Slow Strain Rate Tension Tests Research Articles

General corrosion behavior and mechanism of ferritic/martensitic steel with and without TaWVCr coating in static oxygen-saturated lead bismuth eutectic at 550 °C

Here in present work, the ferritic/martensitic (F/M) steel HT9 and refractory TaWVCr high entropy alloy coated HT9 were tested in a static oxygen-saturated lead bismuth eutectic (LBE) at 550 °C through corrosion tests and slow strain rate tension tests to investigate the corrosion behavior and mechanism. The fracture pattern of HT9 and TaWVCr/HT9 both show the ductile fracture. Comprehensive microstructural characterizations from atomic-scale examinations to micro-scale fracture analyses were performed to illustrate the underlying mechanisms of the liquid LBE corrosion. It was revealed that the corrosion of HT9 is related to the surface oxide scale cracking, which propagates into the matrix but terminated in the Cr2O3 enriched zone at the crack tip. On the contrary, the stress concentration caused by local degradation of the TaWVCr coating accelerates the oxidation and dissolution of the coating in LBE, leading to the formation of a duplex oxide layer underneath the coating, which allows cracks initiate in the magnetite layer and annihilate in the chromite layer. The micrometer-scale penetrative oxide layer was found within the matrix, due to the inward diffusion of O through the diffusion channels such as dislocation channels of the matrix and the dissolution channels of the coating and this can accelerate the oxidation corrosion of the matrix.

Insights into the role of CO in inhibiting hydrogen embrittlement of X80 steel weld at different hydrogen blending ratios

In this study, slow strain rate tension tests were conducted on an X80 steel weld in 12 MPa mixed gases with 2 %–75 % H2 ([H2]) and 0 %–0.75 % CO ([CO]). The influence mechanism of CO on inhibiting hydrogen embrittlement (HE) was explored with the aid of the first-principles method and hydrogen permeation tests. The results show that the HE index first decreases rapidly with the increase of [CO] or [CO]/[H2], and then tends to stabilize. CO can restore the hydrogen induced plastic loss to a certain value, and the recovery degree decreases with the increase of [H2]. CO preferentially occupies the hydrogen adsorption site when co-existing with H2, and can reduce but not completely inhibit hydrogen permeation, this is the essential reason why the change of [CO] affects HE susceptibility.

Microstructure and stress corrosion cracking of a SA508-309L/308L-316L dissimilar metal weld joint in primary pressurized water reactor environment

Stress corrosion cracking (SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at γ/δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal. The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.

Comparison of hydrogen embrittlement susceptibility of three cathodic protected subsea pipeline steels from a point of view of hydrogen permeation

Revealing the hydrogen permeation behavior in steel is the foundation to analyze hydrogen induced fracture. Herein, slow strain rate tension tests were used to investigate the susceptibility of X70, X80 and X100 steel to hydrogen embrittlement induced by cathodic polarization, and the subsurface hydrogen concentration (C0) of three steels was accurately determined by two kinds of hydrogen permeation tests. Results showed that the HE index range of ductile-to-brittle transition should be determined by fracture analysis. The C0 increased in turn from X70, X80 to X100 at any given applied potential, that’s why X100 presented the highest hydrogen embrittlement susceptibility.

Effect of high energy shot peening pressure on the stress corrosion cracking of the weld joint of 304 austenitic stainless steel

The weld joint of 304 stainless steel is treated using high energy shot peening(HESP) with various shot peening pressures. The grain size and metallographic microstructure of the specimen surface layer are analyzed using the X-ray diffraction method, and the surface hardness is measured. Slow strain rate tension tests are then performed to investigate the effect of shot peening pressure on the stress corrosion sensitivity. The results show that in the surface layer of the specimen, the grain refinement, hardness and the strain-induced plastic deformation all increase with the increasing shot peening pressure. Martensitic transformation is observed in the surface layer after being treated with HESP. The martensite phase ratio is found to increase with increasing shot peening pressure. The result also shows that the effects of the shot peening treatment on the stress corrosion sensitivity index depend on the shot peening pressure. When the shot peening pressure is less than 0.4MPa, the grain refinement effect plays the main role, and the stress corrosion sensitivity index decreases with the increasing shot peening pressure. In contrast, when the shot peening pressure is higher than 0.4MPa, the martensite transformation effect plays the main role, the stress corrosion sensitivity index increases with increasing shot peening pressure.

Effect on New Corrosion Inhibitor to Stress Corrosion Cracking of Prestressed Steel Wire in Simulated Concrete Pore Solution

Slow strain rate tension tests were carried out in order to investigate effect on new corrosion inhibitor to stress corrosion cracking of prestressed steel wire in simulated concrete pore solution. Indeed, the results suggest that C4H13N3 can form adsorption film on the metal surface, prevent chloride ion erosion. Meanwhile, MoO42- may make the passive film become denser. The synergistic effect of C4H13N3 with MoO42-, can reduce the prestressed steel wire SWRH77B in 3.5%NaCl+ saturated Ca (OH)2 solution stress corrosion sensitivity, prevent stress corrosion cracking effectively.

Oxide properties and stress corrosion cracking behaviour for Alloy 600 in leaded caustic solutions at high temperature

The stress corrosion cracking behaviour of Alloy 600 in caustic solutions with and without PbO at 315 °C was investigated by means of slow strain rate tension tests. The characterisation of the oxide that formed on Alloy 600 was derived from transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. Lead was incorporated into the oxide in a metallic lead state and a lead oxide state, which degraded the passivity and induced PbSCC susceptibility. NiB was used as an inhibitor. It reduced the lead incorporation level in the oxide layer and decreased PbSCC susceptibility.

新型転換炉ふげん発電所における系統化学除染技術の開発と経験 構成材料健全性確認試験・評価

Fugen, a heavy-water-moderated pressure-tube type reactor, has operated satisfactorily for over 17 years since the start of commercial operation in March 1979. In August 1989 at the 8tb annual inspection, the full system decontamination of primary reactor circulation system was successfully performed for the first time in Japanese operational power reactors, which yielded the large reduction of occupational radiation exposure. Research & Development on the full system decontamination has been conducted since 1977, and the reagent KD203, a dilute chelate one, was selected through fundamental capability tests and application tests for the use. Prior to the decontamination, the structure material integrity tests and evaluations with the reagent KD203 were conducted. Slow Strain Rate Tension (SSRT) tests and Uni-axial Constant Load (UCL) tests for stainless steel, and SSRT tests for the pressure tube material were performed. From the results it was confirmed that tbe reagent never affected harmful influence upon the Fugen structulral materials on general corrosion, stress corrosion cracking, hydrogen degradation and the integrity of pressure tube rolled joints.

ステンレス鋼の腐食性環境中における電気化学的挙動と機械的性質に関する研究 第９報 ６０℃の３０％ＨＮＯ３水溶液において不働態化処理を施したＳＵＳ３０４ステンレス鋼の水素ぜい化挙動

This study was intended to develop the alleviation countermeasures against hydrogen embrittlement of an austenitic stainless steel (SUS304). As the first step, the passivation treatment which is recommended to be used for prevention of crevice corrosion in “Method of pitting potential measurement for stainless steel” in JIS was adopted. Slow strain rate tension tests were carried out for the passivation treated specimens under the environment of hydrogen evolution immediately after the specimens were held for various time periods at hydrogen evolution potentials on the cathodic polarization curve which was obtained in 3%NaCl solution. The main results obtained are as follows.(1) The pitting initiation potential of the passivation treated specimen showed a more noble potential of 0.087V (vs. S.C.E.) than the untreated specimen. The passivity maintaining current also showed a stable state. Therefore, the passive state film which was formed on the specimen is considered stable.(2) The passivation treated specimen immersed for 90 minutes in 30%HNO3 solution at 60°C showed a larger change of mechanical properties, i.e., reduction in area and time to fracture, than the untreated specimen at cathodically charged potential under each setting condition.From the SEM observation of fracture surfaces, the fraction of brittle region in the treated specimen, characterized by transgranular fracture including quasi-cleavage fracture, decreased from that of the untreated specimen. The effect of passive state film was well recognized, and the hydrogen embrittlement behavior appeared alleviated.

ステンレス鋼の腐食性環境中における電気化学的挙動と機械的性質に関する研究 第７報 定電位ＳＳＲＴ法による３％ＮａＣｌ水溶液におけるＳＵＳ３０４ステンレス鋼の水素ぜい化挙動

It is well known that the metallic materials show the environmental embrittlement phenomena which cause ruptures at short period when stress is applied in various corrosive environments. The hydrogen embrittlement accompanied with the cathodic reaction is also included in these phenomena. It is said that the austenitic stainless steel SUS304 employed in structural materials causes stress corrosion cracking, but hydrogen embrittlement may or may not occur.In this study, in order to examine the hydrogen embrittlement behavior of SUS304 stainless steel from the change of mechanical properties or the change of fracture surface morphology, slow strain rate tension tests were carried out under the environment of hydrogen evolution immediately after the specimens were held for various time periods at hydrogen evolution potentials on the cathodic polarization curve which was obtained in 3%NaCl solution. The main results obtained are summarized as follows.(1) The reduction in area, which indicates, usually a remarkable change in the embrittled materials, decreased continuously with increasing holding time in each setting potential. This tendency became more pronouned at lower setting potential of -2.0V (vs. S.C.E.), and an embrittlement phenomenon could be found. The same results were also obtained for the change of time to fracture.(2) The fracture surface morphology accompanied with the embrittlement was represented by the transgranular fracture. The region of transgranular fracture containing the cleavage fracture occupied a wide range of fracture surface when the specimen was held for longer time at lower setting potential.

異なる表面粗さを施したＳＵＳ４３０ステンレス鋼の水素発生電位下における低ひずみ速度引張試験

In order to elucidate the relation between hydrogen embrittlement and surface roughness, slow strain rate tension tests were carried out under various hydrogen evolution potentials, -0.1--2.0V (vs. S.C.E.), on ferritic stainless steel SUS430, surface roughness of which is varied in there sizes, 0.75, 3.5 and 5.0μm.The results obtained are summarized as follows:(1) The reduction in area and the time to fracture, which are the indicators of the degree of embrittlement of specimen, decreased at low hydrogen evolution potentials. The similar behavior was also observed when the specimen was held for longer time at each hydrogen evolution potential.(2) When the specimen surface roughness was large, the reduction in area and the time to fracture decreased at all setting potentials. The influence of specimen surface roughness on the embrittlement phenomena is summarized in the order of specimen A (0.75μm)<specimen B (3.5μm)<specimen C (5.0μm) because the reduction in area becomes smaller and the time to fracture becomes shorter in this order.

水素発生電位下におけるＳＵＳ４３０ステンレス鋼の低ひずみ速度引張試験（カソード電位の保持時間の影響）

In the previous paper, the holding time was found to be an influencing factor for the hydrogen embrittlement of stainless in 3% NaCl solution. In this study, in order to elucidate the relation between the cathodic potential and mechanical properties, the slow strain rate tension tests were carried out under the environment of hydrogen evolution successively after the specimens were held for various time periods in hydrogen evolution potential.The main results obtained are summarized as follows.(1) The embrittlement ratio obtained from the reduction of area decreased continuously with increasing holding time in each setting potential. This tendency became more pronounced at lower setting potential. Consequently, although the contraction of specimen decreased only slightly in every direction, a remarkable embrittlement phenomenon could be found. The same results were also obtained for the time to fracture.(2) The degradation of mechanical properties accompanied with the hydrogen embrittlement was also noticed in the rupture behavior or the observation of fracture surface by S.E.M.. In particular, the results observed by S.E.M. indicated that the transgranular fracture including quasi-cleavage fracture increased in the outside region of specimen and the dimple caused by ductile fracture decreased in the inside region of specimen.

ステンレス鋼の種々なカソード電位下における低ひずみ速度引張試験

ステンレス鋼の種々なカソード電位下における低ひずみ速度引張試験