Common Austenitic Stainless Steels Research Articles

Performance of Structural Alloys in Bio-oil Production, Upgrading, and Storage Systems

Selection of corrosion-resistant, cost-effective structural materials for the process and containment vessels required for the production, upgrading, and storage of biomass-derived oils has been the subject of study in our laboratory for many years. The wide variety of biomass resources and the many liquefaction techniques and processing conditions result in products with a broad range of properties and compositions. This paper will address the materials issues in three distinct areas. In production, materials are exposed to temperatures that range from 350 to 550 °C depending upon the process. Generally, austenitic stainless steels have performed reasonably well, although thicker oxide scales and intergranular attack have sometimes been observed. For storage and transport of the bio-oil products, temperatures experienced by the containment materials are not expected to exceed 50 °C. Our studies have shown that most raw bio-oils contain significant concentrations of organic acids, and low-molecular-weight organic acids were quite corrosive to carbon and low alloy steels. For some applications, subsequent processing is required, which includes hydrotreating or co-processing with a petroleum-derived liquid. These processes utilize a catalyst that requires periodic retreatment with a sulfidizing gas, and the exposure to this gas at elevated temperatures can cause appreciable corrosion to the more common austenitic stainless steels. The materials considered most cost-effective and sufficiently corrosion-resistant for each of these environments were identified.

AK STEEL 309

Abstract AK Steel 309 is a chromium-nickel austenitic stainless steel. It is typically used for elevated temperature applications. Its high chromium and nickel contents provide comparable corrosion resistance, superior resistance to oxidation, and the retention of a larger fraction of room temperature strength than the common austenitic stainless steels, such as type 304. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1333. Producer or source: AK Steel Corporation.

ATI 310S

Abstract ATI 310S is a 25Cr-20Ni austenitic stainless steel that is typically used for elevated temperature applications. Owing to its higher chromium and nickel contents the alloy provides comparable corrosion resistance, superior resistance to oxidation, and the retention of a larger fraction of room temperature strength than the common austenitic stainless steels such as Type 304. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-1328. Producer or source: ATI.

High-temperature low cycle fatigue behavior of an equiatomic CoCrFeMnNi high-entropy alloy

In the present work, low cycle fatigue (LCF) behavior of an equiatomic CoCrFeMnNi high entropy alloy (HEA) is correlated to the microstructural evolution at 550 °C. The fully reversed strain-controlled fatigue tests were conducted in air under strain amplitudes ranging from 0.2% to 0.8%. The measured cyclic stress response showed three distinct stages which include initial cyclic hardening followed by a quasi-stable cyclic response until failure. The rate and amount of cyclic hardening increased with the increase in strain amplitude. In comparison to common austenitic stainless steels, CoCrFeMnNi HEA shows comparable strength and improved LCF lifetime at similar testing conditions. Electron-microscopy investigations after failure reveal no noticeable change in grain size, texture and annealing twins density. Initial cyclic hardening is attributed to the dislocations multiplication and dislocation-dislocation as well as dislocation-solute atom interactions. The quasi-stable cyclic response is associated with the equilibrium between dislocation multiplication and annihilation, which also leads to the formation of complex dislocation structures such as ill-defined walls and cells, particularly at higher strain amplitudes. Besides, the material exhibits serrated plastic-flow due to interactions between mobile dislocations and diffusing solute atoms (such as Cr, Mn and Ni). Lastly, segregation in the form of Cr- and NiMn-enriched phases were observed near grain boundaries, which appears to have a detrimental effect on the fatigue life.

Improvement of Fatigue Resistance and Fracture Toughness of Thermally Aged Duplex Stainless Steel by Laser Shock Peening

Duplex stainless steels (DSSs) offer high strength compared to common austenitic stainless steels; however, when this steel type is exposed to high temperature, the precipitation of sigma phase due to its fast formation kinetics may affect significantly the mechanical properties of the alloy. In this research, the feasibility of using laser shock peening (LSP) to reduce the negative effects of sigma phase precipitation on the mechanical properties of samples with thermal aging is studied. The LSP treatment was performed using a Nd:YAG pulsed laser operating at 10 Hz. The LSP setup was the waterjet arrangement without sample coating. The tensile, yield strength, fatigue crack growth, fracture toughness and hardness of samples aged at 750 °C for different holding times were determined. In order to assess the effect of LSP on fatigue crack growth and fracture behavior, another set of thermally aged compact tension specimens with pre-crack was LSP-treated on both faces and then fatigue loading was applied. Experimental results demonstrate that, while thermal aging accelerates fatigue crack growth of DSS samples, LSP significantly reduces the effect of thermal aging, by reducing the fatigue crack growth rate and increasing the fracture toughness of DSS aged samples.

Basic modelling of creep rupture in austenitic stainless steels

Creep rupture can happen in two ways, brittle and ductile creep rupture. Brittle creep rupture of austenitic stainless steels proceeds with the nucleation, growth and coalescence of grain boundary cavities. A creep cavity nucleation model has been developed previously, which considers cavity nucleation at particles and sub-boundary corners due to grain boundary sliding. A modified constrained cavity growth model has been used to describe the cavity growth behavior with combination of the cavity nucleation models. In this paper, the brittle creep rupture has been analyzed by combining the cavity nucleation and growth models. The physically based models where no adjustable parameters were involved were used to predict the brittle creep rupture strength. On the other hand, previously developed basic models for ductile creep rupture based on exhaustion of the creep ductility have been used. The creep rupture strength of common austenitic stainless steels has been predicted quantitatively by taking both ductile and brittle rupture into account. The predicted rupture times for ductile rupture are longer than those for brittle rupture at high stresses and low temperatures with a reversed situation at low stresses and high temperatures. This reproduces the characteristic change in slope in the creep rupture curves.

Introduction of a novel tribometer especially designed for scratch, adhesion and hardness investigation up to 1000℃

In order to gain a fundamental understanding of material behaviour at elevated temperatures a unique tribometer was designed which can operate at temperatures up to 1000℃. The test takes place in vacuum in order to avoid oxidation and the normal load range varies from 10 to 500 N. It is thus possible to describe the evolution of hardness over a broad range of temperatures and loads. This can give indications of possible microstructural modifications, which can be investigated afterwards on cross sections. For the characterisation of single abrasive phenomena on a very fundamental level, scratch tests at variable loads are proposed. The interaction of sliding surfaces can be simulated by adhesion testing. To this end an application specific counter body, e.g. taken from a field specimen, can be slid over the specimen surface at variable loads. Finally, it can be stated that this newly designed tribometer offers an enormous potential for deeper understanding of fundamental wear phenomena like ploughing, micro-breaking or adhesion occurring at high temperature. The possibilities of high temperature scratch and hardness testing with the new measurement system are shown on the common austenitic stainless steel 1.4301 (AISI 304).

Retracted: Stress corrosion cracking of high strength stainless steels for use as strand in prestressed marine environment concrete construction

Stainless steel reinforcement has an elevated chloride threshold and is an attractive alternative for prestressed concrete applications. However, due to the high strength requirements for prestressing strands, concern exists about the possibility of stress corrosion cracking (SCC). A possible candidate high strength alloy for use as prestressed strands in a Florida marine environment is UNS# S24000. Previous testing methods used on other stainless steel alloys were investigated to determine the best way to evaluate the UNS# S24000 as compared to other alloys. The alloys tested were a common austenitic stainless steel with high nickel content UNS # S31603, UNS# S24000, and a duplex stainless steel with high chromium and an additional constituent, molybdenum UNS# S32205. Prior work on high strength stainless steels have tested various alloys of austenitic steels or austenitic and duplex steels, but did not include UNS# S24000. The alloys examined were evaluated at various temperatures in magnesium chloride solutions and in a simulated concrete pore water solution at 60 °C, followed by an anodic polarization regime as an alternative test acceleration method. The results suggest that duplex high‐strength stainless UNS# S32205 performed overall better than the other two alloys. The UNS# S24000 still performed well in simulated concrete pore water and chloride solution tests, and performed better that UNS#S32205 at high temperatures in the tests in the magnesium chloride solution.

Potential for Application of Special Stainless Steels for Chemical Process Equipments

The most predominant material of construction (MOC) for process equipments in chemical process industries (CPI) is plain carbon steel only. This is because of its lowest cost, easy availability, adequate thermal and mechanical properties, ease of fabrication etc. The only limitation is its low corrosion resistance. When corrosion resistance becomes the deciding factor, for overall resistance to general uniform corrosion, the common austenitic stainless steel Type 304(L) SS, 18/8(L) SS, is used. This has limitation with respect to uniform corrosion in reducing acids and to pitting corrosion, crevice corrosion and stress corrosion cracking in chloride containing media. In such situations, Type 316(L) SS, 18/8/2.5Mo/(L), shows somewhat better performance. These are called Standard Austenitic Stainless Steels. Even 316(L) SS shows unsatisfactory corrosion behavior in strong reducing acids, in concentrated chloride solutions at elevated temperatures and in fluids flowing with high velocities. In such cases, if the process conditions cannot be made milder with respect to corrosion phenomena, then there is a strong potential for upgrading the MOCs to Special Stainless Steels. These special stainless steels are either high nickel high molybdenum (~25 % Ni and ~6 % Mo) Super Austenitic Stainless Steels or low nickel (4 to 7 %) Duplex Stainless Steels. With respect to cost, the former are highly expensive than 316(L) SS because of widely varying amounts of nickel and of the presence of high molybdenum and the latter are marginally comparable with 316L SS. It is a common experience in industry that the usage of such special stainless steels is felt necessary only after facing severe corrosion problems in equipments made of standard stainless steels. The purpose of this paper is to present a few case studies of severe corrosion problems analyzed by the author resulting in recommendation of special stainless steel as the corrosion preventive step. The following case studies would be presented. Fertilizer Industry, Ammonia plant, Synthesis Gas Coolers Petrochemical Plant, Proprietary Amine manufacturing Reactor in the presence of Orthophosphoric Acid Petrochemical Plant, Proprietary Amine manufacturing process, Ammonia recovery column. Petrochemical Plant, Reboiler Tubes processing concentrated acetic acid.

Cross-section stability of lean duplex stainless steel welded I-sections

Despite growing interest in the use of stainless steel in construction and the development of a number of national and regional design codes, stainless steel is often still regarded as only suitable for specialised applications. This is partly due to the high initial material cost associated with the most commonly adopted austenitic grades. The initial material cost of stainless steel is largely controlled by the alloy content, in particular the level of nickel, which is around 8%–10% for the common austenitic grades. A recently developed grade, known as lean duplex stainless steel (EN 1.4162), has a far lower nickel content, around 1.5%, and hence lower cost. Despite the low nickel content, it possesses higher strength than the common austenitic stainless steels, along with good corrosion resistance and high temperature properties and adequate weldability and fracture toughness. The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed. For this reason, an experimental and analytical research programme investigating the structural characteristics of lean duplex stainless steel was initiated. The present paper summarises the laboratory tests performed on lean duplex stainless steel welded I-sections. The experiments include material testing, stub column tests and 3-point and 4-point bending tests. The experimental data were supplemented by results generated by means of a comprehensive numerical investigation including parametric studies covering a wide range of cross-sections. The obtained experimental and numerical results, together with the results of previous tests performed on lean duplex stainless steel cold-formed hollow sections are reported and used to assess the applicability of existing cross-section classification limits and the continuous strength method (CSM) to lean duplex stainless steel. Furthermore, the structural performance of lean duplex stainless steel was compared to the more commonly used stainless steel grades. Finally, based on the obtained results, design recommendations suitable for incorporation into Eurocode 3: Part 1.4 are proposed.

Shear Stress Measurements in Stainless Steel 2169 under 1D Shock Loading

The material addressed in this research is stainless steel 2169, a 200 series stainless steel which has so far found applications in aviation, demolition, motor-vehicle design and nuclear reactor containment. Longitudinal and lateral stresses during the shock loading of 2169 have been measured using manganin stress gauges. The shear strength has been shown to increase with impact stress and it is seen that when compared with another common austenitic stainless steel (304L) the initial HEL is greater, but that 2169 has a lesser degree of hardening with increased impact stress. The results are discussed in terms of structure and degree of alloying.

Forming characteristics of austenitic stainless steel sheet alloys under warm hydroforming conditions

Stainless steel sheet alloys have been increasingly used in heating, ventilating, and air conditioning; appliance; sanitary and medical devices; as well as several structural and transportation applications, due to their high strength-to-weight ratio, corrosion resistance, biomedical compatibility, and esthetic appearance. Among various stainless steel alloys, austenitic stainless steels are the most commonly used type. Due to the forming limitations into complex shapes at room temperature conditions and stress-corrosion cracking issues, forming at elevated temperature has been considered as an enabling technique. Formability of stainless steels is affected by strain rate and temperature due to martensitic transformation of meta-stable austenite microstructure. In this study, deformation characteristics of three common austenitic stainless steels (AISI 201, 301, and 304) were investigated using closed-die hydroforming under different process conditions. Specifically, effects of pressure, temperature, and die/part geometry on the material forming characteristics quantified using cavity filling ratio and thinning distribution were investigated. Results suggested that, in terms of cavity filling, pressure and material grade are significant factors while temperature is not in the case of axisymmetric part. For the non-axisymmetric case, all parameters were found to be significant. In addition, finite element (FE) modeling was performed to simulate several forming cases that were experimentally conducted in this study. The FE model was simulated based on material flow curves obtained from previous studies under similar conditions (strain rate and temperature) by the authors. FEA results were shown to be in good agreement with experimental findings, particularly for cavity filling and part profile predictions. Hence, the FE model and the material models can be used for further predictions of complex and different parts with confidence.

Effect of nitrogen on the plasma (ion)-carburized layer of high nitrogen austenitic stainless steel

Austenitic stainless steel or high nitrogen austenitic steel are used extensively as structural non-magnetic materials. The former, because of their low surface hardness, have low wear resistance. Recently developed plasma (ion)-carburizing improves the surface of austenitic stainless steel by removing the oxide scale. In contrast, high nitrogen austenitic stainless steel are expected as wear-resistance material because the hardness is higher than that of conventional austenitic stainless steel.In this study, two kinds of austenitic stainless steel were plasma (ion)-carburized in an atmosphere of CH4+H2 plasma at 1303 K for 14.4 ks. The metallurgical characteristics were then investigated using XRD (X-ray diffraction method), OM (optical microscopy), hardness testing, glow discharge optical emission spectroscopy (GDOES) and a scanning electron microscopy (SEM).The results show that the plasma (ion)-carburized low nitrogen austenitic stainless steel had the layer with structure similar to the common austenitic stainless steel. The plasma (ion)-carburized high nitrogen austenitic stainless steel had the carbide layer at the top surface, carbide dispersed layer in the matrix, and then lamellar structure of carbides toward the inner layer.

Effect of dual torch technique on duplex stainless steel welds

Duplex stainless steels are characterized by balanced ferrite/austenite microstructures and are well known for their superior corrosion resistance and higher strength compared with the common austenitic stainless steels. One major concern, however, is that welding might degrade the corrosion resistance by producing unbalanced phase content, detrimental precipitates, and possible embrittlement of the weldment. In this paper, a dual-torch arc welding technique (plasma torch followed by a gas tungsten arc (GTA) torch) was proposed. Effects of the dual-torch technique on the microstructural changes and corrosion properties were investigated. The preliminary study indicated that a correlation between the welding parameters and the microstructural changes and corrosion resistance existed. It was found that the corrosion rate increases with increasing torch pitch and/or decreasing GTA welding current. By adjusting the distance between the torches, modification of weld microstructure may be realized. Although further studies are required to fine-tune the technique, the present study demonstrated the potential of using dual torch technique to improve weldability of duplex stainless steels.

The effect of Mn-depleted surface layer on the corrosion resistance of shape memory Fe-Mn-Si-Cr alloys

In this work, we have examined Fe-Mn-Si-Cr alloys possessing a good shape memory effect due to a high Mn content (28 wt pct). The addition of Cr (5 wt pct) was made in order to give fairly good corrosion resistance to the alloy. But we have verified that even in moderately corrosive environments, the presence of chromium does not bear any passivation. On the other hand, we have found that the alloy can acquire corrosion resistance by means of the formation of a Mn-depleted surface layer obtained by heating the alloy at high temperature (⋍ 1050 °C) in air. This modified layer forms since manganese is selectively oxidized with respect to the other components. The adhesion of this layer is maintained even under severe stress if the thickness of the modified region does not exceed 20 µm. Under this limit, the shape memory characteristics of the alloy are not affected, and at the same time, the specimen acquires properties of passivity comparable with one of the most common austenitic stainless steels at the presence of the same environmental conditions.

In vivo behavior of a high performance duplex stainless steel.

An in vivo investigation of a new high molybdenum and nitrogen duplex stainless steel (25Cr--7Ni--4Mo--0.3N) has been performed. Cylindrical pins and specially developed devices, to test in static conditions the in vivo localized corrosion resistance, made of this new duplex steel and of a common austenitic stainless steel were implanted in rabbit's femurs for 6 and 12 months. After sacrifice, SEM observations and EDS microanalyses to detect metallic ion release were carried out on the femur sections surrounding the pins. Morphologic observations with stereoscope and SEM were performed on the metallic surfaces of the special devices in order to detect the presence of localized corrosion. Both ion release and localized corrosion were observed for the specimens made of austenitic stainless steel, but not for those made of 25Cr--7Ni--4Mo--0.3N duplex stainless steel.

Ferrite decomposition in austenitic stainless steel weld metals

Residual ferrite decomposition in several common austenitic stainless steel weld metals, with or without molybdenum additions, has been investigated. It is shown that ferrite decomposes in α and chromium rich α′ phase at temperatures below about 490°C, whereas it transforms to σ at temperatures above 540°C. At temperatures between 490 and 540°C, α + α′ and α + σ transformations occur simultaneously. These transformations are accompanied by precipitation of carbides and in molybdenum bearing alloys by Mo containing phases such as R. Using the LSW (Lifshitz, Slyozov, Wagner) theory of diffusion controlled coarsening, the apparent activation energy for α → α + α′ decomposition is estimated (Q = 67 kJ mol−1) and a general equation giving the particle size of α′ as a function of aging time and temperature is derived. This equation is used to predict the kinetics of embrittlement owing to α + α′ decomposition at low temperatures.

CRONIFER 1925 HMo

Abstract CRONIFER 1925 HMo is an austenitic chromium-nickel-molybdenum stainless steel. The high contents of chromium and especially molybdenum make this steel highly resistant to pitting and crevice corrosion. Because of its high nickel content, its resistance to stress-corrosion cracking is considerably higher than that of the common austenitic stainless steels. CRONIFER 1925 HMo has good strength and ductility, high impact values and good weldability. Its applications include heat exchangers for use with salt water, bleaching-plant equipment and flue-gas scrubbers. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-403. Producer or source: Vereingte Deutsche Metallwerke AG.