Influence of ageing on wear resistance of an Fe–Mn–Si–Cr–Ni–Ti–C shape memory alloy

To further improve the wear resistance of Fe–Mn–Si–Cr–Ni based shape memory alloys, the effects of ageing at 1123 K with and without pre-deformation at room temperature on the precipitation of second-phase particles and their effects on wear resistance were investigated in an Fe–Mn–Si–Cr–Ni–Ti–C alloy. Results showed that the solution treated Fe–Mn–Si–Cr–Ni–Ti–C alloy exhibited much better wear resistance than the solution treated AISI 321 stainless steel; ageing with pre-deformation improved the wear resistance of Fe–Mn–Si–Cr–Ni–Ti–C alloy more effectively than ageing without pre-deformation, especially under the heavy load condition.     

Microstructure and wear behavior of a porous nanocrystalline nickel-free austenitic stainless steel developed by powder metallurgy

This paper investigates the microstructure and dry sliding wear characteristics of a porous Cr–Mn–N austenitic stainless steel prepared by powder metallurgy. The densification of the mechanically alloyed 18Cr–8Mn–0.9N stainless steel powder is performed by sintering at 1100 °C for 20 h and subsequently water-quenching. This procedure gives rise to the development of a nanostructured austenitic stainless steel with a relative density of 85%. The porous biocompatible stainless steel exhibits an outstanding wear resistance compared with AISI 316L stainless steel samples. This is attributed to its considerable intrinsic hardness and its specific configuration of pores.     

Plastic deformation and fracture behaviors of nitrogen-alloyed austenitic stainless steels

The plastic deformation and fracture behaviors of two nitrogen-alloyed austenitic stainless steels, 316LN and a high nitrogen steel (Fe–Cr–Mn–0.66% N), were investigated by tensile test and Charpy impact test in a temperature range from 77 to 293 K. The Fe–Cr–Mn–N steel showed ductile-to-brittle transition (DBT) behavior, but not for the 316LN steel. X-ray diffraction (XRD) confirmed that the strain-induced martensite occurred in the 316LN steel, but no such transformation in the Fe–Cr–Mn–N steel. Tensile tests showed that the temperature dependences of the yield strength for the two steels were almost the same. The ultimate tensile strength of the Fe–Cr–Mn–N steel displayed less significant temperature dependence than that of the 316LN steel. The strain-hardening exponent increased for the 316LN steel, but decreased for the Fe–Cr–Mn–N steel, with decreasing temperature. Based on the experimental results and the analyses, a modified scheme was proposed to explain the fracture behaviors of austenitic stainless steels.     

Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

In order to reduce the cost of duplex stainless steel (DSS), the Ni could be partially substituted by Mn and N, to maintain the alpha/gamma microstructure, the corrosion resistance and mechanical strength similar to the common Ni–Cr–Mo DSS. In this paper the microstructure stability, impact strength and the general corrosion behaviour of a low Ni grade, 22Cr–4Mn–0,2N DSS, were examined. In the solution annealing condition the corrosion resistance is quite similar to the austenitic grade. A moderate precipitation of nitrides and carbides was evidenced after isothermal treatment in the range 600–900 °C, while no dangerous topologically close packed phases (TCP-phases) were detected. The precipitation affects the impact strength, which decreases to about 50 J, while the corrosion resistance is less markedly affected.     

Bimodal grain size distribution: an effective approach for improving the mechanical and corrosion properties of Fe–Cr–Ni alloys

The effect of nanocrystalline grain size and bimodal distribution of nano- and microcrystalline grain sizes on the oxidation resistance and mechanical properties of Fe-based alloys has been investigated. Nanocrystalline and bimodal Fe–10Cr–5Ni–2Zr alloy pellets, prepared by mechanical alloying route, have been compared with conventional microcrystalline stainless steel alloys having 10 and 20 wt% Cr. Zr addition has been shown to improve the grain size stability at high temperatures. A significant improvement in the ductility of bimodal alloys with respect to nanocrystalline alloys was seen presumably due to the presence of the microcrystalline grains in the matrix. The high temperature oxidation of nanocrystalline and bimodal alloys at 550 °C shows superior oxidation resistance over microcrystalline alloy of similar composition (Fe–10Cr–5Ni) and comparable to that of microcrystalline alloy having twice as much Cr (Fe–20Cr–5Ni). Secondary Ion Mass Spectroscopy depth profiling confirms the hypothesis that nanostructure facilitates the enrichment of Cr at the oxide metal interface resulting in the formation of a passive oxide layer.     

Evaluation of Mn substitution for Ni in alumina-forming austenitic stainless steels

There has been increasing interest in the substitution of low-cost Mn for Ni in austenitic stainless steels due to the rising price of Ni. This paper investigates the possibility of such a substitution approach for the recently developed alumina (Al₂O₃)-forming austenitic (AFA) class of heat-resistant stainless steels. Computational thermodynamic tools were utilized to predict the alloy composition range to maintain an austenitic matrix microstructure when Mn is substituted for Ni in the presence of Al, which is a strong body-centered-cubic (BCC) phase stabilizer. Phase equilibria, oxidation behavior, and creep properties of Fe–(10–14)Cr–(5–15)Mn–(4–12)Ni–(2.5–3)Al–Cu–Nb–C–B (in weight percent) based alloys were studied. The alloys based on Fe–14Cr–2.5Al–(5–9)Mn–(10–12)Ni exhibited the best balance of oxidation and creep resistance, which represents approximately 50% reduction in Ni content compared to previously developed AFA alloys. These low-Ni, high-Mn AFA alloys formed protective Al₂O₃ scales up to 973–1073 K in air and at 923 K in air with 10% water vapor. Creep-rupture lives of the alloys under a severe screening condition of 1023 K and 100 MPa were in the 7.2 × 10⁵–1.8 × 10⁶ s (200–500 h) range, which is comparable to or somewhat improved over that of type 347 stainless steel (Fe–18Cr–11Ni base).     

The effect of TiN inclusions and deformation-induced martensite on the corrosion properties of AISI 321 stainless steel

Stainless steel of type 321 is commonly used for the production of exhaust systems because of its temperature resistance and welding properties, which are better than those of AISI 304 or similar steels. AISI 321 is a titanium stabilized austenitic stainless steel, where this element is added to form carbides in order to avoid chromium impoverishment due to chromium carbide formation. Cold shaping can, in the case of austenitic stainless steel, cause the formation of deformation induced martensite, which can improve its mechanical properties, but unfortunately can also spoil its good resistance to corrosion. Titanium nitride inclusions are cathodic with respect to steels, and therefore cause their anodic dissolution. Martensite is, however, more susceptible to the corrosion than austenite in steels. The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.     

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.     

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.     

Alloying effects on the microstructure and phase stability of Fe–Cr–Mn steels

Austenitic Fe–Cr–Mn stainless steels interstitially alloyed with nitrogen have received considerable interest lately, due to their many property improvements over conventional Fe–Cr–Ni alloys. The addition of nitrogen to Fe–Cr–Mn stabilizes the fcc structure and increases the carbon solubility. The benefits of increased interstitial nitrogen and carbon content include: enhanced strength, hardness, and wear resistance. This study examines the effect of carbon, silicon, molybdenum, and nickel additions on the phase stability and tensile behavior of nitrogen-containing Fe–Cr–Mn alloys. Nitrogen and carbon concentrations exceeding 2.0 wt.% were added to the base Fe–18Cr–18Mn composition without the formation of nitride or carbide precipitates. Minor additions of molybdenum, silicon, and nickel did not affect nitrogen interstitial solubility, but did reduce carbon solubility resulting in the formation of M₂₃C₆ (M=Cr, Fe, Mo) carbides. Increasing the interstitial content increases the lattice distortion strain, which is directly correlated with an increase in yield stress.     

Oxidation and abrasive wear of Fe–Si and Fe–Al intermetallic alloys

In the present work, intermetallic alloys Fe–Si and Fe–Al (Fe₃Si–C–Cr and Fe₃Al-C), produced by induction melting, were evaluated regarding their oxidation and abrasive resistance. The tests performed were quasi-isothermal oxidation, cyclic oxidation, and dry sand/rubber wheel abrasion. As reference, the ASTM A297-HH grade stainless steel was tested in the same conditions. In the oxidation tests, the Fe–Al based alloy presented the lowest oxidation rate, and the Fe–Si based alloy achieved the best results in the abrasion test, showing better performance than the HH type stainless steel.     

Using direct hot-rolling approach to obtain dual-phase weathering steel Cu–P–Cr–Ni–Mo

A weathering steel Cu–P–Cr–Ni–Mo has been developed which exhibits special continuous cooling transformation characteristics which permit the desired dual-phase (DP) microstructure to be obtained by direct hot-rolling. Hot-rolling procedures to obtain DP microstructures have been designed based on the continuous cooling transformation diagram of weathering steel Cu–P–Cr–Ni–Mo. The results show that the microstructures of DP weathering steels Cu–P–Cr–Ni–Mo are characterized by an irregular distribution of island-shaped martensite–austenite in the matrix of polygonal ferrite grains. DP weathering steel Cu–P–Cr–Ni–Mo with favorable corrosion resistant property, weldability and mechanical properties, such as, high strain hardening exponent values, a lower ratio of yield to tensile strength, and higher strengths; and is obtained successfully by direct hot-rolling.     

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773 K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000 HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.     

Wear mechanisms of Ti(C, N) ceramic in sliding contact with stainless steel

Austenic stainless steel AISI 321 is one of the most difficult materials to cut. In order to investigate the wear behaviour of Ti(C, N) ceramic when cutting the stainless steel, wear tests were carried out on a pin-on-disc tribometer, which could simulate a real cutting process. The selected load range is 58.8–235.2 N; the selected speed range is 0.8–3.2 m s-1. The test results show that the wear of Ti(C, N) ceramic is mainly caused by adhesion between the rubbing surfaces; the wear increases with increasing load and increasing speed. When oil is used for lubrication, the friction coefficient of the sliding pairs and the wear rate of the ceramic are reduced. Scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction analysis are used to examine the worn surfaces. The wear mechanisms of Ti(C, N) ceramic sliding against the stainless steel are discussed in detail. This revised version was published online in November 2006 with corrections to the Cover Date.     

Wear resistance of eutectic coatings of the Fe–Mn–C–B system alloyed with Si,Ni, and Cr

We analyze the wear resistance, structures, and compositions of eutectic coatings of the Fe–Mn–C–B system alloyed with Si, Ni, and Cr and obtained on 45 steel by the methods of electric-arc and plasma spraying performed by using eutectic powder wires. The process of wear of eutectic coatings is accompanied by the intense diffusion processes leading to segregation and, hence, to the increase in the C, B, and Si contents on the friction surface. Boron and silicon form nonstoichiometric oxides in the actual contact spots. Carbon is in the free state. As a result, the friction coefficient decreases and, therefore, the wear resistance of eutectic alloys increases.     

Corrosion properties of S-phase layers formed on medical grade austenitic stainless steel

The corrosion properties of S-phase surface layers formed in AISI 316LVM (ASTM F138) and High-N (ASTM F1586) medical grade austenitic stainless steels by plasma surface alloying with nitrogen (at 430°C), carbon (at 500°C) and both carbon and nitrogen (at 430°C) has been investigated. The corrosion behaviour of the S-phase layers in Ringer’s solutions was evaluated using potentiodynamic and immersion corrosion tests. The corrosion damage was evaluated using microscopy, hardness testing, inductive coupled plasma mass spectroscopy and X-ray diffraction. The experimental results have demonstrated that low-temperature nitriding, carburising and carbonitriding can improve the localised corrosion resistance of both industrial and medical grade austenitic stainless steels as long as the threshold sensitisation temperature is not reached. Carburising at 500°C has proved to be the best hardening treatment with the least effect on the corrosion resistance of the parent alloy.     

Methods to overcome embrittlement problem in 9Cr–1Mo ferritic steel and its weldment

This article presents the issues that need to be addressed in ferritic steel, for their use in nuclear core, namely, the embrittlement and type IV cracking of weldment. It has been established that the ferritic steels possess a significantly higher resistance to radiation damage as compared to the present generation austenitic stainless steels and the creep behavior is satisfactory for applications up to 873 K. The major challenges that need to be addressed are the poor creep resistance of the weld joints and embrittlement of ferritic steels. This article describes the efforts taken at IGCAR to overcome the embrittlement problem by impurity control, grain boundary engineering or design of suitable thermomechanical treatments in a 9Cr–1Mo ferritic steel.     

Nitrogen Containing Austenitic Stainless Steels

Nickel and nitrogen are the two most widely used alloying elements which can impart the face‐centered‐cubic crystal lattice to stainless steels. With the recent price increases and the price volatility of nickel, nitrogen is ever more important as an alloying element for a number of reasons. First, nitrogen is easily available everywhere and thus is not subject to speculation at the Metal Exchange. Second, in addition to making stainless steels austenitic, nitrogen can also make them stronger and more corrosion resistant. It is also a well and clearly established fact since many years, that nitrogen in solid solution makes austenitic stainless steels more wear resistant and more fatigue resistant. Austenitic stainless steel alloy design with nitrogen has for many years now taken account of the role of carbon. This is not only because carbon is just a useful austenite former, but also because nitrogen reduces the temperature where carbides begin to form. Thus there is always an optimum carbon to nitrogen ratio. Finally it is now well established that carbon in solid solution helps to increase the strength, the corrosion resistance and the wear resistance of austenitic stainless steels. A number of quantitative correlations between alloy composition and materials properties are presented and their useful role in alloy design is pointed out. This will further help to lower the nickel content in austenitic stainless steels or even replace nickel altogether.     

Studies on electrodeposition of corrosion resistant Ni–Fe–Mo alloy

A study to optimize the process parameters for electrodeposition of a Ni–Fe–Mo alloy is reported. A 2²full factorial design was successfully employed for the experimental design analysis of the results. The optimum experimental conditions for producing the corrosion resistant alloy were 120 mA/cm² current density, 20 rpm cathode rotation, 9.0 pH at 30 °C. The alloy was deposited at 61% current efficiency, with an average composition of 62 wt% Ni, 17wt% Fe, 21wt% Mo and traces of boron, and with E _corr −0.506 V, R _p 8.883 × 10³ Ohm cm² and I _corr 6.468 × 10⁻⁷ A/cm². The deposit obtained under these conditions had an amorphous character, good adherence, high corrosion resistance and a nodular morphology. Electrochemical corrosion tests verified that the electrodeposited Ni–Fe–Mo alloy had better corrosion resistance than the Fe–Mo alloy.     

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.