Wear characteristics of a new type austenitic stainless steel

In order to solve the problem of the poor wear resistance in conventional austenitic stainless steels, a new type austenitic stainless steel was designed based on Fe–Mn–Si–Cr–Ni shape memory alloys in this article. Studies on its wear resistance and wear mechanism have been carried out by comparison with that of AISI 321 stainless steel using friction wear tests, X-ray diffraction, scanning electron microscope. Results showed that the wear resistance of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was better than that of AISI 321 stainless steel both in dry and oily friction conditions owing to the occurrence of the stress-induced γ → ε martensitic phase transformation during friction process. This article also compared the corrosion performance of the two stainless steels by testing the corrosion rate. Results showed that the corrosion rate of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was notably lower in NaOH solution and higher in NaCl solution than that of AISI 321 stainless steel.     

铁素体不锈钢在高温尿素环境中的腐蚀行为研究

对三种商用车排气系统用铁素体不锈钢(436L、439M、441)进行了尿素结晶腐蚀试验,以模拟铁素体不锈钢在商用车排气系统内选择性催化还原器(SCR)中的渗氮腐蚀行为。探究了合金成分及夹杂物对不锈钢耐高温尿素腐蚀的影响,并依据EDS表征结果阐释了材料内部腐蚀的渗氮机理。研究表明,在高温热震疲劳和氧化的协同作用下,高温高氮的环境导致铁素体不锈钢晶界及晶内局部区域快速析出氮化铬颗粒,造成晶界及基体局部区域贫铬。由于436L和441不锈钢含有较高的Mo和Nb,其耐高温尿素腐蚀能力显著优于439M。此外,由于436L和441不锈钢中夹杂物细小弥散,也降低了氮化铬在夹杂物的形核析出几率,成为提高抗高温尿素腐蚀的另一个因素。     

含Cu抗菌不锈钢的工艺与耐蚀性能

与普通0Cr17铁素体不锈钢和0Cr18Ni9奥氏体不锈钢相比，含铜铁素体和奥氏体抗菌不锈钢均具有良好的冷热加工性能和焊接性能．通过提高浇铸温度，抗菌不锈钢能保持良好的铸造性能．奥氏体抗菌不锈钢的抗应力腐蚀性能比0Cr18Ni9不锈钢有很大的提高，而铁素体抗菌不锈钢比0Cr17有明显的下降．与相应的普通不锈钢相比，两种类型抗菌不锈钢的耐点蚀性能均略有下降．     

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt–chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of “nickel-free nitrogen containing austenitic stainless steels” for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels.     

Super austenitic stainless steels — a promising replacement for the currently used type 316L stainless steel as the construction material for flue-gas desulphurization plant

Potentiodynamic anodic cyclic polarization experiments on type 316L stainless steel and 6Mo super austenitic stainless steels were carried out in simulated flue-gas desulphurization (FGD) environment in order to assess the localized corrosion resistance. The pitting corrosion resistance was higher in the case of the super austenitic stainless steel containing 6Mo and a higher amount of nitrogen. The pit-protection potential of these alloys was more noble than the corrosion potential, indicating the higher repassivation tendency of actively growing pits in these alloys. The accelerated leaching study conducted for the above alloys showed that the super austenitic stainless steels have a little tendency for leaching of metal ions such as iron, chromium and nickel at different impressed potentials. This may be due to surface segregation of nitrogen as CrN, which would, in turn, enrich a chromium and molybdenum mixed oxide film and thus impedes the release of metal ions. The present study indicates that the 6Mo super austenitics can be adopted as a promising replacement for the currently used type 316L stainless steel as the construction material for FGD plants.     

A new ferritic stainless steel with improved thermo-mechanical fatigue resistance for exhaust parts

Abstract

Over the past few years, car manufacturers have been considering ever higher service temperatures for the engine in order to comply with the constraints of depollution standards. The requirements in terms of exhaust gas temperature could easily reach and overtake the limits of common stainless steel grades used for such applications in the coming years.

A new ferritic stainless steel – named K44X – with increased high temperature resistance has therefore been developed to withstand service temperature up to 1000 °C. K44X belongs to EN 1.4521 and AISI 444 classifications and is composed of approximately 19% Cr, 2%Mo and 0.6% Nb. This specific composition leads to better mechanical properties, higher creep and fatigue resistance than EN 1.4509, while keeping comparable weldability and formability. Its coefficient of thermal expansion is lower in comparison to austenitic stainless steel grades and its resistance to cyclic oxidation is improved significantly.

High-temperature properties (mechanical properties, creep, cyclic oxidation resistance, and high cycle fatigue) of K44X are presented in this paper and compared with common ferritic and austenitic stainless steels used in the hot end of exhaust lines. A thermal fatigue test – designed to reproduce exhaust manifold service conditions – has also been carried out with the highest temperatures of the cycle in the range of 850–1000 °C. The results of these thermal fatigue tests were compared with the above-mentioned stainless steels. A thermal fatigue damage criterion was then identified based on these experimental results and using a cyclic behaviour law obtained from isothermal low cycle fatigue tests.     

A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献   

Corrosion of a stainless steel handrail

AISI 304 and 304L stainless steels are “workhores” grades of austenitic stainless steel frequently used in architectural applications, as well as in cookware, appliances, and numerous other applications where resistance to corrosion is required. This paper examines a corrosion failure (the appearance of rustlike stains on the surface) of a 304 stainless steel handrail that appears to have occurred as a result of contamination during the fabrication process.     

Failure Analysis of AISI 321 Austenitic Stainless Steel Water Piping in a Power Plant

The objective of this work was to analyze a reported pitting damage mechanism in water piping of a power plant. The investigated material was a longitudinal-seam welded pipe which was made of AISI 321 austenitic stainless steel. Pitting occurred on the internal surfaces of the pipe and adjacent to the girth welds. Optical emission spectrometry, metallography, and electrochemical testing were the techniques employed to analyze the failure. The investigation showed that the flowing water contained chloride ions in which AISI 321 austenitic stainless steel is not immune against pitting corrosion. In addition, the polarization data showed the susceptibility of the material to pitting corrosion in the service conditions. Furthermore, the result of double loop electrochemical potentiokinetic reactivation tests showed that the material was sensitized during welding. It was found that the damage was due to pitting corrosion in chloride-containing water. Thus, it was recommended to replace the pipe with material having higher pitting resistance equivalent number to be more resistant against pitting corrosion.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

Surface-protein interactions on different stainless steel grades: effects of protein adsorption, surface changes and metal release

Implantation using stainless steels (SS) is an example where an understanding of protein-induced metal release from SS is important when assessing potential toxicological risks. Here, the protein-induced metal release was investigated for austenitic (AISI 304, 310, and 316L), ferritic (AISI 430), and duplex (AISI 2205) grades in a phosphate buffered saline (PBS, pH 7.4) solution containing either bovine serum albumin (BSA) or lysozyme (LSZ). The results show that both BSA and LSZ induce a significant enrichment of chromium in the surface oxide of all stainless steel grades. Both proteins induced an enhanced extent of released iron, chromium, nickel and manganese, very significant in the case of BSA (up to 40-fold increase), whereas both proteins reduced the corrosion resistance of SS, with the reverse situation for iron metal (reduced corrosion rates and reduced metal release in the presence of proteins). A full monolayer coverage is necessary to induce the effects observed.     

In vitro corrosion resistance of Lotus-type porous Ni-free stainless steels

The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.     

AES study of passive films formed on a type 316 austenitic stainless-steels in a stress field

The type AISI 316 stainless steel, in addition to the principal alloying elements chromium and nickel, contains 2.5–3.5% of molybdenum. This element is added to improve the mechanical properties and the pitting resistance of austenitic alloys. Concerning the Stress Corrosion Cracking (SCC) resistance of austenitic stainless steels, molybdenum additions to alloys have a variable effect: the effect is detrimental for small additions of Mo, and it is beneficial for the alloy containing more than 4% Mo. Thus the Mo concentration on passive film plays an important role on the SCC resistance of steels. On the other hand, in a previous investigation, it was shown that the composition of passive films formed on the stressed 302 alloy depended on the compressive or tensile nature of stresses. Consequently, the aim of the present work is to study the composition of passive films formed on 316 steel and the migration of molybdenum in a stress field. Thus, Auger electron spectroscopy spectra were recorded to determine the chemical composition of the passive films formed on both sides of the type AISI 316 stainless steel U-bend samples. The results obtained show that the behaviour of chromium and oxygen in passive films formed on 316 steel in the stress field was nearly similar to that formed on 302 steel. Concerning the molybdenum diffusion outwards the passive film formed on the 316 steel was reduced by either the tensile or compressive stress field.     

Degradation of mechanical and corrosion resistance properties of AISI 317L steel exposed at 550 °C

The use of austenitic stainless steel type AISI 317L has increased in the last years, in substitution to AISI 316L and other austenitic grades. The higher Mo content (3.0 wt.%. at least) gives higher corrosion resistance to AISI 317L. However, some concern arises when this material is selected to high temperature process services in refineries. Microstructural changes such as chromium carbide precipitation and sigma phase formation may occur in prolonged exposure above 450 °C. In this work, the microstructure evolution of AISI 317L steel during aging at 550 °C was analyzed. Thermodynamic calculations with Thermocalc® and detailed microstructural analysis were performed in steel plate base metal and in weld metal produced by GTAW process. The aging for 200, 300 and 400 h promoted gradual embrittlement and deterioration of corrosion resistance of both weld and base metal. The results show that the selection of AISI 317L steel to services where temperatures can reach 550 °C is not recommended.     

MHB4新型合金抗蚀性能研究

用中频感应炉熔炼了新型超低碳高合金奥氏体不锈钢ＭＨＢ４和３１６Ｌ不锈钢,研究了它们在不同介质中的抗腐蚀性能。结果表明,由于ＭＨＢ４增加了Ｃｒ、Ｎｉ、Ｍｏ的含量,并加入Ｗ,极大地提高了抵抗Ｃｌ＾－离子引起的点蚀能力,因此ＭＨＢ４的耐点蚀、耐缝隙腐蚀以及在合成海水中的抗蚀性均优于３１６Ｌ不锈钢。     

不锈钢晶间腐蚀弯曲评价方法的影响因素

用嵌含有GTN延性损伤模型的ABAQUS有限元法,模拟研究了不锈钢晶间腐蚀弯曲评价方法中材料力学性能、弯曲角度和压头直径对弯曲试样塑性应变分布、延性损伤和裂纹起裂的影响规律,分析了其对晶间腐蚀弯曲评价结果的影响。结果表明：随着试样弯曲角度的增大和弯曲压头直径的减小,试样拉伸面的塑性应变增加,试样越容易产生弯曲开裂;在晶间腐蚀弯曲评价标准中,当固定弯曲角度和压头直径时,对于塑性、韧性和抗断裂综合力学性能较低的不锈钢材料,在弯曲过程中材料本身会发生开裂;因此,需要考虑材料力学性能对晶间腐蚀弯曲评价结果的影响;对于该研究中的典型的奥氏体不锈钢材料,当其弯曲断裂应变低于0．51左右时,在弯曲过程中材料本身会发生开裂,不宜用弯曲方法来评价其晶间腐蚀敏感性。     

Grain boundary engineering of titanium-stabilized 321 austenitic stainless steel

Grain boundary engineering (GBE) primarily aims to prevent the initiation and propagation of intergranular degradation along grain boundaries by frequent introduction of coincidence site lattice (CSL) boundaries into the grain boundary networks in materials. It has been reported that GBE is effective to prevent intergranular corrosion due to sensitization in unstabilized 304 and 316 austenitic stainless steels, but the effect of GBE on intergranular corrosion in stabilized austenitic stainless steels has not been clarified. In this study, a twin-induced GBE utilizing optimized thermomechanical processing with small pre-strain and subsequent annealing was applied to introduce very high frequencies of CSL boundaries into a titanium-stabilized 321 austenitic stainless steel. The resulting steel showed much higher resistance to intergranular corrosion after sensitization subsequent to carbon re-dissolution heat treatment during the ferric sulfate–sulfuric acid test than the as-received one. The high CSL frequency resulted in a very low percolation probability of random boundary networks in the over-threshold region and remarkable suppression of intergranular corrosion during GBE.     

Monitoring fatigue degradation in austenitic stainless steels

During cyclic loading of austenitic stainless steel, microstructural changes occurred, which affected both mechanical and physical properties. For certain steels, a strain‐induced martensitic phase transformation was observed. The investigations showed that for the given material and loading conditions the volume fraction of martensite depended on the cycle number, temperature and initial material state. It was found that the martensite content continuously increased with the cycle number. Therefore, the volume fraction of martensite was used for indication of the fatigue usage. The temperature dependence of the martensite formation was described by a Boltzmann function. The martensite content decreased with increasing temperature. Two different heats of the austenitic stainless steel X6CrNiTi18‐10 (AISI 321, DIN 1.4541) were investigated. The martensite formation rate was much higher for the cold‐worked material than for the solution‐annealed one. All applied techniques, neutron diffraction and advanced magnetic methods allowed the detection of martensite in the differently fatigued specimens.     

Development of high nitrogen, low nickel, 18%Cr austenitic stainless steels

Two high nitrogen stainless steels are studied through metallographic, mechanical and corrosionistic tests and the results are compared with those shown by a standard AISI 304. These high nitrogen steels show a significantly higher mechanical strength than usual AISI 304 while their corrosion resistance lie among that of standard austenitic and that of standard ferritic stainless steels.     

三元混合氯化盐NaCl-KCl-MgCl2对合金的腐蚀特性实验研究

熔盐是目前太阳能热电站中应用最广泛的储热蓄热材料。为满足太阳能热发电系统对于熔盐的储热需求,该文将304、316L、321、310S不锈钢置于550℃的三元混合氯化盐NaCl-KCl-MgCl₂（7：1：2）体系中,开展混合熔盐的腐蚀特性实验研究,并探讨其中的腐蚀机理。研究结果表明,在三元混合氯化盐NaCl-KCl-MgCl₂（7：1：2）体系中,310S表现出较好的耐腐蚀性能,304的耐腐蚀性较差。MoO₃、NiO、TiO₂氧化物的生成可提高316L、310S、321不锈钢的耐腐蚀性能;混合氯化盐在高温下生成的Cl₂是不锈钢腐蚀的重要原因,外部空气中的O₂和H₂O会进入熔盐侧与合金发生反应,加剧腐蚀。