280～320HBS
Soft plastic filler-free (1) During mold heat treatment, special attention should  be put on protecting the cavity surface to
prevent surface oxidation, corrosion, decarburization or carbon. If the surface carbon content is too
high ,it will cause an increase in retained austenite, it is difficult or impossible to finish. Quenching
should be used more moderate and the cooling medium, so as to avoid deformation and quenching crack.
It is necessary to use delaying cooling quenching or heat-bath quenching or air-cooled.  
(2) Easy cutting pre-hardened steel can avoid quenching and deformation; Martensite aging steel or
high-quality low-alloy aging steel can control the deformation rate less than 0.05%; between roughing
and finishing or before precise finishing using removing stress treatment, can remove residual stress
caused by manufacturing deformation; using reasonable heat treatment process, the die steel is in stable
organization to avoid the distortion caused by tissue changes; using low coefficient of thermal expansion
steel can reduce the deformation caused by thermal expansion and contraction.  
(3) die should be fully tempered, tempering temperature should be higher than the working
temperature, so as tempering changes not to continue  at work, and thus occur stress on the surface of
cavity.
(1) The requirements of the carburized layer  
After Molds made in the type of steel are carburized ,their surface has high wear resistance and heart
ministry  maintain high strength and toughness, so as to avoid the early wear and brittle fracture.  
Carburized layer thickness: when mold is used to pressing hard plastic parts , the thickness of
carburized layer is 1.3～1.5mm;when suppress soft plastic parts, the thickness of carburized layer is
0.8～1.2nnn; mold with sharp corners, and thin edges, taking diffusion layer 0.2～0.6mm.  
Carburized layer chemical composition: Itis appropriate that carbon content in carburized layer is of
0.7%～1.0%, too high carbon content  would increase the amount of residual austenite, deteriorate
polishing performance. If mold are carbonitriding, their surface abrasion resistance,oxidation resistance,
corrosion resistance and anti-adhesion are better than a single Carburized layer.  
Infiltration layer: should avoide coarse undissolved carbide, carbide network, such as excessive
retained austenite.  
(2)Carburizing process: It is appropriate to adopt the classification of carburizing process, that is ,the
temperature at 900～920℃ is used to rapid carburizing,while moderate temperature(820～840℃) is used
to increase the carburization thickness mainlly.  
Carburizing temperature: generally at 900～920℃, a small complex cavity mold preferred temperature
is at 840～860℃ for carbonitriding permeation.  
Holding time: Selection carburizing holding time according to the requirements of the infiltration layer
thickness. Holding time is different that access the  same thickness of diffusion layer for carburizing
different ways,such as solid Carburizing and gas carburizing.  
(3)Quenching process after carburizing  according to different type of steel,after carburizing different
processes are used: re-heating and quenching;direct quenching after carburizing grade (such as
carburizing alloy steel);after the medium temperature carbonitriding directly quenching (such as industrial
pure iron or small precision and cold formed molds with low carbon steel);carburizing quenching
followed by air cooling (such as high alloy steel carburizing mold with large and medium-sized).  
References
[1]Feng Xiao Zeng, Heshi Yu, Guo Baolian. Failure Analysis of Die. Beijing: Mechanical Industry
Press, 1987  
[2]Shimei Tang. The heat treatment performance of common tool steel. Shanghai: Shanghai Science 塑料模具材料选择英文文献和中文翻译(5):http://www.youerw.com/fanyi/lunwen_17557.html