Effect of thermomechanical treatment on the susceptibility of structural steel to hydrogen embrittlement

It was established that high-temperature thermomechanical treatment (HTMT) produces a substantial reduction in the susceptibility of a medium-carbon steel 37KhN3A (tempered at a low temperature) to hydrogen embrittlement. An anisotropy of the ductility and the resistance to fracture of hydrogen-charged steel was observed after HTMT which points to a selective character of hydrogen charging and hydrogen embrittlement at the boundaries of the initial austenite grains. Torsion test results showed that hydrogen charging has practically no effect on the shear strength and affects only such structure-sensitive properties as tensile strength and ductility.     

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.     

On the use of varying die angle for improving the resistance to hydrogen embrittlement of cold drawn prestressing steel wires

Residual stresses produced by cold drawing are an undesirable effect of the non-uniform plastic strain distribution generated during the conforming process used for obtaining prestressing steel wires. Among the diverse parameters of the process influencing the residual stress generation, one of the most relevant is the geometry of the drawing die and, in particular, the inlet die angle. Wires drawn with die angles as low as possible will exhibit a lower and more homogeneous plastic strain state and, therefore, a smaller and more uniform residual stress state. Thus the hydrogen embrittlement (HE) susceptibility of such wires is also lower, thereby enlarging the life in service of these components. In this paper an innovative design of the drawing die is proposed using two consecutive angles (i.e., varying die angle) for reducing the residual stress and strain state in the cold drawn wires and, consequently, for improving the resistance to HE of prestressing steel wires.     

Effect of cold work on hydrogen embrittlement susceptibility of Ni60Nb40 glass

Ni₆₀ Nb₄₀ glass ribbons were cold rolled to a reduction of ∼ 25%. As-quenched and cold-rolled ribbons were embrittled by cathodic charging in 1.0N H₂SO₄. It was observed that hydrogen embrittlement susceptibility is enhanced on cold-rolling. Kinetics of recovery of ductility was employed to estimate the diffusion coefficient of hydrogen. These investigations indicate an increase in hydrogen diffusivity on deformation.     

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.     

Influence of the die geometry on the hydrogen embrittlement susceptibility of cold drawn wires

Residual stress and strain states produced by wire drawing play an essential role in the main cause of failure of cold drawn wires: hydrogen embrittlement (HE), because of the influence of such fields on hydrogen diffusion within the material lattice. Therefore, variations on stress and strain fields, due to changes in the wire drawing process conditions, could modify the service life of these structural components. In this work the influence on HE of two parameters of the wire drawing process (the inlet die angle and the die bearing length) are analyzed by means of diverse numerical simulations by the finite element method (FEM). According to the obtained results, the effects of residual stress and strain fields produced by wire drawing on HE are less dangerous when the inlet die angle decreases or when the bearing length exceeds a characteristic value (wire radius), with a remarkable reduction of the driving forces for hydrogen diffusion. Consequently, wires drawn under such conditions (lower inlet die angle and longer bearing length) will exhibit a lower susceptibility to HE, thereby increasing their resistance to engineering failure.     

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...     

Effect of low temperature on resistance of stable austenitic steel to embrittlement by hydrogen

Abstract

Tensile straining of a ‘stable’ austenitic stainless steel at subambient temperatures has revealed deformation induced transformation to martensite reaching a maximum at about 200 K. Although the particular steel concerned is only marginally embrittled by hydrogen charging at ambient temperature, the transformation to martensite coincides with increasing embrittlement at lower temperatures. The recovery of a resistance to embrittlement below 215 K is attributed to the decreasing transport of hydrogen by moving dislocations as the temperature is further decreased.

MST/1701     

Effect of cold drawing on environmentally assisted cracking of cold-drawn steel

The fracture behaviour in air and aggressive environments of two eutectoid steels in the forms of hot-rolled bar and cold drawn wire has been compared to elucidate the consequences of cold drawing on their susceptibility to environmentally assisted cracking (EAC) in aqueous environments. Cold drawing produces a microstructural effect on the material: a preferential orientation of the pearlite lamellae aligned parallel to the cold-drawing direction, resulting in anisotropic properties with regard to fracture behaviour in air and aggressive environments. The main consequence is the change in crackpropagation direction approaching that of the wire axis (cold-drawing direction or main average orientation of the pearlite lamellae) and producing a mixed-mode state. The results reported provide insight into the macro- and micro-mechanical effects of cold drawing on the fracture and EAC-behaviour of eutectoid pearlitic 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.     

Assessment of the susceptibility to hydrogen embrittlement. II: Effect of specimen geometry on delayed failure time of 38 NiCrMo 4 steel

Delayed failure tests, in which suitable samples were cathodically charged with hydrogen (current density 8 mA·cm^?2) in 0.1N sulphuric acid, while under sustained tensile loads, were carried out on a low alloyed Ni-Cr steel (UNI 38 NiCrMo 4). The effect of the geometry on the delayed failure time was assessed using specimens with different diameters (2,3,4 mm) and different lengths (13, 23, 33 mm). The experimental results showed that the specimen geometry does not influence the material behaviour: only a minor effect on the threshold stress value was noted due to diameter variations.