Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was determined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treatedsteel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested     

Hydrogen-induced embrittlement of nickel-chromium-molybdenum containing HSLA steels

ABSTRACT

Several advanced nickel-chromium-molybdenum high strength lowalloy steels newly developed by our research team exhibit excellent mechanical strength, toughness and hardenability. However, the phenomenon of hydrogen-induced embrittlement will easily occur for these high strength steels. In this research, the hydrogeninduced embrittlement of 8625-Modified steel (8625M steel) was studied. Experimental results show that the dominant hydrogen trapping site of the 8625M steel is dislocation, of which trapping energy is about 20 kJ/mol, indicating that the hydrogens trapped in the dislocations are diffusible. The as-quenched 8625M steel has the highest dislocation density and accordingly the highesthydrogen content after hydrogen charging. This makes the asquenched 8625M steel exhibit severe hydrogen embrittlement. After tempering at 200°C and 300°C, the dislocation density drops, and hence these tempered specimens have lower ultimate tensile strength loss. After 400°C tempering, the hydrogen embrittlement phenomenon becomes serious again, being ascribed to the formation of needlelike and film-like cementite which will weaken the strength of martensite. After 500°C tempering, the 8625M steel has the lowest dislocation density, and the inter-lath cementite become discontinuous and spheroidal, making the 500°C tempered specimen have the lowest ultimate tensile strength loss and the highest elongation after hydrogen charging in this study.     

Influence of hydrogen on mechanical properties of nitrogen supersaturated austenitic stainless steels

Abstract

Alloying austenitic stainless steels with nitrogen up to a concentration of 1 wt-% improves yield strength, tensile strength, and ductility. Further increase in the nitrogen concentration results in chromium nitride precipitation at the grain boundaries and a decrease in the ductility with a change in the fracture mode from ductile to intergranular. Hydrogen charging causes high reversible dilatation in the lattice and remarkable reduction in the ductility. The ductility losses caused by hydrogen are more pronounced at higher nitrogen concentrations and a change of the fracture mode from intergranular to transgranular is observed in steels with more than 1 wt-% nitrogen. Chromium nitride precipitates are shown to have an insignificant role in the hydrogen embrittlement. Hydrogen charging steels with nitrogen concentrations of below 1 wt-% enhances the strengthening effect of nitrogen but, at higher nitrogen concentrations, hydrogen is shown to be detrimental to the strength.     

Hydrogen embrittlement of an HSLA 80 steel in sea water under cathodic charging conditions

Abstract

Hydrogen embrittlement of a copper precipitation strengthened and niobium microalloyed HSLA 80 steel on cathodic charging in synthetic sea water has been studied using a slow strain rate technique. The effects of strain rate and potential applied for hydrogen charging have been studied. Hydrogen measurement at different potentials has also been carried out. A loss in ductility in terms of a drop in percentage elongation and percentage reduction in area has been observed, the effect being prominent at potentials beyond —800 mV(SCE). Fractography by SEM shows a dominance of microvoid coalescence with increasing quasicleavage features at higher negative potentials. A hardening effect of hydrogen charging up to —600 mV(SCE) followed by a softening effect has been observed. The results are discussed in the light of the existing models of hydrogen–dislocation interaction and hydrogen induced microvoid coalescence.     

有序度对Ni2Cr合金氢致脆断的影响

研究了环境气氛、动态渗氢及预渗氢对不同有序度Ni2Cr合金脆化的影响.结果表明,有序度对Ni2Cr合金在室温空气及氢气中的环境氢脆没有明显影响;动态渗氢拉伸时Ni2Cr合金存在严重的氢脆敏感性,无序和高度有序合金比部分有序合金脆化严重;预渗氢时,氢原子通过晶格扩散及晶界扩散进入合金,Ni2Cr合金氢脆敏感性随有序度的增大而减小.     

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。     

Characterization of Hydrogen Embrittlement in 2.25cr-1mo-0.25v Steel by Eddy Current Method

Eddy current method has been recently developed to characterize mechanical properties of materials and assess internal hydrogen content of high strength low alloy steels. The application of eddy current testing in evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V ferritic steel has been investigated using tensile test and electrochemical hydrogen charging test. The relationship between the embrittlement index and eddy current signal is well established. It found that there is a good linear relation between the hydrogen-induced plasticity loss and the eddy current signal. This shows eddy current testing is an effective method for evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V steel.     

Effect of Hydrogen on Cryogenic Mechanical Properties of Cr-Ni-Mn-N Austenitic Steels

1.IntroductionTheCr-Ni-Mn-Nausteniticsteelsarewidelyusedasstructuralmaterialsinthefieldsofcryogenicengi-neering,nuclearengineering,aeronauticaltechnique,chemical,petroleumandenergyindustriesetc.,be-causeoftheirhightoughnessandstrength,highre-sistancetocorrosion,lowmagneticpermeabilityandverygoodcryogenicmechanicalproperties.InCr-Ni-Mn-Nausteniticsteelsausteniteisstabilizedbyman-ganeseandnitrogeninplaceofpartofthenickel.SomestableCr-Ni-Mn-Nausteniticsteelspresentgoodhydrogen-resistantprope…     

Effect of pre-charged hydrogen on fatigue crack growth of low alloy steel at 288 °C

Hydrogen effects on mechanical strength and crack growth were studied at high temperatures. The study was motivated by the fact that the environmentally assisted cracking (EAC) of pressure vessel steel SA508 Cl.3 in 288 °C water was suspected to be related to hydrogen embrittlement. Fatigue crack growth rate and tensile tests were performed with hydrogen pre-charged specimens at high temperatures. At 288 °C the fatigue crack growth rate of the hydrogen pre-charged specimen was faster than that of as-received; the fatigue fracture surface of hydrogen pre-charged specimen correspondingly showed EAC like feature. Meanwhile, ductile striation was evident for the case of as-received in both air and argon gas environments. In the dynamic strain aging (DSA) loading condition at 288 °C during tensile tests, the pre-charged hydrogen induced a marked softening (decrease in ultimate tensile strength; UTS) as well as a little ductility loss; this was accompanied by the macrocracks grown from microvoids/microcracks promoted by DSA and hydrogen. These experiments showed that hydrogen embrittlement is an effective mechanism of EAC not only at low temperature but also at the high temperature.     

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     

Effect of charging parameters on hydrogen embrittlement behaviour of Ni60Nb35Cr5 glass

Hydrogen embrittlement behaviour of Ni₆₀Nb₃₅Cr₅ glass was studied as a function of the time of cathodic charging and temperature and concentration of the electrolyte. Sulphuric acid solution was taken as electrolyte and hydrogen embrittlement susceptibility determined in terms of fracture strain evaluated from bend ductility test. A considerable loss in ductility was noted with increase in the time of charging and temperature and concentration of the electrolyte for a fixed current density. The loss in ductility was accompanied by a change in the appearance of shear bands from wavy to straight.     

THE EFFECT OF HYDROGEN ON SHORT FATIGUE CRACK GROWTH IN AN Al-Li ALLOY

Abstract— Experimental results are presented to illustrate the degree of susceptibility to hydrogen embrittlement in an Al-Li 8090 alloy. The ductility of the alloy (as recorded in slow strain rate tests) is reduced by hydrogen charging which induces microcrack formation on the surface of the hydrogen treated specimens. Results of fatigue tests show that small fatigue cracks propagate 1.5 to 10 times faster in specimens charged with hydrogen and fractographic evidence shows that short crack growth in hydrogen precharged specimens is transgranular, along persistent slip bands. The effect of hydrogen is reversible, the embrittlement effect being eliminated by holding the specimens for 24 hr at 470°C.     

Hydrogen and temper embrittlement in 9Cr–1Mo steel

Abstract

The synergism between hydrogen embrittlement and temper embrittlement has been investigated in a 9Cr–1Mo martensitic steel. Measurements of tensile ductility were used to monitor the development of embrittlement with increasing hydrogen content in material as tempered and aged for up to 5000 h at 500 or 550°C. A detailed examination was made of associated changes in fracture mechanism, precipitate microstructure, and interfacial and precipitate chemistry. A strong interaction between hydrogen and temper embrittlement was observed. Both types of embrittlement in isolation reduced tensile ductility by promoting a ductile interlath fracture mechanism: ‘chisel fracture’. Hydrogen and temper embrittlement acted synergistically to reduce ductility further by the promotion of brittle intergranular fracture and transgranular cleavage. The dominant factor controlling the interaction was the precipitation of a brittle intermetallic Laves phase containing phosphorus in solution. Phosphorus segregated to interfaces was considered to make an important, but secondary, contribution to the embrittlement observed.

MST/791     

Nondestructive detection of hydrogen in steel by vibration damping

The application of forced vibration measurements as a nondestructive testing method for the detection of hydrogen in steel has been investigated. The method is based on the influence of hydrogen on the internal friction of steel. Tensile test specimens of 50CrV4 steel were set into forced vibration before and after hydrogen charging. By sweeping the exciter frequency continuously over a wide range, resonances occurred at certain frequencies. The tests show close correlation between hydrogen embrittlement, hydrogen content and damping of forced vibrations in the resonance case. While the absorbed hydrogen effuses during ageing at room temperature, the resonance amplitudes increase and the hydrogen embrittlement decreases as a function of time. After an ageing period of eight days all measured values returned to their initial value before hydrogen charging. It can therefore be concluded that this method is suitable for the nondestructive testing of hydrogen-sensitive components.     

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     

Effect of heat treatment on susceptibility of duplex stainless steel to embrittlement by hydrogen

Abstract

Slow straining of smooth tensile specimens of heat treated duplex stainless steel from a fabricated pipe has been used to assess susceptibility to embrittlement by hydrogen. The effect of the proportions of ferrite and austenite in the microstructure, produced by quenching after solution treatment at temperatures between 1000 and 1300°C, on the ductility was measured. Tests were carried out by either straining in a hydrogen atmosphere or in air after thermal charging in high pressure hydrogen. The measured susceptibility increases proportionately with increase in the amount of ferrite in the structure and reflects the role of austenite in arresting propagating cracks. However, there is little doubt that the amount of austenite presents greater dominance than its orientation in this respect.     

Effect of iron additions on mechanical properties of Co3 Ti alloy

High temperature tensile tests were carried out on L1₂ type Co₃ Ti alloys, both undoped and doped with 1–4 at.-%Fe. There were anomalous increases of the 0·2% yield stress (yield strength) with increasing test temperature from 473 to 1073 K (or 1173 K, depending on the composition). The elongation and ultimate tensile stress (UTS) monotonically decreased with increasing temperature. The fracture surfaces of specimens showed a variety of fracture modes which were dependent on the test temperature and composition. There was a correlation between the ductility and the fracture mode: the more transgranular the fracture mode, the higher the ductility. It was found that Co₃ Ti with 2 at.-%Fe exhibited improved ductility and it exhibited the highest peak value of yield strength and peak temperature. The alloys were also hydrogen charged to investigate their hydrogen embrittlement behaviour. Room temperature tests indicated that the addition of 2 at.-%Fe decreased the hydrogen related embrittlement.

MST/3479     

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

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.     

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.     

Boron effects on the ductility of a nano-cluster-strengthened ferritic steel

The mechanical properties of Cu-rich nano-cluster-strengthened ferritic steels with and without boron doping were investigated. Tensile tests at room temperature in air showed that the B-doped ferritic steel has similar yield strength but a larger elongation than that without boron doping after extended aging at 500 °C. There are three mechanisms affecting the ductility and fracture of these steels: brittle cleavage fracture, week grain boundaries, and moisture-induced hydrogen embrittlement. Our study reveals that boron strengthens the grain boundary and suppresses the intergranular fracture. Furthermore, the moisture-induced embrittlement can be alleviated by surface coating with vacuum oil.