Third Shape Casting Symposium

The various microstructures of cast irons are reviewed, including carbidic and graphite forms (flake, compacted, spheroidal, and undercooled, etc.), exploring whether the presence of externally introduced defects in the form of oxide double films (bifilms) in suspension in melts seem to provide, for the first time, a uniform explanation for all the structures and their properties. Silica-rich oxide bifilms provide the substrates on which oxysulfide particles form, nucleating graphite. The presence of the film provides the favored substrate over which graphite grows, which leads to the development of flake graphite. The addition of limited Mg to form compacted graphite destroys all but a remnant of the silica-rich bifilms. The oxide film remnant is stabilized by the presence of the graphite nucleus, which causes the graphite to grow unidirectionally in a filamentary form. The addition of excess Mg destroys all traces of the oxide bifilms, leaving only the original nuclei, around which graphite is now free to entirely enclose, initiating the spherical growth mode. Undercooled graphite is the true coupled growth form, nucleated at even lower temperatures in the absence of favorable film substrates in suspension; the graphite adopts a continuous growth mode in a matrix of austenite. Carbides in mottled and white irons form on the oxide bifilms that often lie along grain and interdendritic boundaries, which explains the apparent brittleness of these strong, hard phases. In most cases of nonspheroidal growth modes (flake and misshaped spheroids), it is proposed that the impairment of the mechanical properties of irons is not strongly determined by graphite morphology but by the presence of oxide bifilms. Spheroidal graphite iron has the potential for high properties because of the absence of bifilms.     

Foreword: International Symposium on the Stress Corrosion Cracking in Structural Materials at Ambient Temperatures

Stress corrosion cracking of the high-strength martensitic steel AISI 4340 (yield stress = 1503 MPa) in NaCl aqueous solutions of different concentrations was studied experimentally using compact tension specimens in free corroding conditions. The experiments were conducted under the controls of constant load, constant crack opening displacement (COD), constant loading rate, and constant COD rate. Despite the differences in controlling conditions, the experiments yielded similar results for the threshold stress intensity factor and the plateau velocity in the 3.5 wt pct NaCl solution. Dependence of the plateau velocity on the NaCl concentration was observed, whereas the values of the threshold stress intensity factors seem to be independent of the NaCl concentration in distilled water.     

Surface Oxide Film Entrainment Mechanisms in Shape Casting Running Systems

During the transient phase of filling a casting running system, surface turbulence can cause the entrainment of oxide films into the bulk liquid. Research has shown that these are detrimental to the material’s integrity. Common mechanisms for this entrainment include returning waves, arising during filling of the runner bar, and plunging jets, found when pouring into a basin. One of these, the returning wave, has been studied in greater depth, using real-time X-ray and process modeling techniques alongside the application of physical principals. It has been concluded that when developed, returning waves cannot attain the more stable and less entraining tranquil flow regime desirable in the running system of castings.     

影响铸轧铝板板形的因素及控制方法

研究了铸轧辊型、磨削正弦角、铸辊冷却水对铸板板形的影响机理和相应的控制方法,通过控制达到改善铸板横向板形、纵向板形的目的。     

薄板坯连铸连轧技术在我国大有可为

薄板坯连铸轧技术是新工艺开发与成熟工艺集成的产物。文中分析了薄板坯连铸连轧技术的优势和弱点及发挥优势的途径，认为在我国薄板坯连铸轧技术大有发展途径。     

近终形连铸用浸入式水口模具设计

由于近终形连铸用浸入式水口形状特异,为了提高生产水平,降低生产成本,设计了组合模具。组合模具由外形模具、内孔模具和密封模具组成,外形模具采用了内外双层胶模,内层胶模设计为双分式,成型后制品外形加工余量约为10%;内孔采用金属组合模具,配合紧密,脱模顺利,可重复使用。组合模具为浸入式水口的批量生产奠定了基础。     

近终形连铸在不锈钢生产中的应用

目前全世界已投产、在建和计划建设的薄板坯连铸生产设备达５２套，其中主要用于或一部分用于生产不锈钢的设备有６套。     

Near-Net Shape Continuous Casting of Aluminum Alloy Billet Using Electromagnetic Field

The present study investigates on the continuous casting of near-net shape aluminum billet using electromagnetic casting and stirring technology.Traditional machine for continuous casting process involves round,square and rectangular billets;therefore it requires additional multistep forging process to fabricate final products.A new process for the designed free-shaped billets offers some advantages:the process of extrusion and forging is simplified and the cost of plastic working can be greatly reduced.In order to reduce the peculiar problems such as surface crack and internal defect due to inhomogeneous heat transfer through solidified billets,electromagnetic casting and stirring technique were adopted.Through the numerical computer simulation,we have calculated the slit design of the free-shaped mold.The free-shaped aluminum billet was continuously cast at the various casting speed and coil current of about 1,200A.Breakout velocity and melt pool depth were measured.Surface and microstructure of the free-shape aluminum billet using EMC and EMS techniques were compared with those of the billet using the conventional DC casting.