显微组织和夹杂物对12Cr2AlMoV钢抗硫化物应力腐蚀开裂的影响

作者研究了钢中显徽组织、流含量及夹杂物对低合金钢12Cr2AlMoV抗硫化物应力腐蚀开裂(SSCC)性能的影响。 结果表明,12Cr2AlMoV钢的抗SSCC的能力随着微显组织的变化而变化。在相同温度下处理的正火回火索氏体加铁素体组织抗SSCC能力比淬火回火的索氏体组织好。特定的硬度规定并不能保证良好的抗SSCC性能,其性能主要取决于显微组织。显微组织和钢中的氢扩散系数D有着较密切的联系。钢中硫含量和夹杂物的增加,可使钢的抗硫性能下降。除硫化锰夹杂外,其它脆性夹杂物也可诱发氢致开裂从而引起SSCC。     

Wasserstoffinduzierte Spannungsrißkorrosion an unverzinkten und verzinkten Baustählen

Hydrogen induced stress corrosion cracking of non galvanized and galvanized construction steels The processes of atmospheric corrosion and corrosion in collected water which may lead to hydrogen induced stress corrosion cracking of high-strength reinforcing steels in casing tubes before injection with concrete are discussed. Hydrogen uptake during corrosion occurs in weakly acid solutions as well as in neutral or alkaline aqueous solutions. The hydrogen uptake by proton discharge in acid solutions decreases with increasing pH of the electrolyte. Hydrogen can also be absorbed in neutral to weakly alkaline solutions if steels are plastically deformed and water reacts with the fresh iron surface. In alkaline solutions, hydrogen uptake is possible if, at the generally passivated steel surface, localized corrosion (pitting or crevice corrosion), local galvanic cells and a sufficient decrease in the pH of the pit electrolyte occurs. In the case of galvanized steels with damaged zinc layers, hydrogen uptake may result from the cathodic polarization of the free steel surface by zinc dissolution. The absorbed hydrogen interacts with the microstructure of the steels and weakens the bonds between the iron atoms. The influence of the microstructure of high-strength steels on the fracture behaviour is discussed on the basic of the so-called decohesion theory.     

12.9级矿车制动盘螺栓断裂失效分析

材料为SCM435钢的12.9级六角头螺栓服役42 h后发生断裂。为了揭示螺栓断裂的原因,采用光电直读光谱仪、光学显微镜、扫描电镜和测氢仪对断裂的螺栓进行了化学成分、宏观和微观等分析。研究结果表明,螺栓断裂是氢致延迟断裂。     

氢在钢的硫化物应力腐蚀破裂中的作用

本文研究了12MnMoVNbTi低合金钢在饱和H_3S溶液中的极化和应力腐蚀行为,并与电解充氢条件下的应力破裂行为进行了对比。证明钢中Mo、Nb含量的变化与热处理条件的不同对其一般腐蚀行为影响很小,但能显著改变其抗应力腐蚀性能,12MnMoVNbTi钢在H_2S介质中的应力腐蚀破裂行为与它们在充氢条件下的应力破裂行为非常类似,显示其应力腐蚀破裂的实质是氢脆。充氢条件下应力弛豫和恒载荷拉伸试验结果表明,氢有引起钢的软化和硬化的双重作用。由于氢的进入所产生的软化作用使钢在屈服强度以下发生塑性变形,但随后的硬化过程又使变形速度逐步减慢。这种由氢的作用引起的在较低应力下发生的塑性变形过程并不直接导致断裂,但塑性变形行为和氢应力破裂行为之间的关系表明,这种变形过程中的位错运动能够帮助氢的移动和向塑变区及裂纹尖端集中,促进氢脆断裂。     

Cold cracking studies on low alloy steel weldments: effect of filler metal composition

Abstract

The resistance to hydrogen cracking of Cr - Mo, Ni - Cr - Mo and Si - Mn steels which are employed in armoured vehicle construction was evaluated under implant test conditions. Austenitic stainless steel filler (AWS E312), which is reported to be resistant to hydrogen assisted cracking, was used to study the cracking tendency of all the three steels. Four other fillers, namely a nickel based filler (ENiCrFe-3), a low carbon, low alloy steel, a mild steel (AWS E6013) and a matching filler for Cr - Mo, were employed to evaluate their relative cracking tendency. Cr - Mo and Ni - Cr - Mo steels exhibited high cracking tendency while Si - Mn steel was resistant to cracking with the E312 filler. Cr - Mo steel was resistant to cracking with the nickel based filler, the low carbon, low alloy steel and the matching filler. The observed cracking tendency of the steels is linked to a susceptible interface/fusion boundary microstructure.     

Einflußgrößen der H-induzierten Spannungsrißkorrosion bei niedriglegierten Stählen

Parameters influencing the hydrogen-induced stress corrosion cracking of low alloy steels Wet H₂S corrosion of steel leads to surface blistering, internal cracking at sharp edged inclusions (HIC), and in stressed specimens to transgranular micro cracks transversal to the main stress. The latter grows to SCC. HIC resistant material displays high purity of non-metallic inclusions. The critical stress level for SCC of lien pipe steels with yield strengths up to 600 N/mm² is proportional to the yield strength. In H²S containing media different grades of low alloy and rolled steels show no correlation between life time and yield strength. In general, the susceptibility for H-induced SCC increases with decreasing pH and with cathodic polarisation, whereas the temperature dependence displays a minium of life time at 20°C.     

Assessment of test methods for evaluation stress corrosion cracking susceptibility of prestressing steels

Prestressing steels can be exposed in prestressed concrete structures in construction stage (ungrouted duct) to environmental conditions causing formation and growth of hydrogen induced cracks with brittle fracture of the steel. The risk of this hydrogen induced stress corrosion cracking can be minimized by appropriate treatment, but there is a requirement for construction to approve only prestressing steel having no enhanced susceptibility to stress corrosion cracking. The paper describes the historical development of the different test methods proposed in the past and gives an overview on the general requirements for a suitable test method to assess the hydrogen‐induced stress corrosion susceptibility of prestressing steels. Since 1982, based on investigations on construction sites and transfer of the results into laboratory tests, a test method is available enabling realistic estimation of suitable application possibilities of prestressing steels. This so called DIBt‐test is approved to distinguish between prestressing steels susceptible to hydrogen induced stress corrosion cracking and those suitable and therefore approvable steels at practical environmental conditions. Furthermore the test enables estimation of corrosion risk for newly developed prestressing steels with higher strength.     

Hydrogen-assisted failure in a twinning-induced plasticity steel studied under in situ hydrogen charging by electron channeling contrast imaging

We investigated the hydrogen embrittlement of a Fe–18Mn–1.2%C (wt.%) twinning-induced plasticity steel, focusing on the influence of deformation twins on hydrogen-assisted cracking. A tensile test under ongoing hydrogen charging was performed at low strain rate (1.7 × 10^?6 s^?1) to observe hydrogen-assisted cracking and crack propagation. Hydrogen-stimulated cracks and deformation twins were observed by electron channeling contrast imaging. We made the surprising observation that hydrogen-assisted cracking was initiated both at grain boundaries and also at deformation twins. Also, crack propagation occurred along both types of interfaces. Deformation twins were shown to assist intergranular cracking and crack propagation. The stress concentration at the tip of the deformation twins is suggested to play an important role in the hydrogen embrittlement of the Fe–Mn–C twining-induced plasticity steel.     

一种用于显示中高强度钢晶粒的方法

中高强度钢随着碳含量的逐渐增加,组织愈发细小,通过直接腐蚀等传统方法得到的晶界往往比较模糊。为了能够清晰地显示中高强度钢的晶粒度,利用其具有氢脆敏感性以及氢脆易于产生沿晶断裂形貌的特点,提出了一种晶粒度检测方法。通过对 55SiCr弹簧钢和 440冷墩钢分别使用直接腐蚀、电子背散射法（EBSD）与氢致开裂断口法显示晶界,对比可以发现在中高强度钢的晶粒度检测中,氢致开裂断口法显示的晶界更为清晰,评定的结果更加准确。     

夹杂物对X120管线钢氢致开裂的影响

研究了X120管线实验钢的抗H_2S氢致裂纹敏感性。用多功能金相显微镜对X120管线实验钢非金属夹杂物进行颗粒度分析,用场发射扫描电子显微镜(SEM)及能谱仪(EDS)观察和分析裂纹形貌和裂纹内夹杂物。结果表明:X120管线实验钢氢致开裂一般都从非金属夹杂物处萌生扩展,并互相交叉连接;实验钢中B类夹杂物较D类夹杂物易于形成长条型裂纹,且B类夹杂物级别越高,其HIC敏感性越大;X120管线钢中S、Al含量越高,其夹杂物级别越高,非金属夹杂物数量越多,氢致开裂敏感性也越大。     

热处理对车轮钢中夹杂物的形态和分布的影响

通过金相显微镜、扫描电镜对车轮钢（CL50）铸态/热轧态和热处理态组织中夹杂物的形态分布进行研究,并利用能谱对夹杂进行成分分析。结果表明,在S含量极低的情况下,CL50车轮钢中氧化物夹杂主要呈球形或多边形,随机分布,在轧制过程中不发生变形;增大S含量,铸态组织中开始出现球状、串珠状以及条状MnS-氧化物复合夹杂物,且有在晶界聚集的趋势,主要分布于网状铁素体或者孤岛铁素体中;热处理后夹杂物则分布于网状铁素体中,说明夹杂物在一定程度上促进铁素体的形核。在890℃热处理过程中夹杂物形态和分布没有明显变化。     

Hydrogen Damage in Superaustenitic 904L Stainless Steels

In this work, results on the influence of hydrogen on corrosion resistance and of hydrogen embrittlement of 904L superaustenitic stainless steel were investigated. The cracking behavior was studied by performing a slow strain rate test in synthetic seawater under varying cathodic polarization conditions. The results showed that the steel’s plasticity varied with the applied cathodic current density. Significant reductions in ductility were found, indicating its susceptibility to hydrogen-assisted fracture at current density of 20 mA/cm². Fractographical examinations showed that an increase in hydrogenation current density causes a stepwise decrease in ductility on the fracture surface. The effect of hydrogen on passivity and on pitting corrosion resistance was qualified with the polarization curves registered in synthetic seawater. The conclusion is that hydrogen may affect the passive film stability and thus may decrease the corrosion resistance of the studied steel. The presence of hydrogen increases corrosion current density and decreases the potential of the film breakdown. It was also found that the degree of the susceptibility to hydrogen degradation was dependent on the hydrogen charging conditions.     

Inclusion‐involved fatigue cracking in high temperature water

The nonmetallic inclusions in low‐alloy pressure vessel steel A533B were carefully examined and the low cycle fatigue (LCF) behavior of the steel was investigated in 288°C air and water. Much attention was paid to the roles of inclusions on fatigue crack initiation and propagation in high temperature water. Three types of inclusions were observed in the steel, consisting of isolated or clustered sulfide inclusions, duplex oxide‐sulfide inclusions and isolated oxide inclusions. In high temperature air, fatigue cracks initiated predominantly from subsurface inclusions. In high temperature water, however, fatigue cracks initiated primarily at corrosion pits on the specimen surfaces resulted mainly from the dissolution of large or clustered sulfide inclusions. The subsurface and bulk inclusions also contributed to the fatigue cracking in high temperature water. Possible influence of the above three types of inclusions on environmentally assisted cracking (EAC) was evaluated. The fatigue fractographic features suggested a synergism between sulfide inclusions and hydrogen‐induced cracking dominate the present EAC in high temperature water.     

Effect of hydrogen on the properties and fracture characteristics of TRIP 800 steels

The paper describes effect of hydrogen on the properties and fracture characteristics of two variants of TRIP 800 C–Mn–Si steels. The effect of hydrogen was studied by means of tensile tests on specimens previously charged by hydrogen. Hydrogen provoked embrittlement in both variants but only for very high hydrogen content. Hydrogen embrittlement manifested itself mainly by a loss of plasticity. Both steel variants were able to absorb a large amount of hydrogen, up to 50 ppm. Concerning fractographic characteristics, steels containing higher hydrogen content displayed transgranular cleavage fracture. In exceptional cases, an irreversible embrittlement was revealed initiating on non-metallic inclusions.     

Wasserstoffinduzierte Korrosion von niedriglegierten Stählen in wäßrigen Medien

Hydrogen induced corrosion of low alloy steels in hydrous media The absorption of hydrogen from media can lead to cracking in steels with a ferritic structure. The interaction of absorbed hydrogen and steel is governed by the hydrogen activity and by stress- and structure-dependent threshold values. Different types of hydrogen-induced corrosion are illustrated by means of tests performed on lowalloy structural steels. Surface blistering and internal cracking can occur on the one hand without external stresses. In the case of hydrogen-induced stress corrosion cracking on the other hand a differentiation is made between corrosion systems in which constant loading displays already cracking and systems in which the cracking is tied to slow strain rates within a critical range.     

Influence of welding consumables on high cycle fatigue life of flux cored Arc welded high strength,quenched and tempered steel joints

Quenched and tempered (Q&T) steels are prone to hydrogen induced cracking after welding. Austenitic stainless steel (ASS) welding consumables are traditionally used for welding of high hardness, Q&T steels as they have higher solubility for hydrogen in the austenitic phase. The use of stainless steel consumables for a non stainless steel base metal is not economical. Hence, in the present work, an attempt was made to explore alternate consumables for welding Q&T steels. Flux cored arc welding process was used to fabricate the joints using austenitic stainless steel and low hydrogen ferritic steel consumables. The joints fabricated using low hydrogen ferritic steel consumables exhibited superior fatigue performances than the joints fabricated using ASS consumables.     

Failure mechanisms of high strength steels in bicarbonate solutions under anodic polarization

High strength steels used in prestressing concrete structures are not exempt from the effects induced by corrosion on the normal concrete reinforcement. Carbonation of surrounding concrete or mortar is not unlikely for prestressing tendons and strands. Moreover, these steels undergo to brittle fracture as a consequence of stress corrosion cracking phenomena. To evaluate if concrete carbonation can promote this kind of failure, constant load tests in bicarbonate aqueous solutions under anodic polarization were carried out on high strength steel wires. Microscopic examination pointed out that the wires exhibited a brittle fracture mode, while its natural feature is ductile, as indicated by air testing. Failure mechanism was evaluated by a fracture mechanic approach. Cracks initiation was attributed to an anodic dissolution mechanism, while its propagation, interpreted by means of the surface mobility theory, was related to interaction between hydrogen atoms and magnetite at a crack tip.     

夹杂物对工程机械用钢Q345FCA疲劳寿命的影响

采用QBWP-6000J型简支梁旋转弯曲疲劳试验机测定了高疲劳寿命工程机械用钢Q345FCA的疲劳寿命;采用扫描电镜(SEM)对疲劳断口形貌进行了观察,并用附带的能谱仪(EDS)寻找断口上的夹杂物;借助夹杂物自动分析系统对钢中的夹杂物进行了分析。通过对试验数据的分析,计算得出了Q345FCA钢和Q345钢夹杂物的表面临界尺寸、次表面临界尺寸和内部临界尺寸。结果表明,Q345FCA钢的疲劳极限为273 MPa,Q345钢的疲劳极限为266 MPa。Q345FCA钢和Q345钢中夹杂物尺寸均小于临界夹杂物尺寸,且断口形貌显示所有疲劳断裂均不是由夹杂物所引起,夹杂物不是疲劳源。     

Effect of Welding Consumables on Fatigue Performance of Shielded Metal Arc Welded High Strength, Q&T Steel Joints

Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to their high strength-to-weight ratio and high hardness. These steels are prone to hydrogen-induced cracking in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel consumables to weld the above steel was the only remedy because of higher solubility for hydrogen in austenitic phase. Recent studies proved that high nickel steel and low hydrogen ferritic steel consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the effect of welding consumables on high cycle fatigue properties of high strength, Q&T steel joints. Three different consumables namely (i) austenitic stainless steel, (ii) low hydrogen ferritic steel, and (iii) high nickel steel have been used to fabricate the joints by shielded metal arc (SMAW) welding process. The joints fabricated using low hydrogen ferritic steel electrodes showed superior fatigue properties than other joints.     

X80 管线钢在酸性环境下的氢致开裂行为研究

目的研究X80管线钢在我国典型酸性环境(鹰潭土壤模拟溶液)下的氢致开裂行为。方法采用电化学动电位扫描技术、慢应变速率拉伸实验和扫描电镜技术,分析氢在X80管线钢中的渗透行为、材料的放氢行为、电化学充氢对材料拉伸性能的影响以及材料断口的形貌。结果通过氢渗透实验测得,在室温下,氢在X80管线钢中的的氢扩散通量J∞=7.31×10-11mol/(cm2·s),有效扩散系数Deff=5.36×10-8cm2/s,可扩散氢浓度C0=7.64×10-5mol/cm3。钢中的氧化铝类非金属夹杂及表面点蚀坑促进了氢致裂纹的萌生,充氢后试样发生穿晶断裂。随着充氢时间的增加,断口由韧性断裂转变为脆性断裂,氢致开裂敏感性增高。结论 X80管线钢在我国典型酸性环境下(鹰潭土壤模拟溶液)具有较高的氢致开裂敏感性。