZnCl2-NH4Cl钎剂分别提高了249.4％和239.3％；添加乳化剂6500能进一步提高钎剂的润湿铺展性能,最大铺展面积可达到157.49 mm2.对优化后的H36-2钎剂匹配Sn-Cu-Ni钎料钎焊304不锈钢钎焊接头力学性能的结果表明,钎焊接头的抗拉和抗剪强度分别达到22.72 MPa和33.93 MPa,优于现有文献报道的数据.     

304奥氏体不锈钢热诱发马氏体相变研究

借助X射线衍射技术,研究了304奥氏体不锈钢热诱发马氏体相变倾向.结果表明:C、Mn、Cr和Ni接近标准规范下限,304不锈钢的稳定性急剧下降,致使液氮内冷却后接近1/3的奥氏体转变为α'或ε马氏体,室温拉伸即形成应变诱发ε和α'马氏体,而且较小的室温变形显著增大随后液氮内冷却的热诱发α'马氏体相变倾向,但随室温预应变增大快速形成应变诱发α'马氏体,致使随后在液氮内发生热诱发α'马氏体倾向下降.此外,研究表明ε马氏体的形成及消失与α'马氏体的累积量有关.     

Inhibition of 304 stainless steel corrosion in acidic solution by Ferula gumosa (galbanum) extract

The inhibition effect of the extract of galbanum (Ferula gummosa Boiss.) on the corrosion of 304 stainless steel in 2 M HCl solution was studied by weight loss measurements, Tafel polarization, and electrochemical impedance spectroscopy (EIS) methods. It was found that the inhibition efficiency (IE) increases as the extract concentration is increased. Tafel polarization method revealed the mixed mode inhibition of galbanum extract (GE) with predominant control of anodic reaction. The effect of temperature on the corrosion behavior of steel indicates that inhibition efficiency of the natural substance increases with the rise in temperature. At all temperatures, the adsorption of the extract components onto the steel surface was found to follow the Temkin adsorption isotherm.     

304不锈钢薄板激光焊搭接接头组织及性能

研究0.8 mm厚度304不锈钢薄板的搭接连续激光焊工艺,分析接头的显微组织和部分力学性能。与电阻缝焊接头进行比较,结果表明:激光焊成形良好,在适当的工艺规范下,激光焊和电阻缝焊的水压试验都可以达到8.0 MPa;激光焊的热影响区更窄并且焊缝中组织为奥氏体;较电阻缝焊焊缝呈更均匀、细小的柱状晶;两种焊接方法的拉伸剪切试验的断裂位置均位于母材。     

304不锈钢法兰焊接裂纹分析及返修

对检修过程中发现的304不锈钢焊缝裂纹及母材本体裂纹进行分析,焊缝存在较多的焊渣,以及根部未焊透是焊缝开裂的原因。母材的金相分析表明,304不锈钢晶界存在碳化物聚集,容易发生晶间腐蚀,引起母材开裂,焊接过程中,多层多道焊也容易使得热影响区晶间腐蚀加剧,引起母材开裂。304不锈钢锻造法兰的制造过程中应避免在敏化温度停留时间过长,固溶处理时应采取快冷的方式避免晶间腐蚀。焊接返修过程中,通过严格控制焊接层间温度,采用快速小热输入的工艺参数使得返修后的304不锈钢焊接质量检验合格。     

304不锈钢喷砂助低温渗铝工艺

采用喷砂技术对304不锈钢板表面进行处理,并对喷砂处理后的试样进行热处理和低温固体粉末包埋渗铝处理,分析讨论了喷砂助低温渗铝的最佳工艺参数。结果表明：表面经喷砂处理后,试样表层形成厚约250 μm的变形区,同时表面发生了马氏体相变,硬度明显提高。喷砂试样经400～600 ℃热处理后,变形层组织仍为马氏体相,硬度有所下降,变形层具有热稳定性。表面喷砂处理可以降低渗铝温度,提高渗铝速度。最佳渗铝工艺为经过优化喷砂工艺处理后在530 ℃渗铝3 h随炉冷却,试样表面可形成约50 μm的渗层,渗层主要由金属间化合物FeAl2构成,表面硬度可达640 HV0.2。     

PMMA与304不锈钢激光焊接

研究聚甲基丙烯酸甲酯(PMMA)塑料与304不锈钢激光焊接热传导技术,采用正交试验法分析聚甲基丙烯酸甲酯和304不锈钢之间的焊接质量. 对焊接后的试样进行拉伸测试和切片试验,用能量密度定量判定焊接结果,分析多种焊接因素对抗拉强度和焊缝宽度的影响. 利用正交试验极差分析法对试验数据进行处理,获得透明聚甲基丙烯酸甲酯和304不锈钢之间激光热传导焊接的最佳焊接工艺参数. 结果表明,焊接因素对焊接强度的影响从大到小的顺序为焊接速度、脉冲宽度、保护气体流量、峰值功率、光斑直径和脉冲频率.