Erosion and Corrosion Behavior of Laser Cladded Stainless Steels with Tungsten Carbide

Laser cladding of tungsten carbide (WC) on stainless steels 13Cr-4Ni and AISI 304 substrates has been performed using high power diode laser. The cladded stainless steels were characterized for microstructural changes, hardness, solid particle erosion resistance and corrosion behavior. Resistance of the clad to solid particle erosion was evaluated using alumina particles according to ASTM G76 and corrosion behavior was studied by employing the anodic polarization and open circuit potential measurement in 3.5% NaCl solution and tap water. The hardness of laser cladded AISI 304 and 13Cr-4Ni stainless steel was increased up to 815 and 725Hv_100?g, respectively. The erosion resistance of the modified surface was improved significantly such that the erosion rate of cladded AISI 304 (at 114?W/mm²) was observed ~0.74?mg/cm²/h as compared to ~1.16 and 0.97?mg/cm²/h for untreated AISI 304 and 13Cr-4Ni, respectively. Laser cladding of both the stainless steels, however, reduced the corrosion resistance in both NaCl and tap water.     

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.     

Accelerated corrosion of five commercial steels under a ZnCl2-KCl deposit in a reducing environment typical of waste gasification at 673-773 K

The corrosion of five Fe-Cr commercial steels containing 0-18 wt.% Cr at 673-773 K has been studied in a reducing H₂-HCl-CO₂ atmosphere under a ZnCl₂-KCl deposit typical of waste gasification environments. In comparison with the behavior of the same steels in a similar gas mixture without salt deposit, all steels suffered from accelerated corrosion induced by the salt and formed porous scales with poor adherence to the underlying steels. Some Cl was detected close to the steels/scale interface, indicating that Cl-containing species were able to go through the scale down to the metal matrix. Even though the corrosion rates generally decreased with increasing Cr content, the high-Cr stainless steel SS304 was still unable to provide a good corrosion resistance against the ZnCl₂-KCl deposit. The reaction mechanisms are discussed on the basis of thermodynamic considerations and of the “active oxidation” model.     

ATMOSPHERIC CORROSION OF 304AND 316 STAINLESS STEELS

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316NG不锈钢在高纯水环境中的腐蚀行为

通过腐蚀失重试验,获得了316NG不锈钢在高纯水环境中的腐蚀失重曲线及均匀腐蚀速率;采用XPS、XRD、SEM等手段对腐蚀产物的组成元素、物相、形貌进行了分析。结果表明:316NG不锈钢在高纯水环境中的平均腐蚀速率为0.05mm/a,远小于304NG不锈钢和321不锈钢的;腐蚀产物膜主要以耐蚀性强的磁铁矿Fe_3O_4、尖晶石类氧化物FeCr_2O_4和NiFe_2O_4、镍和铬氧化物及氢氧化物等形式存在,且(铬+镍)与铁的原子比高于基体的,说明316NG不锈钢具有良好的耐腐蚀性能。     

Corrosion behavior of various steels in the simulated fluidized bed boiler environment

The corrosion behavior of various austenitic stainless steels and high-alloy steels has been studied in simulated fluidized bed boiler environment to develop a new corrosion resistant austenitic stainless steel for the superheater tube. The superheater is usually not installed within the bed position, which is different from the evaporator installed within the bed position. Therefore, the superheater tubes are exposed to an oxidizing environment; but it is also necessary to estimate the corrosion resistance of the steels in a reducing environment. It is already known that the high temperature corrosion behavior in conditions where CaSO₄ is coated on the steels is more important than the erosion of the superheater tubes. The main results in this present study are as follows: The Nb bearing steels and low C steels showed good resistance to high-temperature corrosion in CaSO₄/CaO, e.g. 347, 304L and HR3C. The corrosion rate of all steels used increased with increase in temperature, particularly at temperatures higher than 650°C. Internal penetration was not detected at temperatures lower than 550°C, but it was detected at temperatures higher than 600°C, in particular, higher than 650°C. The corrosion thickness loss was almost the same as the internal penetration depth at 700 and 750°C in the 300 series steels placed in CaSO₄/CaO, including the fine grained 347 steel, while the internal penetration depth was larger than the corrosion thickness loss in high-alloyed materials such as Alloy 800 and 310 steels. At temperatures higher than 800°C, the same result was also obtained for the fine grained 347 steel. The corrosion during exposure to oxidizing or reducing gases without CaSO₄/CaO or CaS was slight, but when the test specimens were placed in CaSO₄/CaO or CaS, the corrosion rate sharply increased, regardless of the atmospheric gas composition. Cr, Si, Mn (less than 5 %), Mo and Nb are beneficial elements while C, Cu and Al are harmful elements. From the above results, the following steel was developed for high temperature corrosion resistance in CaSO₄/CaO: low C-22/25Cr-17/25Ni-3/5Mn-(2Mo)-Nb-0.08/0.2N-Al-(B).     

常减压装置常用钢材在高温原油馏分中的腐蚀研究

利用高压釜模拟常减压装置中的腐蚀环境,采用腐蚀失重法并结合SEM,研究了4种常减压装置常用钢材在高温原油馏分中的腐蚀行为,分析了馏分、材质、温度的影响规律。结果表明,原油馏分的酸值、S含量和盐含量越高,对20钢腐蚀性越强,3种原油馏分对20钢的腐蚀性强弱为：脱盐后原油＞常二线馏分＞常一线馏分。提高钢材中Cr,Ni和Mo等合金元素的含量有助于提高其抗腐蚀能力,4种钢材在高温原油馏分中的抗腐蚀性能优劣为：316钢＞304钢＞1Cr5Mo钢＞20钢。温度对钢材在高温原油馏分中的腐蚀行为会产生多方面的影响,腐蚀速率总体上随着温度的升高而增大,某些温度范围内可能出现腐蚀速率极值。     

22Cr双相不锈钢与304L、316L钢在氯化物溶液中耐应力腐蚀性能的比较

采用恒载荷法、恒应变法研究了22Cr双相不锈钢在不同Cl-浓度、不同温度的氯化物渗液中耐应力腐蚀的性能,并与316L和304L普通奥氏体不锈钢进行了对比.结果表明,22Cr双相不锈钢在氯化物环境中具有更好的应力腐蚀破裂(SCC)抗力.     

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.     

445铁素体不锈钢内胆水箱的加工性能和耐蚀性

将445铁素体不锈钢的主要化学成分、力学性能、成型性能和焊接性能等基本性能与304奥氏体不锈钢进行对比,结果表明,445不锈钢具有较好的机加工性能。采用盐雾试验及10%的NaCl溶液加速腐蚀试验等方法,对比445水箱、304水箱及两者混合搭配的内胆水箱的太阳能热水器的耐腐蚀性能。结果表明,445不锈钢耐腐蚀性稍逊于304不锈钢,在80～120℃时,445与304不锈钢均发生蒸汽腐蚀、水线腐蚀,且445不锈钢出现较为严重的点蚀现象。     

不同热处理态的304和321奥氏体不锈钢在氯化铵环境中的应力腐蚀行为对比研究

目的 对比研究原始、固溶和敏化态的304和321奥氏体不锈钢在模拟加氢催化氯化铵环境中的应力腐蚀（SCC）行为及机理。方法 将304和321奥氏体不锈钢经过热处理制备成固溶和敏化态试样,采用U形弯试样在模拟加氢催化氯化铵环境中浸泡的应力腐蚀试验方法对其进行研究,通过观察U形弯弧顶的腐蚀形貌和开裂时间,并结合腐蚀及裂纹的SEM照片和电化学测试结果进行分析。结果 原始和固溶状态304不锈钢U形弯试样在氯化铵溶液环境中开裂时间为25 d左右,断口形貌分别为穿晶断口和沿晶断口;敏化态试样18 d后发生开裂,断口形貌为穿晶和沿晶的混合断口。原始和固溶态321不锈钢U形弯试样在该环境中经过39 d均无应力腐蚀裂纹;敏化试样经30 d后产生宏观开裂。电化学测试结果显示,不同热处理态的304不锈钢在氯化铵溶液中均具有明显的点蚀敏感性,321不锈钢在该环境中耐点蚀和应力腐蚀的能力优于304不锈钢。结论 不同状态的304不锈钢在高温氯化铵环境中具有较强的应力腐蚀倾向,特别是敏化态试样;321不锈钢在该环境中的应力腐蚀敏感性相对较小,但敏化处理显著增加了其沿晶应力腐蚀倾向,而固溶态试样具有明显的沿晶腐蚀特征。     

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).     

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。     

不锈钢盐酸露点腐蚀行为的原位研究

利用一种新型的露点腐蚀模拟装置结合原位的电化学阻抗谱,电化学噪声等测试手段评价了304和316L两种不锈钢的盐酸露点腐蚀行为.结果表明,316L不锈钢表现出更优异的耐盐酸露点腐蚀性能,主要原因可归结为两点:一是316L不锈钢钝化膜中含有较高的Cr/(Cr+Fe) 比以及较低含量的Fe;二是316L不锈钢钝化膜中含有能改善抗点蚀性能的Mo.     

Formation of Si diffusion layer on stainless steels and their high temperature corrosion resistance in molten salt

The surface alloying of Si into SUS430 and SUS304 stainless steels was achieved by a pack-cementation method. A high-temperature corrosion test was undertaken under a corrosive ash in a high-temperature gas, which simulated the environment of a waste incinerator. The effect of the surface alloying of Si on the high temperature corrosion resistance of these stainless steels was examined. The result of the corrosion test showed that the corrosion mass loss of the siliconized stainless steel was lower than that of non-treated stainless steel. It was thought that the high temperature corrosion resistance in the corrosive ash containing large amounts of molten salt was improved by the surface alloying of Si. The change in corrosion loss with test time in the corrosive ash was also examined. The corrosion loss of the non-treated stainless steels rapidly increased. On the other hand, the corrosion rate of the siliconized stainless steels was small.It was found from the observation and EPMA analysis of a cross-section of the specimen after the corrosion test that, for the non-treated stainless steels, the metallic elements were dissolved into the molten salt. On the other hand, for the siliconized stainless steels, a scale consisting of silicon oxide was formed on the steels. As a result, the dissolved metallic elements were small.The electrochemical studies indicated that there was an effect of the surface alloying of Si on the hot corrosion resistance of the stainless steels. Hence, the corrosion potentials of the siliconized steels were higher than those of the non-treated steels. The increase in the anodic current densities for the siliconized steels was smaller than that for the non-treated steels. It was thought that the electrochemical corrosion reaction was difficult to occur due to the surface alloying of Si into the stainless steels.     

尿素对模拟汽车废气环境中不锈钢冷凝液腐蚀行为的影响

采用高温废气氧化-酸性冷凝液浸泡循环法模拟柴油机的排气环境,对比研究废气中引入尿素后排气系统用304和439不锈钢的冷凝液腐蚀行为,并分析了尿素对不锈钢氧化与腐蚀的作用。电化学测试结果表明：经400 ℃氧化后,304不锈钢在冷凝液中的腐蚀处于钝化状态,而439不锈钢的腐蚀趋于活化状态;在有/无尿素条件下,试样表面产物膜在氧化和腐蚀的循环作用下均会发生破坏而形成局部腐蚀坑;废气中引入尿素会增强其对两种不锈钢的氧化作用,进而导致不锈钢的均匀腐蚀量增大而局部腐蚀深度减小。     

Multi-scale characterization of stress corrosion cracking of cold-worked stainless steels and the influence of Cr content

This paper describes a novel multi-scale study of stress corrosion cracking in cold-worked 304 type stainless steels, which are widely used in pressurized water reactors and boiling water reactors. The influence of cold work and Cr concentration on the stress corrosion cracking behaviour of the steel has been examined. A methodology has been developed in order to characterize the same crack tip region with nanoscale secondary ion mass spectroscopy, electron back-scattering diffraction and transmission electron microscopy. This has offered a unique insight into the chemistry and microstructure, showing that the right combination of techniques can provide much of the information needed to understand the processes involved in crack propagation. A model for crack propagation based on brittle fracture and localized oxidation and shearing near the crack tip has been proposed.     

合金元素对铸造Fe-Cr铁素体不锈钢耐浓硫酸腐蚀性能的影响

采用电化学技术、浸泡腐蚀及能谱分析等研究了合金元素对铸造Fe-Cr铁素体不锈钢耐浓硫酸腐蚀行为的影响。结果表明:随铬含量的增加,Fe-Cr合金的耐浓硫酸腐蚀性能增强,单一的铬合金化不能使Fe-Cr合金在60℃,98%H2SO4中自钝化;钼能促进Fe-Cr25-Mo合金的钝化和自钝化,随钼含量的增加,Fe-Cr25-Mo合金的耐浓硫酸腐蚀性能增强;辅助合金元素镍、铜可促进Fe-Cr25Mo2合金的钝化和自钝化,而钛、铌的影响不大。     

Studies on Stress Corrosion Cracking of Super 304H Austenitic Stainless Steel

Stress corrosion cracking (SCC) is a common mode of failure encountered in boiler components especially in austenitic stainless steel tubes at high temperature and in chloride-rich water environment. Recently, a new type of austenitic stainless steels called Super304H stainless steel, containing 3% copper is being adopted for super critical boiler applications. The SCC behavior of this Super 304H stainless steel has not been widely reported in the literature. Many researchers have studied the SCC behavior of steels as per various standards. Among them, the ASTM standard G36 has been widely used for evaluation of SCC behavior of stainless steels. In this present work, the SCC behavior of austenitic Fe-Cr-Mn-Cu-N stainless steel, subjected to chloride environments at varying strain conditions as per ASTM standard G36 has been studied. The environments employed boiling solution of 45 wt.% of MgCl₂ at 155 °C, for various strain conditions. The study reveals that the crack width increases with increase in strain level in Super 304H stainless steels.     

Development of high Mn-N duplex stainless steel for automobile structural components

A new high Mn-Ni free (duplex stainless steel) DSS containing 18Cr-6Mn-1Mo-0.2N has been developed by examining the effects of manganese on the corrosion and mechanical properties of high Mn SSs containing 18Cr-4 ∼ 11Mn-0 ∼ 2Ni-0 ∼ 1Mo-0.2N. The alloy with 45% ferrite is found to be an optimum alloy with much higher mechanical strength and similar corrosion resistance compared with those of standard SS304. In addition, the alloy was free of precipitation of sigma phase and Cr-nitride when exposed to high temperatures due primarily to relatively low contents of Cr, N and Mo. With an increase in Mn content, the resistance to pitting and metastable pitting corrosion of high Mn DSS decreased since the number of (Mn, Cr) oxides, acting as preferential sites of pitting, increased with the Mn content.