奥氏体不锈钢厚板埋弧自动焊工艺

对大庆甲醇厂改造工程中入塔器预热器壳体所采用的奥氏体不锈钢厚板的焊接性进行了分析 ,确定了焊接工艺。实践证明 ,该焊接工艺是可行的     

Effect of carbonitriding temperature process on the adhesion properties of diamond like-carbon coatings deposited by PECVD on austenitic stainless steel

The deposition of adherent coatings such as diamond-like carbon (DLC) on substrates of iron-based materials is difficult to obtain for two reasons: high residual compressive stress occurs in the inner film formation, and the mismatch of thermal expansion coefficient between steel and DLC film generates delamination effects. In order to determine the carbonitriding temperature prior to film deposition, the steel substrate and the DLC films were analyzed for their microstructure and mechanical properties of adhesion as a function of temperature. The technique used to deposit the coating was DC-pulsed plasma enhanced chemical vapor deposition. The delamination distances and the critical load of the film were obtained by scratch testing. The surface analysis by X-ray diffraction indicated the formation of nitride phases on the steel. Raman spectroscopy showed the fraction of sp³ carbon bonds in DLC films. Hardness profiling was used to verify the extent of the interface modified by carbonitriding along the cross section. For this, the steel sample with the appropriate surface modification to have high adhesion of the DLC film was used.     

Diamond-like carbon film deposited on nitrided 316L stainless steel substrate: A hardness depth-profile modeling

Adhesion and hardness of Diamond-Like Carbon films are improved by nitriding of the steel substrate prior to PVD deposition. Since the mechanical properties of the nitrided steel layer are not homogeneous, i.e. a significant hardness decrease is observed in the upper nitrided layer close to the surface, an outer surface layer of ~ 15 μm is removed prior to the film deposition. In the present work, a 316L stainless steel substrate is nitrided in a cyanide-cyanate solution at 570 °C during 3 h. The coated system involved the deposition of a hydrogenated, amorphous carbon (a-C:H) solid lubricant of ~ 2 μm including a chromium carbide interlayer. The comparison between the hardness behavior of the DLC/steel and the DLC/nitrided steel systems reveals the existence of a very important hardness gap, which highlights the benefit of the nitriding treatment prior to coating deposition. In addition, the microhardness-depth profile is determined from a load-depth curve, by applying a simple hardness model. The predicted change in hardness is found to be in a very good agreement with the experimental profile, which allows the hardness determination both in the white layer and in the diffusion zone over ~ 30 μm in total depth. However, only the composite hardness modeling allows the accurate determination of the intrinsic hardness of the film.     

Electrochemical behaviour of silica basic hybrid coatings deposited on stainless steel by dipping and EPD

The aim of this work is the characterisation of the corrosion behaviour of stainless steel (AISI 304) substrates coated by dipping and electrophoretic deposition (EPD) from a sol-gel basic sol. Particulate silica sols (labelled NaSi) were prepared by basic catalysis from ethyltriethoxysilane (TEOS), methyltriethoxysilane (MTES) and sodium hydroxide. Coatings between 2 and 10 μm were prepared by using concentrated and diluted sols by dipping and EPD process and the corrosion behaviour of the coated substrates were studied through potentiodynamic and impedance spectroscopy measurements (EIS). Potentiodynamic studies of coatings produced by dipping reveal a strong dependence of the protective properties with the concentration of the sol. This behaviour was confirmed by EIS showing that only the coatings obtained from concentrated sol present enough protective properties. On the contrary, EPD coatings prepared from diluted NaSi sol showed an excellent corrosion resistance, maintaining a pure capacitive behaviour for long periods of immersion. EPD deposition is thus proposed as a good alternative method for obtaining thicker and denser coatings with good protective properties from dilute and stable sols.     

Accumulation of uranium on austenitic stainless steel surfaces

The surface contamination by uranium in the primary circuit of PWR type nuclear reactors is a fairly complex problem as (i) different chemical forms (molecular, colloidal and/or disperse) of the uranium atoms can be present in the boric acid coolant, and (ii) only limited pieces of information about the extent, kinetics and mechanism of uranium accumulation on constructional materials are available in the literature. A comprehensive program has been initiated in order to gain fundamental information about the uranium accumulation onto the main constituents of the primary cooling circuit (i.e., onto austenitic stainless steel type 08X18H10T (GOSZT 5632-61) and Zr(1%Nb) alloy). In this paper, some experimental findings on the time and pH dependences of U accumulation obtained in a pilot plant model system are presented and discussed. The surface excess, oxidation state and chemical forms of uranium species sorbed on the inner surfaces of the stainless steel tubes of steam generators have been detected by radiotracer (alpha spectrometric), ICP-OES and XPS methods. In addition, the passivity, morphology and chemical composition of the oxide-layers formed on the studied surfaces of steel specimens have been analyzed by voltammetry and SEM-EDX. The experimental data imply that the uranium sorption is significant in the pH range of 4-8 where the intense hydrolysis of uranyl cations in boric acid solution can be observed. Some specific adsorption and deposition of (mainly colloidal and disperse) uranyl hydroxide to be formed in the solution prevail over the accumulation of other U(VI) hydroxo complexes. The maximum surface excess of uranium species measured at pH 6 (Γ_sample = 1.22 μg cm⁻²U ≅ 4 × 10⁻⁹ mol cm⁻² UO₂(OH)₂) exceeds a monolayer coverage.     

奥氏体不锈钢设备的化学清洗和钝化

从奥氏体不锈钢的钝化机理入手,分析了钝化膜存在的意义、破坏机理和防护措施,给出了参考的清洗钝化剂配方、清洗钝化工艺、操作注意事项,明确了奥氏体不锈钢钝化膜质量的检验方法。     

奥氏体不锈钢管道清洗技术简述

介绍了奥氏体不锈钢管道常用的清洗技术,包括物理清洗、化学清洗、静态清洗、动态清洗、除垢清洗、脱脂清洗等,对各种清洗技术的特点,适用的工艺条件进行了总结。     

A comparative study of duty cycle and argon / methane flow ratio effect on the tribological behavior of DLC coatings over nitrided Astaloy Mo-based steel

Surface properties of Astaloy Mo-based steel were enhanced by using DLC deposition. The specimens were formed by double-sided compaction and heated for 30 min at 1393 K, in the NH₃ atmosphere. Following this, the plasma nitriding process was applied to improve the adhesion of the DLC coating. Afterward, the DLC coating was performed by Pulsed DC PACVD. Surface characteristics were studied by changing the duty cycle and the Argon/Methane flow ratio. The reciprocating method was carried out to evaluate wear behavior. Field emission scanning electron microscopy equipped with EDS and Raman spectroscopy, hardness tester, nanoindentation test and surface roughness tester were used to evaluate the chemical structure, wear mechanisms of DLC coatings. This study proved that hardness reached up to 12.2 ± 1.11 GPa and the wear behavior was enhanced significantly by the DLC coating deposition. The mass loss increased with a rise in the duty cycle. Increasing the Argon/Methane ratio from 4:1 to 6:1 caused a decrease in the mass loss of DLC coatings. Burnishing, pulling out and adhesive wear were the dominant mechanisms.     

Growth and properties of hydrogen-free DLC films deposited by surface-wave-sustained plasma

Hydrogen-free diamond-like carbon (DLC) films were deposited by a new surface-wave-sustained plasma physical vapor deposition (SWP-PVD) system in various conditions. Electron density was measured by a Langmuir probe; the film thickness and hardness were characterized using a surface profilometer and a nanoindenter, respectively. Surface morphology was investigated using an atomic force microscope (AFM). It is found that the electron density and deposition rate increase following the increase in microwave power, target voltage, or gas pressure. The typical electron density and deposition rate are about 1.87 × 10¹¹–2.04 × 10¹² cm^− 3 and 1.61–14.32 nm/min respectively. AFM images indicate that the grain sizes of the films change as the experimental parameters vary. The optical constants, refractive index n and extinction coefficient k, were obtained using an optical ellipsometry. With the increase in microwave power from 150 to 270 W, the extinction coefficient of DLC films increases from 0.05 to 0.27 while the refractive index decreases from 2.31 to 2.11.     

Photoconductivity of DLC film deposited by pulsed discharge plasma CVD

DLC films were deposited by a new pulsed DC discharge plasma chemical vapour deposition (CVD) using hydrogen and methane gas mixture. When methane concentration (Cm) i.e. CH₄/(H₂ + CH₄) was increased from 3 to 40%, the graphitization of the carbon film increases as evident from Raman study. When Cm was increased to 30%, DLC film shows photoconducting property. The white light photoconductivity (S = I_l/I_d, where I_l is light current and I_d is dark current) measured with solar simulator under AM 1.5 condition was approximately 20 at room temperature. The photoconductivity was not clear when Cm was lower than 20%. ESR measurements also show that the electron spin density was slightly decreased with decreasing concentration of methane. Thus we can conclude here that at higher concentrations of methane at 30%, Sp² content of the film increases and the DLC film becomes photoconducting.     

Influence of plasma nitriding treatment on the adhesion of DLC films deposited on AISI 4140 steel by PVD magnetron sputtering

Duplex surface treatments composed of diamond like carbon (DLC) coating followed by plasma nitriding have drawn attention for a while. In this study, AISI 4140 steel substrates were plasma nitrided at different treatment temperatures and times. Then, DLC films were deposited on both untreated and plasma nitrided samples using PVD magnetron sputtering. The effect of different plasma nitriding temperatures and times on the structural, mechanical and adhesion properties of DLC coatings was investigated by XRD, SEM, microhardness tester and scratch tester, respectively. It was found that surface hardness, intrinsic stresses, layer thickness values and phase distribution in modified layers and DLC coating were the main factors on adhesion properties of duplex coating system. The surface hardness and residual stress values of AISI 4140 steel substrates significantly increased with both DLC coating and duplex surface treatment (plasma nitriding + DLC coating). Increasing plasma nitriding temperature and time also increased the diffusion depth and the thickness of modified layers. Hard surface layers led to a significant improvement on load bearing capacity of the substrate material. However, it was also determined that the process parameters, which provided lower intrinsic stresses, improved the adhesion properties of the duplex coating system.     

Effect of plasma pretreatment on durability of sol-gel superhydrophobic coatings on laser modified stainless steel substrates

Superhydrophobic surfaces were generated on stainless steel SS 304 substrates, using a combination of physical as well as chemical modification of the surface and tested for use in biomedical applications. Nanosecond pulsed laser was used for physical modification, i.e. creating nanoscaled roughness on the substrates. An additional chemical modification was performed using fluorosilane-based sol-gel nanocomposite coatings to further improve the hydrophobicity. Presently, the key challenge that such surfaces face, is to possess a substantial durability. In this study, a surface activation technique such as plasma pre-treatment was adopted to improve the adhesion of coatings on the laser treated substrates. The coatings deposited using dip coating technique were cured at 150 °C. The surface morphology and the roughness of the processed substrates and the coated samples were characterized using Atomic Force Microscope and Scanning Electron Microscope. The wettability of the surface was monitored and evaluated throughout the study using water contact angle measurements. Weathering tests and scratch resistance measurements using a crockmeter were carried out to evaluate the durability, which revealed that the adhesion could be improved with plasma treatment of the laser textured substrates, prior to coating deposition. Maximum anti-bacterial activity of up to 90% towards the bacterial species Escherichia coli was found on the substrates coated with the fluorosilane-based superhydrophobic coatings for an exposure time of 30 min, without any addition of external anti-bacterial agents. Thus, the preliminary results obtained from the present investigation were found to be promising and were indicative of use of these surfaces for biomedical applications.     

Influence of nitrided and carbonitrided interlayers on enhanced nucleation of diamond on stainless steel 304

As previously reported by various investigators, interlayers may be a successful solution for the problem of depositing diamond on steel substrates. The properties of the interlayers have been found to have a strong effect on the initial stages of CVD diamond formation. In this paper, the effect of different nitrided steel phases has been investigated for enhancing nucleation on stainless steel 304 substrates. Carburization of the nitrided substrate surface during the initial stages of diamond deposition leads to the formation of chromium carbide and the resulting microstructure of the interface between substrate and diamond film is probably responsible for enhanced adhesion of the diamond film.     

Tribological properties of DLC films deposited on steel substrate with various surface roughness

Tribological properties of diamond-like carbon (DLC) films in water were investigated concerning with the influence of surface roughness and various mating materials. The DLC films were deposited by pulsed-bias CVD method on AISI630 stainless steel. The substrate roughness (R_a) is in the range of 1.4–740 nm. AISI 440C, AISI 304 stainless steel and brass balls were used as a mating ball. The friction coefficients of DLC films against with AISI 440C stainless steel ball indicated under 0.1 irrespective of the roughness. The film having smooth surface (R_a=1.4 nm) had severe damage at a load of 9.4 N. However, the film having rough surface (R_a=263 nm) had no damage at the same load. The specific wear rate of the steel ball increased with increase of roughness of the surface. In the case of AISI 304 stainless steel ball, the specific wear rate of the ball showed similar tendency. The friction with brass ball showed relatively high friction coefficient in the range of 0.12–0.25. However, the damage on the films could not be observed after friction test. It is considered that the roughness of the surface is important factor for the rupture of the film in water environment.     

High coercivity of iron-filled carbon nanotubes synthesized on austenitic stainless steel

Multiwalled carbon nanotubes synthesized directly on austenitic stainless steel result in being filled with pure iron nanoparticles. X-ray diffraction shows that the nanoparticles are either in the γ- or α-phase, although iron in the original alloy is in γ-phase because of the presence of nickel. This phase transformation is due to the selective extraction of iron, performed by carbon nanotubes during their growth. A high coercivity of iron-filled carbon nanotubes is measured although the starting steel is paramagnetic. The presence of the α-phase, the magnetic anisotropy and the single domain character of the Fe nanoparticles explain their magnetic behavior.     

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H₂SO₄ in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H₂SO₄, concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge‐discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Hydrogenated amorphous carbon films deposited on 316L stainless steel

Research on hydrogen amorphous carbon films (a-C:H), which possess the diamond-like characteristic, has been stimulated for many years by need to simultaneously optimizing the mechanical, optical and biological properties, and by challenges related to the deposition of a-C:H films on medical implants. In the present work, we investigate the structure, optical and mechanical properties (hardness, elastic modulus and stress) of a-C:H films deposited on 316L stainless steel substrate by the radio frequency plasma enhanced chemical vapor deposition (RF PECVD). The negative self-bias voltages significantly influence on temperature of steel substrates during the deposition process and films properties. Specifically, the high energetic deposition leads also to stabilization of the sp² content and thermally-activated relaxation in the stress of a-C:H films. Presented correlation between the obtained results and literature analysis let deem the Raman spectra as a good tool to control the properties of implants made of 316L stainless steel with a-C:H film for general use.     

Pitting and stress corrosion cracking behavior in welded austenitic stainless steel

The effect of microstructural changes in 304 austenitic stainless steel induced by the processes of gas tungsten arc welding (GTAW) and laser-beam welding (LBW) on the pitting and stress corrosion cracking (SCC) behaviors was investigated. According to the in situ observations with scanning reference electrode technique (SRET) and the breakdown potentials of the test material with various microstructures, the GTAW process made the weld metal (WM) and heat-affected zone (HAZ) more sensitive to pitting corrosion than base metal (BM), but the LBW process improved the pitting resistance of the WM. In the initiation stage of SCC, the cracks in the BM and HAZ propagated in a transgranular mode. Then, the crack growth mechanism changed gradually into a mixed transgranular + intergranular mode. The cracks in the WM were likely to propagate along the dendritic boundaries. The crack initiation rate, crack initiation lifetime and crack propagation rate indicated that the high-to-low order of SCC resistance is almost the same as that for pitting resistance. High heat-input (and low cooling rate) was likely to induce the segregation of alloying elements and formation of Cr-depleted zones, resulting in the degradation in the corrosion resistance.     

Preparation of electrolytic ceramic films on stainless steel conversion coatings

An electrolytic method for the synthesis of an alumina barrier on stainless steel with strong interfacial bonding is described for a Fe-17%Cr alloy. The deposit was laid down electrochemically after a specific conversion treatment by chemical oxidation of the substrate in acid solution. The conversion coating was very porous and had excellent adhesion at the substrate interface. Alumina was obtained by thermal dehydration of aluminium hydroxide deposited from an aqueous solution of an aluminium salt, according to a two-step mechanism: generation of hydroxyl ions at the cathodic substrate by reduction of H₂O or dissolved oxygen and a precipitation reaction forming aluminium hydroxide. Thermal treatment induced interfacial reactions between aluminium oxide and conversion coating compounds which led to spinel formation beneath the superficial alumina layer. The coating presented chemical composition gradients suitable for strong adhesion. Thermal oxidation resistance was studied in air at 1000° C.