Quality Control for Tungsten Carbide Drawing Dies
The quality of raw WC is very important for the service life of tungsten carbide drawing dies. The total carbon content of carbide drawing dies is 6.12%~6.18% in Italy, Sweden and Germany, actually this range is very small .However, in our country, the range is comparative big as 5.85%~6.10%.Everybody know that we have to eliminate eta phase and graphite by control the total carbon fluctuating value in very small range, so as to improve the wear-resistance and achieve high-speed drawing requirement. No matter what tools we would use the tungsten carbide for, the total carbon control is very important, it is life line, however there are also a lot factors to influence it such as raw powders, mixture preparation, material storage, sinter etc.
The grain-size of raw carbide powders and porosity of tungsten carbide play very important role to influence the carbide drawing dies mechanical performance. The ultrafine grain tungsten carbide is used to make drawing dies due to the high-speed drawing requirement. The grain-size is divided into four levels .The ultrafine grain size at 0.2~0.5um,fine grain size 0.5~1.3um,middle size at 1.3~2.5um,and coarse size at 2.5~6.0um.The grain-size of carbide drawing dies from Italy is 1.0~1.2um ,it is 0.5~1.5um or 1.5~2.5um in Japan, but it is 1.2~1.6um in domestic. The finer of the raw WC powder ,the fuller of carbonization and the more saturated carbon but less content of W2C,it greatly influence the tungsten carbide performance .Now the finest raw WC powder is 0.4um in domestic with distribution ununiformly ,but Japan has produced the good quality raw WC powder with grain size as 0.2um.
The porosity control in tungsten carbide by foreign manufactures is very strictly including graphite inclusion which is below 0.1%,however our level for the porosity is 0.2% ,if include the graphite inclusion is 0.5%.On the other hand ,foreign manufacturers also take HIP process on the products to reduce porosity badly and improve the carbide drawing dies’ wear-resistance and transverse rupture strength ,especially for drawing thick wires ,it is capable to afford stable T.R.S and make the high-speed drawing more reliable.
