Modified DHTT Equipment for Crystallization Studies of Mold Slags
- PDF / 1,736,341 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 39 Downloads / 184 Views
THE crystallization behavior of mold slags plays an important role in the continuous casting of liquid steel. The mold powder is added to the top of the liquid steel in the mold and is liquefied. The slag is subsequently trapped in the gap between the strand and the watercooled copper mold and solidifies. A glassy layer appears and is in contact with the mold, and a liquid slag layer is in contact with the strand. In between these layers, a crystallized layer with various crystals is formed. The sizes, shapes, and quantities of these crystals vary depending on the mold slag itself and other conditions such as the temperature gradient of the slag film or the position within the layer. To investigate the crystallization behavior of mold slags at near-service conditions, the double hot thermocouple technique (DHTT) was developed. In this technique, the liquid slag is stretched between two platinum wires that are heated to different temperatures.[1,2] The equipment
NATHALIE K¨OLBL, HARALD HARMUTH and IRMTRAUD MARSCHALL are with the Chair of Ceramics, Montanuniversitaet Leoben, Peter Tunner Straße 5, 8700, Leoben, Austria. Contact e-mail: [email protected] Manuscript submitted May 8, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
consists of the experimental unit, the hot thermocouple drivers, and a video capture system. The experimental unit is a housing chamber for the wires, or it can act as a vacuum chamber.[3,4] Other devices, include a supplemental heater, located in the chamber at the bottom[1,2] or surrounding the sample to reduce heat loss from the sample surface into the ambient environment (Figure 1(a)). Two heating wires made from type-B thermocouples welded without a bead are situated close to the heater. The hot thermocouple driver enables simultaneous measurement of the temperature, while the thermocouple is heated. For this purpose, the electric current is rectified into a half-wave using a silicon-controlled rectifier. One half-period is used in the heating cycle, and only 1/3 of the following period is used in the temperature measurement to reduce the sampling noise.[1,2] In certain cases, the equipment includes an air-cooling device to support the high cooling rates of the sample for isothermal experiments (see below).[4,5] The crystallization behavior can be investigated via 3 different experimental procedures.[6] For isothermal experiments, the sample is liquefied between the thermocouples and quenched to the desired temperatures to investigate crystallization. Subsequently, the images are evaluated to create time–temperature–transformation (TTT) diagrams for defined crystallinities. For the continuous cooling experiments, the sample is cooled between both thermocouples with defined cooling rates
Fig. 1—Schematic illustration of the DHTT set up according to (a) the literature[9] and to (b) the newly developed equipment with (c) the related stretching devices: (1) U-shaped B-type thermocouple, (2) slag film, (3) additional heater, (4) ceramic rod of the stretching device, (5) furnace chambe
Data Loading...
