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The purpose of this paper is to present the results of a study on friction characteristics of plasma, salt‐bath and gas nitrided layers produced in AISI 304 type austenitic and AISI 420 type martensitic stainless steels.

Plasma nitriding processes were carried out with DC‐pulsed plasma in 80% N₂+20% H₂ atmosphere at 450°C and 520°C for 8 h at a pressure of 2 mbar. Salt‐bath nitriding was performed in a cyanide‐cyanate salt‐bath at 570°C for 1.5 h. Gas nitriding was also conducted in NH₃ and CO₂ atmosphere at 570°C for 13 h. Characterization of all nitrided samples has been carried out by means of microstructure, microhardness, surface roughness measurement and friction coefficient. The morphologies of the worn surfaces of the nitrided samples were also observed using a scanning electron microscope. Friction characteristics of the nitrided samples have been investigated using a ball‐on‐disc friction and wear tester with a WC‐Co ball as the counterface under dry sliding conditions.

The plasma nitrided and salt‐bath nitrided layers on the 420 steel surfaces were much thicker than on the 304 steel surfaces. However, there was no obvious and homogeneous nitrided layer on the gas nitrided samples' surface. The plasma and salt‐bath nitriding techniques significantly increased the surface hardness of the 304 and 420 samples. The highest surface hardness of the 304 nitrided samples was obtained by the plasma nitrided technique at 520°C. On the other hand, the highest surface hardness of the 420 nitrided layers was observed in the 450°C plasma nitrided layer. Experimental friction test results showed that the salt‐bath and 450°C plasma nitrided layers were more effective in reducing the friction coefficient of the 304 and 420 stainless steels, respectively.

The relatively poor hardness and hence wear resistance of austenitic and martensitic stainless steels needs to be improved. Friction characteristic is a key property of performance for various applications of austenitic and martensitic stainless steels. This work has reported a comparison of friction characteristics of austenitic 304 and martensitic 420 stainless steels, modified using plasma, salt‐bath and gas nitriding processes. The paper is of significances for improving friction characteristics, indirectly wear performances, of austenitic and martensitic stainless steels.

This study aims to report the oxidation behaviors of the T91 ferritic/martensitic steel (T91 steel) and 304 austenitic stainless steel (304 steel) in supercritical water (SCW) at 600°C.

The microstructure, elemental distribution and phase structure of the oxidation layers derived from the corrosion of the T91 steel and 304 steel were analyzed by scanning electron microscopy, Oxford Instrument X-ray spectroscopy, electron scattered diffraction and transmission electron microscopy.

The oxidation layers on the T91 steel and 304 steel have duplex structure. The two steels all suffer internal oxidation, and the phase of the internal oxidation layers are indexed as Fe-Cr spinel, although their morphologies are different. The formation of a continuous Cr-rich layer is not detected because of the relatively low Cr content of the steels, which is attributed to the corrosion property.

The accelerated corrosion and corrosion mechanism of the T91 steel and 304 steel with low Cr occurring in SCW at 600°C was clarified.

The purpose of this study is to investigate the effect of ferrite on hydrogen embrittlement (HE) of the 17-4PH stainless steels.

The effects of ferrite on HE of the 17-4PH stainless steels were investigated by observing microstructure and conducting slow-strain-rate tensile tests and hydrogen permeability tests.

The microstructure of the ferrite-bearing sample is lath martensite and banded ferrite, and the ferrite-free sample is lath martensite. After hydrogen charging, the plasticity of the two steels is significantly reduced, along with the tensile strength of the ferrite-free sample. The HE susceptibility of the ferrite-bearing sample is significantly lower than the ferrite-free steel, and the primary fracture modes gradually evolved from typical dimple to quasi-cleavage and intergranular cracking. After aging at 480°C for 4 h and hydrogen charging for 12 h, the 40.9% HE susceptibility of ferrite-bearing samples was the lowest. In addition, the hydrogen permeation tests show that ferrite is a fast diffusion channel for hydrogen, and the ferrite-bearing samples have higher effective hydrogen diffusivity and lower hydrogen concentration.

There are a few studies of the ferrite effect on the HE properties of martensitic precipitation hardening stainless steel.

WEAR resistance is never the sole requirement of an engineering material. All engineering components have a function to perform and any particular function will impose a series of requirements on the material of manufacture. In the search for improved wear resistance, these other requirements must never be forgotten: no industrially useful material will survive on wear resistance alone.

FROM a machinability aspect, stainless steels may be classified into three categories, the general analysis of which influences the machinability factor.

Under severely aggressive conditions, such as those experienced in the chemical industry, there has been extensive use of stainless steels in order to reduce corrosion losses. The successful industrial use of stainless steels led to requests for information on the corrosion resistance of stainless steels and similar alloys in sea‐water. This paper was awarded a prize in the Essay competition organised by the Corrosion Group of the Society of Chemical Industry, 1959.

The purpose of this study is to critically analyze the properties of quenched and tempered steel samples. Austenite to martensite transformation of steel is a common process in any steel industry. Water quenching is the best suited technique to convert the steel into martensitic structure. Although quenched products are very hard, yet they possess brittleness. Due to which, their industrial applications become very limited. To avoid this problem, tempering of the martensite is usually done to achieve the required combination of hardness and toughness.

The present work deals with comparative analysis of mechanical properties and microstructural behavior of quenched and tempered steel samples. For the purpose, a low carbon steel (0.2%-C) was taken under study. Quenching was done in water, and tempering was done in atmospheric air. Four different mechanical properties such as tensile strength, toughness, hardness and shear strength were analyzed on steel samples that underwent through two different above-mentioned heat treatment processes.

An improvement in all the four mechanical properties was reported after tempering the quenched products. Also, the microstructural images of quenched and tempered specimens showed a good corroboration with mechanical properties.

A significant improvement in mechanical properties was reported in tempered specimens. Also, there was a strong corroboration between mechanical properties and microstructural attributes. A clear view of needle-shaped martensite and lamellar-shaped pearlite was observed in water-quenched and tempered specimens, respectively.

The purpose of this study is to clarify both tensile and shear strength for self-drilling screws, which are manufactured from high-strength, martensitic-stainless and austenitic stainless-steel bars, and the load-bearing capacity of single overlapped screwed connections using steel sheets and self-drilling screws at elevated temperatures.

Tensile/shear loading tests for the self-drilling screw were conducted to obtain basic information on the tensile and shear strengths at elevated temperatures and examine the relationships between both. Shear loading tests for the screwed connections at elevated temperatures were conducted to examine the shear strength and transition of failure modes depending on the test temperature.

The tensile and shear strengths as well as the reduction factors at the elevated temperature for each steel grade of the self-drilling screw were quantified. Furthermore, either screw shear or sheet bearing failure mode depending on the test temperature was observed for the screwed connection.

The transition of the failure modes for the screwed connection could be explained using the calculation formulae for the shear strengths at elevated temperatures, which were proposed in this study.

THE previous articles in this series, concerning the titanium, magnesium and aluminium alloys, followed a very similar form, in that in each case consideration of the aircraft engineering applications was preceded by a metallurgical appreciation of the alloy systems under review. In the case of steels, a comprehensive article on similar lines would be nothing less than a monograph, and if steels are to be discussed within the space of a single article, then a quite different approach must be adopted. This review will not, then, examine steels generally in any great metallurgical detail, but will rather consider their special merits in aircraft engineering, particularly in the context of supersonic aircraft.

The purpose of this paper is to evaluate the electrochemical behaviour of two carbon steels exposed to acidic geothermal solutions and their resistance to hydrogen induced cracking (HIC), in order to determine the effect of hydrogen damage on the failure process of the steels used for line pipe and casings at a geothermal plant.

Samples of two different steels: ASTM A‐53 Grade B (line pipe) and API L‐80 (casing) were immersed for a duration of 96 h in the electrolyte proposed by NACE to evaluate susceptibility to HIC. Samples of the two steels embedded in non‐conducting Bakelite were subjected to potentiodynamic polarisation scans at room temperature using as the electrolyte brines obtained from different wells at the Cerro Prieto geothermal plant. Hardness tests were performed on the samples before and after the HIC tests in order to determine hardness changes induced by hydrogen penetration as field results indicated embrittlement of the steels after four months of service.

The steels, ASTM A‐53 Grade B and API L‐80 did not exhibit crack sensitivity as no cracks are observed in the tests specimens, though they showed an increase in hardness. The steels exhibited high‐corrosion rates in the brine media at room temperature (3.3 mm/yr), which is expected to increase at higher temperatures.

The work revealed that carbon steels used for line pipes and casings at geothermal plants can exhibit high resistance to HIC, however they corrode at high rates and may show embrittlement. It is suggested that due to the high‐operation temperature, the damage induced by hydrogen resulted in hardness increase but was not sufficient to develop cracks.