Localized corrosion properties of low interstitial ferritic,high purity austenitic and high chromium duplex stainless steels

Within the framework of a research aimed at characterizing the behaviour of new materials to pitting and crevice corrosion, an investigation has been made, using electrochemical techniques, of the following materials: ELI ferritic stainless steels (18 Cr-2 Mo-Ti; 21 Cr-3 Mo-Ti; 26 Cr-1 Mo); high chromium duplex stainless steel (Z 5 CNDU 21-08) and high chromium-nickel austenitic stainless steel (Z 2 CNDU 25-20); commercial austenitic stainless steels (AISI 304 L and 316 L) and laboratory heats of austenitic stainless steels with low contents of interstitials (LTM/18 Cr- 12 Ni, LTM/16 Cr- 14 Ni-2 Mo). It was possible to graduate a scale of resistance to pitting and crevice corrosion in neutral chloride solutions at 40 C; in particular the two experimental austenitic stainless steels LTM/18 Cr- 12 Ni and LTM/16 Cr- 14 Ni-2 Mo are at the same level as the AISI 316 L and 18 Cr-2 Mo-Ti, respectively. An occluded cell was developed and used for determining the critical potential for crevice corrosion (E_{localized corrosion}). For the steels under investigation E_{localized corrosion} is less noble than E_pitting especially for ELI ferritic 18 Cr-2 Mo-Ti and 21 Cr–3 Mo-Ti.     

304LN不锈钢表面激光熔覆钴基合金组织和性能

为了提高304LN不锈钢的耐磨性,延长控制棒导向筒组件使用寿命,采用激光熔覆技术在304LN不锈钢表面制备了Stellite 6钴基熔覆层.利用光学显微镜(OM)、能谱仪(EDS)、显微硬度计、摩擦磨损试验机、腐蚀试验装置等多种试验测试设备,分析了熔覆层组织形貌、成分、显微硬度、摩擦磨损性能及腐蚀行为,确定了多道多层钴基熔覆层的工艺参数.结果表明,熔覆层与基体之间形成了冶金结合,显微组织主要由平面晶区、胞状和柱状晶区、树枝晶区和等轴晶区组成.熔覆层硬度为500 ~ 550 HV,摩擦磨损系数为0.30 ~ 0.35,熔覆层均匀腐蚀速率和缝隙腐蚀速率分别为0.153 和0.143 mg/(dm2·d). 激光熔覆钴基合金可以有效提高304LN不锈钢表面的硬度、耐磨性能和耐腐蚀性能.     

Improvement of pitting corrosion resistance of AISI 444 stainless steel to make it a possible substitute for AISI 304L and 316L in hot natural waters

The pitting corrosion resistance of AISI 444, 304L and 316L stainless steels in two tap waters with different chloride concentrations at 80 °C was studied. Cyclic potentiodynamic polarization (CPP) tests were carried out starting from E_corr ? 30 mV until the current density reached 0.1 mA/cm² (scan rate 0.166 mV/s); the scan was then reversed and continued until new passivity conditions were achieved. The corrosion potential was measured before the polarization experiments. From the E‐log i plots, the values of pitting and protection potential were obtained; from these potentials, the perfect and the imperfect passivity regions were defined to compare the corrosion resistance of the studied steels. CPP tests were performed both on as received stainless steel samples and on samples submitted to different cleaning–passivation treatments to improve their corrosion resistance. The results indicate that, for industrial production, AISI 444 stainless steel can substitute the more expensive AISI 304L or 316L after a cleaning–passivation treatment that reduces the presence of inclusions.

     

0Cr25Ni7Mo4、316与304不锈钢临界点蚀温度研究

采用外加恒定电位下腐蚀电流-温度扫描方法研究了0Cr25Ni7Mo4、304和316不锈钢在1 mol/L NaCl水溶液中的点蚀行为。利用不锈钢临界点蚀温度评价了材料的耐点蚀性能.测得0Cr25Ni7Mo4和316不锈钢的临界点蚀温度分别为79.5 ℃和15 ℃,304不锈钢在0 ℃以下.对0Cr25Ni7Mo4不锈钢材料优良耐点蚀性能的原因进行了分析讨论.     

Corrosion behavior of T24, T92, VM12, and AISI 304 steels exposed to KCl–NaCl–K2SO4–Na2SO4 salt mixtures

The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na₂SO₄, and KCl–K₂SO₄ salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na₂SO₄ and KCl–K₂SO₄. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na₂SO₄ and to KCl–K₂SO₄, respectively.     

激光增材制造技术在核电堆内构件304LN不锈钢大型复杂结构件上的应用

为了提高304LN不锈钢的耐磨性,延长控制棒导向筒组件使用寿命,采用激光熔覆技术在304LN不锈钢表面制备了Stellite 6钴基熔覆层.利用光学显微镜(OM)、能谱仪(EDS)、显微硬度计、摩擦磨损试验机、腐蚀试验装置等多种试验测试设备,分析了熔覆层组织形貌、成分、显微硬度、摩擦磨损性能及腐蚀行为,确定了多道多层钴基熔覆层的工艺参数.结果表明,熔覆层与基体之间形成了冶金结合,显微组织主要由平面晶区、胞状和柱状晶区、树枝晶区和等轴晶区组成.熔覆层硬度为500 ~ 550 HV,摩擦磨损系数为0.30 ~ 0.35,熔覆层均匀腐蚀速率和缝隙腐蚀速率分别为0.153 和0.143 mg/(dm²·d). 激光熔覆钴基合金可以有效提高304LN不锈钢表面的硬度、耐磨性能和耐腐蚀性能.     

Formation of WC-iron silicide (Fe5Si3) composite clad layer on AISI 316L stainless steel by high power (CO2) laser

An attempt was made to produce WC-iron silicide cladded layer on AISI 316L stainless steel by laser processing to obtain high hardness and lesser variations in hardness distribution in the layer. Different compositions of coating materials (WC, Si and Ni) and laser processing parameters were used. A good and defect free cladded layer of WC-iron silicide was obtained for an energy density of 22.5 J/mm² and coating composition of 40WC-40Si-20Ni (wt.%). The layer exhibited average hardness of about 883 HV with lesser variations in the hardness distribution and also higher wear resistance compared to the substrate.     

Corrosion behaviour of carbon S-phase created on Ni-free biomedical stainless steel

Following the success of forming a carbon S-phase (expanded austenite) surface layer on medical grade Ni-free austenitic stainless steel by DC plasma carburising, the established commercial carburising process Kolsterising® was performed on both Ni-containing (AISI 304) and Ni-free austenitic stainless steels. While the Ni-containing stainless steel responded very well to Kolsterising®, the Ni-free alloy did not. The carbon absorption and the hardness of the Kolsterised® Ni-free alloy are inferior to Kolsterised® AISI 304 Ni-containing stainless steel, however, the hardness of the untreated Ni-free alloy was doubled by Kolsterising®. The response of both Kolsterised® Ni-free and Ni-containing alloys to pitting, crevice corrosion and intergranular corrosion resistance was similar. From this work it can be concluded that the Kolsterised® austenitic stainless steels do not suffer from intergranular corrosion but are susceptible to intragranular pitting when tested in boiling sulphuric acid and copper sulphate solution. It was also observed that Kolsterising® improves significantly the pitting and crevice corrosion resistance of the alloys used in this study.     

奥氏体不锈钢耐蚀渗氮工艺的研究

对AISI 321和AISI 304不锈钢进行了低温离子渗氮,其表面获得了均匀的渗氮层即白亮层。与未经渗氮的钢相比,经离子渗氮的钢表面硬度和耐磨性显著提高,而耐蚀性也并不降低;与经传统的盐浴氮碳共渗的钢相比,经离子渗氮的钢的耐磨性和耐蚀性也均有所提高。对经低温离子渗氮的AISI 321纲渗层进行了XRD分析,发现试样的谱峰明显向低角度偏移。     

Surface modification of low carbon steel substrate by Al-rich clad layer applied by GTAW

Low cost and good properties of low carbon steels introduce this material suitable for a wide variety of industrial applications. Developing overlays cladding with desired properties on the surface of these steels seems to be the best way to increase the corrosion and wear resistances of low carbon steels. In the present research, the solidification sequence and the characteristics of Al base weld cladding on AISI 1006 substrate were studied. The optical and scanning electron microscopic studies revealed the formation of acicular-like intermetallic compounds in the clad overlayer. XRD phase analysis illustrated that the clad layer consisted of ordered Fe₃Al and FeAl₃ intermetallic compounds in the FeAl intermetallic matrix. The formation of these intermetallics in the Fe–Al overlayer cladding resulted in a significant improvement of hardness and oxidation resistance of Fe–Al cladded samples.     

Corrosion Testing of some Austenitic Stainless Steels and of Inconel Alloy at 25°c in Acidic Chloride Solutions

Abstract

The corrosion of austenitic stainless steels types AISI 304, 310 and 316, and of Inconel alloy, was studied at 25°c, in 5% NaCl solution at an initial pH value of 2·5, and in 5% FeCl³ at pH 1·2. The resistance of the alloys in both corrosive environments was in the order: 310 > 316 > 304 > Inconel. Pre-treatment of the specimens with bubbling chlorine gas increased the subsequent corrosion rates of the alloys. Intermittent bubbling of gas mixtures such as Cl₂, N₂, and/or H₂S, increased the corrosion rate of Inconel alloy when Cl₂ was present, but decreased the corrosion rate when H₂ was present. Heat treatment of austenitic stainless steels increased the subsequent corrosion rates, whereas 16% pre-straining of annealed specimens slightly reduced the rates. Addition of trisodium phosphate to the corrosive solution reduced the corrosion rates and pitting tendency for all three types of austenitic stainless steel.     

Influence of Cu and Sn content in the corrosion of AISI 304 and 316 stainless steels in H2SO4

This paper addresses the influence of Cu and Sn addition on the corrosion resistance of AISI 304 and 316 stainless steels in 30 wt% H₂SO₄ at 25 and 50 °C. The corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The corrosion products were analysed by SEM, X-ray mapping and XPS before and after accelerated tests. The behaviour of both AISI 304 and 316 stainless steels in sulphuric acid solution was greatly improved by increasing Cu concentration and the synergic effect of Cu and Sn. Addition of Sn increased corrosion resistance, but less than addition of copper.     

1Cr18Ni9Ti 不锈钢表面电火花熔覆 WC 涂层特性研究

目的研究1Cr18Ni9Ti不锈钢经电火花强化后,WC涂层的显微组织和性能。方法采用电火花熔覆技术在不锈钢1Cr18Ni9Ti基体表面制备WC熔覆层,并分析熔覆层的表面形貌、显微组织、显微硬度、耐磨性,采用线性极化法研究熔覆层在3.5%(质量分数)Na Cl腐蚀溶液中的耐腐蚀性能。结果熔覆层组织均匀、连续、致密,与基体呈冶金结合。显微硬度最大值达到1680HV0.3,平均值为1336HV0.3,比不锈钢基材提高了4倍,耐磨性是不锈钢基材的4倍。在3.5%Na Cl腐蚀溶液中,熔覆层的自腐蚀电位较不锈钢减小了约165 m V,击破电位低于不锈钢基材,维钝电流密度高于不锈钢基材。结论熔覆层具有高硬度和高耐磨性能,磨损机理主要是粘着磨损和磨粒磨损,但在3.5%Na Cl腐蚀体系中,耐腐蚀性能低于1Cr18Ni9Ti不锈钢。     

316L不锈钢表面激光熔覆Stellite-F合金层的电化学腐蚀行为

采用CO₂激光器在316L不锈钢表面熔覆Stellite-F合金,通过电化学方法研究了Stellite-F熔覆合金层在5wt%NaCl溶液中的腐蚀行为。结果表明:与316L不锈钢相比,与基材呈冶金结合的Stellite-F合金层自腐蚀电位较正、自腐蚀电流密度较小,无点腐蚀现象出现,耐海水腐蚀性能较好;研究发现,熔覆合金层物相主要由γ-Co固溶体与Ni₃C、Cr₂₃C₆碳化物构成,在盐溶液中其腐蚀失效机制为选择性腐蚀,即固溶体合金相作为阳极被腐蚀浸出,碳化物相得到阴极保护暴露析出,同时固溶体相中的Co、Ni组分优先被腐蚀浸出,其余组分形成海绵状结构。     

热处理对激光熔覆Ni合金层的组织及冲蚀磨损性能的影响

借助于扫描电镜、Ｘ射线衍射仪、能谱仪和显微硬度计研究了２Ｃｒ１３不锈钢激光熔覆Ｎｉ基合金及后续热处理前后的组织结构、显微硬度和耐冲蚀磨损性能。结果表明,Ｎｉ基合金激光熔覆层的显微硬度高达５００～７００ＨＶ,而后继热处理又进一步使熔覆层硬度提高到８５０～１１２０ＨＶ。在含有Ｈ２ＳＯ４和ＮａＣｌ的砂浆水溶液中冲击速度７ｍ·ｓ－１、冲击角４５°的条件下激光熔覆Ｎｉ基合金并经处理后可使冲蚀磨损率下降约９０％。热处理使熔覆层的硬度和韧度增加。组织细化以及γＮｉ基体中沉淀析出Ｆｅ４．５Ｎｉ１８．５Ｂ６化合物被认为是覆层强化和冲蚀磨损性能改善的主要原因     

Corrosion resistance of laser cladded 304L stainless steel enriched with Ru in hydrochloric acid

The corrosion behaviour of laser surface cladding made from 304L stainless steel alloyed with varying concentrations of ruthenium in 1M HCl at 25°C was evaluated, fresh and after 12 hours, by electrochemical tests including open circuit potential and potentiodynamic polarisation scans. The ruthenium concentration in the 800?µm cladded layer varied from 0.82?wt-% to 4.67?wt-% ruthenium. The ruthenium doped samples were compared against a 304L stainless steel laser surface cladding with no ruthenium, 304L stainless steel samples with no laser cladding, 316L stainless steel, SAF2205 duplex stainless steel and Hastelloy C276®. Initial passivation was not observed in the 1M HCl but after 12 hours the addition of ruthenium led to reduced corrosion rates and improved passivation characteristics compared to the surface cladding without ruthenium. An optimum ruthenium range was observed between 3?wt-% and 5?wt-%. It was shown that at this optimum concentration, the ruthenium containing stainless steel clad on 304L stainless steel can compete commercially with the SAF2205 and Hastelloy C276® as long as the clad is 200?µm or less.     

激光熔覆镍基合金涂层及其应用研究

采用激光熔覆技术在４５钢表面获得镍基合金涂层。研究了激光熔覆涂层工艺、熔覆层的组织结构、硬度和腐蚀－冲蚀磨损特性,并用２Ｃｒ１３不锈钢进行了腐蚀－冲蚀磨损对比试验。激光熔覆镍基合作层已经成功地应用于矿用渣浆泵的平衡盘等零件。     

节镍型不锈钢的耐腐蚀性能比较

通过3.5%NaCl溶液中动电位极化曲线测定和中性盐雾试验,对200系列奥氏体不锈钢和400系列铁素体不锈钢两类节镍型不锈钢与304不锈钢的耐腐蚀性能进行了对比研究。结果显示,400系列铁素体不锈钢的耐点蚀性能优于200系列奥氏体不锈钢,两种节镍型不锈钢的耐点蚀性能均不如304不锈钢好;200系列奥氏体不锈钢的耐均匀腐蚀性能最差,443不锈钢耐均匀腐蚀性能与304不锈钢相当,439不锈钢比304不锈钢耐均匀腐蚀性能稍差。201、202、304、439和443不锈钢在3.5%NaCl溶液中的点蚀电位分别为(vs.SCE)-32 mV、-22 mV、312mV、165 mV和227 mV,腐蚀速率分别为0.0071 mm/a、0.0062 mm/a、0.0026 mm/a、0.0038 mm/a和0.0024mm/a。     

Codeposited chromium and silicon diffusion coatings for Fe-Base alloys via pack cementation

The simultaneous deposition of Cr and Si into plain carbon, low-alloy, and austenitic steels using a halide-activated pack-cementation process is described. Equilibrium partial pressures of gaseous species have been calculated using the STEPSOL computer program to aid in designing specific processes for codepositing the desired ratios of Cr and Si into a given alloy. The calculations indicate that NaCl-activated packs are chromizing, while NaF-activated packs deposit more Si with less Cr. The use of a dual activator (e.g., NaF+NaCl) allows for the deposition of both Cr and Si in the desired amounts. Single-phase ferritic coatings (150–250 microns thick) with a surface concentration of 20–35 wt.% Cr and 2–4% Si have been grown on AISI 1018, Fe-2.25 Cr-1.0Mo-0.15C, and Fe-0.5 Cr-0.5 Mo-0.2C steels using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF+NaCl activator, and a silica filler. Two-phase coatings (approximately 75 microns thick) containing 20–25 wt.% Cr and 2.0–2.4% Si have been obtained on 304 stainless steel using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF activator, and an alumina filler. The same pack chemistry allowed the diffusion of Cr and Si into the austenitic Incoloy 800 alloy without a phase change. A coated Fe-2.25 Cr-1.0 Mo-0.15 C coupon with a surface concentration of Fe-34 wt.% Cr-3Si was cyclically oxidized in air at 700°C for over four months and 47 cycles. The weight gain was very low (<0.2 mg/cm²) with no scale spalling detected. Coated coupons of AISI 1018 steel, and Fe-0.5 Cr-0.5 Mo-0.2C steel have shown excellent oxidation-sulfidation resistance in reducing, sulfur-containing atmospheres at temperatures from 400 to 700°C and in erosion and erosion-oxidation testing in air at 650 and 850°C.     

304不锈钢局部干法水下激光填丝熔覆层微观组织及性能

采用自行研发的水下激光填丝熔覆装备,在304奥氏体不锈钢板材表面进行激光填丝熔覆试验,并对空气环境和水下环境的熔覆结果进行对比分析,以探索在水下环境进行304不锈钢的缺陷修复. 通过XRD,EDS,光学显微镜分析了熔覆层的显微组织、化学成分和物相组成,采用显微硬度仪进行了硬度测试,利用动电位极化与交流阻抗谱技术研究熔覆层电化学腐蚀行为. 结果表明,在两种环境下均制备了单层多道熔覆层,且无明显气孔、裂纹等缺陷;熔覆层包括熔覆区、搭接区、相变影响区、熔合区、热影响区,显微组织主要由奥氏体、铁素体、马氏体组成;由于各区域内微观组织及晶粒的大小不同,使得熔覆层硬度呈阶梯分布;在3.5%NaCl溶液中,两种环境熔覆层均呈现出明显的钝化行为,且两种熔覆层耐腐蚀性能相近;所研制的水下激光填丝熔覆装备及工艺,可以满足实际工程对于熔覆层高效制备、成形质量控制及耐蚀性能的要求,可用于水下环境304不锈钢表面的防护与修复.