Steel Teeming Ladle and its Refractory Lining Nov08

Steel Teeming Ladle and its Refractory Lining...

Steel Teeming Ladle and its Refractory Lining Steel teeming ladle (STL) is needed in a steel plant to contain and transport liquid steel from the steel making furnace to the casting facility. These days STL is used in a significantly more complex manner than the older steel melting shops where ladles were used simply to transport liquid steel from a steel making furnace to the ingot moulds. Other functions carried out in the STL are temperature control, deoxidation, additions of carburizer and ferro-alloys and inclusion floatation. In the recent past, the demand for various grades of steel with stringent specifications has increased considerably. These steels are produced using secondary refining processes. The lining of the STL must withstand increasingly severe service conditions associated with the secondary refining processes. These severe conditions are longer holding time, higher liquid temperature and arc/chemical heating. Rinsing with inert gas and degassing of the liquid steel, alloying and use of synthetic slag also accelerate the wear of lining. Because of these activities the demand on the quality of STL refractories has increased very much. In present day steel melting shops STL functions as traveling components of skimming, rinsing, reheating, and degassing processes. The exposure time for a given heat in these shops has expanded from two to five times of the time earlier needed for ingot teeming. STL is also required to conserve heat by minimizing heat loss during transport and during the various process steps. In this regard, significant developments have been made to properly preheat ladles prior to the first heat, and to cycle ladles on subsequent heats in a manner to minimize heat losses. STL is designed to be heat resistant and strong. Also it is necessary to heat insulate the ladle. Proper heat insulation is...

Pickling of scale formed on hot rolled strip of carbon steel Apr23

Pickling of scale formed on hot rolled strip of carbon steel...

Pickling of scale formed on hot rolled strip of carbon steel During the hot rolling or heat treatment of steel, oxygen from the atmosphere reacts with the surface iron to form a crust that is made up of oxides of iron. This crust is known as scale and need to be removed before steel is further processed in cold rolling mill. Non removal of scale will have the following detrimental effects. Scale not only give bad appearance to the product but also accelerate corrosion During cold rolling of the strip scale patches affects the reduction with the possibility of the skidding of rolls. Effective scale removal is essential for the success of not only for cold rolling but also of subsequent annealing and coating operations. During cold rolling and annealing the scale will produce a dirty surface and cause the rusting of the strip During coating of the strip, presence of scale causes poor to total adhesion failure. Fig 1 shows hot rolled strip surface as well as pickled surface.   Fig 1 hot rolled surface and pickled surface Scale and its origin The normal scale found on hot rolled strip is blue/grey in colour and covers the entire strip surface. This scale is generated during rolling in the last stands of the finishing mill, across the run out table (ROT) and during cooling of the coil. It is composed of three well defined layers of iron oxides. Adjacent to the steel is the thickest layer consisting of wustite having an approximate composition of FeO. The intermediate layer consists of magnetite (Fe3O4) while the outermost layer is hematite (Fe2O3). The thickness of these layers will depend on the temperature of the strip at the exit of the finishing mill, temperature of the coiling and...