Properties Of Austenitic Stainless Steel Research Articles

The Phenomenon of High Hardness Values on the S-Phase Layer of Austenitic Stainless Steel via Screen Plasma Nitriding Process

The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect; that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).

Change of magnetic properties in austenitic stainless steels due to plastic deformation

Austenitic stainless steels, investigated in this research, belong into a group of the so-called high-alloy TRIP (Transformation Induced Plasticity) steels. The nondestructive evaluation (NDE) methods were used for determination of plastic deformation influence in investigated materials. The NDE methods permit products to be inspected throughout their service life, to determine when to repair or replace a particular part. The main goal of this study was to measure and thus separate different levels of applied plastic deformation of selected conductive biomaterials. Two different devices were used to evaluate the effect of plastic deformation. The first device was commercially available magnetic field sensor GF708. The second device was Magnet Physik, on which is possible to determine magnetic quantities (remanence, coercivity), make measurements with surrounding coils to determine the magnetic mean values and measure at temperatures up to 200 °C. Both of those devices are suitable for measuring the magnetic properties. Effect of plastic deformation was observed by the light microscope, as well.

Nitrogen mass transfer and surface layer formation during the active screen plasma nitriding of austenitic stainless steels

Active screen plasma nitriding (ASPN), a novel surface modification process, has been widely applied to improve various surface properties of austenitic stainless steels, such as wear resistance, electrical conductivity and corrosion resistance. All the improvement of surface properties attributes to the formation of a unique phase under low nitriding temperature, called S-phase. A “sputter – deposit – decompose –diffusion model” has been established to explain the formation of S-phase, however, the mechanism of nitrogen mass transfer to the substrate during ASPN still remains controversial. By comprehensively comparing the surface responds of three different surfaces (bare 316L stainless steel surface, Au-coated 316L stainless steel surface and Si wafer surface) during ASPN treatments, this paper provides the direct evidence and clarifies the mechanism of nitrogen mass transfer between the deposition layer and the substrate during ASPN treatment.

Investigations of material hardness and structural changes in the heat-affected zone during plasma cutting

Investigation of the heat-affected zone during plasma cutting can significantly contribute to a better understanding of mechanical, structural, and chemical properties of a material in the kerf zone. The experimental research in this paper is concerned with the intense heat impact of a plasma jet on the surface layers of stainless steel. The heat-affected zone was investigated by measurement of its approximate width, analysis of its phase content, and transformations during the material cooling process, as well as measurements of micro-hardness near the cut edge. The material structural changes were related to the micro-hardness and temperature distribution in the workpiece. This research provides useful information about the heat-affected zone, its impact on the workpiece material properties, and the need for the secondary operations. The narrow heat-affected zone and the good quality and consistency of the cut result from favourable mechanical and thermophysical properties of austenitic stainless steel.

Adaptive laser-based local transformations of the magnetic properties in austenitic stainless steel using optical feedback

This paper presents a laser-based system for a local transformation of the magnetic properties in austenitic stainless steel. The process is applied to linear actuators with an integrated, in-axis position measurement where durability and high precision are needed. The developed system consists of a 400-W, single-mode fiber laser, the focusing optics, and a three-axis actuation system. An important feature is the optical feedback for the adaptive, high-speed (40 kHz) laser power regulation. The experimental results show that the optical feedback effectively compensates for the external disturbances, like an increased roughness and a gradual heat accumulation. The regulation decreases the dispersion of the magnetic signal’s response by more than 100% and shortens the transient time at the beginning of the inscription process from 100 to 15 ms.

Effect of Hydrogen Embrittlement on Mechanical Properties of Austenitic Stainless Steel

Effect of Hydrogen Embrittlement on Mechanical Properties of Austenitic Stainless Steel

A Hybrid Neural Network - Genetic Algorithm for Prediction of Mechanical Properties of ASS-304 at Elevated Temperatures

In the present work, genetic algorithm is implemented, to optimize the artificial neural networks used, to predict the mechanical properties of Austenitic Stainless Steel 304 (ASS-304) at elevated temperatures. ASS-304 is a very important alloy used in various applications involving high temperatures which make it very important to study the mechanical properties at elevated temperatures. The dynamic neural networks have been employed first for predicting the mechanical properties such as Ultimate Tensile Strength (UTS), Yield Strength (Ys),% elongation, Strain Hardening Exponent (n) and Strength Coefficient (K) at elevated temperatures. Genetic algorithm was then integrated with the neural network model for optimization, to achieve better regression statistics, taking the mean square error as the fitness function. The results show that the proposed hybrid, neural network - genetic model is more accurate and effective method for predicting the mechanical properties of ASS-304 at elevated temperatures.

Regularities of Microstructure Evolution and Strengthening Mechanisms of Austenitic Stainless Steels Subjected to Large Strain Cold Working

The deformation microstructures and their effects on mechanical properties of austenitic stainless steels processed by cold rolling at ambient temperature to various total strains were studied. The cold working was accompanied by the development of strain-induced martensitic transformation because of meta-stable austenite at room temperature. The strain-induced martensitic transformation and deformation twinning promoted the grain refinement during cold rolling, leading to nanocrystalline structures consisting of a mixture of austenite and martensite grains with their transverse grain sizes of 50-150 nm containing high dislocation densities. The rolled samples experienced substantial strengthening resulted from high density of strain induced grain/phase boundaries and dislocations. The yield strength of austenitic stainless steels could be increased to 2000 MPa after rolling to total strains of about 4. The martensite and austenite provided almost the same contribution to overall yield strength. The dislocation strengthening was much higher than the grain boundary strengthening at small to moderate strains of about 2, whereas the latter gradually increased approaching the level of dislocation strengthening with increasing the strain.

Microstructural Characterization and Mechanical Properties of Stainless Steel Inlay Welded Dissimilar Materials

This present work was carried out to characterize the microstructure and mechanical properties of austenitic stainless steel (SS) 316L to dissimilar welding of Inconel 52 and Inconel 82 fillers that were treated by ultrasonic nanocrystalline surface modification (UNSM) technique. The microstructure and hardness map of the specimens were characterized by optical microscope (OM) and micro-hardness tester. The increase in hardness and refinement in grain size after UNSM treatment were found for the SS 316L/52 and SS 316L/82. In addition, the induced compressive residual stress in the surface layer of base SS 316L was measured. It is expected that the increased hardness into several microns in depth and modified microstructure with a severe plastically deformed surface layer by UNSM technique can increase the resistance to corrosion and extend the service life of pressurized water reactors (PWRs).

Effect Of Temperature Variation On Wear Behaviour Of Austenitic Stainless Steel

The effects of boronizing temperatures on the wear and hardness properties of austenitic stainless steel were investigated in this study. The samples were prepared in accordance to standard samples preparation for wear and hardness test. Pack boronizing were conducted using EKabor®1 powder medium at two different temperatures which are 850°C and 950°C. The wear resistance properties were evaluated though pin on disk test and the surface characterization was analyzed through scanning electron microscopy (SEM), observation. Vickers microhardness tester was performed to obtain the hardness of the samples. The results indicated that there are presences of FeB and Fe2B phases on both samples, but thicker FeB phase was produced at Po-950 samples. This resulted in reduction of abrasion wear properties but major improvement of the hardness properties of boronized stainless steel.

Effect of Nitriding Time on the Structural Evolution and Properties of Austenitic Stainless Steel Nitrided Using High Power Pulsed DC Glow Discharge Ar/N2 Plasma

A high power pulsed DC glow discharge plasma (HPPGDP) system was employed to perform fast nitriding of AISI 316 austenitic stainless steel in Ar and N2 atmosphere. In-situ optical emission spectroscopy and Infrared pyrometer measurements were used during the plasma nitriding to investigate the effect of dynamic plasma on the nitriding behaviour. SEM and EDX, XRD, Knoop indentation, and tribo-tests were used to characterise microstructures and properties of the nitrided austenitic stainless steel samples. HPPGDP produced high ionization of both Ar and N2 in the plasma that corresponded to dense ion bombardment on the biased steel samples to induce effective plasma surface heating and to form high nitrogen concentration on the biased steel surfaces, and therefore fast nitriding (> 10µm/hour) was achieved. Various phases were identified on the nitrided stainless steel samples formed from a predominantly a single phase of nitrogen supersaturated austenite to a multi-phase structure comprising chromium nitride, iron nitride and ferrite dependent on the nitriding time. All the nitrided AISI 316 austenitic stainless steel samples were evaluated with high hardness (up to 17.3 GPa) and exceptional sliding wear resistance against hardened steel balls and tungsten carbide balls.

Mechanical properties of austenitic stainless steel with high niobium contents

To better understand the influence of the microstructural characteristics on the mechanical properties of Fe-Cr22-Ni25-Nbx austenitic stainless steel (ASS-Nbx), the mechanical properties were investigated. Nb addition was conducted with four different amounts: 0, 0.29, 0.58 and 0.86%. With the increasing Nb content, the mean grain size for the Fe-Cr-Ni-based alloys decreased, while the size of Nb precipitate increased. Owing to the different microstructural characteristics, their mechanical properties were altered. The highest tensile strength was obtained for ASS-Nb0.29 alloy. However, with the increasing Nb content in ASS-Nb0.29–0.86 alloys, the tensile strength decreases despite the grain refinement. The mechanical properties of the ASS-Nb alloys were influenced by the Nb precipitation hardening and the grain boundary cohesive strength, arising from the size of Nb precipitations.

Mechanical properties of austenitic stainless steel treated by active screen plasma nitriding

In the active screen plasma nitiriding method, the materials to be processed are insulated and a voltage is applied to a metallic and basket-shaped mesh screen installed around the material as the cathode and the furnace wall as the anode. In this research, we subjected austenitic stainless steel to active screen plasma nitiriding treatments and evaluated the mechanical properties of the treated samples. Active screen plasma nitiriding experiments were carried out using a direct current plasma-nitriding unit. Nitriding treatments were performed in a nitrogen-hydrogen atmosphere for 7.2–28.8 ks at 673 K. The S-phase formed on the surface of the nitrided samples. The thickness of the S-phase increased with increasing treatment time. The hardness of the nitrided samples increased with increasing treatment time. The wear resistance and fatigue strength of austenitic stainless steel were improved by active-screen plasma nitriding.

Influence of temperature histories during reactor startup periods on microstructural evolution and mechanical properties of austenitic stainless steel irradiated with neutrons

This paper addresses influence of two different temperature profiles during startup periods in the Japan Materials Testing Reactor and a boiling water reactor upon microstructural evolution and mechanical properties of austenitic stainless steel irradiated with neutrons to about 1 dpa and 3 dpa. One of the temperature profiles was that the specimens experienced neutron irradiation in both reactors, under which the irradiation temperature transiently increased to 290 °C from room temperature with increasing reactor power during reactor startup periods. Another was that the specimens were pre-heated to about 150 °C prior to the irradiation to suppress the transient temperature increase. Tensile tests at 290 °C and Vickers hardness tests at room temperature were carried out, and their microstructures were observed by FEG-TEM. Difference of the temperature profiles was observed obviously in interstitial cluster formation, in particular, growth of Frank loops. Although influence of neutron irradiation involving transient temperature increase to 290 °C from room temperature on the yield strength and the Vickers hardness is buried in the trend curves of existing data, the influence was also found certainly in increment of in yield strength, existence of modest yield drop, and loss of strain hardening capacity and ductility. As a result, Frank loops, which were observed in austenitic stainless steel irradiated at doses of 1 dpa or more, seemed to have important implications regarding the interpretation of not irradiation hardening, but deformation of the austenitic stainless steel.

Effect of Sensitization Treatment on Corrosion Properties in Austenitic Stainless Steel 304

Chromium depletion in AISI304 stainless steel can lead to intergranular corrosion due to temperature conditions and degree of deformation, and consequently to materials failure. The aim of this work is to study the effect of sensitization treatment on the corrosion resistance in AISI304 stainless steel after solution heat treatment at 1,000°C. Sensitization treatments were carried out at 670°C for 1 h, 2h, 5h and 10h in the electrical furnace. The intergranular corrosion resistance of the sensitized specimens was evaluated by double loop electrochemical potentiokinetic reactivation test. The microstructure of the specimens before and after the corrosion tests was observed through optical and scanning electron microscope. Solution treatment shows the dual structure, however, aging for 5 hours depicts the ditch structure. The ratio of current density increased as a function of aging time resulted in increase in the degree of sensitization.

Methodology for Estimating Thermal and Neutron Embrittlement of Austenitic Stainless Steel Welds During Service in Light Water Reactors

The effect of thermal aging on the degradation of fracture toughness and Charpy-impact properties of austenitic stainless steel (SS) welds has been characterized at reactor temperatures. The solidification behavior and the distribution and morphology of the ferrite phase in SS welds are described. Thermal aging of the welds results in moderate decreases in Charpy-impact strength and fracture toughness. The upper-shelf Charpy-impact energy of aged welds decreases by 50–80 J/cm2. The decrease in fracture-toughness J integral-resistance (J-R) curve or JIc is relatively small. Thermal aging has minimal effect and the welding process has a significant effect on the tensile strength. However, the existing data are inadequate to accurately establish the effect of the welding process on fracture properties of SS welds. Consequently, the approach used for evaluating thermal and neutron embrittlement of austenitic SS welds relies on establishing a lower-bound fracture-toughness J-R curve for unaged and aged and nonirradiated and irradiated SS welds. The existing fracture-toughness J-R curve data for SS welds have been reviewed and evaluated to define lower-bound J-R curves for submerged arc (SA)/shielded metal arc (SMA)/manual metal arc (MMA) welds and gas tungsten arc (GTA)/metal inert gas (MIG)/tungsten inert gas (TIG) welds in the unaged and aged conditions. At reactor temperatures, the fracture toughness of GTA/MIG/TIG welds is a factor of about 2.3 higher than that of SA/SMA/MMA welds. Thermal aging decreases the fracture toughness of all welds by about 20%. The potential combined effects of thermal and neutron embrittlement of austenitic SS welds are also described. Lower-bound curves are presented, which define the change in coefficient C and exponent n of the power-law J-R curve and the JIc value for SS welds as a function of neutron dose. The potential effects of reactor coolant environment on the fracture toughness of austenitic SS welds are also discussed.

Microstructure and experimental design analysis of nickel based clad developed through microwave energy

Summary In the present investigation microwave processing method was explored for the enhancement of surface properties of austenitic stainless steel (SS-304). The nickel based clads were developed through microwave energy. Taguchi's L9 orthogonal array was successfully adapted to study the slurry erosive wear rate. The obtained result indicated that erosion rate of the developed clad varied between 0.03363 g to 0.03570 g as an increase in slurry parameters like slurry velocity and impingement angle respectively. It is confirmed by the response table for means of DOE that the wear rate of the developed clad was more influenced by the rotational slurry speed and impingement angle; finally the possible mechanisms of the worn surface of the tested samples were observed through SEM.

Correlation between locally deformed structure and oxide film properties in austenitic stainless steel irradiated with neutrons

To elucidate the mechanism of irradiation-assisted stress corrosion cracking (IASCC) in high-temperature water for neutron-irradiated austenitic stainless steels (SSs), the locally deformed structures, the oxide films formed on the deformed areas, and their correlation were investigated. Tensile specimens made of irradiated 316L SSs were strained 0.1%–2% at room temperature or at 563 K, and the surface structures and crystal misorientation among grains were evaluated. The strained specimens were immersed in high-temperature water, and the microstructures of the oxide films on the locally deformed areas were observed. The appearance of visible step structures on the specimens' surface depended on the neutron dose and the applied strain. The surface oxides were observed to be prone to increase in thickness around grain boundaries (GBs) with increasing neutron dose and increasing local strain at the GBs. No penetrative oxidation was observed along GBs or along surface steps.

Phase diffusionless γ↔α transformations and their effect on physical, mechanical and corrosion properties of austenitic stainless steels irradiated with neutrons and charged particles

The work presents relationships of γ→α' and α'→γ-transformations in reactor 12Cr18Ni10Ti and 08Cr16Ni11Mo3 austenitic stainless steels induced by cold work, irradiation and/or temperature. Energy and mechanical parameters of nucleation and development of deformation-induced martensitic α'-phase in the non-irradiated and irradiated steels are given. The mechanisms of localized static deformation were investigated and its effect on martensitic γ→α' transformation is determined. It has been shown that irradiation of 12Cr18Ni10Ti steel with heavy Kr ions (1.56MeV/nucleon, fluence of 1·1015 cm-2) results in formation of α'-martensite in near-surface layer of the sample. Results of systematic research on reversed α'→γ-transformation in austenitic metastable stainless steels irradiated with slow (VVR-K) and fast (BN-350) neutrons are presented. The effect of annealing on strength and magnetic characteristics was determined. It was found that at the temperature of 400 °C in the irradiated with neutrons samples (59 dpa) an increase of ferromagnetic α'-phase and microhardness was observed. The obtained results could be used during assessment of operational characteristics of highly irradiated austenitic steels during transportation and storage of Fuel Assemblies for fast nuclear reactors.

Effect of Alternate Supply of Shielding Gases of Tungsten Inert Gas Welding on Mechanical Properties of Austenitic Stainless Steel

In the present study, an attempt is made to study the effect of alternate supply of the shielding gas in comparison with the conventional method of TIG welding with pure argon gas. The two sets of combination are used as 10–10 and 40–20 s for alternate supply of the Argon and Helium shielding gas respectively. The effect of alternate supply of shielding gas is studied on the mechanical properties like bend test, tensile test and impact test. The full factorial experimental design is applied for three set of combinations. The ANOVA is used to find significant parameters for the process and regression analysis used to develop the mathematical model. The result shows that the alternate supply of the shielding gas for 10–10 s provides better result for the bend, tensile and impact test as compared with the conventional argon gas and the alternate supply of 40–20 s argon and helium gas respectively. Welding speed can be increased for alternate supply of the shielding gas that can reduce the total welding cost.