Investigation of Boronizing Kinetics of AISI 51100 Steel

In this study, some mechanical properties of borided AISI 51100 steel with high C concentration were investigated. Boronizing heat treatment was carried out in solid medium consisting of Ekabor-II at 850, 900, and 950 °C for 2, 4, 6, and 8 h. Morphology and mechanical properties of boride layer, and the effect of chemical composition on properties and kinetics of borides were investigated. The results of this study indicated that the morphology of the boride layer has a saw-tooth nature, and its hardness is over 1500 HV. Depending on process time and temperature, the depth of boride layer ranged from 30 to 106 μm. Optical and SEM studies and XRD analysis revealed that borides formed on the surface of steel substrates have dominantly single Fe₂B boride phase in addition to small amount of Cr₂B.     

离子渗氮对AISI304L不锈钢磨损性能的影响

对AISI 304L不锈钢在450和500℃离子渗氮处理进行了研究,分析了渗氮对析出相、硬度、厚度、冲蚀磨损和高压釜中微动磨损性能的变化。详细分析了渗氮试样在垂直粒子冲蚀下的耐冲蚀磨损性能,并探讨了其冲蚀磨损机制。结果表明,渗氮层有γN和Cr N相析出;450℃和500℃下的渗层厚度分别为2和20μm;渗氮层的硬度都高于1000 HK。渗氮试样在高压釜中的耐微动磨损性能有大幅度的提高,尤其是450℃离子渗氮处理的试样,比未处理试样提高了29.4倍。     

爆炸加载下AISI304不锈钢板表面硬化和数值模拟

目的 提高AISI304不锈钢板表面硬度。方法 利用爆炸加载表面硬化方法对3 mm厚的AISI304不锈钢板进行了表面硬化处理,通过HXD-1000YM型显微硬度计和JEM-2010型透射电子显微镜对爆炸加载处理后试样的不同部位横截面进行了硬度测量和微观组织表征。采用大型有限元数值模拟软件ANSYS/LS-DYNA对爆炸加载表面硬化过程进行了数值模拟,计算了撞击面平均压力和速度。通过对比数值模拟结果与理论计算结果,分析了特征点碰撞压力和速度对爆炸加载处理后表面硬度的影响。结果 数值模拟结果表明,撞击面压力平均值为5.5 GPa,撞击面平均速度达到了178 m/s,撞击面压力和速度的理论计算值与数值模拟值误差不超过5%。试验结果与数值模拟结果具有一致性。爆炸加载后,试样近起爆端和爆轰末端的撞击压力和撞击速度小于稳定爆轰阶段,导致前者表面硬度小于后者。横截面硬度分布表明撞击表面硬度大于炸药接触面硬度,撞击表面硬度值从210HV提高至450HV,炸药接触面硬度值从210HV提高至390HV。结论 爆炸表面硬化过程中存在边界效应。爆炸表面硬化方法能够显著提高板材表面硬度,同时可以提高板材整体硬度,且硬度提高与变形带和位错阵列形成有关。     

Failure Analysis of an Oxidative Chlorination Reactor Clad with AISI 304L Stainless Steel

Failure analysis of the hermetical AISI 304L stainless steel cladding in oxidative chlorination reactor shows that its pitting and stress corrosion arose due to the presence of chlorine ion in the working environment. In order to improve its corrosion resistance, AISI 316L stainless steel should be utilized.     

Microstructure and Mechanical Properties of Plasma Arc Brazed AISI 304L Stainless Steel and Galvanized Steel Plates

Plasma arc brazing is used to join the AISI 304L stainless steel and galvanized steel plate butt joints with the CuSi3Mn1 filler wire. The effect of parameters on weld surface appearance, interfacial microstructure, and composition distribution in the joint was studied. The microhardness and mechanical tests were conducted to determine the mechanical properties of the welded specimens. The results indicated that good appearance, bead shape, and sufficient metallurgical bonding could be obtained when the brazing process was performed with a wire feeding speed of 0.8 m/min, plasma gas flow rate of 3.0 l/min, welding current of 100 A, and welding speed of 27 cm/min. During plasma arc brazing process, the top corner of the stainless steel and galvanized steel plate were heated and melted, and the melted quantity of stainless steel was much more than that of the galvanized steel due to the thermal conductivity coefficient difference between the dissimilar materials. The microhardness test results shows that the microhardness value gradually increased from the side of the galvanized steel to the stainless steel in the joint, and it is good for improving the mechanical properties of joint. The tensile strength was a little higher than that of the brazing filler, and the fracture position of weld joint was at the base metal of galvanized steel plate.     

离子渗氮对AISI304L不锈钢耐磨损性能的影响

对AISI 304L不锈钢在450和500 ℃离子渗氮处理进行了研究,分析了渗氮处理的析出相、硬度、厚度、冲蚀磨损和高压釜中微动磨损性能的变化。详细分析了渗氮试样在垂直粒子冲蚀下的耐冲蚀磨损性能,并探讨了其冲蚀磨损机制。结果表明：渗氮层有γ_N和CrN相析出;450和500 ℃下的渗层厚度分别为2和20 µm;渗氮层的硬度都高于1000 HK。渗氮试样在高压釜中的耐微动磨损性能有大幅度的提高,尤其是450 ℃离子渗氮处理的试样,比未处理试样提高了29.4倍。     

Corrosion Resistance of PAPVD TiN Coating on AISI 304 Stainless Steel

In this work the corrosion resistance of PAPVD TiN hard coatings on AISI 304 stainless steel with a titanium interlayer has been addressed. Cyclic voltammetry corrosion tests in NaCl 3.5% solutions were performed for samples prepared by depositing TiN/Ti onto steel using different deposition parameters. The surface morphology of the samples was examined by using a scanning electron microscope (SEM) and phase analysis was performed by X-ray diffraction (XRD). The cyclic voltammetry curves showed two distinct behaviours. Firstly, a reduction in corrosion resistance was observed when current density was increased for the whole potential range studied. The second observation, no less important, was the increase in corrosion resistance compared to the uncoated steel. The TiN films deposited showing (III) preferred orientation showed better corrosion resistance than films presenting other orientations.     

Investigation of Diffusion Kinetic Values of Boronized AISI 303 Steel by Pack Boronizing

Protection of Metals and Physical Chemistry of Surfaces - In this study, AISI 303 steels are boronized by pack boring method at 1123, 1173 and 1223 K for 2, 4 and 6 h. The morphology of the boride...     

Optimizing HVOF Spray Parameters to Maximize Bonding Strength of WC-CrC-Ni Coatings on AISI 304L Stainless Steel

High velocity oxygen fuel (HVOF)-sprayed cermet coatings are extensively used to combat erosion-corrosion in naval applications and in slurry environments. HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance have significant influence on coating characteristics like adhesion bond strength and shear strength. This paper presents the use of statistical techniques in particular response surface methodology (RSM), analysis of variance, and regression analysis to develop empirical relationships to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings. The developed empirical relationships can be effectively used to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings at 95% confidence level. Response graphs and contour plots were constructed to identify the optimum HVOF spray parameters to attain maximum bond strength in WC-CrC-Ni coatings.     

Effect of cutting process on the stress corrosion susceptibility of AISI 304L stainless steel

During manufacturing of a component, cutting, turning, grinding, and milling operations are inevitable and these operations induce surface residual stresses. In this study, it is shown that, depending on the process employed for cutting, residual stresses generated at the cut surfaces can vary widely and they can, in turn, make the cut surfaces of austenitic stainless steel (SS) prone to stress corrosion cracking (SCC). An austenitic SS 304L plate was cut using three different procesess: bandsaw cutting, cutting using the cut-off wheel, and shearing. Surface residual stress measurement using the X-ray diffraction (XRD) technique is carried out close to the cutting edges and on the cross-section. SCC susceptibility studies were carried out as per ASTM G36 in 45% boiling magnesium chloride solution. Optical microscopic examination showed the presence of cracks, and confocal microscopy was used to measure the depth of cracks. The study confirmed that high tensile residual stresses present in the cut surfaces produced by cut-off wheel and shear cutting make the surfaces susceptible to SCC while the surfaces produced by bandsaw cutting are resistant to SCC. Hence, it is shown that there is a definite risk of SCC for product forms of austenitic SS with cut surfaces produced using cutting processes that generate high tensile residual stresses stored for a long period of time in a susceptible environment.     

The Study of Plasma Nitriding of AISI304 Stainless Steel

This paper presents results on the plasma nitriding of AISI 304 stainless steel at different temperatures in NH3gas. The working pressure was 100～200 Pa and the discharge voltage was 700～800V. The phase of nltrided layer formed on the surface was confirmed by X-ray diffraction. The hardness of the samples was measured by using a Vickers microhardness tester with the load of 50g. After nitriding at about 400℃ for two hours a nitrided layer consisting of single γN phase with thickness of 51.tm was obtained. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 950 HV (for nltrided samples at temperature of 420℃). The phase composition, the thickness, the microstructure and the surface topography of the nltrided layer as well as its properties depend essentially on the process parameters.     

45钢在超细SiC颗粒作用下的正向冲蚀行为*

选用超细SiC颗粒作为磨料,研究了韧性材料45钢在正向冲击条件下的冲蚀行为并与7075-T6铝合金对比。使用高强度磁铁捕获了45钢冲蚀磨屑,利用扫描电子显微镜(SEM)对冲蚀磨损后试样表面以及磨屑形貌进行观测;采用质量分析法,分析45钢在不同冲蚀条件下的失重情况与材料去除率;利用X射线应力测定仪,分析45钢在不同冲蚀条件下的表层及深度方向的残余压应力分布情况。结果表明,正向冲击条件下,韧性材料表面主要发生塑性变形,偏向堆积脊部还存在片层剥落的材料去除形式,超细磨料产生的材料去除率相对较小,材料去除率随磨料量的增加呈先增加后减小的趋势;表层应力随磨料量呈先增加后降低的趋势,微磨料冲蚀残余压应力的影响深度约为10μm。     

Corrosion Resistance of Friction Surfaced AISI 304 Stainless Steel Coatings

Corrosion resistance of friction surfaced AISI 304 coating in boiling nitric acid and chloride containing environments was found to be similar to that of its consumable rod counterpart. This was in contrast to the autogenous fusion zone of GTAW weld which showed inferior corrosion resistance with respect to the consumable rod. The superior corrosion resistance of friction surfaced coatings was attributed to the absence of δ-ferrite in it.     

Oxidation of AISI 304 Steel in Al- and Ti-Containing Solutions

Protection of Metals and Physical Chemistry of Surfaces - The present work was devoted to a study of the effect of the electrolyte composition on the anodic behavior of stainless steel. Morphology...     

Impedance investigation of thermally formed oxide films on AISI 304L stainless steel

Thin oxide layers on 304L stainless steel were grown by thermal oxidation at 300 °C at different durations ranging from 2 to 4 h. The structural characterization of the oxide films was carried out by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy was used to investigate the effects of exposure time and applied potential on the electronic properties of these films. Oxide films are described by a multilayer structure, with n-type iron oxide and oxyhydroxide in the outer layers and p-type chromium oxide in the inner layer. Doping densities evaluated from Mott-Schottky plots increased with the oxidation duration, with characteristics of highly disordered semiconductor.     

Pack Cementation Coatings for High-Temperature Oxidation Resistance of AISI 304 Stainless Steel

Aluminum and titanium are deposited on the surface of steel by the pack cementation method to improve its hot-corrosion and high-temperature oxidation resistance. In this research, coatings of aluminum and titanium and a two-step coating of aluminum and titanium were applied on an AISI 304 stainless steel substrate. The coating layers were examined by carrying out scanning electron microscopy (SEM) and x-ray diffraction (XRD). The SEM results showed that the aluminized coating consisted of two layers with a thickness of 450???m each, the titanized coating consisted of two layers with a thickness of 100???m each, and the two-step coatings of Al and Ti consisted of three layers with a thickness of 200???m each. The XRD investigation of the coatings showed that the aluminized coating consisted of Al₂O₃, AlCr₂, FeAl, and Fe₃Al phases; the titanized layers contained TiO₂, Ni₃Ti, FeNi, and Fe₂TiO₅ phases; and the two-step coating contained AlNi, Ti₃Al, and FeAl phases. The uncoated and coated specimens were subjected to isothermal oxidation at 1050?°C for 100?h. The oxidation results revealed that the application of a coating layer increased the oxidation resistance of the coated AISI 304 samples as opposed to the uncoated ones.     

Thermal Stability Study of Ultrafine Grained 304L Stainless Steel Produced by Martensitic Process

An ultrafine grain 304L stainless steel with average grain size of about 650 nm was produced by martensitic process. 10 mm as-received sheets were 80% cold rolled in the temperature of ?15 °C and then annealed at 700 °C for 300 min to obtain ultrafine grained microstructure. The results showed that the ultrafine grained 304L steel has yield strength of 720 MPa, tensile strength of about 920 MPa, and total elongation of 47% which is about twice that of coarse grain structure. The effect of annealing temperature (750-900 °C) on the grain growth kinetics was modeled by isothermal kinetics equation which resulted in the grain growth exponent (n) and activation energy for grain growth of 4.8 and 455 KJ/mol, respectively. This activation energy was also compared with those for other austenitic steels to better understanding of the nature of grain growth and atoms mobility during annealing. It was found that activation energy for grain growth is about twice higher than self-diffusion activation energy of austenite that is related to the Zener pinning effects of the second phase particles.     

Assessment of Sensitization in AISI 304 Stainless Steel by Nonlinear Ultrasonic Method

A nonlinear ultrasonic technique has been developed to evaluate sensitization in Type 304 stainless steel.In order to achieve diferent degree of sensitization(DOS),specimens have been subjected to heat treatment at 675℃ at varying soaking time(0.5,1.0,2.0,3.0 and 4.0 h).Heat treated specimens were subjected to intergranular corrosion tests as per ASTM standards A262 and G108.Sensitization in longer soaked material has been confirmed through ditch microstructures,cracks on the bend tested specimens and higher degree of sensitization.Nonlinear ultrasonic studies showed variation in the nonlinearity parameter with soaking time which also confirms sensitization.A good correlation was observed between the degree of sensitization measured by the electrochemical potentiokinetic reactivation test and the ultrasonic nonlinearity parameter.This study clearly demonstrated that nonlinear ultrasonic technique can be used as a potential technique for non-destructive characterization of sensitization in austenitic stainless steel.     

稀土对40Cr钢固体渗硼过程的影响

采用一种廉价的新型固体渗硼剂对40Cr钢进行了渗硼工艺试验,研究了稀土对钢的渗硼过程、渗层组织和性能的影响,结果表明,采用该渗硼剂是可行的,稀土能提高渗硼速度和渗层的硬度,并能改善渗层的硬度分布。