Ⅲ型裂纹试样的氢致滞后断裂

利用复合型(Ⅰ+Ⅲ型)试样研究了应力状态对氢致表观屈服应力(它是产生局部宏观塑性变形所需的外应力)的影响,探讨了Ⅲ型裂纹试样产生氢脆(即氢致裂纹)的可能性。结果表明,对Ⅲ型裂纹试样,即使严重充氢也不会使表观扭转屈服应力下降。从而也不会沿原裂纹面产生氢致滞后裂纹。对复合型试样,只有当K_Ⅰ本身就能使原裂纹面产生滞后塑性变形时才能使表观扭转屈服应力随K_Ⅰ增大而下降。 对充氢的纯Ⅲ型裂纹试样,当扭矩大于临界值后保持一定时间就能在和原裂纹面成3/4π或-45°的面上产生氢致滞后裂纹,它导致典型的沿晶断口。如充氢试样直接扭断则得沿原裂纹面断裂的平剪切断口。当钢的强度和氢含量低于临界值就不会产生沿3/4π面的滞后裂纹。计算了Ⅲ型裂纹应力场和氢应变场的互作用能。结果表明,在和原裂纹面成3/4π的诸平面上互作用能有极小值,从而导致氢向该面浓集而形成氢致滞后裂纹。     

Ⅲ型裂纹剪应力场和氢的互作用

当试样中存在拉应力梯度时,氢能使表观屈服应力明显下降,从而能引起氢致滞后塑性变形和氢致滞后裂纹,对Ⅲ型裂纹,由于不存在流体静压力,故一般认为它不能产生氢致裂纹。但我们的工作表明,对充氢的Ⅲ型试样,在扭矩大于临界值后保持一定时间就能在和原裂纹面成-45°的诸平面上产生氢致滞后裂纹,它导致典型的沿晶断口。对三个钢种都有类似结果。如充氢试样直接扭断,则     

氢致滞后塑性变形机理研究

利用光滑拉伸试样以及带有应力梯度的弯曲试样和预裂纹试样(Ⅰ型、Ⅲ型以及Ⅰ—Ⅲ复合型),研究了氢对产生局部宏观塑性变形所需外应力(称为表观屈服应力)的影响。结果表明,氢对低合金钢的屈服强度影响不大,但如试样中存在拉应力梯度,则当钢的强度和进入试样的氢浓度超过临界值后,氢能使表观屈服应力明显下降,这就是氢致滞后塑性变形的原因。氢致表观屈服应力的下降是由氢的扩散所控制的。它明显依赖加载速度和试验温度。但它随试验温度的变化不是单调的,在室温附近存在一个极值。对仅存在剪应力梯度的Ⅲ型裂纹试样,充氢后表观扭转屈服应力并不降低,沿原裂纹面也不产生滞后裂纹,即K_(ⅢH)=K_(ⅢC),但在和原裂纹面成-45°的平面上却能产生氢致滞后塑性变形和裂纹。对Ⅰ—Ⅲ复合型试样,只有当恒定的K_Ⅰ大到足以单独就能产生滞后塑性变形时才能使表观扭转屈服应力开始下降。提出了一个氢使表观屈服应力下降的机构。     

INTERACTION BETWEEN HYDROGEN AND A TYPE Ⅲ CRACK

<正> 当试样中存在拉应力梯度时,氢能使表观屈服应力明显下降,从而能引起氢致滞后塑性变形和氢致滞后裂纹,对Ⅲ型裂纹,由于不存在流体静压力,故一般认为它不能产生氢致裂纹。但我们的工作表明,对充氢的Ⅲ型试样,在扭矩大于临界值后保持一定时间就能在和原裂纹面成-45°的诸平面上产生氢致滞后裂纹,它导致典型的沿晶断口。对三个钢种都有类似结果。如充氢试样直接扭断,则     

稳定型奥氏体不锈钢的氢致滞后开裂

用单边裂纹恒载荷试样研究了三种奥氏体不锈钢(18-8,310,K-55)充氢后的氢致滞后开裂行为。三种钢在恒载荷下充氢都出现滞后断裂,其门槛值分别约为K_(IH)/K_c=0.55,0.70和0.80,如果预先充氢再在空气中加载,也能产生氢致滞后开裂,如充氢后除气,则不能,这就表明,无论是不稳定型(18-8)还是稳定型(310,K-55)奥氏体不锈钢都能产生氢致滞后开裂。18-8钢充氢时能发生马氏体相变,从而促进氢致开裂过程,其K_(IH)/K_c比不产生马氏体的310和K-55要低。所有奥氏体不锈钢的氢致滞后断口形貌都和K_I有关。当滞后断裂的K_I较大时是韧性断口,K_I较小时则是脆性断口。     

HYDROGEN INDUCED DELAYED CRACKING IN STABLE AUSTENITIC STAINLESS STEELS

用单边裂纹恒载荷试样研究了三种奥氏体不锈钢(18-8,310,K-55)充氢后的氢致滞后开裂行为。三种钢在恒载荷下充氢都出现滞后断裂,其门槛值分别约为K_(IH)/K_c=0.55,0.70和0.80,如果预先充氢再在空气中加载,也能产生氢致滞后开裂,如充氢后除气,则不能,这就表明,无论是不稳定型(18-8)还是稳定型(310,K-55)奥氏体不锈钢都能产生氢致滞后开裂。18-8钢充氢时能发生马氏体相变,从而促进氢致开裂过程,其K_(IH)/K_c比不产生马氏体的310和K-55要低。 所有奥氏体不锈钢的氢致滞后断口形貌都和K_I有关。当滞后断裂的K_I较大时是韧性断口,K_I较小时则是脆性断口。     

MECHANISM OF HYDROGEN INDUCED DELAYED PLASTICITY

利用光滑拉伸试样以及带有应力梯度的弯曲试样和预裂纹试样(Ⅰ型、Ⅲ型以及Ⅰ—Ⅲ复合型),研究了氢对产生局部宏观塑性变形所需外应力(称为表观屈服应力)的影响。结果表明,氢对低合金钢的屈服强度影响不大,但如试样中存在拉应力梯度,则当钢的强度和进入试样的氢浓度超过临界值后,氢能使表观屈服应力明显下降,这就是氢致滞后塑性变形的原因。 氢致表观屈服应力的下降是由氢的扩散所控制的。它明显依赖加载速度和试验温度。但它随试验温度的变化不是单调的,在室温附近存在一个极值。 对仅存在剪应力梯度的Ⅲ型裂纹试样,充氢后表观扭转屈服应力并不降低,沿原裂纹面也不产生滞后裂纹,即K_(ⅢH)=K_(ⅢC),但在和原裂纹面成-45°的平面上却能产生氢致滞后塑性变形和裂纹。对Ⅰ—Ⅲ复合型试样,只有当恒定的K_Ⅰ大到足以单独就能产生滞后塑性变形时才能使表观扭转屈服应力开始下降。 提出了一个氢使表观屈服应力下降的机构。     

氢在铁中的应变场

计算了有应力和无应力状态下产生非球对称应变的氢原于的化学位之差,μ_σ-μ_0=-VΣσ_iε_(ii)~′,其中U就是氢应变场和外应力场的互作用能.对纯剪应力τ,则U=-0.55133Vτ(ε_(11)-ε_(22)),因而当氢在α-Fe中引起四方畸变时,它和剪应力就有互作用,从而可导致氢在45°面上富集,这就可解释充氢的无裂纹扭转试样以及III型裂纹试样能沿45°面产生氢致滞后断裂的实验事实.当非球对称应变的氢择优分布时,在拉伸和压缩条件下的氢浓度公式并不相同,分别为C_t=C_0exp[(0.70089ε_(11) 0.29911ε_(22))Vo/RT],C_0exp[(0.14956ε_(11) 0.85044ε_(22))Vσ/RT].因此,根据氢渗透实验所获得的C_t/C_0和C_p/C_0,就可定出ε_(11)/ε_(22).例如,用Bockris的数据可得ε_(11)/ε_(22)=1.27.这表明氢在α-Fe中的应变是非球对称的.     

单晶硅压痕裂纹的氢致滞后扩展

利用压痕裂纹恒载荷试样，研究了单晶硅在空气中应力腐蚀以及动态充氢时氢致滞后开裂的可能性；利用卸载的压痕裂纹试样研究了残余应力引起氢致滞后开裂的可能性．结果表明，单晶硅压痕裂纹恒载荷试样当KI=KIC时在空气中并不发生应力腐蚀．在H2SO4溶液中动态充氢，则能发生氢致滞后开裂，止裂时归一化门槛应力强度因子为KIH／KIC≈0.9、卸载压痕裂纹的残余应力在充氢过程中也能引起氢致滞后开裂，归一化门槛应力强度因子为KIH／KIC≈0．9．     

STRAIN FIELD OF HYDROGEN ATOMS IN IRON

计算了有应力和无应力状态下产生非球对称应变的氢原于的化学位之差,μ_σ-μ_0=-VΣσ_iε_(ii)~′,其中U就是氢应变场和外应力场的互作用能.对纯剪应力τ,则U=-0.55133Vτ(ε_(11)-ε_(22)),因而当氢在α-Fe中引起四方畸变时,它和剪应力就有互作用,从而可导致氢在45°面上富集,这就可解释充氢的无裂纹扭转试样以及III型裂纹试样能沿45°面产生氢致滞后断裂的实验事实.当非球对称应变的氢择优分布时,在拉伸和压缩条件下的氢浓度公式并不相同,分别为C_t=C_0exp[(0.70089ε_(11)+0.29911ε_(22))Vo/RT],C_0exp[(0.14956ε_(11)+0.85044ε_(22))Vσ/RT].因此,根据氢渗透实验所获得的C_t/C_0和C_p/C_0,就可定出ε_(11)/ε_(22).例如,用Bockris的数据可得ε_(11)/ε_(22)=1.27.这表明氢在α-Fe中的应变是非球对称的.     

HYDROGEN INDUCED CRACKING IN FERRITICAUSTENITIC DUPLEX STAINLESS STEEL

Hydrogen induced cracking in a ferritic-austenitic duplex stainless steel has been investigatedusing compact tension tests.The stress intensity threshold K_H of the steel rises with increasingaustenite content and decreases with increasing current density during hydrogen charging.Thehydrogen induced cracking initiates and propagates on {100} planes of the ferrite grains.Theaustenite grains play a “fibre-toughened” role during obstructing crack propagation.     

铁素体—奥氏体双相不锈钢的氢致开裂研究

用紧凑拉伸实验研究了铁素体-奥氏体双相不锈钢的氢致延迟开裂过程,发现氢致开裂应力强度因子门槛值K_H随γ量增加而增加,随充氢电流密度增加而下降。氢致裂纹在α相内{100}面形核,扩展连通,最后将γ相和晶界撕裂,γ相阻碍氢致延迟裂纹的扩展,在断裂方面起到“纤维韧化”的作用。     

Effect of hydrogen concentration on the embrittlement of a duplex stainless steel

Hydrogen embrittlement of 23Cr-5Ni-3Mo duplex stainless steel, charged with hydrogen cathodically evolved from various aqueous solutions, was investigated. The constant slow strain rate tests were employed to provide comparative data for the cracking susceptibility, whereas the electrochemical desorption technique was used to determine the amount of absorbed hydrogen. The obtained results showed that the reduction in ductility of the steel is closely connected with the concentration of hydrogen introduced.     

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.     

Hydrogen embrittlement of nodular cast iron

Ferritic nodular cast iron, intended for use as the material for inserts of canisters for long-term geological disposal of spent nuclear fuel, was studied for hydrogen sensitivity. In the canisters, the insert provides the mechanical strength against external loads. Hydrogen was charged from 0.1 N H₂SO₄ solution in free-corrosion tests and under controlled cathodic potential. Hydrogen uptake and trapping were then measured using thermal desorption spectroscopy. The hydrogen desorption rate after hydrogen charging manifests two distinct peaks. Plastic deformation during hydrogen charging increases the hydrogen uptake considerably. Hydrogen reduces the elongation to fracture and time to fracture in slow strain rate testing and constant load testing (CLT), respectively. Especially, the strain rate in CLT is dramatically increased. The appearance of hydrogen-induced cracking in the ferrite phase changes from ductile dimple fracture to brittle cleavage fracture due to hydrogen charging, which initiates from the interphases of the graphite nodules. The results are discussed in terms of the role of hydrogen and the graphite nodules in hydrogen embrittlement of ductile cast iron.     

STRESS CORROSION AND HYDROGEN INDUCED CRACKING BEHAVIOUR IN AN Al ALLOY

用恒位移试样跟踪观察了铝合金在电化学充氢和应力腐蚀条件下氢致裂纹的产生和扩展过程。结果表明,裂纹前端的塑性区及其变形量随时间延长而逐渐增大,当它发展到临界条件时就导致氢致滞后裂纹和应力腐蚀裂纹的产生和扩展。 试验温度、外加极化电压以及氯离子对K_(ISCC)以及da/dt的影响和它们对浸泡充氢后的放氢总量的影响相一致。     

Einfluß der Festigkeit unlegierter und niedriglegierter Stähle auf H-induzierte Korrosionserscheinungen bei zügiger plastischer Belastung

Influence of mechanical strength on hydrogen-induced corrosion effects on unalloyed and low-alloysteels subjected to slow strain rate tests Three steels were subjected to various heat treatments or cold working to produce 7 variants of strength. Specimens from these materials were tested in 9 aqueous solutions containing various acidic components by the constant strain rate technique under cathodic polarisation or free corrosion conditions. Hydrogen induced cracks were only observed after passing the maximum load. Hydrogen induced cracking and the decrease in the reduction of area (hydrogen embrittlement) show a good correlation with the mechanical properties of the materials. For less ductile materials the number of cracks decreased with increased embrittlement. The magnitude of hydrogen embrittlement depends on the concentration of undissociated acid in the test solution and is independent of pH value. O₂ can reduce the embrittlement. The effect of test solution composition decreases as the cathodic polarisation potential becomes more negative, because hydrogen will then be generated from H₂O. There is no correlation between the type of corrosion effects and the strength of the material, except in the case of highly sensitive high strength variants with R_m in excess of 1000 N/mm². Quenched and tempered low alloy steels, even at high strength levels, have significantly higher resistance to hydrogen embrittlement than significantly higher resistance to hydrogen embrittlement than unalloyed steels. The same is also ture for workhardened variants. For unalloyed steels, metallurgical cleanness seems to have a favourable influence. No hydrogen induced corrosion effects were observed in specimens tested at 907°C under free corrosion conditions.     

低碳钢在模拟含SO2海洋大气中的氢致开裂机理

在模拟海洋大气环境中,采用电化学渗氢试验及慢应变速率拉伸方法,研究了SO2的存在对于低碳钢发生应力腐蚀断裂的影响及SO2的存在对氢渗透行为的影响。结果表明,随着SO2浓度的增大,试样断裂敏感性增大;SEM表明,其断裂特征由塑性断裂逐渐转变为脆性断裂。电化学渗氢试验表明,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导致。     

X70管线钢在不同温度近中性pH溶液中的应力腐蚀破裂行为

采用慢应变速率实验(SSRT)研究了不同温度和电位下X70管线钢在近中性pH溶液中的应力腐蚀破裂(SCC)行为．结果表明，不同温度下，X70管线钢在近中性pH溶液中的开裂方式都是穿晶型的，具有准解理特征，并且随着外加阴极电位的降低，SCC敏感性增加，氢致开裂占主导．随温度的下降，溶液pH值略有降低，SCC敏感性增加。