A new aspect on intergranular hydrogen embrittlement mechanism of solution annealed types 304, 316 and 310 austenitic stainless steels

The objective of this paper is to propose a new intergranular hydrogen embrittlement mechanism of solution annealed austenitic stainless steels (types 304, 316 and 310) on the basis of the results already reported. An intergranular hydrogen embrittlement (IG-HE) took place for type 316 at potentials less noble than the open-circuit potential in a HCl solution, and for types 304 and 316 at a lower test temperature under an open-circuit condition in saturated boiling magnesium chloride solutions by using a constant load method, while type 310 suffered only a transgranular stress corrosion cracking (TG-SCC) in both solutions under the same experimental conditions, but not IG-HE. In addition, TG-SCC occurred for types 304 and 316 under an open-circuit condition in the HCl solution irrespective of test temperature and in saturated boiling magnesium chloride solutions at higher test temperatures. Thus, the occurrence of IG-HE depended upon the material and test temperature. The new IG-HE mechanism was developed that explains the results obtained in terms of martensite transformation, hydrogen-enhanced local plasticity (HELP), grain boundary sliding (GBS) and so on.     

Stress corrosion cracking and hydrogen embrittlement of sensitized austenitic stainless steels in boiling saturated magnesium chloride solutions

Stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of the sensitized stainless steels of type 304, 310 and 316 were investigated as a function of test temperature in boiling saturated magnesium chloride (MgCl₂) solutions under a constant applied stress condition. The test temperature dependence of fracture appearance and three parameters of time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio (t_ss/t_f) suggests that type 304 suffered SCC and HE, while type 316 suffered only HE and type 310 SCC. It was also found that the test temperature dependence of three parameters for the sensitized type 304 and 310 was almost similar to that of the solution annealed stainless steels, whereas that of type 316 showed a clear difference between sensitized and solution annealed specimens. The relationships between the logarithms of the time to failure and the steady-state elongation rate became a straight line for all stainless steels. However, its slope depended upon the fracture mode; −2.0 for SCC and −1.5 for HE. This showed that the steady-state elongation rate was the parameter for predicting the time to failure for the stainless steels in the MgCl₂ solutions. The results obtained were explained in terms of martensite transformation, hydrogen entry site, sensitization, and so on.     

On the stress corrosion cracking and hydrogen embrittlement of sensitized austenitic stainless steels in boiling saturated magnesium chloride solutions: Effect of applied stress

Stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of sensitized stainless steels of types 304, 310 and 316 were investigated as a function of applied stress at different test temperatures in boiling saturated magnesium chloride (MgCl₂) solutions under a constant applied stress condition. The stress dependence of fracture appearance and three parameters of time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio suggests that types 304 and 310 suffered SCC, while type 316 suffered only HE. It was also found that the applied stress dependence of three parameters for the sensitized types 304 and 310 was almost similar to that of the solution-annealed stainless steels, whereas that of type 316 showed a clear difference between sensitized and solution-annealed specimens. The relationships between the logarithms of the time to failure and the steady-state elongation rate became a straight line for all stainless steels. However, its slope depended upon the fracture mode: −2.0 for SCC and −1.5 for HE. This showed that the steady-state elongation rate was a good parameter for predicting the time to failure for the stainless steels in the MgCl₂ solutions. The results obtained were explained in terms of martensite transformation, hydrogen entry site, and sensitization.     

The stress corrosion cracking behavior of austenitic stainless steels in boiling magnesium chloride solutions

The change in the mechanism of stress corrosion cracking with test temperature for Type 304, 310 and 316 austenitic stainless steels was investigated in boiling saturated magnesium chloride solutions using a constant load method. Three parameters (time to failure; t_f, steady-state elongation rate; l_ss and transition time at which a linear increase in elongation starts to deviate; t_ss) obtained from the corrosion elongation curve showed clearly three regions; stress-dominated, stress corrosion cracking-dominated and corrosion-dominated regions. In the stress corrosion cracking-dominated region the fracture mode of type 304 and 316 steels was transgranular at higher temperatures of 416 and 428 K, respectively, but was intergranular at a lower temperature of 408 K. Type 310 steel showed no intergranular fracture but only transgranular fracture. The relationship between log l_ss and log t_f for three steels became good straight lines irrespective of applied stress. The slope depended upon fracture mode; −2 for transgranular mode and −1 for intergranular mode. On the basis of the results obtained, it was estimated that intergranular cracking was resulted from hydrogen embrittlement due to strain-induced formation of martensite along the grain boundaries, while transgranular cracking took place by propagating cracks nucleated at slip steps by dissolution.     

The effect of test temperature on SCC behavior of austenitic stainless steels in boiling saturated magnesium chloride solution

The stress corrosion cracking (SCC) of the austenitic stainless steels of types 304, 310 and 316 was investigated as a function of test temperature in boiling saturated magnesium chloride solution (MgCl₂) using a constant load method. Both of types 304 and 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different from those of types 304 and 316, in terms of the three parameters such as time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio (t_ss/t_f) obtained from the corrosion elongation curves for these stainless steels. The relationship between the time to failure and a reciprocal of test temperature fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and a reciprocal of test temperature. These regions were considered to correspond to a SCC-dominated region and a hydrogen embrittlement (HE)-dominated region from the value of (t_ss/t_f) and the fracture appearance. The relationship between the steady state elongation rates versus time to failure on a logarithmic scale became a straight line, whereas the slopes of the line for the stainless steels were different with the different fracture mechanism such as SCC and HE. It was found that the linearity of the relationship can be used to predict the time to failure for the stainless steels in the corrosive environment. In addition, type 310 did not suffer from HE, which means that type 310 showed only SCC. This would be explained by whether or not a formation of α′-martensite takes place.     

Studies of the tensile and corrosion fatigue behaviour of austenitic stainless steels

Corrosion fatigue behaviour of four types of austenitic stainless steels were investigated in boiling 45% magnesium chloride solution at a stress ratio of 0.25 and a frequency of 0.1 Hz. Type 316LN stainless steel possessed the best resistance and type 304 stainless steel had the lowest resistance to corrosion fatigue. XPS studies on the fracture surface indicated that the presence of nitrogen as ion in the surface film of type 316LN stainless steel gave it the highest resistance to corrosion fatigue. Fractographic examination showed wholly transgranular cracking in all cases.     

The effect of sensitization on the hydrogen-enhanced fatigue crack growth of two austenitic stainless steels

Fatigue crack growth tests were performed to evaluate the susceptibility to hydrogen-enhanced crack growth of AISI 304 and 316 stainless steels (SSs). Sensitization treatment at 650 °C 100 h played little effect on the fatigue crack growth behavior in air, regardless of testing specimens. However, hydrogen accelerated the fatigue crack growth of various specimens to different degrees; sensitized specimens were more susceptible as compared with the un-sensitized ones.

Fatigue fracture appearance of various specimens tested in air exhibited mainly transgranular fatigue fracture together with rarely intergranular fracture and twin boundary separation. Meanwhile, intergranular fracture was found for sensitized specimens tested in hydrogen. Extensive quasi-cleavage fracture related to the strain-induced martensite accounted for the hydrogen-accelerated fatigue crack growth of unstable austenitic SSs. On the other hand, the lower susceptibility of 316H specimens could be attributed to the partial austenite transformation, as evidenced by a mixture of transgranular fracture feature and quasi-cleavage.     

Corrosion Testing of some Austenitic Stainless Steels and of Inconel Alloy at 25°c in Acidic Chloride Solutions

Abstract

The corrosion of austenitic stainless steels types AISI 304, 310 and 316, and of Inconel alloy, was studied at 25°c, in 5% NaCl solution at an initial pH value of 2·5, and in 5% FeCl³ at pH 1·2. The resistance of the alloys in both corrosive environments was in the order: 310 > 316 > 304 > Inconel. Pre-treatment of the specimens with bubbling chlorine gas increased the subsequent corrosion rates of the alloys. Intermittent bubbling of gas mixtures such as Cl₂, N₂, and/or H₂S, increased the corrosion rate of Inconel alloy when Cl₂ was present, but decreased the corrosion rate when H₂ was present. Heat treatment of austenitic stainless steels increased the subsequent corrosion rates, whereas 16% pre-straining of annealed specimens slightly reduced the rates. Addition of trisodium phosphate to the corrosive solution reduced the corrosion rates and pitting tendency for all three types of austenitic stainless steel.     

Oxidation resistance of sintered stainless steels: effect of yttria additions

The porosity of sintered stainless steels modifies their oxidation behavior, as compared to that of wrought stainless steels. This work studies the oxidation behavior of three sintered stainless steels: one ferritic (AISI 434L) and two austenitic (AISI 316L and 304L). 304L with yttria additions is also been studied to explore the possibility of reducing the oxidation rate of austenitic stainless steels by using this reactive element. The results demonstrate the influence of the formation of NiFe₂O₄ on the high-temperature behavior of sintered austenitic stainless steels and the effectiveness of yttria additions in increasing the oxidation resistance at 800 °C.     

22Cr双相不锈钢与304L、316L钢在氯化物溶液中耐应力腐蚀性能的比较

采用恒载荷法、恒应变法研究了22Cr双相不锈钢在不同Cl-浓度、不同温度的氯化物渗液中耐应力腐蚀的性能,并与316L和304L普通奥氏体不锈钢进行了对比.结果表明,22Cr双相不锈钢在氯化物环境中具有更好的应力腐蚀破裂(SCC)抗力.     

Effect of Cold-Rolling on Precipitation Phenomena in Sensitized Type 316L and 340L Austenitic Stainless Steels

Precipitation phenomena in Type 316L and 304L stainless steels were studied mainly by transmission electron microscopic (TEM) observations after cold-rolling ranging from 0% (as solution annealed) to 80% reduction in thickness,and then by sensitization treatment. Precipitates were identified by electron diffraction analysis and EDS analysis.Precipitates observed in sensitized 316L stainless steel were sigma and chi phases, whereas carbide and sigma were observed in sensitized 304L stainless steel. Recrystallized grains were formed in 30% cold-rolled and sensitized 304L.However, the tendency toward recrystallization in sensitized 316L was much lower than in 304L. Precipitation of sigma and chi phases was accelerated by cold-rolling and they were observed at grain boundaries in lower cold-rolling; they were also seen, in grain interiors in higher cold-rolling. Higher deformation induced partially recrystallization combined with precipitation, resulting in the formation of heterogeneous microstructures.     

Effect of Cold-Rolling on Precipitation Phenomena in Sensitized Type 316L and 304L Austenitic Stainless Steels

Precipitation phenomena in Type 316L and 304L stainless steels were studied mainly by transmission electron microscopic (TEM) observations after cold-rolling ranging from 0% (as solution annealed) to 80% reduction in thickness,and then by sensitization treatment. Precipitates were identified by electron diffraction analysis and EDS analysis.Precipitates observed in sensitized 316L stainless steel were sigma and chi phases, whereas carbide and sigma were observed in sensitized 304L stainless steel. Recrystallized grains were formed in 30% cold-rolled and sensitized 304L.However, the tendency toward recrystallization in sensitized 316L was much lower than in 304L. Precipitation of sigma and chi phases was accelerated by cold-rolling and they were observed at grain boundaries in lower cold-rolling; they were also seen, in grain interiors in higher cold-rolling. Higher deformation induced partially recrystallization combined with precipitation, resulting in the formation of heterogeneous microstructures.     

Stress-corrosion cracking of 15cr-15ni-2.2mo titanium-modified austenitic stainless steels

The stress- corrosion cracking (SCC) behavior of two alloys of titanium- modified austenitic stainless steels with different TiJC ratios in the 20% cold worked condition was studied in 45% boiling magnesium chloride (BP427 K) using the constant- extension rate testing (CERT) technique. The SCC susceptibility of the two titanium-modified alloys was assessed using the ratios of the values of ultimate tensile strength (UTS) and percent elongation in magnesium chloride and liquid paraffin, the susceptibility index (I), crack propagation rates (CPR), and stress ratios at different values of plastic strains. The results obtained on these alloys were compared with AISI type 316 stainless steel. It was observed that the two titaniummodified austenitic stainless steels had better SCC resistance than type 316 stainless steel, mainly due to their higher nickel content and, to a lesser extent, to the presence of titanium. Increasing the value of the TiJC ratio led to increased SCC resistance due to the availability of more free titanium in the solid solution. Fractography of the failed samples indicated failure by a combination of transgranular SCC and ductile fracture.     

敏化处理对不同状态304奥氏体不锈钢氢脆敏感性的影响

研究固溶态和冷轧态304奥氏体不锈钢分别在650 ℃敏化2 h和24 h后的氢脆敏感性。结果表明:冷轧态与固溶态相比,因产生了应变诱导马氏体,氢脆敏感性增加;敏化处理会增加固溶态试验钢的氢脆敏感性,敏化时间越长,氢脆敏感性越高;相反,冷轧态试验钢在高温敏化时马氏体部分逆相变成奥氏体,会在一定程度上降低试验钢的氢脆敏感性,敏化时间越长,氢脆敏感性越低。     

The chloride corrosion of austenitic stainless steels and of an inconel alloy in hot acidic media

Open circuit corrosion testing of austenitic stainless steels, AISI types 304, 310 and 316, and of an Inconel alloy in boiling 5% NaCl solution at pH 2.5 was carried out. The influences of aeration and the introduction of Cl₂ and/or H₂S were also examined. Cl₂ accelerated corrosion, pitting and crack formation whereas H₂S had an inhibiting effect on the corrosion rates and pitting but induced hydrogen attack, which appeared in the form of blisters on the surface specimen. H₂S in the absence of oxygen resulted in the growth of corrosion product on the specimen surface, instead of dissolution, but the cracking tendency also increased due to hydrogen penetration. Addition of trisodium phosphate to the corrosive solution markedly reduced pitting and lowered the corrosion rate by approximately half. Throughout the various tests it was found that the resistance of different alloys to hot chloride corrosion was in the order 310 > 316 > 304 > Inconel.     

Effects of molybdenum on the pitting of ferritic- and austenitic-stainless steels in bromide and chloride solutions

The effect of Mo on the pitting potential, dissolution kinetics, and repassivation behavior of high purity ferritic stainless steels, Fe-18%Cr-x%Mo, and austenitic stainless steels, Fe-18%Cr-12-15%Ni-x%Mo, was studied in solutions of bromide and of chloride. Large increases in the pitting potential of Fe-18%Cr-x%Mo in chloride solution were found with increasing Mo content, compared with the distinctly smaller increases in bromide solution. There was an excellent correlation between the increase in pitting potentials of ferritic alloys between Fe-18%Cr-2% and 5%Mo in the chloride and bromide solutions with the increased dissolution overvoltages in the saturated solution of dissolved products within artificial pits. Austenitic stainless steels also showed larger increases in pitting potential in chloride solution than in bromide solution. Higher pitting potentials were recorded for the austenitic than the ferrite steels with the same Mo content. For austenitic steels, the pitting potentials in bromide and chloride solutions were not attributable solely to the difference in dissolution rates or repassivation characteristics in saturated solution of the dissolved products. It was concluded that initiation processes play an important role in the pitting of austenitic stainless steels.     

Corrosion behaviour of Lotus-type porous high nitrogen nickel-free stainless steels

Corrosion behaviour of three austenitic Lotus-type porous high nitrogen Ni-free stainless steels exposed to an acidic chloride solution has been investigated by electrochemical tests and weight loss measurements. Polarization resistance indicates that the corrosion rate of Lotus-type porous high nitrogen Ni-free stainless steels is an order of magnitude lower than that of Lotus-type porous 316L stainless steel in acidic environment. The localised corrosion resistance of the investigated high nitrogen Ni-free stainless steels, measured as pitting potential, E_b, also resulted to be higher than that of type 316L stainless steel. The influences of porous structure, surface finish and nitrogen addition on the corrosion behaviour were discussed.     

真空低压渗碳对304与316L奥氏体不锈钢组织和性能的影响

采用真空低压渗碳技术对304和316L奥氏体不锈钢进行表面强化,利用光学显微镜、扫描电镜、Thermo-Calc热力学软件、X射线衍射仪和显微硬度计等对渗碳层显微组织、相组成及硬度分布进行分析表征,计算了奥氏体不锈钢渗碳层中不同衍射峰的偏移量及渗碳前后晶格常数的变化量。结合钼对奥氏体不锈钢渗碳过程的影响,对比研究了304和316L奥氏体不锈钢渗碳后,在渗碳层深度、表面硬度及碳化物的析出规律等方面的差异。结果表明,经750 ℃真空渗碳2.6 h后,304和316L奥氏体不锈钢晶格常数分别增加了1.33%和1.14%,形成了由膨胀奥氏体和Cr₂₃C₆组成的渗碳层,Cr₂₃C₆在渗碳层中主要以条状沿膨胀奥氏体晶界析出,表面硬度较基体硬度均提升了两倍以上。     

Corrosion of aluminium,stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.