In the production of refractory castables, some fibrous products of different diameters are often added and the fiber is what we refer to as heat-resistant steel fiber which is made of stainless steel or heat-resistant steel containing alloying elements such as chromium nickel. Its manufacturing methods are divided into: steel wire cutting pressing method, steel block cutting method and molten steel melting method. The first two methods are stable in quality and high in strength, but the price is more expensive: the latter method is simple in process, strange in shape, strong in gripping force, low in cost, and has many producers, so it is widely used.
The shape of heat-resistant steel fiber is like a boat shaped saggar, its specifications are 0.2mm×1.0mm, the length is 20mm, 25mm, 30mm and 35mm: the grade of heat-resistant steel fiber, the international heat-resistant steel fiber grades are divided into 330, 310, 304, 446, and 430, etc., which is similar to the national standard (GB).
Experiments and production practice at home and abroad have proved that in any kind of refractory castable, refractory plastic and refractory ramming material, plus the mass of 1% to 5% of heat-resistant steel fiber, can achieve the effect of strengthening and toughening. However, the melting temperature and critical oxidation temperature of heat-resistant steel fiber are low and should not be used at high temperatures. Otherwise, due to the melting and oxidation of steel fibers, the organizational structure of refractory castables will be damaged or destroyed, resulting in a decline in the service life of furnaces or thermal equipment.
The main functions of adding steel fiber to refractory castable are :
(1) enhancing toughness, improving stress-strain resistance, and improving mechanical impact resistance;
(2) Improve thermal shock resistance, improve cracking and spalling resistance;
(3) Inhibit linear shrinkage after curing, drying and heat treatment.
The amount of steel fiber added is generally 0.6~2.5%(volume ratio) is the most appropriate.
Some customers emphasize that the amount of steel fiber refractory castable is between 3 and 5%, which is a wrong judgment. Why can't the amount of steel fiber in castable be too large? Because the addition of too much steel fiber will make the high temperature physical and chemical properties of refractory castable deteriorate, such as steel fiber will make the residual linear expansion of castable after high temperature burning. At the same time, the increase of iron oxide content in castable reduces its erosion resistance, and will affect the workability of castable during construction, so the selection of the amount of addition should be judged most appropriate according to the temperature of the kiln type.