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 cold drawing on susceptibility to hydrogen embrittlement of prestressing steel

This paper compares the behaviour under aggressive environmental conditions of a prestressing steel in two forms (bar and wire) of different yield strengths, to investigate the influence of this material parameter on their susceptibility to hydrogen-assisted cracking in aqueous environments. Slow strain-rate tests using pre-cracked, specimens were performed under various environment conditions. Different fatigue pre-cracking loads were used to analyse the influence of the stress state in the vicinity of the crack tip on the hydrogen-assisted cracking process. The results confirm the well-known fact that the highest-strength steel is the most susceptible to hydrogen embrittlement. A model of hydrogen diffusion in metals— including the effects of both hydrogen concentration and hydrostatic stress distribution—is proposed to explain these results on the basis of the stress-strain curve of the material. Consideration is given to compressive residual stresses induced in the vicinity of the crack tip during the fatigue pre-cracking process. The model is able to explain the different susceptibility to hydrogen embrittlement of the two steels.

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Resume On utilise couramment deux types d’aciers dans le béton armé: les aciers tréfilés (C−Mn) ou trempés (Si−Cr). Bien que leur limite élastique soit assez élevée pour garantir une durée de service normale dans la zone d’élasticité, leur résilience est moindre que celle des aciers ductiles de limite élastique inférieure, et ils sont, par conséquent, plus sujets à des défauts tels que fissures ou encoches. De plus, ces aciers peuvent se fissurer sous l’influence d’une ambinace corrosive. On compare ici le comportement dans des conditions agressives, d’un acier de précontrainte C−Mn sous forme de barre ou de fil, de limites élastiques différentes, afin d’étudier l’influence, de ce paramètre du matériau sur la fissuration favorisée par l’hydrogène en milieux aqueux et, par suite, l’effet (bénéfique ou non) du procédé de tréfilage de ce point de vue particulier. Le programme expérimental consistait en une série d’essais de déformation à vitesse lente sur des éprouvettes pré-fissurées dans des conditions ambiantes variées. On a utilisé différentes charges de pré-fissuration en fatigue pour analyser l’influence de l’état de contrainte au voisingage de l’extrémité de la fissure sur le processus de fissuration favorisé par l’hydrogène. Les résultats confirment le fait bien connu, à sovoir que le fil tréfilé (acier de haute résistance) est davantage sujet à la fragilisation par l’hydrogène que la barre laminée à chaud (résistance plus basse), ce qui montre que le tréfilage réduit la résistance d’un acier de précontrainte à la fissuration favorisée par l’hydrogène. Dans la partie théorique, on propose un modèle de diffusion de l’hydrogène dans les métaux—qui tient compte des effets de la concentration en hydrogène et de la distribution des contraintes hydrostatiques—pour expliquer les résultats expérimentaux à partir de la courbe contrainte/déformation établie pour chaque matériau. On tient compte des contraintes en compression résiduelles qui se produisent au voisinage de l’extrémité de la fissure pendant le processus de pré-fissuration en fatigue, et qui sont modélisées selon les distributions de Rice pour un matériau élastique idéalement plastique. Le modèle permet d’expliquer les différentes susceptibilités à la fragilisation à l’hydrogène des deux formes d’acier de précontrainte à haute résistance (barre et fil): après la pré-fissuration en fatigue, la barre laminée à chaud présente une zone plastique plus large que le fil tréfilé, et l’hydrogène doit couvrir une plus longue distance avant d’atteindre le point critique, ce qui explique pourquoi la barre laminée est moins susceptible à la fragilisation à l’hydrogène.

     

Effect of high-temperature thermomechanical treatment on hydrogen embrittlement of a high-strength aluminum alloy

Chelyabinsk State Technical University. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 1, pp. 73–76, January–February, 1993.     

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.     

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 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.     

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.     

Evaluating the susceptibility of steels to hydrogen embrittlement using statistical analyses

Delayed failure tests of hydrogen-charged specimens result in a large scatter of failure times and failure stresses, analogous to the brittle behaviour exhibited by ceramics. Because of the considerable variation in results, a large number of specimens have to be tested in order to gain an indication of the performance of a particular material; when two materials of similar susceptibility to hydrogen embrittlement are tested, interpretation of the results is often difficult. In the present investigation, seven similar steels were tested in the delayed failure mode to determine their relative susceptibilities to hydrogen embrittlement. These steels were of similar composition and microstructure and showed a low susceptibility to hydrogen embrittlement. The results were analysed using established statistical analysis methods, and by a modified statistical analysis which was developed to describe the failure behaviour. The results of the delayed failure tests and the statistical analyses are presented.