Hydrogen enhanced crack propagation of SCM440H low-alloy steel under long-term varying load

Crack propagation behavior of SCM440H low-alloy steel enhanced by absorbed hydrogen is investigated. Six materials tempered at different temperatures are used. Effects of stress ratio, loading frequency, hold time and material hardness on the crack propagation rate are examined under long-term varying load. Tests have been performed under continuous hydrogen charging, in which the crack tip has been isolated from the electrolyte and kept dry. An acceleration of crack propagation rate about six times compared to the uncharged material is found in all materials. In addition to this, however, an unexpected acceleration of crack propagation up to 1000 times is experienced under certain conditions. In materials with Vickers hardness higher than 280 tested at low frequency, the above marked acceleration is experienced. The crack surface morphology is quasi-cleavage. This critical hardness (HV = 280) is a little lower than the usually accepted critical hardness for delayed failure (HV = 350). In material with Vickers hardness lower than 268, however, such a marked acceleration is not experienced.     

Hydrogen effect on cyclic plasticity and crack growth in coarse-grained iron

The effects of hydrogen with a concentration of ∼0.1 mass ppm on cyclic plasticity and crack growth were investigated on a Fe-0.01 mass% C alloy. In polycrystalline specimens, the grains covered with multiple gliding were decreased but those including discrete slip bands were increased in the presence of hydrogen. The hydrogen effect on cyclic plasticity of the coarse-grained specimens is characterized by the increased spacing and the decreased height of slip bands. Crystallographic crack growth was retained in the hydrogen-charged specimen unlike the uncharged specimen. This suggests that dissolved hydrogen restricts the number of the activated slip systems at the crack tip.     

ASSISTED CRACK GROWTH IN MARAGING STEEL WELDS BY GASEOUS HYDROGEN

Abstract— The effects of environmental hydrogen content on fatigue crack growth rates (FCGRs) in T-250 maraging steel plates and laser welds were investigated. The influence of ageing treatments on fatigue characteristics of the alloy was also studied. Experimental results revealed that the accelerated FCGRs in the presence of hydrogen were always associated with changes in fracture modes that appear in compact-tension specimens. Even for overaged specimens with excellent resistance to gaseous hydrogen embrittlement, such an acceleration of crack growth in hydrogen could not be avoided. The crack path of underaged specimens in hydrogen was found mainly along prior austenite boundaries for steel plates and along coarse columnar boundaries for welds. In gaseous hydrogen, peak-aged welds exhibited intergranular and quasi-cleavage mixed fracture modes, compared to mainly quasi-clevage for similar aged steel plates. Hence, the enhancement of crack growth in hydrogen was more pronounced for the welds. Overaged welds showed higher FCGRs than the same aged steel plates only in hydrogen and for Δ K values greater than 20MPa√m.     

30CrMnSiNi2A螺栓断裂分析

材料为30CrMnSiNi2A的一螺栓在正常装配预紧时断裂。经化学分析、宏微观检验,认为,螺栓的断裂系氢脆所致。     

锌基合金氢脆行为研究进展

文章综述了Zn-Fe、Zn-Ni和Zn-Co等主要锌基合金电沉积过程中氢脆性的研究状况.指出锌合金镀层具有良好的性质,将会得到更广泛的应用.     

Performance of Amperometric and Potentiometric Hydrogen Sensors

The principle, design, construction and performance of the amperometric and potentiometric sensors for measuring the permeation rate of hydrogen through the wall of metal equipment were investigated in order to develop a new type of hydrogen sensor with high accuracy. The transient curves of hydrogen permeation under a given charging condition were employed to evaluate the performance of two types of hydrogen sensors. The relative deviation of the hydrogen concentration detected with two types of sensors under the same condition varied from 3.0% to 13%. The accuracy, response time, reproducibility, and installation were discussed and compared. Response time of the potentiometric sensor （E-sensor） was shorter than that of the amperometric sensor （I-sensor）. Both types of sensors exhibited good reproducibility. Development of I-sensor composed of a kind of proton conductor adhesives or non-fluid electrolytes which contain two functions of high electrical conductivity and a strong adhesion will be a promising prospect in order to measure hydrogen permeation at high temperature.     

弹簧断裂原因分析

弹簧在弹栓试验时发生断裂。采用化学成分分析、金相检验和扫描电镜分析等手段,对断裂弹簧进行了分析。结果表明,弹簧在去氢时未严格按工艺要求执行,致使大量的氢残留并呈弥散分布形态,进而形成沿晶裂纹。在外力作用下,导致沿晶脆性断裂。     

Fatigue characteristics of a type 304 austenitic stainless steel in hydrogen gas environment

The effects of a hydrogen gas environment on the fatigue characteristics of a type 304 austenitic stainless steel were investigated and the following results were obtained. The hydrogen effect is not clearly seen by judging fatigue life diagram. However, crack initiation retards and crack propagation accelerates in hydrogen gas environment. The retardation seems to be caused by the absence of oxygen and water vapour. The acceleration seems to be caused by the intrinsic hydrogen effect.     

氢对钛合金的影响

介绍了钛合金的基本性质,分析了钛合金氢脆机理及表现,概括了氢对钛合金裂纹扩展速率和疲劳寿命的影响,总结了氢致裂纹的影响因素。     

Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

电解充氢对堆焊熔合区疲劳裂纹扩展行为的影响

研究了阴极充氢前后堆焊熔合区疲劳裂纹扩展行为,发现堆焊熔合区对疲劳裂纹的扩展有阻碍作用,充氢对裂纹扩展速率无明显影响,但使熔合区出现大量二次裂纹,随着充氢时间的延长,二次裂纹将更加严重。     

A MODEL FOR THE BEHAVIOUR OF MATERIALS WITH CRACKS UNDER HYDROGEN EMBRITTLEMENT CONDITIONS

Abstract— We consider the slow growth of normal tension cracks as quasi-brittle behaviour under hydrogen embrittlement conditions. Experiments show that the cracking resistance of a material in such cases is not a constant of the material, but is characterized by some function that relates the rate of crack growth to the stress intensity factor. We propose a numerical method for the calculation of opening mode crack growth when the kinetics are controlled by the gas diffusion into the material. The problems under consideration model the fracture phenomena inherent to structures (e.g. pressure vessels, pipelines) that operate in an aggressive medium and in particular a hydrogen environment.
In such problems it is necessary to calculate the pressure variation inside a crack as a result of gas diffusion and crack growth under the action of this pressure. Hence it is necessary to solve problems of diffusion theory and elasticity theory for a cracked medium together with some additional conditions that provide the link between these two fundamental problems.
We study the case of an infinite medium containing a crack which occupies a plane domain of arbitrary shape. To avoid difficulties related to the three-dimensionality of the problems, we reduce them to two-dimensional integro-differential equations for the crack domain. The integro-differential equation of the elasticity problem of the crack is solved on the basis of the Boundary Element Method (BEM). The crack kinetics are calculated using a scheme previously introduced by one of the authors and then the BEM is used to solve the integral equation for the diffusion-into-the-crack problem similar to the analogous problem of filtration of the fluid into a crack.     

应变速率与40Cr钢氢脆特性关系的研究

本文通过考察不同应变速率下渗氢试样机械性能的变化情况，用扫描电镜（ＳＥＭ）分析断口的宏观微观形貌，研究了４０Ｃｒ钢的应变速率与氢脆敏感性的关系、     

Ultrasonic investigation of the interaction of hydrogen-dislocations in copper crystals

In this paper we present experimental data of ultrasonic velocity and attenuation obtained in a high purity crystalline sample of copper hydrogenated by gaseous charge. The sample is oriented in the 〈1 1 1〉 crystallographic direction and aged for this work in three stages between 64 and 97 days. The results indicate that the hydrogen is mainly segregated at the dislocation core, inhibiting the hydrogen Snoek-Köster relaxations verified at earlier ageing stages. Despite this, a contribution to viscosity in the kink-chain resonance is provided by the mobile hydrogen in the dislocation core by its side movement along the dislocation line. At temperatures at which the hydrogen begins to freeze in the lattice the geometrical kinks find a gradual increase on the hindering of their movements along dislocation lines, becoming immobile when the hydrogen is completely frozen in the crystal, anchoring the dislocations in short loops. Although the viscosity associated with the mobile hydrogen is removed, the resonance associated with geometrical kinks is not completely cancelled. The interaction of hydrogen-dislocation can be fully described in terms of kinks in dislocations.     

Improved resistance to hydrogen embrittlement by tailoring the stability of retained austenite

ABSTRACT

The susceptibility of hydrogen embrittlement (HE) in GCr15 bearing steel under two types of heat treatments: quenching and tempering (QT) and pre-quenching and austempering (PQA) were investigated. Results showed that PQA-treated specimen have higher mechanical stability of the retained austenite (RA) compared with QT-treated specimen. The experiment of indentation test and hydrogen bubbles suggested that PQA-treated specimen was less susceptible to hydrogen than the QT-treated sample. Subsequently, hydrogen permeation tests revealed significant differences in diffusion coefficient and the number of hydrogen trapping sites between QT and PQA specimens. It was demonstrated that PQA is an appropriate heat treatment to tailor the stability of the RA and enhances the resistance to HE of GCr15 bearing steel.

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

Hydrogen-induced cracking in a very-high-purity high-strength steel

It is shown that intergranular fracture along prior-austenite grain boundaries in a ultrahigh-strength quenched and tempered 4340-type steel is not suppressed by eliminating all segregated embrittling elements. This leaves open the question of how brittle intergranular cracks are nucleated in hydrogen in the absence of such impurities.     

提高漏磁法检测抽油杆疲劳裂纹灵敏度的新方法

采用漏磁法可检测抽油杆表面存在的各种缺陷,但对于在现场检测的抽油杆表面却存在油污(虽然经过清洗)、表面粗糙及直线度低(虽然经过矫直)等问题,使得检测过程中的检测探头与被检测的抽油杆接触不严密,造成对微小缺陷特别是疲劳裂纹的检测信号不敏感.研制了拉伸式管/杆漏磁无损检测实验台,对拉伸实验杆预制疲劳裂纹并对其进行了检测试验,结果采集到了更大的疲劳裂纹信号,因此用该方法提高了漏磁法检测抽油杆疲劳裂纹的灵敏度.