Laser surface hardening of martensitic stainless steel hollow parts

This paper deals with numerical simulation and experimental validation of laser heat treatment of an industrial axisymmetric hollow mechanical part by means of a strategy based on helical tracks. This component, made of AISI 420B martensitic stainless steel, features a low wall thickness and, according to this, it is not easily treatable by means of laser surface hardening. The work carried out was aimed at demonstrating that numerical simulation allows a drastic reduction of the experimental activity and that it makes possible to prove a very high sensitivity of the results to process parameters variation.     

Effect of simultaneous surface modification process on wear resistance of martensitic stainless steel

In order to improve the wear resistance of martensitic stainless steel, a surface treatment system was developed that combines high-frequency induction heating (IH) with fine particle peening (FPP). In this system, a compressed air spray from the FPP nozzle rapidly cools the specimen surface, which is heated by the IH system. The specimen surface can be simultaneously modified by work hardening and quenching. Vickers hardness and retained austenite measurements were conducted to characterize the surface-modified layer generated by the developed process. Surface microstructures were also observed by scanning electron microscopy (SEM) and optical microscopy. The process created a surface with a high hardness and an extremely fine-grained microstructure. The fine-grained microstructure was generated by dynamic recrystallization. The process reduced the amount of retained austenite in the surface layer because it increased the precipitated chromium carbide content. Reciprocating sliding wear tests were conducted to evaluate the wear resistance of the surface. The specimen modified by the developed process exhibited higher wear resistance than specimens that had only been quenched. This implies that the developed simultaneous process can significantly improve the wear resistance of steel surfaces.     

Chemical assembly of silver nanoparticles on stainless steel for antimicrobial applications

Microbial adhesion on stainless steel is the most common contamination in many applications. In this work, we present a simple method to fabricate stainless steel-based antimicrobial composites by fixing silver nanoparticles onto the surface. Silver nanoparticles were covalently assembled on the surface of stainless steel by using 3-aminopropyltriethoxysilane (APTES) as the coupling agent. After 24 h immersion the release of silver ions amounts to a total of 0.07 ppm, as measured by atomic absorption spectrophotometry. The bactericidal rate of the composite on Escherichia coli (E. coli) is greater than 99%, and the inhibition zone is about 28 mm in diameter. Combining the low cost and high effectiveness in inhibiting the growth of bacteria, such composites are expected to be useful as antimicrobial materials that may have great potential antimicrobial applications.     

Study on process of dual-frequency electromagnetic confinement and shaping for stainless steel

Electromagnetic confinement and shaping (EMCS) is an advanced materials processing technique. In this paper, a novel dual-frequency EMCS was proposed, i.e. lower frequency magnetic field (20 kHz) was used to produce the electromagnetic force, and higher frequency magnetic field (50 kHz) to heat and melt metal materials without effect on the electromagnetic force. Shaping inductors and heating inductors were designed according to the experimental results and our previous works, and distance between them was experimentally determined. Stability of dual-frequency EMCS of melt was detailedly analyzed. At last, several stainless steel samples were produced by the new method, and results show that it can easily achieve good coupling of temperature field and electromagnetic force by separately designing and controlling the two magnetic fields.     

不锈钢薄板拉延SDL水基润滑剂研究

本文根据不锈钢薄板拉延变形的工艺特点,简要讨论了在模具表面上形成粘接瘤的原因及润滑剂对拉延工艺的影响、金属表面上的润滑剂膜及SDL水基润滑剂配方选择原则,并对所配的水基润滑剂进行了摩擦系数的实验研究。     

厨具用不锈钢的表面化学着色

研究了一种厨具用不锈钢的表面化学着色工艺.探讨了硫酸锌用量、温度、时间和封闭方法对着色膜性能的影响,得出了最佳工艺参数.结果表明:该工艺操作温度范围宽,维护简单,具有推广价值.所得的着色膜色泽鲜艳,均匀,耐蚀性、耐磨性、耐热性、耐油污性好,能满足厨具的要求.     

冷轧工艺对301L不锈钢组织及性能的影响

对1.5 mm厚的301L不锈钢板材进行多道次冷轧试验,得到压下率分别为20%,30%,40%的板材;通过对冷轧板材的拉伸试验、金相分析、SEM分析、XRD衍射分析及硬度测试,研究冷轧压下率对301L不锈钢组织及性能的影响规律。研究表明,随着冷轧压下率的增大,301L不锈钢中的应变诱发马氏体会逐渐增多,材料的屈服强度由789 MPa提高至1260 MPa,抗拉强度由977 MPa提高至1317 MPa,显微硬度则提高了120 HV;材料出现晶粒碎化现象,产生细晶强化;同时,由于301L不锈钢中的马氏体相变,20%压下率的301L不锈钢拉伸应变硬化指数要高于30%压下率的301L不锈钢。     

On the aluminisation of stainless steel by CVD in fluidised beds

The effect of coating parameters such as bed composition, H₂/HCl reactive gas ratio and temperature is investigated so as to obtain Al diffusion coatings on AISI 304 stainless steel substrates by chemical vapour deposition in fluidised bed reactors (CVD-FBR). It will be shown that thicker coatings are obtained when the beds are composed of AlCl₃ (s) instead of pure Al powders. An increase in the reactive gas mixture also produces thicker coatings but some porosity may be found occluded in the proper coatings. Finally, moderate temperatures and times seem to be the most suitable to produce the best coatings avoiding the presence of sharp coating/substrate interfaces. A post-coating heat treatment brings about double-layered coatings based on FeAl and Fe_xNi_yAl containing Cr derivatives.     

Performance of activated TIG process in austenitic stainless steel welds

Five kinds of oxide fluxes, MnO₂, TiO₂, MoO₃, SiO₂, and Al₂O₃, were used to investigate the effect of activated tungsten inert gas (activated TIG) process on weld morphology, angular distortion, delta-ferrite content, and hardness of Type 316L stainless steels. An autogenous TIG welding was applied to 6 mm thick stainless steel plates through a thin layer of flux to produce a bead-on-plate welded joint. The oxide fluxes used were packed in powdered form. The experimental results indicated that the SiO₂ flux facilitated root pass joint penetration, but Al₂O₃ flux led to the deterioration in the weld depth and bead width compared with conventional TIG process. Activated TIG welding can increase the joint penetration and weld depth-to-width ratio, thereby reducing angular distortion of the weldment. On the basis of the present results, it is considered that the centripetal Marangoni convection and constricted arc plasma as a mechanism in increasing the penetration of activated TIG joint.     

不锈钢化学着色的低温工艺研究

为了降低不锈钢化学着色的高温条件,在CrO3-H1SO4着色体系中加入过渡金属无机盐添加剂,对不锈钢进行化学着色,使用正交设计方法优化工艺条件为铬酐浓度250g/L,着色温度60℃,添加剂用量5g/L,得到不同颜色的不锈钢,并对不锈钢的性能进行测定,结果表明:添加剂的使用可明显降低着色温度,减少铬酸挥发带来的环境污染,同时彩色钝化膜保持良好的性能.     

电化学不锈钢着色工艺的研究

对电化学不锈钢着色工艺进行了系统的研究，通过电流变化研究着色的变化规律，得出了着色时间、颜色种类与电量密度的关系，以及各种颜色着色时间与电流变化的关系，提出电量控制不锈钢着色能提高电化学不锈钢着色工艺的效率，为在生产中应用提供了重要的参考依据。     

高档不锈钢灶具面板成形工艺与模具设计

以SUS201为材质的不锈钢灶具面板成形为例,分析对比了新旧工艺,找出原有工艺存在工序多,成形零件表面平面度差,角部成形后开裂,如不成形角部需要增加塑料围边从而降低产品的精度等问题。对原有工艺和模具进行了改进,既缩短了生产工序,又提高了产品精度。此新工艺和模具在行业内具有先进性和可复制性。     

A study on stainless steel mirror surface polishing by using the electrophoretic deposition method

Polishing wheels with homogeneously organized micro abrasive grains, uniformly dispersed by electrophoretic deposition (EPD), can be applied in mirror-like polishing process. This work studies the characteristics of EPD and mechanical polishing when SUS316LVV is polished. Abrasive grains with blunt edges are easily ablated from the polishing wheel by friction during polishing. The polishing wheel can be continuously refreshed by adding new abrasives. A superior surface polishing quality can thus be obtained. The control parameters of the EPD polishing process include the working voltage, the rate of rotation of the polishing wheel, the polishing feed rate, the polishing time, the axial loading and the pH value of the electrolyte, etc. Experimental results indicate not only that SiC particles of size 0.9–1.5 μm were used in EPD polishing, but also that the initial roughness of a machined surface could be improved from 0.5 μm Ra to 0.02 μm in 8 min, yielding a mirror-like surface.     

The kinetics of duplex scale formation on 18/8 type stainless steel

A previous model of duplex scale growth on 18/8 stainless steels based on the formation of an impervious barrier at hemispherical alloy grain boundaries has been extended to consider the influence of a finite healing layer growth rate. The analysis shows that true primary and secondary or healing layer parabolic rate constants can best be calculated from weight gain vs. the square root of time plots. Accurate determinations of the secondary rate constant requires oxidation exposures a factor of 3 or 4 times greater than the time to form a complete healing layer at the oxide-metal grain boundary interface. Good agreement is found between the present theory and expeimental data and the model gives a simple extrapolation method for the evaluation of long-term metal losses or oxide thicknesses.     

不锈钢基板化学机械抛光过程温度研究

鉴于不锈钢化学机械抛光的复杂环境,研究了其抛光过程中温度的变化规律。设计并搭建了过程温度在线检测系统,检测并研究了不同工艺参数与温度之间的关系。实验结果表明:抛光温度随着抛光压力和抛光垫转速的增大而增大,随着抛光液流量的增大而减小。不锈钢基板边缘点抛光温度高于中心点抛光温度,聚氨酯材料比合成革和磨砂革材料的温升更大。当抛光垫加沟槽时,温升将明显下降,且径向型与周向型沟槽温度变化相差不大,网格型沟槽温差变化最小。抛光垫沟槽间距增大,温升增大;沟槽宽度对温升影响较小。     

Understanding the effect of nitrogen in austenitic stainless steel on the intergranular stress corrosion crack growth rate in high temperature pure water

Understanding the effect of nitrogen content on the crack growth rate (CGR) due to intergranular stress corrosion cracking (IGSCC) in high temperature (288 °C) pure water, in non-sensitised and strain-hardened stainless steel (SS) type 304 LN was the focus of this study. Non-sensitised SS containing two different levels of nitrogen (0.08 and 0.16 wt.%) in the solution annealed condition was strain-hardened by cross-rolling at 200 °C (warm rolling). It has earlier been reported that SS with a higher nitrogen level in the warm rolled condition has a higher CGR in high temperature pure water. Tensile testing was carried out using both the SS in the warm rolled as well as in the solution annealed condition at 288 °C. Samples were prepared for transmission electron microscopy (TEM) from the warm rolled SS and from the tensile tested (at 288 °C) specimens. TEM studies indicated that twinning and shear band formation were the major modes of deformation due to rolling at 200 °C and these feature were observed to terminate at grain boundaries, leading to regions of higher strain and stresses at grain boundaries. Higher nitrogen SS has higher grain boundary strain and stresses making the grain boundary regions more susceptible to IGSCC, resulting in higher CGR values. At 288 °C dislocation entanglement and cross-slip were the predominant modes of deformation.     

Electrolytic pickling of the oxide layer on hot-rolled 304 stainless steel in sodium sulphate

Electrolytic pickling of hot-rolled 304 stainless steel in Na₂SO₄ electrolyte was investigated with electrochemical, weight loss and SEM-EDX measurements. Pickling took place upon both active and transpassive polarisations. Mechanism and kinetics of pickling during active and transpassive polarisations were unravelled. Metallic phase in oxide layer was dissolved during active polarisation while the oxide layer was significantly undercut. Chromium oxide in the oxide layer was oxidised to soluble anions during transpassive polarisation, while iron oxide and metallic phase could either be remained or removed. Pickling due to undercutting with active polarisation was highly pronounced.     

焊条电弧焊堆焊双相不锈钢2205工艺研究

对双相不锈钢2205堆焊工艺进行分析,采用小电流、快速焊、水中冷却的工艺规范,使用国产E309MoL(φ4mm)和E2209(φ4mm)型焊条分别进行过渡层和复层的堆焊;复层铁素体面积含量达到47.14%,通过常规力学性能试验、FeCl3溶液点蚀试验和NaOH溶液电解腐蚀试验,无金属析出物,化学成分满足堆焊E2209型要求,堆焊面层硬度在23.8～24.7HRC之间,成功堆焊出满足使用要求的双相钢堆焊层。     

Electrochemical and SEM study on Type 254 SMO stainless steel in chloride solutions

An investigation was conducted to examine the critical crevice potential (E_crev) and the critical protection potential (E_prot) for Type 254 SMO stainless steel in 4% NaCl solution by using potentiodynamic cyclic anodic polarization (PCAP) technique at temperature ranging from 30 to 90 °C. The critical crevice temperature (CCT) and the critical crevice protection temperature (T_prot) were determined by plotting the values of breakdown potential and E_prot versus solution temperature, respectively. The values of CCT and T_prot were recorded at the abrupt transition with increasing the temperature from transpassive corrosion to crevice corrosion and were found to be at 55 and 52 °C, respectively. Above CCT (70 °C) the following points were recorded. The E_crev and E_prot decreased linearly with log [Cl⁻]. The addition of bromide ions to chloride ions at a fixed halide content of 4% increased both E_crev and E_prot. The E_crev value in 4% NaCl increased linearly with increasing pH in the range 1-10. The addition of 0.5 M bicarbonate ions to 4% NaCl completely removed the crevices effect while increasing the addition of sulphate ions to 4% NaCl increased both of E_crev and E_prot. The morphology of the crevice corrosion produced on the steel surface was examined by scanning electron microscope (SEM) after PCAP treatment under different test conditions.     

Inhibitory effect of cetyltrimethyl ammonium bromide on the corrosion of 904L stainless steel in LiBr solution

The inhibitory influence of cetyltrimethyl ammonium bromide (CTAB) on 904L stainless steel (SS) in LiBr solution was investigated by potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy techniques. The results showed that the inhibition efficiency of CTAB increases with the increasing concentration. The adsorption of CTAB on 904L SS surface obeys the Langmuir isotherm equation. The data reveal that the CTAB was of mixed-type inhibitor. The thermodynamic parameters for the corrosion of 904L SS in 1.0?M LiBr solution were calculated and discussed. The EIS data are in agreement with potentiodynamic polarisation measurements.