The working face of the firebrick formwork is large, and it is subjected to the extrusion, scraping and grinding of the hard refractory particles on the 200t press machine, so its service condition is relatively bad. Therefore, the working face of the die is required to have high hardness, high wear resistance, enough strength and appropriate toughness. In foreign countries, high alloy cold work die steel is used to make the template. After heat treatment, the surface hardness is high and the wear resistance is good, but the brittleness is large, and the mold is easy to crack during installation, and the cost is high. Many domestic refractory materials factories have tried high chromium cast iron, high carbon chromium molybdenum wear-resisting alloy and hard alloy, or carbon steel molds for boronizing surface strengthening, or carburizing and boron nitriding combined treatment, but the life is still ordinary, the template wear is the most serious, early failure. In general, each set of die about 2000~4000 pieces of refractory bricks will fail.
There are various forms of template failure. In addition to the failure caused by improper operation and installation, the following types of failure are common.
(1) The service surface of the formwork is worn evenly. When the forming part of the lower part of the formwork is worn greatly, the size of the brick is out of line, or the brick is demoulded difficult, the formwork will fail. This failure is normal failure.
(2) the lower part of the formwork, the plate surface wear is not synchronized, resulting in the surface of different sizes, different shapes of pits. When the brick is demoulded, it is obstructed, and the surface of the brick is cracked after demoulding. This kind of failure is more common.
(3) the surface of the template first forms pits, and then pits continue to expand along the length of the plate under the scraping action of hard particles and grind out one or more grooves of different depths and widths, resulting in the scrap of the template. This failure form is also more common.
Cause of template failure
The finished template is cut laterally by wire cutting machine and made into specimen for metallographic analysis and hardness test.
The failure reasons of steel formwork mainly include the following aspects.
(1) the template carburizing layer is shallow, and the carbon concentration is not high. The depth of the carburizing layer and the carbon content of the surface layer were measured by metallographic method after the samples were annealed with high temperature anti-oxidation decarburizing coating. The depth of infiltration layer is only 1.4 ~ 2.0mm. The microscopic observation shows that the surface carbon content is not high, only a few discontinuous secondary cementite networks appear in the most surface of the template, and the surface carbon content is estimated to be about 0.8% ~ 0.9%. Template permeability layer is shallow, the depth of hardened layer is shallow after quenching. Because the surface carbon concentration is not high, there is no secondary carbide in the quenching state, so the wear resistance of the template will not be too high.
(2) the template carburizing layer is shallow, the transition zone is narrow, and the inner layer is low in hardness. The hardness test showed that the hardness from the surface to the core of the template decreased rapidly, and the hardness gradient was very large. The hardness of some parts 1.5mm away from the surface had dropped to HRC30 below. Once the surface is worn, the wear resistance of the formwork will decrease sharply.
(3) the hardness of the template everywhere is very uneven, there are many soft spots. The hardness of the high hardness area is HRC62, and the hardness of the soft spot area is HRC35. High hardness area wear resistance is good, not easy to wear, and soft point area wear resistance is poor, easy to wear and sag, that is, everywhere wear out of sync causes the template premature pits.
These are the main reasons for premature template failure. This is caused by improper selection of formwork materials and some problems in heat treatment process.
Our company has a mature technical solution on the wear-resistant coating of firebrick molds, which has been verified by many customers. By adopting the process of heat treatment and spraying tungsten carbide, the service life of the molds can be increased by more than 3 times. Generally, each set of molds can press about 10000~20000 pieces of firebrick.