Evaluation of temperature effect on the corrosion process of 304 stainless steel in high temperature water with electrochemical noise

The effect of temperature on corrosion process of 304 stainless steel (SS) in high temperature water was investigated by electrochemical noise (EN), scanning electron microscope (SEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the corrosion process could be divided into two stages (passivity and active dissolution) with the increasing temperature. At 100 °C, the oxide film was a single layer mainly consisting of Cr₂O₃. However, at 250 °C, it became a double layer with an inner layer of Cr–Fe spinel compound and an out precipitated layer. The related growth mechanisms of the oxide film were also discussed.     

The effect of niobium on the microstructure of ferritic stainless steel

The effect of different amounts of Nb and of homogenization on the ferritic stainless steels containing 17–18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). It was observed that M₂₃C₆, NbC and sigma phase formed in these steels. In addition, the formation of Nb₂C was observed in the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amount of M₂₃C₆ decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containing 1.5–3.0 wt.%Nb was considerable and impressive.     

Corrosion in water supply pipe stainless steel 304 and a supply line of helium in stainless steel 316

A corrosion spreading throughout the 304 stainless steel tubing of a water system to supply various buildings was observed, and also leaks were detected in welding zones. The same place is also crossed by a gas distribution network, with a helium pipe 316 of stainless steel that required periodic repairs more or less every two years, due to the presence of leaks. The tests showed that both types of stainless steel have suffered localized corrosion induced by hypochlorite ion, in a mechanism of dry/wet, and that the welding procedure performed on the 304 stainless steel is unacceptable. Some immediate procedures were undertaken to keep systems running, but recommendations were given for a final resolution of the problems.     

Tensile behaviour of 316LN stainless steel at elevated temperatures

Abstract

The tensile deformation behaviour of 316LN stainless steel was investigated from ambient temperature up to 1000°C. The hardness and microstructure of area near tensile fracture were characterised. The results show that the engineering stress increases smoothly with engineering strain when the tensile temperature is at 400°C or below, while the plastic deformation stage displays a serrated/jerky flow at 600°C. At tensile temperatures of 800°C or above, the plastic deformation stage is dramatically prolonged. The deformation mechanisms of 316LN stainless steel are proposed to be sliding and twinning at 400°C or below, tangle dislocations due to cross-slipping at 600°C, dynamic recovery at 700°C, and dynamic recrystallisation at 800°C or above. The finding provides useful guidelines for the processing and service of 316LN stainless steel components at high temperatures.     

Effect of oxide scale on corrosion behavior of HP-13Cr stainless steel during well completion process

The well completion process in oil and gas industry,aiming to build effective exploitation,is divided into acidizing and formation water production process.Oxide scale(OS)formed on the inner wall of the HP-13Cr stainless steel tubes during the hot extrusion process changes the surface roughness.The effects of OS on the corrosion of HP-13Cr stainless steel during well completion process were studied by corrosion measurement,spectra analysis,microscopic observation and numerical simulation.The results indicate that the OS make no change of phase distribution and element composition of corrosion scale,while the increasing OS roughness is the dominant factor for accelerating corrosion rate during the well completion process.In acidizing process,the greater surface roughness OS of HP-13Cr stainless steel increases the corrosion rate obviously due to a larger interfacial area in contact with the aggressive environment.During subsequent formation water production process,the turbulence eddy,formed at locations characterized with greater surface roughness OS,can deteriorate the corrosion scale and accelerate the mass transfer of the corrosive species,resulting in more serious corrosion.     

Notch effect on torsional fatigue of austenitic stainless steel: Comparison with low carbon steel

Notch effect in austenitic stainless steel under cyclic torsion is quite different depending on the superposition of static tension. In pure torsion, the rubbing of the serrated factory-roof type crack faces delays the crack growth along the notch root. Thus, the lifetime in notched specimen becomes longer than in smooth specimen. However, in cyclic torsion with static tension, the flat crack path and mean tensile stress reduce the influence of the crack face contact. Accordingly, shorter lifetime resulted from higher strain concentration at the notch root. Crack growth in low carbon steel under cyclic torsion is highly affected by the ferrite/pearlite banded microstructure besides the addition of static tension. Because of a small amount of the crack face contact, the reduction of lifetime in notched specimen is revealed irrespective of superposition of static tension.     

Deformation behavior and the Portevin-Le Chatelier effect in a modified 18Cr-8Ni stainless steel

Mechanical behavior and microstructural evolution of a 2.5%W + 0.4%Nb + 0.3%V + 0.17%N modified 18Cr-8Ni austenitic steel was studied in the temperature interval 410-740 °C at initial strain rates ranging from 6.7 × 10⁻⁶ to 1.3 × 10⁻² s⁻¹. The Portevin-Le Chatelier (PLC) effect attributed to dynamic strain aging (DSA) was found to occur in the temperature range 530-680 °C. The PLC effect is manifested in the form of serrated (jerky) flow and planar slip. DSA increases yield strength, σ_0.2, and ultimate tensile strength, σ_UTS, in comparison with conventional SUS304 steel due to the additional alloying that provides the formations of the clouds of solutes around the dislocations that exert the solute drag force.     

Synergistic effect of erosion and hydrogen on properties of passive film on 2205 duplex stainless steel

Stainless steels have shown great potential in the application of offshore oil and gas industry.However,the internal surface of stainless steel pipeline may simultaneously suffer erosion from the fluid media inside the pipeline and the damage of hydrogen that is generated from the external activities such as cathodic protection.The synergistic effect of erosion and hydrogen on the properties of passive film on 2205 duplex stainless steel was studied for the first time in a loop system coupled with a hydrogen-charging cell.The components,protective performance and semiconductive structure as well as properties of the passive film under different conditions were investigated using in-situ electrochemical techniques,surface characterization and computational fluid dynamics simulation.The results show that the combination of erosion and hydrogen could greatly thin the passive film,furthermore,the Fe³⁺/Fe²⁺ratio and O₂^-/OH^-ratio in the passive film also decrease dramatically under such a condition.Therefore,the hydration degree of the passive film greatly increases,resulting in an increase in active sites and a decrease in the stability of the passive film.Erosion could destroy the passive film through the impact of sand particles and accelerate the mass transfer process of electrochemical reaction.While hydrogen can not only enhance the charge transfer process,but also make the passive film highly defective.Under the combination of erosion and hydrogen condition,erosion could enhance the hydrogen damage and simultaneously hydrogen could also enhance erosion.Therefore,the synergistic effect of erosion and hydrogen could dramatically change the passive film component,decrease the protective performance,and increase the susceptibility of pitting corrosion of 2205 stainless steel in Cl-containing environment.     

Mean stress effect on fatigue strength of stainless steel

Influence of mean stress on fatigue life and fatigue limit was investigated for Type 316 stainless steel. The results for prestrained specimens revealed that fatigue life was almost the same in the same strain range regardless of stress amplitude, maximum peak stress and mean strain. The fatigue life was shortened when applying the mean stress for the same strain range, whereas it was increased for the same stress amplitude. It was shown that the reduction in fatigue life was brought about by the change in the effective strain range, which was caused by the increase in minimum peak stress and the ratcheting strain. The fatigue life could be predicted conservatively even if the mean strain was applied by assuming the effective strain range to be equal to the total strain range (by assuming the crack mouth to be never closed). It was concluded that the mean stress correction was not necessary for the load-controlled cyclic loading and for the region where the ratcheting strain was constrained.     

不锈钢基体温度对NiCrCoAlY 和ZrO2涂层颗粒变形的影响

研究了等离子喷涂过程中, 不同基体预热温度下NiCrCoAl Y金属与ZrO₂ 陶瓷颗粒的变形规律。结果表明: 基体无预热时, NiCrCoAl Y金属颗粒沉积形貌呈盘形, 并伴随边缘堆积和飞溅碎块等不规则现象, 影响后续颗粒的顺利铺展; 基体预热至200 ℃时, 不规则现象减少, 后续颗粒铺展良好。ZrO₂ 颗粒在基体无预热条件下凝固后呈圆盘状, 并产生龟裂纹和条束状溅射, 随着基体预热温度的升高, 龟裂和溅射现象减少。基体预热对NiCrCoAl Y涂层孔隙率影响不大, 而ZrO₂涂层在基体预热至200 ℃时孔隙率明显降低。      

常温制备抗菌不锈钢的研究

抗菌不锈钢是目前材料领域研究的热点.本文以AgNO3、ZnSO4和TiO2为主要原料,制备含有Ag 、Zn2 和TiO2的浸泡液.在常温条件下,将普通不锈钢浸入浸泡液中,制备出表面含有抗菌离子的新型抗菌不锈钢,并对其抗菌性能和持久性进行了表征,结果表明,在经过50次的反复冲洗及NaCl和CH3COOH溶液浸泡,其对金黄色葡萄球菌的平均抑菌率为99.48%,对大肠杆菌的平均抑菌率为99.09%.     

Effects of rare earths on nanocrystalline for nitrocarburised layer of stainless steel

Solution-treated stainless steel was plasma-nitrocarburised at the precipitation-sensitive temperature with and without rare earth (RE) addition. The nitrocarburised layers were characterised by means of X-ray diffraction, transmission electron microscope, nanoindentation and anodic polarisation test. Experimental results show that the depth of plasma-nitrocarburised layer can be apparently increased from 60 to 75?μm after RE addition. More importantly, microstructure of stainless steel surface is refined into nano-sized grains after plasma nitrocarburising. At the depth of 20?μm, the hardness and the modulus of the nanocrystallised layer are as high as 13.6 and 218?GPa. After RE addition, the hardness and the modulus of the nanocrystallised layer increase to 17.5 and 255?GPa, respectively.     

常温下赋予不锈钢抗菌性能的实验研究

以AgNO3为主要原料制备了含有Ag^ 的冷敷液，在常温条件下，采用将冷敷液涂抹在不锈钢表面上或将不锈钢浸入冷敷液中的方法，制备了出表面含有抗菌Ag^ 离子的新型抗菌不锈钢。用扫描电镜(SEM)、X射线衍射(XRD)和原子吸收光谱(AAS)进行表征，表征结果表明，不锈钢表面形成一层含有柠檬酸银和过氧化银的薄膜，Ag^ 还渗透到不锈钢的内部。还对此材料的的抗菌性能进行了奎因实验，实验结果显示，抗菌不锈钢在接种金黄色葡萄球菌和大肠杆菌后培养24h后，不锈钢表面的菌落数均为0。     

Radial growth of carbon nanocoils on stainless steel wires coated with tin particles using chemical vapor deposition from acetylene

Radial growth of carbon nanocoils (R-CNCs) on stainless steel (SS) wire has been achieved using thermal chemical vapor deposition from acetylene. A solution of tin acetate in ethanol with molarities of 0.01-0.2 M was coated on SS wire and oxidized as an active catalyst in air at 600-1000 °C. It was found that SS wire oxidized at 900 °C for 30 min with a tin solution of 0.1 M exhibited the highest catalytic activity. The optimum grain size of Fe-Sn was approximately 0.49 ± 0.15 μm for R-CNCs. The R-CNCs, which were hollow in the center, had an average fiber diameter of 360 nm, a coil diameter of 960 nm and a pitch of 1140 nm. The yield, which was the ratio of the number of R-CNCs to the total carbon products, was 80%. The resistance of as-grown CNC/SS wire coated with higher-molarity solutions was lower than that of the CNC/SS wire coated with lower-molarity solutions. Growing R-CNCs on metal wire provides excellent electrical contact, good alignment, and ease of handling and manipulation.     

Effect of high temperature post-oxidizing on tribological and corrosion behavior of plasma nitrided AISI 316 austenitic stainless steel

In this research, the microstructure, tribological and corrosion properties of plasma nitrided-oxidized AISI 316 austenitic stainless steel at high oxidation temperature were studied and compared with conventional plasma nitride. The structural, tribological and corrosion properties were analyzed using XRD, SEM, microhardness testing, pin-on-disk tribotesting and electrochemical polarization. Plasma nitriding was conducted for 5 h at 450 °C with gas mixture of N₂/H₂ = 1/3 to produce the S-phase. The nitrided samples were post-oxidized at 500 °C with gas mixture of O₂/H₂ = 1/5 for 15, 30 and 60 min. X-ray diffraction confirmed the development of CrN, ? and γ′ nitride phases and magnetite (Fe₃O₄) oxide phase under plasma nitriding-oxidizing process. In addition, it was found that oxidation treatment after plasma nitriding provides an important improvement in the friction coefficient and the corrosion resistance. The optimized wear and corrosion resistance of post-oxidized samples were obtained after 15 min of oxidation.     

Loading sequence effect on fatigue life of Type 316 stainless steel

The change in fatigue life due to variable cyclic loading was investigated experimentally in order to consider the loading sequence effect in fatigue damage assessment for a component design, and the reason for the change was discussed. Strain-controlled fatigue tests, that is, two-step, surface removal two-step, repeating two-step and periodical overload tests were conducted using Type 316 stainless steel specimen in a room temperature laboratory environment. The high-low loading amplitude sequence for the two-step test, and the repeating two-step and periodical overload tests showed a shorter fatigue life than that predicted by the linear damage accumulation rule. On the other hand, the low–high loading amplitude sequence for the two-step test exhibited a longer fatigue life. The reduction in the fatigue life was mainly attributed to the change in effective strain amplitude. The fatigue life reduction due to the loading sequence effect could be assessed conservatively by determining the allowable number of cycles for effective stress amplitude. Namely, by assuming the crack mouth was fully opened in the assessment, predicted fatigue life became shorter than the experimental results. It was concluded that the margin of 1.3–2.3 should be considered in the design fatigue curve in order to take account of the reduction in fatigue life due to the loading sequence effect.     

Microstructure and corrosion behavior of the heat affected zone of a stainless steel 308L-316L weld joint

Microstructure of the heat affected zone (HAZ) of a 308L-316L stainless steel (SS) weld joint and its corrosion behavior in high temperature water were studied. Peak of the residual strain was observed to approach to the fusion boundary in the HAZ while the strain increased from the top to root areas of the HAZ. The root area of the HAZ shows a lower corrosion resistance in high temperature water than the top and middle areas of the HAZ. This is attributed to a higher level of residual strain in association with a higher density of tangled dislocations in the top area of the HAZ. The results suggest that the residual strain in the HAZ could also promote the SCC through its effect on corrosion, in addition to that on the local microstructure and mechanical property of the steel.     

Influence of dynamic strain aging pre-treatment on creep-fatigue behavior in 316L stainless steel

Stress controlled creep-fatigue tests were carried out for hot rolled and dynamic strain aging pre-treated 316L stainless steel different loading levels at 550 °C. For both pre-treatment state materials, dynamic strain aging was found to manifest itself macroscopically as displacement or mean strain abrupt jumps during cyclic deformation. Comparing with hot rolled material, by DSA pre-treatment, the creep-fatigue cyclic strain amplitude is decreased, the cycle at the 1st abrupt displacement jump is postponed and the material creep-fatigue life is effectively prolonged. Moreover, it is found that, the material creep-fatigue life monotonically increases with pre-deformation strain, no matter the maximum pre-deformation stress is larger than the maximum creep-fatigue applied stress or not.     

Tensile ductility and deformation mechanisms of a nanotwinned 316L austenitic stainless steel

A nanotwinned 316 L austenitic stainless steel was prepared by means of surface mechanical grinding treatment.After recovery annealing,the density of dislocations decreases obviously while the average twin/matrix lamella thickness still keeps in the nanometer scale.The annealed nanotwinned sample exhibits a high tensile yield strength of 771 MPa and a considerate uniform elongation of 8%.TEM observations showed that accommodating more dislocations and secondary twinning inside the nanotwins contribute to the enhanced ductility and work hardening rate of the annealed nanotwinned sample.