Pulse electrochemical polishing (PECP) was used to improve the mechanical properties,such as surface roughness and corrosion resistance,of conductive metallic materials.PECP can provide a ...smooth,bright,reflective,and deburred surface that exhibits superior corrosion resistance.In this work,stainless steel was used as the anode,and copper was used as the cathode due to their low electrical resistances.The surface roughness of the PECP sample was measured by atomic force microscopy (AFM).A scanning electron microscope (SEM) was used to observe surface characteristics,and an Auger electron spectroscope (AES) was used to analyze the metallurgical composition and thickness of the passive film.The aim of this research was to compare the corrosion resistance rates of the unprocessed and PECP-processed stainless steel.
A severe peak tailing was observed for adenosine 5'‐monophosphate in flow injection analysis with stainless steel tubing and water/methanol mixture (1:1, v/v) as carrier. The cause of the peak ...tailing was investigated by focusing on the chemical structure of the analytes, the material used for the analytical systems and the composition of the carrier. We clarified that the peak tailing was caused by the interaction between phosphate residues in the analytes and stainless steel. The severe peak tailing did not occur with stainless steel tubing when the phosphate compounds were analyzed with carrier containing phosphoric acid or phosphate buffer. The findings indicate that such ill peak profiles are usually not considerable in conventional HPLC separation because phosphoric acid or phosphate buffer is quite commonly used in eluents. In LC‐MS, however, the use of phosphoric acid and phosphate buffer is usually avoided because of their non‐volatility; therefore this interaction between stainless steel and phosphate compound becomes predominant and results in severe peak tailings. We also found an effective method for avoiding the interaction. When stainless parts, such as LC tubing and ESI spray capillary, were treated with phosphoric acid prior to analysis, the peak profiles of the phosphate compounds were dramatically improved, even when non‐phosphate buffer is used as carrier.
The functional properties of “TiNi–stainless steel” bimetal composite produced by explosion welding were studied. The influence of the ratio of the TiNi layer thickness to the total thickness of the ...sample as well as the influence of preliminary deformation on the recoverable strain and a temperature of shape memory effect were studied. It was found that the best combination of strain variation observed in repeated thermal cycles was demonstrated by the bimetal sample in which the thickness of the TiNi layer was 64% of the thickness of the sample. The preliminary deformation resulted in an increase in stress stored in the sample and led to an increase in recoverable strain.
This document presents an overview of the findings of several investigations into the susceptibility of 12% Cr Type 1.4003 ferritic stainless steel to heat-affected zone sensitization and ...intergranular stress corrosion cracking. A description of the sensitization behavior of these steels is complicated by the partial transformation of δ-ferrite to austenite on cooling. During slow cooling or annealing below the A1 temperature (representing the phase boundary between the austenite and austenite+ferrite phase fields), this austenite decomposes to form desensitized ferrite and M23C6-type carbide precipitates. The rapid cooling rates associated with welding, however, prevent the transformation of austenite to ferrite at lower temperatures, and any austenite formed on cooling transforms to martensite below the Ms (martensite start) temperature. Four distinct modes of heat-affected zone sensitization have been identified to date. Sensitization of the martensite phase may occur on welding material inadvertently annealed above the A1 temperature (Mode 1), or when multiple welds are positioned in such a way that the heat-affected zone of the second pass overlaps the heat-affected zone of the first pass (Mode 2). Rapid cooling after very low heat input welding may sensitize the ferrite phase (Mode 3), whereas very slow cooling after welding at excessively high heat input levels may lead to the sensitization of the austenite phase (Mode 4). Results examining the influence of Modes 1 and 2 heat-affected zone sensitization on the incidence of intergranular stress corrosion cracking are presented.
L'objectif de ce travail de thèse, est de développer un matériau d'apport et un mode opératoire de soudage associé permettant d'assembler des tôles d'acier K44X pour la fabrication de collecteurs ...d'échappement automobiles. Les propriétés de l'acier K44X ayant été optimisées pour répondre au mieux aux contraintes de l'application, les conditions de soudage recherchées devront, dans la mesure du possible, éviter de dégrader les caractéristiques de l'acier, en particulier en termes de tenue mécanique à haute température et de résistance à l'oxydation et à la fatigue thermique. Ce mémoire est divisé en quatre chapitres. Le premier chapitre est consacré à une présentation synthétique des évolutions dans le domaine de la fabrication des collecteurs d'échappement automobiles, et des connaissances actuelles dans les domaines des aciers inoxydables ferritiques et sa soudabilité, des procédés de soudage à l'arc. Le second chapitre présente les caractéristiques de l'acier K44X et la problématique de l'étude, puis décrit le travail d'élaboration des matériaux d'apport de différentes compositions. Ainsi que les résultats d'une caractérisation préliminaire des soudures obtenues avec les différents matériaux. Le chapitre 3 traite de la caractérisation de la tenue en service de l'assemblage retenu à l'issu du chapitre précédent. Les tests d'oxydation, de traction à chaud sur zone fondue des soudures ou sur assemblages complets, et de fatigue thermique, utilisés pour réaliser cette caractérisation sont décrits, et les résultats sont discutés. La fin de ce chapitre est consacrée à la caractérisation des précipités formés dans les zones fondues. Enfin, le dernier chapitre est consacré à la modélisation thermique du soudage et à la modélisation de la solidification, dans le but de tenter de prédire le type de microstructure de zone fondue formée lors d'une opération de soudage, en fonction des paramètres procédés. Cette modélisation, qui s'appuie sur les résultats d'un essai de soudage instrumenté, doit notamment permettre de prédire si les conditions de soudage, pour une composition d'acier donnée, permettent ou non de former une structure de grains équiaxe en zone fondue des soudures.
The objective of this work is to develop a filler metal and an associated welding procedure allowing to join sheets of steels K44X for the manufacturing of exhaust manifolds for automotive. The properties of the steel K44X having been optimized to answer at best the constraints of the application, the welding conditions will have to, as possible, avoid degrading the characteristics of the steel, in particular in terms of mechanical strength with high temperature, oxidation resistance and in thermal fatigue.This report is divided into four chapters.The first chapter is dedicated to a synthetic presentation of the evolutions in the field of the manufacturing of the automotive exhaust manifolds, and current knowledge in the domains of ferritic stainless steels and its weldability, and in arc welding processes.The second chapter presents the characteristics of the steel K44X and the problem of the study, then described the work of elaboration of the filler metals with various compositions. As well as the results of a preliminary characterization of the welds obtained with the various materials.The chapter 3 is about the characterization of the in-service behavior of the assembly stemming from the previous chapter. The tests of oxidation, hot traction on molten zone of the welds or on complete assemblies, and of thermal fatigue, used to realize this characterization are described, and the associated results are discussed. The end of this chapter is dedicated to the characterization of precipitates formed in the molten zones.Finally, the last chapter is dedicated to the thermal modelling of the welding and to the modelling of the solidification, with the aim of trying to predict the type of microstructure of molten zone formed during a welding operation, according to the process parameters. This modelling, based on the results of a instrumented experimental test of welding, has to allow in particular to predict if the welding conditions, for a given composition of steel, allow or not to form a structure of grains equiaxed in molten zone of the welds.
Gigacycle fatigue properties of two martensitic stainless steels with different level of inclusion size were investigated by using ultrasonic fatigue tests at room temperature. As a result of the ...tests, the S-N curves for the both materials were straight on the downside. All of the fatigue fracture started from defects at the internal or at the surface. And almost fracture surfaces had facet regions around the defects. There were not facet regions under 2×105 cycles for SUS-A with larger level of inclusion and under 5×105 cycles for SUS-B with smaller level of inclusion. There were some specimens of SUS-B which didn't break in the regime from 109 to 1010 cycles, and which had smaller facet regions than those of the broken specimens. This gives a suggestion that the fatigue limit for internal fatigue fracture exists. For SUS-A and SUS-B, the √area parameter model with √areafac can explain whether a specimen breaks.
Le micro-fraisage (diamètre fraise < 1 mm) permet l’usinage précis de structures en 3D, à des dimensions micrométriques, dans desmatériaux d’ingénierie, se plaçant aux frontières de deux mondes : ...d’une part, le fraisage traditionnel appelé « fraisage macro » et d’autre part,la micro-fabrication et ses techniques dites de « salle blanche ».L'étude innovante porte sur le micro-fraisage d’aciers inoxydables 316L avec des micro-fraises cylindriques en carbure de tungstèneavec un équipement industriel (machine outil commercialisée et non optimisée) permet d’accentuer les nombreuses difficultés technologiquesliées à la mise en oeuvre du micro-fraisage et d’effectuer directement un transfert de compétences vers l’industrie. L’acier 316L(biocompatible, réputé de difficilement usinable) n’a jamais été étudié en micro-fraisage.L’étude aborde, au travers de neufs ratios caractéristiques du micro-fraisage, les problématiques de choix de moyens et de méthodespour caractériser la technique du micro-fraisage.Après analyses des paramètres de l’étude et des caractérisations des usinages, la définition géométrique optimale d’une micro-fraiseinnovante est proposée. Sa tenue en service est validée par des tests en usinage dans l’acier 316L, répondant ainsi, à une problématique decoupe négative à basse vitesse de coupe avec des effets d’échelle du matériau.Une originalité de l’étude est d’aborder l’effet de la population inclusionnaire visant à améliorer l’usinabilité. En comparant lesrésultats obtenus par micro-fraisage de 2 nuances d’acier 316L, la population inclusionnaire de l’acier 316L n’est pas identifiée comme unfacteur améliorant l’usinabilité à l’échelle de la coupe micro.
The micro-milling ( tool diameter < 1 mm) target the precise machining of 3D structures to micrometric dimensions, in engineeringmaterials, to be placed at the borders of two worlds : the one hand , the traditional milling called "macro milling" and other hand, the microfabricationand its so-called "clean room" techniques.The innovative study focuses on the micro-milling of 316L steel with carbide micro end mills with industrial equipment (machine toolmarketed unoptimized) can caricature the many technological challenges related to the implementation of the micro-milling and make a directtransfer of skills to the industry. 316L steel (biocompatible, reputed difficult to machine) has never been studied in micro-milling.The study looks at ratios through new features of the micro-milling, the problems of choice of means and methods to characterizemicro-milling.After analysis study parameters and machined parts, the optimal geometric definition of an innovative micro end mill is proposed.Service behavior is validated by testing machining in 316L steel, responding to a question of negative cutting with low cutting speeds andscale effects of the material.An originality of the study is to address the effect of the inclusion population to improve machinability. Comparing the resultsobtained by micro-milling two 316L steel grade, the inclusion population of 316L steel is not identified as a factor improving themachinability cutting at micro scale.
This article presents the galvanostatic anodic oxidation of two types of stainless steel alloys, ferritic (15.03% Cr) and austenitic (20.45% Cr, 8.37% Ni), in molten NaNO3-KNO3 eutectic mixture at ...different temperatures ranging from 673-873K. At a temperature of 673K the shape of polarization curves for the alloys is complex, while at higher temperatures it is simple. The passivity potential range was calculated as the difference between the passivation potential, Ep, and the breakdown potential, Eb. The value of Eb - Ep decreases with the increase of temperature. The amount of iron, chromium and nickel dissolved in the melt was determined after each experiment using atomic absorption spectroscopy. The composition and structure of the corrosion products formed on the surface of electrodes were examined by X-ray diffraction analysis. Corrosion parameters derived from the polarization curves are calculated; these are: polarization resistance at low current densities, Rp, exchange current density, io, corrosion current density, icorr, passivation current density, ip. It was found that the increase of temperature increases io, icorr, and ip while Rp, decreases. From these results it was found that, under the given conditions, the austenitic stainless steel alloy is more corrosion resistant than the ferritic one. The activation energy of corrosion was estimated for the two alloys.
A field test in a multi-stage flash (MSF) once-through plant has been evaluated. Six metallic construction materials, five stainless steels and one nickel base alloy, were exposed for a period of 28 ...months in the hot chlorinated and air saturated seawater stream of the first flash chamber at a temperature of 100°C. The lowest alloyed grades, i.e., type 316, S31726 (“317LMN”), and S31803 suffered pitting and crevice corrosion while the highly alloyed grade S31254 suffered superficial crevice corrosion. The most highly alloyed stainless steel S32654 and the nickel base alloy N06625 were fully resistant. No material suffered stress corrosion cracking. A 6Mo grade such as S31254 is a good choice for the first stage of evaporator vessels. The first six stages of the plant where the test was performed are made of solid S31254.
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