Anode plasma electrolytic nitrocarburizing of steel in an aqueous electrolyte based on glycerol,ammonium nitrate,and ammonium chloride

The mechanism of transport of saturating components from the electrolyte into the treated material during the anode nitrocarburizing of steel in an electrolyte containing glycerol, ammonium nitrate, and ammonium chloride has been described. The effect of the electrolyte component concentrations and treatment conditions on the pattern of formation and properties of the diffusion layers has been determined. The possibility of preparing a nitrocarburized layer with a thickness of up to 0.2 mm and a surface microhardness of up to 870 HV has been shown.     

Formation mechanism and control of aluminum layer thickness fluctuation in embedded aluminum–steel composite sheet produced by cold roll bonding process

The influences of rolling reduction and aluminum sheet initial thickness (AIT) on the thickness fluctuation of aluminum layer (TFA) of embedded aluminum–steel composite sheet produced by cold roll bonding were investigated, the formation mechanism of TFA was analyzed and method to improve the thickness uniformity of the aluminum layer was proposed. The results showed that when the reduction increased, TFA increased gradually. When the reduction was lower than 40%, AIT had negligible effect on the TFA, while TFA increased with the decrease of AIT when the reduction was higher than 40%. The non-uniformities of the steel surface deformation and the interfacial bonding extent caused by the work-hardened steel surface layer, were the main reasons for the formation of TFA. Adopting an appropriate surface treatment can help to decrease the hardening extent of the steel surface for improving the deformation uniformity during cold roll bonding process, which effectively improved the aluminum thickness uniformity of the embedded aluminum/steel composite sheets.     

Research of the Tribological Properties of the Surface on 16Mn Steel by Plasma Nitriding and S-N-C Plasmas Composite Treatment

Sulfide layer with certain thickness was made on the nitrided surface of 16Mn steel by means of plasma S-C-N composite treatment. Under half lubricated condition, friction coefficient and wear loss of LY12 aluminum alloy were measured in sliding against samples of 16Mn treated by cubrizing and sulphiding respectively; In order to avoid the transfer of aluminum to the steel that lead to the inaccurate measurement of wear loss of carburized samples, Grl5 steel was adopted as counterpart face to measure the wear loss of them. SEM and EDAX were used for the morphological and chemical characterization of the wear surface and longitudinal cross-sections beneath sliding surface of LY12 aluminum alloy cirque and the wear tacks of the carburized samples and sulphided samples. Results show: The surface roughness,wear rate, average friction coefficient and magnitude of friction fluctuations of LY12 aluminum alloy cirque sliding against sulphided sample were all lower than sliding against carburized sample; Compared with carburized layer, sulfide layer of 16Mn steel can not only efficiently prevent the occurrence of adhesion when sliding against LY12 aluminum alloy, but also greatly lower the wear loss when sliding against Gr15 steel.     

Anodising of 2024-T3 aluminium alloy in electrolyte of sulphuric– boric–phosphoric mixed acid containing cerium salt as corrosion inhibitor

The effect of cerium salt as an inhibitor in anodising of the 2024-T3 aluminium alloy was studied. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy was used to study the surface composition of the alloy before and after surface preparation. A mixed electrolyte of 10% sulphuric acid, 5% boric acid and 2% phosphoric acid containing 0.1 mol/L cerium sulphate salt was used as the anodising electrolyte. Sealing treatment was also done in boiling water and molten stearic acid. Electrochemical impedance spectroscopy and salt spray techniques were performed in order to investigate the corrosion behaviour and durability of the oxide films, respectively. It was concluded that the presence of cerium ions in anodising electrolyte resulted in the increase in homogeneity, the rate of oxide film growth and also the thickness of the oxide layer, owing to the high oxidising power of cerium ion.     

Atmospheric corrosion monitoring of a weathering steel under an electrolyte film in cyclic wet–dry condition

Electrochemical Impedance Spectroscopy (EIS) and film thickness measurements have been employed to study the corrosion monitoring of steel under an electrolyte film in wet–dry cycles simulating a coastal atmosphere. The results indicate that within each cycle, the corrosion rate increases during drying process due to an increase in Cl⁻ concentration and an enhancement of oxygen diffusion by thinning out of the electrolyte. As corrosion process proceeds, the corrosion rate increases greatly and reaches a maximum. During subsequent corrosion stage, the corrosion rate decreases greatly and keeps at a low value due to the formation of a stable rust layer.     

二氧化碳在A3钢大气腐蚀中的作用

通过电化学法并结合ＸＲＤ及ＳＥＭ,研究了大于临界相对湿度条件下,ＣＯ２浓度对Ａ３钢在薄层液膜下大气腐蚀的影响。电化学实验结果表明,Ａ３钢的大气腐蚀速率随ＣＯ２浓度的上升而增加。Ｘ射线衍射分析及ＳＥＭ观察表明,金属表面腐蚀 产物中无碳酸盐生成;腐蚀产物在金属表面分为内、外双层结构,ＣＯ２在Ａ３钢表面的吸附是不均匀的。故ＣＯ２对金属的大气腐蚀起着加速作用,腐蚀产物膜对金属的保护作用微弱,同时提出了ＣＯ     

AISI 316L奥氏体不锈钢低温离子-气体渗碳工艺优化

目的将低温离子-气体乙炔渗碳应用于AISI 316L奥氏体不锈钢表面硬化处理,同时探讨其硬化处理的最优工艺参数及优化效果。方法采用离子轰击去除不锈钢表面钝化膜并活化其表面,再进行低温气体乙炔渗碳,实验过程使用脉冲式供气循环处理方式。进行温度梯度实验,寻找渗碳处理的临界温度。并采用正交试验法设计3因素3水平共9组实验,分析气体比例、离子轰击时间、保温压强3个因素对渗碳层硬度和厚度产生的影响,以期得到不锈钢低温离子-气体乙炔渗碳优化工艺。通过对经过最优化工艺处理过后的不锈钢硬化层组织、成分、厚度、硬度、耐磨性、耐蚀性能的研究分析,验证此工艺对AISI 316L奥氏体不锈钢硬化处理的适用性。结果处理温度为540℃时渗碳层有碳的铬化物析出;离子轰击时间对渗碳层硬度影响最大,保温压强对硬化层厚度影响最明显。在硬化处理温度为520℃,V(H2)∶V(C2H2)=1∶1,渗碳压强为-0.02 MPa,离子轰击时间为20 min时,316L奥氏体不锈钢离子-气体乙炔渗碳效果最优。经优化工艺处理后不锈钢硬化层厚度达到30μm左右,表面硬度达到838HV0.05,耐蚀性和耐磨性能等都显著提高。结论低温离子-气体乙炔渗碳硬化处理适用于AISI 316L奥氏体不锈钢,其处理最合适温度为520℃。经优化工艺处理后的不锈钢具有较高的硬度、厚度,良好的硬度梯度,高耐蚀性能及高耐磨性能。     

脉冲电子束处理对高速钢表面组织的影响

研究了真空脉冲电子束处理对W6M05Cr4V2高速钢表面熔凝层组织的影响。结果表明，经过脉冲电子束处理后，高速钢试样表面形成组织明显细化的表面熔凝层，同时在熔凝层下还形成了晶粒细小的热影响区。这将对提高高速钢的硬度及耐磨性等有一定意义。     

Study on the factors in creating the IMC-free region: dissimilar metal joining of aluminium alloys to steel by a MIG-braze welding by using the advanced hot-dip aluminized steel sheet

Dissimilar metal joining of aluminium alloys to steel is generally difficult to be in practical use because of a formation of brittle intermetallic Fe–Al compound (IMC) at the interface of the joint. The authors have been researching in order to minimize the thickness of this brittle IMC in order to get excellent joint strength and have found that the formation of this brittle IMC is regionally prevented by using the advanced hot-dip aluminized steel sheet and by adopting suitable joining conditions. In particular, this paper focuses on the mechanism of creating this IMC-free region in the case of MIG-braze welding and the results obtained are as follows. (1) The creation of IMC-free region is initiated as the first process by the dissolution of the τ₅ phase (Fe–Al–Si) in the aluminized layer into the weld metal, and temperatures of more than 886 K for dissolution during MIG-braze welding and the use of filler metal for dilution of Fe and Si in τ₅ phase have significant effects. (2) In the second process, the diffusion between aluminium-alloy weld metal and base steel is restricted by AlN on the surface thin layer of the base steel which existed under 908 K temperature conditions during MIG-braze welding.     

Controlling of metal removal thickness in ECM process

Electrochemical machining (ECM) offers the unique advantage of better accuracy and high surface integrity of hard-machined components. A new technique has been developed to utilize a simultaneously moving and rotating electrode to remove a specific amount of material from pre-machined holes and rods of hardened steel specimens. One of the electrodes was provided with two simultaneous movements, traverse speed and rotational speed. The electrolyte was pumped into the gap between the tool and the workpiece, through a matrix of fine holes distributed along one of the electrode surface. A mathematical model has been proposed for accurately estimating the thickness of the workpiece layer under different working conditions. Experimental results revealed that this technique could lead to the removal of a surface layer thickness up to 200 μ, which consequently classified this method as a super-finishing process. Finally, the results of the experiments and the simulation are compared with each other. The obtained results are an endeavour to enhance the controllability of the ECM process.     

Influence of oxide layer on carbon diffusion during anode plasma electrolytic carburizing

This study is devoted to the effect of the oxide layer formed upon anodic plasma-electrolytic carburization on the rate of carbon diffusion in low carbon steels upon application of an aqueous solution of ammonium chloride with glycerol as a working electrolyte. Approximate determinations of carbon distribution in the surface layer of low carbon steels after their anodic plasma-electrolytic carburizing confirmed the hypothesis that there is deceleration of carbon diffusion by the oxide layer. Different structures of the oxide layer were revealed that depend on the method of sample cooling after their saturation with carbon in an anodic vapor-gas envelope. A possibility of controlling the thickness of the oxide layer was shown, as well as clarification of the surface by the choice of an electrolyte and treatment mode, was shown. A reduction in the roughness of the carburized surface from 0.62 ± 0.02 to 0.22 ± 0.02 μm was revealed.     

Study on composite surface treatment of 38CrMoAl steel

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Structure,mechanical, and tribotechnical properties of an austenitic nitrogen steel after frictional treatment

The features of the structure and the mechanical and tribotechnical properties of an austenitic nitrogen steel (Cr16.5, Mn18.8, C0.07, N0.53, Si0.52 wt %, and Fe for balance) after frictional treatment have been studied. It has been shown that, along with twinning, the nitrogen austenite upon frictional treatment undergoes a γ → stacking fault → ε transformation. The strengthening of the steel by the frictional treatment manifests in a delay of the onset of the plastic flow. In the structure of the surface layer with a thickness of 5 μm, a high concentration of stacking faults has been detected. The mechanical properties depend on the orientation of the acting stresses relative to the direction of the frictional treatment. Upon the sliding friction of a ball made of hard alloy (94%WC + 6%Co) on the strengthened surface, an anomalously low coefficient of friction of 0.13 is observed. The coefficient of friction in the presence of abrasive particles in the form of wear debris increases to 0.50; however, the wear rate is almost two times lower compared to the same characteristic for a nonstrengthened surface of the nitrogen steel tested under the same conditions.     

Influence of prolonged heating on thermal softening,chemical composition,and evolution of the nanocrystalline structure formed in quenched high-carbon steel upon friction treatment

Methods of transmission and scanning electron microscopy, X-ray diffraction analysis, micro-hardness, and wavelength dispersive X-ray microanalysis have been used to investigate the changes (in the process of vacuum treatment for 10–1200 min at temperatures of 350–550°C) in the structure, microhardness, and chemical composition of the surface layers of steel U8 (0.83 wt % C) in the initial quenched state and after friction treatment in the argon medium under the conditions of sliding friction using a like spherical indenter-flat sample pair. It has been shown that the layer nanostuctured by friction treatment possesses an enhanced resistance to thermal softening compared with the undeformed quenched steel, not only upon relatively short heating (1–2 h), but also prolonged heating (to 20 h) at temperatures of 350, 450, and 550°C. This is due to the retention of predominantly nanocrystalline structure in the deformed layer upon the prolonged heating to a temperature of 350°C by retarding the processes of the formation of carbide particles and recovery in the α phase and by decelerating the development of recrystallization, including the absence of anomalous growth of separate recrystallized grains upon prolonged high-temperature holdings. After vacuum annealing for 10–1200 min at a temperature of 350°C, an increase was revealed in the carbon concentration by 0.2–0.4 wt % in a layer up to 1 μm thick on the surface of quenched eutectoid steel deformed by friction action.     

New methods of the improvement of metal corrosion resistance through surface impregnation with anode electrolyte heating

It is shown that the use of the electrolyte composition developed in this work allows one to reduce by almost twice the carbon content in the surface layer of steel 45 and, with the introduction of an additional operation after the electrolytic heating (oxidation in an aqueous solution of caustic soda with a concentration of 50–100 g/L), to reduce the corrosion rate almost by a factor of two. It is also established that processing in another electrolyte formulated in the course of the research leads to the reduction of the corrosion rate of electrolytic iron coverings by more than 2 times.     

使用Kelvin探头参比电极技术研究液层厚度对氧还原速度的影响

使用Ｋｅｌｖｉｎ探头参比电极技术研究了薄液上氧还原过程的特征。实验中发现随着液层的蒸发减薄，氧还原反应速度先逐渐增加，而后又逐渐降低，呈出了速度极大值现象。尽管溶液中氧的盐效应对氧还原速度可能有一定的影响，实验结果表明，它并不是造成氧还原速度降低的主要原因。     

Effect of the origin of the modified surface layer on the structural strength of workpieces

Changes in the deformation behavior of steel solids and their properties have been considered after different methods of surface treatment (carburizing, nitriding, bombardment with low-energy ions, epilam application). Distinctions between concepts “structural strength of a material” and “structural strength of a workpiece” have been illustrated. It has been shown that, at the same material structural strength, the metal mechanical characteristics of a finished metal workpiece (i.e., the workpiece’s structural strength) change cardinally depending on the genesis of the modified layer (features of the structure that arise at the surface) and its contribution to the general state of the workpiece. After ion bombardment (layer thickness less than 1 μm) for the same material with the full retention of its structural strength, we can obtain in workpieces of the material either a very high (25–40%) strengthening without reducing plasticity or huge growth in the plasticity (increase in the elongation by a factor of 1.6) with enhanced strength. The effect is due to the nondislocation mechanism of plastic deformation of the surface layer nanostructurized upon ion bombardment and competition between strengthening and plasticizing depending on the magnitude of its contribution. The effectiveness of the strengthening action of ion bombardment is shown on connecting rod bolts 10 mm in diameter; the plasticizing effect is observed on thin sheet cold-rolled steels (improved stampability).     

Plasma nitriding of plastic mold steel to increase wear- and corrosion properties

In this study, the wear- and corrosion resistance of the layers formed on the surface of a precipitation hardenable plastic mold steel (NAK55) by plasma nitriding were investigated. Plasma nitriding experiments were carried out at an industrial nitriding facility in an atmosphere of 25% N₂ + 75% H₂ at 475 °C, 500 °C, and 525 °C for 10 h. The microstructures of the nitrided layers were examined, and various phases present were determined by X-ray diffraction. Wear tests were carried out on a block-on-ring wear tester under unlubricated conditions. The corrosion behaviors were evaluated using anodic polarization tests in 3.5% NaCl solution.The findings had shown that plasma nitriding does not cause the core to soften by overaging. Nitriding and aging could be achieved simultaneously in the same treatment cycle. Plasma nitriding of NAK55 mold steel produced a nitrided layer consisted of a compound layer rich in ε-nitride and an adjacent nitrogen diffusion layer on the steel surface. Increasing the nitriding temperature could bring about increase in the thickness of the nitrided layer and the nitride volume fraction. Plasma nitriding improved not only surface hardness but also wear resistance. The anti-wear property of the steel was found to relate to the increase in the thickness of the diffusion layer. Corrosion study revealed that plasma nitriding significantly improved corrosion resistance in terms of corrosion potential and corrosion rate. Improvement in corrosion resistance was found to be directly related to the increase in the nitride volume fraction at the steel surface.     

低温低压等离子弧辅助离子渗316L不锈钢的耐磨耐蚀性能

目的提高316L不锈钢的硬度、耐磨性。方法在400℃、2 Pa下,利用空心阴极直流弧辅助,进行了316L奥氏体不锈钢离子渗氮(PN)、离子氮碳共渗(PNC)及离子氮碳共渗加离子渗氮复合(PNC+PN)处理。针对处理后的样品,用莱卡显微镜、扫描电镜(SEM)、X射线衍射仪(XRD)、维氏硬度仪、3D形貌仪、球盘式摩擦磨损仪及电化学工作站等对组织、形貌、物相、机械性能及耐蚀性能进行表征。采用显微硬度计、微纳米综合力学系统测试分析处理后样品的力学性能。结果在空心阴极直流弧辅助下,三种工艺可获得超过3 mm/h的渗层生长速度。同316L不锈钢基体相比,PNC+PN复合处理样品的表面硬度提高3倍以上,在3.5%Na Cl中性电解质中的耐蚀电流密度降低约50%。结论 PNC处理和PNC+PN复合处理可获得更大的渗层厚度和更高的表面硬度,渗层中C、N含量越高,渗层组成相的晶格参数越大,渗层中产生的滑移带密度越大。低温低压等离子弧辅助离子渗不仅能有效提高316L不锈钢的表面硬度,还能提高不锈钢的耐蚀能力。