针对连铸过程中边角裂纹给产品质量控制带来的严峻考验,分析了边角裂纹产生的机理,介绍了传统的水冷控制解决方案,并指出其不足.在此基础上,介绍了一种最新的水冷技术--三维喷水宽度调整系统.该系统能根据实际生产情况,动态调整喷水宽度和喷嘴位置,使喷水控制策略更加灵活,包括故障保护系统和人机交互界面.并且,采用了模块化单元,具有较高的可靠性、易操作性和可维护性,能大大增加连铸机的灵活性,减少边角裂纹出现的几率,使产品达到较好的品质.

Medium-slab casting combines all of the benefits of conventional thick-slab casting and some of the benefits from thin-slab casting. The medium-slab caster incorporates the proven equipment design, operational aspects and automation features from conventional casting.

Most steel grades undergo a ductility trough in the temperature range 700 to 1100 degrees C that may bring about surface cracks in the CC strands.Micro-mechanical modelling of the as solidified austenite-ferrite microstructure, supported by experimental evaluations of the fracture surfaces, affords a comprehensive description of the crack formation mechanism. This opens the way for a quantitative evaluation of the sensitivity of CC strands to transverse cracks.

improved numerical simulation tools provide valuable information for equipment designers and operators of continuous casting plants. In comparison to the collection and evaluation of process data, simulation models based on physical principles are able to provide a more detailed understanding of how individual process parameters can influence the production process and final product quality. One major goal of the numerical modelling of metallurgical processes is to predict the material behaviour using a proper description of production processes and their correlation to product properties and quality. Thus, the amount of expensive experimental trials can be reduced in the process of development. Later for standard production a numerical quality assessment is appropriate to reduce inspection efforts. Utilising commercial and in house made simulation software, the continuous casting process is simulated regarding thermal, mechanical, and phase transformation aspects. In a practical example, metallographic observations of strand surface defects, such as transverse corner cracks, are correlated to material history during the production process. As a result, the initiation of material failure can be localised more precisely and countermeasures can be taken with a higher chance of success compared to models that use only linear combinations of steel analysis and process parameters. The applicability of these simulation tools for computer aided quality control (CAQC) systems is discussed.

The technological package SMART(R)/ASTC, developed by VAI and already applied in many continuous casting plants worldwide, combines automatic strand taper control (ASTC) with hydraulically adjustable SMART(R) segments. It allows to improve significantly the internal quality of both slabs and blooms. The principle and working mode of these equipments are described and their multiple benefits are presented.

The thermal behaviour of the continuous casting mould has a critical influence on strand surface quality, casting productivity and operating safety. voestalpine Stahl GmbH has long been interested in the field of research into mould behaviour, and began with the investigation of heat flux in 1995, and then of thermal variability in 1999. Since 2000, an online mould thermal monitoring system for heat flux density, thermal variability and friction has been installed. The heat flow density in the mould is determined by measuring the inflow and outflow temperatures and the throughflow volume of the primary cooling water. Temperature as measured by a thermocouple based breakout detection system in the mould copper plate is used to investigate the thermal variability. These online measured values have been employed to examine the influence of casting parameters, steel analysis and casting powder on the heat flux and thermal variability, and the relationship between these variables and cracking. The knowledge gained through these wide ranging plant based investigations has been used as a major tool in the diagnosis of problems ( such as breakout and sticking), for optimisation of the process, particularly in the field of casting powders, and for control of slab quality. In particular, this knowledge has been incorporated into online mould thermal monitoring.

The single strand slab caster CC5 of voestalpine Stahl Linz was put into operation in 1997. Its uncompromising modular designs both for hardware and software made it possible to integrate newly developed technological packages for a reasonable price. Two developments aiming for improved internal quality are subject of this article. A parabolically shaped narrow face with chamfered corners (Diaface) was developed to assure a homogenous shell growth in the mold. The positive influence on metallurgical quality was verified evaluating narrow face bulgin and internal crack formation close to the surface of slab samples. In parallel a significant reduction in the defect rate of heavy plates was recorded. Aiming for improved centerline quality all segments of CC5 were upgraded to Smart segments, which allow dynamic gap adjustment. The revamps of the individual segments were realized during regular segment maintenance. Using a dynamic process model (ASTC) the setpoints for the individual segments are calculated cyclically thus allowing the application of dynamic soft reduction. Quality improvements were shown in particular evaluating samples of sour gas resistant products.

This paper describes the first industrial application of the new DYNAFLEX oscillator developed by VAI on the two billet casting machines at Lech-Stahlwerke (Germany). Its main features are : no servohydraulic components, a system of leaf-springs arranged in cascade, simplicity of adjustment of stroke, frequency and wave form during casting. These factors suppress the need for maintenance of the oscillator, prevent mechanical backlash and result in a significant increase in machine availability and product quality, as well as in reduced maintenance costs.

In 1995, Rautaruukki decided to replace the three vertical casters at Raahe Steel by a new bow-type easter with a straight mould and with liquid core bending and straightening. As the new easter had to replace three individual CC machines, maximum flexibility with respect to the adjustment of all operational parameters, including the casting thickness, was one of the major design criteria. The engineering, supply and installation of the new CC machine was carried out by VAI.

Using a periodic microfield approach a micromechanical study is presented, which is capable to describe the ductility losses due to a film like ferrite precipitation in the high temperature region of iron based alloys by considering the two phase microstructure close to phase transformation temperatures and explicitly accounting for the elasto-plastic material properties of each present phase.For the temperature range close to the A(e3) temperature it will be demonstrated that the hot ductility behavior is directly correlated to the volume fraction of ferrite which develops along the austenitic grain boundary and the global strain rate of the specimen.

Measurements of roll loads with strain gauges implemented on roll girders were carried out on a thin slab easter. Numerical calculations and shop tests indicated the applicability of this measurement arrangement. It has to be considered under the specific aspect that, owing to the low design height of thin slab casters, the occurring loads are considerably smaller than in standard slab casters. The evaluation of the measurement data obtained during operation of the thin slab easter was done from two main viewpoints. First, it was of interest whether it is possible to measure the presence of a liquid core at a given distance from the meniscus. Second, the measurements were supposed to be used for verification of the liquid core position calculated on line by Dynacs(R), VAI's dynamic cooling model. Essential difficulties in evaluating the data originated from the changing thermal and mechanical loads. The slowly changing thermal loads that are superimposed on the mechanical loads make it impossible to determine the presence of a liquid pool simply by checking the strain gauge signal and comparing it with results collected during the shop tests. Mechanical load changes at relatively high frequencies occurred owing to varying roll forces even with minor eccentricities of the rolls. Thus, checking for critical values of the load changes also seems impractical. For on line prediction of the liquid core position, a combination of numerical estimation of the liquid core position with on line thermal tracking as an approximate approach and measurements for exact prediction seems to be the most promising strategy. An interesting alternative to this strategy could be the on line evaluation of fast Fourier transformed (FFT) strain gauge signals. IS/1344 (C) 1998 The Institute of Materials.

Dynacs(R), a package for dynamic secondary cooling in slab casters, was developed by Voest-Alpine Industrieanlagenbau (VAI). This package includes an online cooling control system and an off line simulation tool. The tailormade integration routine allows on line calculation of the temperature field within the strand of a slab easter with the cycle time of existing level 2 control systems. For the integration, actual process data are used to derive the initial and boundary conditions. The dynamic cooling system can be tuned to fit the needs of different steel grades using highly tunable cooling practices. In addition to previously established cooling practices, the newly developed 'surface temperature control' and 'bulging limiting control' are included. Cooling practices are defined and maintained using the cooling practice setup system. This setup system can also be used to simulate and evaluate the strand temperature and the zone water flowrates under all relevant cooling situations. Temperature measurements with optical pyrometers positioned in various locations in a easter have been performed to verify the integration and control algorithm. IS/1360 (C) 1998 The Institute of Materials.