316L不锈钢强流脉冲电子束表面钛合金化及其耐蚀性

利用强流脉冲电子束对不锈钢表面进行了快速钛合金化。将精细钛粉预涂在基体表面后采用强流脉冲电子束对其进行后处理。在电子束对表面的快速加热熔化、混合及增强扩散效应的作用下,部分钛熔入基体表层形成一层富钛层。由于钛的添加有利于形成α相,合金层由α相和γ相混合组成。在模拟体液中的动态极化测试表明,316L医用不锈钢经强流脉冲电子束表面钛合金化后,其在模拟体液中的耐腐蚀性能获得了显著的提高。     

Surface treatment of 0.20% C carbon steel by high-current pulsed electron beam

A high-current pulsed electron beam（HCPEB） generated on the system of Nadezhda-2 was applied to improve the microstructure and performance of 0.20% C low carbon steel. Surface layers of the samples bombarded by explosive electron beam at different pulses was observed by using electron microscopy. The physical model of the thermal-stress process and related modification mechanism as a result of HCPEB irradiation was also investigated. After HCPEB post treatments, obvious changes in microstructure and significant hardening occur in the depth of 200-250 μm from the surface after HCPEB irradiation. Rapid heating and subsequent rapid solidification induce heavy plastic deformation, which results in that the laminated structure of pearlite is substituted by dispersive rounded-like cementites in the near-surface. The effect of HCPEB treatment can reach more than 500 m depth from the surface. The original crystalline structure is changed to a different degree that grows with the numbers of bombardment, and in the surface layer amorphous states and nanocrystaline structures consisting of grains of γ-phase and cementite are found. The violent stress induced by HCPEB irradiation is the origin of the nanostructured and amorphous structure formation.     

Microstructure and corrosion resistance of Fe-Al intermetallic coating on 45 steel synthesized by double glow plasma surface alloying technology

A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.     

1.7%C超高碳钢高频感应淬火工艺及组织特征

研究了含1.7%C超高碳钢高频感应淬火后的组织特征.试验表明,该钢经淬火与高温回火预处理后再进行高频感应淬火后的组织中存在大量的板条马氏体,且板条马氏体数量随感应循环次数的增加而增多,讨论了该钢感应加热淬火后的组织特征.     

Surface modification of die casting mold steel by a composite technique of hot-dipping and plasma electrolytic oxidation

The hot dipping process of pure aluminum on H13 steel substrates followed by plasma electrolytic oxidation（PEO） was studied to form alumina ceramic coatings for protective purpose.H13 steel bars were first dipped in pure aluminum melts,and then,a reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate.The reactive layer was mainly composed of intermetallic Fe-Al（Fe₂Al₅）;the thickness of aluminum layer and Fe-Al intermetallic layer were mainly influenced by dipping time（1.5～12.0 min） and dipping temperature（710～760 ℃）.After PEO process,uniform Al₂O₃ ceramic coatings were deposited on the surface of aluminized steel.The element distribution,phase composition and morphology of the aluminized layer,and the ceramic coatings were characterized by SEM/EDS and XRD.The distribution of hardness across the composite coating is demonstrated,and the maximum value reaches 1864 HV.The thermal shock resistance of the coated sample is also well improved.     

不同工艺下马氏体不锈钢组织演变及其对表面光洁度和耐蚀性的影响

通过金相、SEM和TEM观察,表面粗糙度测试和电化学实验方法,对经过不同温度淬火和回火的国产Cr13型马氏体不锈钢的微观组织演变及其对材料硬度,表面光洁度和耐蚀性能的影响进行了分析研究.结果表明,马氏体是基体中的主要相,当回火温度为650℃时,铁素体变成基体中的主要相,随着回火温度的提高,不锈钢基体组织发生了由回火马氏体到回火索氏体的演变.回火后,材料的硬度降低,当回火温度达到650℃,材料硬度降至22 HRC,其表面光洁度大幅度降低.同时,回火材料的耐点蚀性能低于淬火态材料,且随着回火温度的提高,马氏体不锈钢的点蚀电位降低,并在500℃时达到最差.     

热处理工艺对新型系泊链钢组织与耐蚀性能的影响

采用920℃水冷淬火后再经560～650℃保温3 h的回火工艺,研究了不同回火工艺对新型系泊链钢组织、耐蚀性能的影响。结果表明,该新型系泊链钢随回火温度从560℃升高到650℃,碳化物析出类型由低温的M3C型向高温的M7C3和M23C6型转变;形态由低温细小棒状和片状逐渐向高温颗粒较大椭圆状和球状转变;耐蚀性能逐渐变好,应力腐蚀敏感性也逐渐减小。耐蚀性能的变化主要是由回火组织中相界、晶界及碳化物的数量和形态的变化所引起的。     

强流脉冲电子束表面改性AZ31镁合金的耐磨耐蚀性能

选用强流脉冲电子束对AZ31镁合金进行表面改性处理,分析了改性后的AZ31镁合金表面显微结构,测量处理前后AZ31镁合金的耐磨性能和耐蚀性能。结果表明,脉冲电子束处理后AZ31合金表面出现了典型的熔坑形貌,同时熔坑周围有应力波作用产生的褶痕。由电子束快速凝固作用所产生的表层晶粒细化和固溶强化显著提高了AZ31合金的耐磨性。此外,电子束表面改性导致表层镁、铝元素含量及分布形式发生变化。样品表层铝元素的升高是改善其腐蚀性能的主要原因。     

Effect of nitrogen on microstructure and corrosion resistance of Cr15 super martensitic stainless steel

ABSTRACT

To investigate the influence of nitrogen on structure and corrosion resistance of Cr15 super martensitic stainless steels (SMSS), two types (N-free and N-0.12%) of specimens were quenched at 1050°C and tempered at different temperatures, and then, optical microscope, transmission electron microscopy, X-ray diffraction, potentiodynamic polarisation, immersion experiments and Kelvin Probe Force Microscope were used to characterize its microstructures and corrosion properties. The experimental results show that the microstructure in the N-free Cr15 super martensitic stainless steel is a biphasic tissue with alternating martensite and austenite distribution while quenched at 1050°C and tempered between 600 and 700°C. The nitrogen addition increases the content of austenite, and changes the austenite morphology significantly into the coarse block and strip distribution. What’s more, micro-galvanic corrosion is formed between austenite and martensite, which deteriorates the corrosion resistance of the SMSS.     

热处理对钼铜奥氏体不锈钢组织和耐腐蚀磨损性能的影响

研究了热处理工艺(不同固溶温度和固溶时间)对钼铜奥氏体不锈钢析出物含量和形态的影响,以及在不同固溶温度下材料的耐腐蚀磨损性能.试验结果表明,钼铜奥氏体不锈钢析出物随固溶温度的升高和固溶时间的延长而增多,其形态也由针棒网状长成块状;在纯磨损环境下,1100 ℃×8 h空冷下的奥氏体不锈钢析出物数量最多,耐磨损性能最好;而在有酸的腐蚀磨损环境介质中,950 ℃×8 h空冷的热处理工艺下的材料耐腐蚀磨损性能最佳.     

Characterization of blasted austenitic stainless steel and its corrosion resistance

It is known that the corrosion resistance of stainless steel is deteriorated by blasting, but the reason for this deterioration is not clear. A blasted austenitic stainless steel plate (JIS-SUS304) has been characterized with comparison to the scraped and non-blasted specimens. The surface roughness of the blasted specimen is larger than that of materials finished with #180 paper. A martensite phase is formed in the surface layer of both blasted and scraped specimens. Compressive residual stress is generated in the blasted specimen and the maximum residual stress is formed at 50–100 μm from the surface. The corrosion potentials of the blasted specimen and subsequently solution treated specimen are lower than that of the non-blasted specimen. The passivation current densities of the blasted specimens are higher those of the non-blasted specimen. The blasted specimen and the subsequently solution treated specimen exhibit rust in 5% sodium chloride (NaCl) solution, while the non-blasted specimen and ground specimen do not rust in the solution. It is concluded that the deterioration of corrosion resistance of austenitic stainless steel through blasting is caused by the roughed morphology of the surface.     

H13热作模具钢微弧氧化复合陶瓷层的组织和性能

通过热浸镀铝/微弧氧化复合工艺对H13模具钢进行表面改性以提高模具表面质量。在热浸镀铝过程中,将H13钢基体浸入710℃纯铝液6 min,得到了以Fe2Al5为主中间合金层,使得镀层与基体紧密结合。经过微弧氧化处理后,镀铝试样表面铝层转化为氧化铝陶瓷,主要由α-Al2O3和γ-Al2O3相组成。用带有能谱分析装置(EDX)的扫描电镜(SEM)、X射线衍射(XRD)分析了膜层的形貌、成分和相组成。微弧氧化陶瓷层主要由Al、O、Si元素组成,其中O、Si主要来源于硅酸盐电解液。     

FCAW repair welding cycles,HAZ microstructure and corrosion resistance of 2304 duplex stainless steel

Flux-cored arc welding (FCAW) is an automatic welding process widely employed to join duplex stainless steel (DSS) structures in industrial plants because of its high productivity. However, when multiple passes are performed, this process can lead to the formation of non-metallic inclusions originating from the slag in the fusion zone. In this case, the welded joint can be repaired using the same welding process. Some regions next to the heat-affected zone are not removed during the repairing operation. Thus, these regions are subjected to repeated welding cycles and to a high heat input, which can cause microstructural alteration that impairs the corrosion resistance of the welded material. The aim of this work was to study the corrosion resistance of 2304 DSS plates joined using the FCAW process and repaired using the same process. The influence of the repair procedure on the corrosion resistance of the welded joints was evaluated using potentiodynamic polarisation and chronoamperometric curves, which allow the determination of the critical pitting temperature of the samples. The microstructure obtained after each repair cycle was evaluated using optical microscopy and scanning electron microscopy. The results showed that the corrosion resistance was depressed as the number of repair cycles increased.     

Influence of heat treatments on microstructure and pitting corrosion resistance of 15%Cr supermartensitic stainless steel

Supermartensitic is a new class of stainless steels in development and consolidation as commercial products. Significant changes on chemical composition of conventional martensitic stainless steels, such as the reduction of the carbon content to <0·03 wt-%, and the addition of Ni and Mo, marked the development of this new group of alloys. New grades containing higher amounts of Cr and small additions of Ti and/or Nb were developed recently. As a result, supermartensitic steels offer an interesting combination of high strength, toughness, weldability and corrosion resistance. In this work, the pitting corrosion resistance of a 15Cr supermartensitic steel with Ni, Mo and Cu additions was studied. It is well known that the mechanical properties and corrosion resistance of martensitic steels are adjusted by the final tempering treatment. Several single tempering treatments in the 300–650°C range and double tempering treatments were performed in order to obtain different microstructures. The pitting corrosion resistance was investigated by electrochemical test in 3·5%NaCl solution. It was found that the pitting potential slightly decreased with the increase in temperature and time of tempering. The analysis of pits formed during the corrosion tests showed that ferrite islands are more corrosion resistant than the martensitic matrix due to the higher Cr and Mo contents.     

Effect of diffusion on coating microstructure and oxidation resistance of aluminizing steel

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热处理中高铬钢激光熔凝层的组织转变

采用激光熔凝处理方法对高铬钢进行表面强化,然后在300～650℃区间回火处理,利用SEM、XRD和TEM等手段分析热处理对激光熔凝层组织的影响.结果表明,高铬钢激光熔凝处理后,得到的奥氏体组织中合金元素固溶度较高且晶粒细小,具有较高的回火稳定性.激光熔凝层450℃回火后硬度开始升高,560℃时达到最大值(672 HV0.2),回火温度高达650℃时硬度迅速降低.450℃回火后细小M23C6碳化物优先从过饱和奥氏体中析出,同时少量马氏体的生成使熔凝层硬度略有增加.560 ℃回火后由于M,C,和M23C6碳化物的析出、大量高硬度马氏体的生成以及位错强化的共同作用使硬度达到峰值,同时,马氏体组织中有少量的M,C渗碳体析出.650℃回火后基体完全转变为铁索体,析出大量层片状M3C渗碳体,硬度显著降低.     

气压对904L奥氏体不锈钢低温离子渗氮组织与耐蚀性能的影响

通过辉光离子低温渗氮对904L超级奥氏体不锈钢(904Lss)进行表面改性处理,采用扫描电镜、X射线衍射仪(XRD)、电化学方法等研究了渗氮后试样的表面形貌、显微组织结构、硬度以及耐蚀性能。结果表明:100 Pa渗氮后的试样形成了强化相γN相,大大提高了904L不锈钢试样的表面硬度,高达1400 HV0.1;150 Pa渗氮后的试样产生了强氮化物CrN,其耐蚀性远远低于原始904L奥氏体不锈钢。     

GD钢组织及低温冲击韧性研究

分析了900℃淬火及200℃回火后GD钢的显微组织、硬度及低温冲击的断口形貌,研究结果表明:900℃淬火后GD钢组织由粗针状马氏体、残余奥氏体、碳化物组成,200℃回火时,马氏体中析出部分碳化物,回火组织由回火马氏体和碳化物组成。900℃淬火+200℃回火后的GD钢冲击时,随着温度的降低,其冲击功随之减小,随着GD钢所处的环境温度不断升高,断口宏观形貌中反映起裂区和裂纹纤维扩展区所占比例越来越大,微观形貌中存在解理面、撕裂棱和韧窝,其断裂机理为准解理断裂。     

The microstructure and properties of 17-4PH martensitic precipitation hardening stainless steel modified by plasma nitrocarburizing

17-4PH martensitic precipitation hardening stainless steel was plasma nitrocarburized at 430 °C and 460 °C for 8 h. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that the microstructure of plasma nitrocarburized layer is characterized by a compound layer with no evident diffusion zone. The phases in the 430 °C treated layer are mainly of γ′-Fe₄N, nitrogen and carbon expanded martensite (α′_N), and some incipient CrN phases. When the temperature increases up to 460 °C, there is no evidence of α′_N phase. The processes of bulk precipitation hardening and surface treatment by plasma nitrocarburizing can be successfully combined in a single-step process on this steel. The hardness of modified layer can reach up to 1186HV, which is 3 times higher than that of untreated steel. The wear and corrosion resistance of the specimens can be apparently improved by plasma nitrocarburizing. The 460 °C/8 h treated specimen has the best wear and corrosion resistance in the present test conditions.