Application of the modified electrochemical potentiodynamic reactivation method to detect susceptibility to intergranular corrosion of a newly developed lean duplex stainless steel LDX2101

The present work aimed at defining optimal conditions using double loop electrochemical potentiokinetic reactivation (DL-EPR) method for evaluating intergranular corrosion (IGC) susceptibility of lean duplex stainless steel (LDX2101) aged at 700 °C between 3 min and 300 h. The results demonstrated that the modified DL-EPR measurement (solution of 33% H₂SO₄ + 0.1% HCl at 20 °C and scan rate of 2.5 mV/s) could successfully characterize the interactions between precipitation, chromium depletion and IGC of LDX2101 with high sensitivity and reproducibility. In addition, there was no indication of healing because the effect of formation of chromium-enriched precipitates was more dominative than that of redistribution of chromium in depleted zones.     

Effect of carbon nanotubes on corrosion of Mg-CNT composites

Carbon nanotubes (CNTs) may be added to Mg matrix to produce composites of better mechanical properties, but their effect on the corrosion behaviour is not well understood. The corrosion resistance of pure Mg and its composites reinforced with 0.3 and 1.3 wt.% CNTs was studied in 3.5 wt.% NaCl solution using immersion testing and electrochemical measurements. It was found that the corrosion rate was increased considerably by the presence of CNTs because of microgalvanic action between the cathodic CNTs and the anodic Mg matrix.     

Effect of ageing heat treatments on the microstructure and intergranular corrosion of powder metallurgy duplex stainless steels

The influence of ageing heat treatments (675 and 875 °C for 1.5 to 48 h) on the microstructure and intergranular corrosion resistance of sintered in nitrogen duplex stainless steels was investigated. The materials were obtained by sintering mixtures of austenitic AISI 316L and ferritic AISI 430L powders. Corrosion behaviour was evaluated by using electrochemical techniques. The beneficial effect of nitrogen on corrosion behaviour of solution annealed samples was established. During ageing, secondary phases were precipitated and the intergranular and transgranular corrosion resistance significantly decreased though repassivation was observed in specimens aged at 875 °C for times up to 8 h.     

基于L1/L2极限学习机的熔池熔透状态识别

针对电弧焊熔池变化过程中非线性因素导致的熔透状态识别准确率低的问题,利用极限学习机（ELM）网络框架,提出一种基于L1/L2范数约束的ELM熔透状态识别模型.通过高速视觉传感系统获取熔池图像,利用主成分分析来进行特征提取.采用结构简单、训练简便的ELM算法来训练熔透识别模型,并利用L1范数约束抑制ELM输出权重中的异常值以改善ELM算法的泛化能力,同时利用L2范数约束来平滑ELM输出权重以获取熔池图像中的团块特征,提高熔池熔透状态的识别准确率.结果表明,基于L1/L2-ELM的熔透状态识别模型能够快速有效地判别熔池的全熔透、未熔透、过熔透三种状态.     

VN复合渗层的制备及对45#耐磨性能的影响

目的对45~#强化处理,提高其强韧性和耐磨性。方法采用热反应扩散法(TRD)对45~#基体进行了3种不同的处理,分别为单渗钒、先渗氮后渗钒及先渗钒后渗氮处理。通过扫描电子显微镜、X射线衍射仪进行了微观形貌和物相组成的分析,采用维氏硬度计和旋转摩擦仪对渗层的硬度及耐磨性能进行分析。结果 TRD法处理后,在45~#表面形成一层均匀致密的渗层,其中单渗钒层的厚度为3.86μm,先渗氮后渗钒渗层(先渗氮层)厚度为6.02μm,先渗钒后渗氮渗层(先渗钒层)厚度为8.44μm。单渗钒层的硬度值在1306.6HV左右,而氮化钒渗层的硬度在1549.2~1710.4HV左右,均比处理前试样的硬度(295HV)有明显提高。单渗钒层是由α-Fe和VC相组成,而复合渗层是由VN、α-Fe、Fe_3N和Fe_2C相组成。渗层与基体之间的界面明显,且存在过渡层。单渗钒层试样的平均摩擦系数为0.22,先渗氮层的平均摩擦系数为0.18,先渗钒层的平均摩擦系数为0.20,均小于45~#基体的摩擦系数(为0.29)。结论 TRD法处理后形成的VC、VN渗层能提高钢基体的表面硬度和耐磨性,且钒元素和氮元素渗入的先后顺序对渗层的力学性能有影响。先渗氮层试样效果最佳,往复摩擦实验表明,试样的耐磨性顺序为:先渗氮层先渗钒层单渗钒层45~#基体。     

道次间冷却工艺对厚板芯部变形及组织的影响

利用道次间冷却技术对特厚钢板轧制开展道次间冷却工艺试验,研究轧制过程中的冷却参数对钢板变形渗透性和晶粒细化的影响规律。研究结果表明:道次间冷却工艺能够促进轧制变形向特厚钢板芯部渗透,在一定程度上消除了芯部带状组织;采用再结晶低温区连续轧制并在轧制道次间进行大强度冷却工艺,特厚钢板芯部组织晶粒明显细化,晶粒尺寸可达10~15μm;粗轧道次间的冷却工艺对轧制变形渗透的提高效果优于中间坯冷却工艺,并且道次间冷却强度的增大有助于进一步提高变形渗透性。     

类金刚石(DLC)膜对2Crl3不锈钢耐蚀性能的影响

采用失重法、极化曲线法和金相显微分析等方法研究了类金刚石(DLC)膜对2Cr13不锈钢耐蚀行为的影响.失重试验结果表明:DLC膜较薄时对2Crl3不锈钢在中性NaCI溶液中耐全面腐蚀的影响不明显,而膜较厚时能显著降低2Crl3不锈钢的腐蚀速度;失重试验和电化学试验均表明DLC膜降低了2Crl3不锈钢在酸性介质中的腐蚀速度;动电位扫描曲线和金相显微分析说明DLC膜明显改善了2Crl3不锈钢基体抗点蚀、晶间腐蚀等局部腐蚀的能力.     

一种新型金属材料的表面改性技术

阐述了通过铸渗法来改善金属零部件的表面性能的原理，主要是铸技术与冶金强化相结合，分析了影响渗层质量的几个主要因素如涂料配比，铸造工艺；铸渗合金成分及工艺可根据实际需要来设计，展望了铸渗法表面改性技术的应用前景。     

Influence of deep cryogenic treatment on the microstructure and properties of AISI304 austenitic stainless steel A-TIG weld

Appropriate deep cryogenic treatment can improve comprehensive mechanical properties of the AISI304 austenitic stainless steel activating flux tungsten inert gas (A-TIG) welds. The microstructure of the welds before and after deep cryogenic treatment was all austenite with a small amount of δ-ferrite. The vermiform ferrite + austenite distributed in the whole weld, but the lath-shaped ferrite + austenite mixed components only distributed in the centre of the weld. The phases in the two welds were all Cr–Ni–Fe–C and Fe–Ni solid solutions, ferric carbide (i.e. Fe₃C) and chromic carbides (i.e. Cr₂₃C₆ and Cr₇C₃). After deep cryogenic treatment, the grain size of the weld was decreased a certain of degree, and the carbide phase content was increased. The strength and micro-hardness of the weld joints were increased due to the grain refinement. The intergranular corrosion resistance of the weld was reduced because the precipitation of chromium carbides at the austenite grain boundary.