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采用IMO(国际海事组织)《货油舱用耐蚀钢试验程序》规定的模拟货油舱内底板腐蚀试验方法,研究了组织为马氏体、贝氏体十铁素珠、珠光体十铁素体的低合金高强度船板钢在酸性氯离子环境下耐蚀性.试验结果显示显微组织对钢的耐蚀性有显著影响.马氏体试验钢具有组织单一、碳化物析出少、产物膜对基体的保护效果最好的特点,其平均腐蚀速率最低.复相的珠光体组织,其渗碳体有较高的电位,与铁素体组织存在相间电位差,从而促进了铁素体的腐蚀,其锈层完整性和保护效果较差,腐蚀速率最高.贝氏体+铁素体试验钢相对马氏体试验钢在组织单一性上较差,但相对于珠光体十铁素体试验钢,其富碳相较少且分布均匀,这些对其在货油舱内底板环境中的腐蚀微电池数量和程度产生影响,因而其耐蚀性介于马氏体钢和铁素体十珠光体钢之间.     

齿轮钢16MnCr的过冷奥氏体连续冷却转变规律

利用DIL805L淬火相变膨胀仪研究了齿轮钢16Mn Cr的过冷奥氏体连续冷却转变行为,结合金相-硬度法,绘制静态CCT曲线。结果表明:试验钢在冷速小于0.2℃/s时,室温下获得铁素体+珠光体组织,冷速大于0.5℃/s,室温下试验钢中出现贝氏体组织,冷速大于5℃/s,试验钢中出现马氏体组织;随着冷速的增加,铁素体、珠光体减少,铁素体的形态由多边形向针状发展,硬度由146 HV30增大至380 HV30。由于Mo推迟了铁素体、珠光体转变,降低了获得铁素体的临界冷速,试验钢获得铁素体+珠光体组织的冷速范围较窄。     

非调质NM400复相耐磨钢的相变行为

为进一步优化非调质NM400复相耐磨钢不同组织配比,利用Gleeble-3800热模拟试验机探究了试验钢在连续冷却条件下的组织转变规律,并结合金相法和硬度法,绘制出试验钢的动态连续冷却转变(CCT)曲线。结果表明,当冷速低于1 ℃/s时,试验钢组织为铁素体+粒状贝氏体+珠光体,部分粗大的原奥氏体晶粒转变为粒状贝氏体和珠光体。在冷却速率为5~40 ℃/s时,试验钢不再发生珠光体转变,显微组织均为铁素体+贝氏体+马氏体。并随着冷速的增加,马氏体含量不断增加,硬度升高;此外,不同分段冷却方案下,较低的中冷温度以及较长的空冷时间均有利于铁素体和贝氏体的转变。同时,残留奥氏体含量则随铁素体含量的增大而增大;由于试验钢的Ms点较高,马氏体板条较宽,并且有自回火现象发生。     

微观组织对X52钢抗H2S腐蚀和开裂性能的影响

通过对X52钢进行热处理获得三种不同组织。SEM观察发现三种组织分别为铁素体/带状珠光体、马氏体/贝氏体和针状铁素体/回火马氏体。通过动电位极化、线性极化电阻、氢致开裂（HIC）实验和硫化物应力腐蚀开裂（SSC）实验,研究了不同热处理对X52钢在H₂S环境中的腐蚀与开裂行为的影响。结果表明马氏体/贝氏体显微组织由于位错密度很高且脆性大,因而腐蚀速率及HIC和SSC敏感性很高。铁素体/带状珠光体组织和针状铁素体/回火马氏体组织腐蚀速率及HIC和SSC敏感性很低。针状铁素体/回火马氏体组织由于不含带状组织且晶粒细小以及碳化物的析出,因此其HIC和SSC抗性优于铁素体/带状珠光体组织。     

初始组织形态对中碳及中碳合金钢退火组织演变的影响

分析了不同强度级别螺栓用冷镦钢盘条不同初始组织形态对退火组织演变的影响。工业轧制试验结果表明：低温轧制SCM435钢得到的多边形铁素体、珠光体、贝氏体及少许马氏体组织不利于获得均匀分布的球状珠光体;Gleeble热模拟组织转变研究结果表明：低温形变后ML35钢晶粒明显偏细,且碳化物部分球化,有利于获得球状 珠光体。     

两段式冷却对C-Mn钢奥氏体中温转变的影响

采用Formastor全自动相变仪进行了两段式冷却条件下C-Mn钢的热膨胀试验,并结合组织观察和显微硬度测量,研究了冷却速度以及发生部分先共析铁素体转变对奥氏体中温转变的影响。结果表明:随着冷却速度的增大和先共析铁素体含量的增加,贝氏体相变开始温度和结束温度均降低,贝氏体转变量减少;奥氏体随冷却速度的增大,转变产物由铁素体+珠光体逐渐变为魏氏组织铁素体+珠光体、网状铁素体+魏氏组织+贝氏体、马氏体的趋势;而对已发生部分先共析铁素体转变的过冷奥氏体,随先共析铁素体含量的减少,组织由魏氏组织+贝氏体向魏氏组织+马氏体转变。     

间隙尺寸对结构钢感应加热淬火淬硬层深度的影响

研究了45、40Cr钢感应加热水冷处理后的组织。感应加热频率为15 kHz,功率、工件相对移动速度分别为40 kW、5~11 mm/s和70 kW、6.5~11 mm/s,感应圈与工件之间的间隙尺寸分别为1.5 mm、3 mm。试验结果表明,淬火试样表面至心部由马氏体、马氏体＋铁素体、马氏体＋铁素体＋珠光体组成,中心为珠光体＋铁素体原始组织。40Cr钢试样与感应圈之间的间隙尺寸由3 mm减小到1.5 mm时,淬硬层深度的增加幅度为：宏观测定法为47%,金相测定法为49%;而45钢试样宏观测定法为45%,金相测定法为46%。     

不同初始状态中碳钢双向温轧组织的退火稳定性

通过扫描电镜(SEM)和电子背散射衍射技术(EBSD)研究了不同初始组织对中碳钢双向温轧退火后的组织演变以及稳定性变化的影响规律。结果表明,轧后铁素体-珠光体钢的平均晶粒尺寸为1.11μm,小角度晶界占比81%;而马氏体钢平均晶粒尺寸为0.99μm,小角度晶界占比65.3%。随退火时间的延长,铁素体晶粒发生回复再结晶后,铁素体-珠光体钢发生二次再结晶,平均晶粒尺寸不断增大,小角度晶界占比逐渐减小最终趋于平稳,退火8 h后分别为1.89μm和54.9%;而马氏体钢仅发生晶粒的均匀长大,晶粒尺寸稍有增加,小角度晶界比例降低较少,保温8 h后分别为1.43μm和58.1%。因此,马氏体钢轧后显微组织的退火稳定性要高于铁素体-珠光体钢。     

一种碳锰曲轴钢的奥氏体连续冷却转变规律

使用DIL805L型膨胀仪分析了曲轴钢的相变规律,得到了其奥氏体连续冷却转变曲线（CCT）。结果表明,试验钢的临界点为：Ac1＝682 ℃,Ac3＝765 ℃;当冷速为0.2～5 ℃/s时,转变产物为铁素体＋珠光体;当冷速大于5 ℃/s时,转变产物为铁素体、珠光体、贝氏体与马氏体的混合组织;当冷速增大到15 ℃/s时,转变产物为贝氏体和马氏体组织;冷速越大冷却后马氏体含量越多,硬度逐渐增加。     

退火温度对镀锌780MPa级双相钢组织性能的影响

研究了不同退火温度对780 MPa级冷轧双相钢组织性能的影响。试验表明:试验钢热轧态组织为铁素体、贝氏体和少量的珠光体,经过冷轧后形成纤维状组织,退火后组织为铁素体和岛状马氏体。对不同退火温度和速度下带钢组织性能进行了分析,带钢在820℃退火、保温100s后,可以获得双相组织且抗拉强度大于780 MPa。     

Influence of heat treatments on microstructure and pitting corrosion resistance of 15%Cr supermartensitic stainless steel

Supermartensitic is a new class of stainless steels in development and consolidation as commercial products. Significant changes on chemical composition of conventional martensitic stainless steels, such as the reduction of the carbon content to <0·03 wt-%, and the addition of Ni and Mo, marked the development of this new group of alloys. New grades containing higher amounts of Cr and small additions of Ti and/or Nb were developed recently. As a result, supermartensitic steels offer an interesting combination of high strength, toughness, weldability and corrosion resistance. In this work, the pitting corrosion resistance of a 15Cr supermartensitic steel with Ni, Mo and Cu additions was studied. It is well known that the mechanical properties and corrosion resistance of martensitic steels are adjusted by the final tempering treatment. Several single tempering treatments in the 300–650°C range and double tempering treatments were performed in order to obtain different microstructures. The pitting corrosion resistance was investigated by electrochemical test in 3·5%NaCl solution. It was found that the pitting potential slightly decreased with the increase in temperature and time of tempering. The analysis of pits formed during the corrosion tests showed that ferrite islands are more corrosion resistant than the martensitic matrix due to the higher Cr and Mo contents.     

含铌沉淀硬化不锈钢的耐蚀性评估

应航空航天工业的需求,沉淀硬化不锈钢自1945年起即开始研发。这类钢具有置换型马氏体组织,随后能产生沉淀硬化。本文研究了两种含沉淀相形成元素铌的钢的力学性能和耐蚀性,并与PH13．8Mo钢进行了比较。结果表明,一种钢的耐蚀性与PH13—8Mo钢类似,另一种钢的力学性能与PH13—8Mo钢相近。     

Effect of heat treatment on H2S corrosion of a micro-alloyed C–Mn steel

The H₂S corrosion resistance of a C–Mn pipeline steel with three different microstructures has been evaluated using electrochemical techniques with a 3% wt. NaCl solution at 50 °C. Microstructures included martensite, ferrite, and ferrite + bainite. Electrochemical techniques included potenthiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and electrochemical noise (EN) measurements. Most of the tests lasted 24 h. All techniques showed that the highest corrosion rate corresponded to the steel with a martensitic microstructure; up to one order of magnitude higher than the corrosion rate for steels with a ferritic + bainitiic microstructure, whereas the steel with the ferritic microstructure showed the lowest corrosion rate. EIS tests showed that the corrosion process was under charge transfer control, whereas EN results indicated that the three steels exhibited a clear tendency towards a localized type of corrosion. However, for longer immersion times, the steel with a martensitic microstructure tended to exhibit a mixture of uniform and localized attack. Results were discussed in terms of grain size, grain boundary energy, amount and distribution of particles found in each steel.     

Relationship Between Microstructure and Corrosion Behavior of Cr12Ni3Co12Mo4W Ultra-High-Strength Martensitic Stainless Steel

The effect of tempering temperature on the microstructure and corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel was investigated using transmission electron microscopy, atomic force microscopy, X-ray diffraction, and electrochemical tests. The microstructures of the ultra-high-strength martensitic stainless steel consisted of some retained austenite and lath/plant martensite with the carbides distributed within the matrix and at the grain boundaries. Tempering of the steel for 4 h at various temperatures resulted in various carbide grain sizes and different amounts of the retained austenite. The results showed that larger carbide grains led to diminished corrosion resistance, whereas larger amounts of the retained austenite resulted in improved corrosion resistance. The steels exhibited good corrosion resistance in 0.017 mol/L NaCl solution and exhibited pitting corrosion in 0.17 mol/L Na Cl solution. The martensite and prior austenite crystal boundaries dissolved in solution with pH 1.     

Influence of carbon content and microstructure on corrosion behaviour of low alloy steels in a Cl containing environment

Corrosion behaviour of low alloy steels (A and B) with different carbon content was studied by a salt fog test and an outdoor test. A commercial weathering steel 09CuPCrNi was used for comparison. The corrosion resistance of steels A and B with homogeneous microstructures was better than that of the commercial weathering steel 09CuPCrNi in the salt fog test. Steel A with an ultra-low-carbon content had far less weathering resistance than the other steels in the outdoor test. Selective corrosion of large pearlite produces stress in initial corrosion product films. Uniform corrosion product films with few cracks tend to form on homogeneous microstructures such as ferrite and bainite, and this is advantageous for the formation of a compact rust layer in the initial stage of atmospheric corrosion. However, uniform microstructures will result in over even interfaces between rust layers and bases, which will lead to frequent peeling of rust layers from bases because stress is induced by large temperature fluctuations and wet-dry alternations. Protection of the rust layer on a low alloy steel is dependent on the rust density and the bonding performance of the rust-base rather than the proportion of the rust phase in the initial stage of atmospheric corrosion. These results indicate that homogenous microstructures, proper amounts of carbon content and fine carbon-rich phases that are produced by appropriate processes are beneficial for the corrosion resistance of steels.     

Effect of nitrogen on microstructure and corrosion resistance of Cr15 super martensitic stainless steel

ABSTRACT

To investigate the influence of nitrogen on structure and corrosion resistance of Cr15 super martensitic stainless steels (SMSS), two types (N-free and N-0.12%) of specimens were quenched at 1050°C and tempered at different temperatures, and then, optical microscope, transmission electron microscopy, X-ray diffraction, potentiodynamic polarisation, immersion experiments and Kelvin Probe Force Microscope were used to characterize its microstructures and corrosion properties. The experimental results show that the microstructure in the N-free Cr15 super martensitic stainless steel is a biphasic tissue with alternating martensite and austenite distribution while quenched at 1050°C and tempered between 600 and 700°C. The nitrogen addition increases the content of austenite, and changes the austenite morphology significantly into the coarse block and strip distribution. What’s more, micro-galvanic corrosion is formed between austenite and martensite, which deteriorates the corrosion resistance of the SMSS.     

Effect of microstructure on the sulphide stress cracking susceptibility of a high strength pipeline steel

The sulphide stress cracking (SSC) susceptibility of a newly developed high strength microalloyed steel with three different microstructures has been evaluated using the slow strain rate testing (SSRT) technique. Studies were complemented with potentiodynamic polarization curves and hydrogen permeation measurements. Material included a C–Mn steel having Ni, Cu, and Mo as main microalloying elements with three microstructures: martensitic, ferritic and ferritic + bainitic. Testing temperatures included 25, 50, 70 and 90 °C. Detailed SEM observations of the microstructure and fracture surfaces were done to identify possible degradation mechanisms. The results showed that in all cases, the corrosion rate, number of hydrogen atoms at the surface and the percentage reduction in area increased with temperature. The steel with a martensitic microstructure had the highest SSC susceptibility at all temperatures, whereas the ferritic steels were susceptible only at 25 °C, and the most likely mechanism is hydrogen embrittlement assisted by anodic dissolution.     

Influence of chromium,molybdenum and cobalt on the corrosion behaviour of high carbon steels in dependence of heat treatment

High chromium martensitic steels are designed to provide high corrosion resistance in combination with high strength. Some of these steel grades contain primary carbides for improving the wear resistance, e.g. the steel 440C. The present paper mainly deals with the effect of chemical composition and microstructure on the corrosion properties. Different experimental alloys were produced in the shape of small ingots. The influence of the alloying elements chromium, molybdenum, cobalt, and carbon on the corrosion properties was studied. The results can be summarized as follows: Chromium and molybdenum improve the corrosion resistance, however, only the content of these elements in solid solution in the steel matrix is effective. In case of cobalt the corrosion resistance decreases. The reason is the interaction between cobalt and carbon and its effect on the chromium content in the steel matrix. The calculated pitting resistant equivalent number of high chromium martensitic steels is only limited valid, because there is a major effect of carbide precipitation on the corrosion behaviour. Further investigations were focused on the heat treatment. Especially the effect of the tempering temperature of these steels was studied. The tempering temperature is most relevant for secondary hardening carbide precipitation, which lowers the chromium content of the matrix with detrimental influence on the corrosion properties. The carbide precipitation and chromium distribution was characterized by means of energy filtered transmission electron microscopy (EFTEM).     

Corrosion of two kinds of cast steels containing chromium in hot concentrated alkaline

A typical hot concentrated alkaline corrosion environment exists in alumina metallurgical industry, so that steel materials with outstanding alkaline corrosion resistance are strongly demanded for its processing equipment. In this paper, the corrosion resistance of two kinds of martensitic cast steels containing chromium in static 303g/L NaOH alkaline solution at 85℃ was studied through polarization and potential-time curves, corrosion weight loss and corrosion morphology analysis. Experimental results showed that protection effect by passive film of cast steel containing Cr was temporary. The low carbon steel without Cr content also exhibited chemical passivity in the same solution. The corrosion mode of the tested Cr-containing cast steel was composed of active dissolving corrosion and caustic embrittlement cracking. Dissolving corrosion was the primary mechanism for the induced weight loss, while severe caustic embrittlement cracking was secondary. With the increase of chromium content in the cast steel, the tendency of the caustic embrittlement cracking decreased, while the active dissolving corrosion increased.     

Anfälligkeit gewindeformender Schrauben aus korrosionsbeständigen Stählen gegenüber Spannungsrisskorrosion

Susceptibility of thread‐forming screws made from stainless steels with relation to stress corrosion cracking Thread‐forming screws, manufactured from martensitic and austenitic stainless steels, were tested concerning their susceptibility with relation to stress corrosion cracking. Based as closely on application usage as possible, testing comprised using the fasteners to clamp steel sheets of different material types at changing corrosion conditions according to DIN 50021‐SS and DIN 50018‐KWF 2,0S. During the exposure until 90% of the martensitic drilling screws had failed due to hydrogen‐induced stress corrosion cracking. Such fasteners represent a safety risk in building practice, even if corrosion resistance requirements are minimal. The screws made of austenitic materials bore the identical test conditions without cracking.