Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

Abstract

The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.     

Hydrogen embrittlement susceptibility of laser-hardened 4140 steel

Slow strain rate tensile (SSRT) tests were performed to investigate the susceptibility to hydrogen embrittlement of laser-hardened AISI 4140 specimens in air, gaseous hydrogen and saturated H₂S solution. Experimental results indicated that round bar specimens with two parallel hardened bands on opposite sides along the loading axis (i.e. the PH specimens), exhibited a huge reduction in tensile ductility for all test environments. While circular-hardened (CH) specimens with 1 mm hardened depth and 6 mm wide within the gauge length were resistant to gaseous hydrogen embrittlement. However, fully hardened CH specimens became susceptible to hydrogen embrittlement for testing in air at a lower strain rate. The strength of CH specimens increased with decreasing the depth of hardened zones in a saturated H₂S solution. The premature failure of hardened zones in a susceptible environment caused the formation of brittle intergranular fracture and the decrease in tensile ductility.     

1 000 MPa级高强钢焊接件的氢脆敏感性研究

利用氢渗透试验、慢应变速率拉伸试验(SSRT)研究了1 000MPa级高强钢(HSS)焊接件在海水中的氢渗透行为及其应力腐蚀敏感性,结合SEM观察了试样的断口特征,并利用电化学试验和显微组织观察分析了焊接件不同区域的氢脆特征。结果表明:相对于焊缝区(WM)和母材区(BM),热影响区(HAZ)的自腐蚀电位最负、析氢电位最正,更容易发生腐蚀和析氢行为。热影响区的氢扩散系数最大,具有较强的吸氢倾向。动态电化学充氢对高强钢焊接件的影响主要体现在对塑性的损减方面;随着极化电位的负移,高强钢焊接件的强度没有明显变化,但断面收缩率、断后延伸率均减小,断裂方式逐渐由韧性断裂变为解理断裂;当极化电位约为-930mV(vs SCE)时,高强钢焊接件的氢脆系数达25%;在不同充氢极化电位下,焊接件试样的断裂位置多在热影响区。     

Critical Assessment 35: Assessment of the intrinsic susceptibility to hydrogen embrittlement for qualification of steels

ABSTRACT

Exact simulations of engineering practice are often difficult to accomplish with test methods of materials performance against hydrogen embrittlement (HE). Instead, it is proposed that assessment of the intrinsic susceptibility to HE be adaptable to diverse usage environments and loading modes. This notion is based on recent findings concerning the predominant role of strain-induced vacancies and their involvement in characteristic features of HE such as microstructural effects and dependence on strain rates and temperatures. The function of hydrogen in enhancing the generation of strain-induced vacancies operates throughout the entire process of fracture, and the density of vacancies is detectable using hydrogen as a tracer. A method is proposed here for using as the parameter the difference in the amounts of tracer-hydrogen between specimens given cyclic stressing with and without hydrogen.     

Hydrogen embrittlement contributions to fatigue crack growth in a structural steel

The detrimental effects of a hydrogen atmosphere on the fatigue resistance of BS 4360 steel have been assessed by a comparison of crack growth rates in air and hydrogen at a low cycling frequency (0.1Hz), and at a number of temperature (25, 50 and 80 °C). The crack propagation rates in air are almost independent of temperature over this range, but those measured in hydrogen differ by more than an order of magnitude between 25 and 80 °C. The greatest enhancement is seen at 25 °C and at high values of ΔK, the maximum occurring between 40–45 MPa √m at each temperature. There is little hydrogen contribution to crack growth at values of ΔK below 20 MPa √m for R = 0.1.

The enhancement of crack growth rates is reflected by the presence of ‘quasi-cleavage’ facets on the fatigue fracture surfaces of specimens tested in hydrogen. These are most apparent where the greatest increases in growth rate are recorded. The facets show linear markings, which run both parallel and perpendicular to the direction of crack growth. The former are analogous to the ‘river’ lines noted on brittle cleavage facets, and reflect the propagation direction. The latter are more unusual, and indicate that facet formation by hydrogen embrittlement during fatigue is a step-wise process.     

海洋大气中SO2含量对16Mn钢腐蚀断裂及渗氢行为的影响

氢还原对钢材在大气腐蚀中的作用不可忽视,过去对其研究较少。采用电化学渗氢试验及慢应变速率拉伸方法研究了模拟海洋大气环境中SO2浓度对16Mn钢应力腐蚀断裂及氢渗透行为的影响。结果表明,随着SO2浓度的增大,试样断裂延伸率减小,断裂特征由塑性断裂逐渐转变为脆性断裂;随着SO2浓度的增大,氢渗透电流增大,SO2对氢渗透电流具有双重促进作用,第一个峰值的出现主要与SO2的酸性有关,第二个峰值的出现主要是由于酸的再生循环所致。     

海水中极化电位对X70钢氢脆敏感性的影响

为探索X70钢最大阴极保护电位,采用电化学测试和慢应变速率实验（SSRT）并结合断口扫描电镜观察,研究了低温低溶解氧和常温海水中阴极极化电位对X70钢氢脆敏感性的影响.结果表明：相对常温海水,X70钢在低温低溶解氧海水中的析氢电位正移;随阴极极化电位的负移,X70钢的最大抗拉强度、屈服强度增加且氢脆敏感性增加;在低温低...     

Hydrogen redistribution under stress-induced diffusion and corresponding fracture behaviour of a structural steel

ABSTRACT

Hydrogen redistribution under stress-induced hydrogen diffusion and corresponding fracture behaviour of a 960?MPa grade martensitic steel were studied. Slow strain rate tensile (SSRT) tests after hydrogen pre-charging were performed and the fracture surface was observed and analysed. The strain rate ranged from 10^?6 to 10^?4?s^?1. In the pre-charged sample with a certain hydrogen content of 0.62?ppm, hydrogen distribution was homogeneous before the SSRT test. After tensile testing, brittle fracture features appeared in the centre of the fracture surface, while ductile features appeared in the surrounding area. Brittle region size increased with the strain rate slowing down in the range from 10^?4 to 5?×?10^?6?s^?1, while it stabilised at the strain rate slower than 5?×?10^?6?s^?1. Relationship between the strain rate and the brittle region size was established and discussed based on the present data of hydrogen content in the material.

This paper is part of a thematic issue on Hydrogen in Metallic Alloys     

Effect of heat treatments on the hydrogen embrittlement susceptibility of API X-65 grade line-pipe steel

Delayed failure tests were carried out on hydrogen charged API X-65 grade line-pipe steel in as received (controlled rolled), normalized, and quenched and tempered conditions. The resistance to hydrogen embrittlement was found in the order of controlled rolled > quenched and tempered > normalized. The fracture mode in the hydrogen embrittled steel was ductile.     

介质及应变速率对10钢的氢脆敏感性的影响

本文研究了 10钢在 H2 SO4溶液和 Na Cl溶液中渗氢后 ,在不同应变速率下其氢脆敏感性 .结果表明 :在 H2 SO4溶液中渗氢后 ,10钢具有明显的氢脆特征 ,应变速率从 3.33× 10 -1.sec-1～ 3.33×10 -6 .sec-1范围内 ,截面收缩率Ψ从 35 .36%降至 18.35 % ;延伸率δ从 2 9.34 %降至 14 .95 % ,10钢显示出最大的氢脆敏感性     

拉深成形对于Q&P980高强钢氢致延迟断裂影响的实验研究

目的从整车厂应用的角度出发,基于拉深工艺,研究QP980高强钢的氢致延迟断裂敏感性。方法选取1.6 mm板厚的QP980高强钢,进行拉深系数为0.56和0.63的两种冲杯实验,以电化学充氢结合摄像头定时拍摄的方法,并结合ABAQUS软件计算杯口应力集中处的应力和应变。结果对于1.6 mm板厚的QP980高强钢,在拉深试样杯口边缘应力集中处,应力大致在900～1000 MPa范围,而应变大于等于0.32,则必然发生延迟开裂;若应变小于等于0.23,则延迟断裂敏感性较低。结论应力和应变同时影响高强钢的氢致延迟断裂敏感性,即对QP 980(1. 6 mm厚度)零件,当拉深边缘应变小于0.23,则该位置氢致延迟断裂可能性低;若应力集中处残余应力达到900 MPa以上,应变达到0.3以上,则该位置氢致延迟断裂敏感性高。此结论对工程应用判断拉深零件氢致延迟断裂有一定指导意义,     

The mechanism of hydrogen embrittlement: the stress interaction between a crack, a hydrogen cluster, and moving dislocations

Mechanisms of dissolvent anodic chemical reaction and hydrogen embrittlement have been proposed as stress corrosion cracking (SCC) mechanisms. The former is feasible for the case of plastic deformation dominant metals (low-yield stress), and the latter is for high-strength metals such as high-strength steels. However, in spite of low-yield stress, a discontinuous cleavage-like fracture is sometimes observed during SCC for ductile fcc alloys, which concerns the interaction between dislocations and the hydrogen cluster. The problem of when these mechanisms will be dominant remains. In this paper, the stress corrosion cracking model on the basis of hydrogen diffusion and concentration toward the elastic-plastic stress field around a crack and the interaction of dislocations and hydrogen around a crack tip are proposed to clarify the mechanism of stress corrosion cracking for ductile and brittle materials. We conducted numerical analyses using these proposed models.     

LC4高强铝合金的慢应变速率拉伸试验

采用慢应变速率拉伸 (SSRT)技术测试了LC4铝合金在空气和质量分数为 3.5 %的NaCl溶液中的应力腐蚀断裂 (SCC)行为 .研究了应变速率对铝合金SCC行为的影响和氢在LC4高强铝合金应力腐蚀断裂过程中的作用 .试验结果表明 ,LC4合金具有SCC敏感性 ,在潮湿空气中发生应力腐蚀断裂 ,而在干燥空气中不发生应力腐蚀断裂 .对于长横取向的LC4铝合金试样 ,在应变速率为 1.331× 10 6s 1时 ,其SCC敏感性比应变速率为 6 .6 5 5× 10 6s 1时的敏感性大 .在潮湿空气和阳极极化条件下 ,铝合金的应力腐蚀断裂机理是以阳极溶解为主 ,氢几乎不起作用 .在预渗氢或阴极极化条件下 ,氢脆起主要作用 ,预渗氢时间延长可加速LC4合金的应力腐蚀断裂 .     

镀锌钢的液态金属脆现象及其在电阻点焊过程中的表现

液态金属脆是指通常具有韧性的固体金属或者合金与液态金属直接接触且受到拉伸应力时,其塑性降低并发生脆性断裂的现象。钢在液态锌中会发生液态金属脆现象,这在镀锌钢的热拉伸实验中得到了证实。此外,研究人员发现在镀锌高强钢的电阻点焊过程中也会出现液态金属脆现象,表现为在焊点表面出现大量裂纹,这些裂纹对焊点性能存在潜在危害。本文回顾了镀锌钢液态金属脆现象的热拉伸实验研究,阐明了影响脆化现象的实验因素;综述了镀锌钢在电阻点焊过程中发生液态金属脆现象的研究进展,分析了产生裂纹的位置及其影响因素,并总结了可能的解决方案。     

Dynamic fracture toughness of a high strength armor steel

This paper summarizes the results of a research being carried out to determine fracture behavior both in static and dynamic conditions of high strength armor steel Armox500T. In this research, notched specimens were cut to be tested in three-point bending test. Specimens were pre-cracked by flexural fatigue. Thereafter, some specimens were tested in bending up to rupture to determine the static fracture toughness K_IC. To obtain fracture toughness in dynamic conditions, a split Hopkinson bar modified to perform three-point bending tests was used. In this device, displacements and velocities of the specimen were measured, as well as the rupture time by means of fracture detection sensors, glued to the specimens. After that, a numerical simulation of the test was performed by using LS DYNA hydrocode, obtaining stresses and strain histories around the crack tip. From these results, the stress intensity factor history was derived. By using the rupture time, measured by the sensors, the value of the fracture toughness computed was unrealistic. Therefore, the use of a numerical procedure to obtain the rupture time was decided, by comparing experimental results of velocities at the transmission bar with numerical results obtained with several rupture times. With this procedure, the computation of dynamic fracture toughness was possible. The method shows that the measurement of the dynamic fracture toughness is possible without the needs of using crack sensors or strain gauges. It can be observed that fracture toughness of this steel under static and dynamic conditions is quite similar.     

Effects of hydrogen on the mechanical response of X80 pipeline steel subject to high strain rate tensile tests

Hydrogen‐induced degradation of X80 pipeline steel was investigated through a high strain rate tensile test (2 × 10^?4/s) with interposed unloading, reloading, aging at 30°C, or annealing at 200°C with or without hydrogen charging. The results indicated that plasticity degradation does not occur in the hydrogen‐precharged specimens; however, hydrogen embrittlement occurs in the reloading stage when the specimens are charged with hydrogen in the unloading stage after applying a prestrain. Interposed aging at 30°C or annealing at 200°C can also increase the degradation. It indicates that the hydrogen traps caused by the strain along with hydrogen charging are the major source of dislocations. The formation of a hydrogen atmosphere around mobile dislocations, which is related to the rates of hydrogen diffusion and dislocation movement, plays an important role in the degradation process. Both pinning and depinning of dislocations affect plasticity degradation.     

Inhibitory effect of oxygen on hydrogen‐induced fracture of A333 pipe steel

The effect of oxygen contained in hydrogen gas environment as an impurity on hydrogen environment embrittlement (HEE) of A333 pipe steel was studied through the fracture toughness tests in hydrogen gases. The oxygen contents in the hydrogen gases were 100, 10, and 0.1 vppm. A significant reduction in the J‐Δa curve was observed in the hydrogen with 0.1‐vppm oxygen. Under given loading conditions, the embrittling effect of hydrogen was completely inhibited by 100 vppm of oxygen. In the case of the hydrogen with 10‐vppm oxygen, initially the embrittling effect of hydrogen was fully inhibited, and then subsequently appeared. It was confirmed that 1‐vppm oxygen reduced the embrittling effect of hydrogen. The results can be explained by the predictive model of HEE proposed by Somerday et al.     

激光冲击对X70焊接接头慢拉伸电化学腐蚀的影响

为了改善X70管线钢焊接接头慢拉伸电化学腐蚀性能,用激光冲击波对X70管线钢焊接接头表面进行强化处理.采用慢应变速率拉伸法分析了X70管线钢焊接接头,在不同H2S浓度的NACE溶液(0.5%HAC+5%NaCl)中电化学腐蚀行为,测试了激光冲击处理前后X70管线钢焊接接头腐蚀电位,讨论了激光冲击处理对X70管线钢焊接接头腐蚀电位和断口形貌的影响.实验结果表明,激光冲击处理改善了X70管线钢焊接接头腐蚀性能,其SCC敏感性指数Iscc降低了6%.经激光冲击处理后试样自然腐蚀电位正移,极化电阻逐渐增大,其耐蚀性比原始状态有所提高.     

Grain boundary engineering for improving stress corrosion cracking of 304 stainless steel

Grain boundary engineering (GBE) via low strain tension and annealing was used to enhance the resistance to stress corrosion cracking of a 304 stainless steel. Electron backscattered diffraction (EBSD) analysis exhibited that the GBE steel had a higher fraction of low-∑ coincidence site lattice (CSL) boundaries, larger grain-clusters, longer twin boundary chains, and fewer paths of connected non-twin boundaries with a more zigzag shape. Slow strain rate tests in high-temperature water showed that the GBE steel performed better plasticity, higher tensile strength, and similar yield strength compared to conventional steel. The low fraction of random boundaries in GBE steel resulted in a lower frequency of intergranular crack initiation, and the zigzag paths of non-twin boundaries made the intergranular crack propagation more difficult.     

Assessment of stress corrosion cracking susceptibility by a small punch test

The object of this study is to establish a new test method for evaluating stress corrosion cracking (SCC) susceptibility of high-strength steel using a small punch (SP) test and acoustic emission (AE). A miniaturized specimen (10 × 10 × 0.5 mm) is adopted for SCC evaluation. The experiments are conducted at various loading rates and at various orientations of the specimen. The cumulative average amplitude of the AE signal per unit equivalent fracture strain ( ε _qf ) increases as the SCC susceptibility increases. Through the load–displacement behaviour, the fracture energy ( E _SP ), the SEM fractographs, and the correlation between the SCC susceptibility and the AE characteristics, it is proved that the small punch test method combined with AE measurements is a useful method to evaluate the SCC susceptibility of high-strength steel.