Grain-size and heat-treatment effects in hydrogen-assisted cracking of austenitic stainless steels

Hydrogen embrittlement of 304L and 316L types austenitic stainless steels has been studied by charging thin tensile specimens with hydrogen through cathodic polarization. Throughout this study we have compared solution-annealed samples, having various prior austenite grain size, with samples given the additional sensitization treatment. The results of the tensile tests while undergoing cathodic charging show that the additional sensitization treatment and coarse-grained samples together, lower the mechanical properties in both 304L and 316L types, and the sensitized steel is more susceptible to hydrogen-assisted cracking. However, the room-temperature yield and ultimate strengths, and the elongation of type 316L, were much less affected depending on the heat treatment and prior austenitic grain size. The fracture surfaces of the specimens tested while cathodically charged show considerable differences between the annealed and the sensitized specimens. The sensitized coarse-grained specimens were predominantly intergranular in both 304L and 316L types, while the annealed 316L type specimens fracture shows massive regions of microvoid coalescence producing ductile rupture and the annealed 304L type specimens fracture were primarily transgranular and cleavage-like. Sensitization seems both to facilitate the penetration of hydrogen along the grain boundaries into the steel and to introduce susceptibility to fracture along grain boundaries while refined grain size improves resistance regardless of the failure mode.     

Hydrogen—induced Cracking of Weld Metal of Austenitic Stainless Steels

For 308L and 347L weld metals of austenitc stainless steels(ASS) ,hydrogen induced cracking(HIC) occurred during dynamically charging under costant load.The threshold stress intensity for HIC,KIH,decreased linearly with the logarithm of the concentration of diffusible hydrogen Co in the weld metals and the rolled plate of type 304L ASS.i,e ,KIH=85.2-10.7ln Co(308L),KIH=76.1-9.3ln Co(347L) ,and KIH=91.7-10.0lnCo(304L).The fracture mode for HIC in the three type of ASS changed from ductile to brittle with the decrease in the applied stress intensity Ki or /and the increase in Co .The boundary line between ductile and brittle fracture surfaces was KI-54 25ep(-Co/153)=0.     

Influence of inclusions and heat treated microstructure on hydrogen assisted fracture properties of aisi 316 stainless steel

An attempt has been made to assess the influence of nonmetallic inclusions and heat treated microstructure on hydrogen assisted cracking of AISI 316 austenitic steel. The steel obtained in two levels of cleanliness was given solution annealing treatment in the temperature range of 1173–1473 K, and additional sensitization treatment of 973 K for 26 hours. Hydrogen embrittlement of this steel has been studied by charging Charpy and Compact Tension specimens of ASTM specification, with hydrogen through cathodic polarization. It is found that hydrogen embrittlement susceptibility increases with the presence of large size inclusions, larger grain and sensitized microstructure.     

Effect of hydrogen charging on fracture behaviour of 304L stainless steel

Abstract

Slow tensile straining of a series of specimens of 304L stainless steel after thermally charging with hydrogen at 31·0 MPa and 350°C resulted in a ductility loss compared with uncharged specimens. The susceptibility to embrittlement was shown to be dependent on the formation of martensite during deformation and, hence, the stability (and composition) of the austenite, but the interface between the austenite and any ferrite stringers acted as a nucleation site for cracking and as a weak propagation path for fracture.

MST/1088     

锌-镍合金电镀中氢的共沉积

用电化学渗透测试方法研究了电镀锌－镍合金时渗氢量的变化规律，能够监控和评价镀层的氢脆性能，初步筛选出两种呆用于高强度钢抗氢脆电镀用槽液组成。在氯化物－硫酸盐槽液体系和含有添加剂B的氯化物糟液中，常温下可获得耐氢脆性能良好的Zn－Ni镀层。此外，缺口拉伸试验结果与电化学渗透测试结果相吻合。     

氢对低合金钢上不锈钢堆焊层性能的影响(英文)

本工作研究了高温高压氢 (35 0℃ ,2 5 MPa H2 ) ,对国产氢反应器壁 30 9L 和 34 7L 不锈钢堆焊层性能的影响 .结果表明 :未经热渗氢的原始试样 ,无论是光滑试样还是缺口试样 (除缺口开在 30 9L 区域试样外 ) ,均断裂在 34 7L 区域内 .而经热渗氢后 ,无论起裂于 2 (1/4 ) Cr- 1Mo和 30 9L 熔合线 ,还是 30 9L 和34 7L的熔合线处 ,最后都断在 30 9L区域内 .这是因为热渗氢使 30 9L和 34 7L的断裂应力 ,分别从 885 MPa降至 478MPa和从 799.9MPa降至 5 6 4MPa,它们的氢脆系数分别为 86 .8%和 80 .9% .SEM断口分析结果与上述结论一致     

Role of shot-peening on hydrogen embrittlement of a low-carbon steel and a 304 stainless steel

Shot-peening surface treatments were performed on a low-carbon steel and a 304 stainless steel. The influence of residual stresses on hydrogen permeation and distribution was investigated. The results were correlated with the tensile properties measured in air after cathodic charging and in a NACE medium under slow load-rate straining. The role of shotpeening on the hydrogen embrittlement of the low-carbon steel is strongly dependent on the severity of the hydrogen environment and testing conditions. The detrimental effect of shotpeening on the hydrogen embrittlement of the stainless steel is related to phase transformations induced by cold work.     

Effect of grain refinement on the hydrogen embrittlement of 304 austenitic stainless steel

The effect of grain size (in the range from 4 μm to 12 μm) on the hydrogen embrittlement (HE) of 304 austenitic stainless steel (ASS) was studied. HE susceptibility result shows that HE resistance increases with grain refinement. Electron backscattered diffraction kernel average misorientation (EBSD-KAM) mapping shows that the strain localization can be mitigated by grain refinement. Hence, strain localization sites which act as highways for hydrogen diffusion and preferred crack initiation sites can be reduced along with grain refinement, leading to a high HE resistance. Meanwhile, grain size shows no influence on the strain induced martensite (SIM) transformation during the hydrogen charging slow strain tensile test (SSRT). Hence, the SIM formed during hydrogen charging SSRT is not responsible for the different HE resistance of 304 ASSs with various grain sizes. Hydrogen diffusion is supposed to be controlled by a competition between short-circuit diffusion along random grain boundary (RGB) and hydrogen trapping at dislocations, leading to a maximum hydrogen diffusion coefficient in the 304 ASS with an average grain size of 8 μm.     

Tensile behaviour of type 304 austenitic stainless steels in hydrogen atmosphere at low temperatures

Abstract

The tensile behaviour of solution annealed type 304L, solution annealed type 304, and solution annealed and sensitised type 304 stainless steels was investigated in hydrogen and helium under a pressure of 1·1 MPa over the temperature range 300–80 K at strain rates ranging from 4·2×10^-5 to 4·2×10^-2 s^-1. For 304L steel, hydrogen environment embrittlement (HEE) increased with decreasing strain rate. For 304L and 304 steels, HEE increased with decreasing temperature, reached a maximum, and then decreased with further decrease in temperature: the decrease was particularly rapid near the minimum temperature for HEE. Sensitisation enhanced the HEE of 304 steel. Above the maximum HEE temperature, the HEE behaviour was similar to the hydrogen embrittlement behaviour of materials in previous studies, but near the minimum temperature for HEE it was different. Three types of hydrogen induced brittle fracture were observed as a result of HEE: transgranular fracture along strain induced martensite laths and twin boundary fracture on the fracture surfaces of solution annealed 304L and 304 steels, and grain boundary fracture on the sensitised 304 steel. It was found that from room temperature to the maximum HEE temperature, the HEE of the materials depended on the transformation of strain induced martensite and below the maximum HEE temperature it depended on the diffusion of hydrogen.     

Effects of nitrogen on hydrogen embrittlement in AlSl type 316, 321 and 347 austenitic stainless steels

Hydrogen embrittlement of AlSl type 316, 321 and 347 stainless steels with nitrogen alloying has been studied by a tensile test through cathodic charging. The results show that addition of nitrogen improved resistance to hydrogen cracking regardless of the failure mode. Fracture surfaces of cathodically charged steels showed intergranular brittle zones on each side of the fracture surfaces. AlSl type 316 with nitrogen alloying stainless steel is more resistant to hydrogen embrittlement than AlSl type 321 with nitrogen alloying steel, whereas AlSl type 347 with nitrogen alloying steel is susceptible to hydrogen embrittlement. Nitrogen alloying of stainless steel increased the mechanical properties in hydrogen environments by increasing the stability of austenite.     

Beitrag zum Einfluß von Druckwasserstoff auf die mechanischen Eigenschaften von Stählen

Contribution to the Influence of Pressurized Hydrogen on the Mechanical Properties of Steels The investigation method of using hollow specimens in tensile tests to examinate steels for hydrogen service is described. Reduction of area after fracture, Z, resulting from these tensile tests with constant strain rates shows not only a significant but also a constant difference between hydrogen and nitrogen when being plotted versus strain rate. Therefore a newly introduced term named “Index of embrittlement” and characterized by the relation of Z with nitrogen and with hydrogen was found to be independent of strain rate. With strain rate ε = 10^?6 s^?1 chosen for a “critical” one because of lacking in a maximum index of embrittlement several European steels for hydrogen service were tested to find out their individual index of embrittlement. Assisted by light optical microscopy it was found that there is a special correlation between microstructure, index of embrittlement and tensile strength of a given steel grade.     

Bruchverhalten eines vergüteten und eines kaltgezogenen Stahles im Gleichgewichtszustand mit Druckwasserstoff

Fracture of Tempered and Cold Drawn Steel in Equilibrium with Compressed Hydrogen Tensile specimens are surface activated and stored in compressed hydrogen until equilibrium is attained. Charged and uncharged reference specimens are tested in air and in compressed hydrogen. The embrittlement of colddrawn steel (plenty of traps) is independent of strain rate and is caused mainly by the prior charging. Tempered steel (fewer traps) is not embrittled by charged hydrogen but by the effect of external hydrogen during the test. The degree of embrittlement decreases with increasing strain rate. In all cases of embrittlement there is in addition a strong notch sensitivity.     

AN ACCELERATED TEST METHOD FOR DETERMINING NEAR-THRESHOLD STRESS INTENSITY VALUES IN HSLA STEELS

Abstract— A new method for accelerating the collection of near-threshold corrosion fatigue crack propagation data, using local hydrogen embrittlement in the crack tip region, has been investigated for ASTM A710 HSLA steel. Fatigue tests were conducted at 10 and 0.2 Hz (stress ratio, R = 0.1) on "constant K " contoured double cantilever beam (CDCB) specimens, to establish near-threshold crack growth rates in a locally hydrogen charged region at the crack tip. Hydrogen charging was then discontinued and crack growth rates were monitored in the uncharged material. Near-threshold fatigue crack growth rates were found to be 100 times faster in the locally hydrogen charged specimens than in the uncharged material. Fatigue thresholds, Δ K _th, were defined in less than one fifth the time required for load shedding tests in air at 0.2 Hz. Although demonstrated for HSLA steels, the technique is applicable to any material which can be embrittled by hydrogen.     

Experimental investigation of local tensile and fracture resistance behaviour of dissimilar metal weld joint: SA508 Gr.3 Cl.1 and SA312 Type 304LN

The aim of the paper is to evaluate the local tensile and fracture toughness properties of the dissimilar metal weld joints between SA508Gr.3 Cl.1 and SA312 Type 304LN pipe. Weld joints have been prepared by manual gas tungsten arc welding (GTAW) process with conventional V‐groove and automatic hot wire gas tungsten arc welding with narrow gap using different filler wires/electrode such as Inconel 82/Inconel 182 and ER309L/ER308L. The tensile and fracture toughness test specimens have been machined from different regions of dissimilar metal weld such as heat affected zones, fusion lines, buttering layer, weld metal and both base metals. Tensile and fracture toughness tests have been carried out as per the ASTM standard E8 and E1820 respectively. Tensile and fracture toughness results of all the regions of dissimilar metal weld joints have been discussed in this paper. Metallurgical and fracture surface examinations have also been reported to substantiate the tensile and fracture toughness results. Need for the local properties for integrity assessment of the dissimilar metal weld joints has also been brought out.     

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.     

Effects of deformation on hydrogen degradation in a duplex stainless steel

Hydrogen embrittlement of annealed, 20 and 40% cold worked 2205 duplex stainless steels has been evaluated using electrochemical permeation measurement, hydrogen microprint technique and tensile test in this study. Due to hydrogen transport in 2205 duplex stainless steel is mainly lattice diffusion in ferritic phase, more hydrogen distribution, higher permeation rate and effective diffusion in ferritic phase were detected. Hydrogen trapping and mechanical property effects were studied for cold worked specimens. Fractographic investigation revealed that hydrogen absorption promoted transgranular fracture in cold worked specimens. These results exhibits that the cold worked duplex stainless steels are more susceptible to hydrogen embrittlement.     

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。     

充氢Cr-Mo钢变形过程的声发射特征

对电化学充氢后的2.25Cr-1Mo钢进行拉伸实验,并在实时拉伸过程中采集声发射信号。结果表明:充氢后2.25Cr-1Mo钢抗拉强度为536.30MPa,下降约57MPa;断面收缩率为43.62%,下降约7%。拉伸断口上出现由氢脆引起的"白点"特征与准解理断裂形貌。充氢后试样拉伸过程弹性阶段的声发射信号活动增强,而屈服阶段的声发射信号活动减弱,变形过程的声发射信号累积绝对能量值要比未充氢试样低约1个数量级。充氢试样拉伸产生的声发射信号比未充氢试样的信号幅值降低约0.33mV,频宽降低0.06MHz。通过对声发射信号的分析发现,充氢试样变形的微观机制为氢促进位错发射与运动,而交叉滑移受到抑制。     

Experimental study of hydrogen embrittlement on AISI 304 stainless steels and Rayleigh wave characterization

Many failures due to hydrogen embrittlement or hydrogen damage are widely reported in oil and refinery industry. Despite many ultrasonic testing methods have been developed to assess hydrogen embrittlement, they are applied well to serious hydrogen attack instead of earlier degradation. This paper aims to characterize nascent hydrogen embrittlement of AISI 304 austenitic stainless steels under cathodic hydrogenation using Rayleigh wave. After cathodic hydrogen charging of AISI 304 stainless steel, XRD and metallographic examination show that martensite transformation occurs within the subsurface region of the specimens. Microhardness testing indicates that hydrogen leads to hardening of the material. It is found that Rayleigh wave are better to inspect local degradation than bulk waves. Rayleigh wave velocity of 5 MHz and 10 MHz decreases significantly with cathodic charging time, while longitudinal wave velocity changes not. Acoustic velocity change is due to elastic modulus reduction resulting from hydrogen-induced phase transformation in the subsurface region.     

储能缝焊工艺对304不锈钢接头性能的影响

为研究电容储能缝焊工艺对304不锈钢接头性能的影响规律,对0.5 mm厚304不锈钢板进行了缝焊工艺实验,通过接头拉剪力检测和金相显微组织观察,对比了不同焊接速度、充电电容和放电频率下的缝焊接头组织特点,并分析了各工艺参数对接头拉剪力、熔核宽度、焊缝重叠量和焊透率的影响.结果表明:储能焊焊缝中心晶粒细小,熔合区为柱状晶,重叠部位晶粒粗大,接头组织呈现不均匀性,随着充电电容的增大晶粒变得更细密,组织不均匀程度显著降低,焊接速度和放电频率增大导致晶粒组织粗化并出现缩孔缺陷,提高电极压力可克服缩孔并使组织趋向均匀;充电电容对接头拉剪力的影响较小,焊接速度、充电电压、放电频率和电极压力调到一个合适值后,继续增大参数值对接头拉剪力影响很小;焊接速度的增大引起焊缝熔核宽度和重叠量急剧下降,充电电压增大引起焊缝焊透率下降过多,导致飞溅、过烧、毛刺等焊接缺陷的产生.因此,304不锈钢储能缝焊应采用低的焊接速度、较小的充电电压和较高的电极压力。