The die’s hardness
The tungsten carbide grade which our manufacturers generally take YG20C,Cr12MoV,Cr12 ,but the Japanese manufacturers take YG15 ,DC53 etc.The tungsten carbide materials that we take are higher in toughness but with lower hardness ,also the contrary for the Japanese ones. Thus the Japanese tungsten carbide cold forging dies is good in wear-resistance ,it is one of the reasons which its service life is longer than ours .For the high carbon steel dies ,its hardness with range 60~62HRC,meanwhile the hardness of sleeve is the same ,all under HRC42.
Interference
The cold forging dies under the same condition ,if the interference coefficient is small or big resulting in preload small or big .The die core of carbide cold forging dies made by domestic factories would be out of sleeve and lose function in working might due to too small interference or unpresioned processing size,however the Japanese manufacturers of carbide dies take the cold-pressing connection with taper shape between the core and sleeve ,its interference is only 0.85% which is low by comparing with Russian 1.3%~1.5%.
The Surface Quality
The tungsten carbide die cores made in the domestic are ground and polished poorly, on the contrary , the Japanese ones have very good quality ,its surface roughness between Ra0.32~Ra0.16um ,even Ra0.08um.The surface roughness of the carbide die cores take very significant influence on its service life, if the surface with very bad quality ,especially with existing of hollow, porosity and crack, they will be the initial point of the stress concentration and fracture .Thus the surface roughness in the inner hole of the tungsten carbide die core influence its service life more significantly .
