INVESTIGATION OF INFLUENCE OF HYDROGEN ATTACK ON FATIGUE PROPERTIES OF PRESSURE VESSEL STEELS

1.IntroductionLowalloysteelsexposedtohydrogenatmoderatepressuresandtemperaturessufferalossinmechanicalandfatigueproperties.Thisphenomenon,calledhydrogenattack(HA)['],isduetothemethanegeneratedbychemicalreactioll:abC. 2H2~ac ACHe.Methaneformationmayoccureitheratafreesurface(surfacedecarburization)oratinternalsiteinthemetal(internaldecarburiatioll)suchasgrainboundariesanddefects.Internalmethaneisunabletodiffuseoutofthesteel,anditmaybllildupintheinterllalvoidsandgrainboundaries,growandcoalesce…     

添加Mo-B对超高强度管线钢相变组织的影响

在超高强度管线钢中添加不同数量的Mo与B,研究了不同Mo/B(s)比(B(s)为酸溶硼)的管线钢的组织相变特性和显微硬度的变化.结果表明,Mo-B(s)共同作用有利于提高钢的淬透性,增加组织中的下贝氏体含量,提高该钢的显微硬度,其共同作用的效果优于两者单独作用之和.在Mo-B(s)共同作用下,钢中的Mo/B(s)比RMo/B(s)=200时,该钢得到最佳的组织和最高的显微硬度.对有关作用机理进行了讨论.     

氮-甲醇保护气氛对45CrNiMoVA高强钢氢致断裂的影响

采用化学成分分析、断口形貌分析、显微组织分析、力学性能测试等方法对断裂后的45CrNiMoVA钢制高强扭杆进行了分析,并开展了氮-甲醇保护气氛下零件表面氢含量的测定,探讨了氢致缺陷对高强钢零件扭转疲劳的影响机理,提出了防止渗氢的预防措施,并进行了试验验证。结果表明,在氮-甲醇保护气氛下进行高强钢加热可导致氢的侵入,产生氢脆现象,影响高强钢零件扭转疲劳寿命。将氮-甲醇可控气氛更改为氮气保护,配合花键部位人工涂刷防脱碳涂料可有效防止表面氧化脱碳。采用改进工艺,高强钢扭杆未发生断裂现象。     

1.25Cr-0.5Mo钢热处理后的组织与力学性能

利用光学显微镜、扫描电镜和力学试验机研究了3种正火组织的1.25Cr-0.5Mo钢在回火和模拟焊后热处理过程中的组织和力学性能演变。结果表明:1.25Cr-0.5Mo钢粗大的铁素体+珠光体组织经模拟焊后热处理,大量粗大的碳化物沿晶界析出,显著降低钢的冲击性能,铁素体晶内细小弥散碳化物的析出略微改善了钢的强度;贝氏体组织中的贝氏体铁素体板条宽化和碳化物粗化降低了钢的强度,但对冲击性能影响不大;1.25Cr-0.5Mo钢的综合力学性能随着铁素体组织含量的增加而变差,当铁素体组织的含量高于38％时,钢板的力学性能将难以满足要求。     

热成形钢的脱碳影响因素分析

采用Gleeble-3500热力模拟试验机模拟热成形工艺过程,分析了不同加热温度(890～950℃)、保温时间(240～1000 s)、化学成分(T1500HS和CR1300/2000HS钢两种不同材料)及不同表面涂油(有油和无油)对冷轧热成形钢表面脱碳的影响.结果表明,在正常加热温度(910～950℃)、保温时间(2...     

不锈钢的大气腐蚀研究—12年暴露试验总结

总结了５种不锈钢在我国７个试验点的１２年大气腐蚀试验结果,材料中包括了最常用的不锈钢,环境中包括了亚热带,温带,工业性,海洋性,干燥环境及湿热环境等各种典型环境。不锈钢在大气中是耐蚀的。当含Ｃｒ量达到１８％以上时耐蚀性很好,钼能明显提高不锈钢的耐蚀性,超低碳也能提高其耐蚀性。     

电子探针面分析法测定钢的脱碳层深度

提出钢表层脱碳层深度测定的一种新方法,即电子探针面分析法。对热轧态高碳工具钢75Cr1、淬火齿轮钢20CrMnTi、冷轧退火低碳车厢板SH1100钢3个典型钢种完成脱碳层深度的测定试验,结果表明:对于珠光体-铁素体型中高碳钢的脱碳层深度测定,金相法测定值是电子探针面分析法测定值的77%左右;对于淬回火钢的脱碳层深度测定,电子探针面分析法的测量精度在10 μm以下,约是显微硬度法测量精度的十分之一;对于脱碳层深度不易准确测定的低碳钢,电子探针面分析法通过较大区域范围的平均碳含量变化曲线来测定脱碳层深度,测量结果准确。电子探针面分析法在脱碳层深度测定方面具有钢种组织状态不限、试样形状不限、数据统计性好、测量精度高、易操作等优势,可在业内大力推广。     

30CrNiMo超高强度钢板硬度不合格原因分析

通过对30CrNiMo超高强度钢板进行化学成分分析、金相高倍组织观察、力学性能和硬度测试以及热处理等一系列检测试验，结合钢板基材的退火热处理过程对成品钢板硬度不合格的原因进行了分析。分析结果表明：钢板基材采用氢气还原气氛进行高温长时间退火处理，在钢板边缘形成较深的表面和内部脱碳，是导致成品钢板硬度不合格的主要原因。     

Mo含量对不锈钢在环烷酸介质中腐蚀与中蚀的影响

制备了以316L为基的不同Mo含量的不锈钢，在精制环烷酸和含环烷酸的油中分别进行了静态和冲蚀实验，结果表明，316L基不锈钢在高温环烷酸介质中具有很好的抗腐蚀和冲蚀性能，随Mo含量增加，不锈钢的环烷酸腐蚀速率和冲刷腐蚀速率均逐渐减小，流体冲刷明显加剧不锈钢的环烷酸腐蚀，综合考虑不锈钢的抗蚀性能及机械性能，在设计抗环烷酸腐蚀和冲蚀的新型不锈钢时，Mo含量应保持在5%（质量分数）左右。     

4Cr16Mo�ֺ�4Cr16MoN�ֵ��������֯����

 4Cr16MoN钢是一种新型钢种,它的平衡相图和CCT曲线可以为试验钢的大生产和热处理提供依据,为了和4Cr16Mo钢进行对比,通过J Matpro模拟软件计算4Cr16MoN和4Cr16Mo钢的平衡相图,再利用DIL805A热膨胀相变仪测定其CCT曲线,试验条件是1 050 ℃奥氏体化,保温5 min,按照10、3、12、1、05、01、008、005、003 ℃/S等不同冷速冷却。试验结果表明：在两种试验钢计算的平衡相图中,高温区很宽的温度范围内保持单相奥氏体,未出现δ铁素体相;两种试验钢CCT曲线都有独立的珠光体和贝氏体转变区域,4Cr16MoN钢的P临界冷速和B临界冷速分别是01 ℃/s和12 ℃/s,而4Cr16Mo钢的P临界冷速和B临界冷速分别小于003 ℃/s和3 ℃/s。     

氢对含(Ti,Mo)C析出相的调质钢的超高周疲劳性能的影响

研究了未溶和回火析出的(Ti,Mo)C析出相的氢陷阱作用对调质铬钼钢的超高周疲劳性能的影响.结果表明:球形未溶(Ti,Mo)C析出相的氢解吸附激活能为142.6 kJ/mol,这种强氢陷阱在电化学充氢条件下不会捕获氢;细小的回火(Ti,Mo)C析出相是有效的氢陷阱,其捕获的氢的解吸附激活能为17.0kJ/mol,这部分...     

Influence of tempering treatment on microstructure and pitting corrosion resistance of a new super ferritic–martensitic–austenitic stainless steels with 17%Cr

Supermartensitic stainless steels (SMSSs) allow high mechanical strength with better corrosion resistance and toughness than conventional martensitic stainless steels. The SMSS steels with 12–13%Cr have been studied and applied in the oil and gas offshore production. The increase of Cr content, and the addition of Mo and W is now being investigated to increase mechanical and pitting corrosion resistance. In this work, a new 17%Cr steel, with Mo and W additions was studied. Depending on the final tempering treatment, the steel has a complex microstructure of austenite, ferrite, martensite and precipitates. The pitting corrosion resistance also depends on the microstructure produced by tempering. It was found that the pitting potential slightly decreases with the increase of tempering temperature and is further decreased by the double-tempering treatment. The pits initiate and grow preferentially in the martensite or tempered martensite islands, due to the lower Cr, Mo and W contents of these areas.     

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.     

Magnetic Barkhausen emissions and microstructural degradation study in 1.25 Cr–0.50 Mo steel during high temperature exposure

Low alloy steel such as 1.25Cr–0.50 Mo steel is widely used in thermal power plants, petro-chemical industries and fertiliser plants. In recent years considerable attention has been paid to estimate the remaining life of a service-exposed component for effective utilising such components beyond the design life. Although these steels are heat treated to obtain a stable microstructure, microstructural changes such as carbide coarsening, increasing inter lamella spacing, formation of more stable carbides, dissolution of carbides, etc. take place due to prolong service exposure at elevated temperatures. This paper describes the systematic investigation on microstructural changes, changes of composition on carbides and their effect on the magnetic Barkhausen emission parameters. The materials were heat-treated at different temperatures (500–700 °C) for various duration of time (0–1000 h) to get wide variation in microstructure. RMS voltage and pulse height distributions of Barkhausen emissions signal were calculated. A good correlation between MBE parameters and microstructural changes has been found. The study will be useful for the non-destructive evaluation of microstructural degradation of in-service 1.25Cr–0.5Mo steel structure.     

THE EFFECT OF W ON THE REPASSIVATION BEHAVIOR OF Ni-ADDED STAINLESS STEELS

The effect of W on the repassivation behavior of Ni-added stainless steels was investigated with respect to the repassivation rate and the SCC susceptibility. It was found that more stable passive film was formed on the W-modified stainless steels than that of steels without W-modification, and the repassivation rate was faster for W-modified stainless steels in acidic chloride solution （0.5M H2SO4＋3.5% Cl^-）. In neutral chloride solution （1M MgCl2）, there were no significant differences on both passivation properties and the repassivation rates for duplex stainless steels, while W-modified austenite stainless steel showed faster repassivation rate. The SCC tests verified that W-modified Ni-added stainless steels exhibited better SCC resistance than steels without W in chloride solution. Moreover, W-modification in higher Ni-added stainless steels exhibited more remarkable SCC resistance than steels with lower Ni content in chloride solution.     

不锈钢海水潮汐区16年腐蚀行为

在青岛、厦门和榆林3个试验站的潮汐区对5种不锈钢暴露16年，总结其腐蚀行为和规律。在潮汐区暴露的不锈钢受点蚀和缝隙腐蚀破坏。不锈钢在潮汐区暴露1至4年的点蚀速度较大，以后点蚀速度减慢。耐点蚀性能较好的不锈钢，耐缝隙腐蚀性能也较好。不锈钢在潮汐区的腐蚀随暴露地点的海水温度升高而加重。增加Cr含量、添加Mo能明显提高不锈钢在潮汐区的耐蚀性。Ni对提高的耐蚀性有效，但影响效果较小。海生物污损能引起不锈钢的局部腐蚀，它对不锈钢在潮汐区的腐蚀有显著影响。     

回火马氏体钢中氢的扩散行为及其氢脆敏感性

通过TDS方法研究了氢在18Cr2Ni4W和25CrNi2MoVNb两种低温回火马氏体钢中的扩散行为,同时结合慢应变速率拉伸实验研究了这两种马氏体钢的氢脆敏感性。结果表明,与18Cr2Ni4W钢相比,25CrNi2MoVNb钢因碳含量较高和晶粒显著细化作用使抗拉强度从1300 MPa级提高到了1500 MPa级后,其氢脆敏感性也明显增加。通过试样充氢后放置试验,测定氢在25CrNi2MoVNb钢和18Cr2Ni4WA钢中的扩散系数分别为7.87×10-7 cm2/s和3.99×10-7 cm2/s。可见,氢在25CrNi2MoVNb钢中更容易扩散,因而在充入相同可扩散氢时,25CrNi2MoVNb钢性能损失更大。     

氮改善00Cr18Ni5Mo3Si2双相不锈钢应力腐蚀破裂性能的机制

用 AES 分析了含氮双相不锈钢在30%MgCl_2(沸)溶液中浸泡后的表面膜。结果表明,氮在表面膜中富集.氮量越高,富集的量越多。钼和镍的富集均与钢中的氮含量有关.钼的富集要求氮含量在0.11%以上,镍的富集要求氮含量在0.073%以上,氮和钼的联合作用使钢表面膜的钝化能力得到加强。恒电位浸泡实验表明,阳极极化增厚了表面膜,降低了氮的作用。在0.5V NaCl(50℃,pH=7)溶液中,由模拟闭塞区实验得出:氮对裂缝尖端的化学状态无明显影响,闭塞区内未发现 NH_4~+。透射电镜(TEM)分析表明,氮量提高使位错由层状结构变为网状结构,增加了层错能。     

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。     

Origin and elimination of hydrogen in basic open-hearth steels

The variation in hydrogen content of basic open-hearth steels during refining and the effect of changing from steam to air atomization were studied. The water content of the furnace atmosphere, the slag basicity, and the degree of oxidation of the slag-metal system largely control the hydrogen in the steel.