Oxidation in wire HVOF-sprayed steel

It is widely held that most oxidation in thermally sprayed coatings occurs on the surface of the droplet after it has flattened. Evidence in this paper suggests that, for the conditions studied here, oxidation of the top surface of flattened droplets is not the dominant oxidation mechanism. In this study, a mild steel wire (AISI 1025) was sprayed using a high-velocity oxy-fuel (HVOF) torch onto copper and aluminum substrates. Ion milling and Auger spectroscopy were used to examine the distribution of oxides within individual splats. Conventional metallographic analysis was also used to study oxide distributions within coatings that were sprayed under the same conditions. An analytical model for oxidation of the exposed surface of a splat is presented. Based on literature data, the model assumes that diffusion of iron through a solid FeO layer is the rate limiting factor in forming the oxide on the top surface of a splat. An FeO layer only a few nanometers thick is predicted to form on the splat surface as it cools. However, experimental evidence shows that the oxide layers are typically 100× thicker than the predicted value. These thick oxide layers are not always observed on the top surface of a splat. Indeed, in some instances the oxide layer is on the bottom, and the metal is on the top. The observed oxide distributions are more consistently explained if most of the oxide forms before the droplets impact the substrate.     

GJW50钢结硬质合金螺纹钢丝轧辊的研制

介绍了一种用锻造态的 GJW5 0钢结硬质合金制作的螺纹钢丝轧辊 ,对其进行热处理强化 ,其使用价值明显高于合金钢和硬质合金的轧辊     

高速线材轧机生产冷镦钢盘条实践

介绍了以ML35为代表的冷镦钢高速线材的技术特点，以及闭环冷却控温生产ML35的技术要点，并分析了此种产品生产过程中的质量情况，并对存在问题提出了改进措施。     

拉丝过程中温升对高碳钢丝扭转性能的影响

设计了一系列的模拟试验,研究了拉丝过程中温升对高碳钢丝扭转性能的影响,确定了钢丝扭转性能恶化的临界回火温度为140℃。三维原子探针分析结果表明:渗碳体中的碳原子在回火过程中发生溶解且在铁素体中局部偏聚,聚集的碳原子对位错运动起到了钉扎作用,降低了铁素体的塑性,这是钢丝扭转性能下降的根本原因。     

Hierarchical structures in cold-drawn pearlitic steel wire

The microstructure and crystallography of drawn pearlitic steel wires have been quantified by a number of electron microscopy techniques including scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and nanobeam diffraction, with focus on the change in the structure and crystallography when a randomly oriented cementite structure in a patented wire during wire drawing is transformed into a lamellar structure parallel to the drawing axis. Changes in the interlamellar spacing and in the misorientation angle along and across the ferrite lamellae show significant through-diameter variations in wires drawn to large strains ? 1.5. The structural evolution is hierarchical as the structural variations have their cause in a different macroscopic orientation of the cementite in the initial (patented) structure with respect to the wire axis. The through-diameter variations subdivide the lamellar structure into two distinctly different types: one (called A_A) has a smaller interlamellar spacing and smaller dislocation density than the other (called A_BC). During drawing, the thickness of the ferrite and cementite lamellae are reduced to 20 and 2 nm, respectively, and high-angle boundaries form in the A_BC structure parallel to the cementite lamellae. The structural and crystallographic analyses suggest that boundary strengthening and dislocation strengthening are important mechanisms in the cold-drawn wire. However, differences in structural parameters between the A_A and the A_BC structure may affect the relative contributions of the two mechanisms to the total flow stress.