The firebrick forming template has a large working face, which is subjected to the extrusion, scraping and grinding of refractory hard particles on the 200t press, and its service conditions are relatively bad. Therefore, the working surface of the die is required to have high hardness, high wear resistance, enough strength and appropriate toughness. Foreign use of high alloy cold work die steel template, heat treatment of high surface hardness, good wear resistance, but brittle, easy to crack when the mold installation, and high cost. Many domestic refractory material factories have tried high chromium cast iron, high carbon chromium molybdenum wear-resisting alloy and hard alloy, or on the carbon steel mold boronizing surface strengthening, or carburizing and boron nitrogen co-infiltration compound treatment, but the life is still general, the template by wear the most serious, failure earlier. Generally, each set of die is about 2000~4000 pieces of refractory bricks are invalid.
There are various forms of template failure. In addition to improper operation and installation, the following types of failure are more common.
(1) uniform wear everywhere on the service surface of the template. When the forming part of the lower part of the template is worn very much, the size of the brick is out of order, or it is difficult to demold the brick, and the template will fail. This failure is normal failure.
(2) the lower part of the template brick forming, the board surface wear is not synchronous, resulting in the surface of different sizes, different shapes of pits. Brick is blocked when demoulding, after demoulding brick surface appears corrugation, this kind of failure form is more common.
(3) the surface of the template formed pits, then pits in the scraping of hard particles along the length of the surface of the expansion and grinding out a or more depth and width of different grooves, resulting in the template scrapped, this failure form is also more common.
Cause of template Failure
The finished template is cut horizontally by wire cutting machine to make samples for metallographic analysis and hardness test.
The main reasons for the failure of steel formwork are as follows.
(1) The template carburizing layer is shallow, and the carbon concentration is not high. After annealed with high temperature anti-oxidation and decarburizing coating, the depth of carburizing layer was determined by metallographic method, and the carbon content of surface layer was estimated roughly. The depth of infiltration layer is only 1.4 ~ 2.0mm. Microscopic observation shows that the carbon content in the surface layer is not high, and only a small amount of discontinuous secondary cementite network appears in the surface layer of the template. It is estimated that the carbon content in the surface layer is about 0.8% ~ 0.9%. The layer of template infiltration is shallow, and the depth of hardened layer is also shallow after quenching. As the surface carbon concentration is not high, there is no secondary carbides in the quenched state, so the wear resistance of the template is not too high.
(2) the template carburizing layer is shallow, the transition zone is narrow, and the inner layer hardness is low. The hardness measurement shows that the hardness decreases rapidly from the surface to the center of the template, and the hardness gradient is very large. The hardness of some parts has dropped below HRC30 at 1.5mm from the surface. Once the surface layer is worn, the wear resistance of the template will be sharply reduced.
(3) The hardness of the template is very uneven, and there are many soft spots. The hardness of the high hardness area is up to HRC62, and the hardness of the soft point area is below HRC35. The area with high hardness wear resistance is better, not easy to wear, and the soft point area wear resistance is poor, easy to wear and sag, namely everywhere wear not synchronous cause template premature pit.
These are the main reasons for premature template failure. This is caused by improper selection of template materials and some problems in heat treatment process.
Our company has a mature technical scheme on the wear-resistant coating of firebrick mould, and has been verified by many customers. By using the process of heat treatment and spraying tungsten carbide, the service life of the mould can be increased by more than 3 times. Generally, each set of mould can press 10000~20000 firebricks.
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