In the work of engineering, die tool steel to withstand the relatively large impact, if the quality is not good die steel, in the use of the process, easy to break, broken situation, in order to solve this problem, many manufacturers will be made in die steel will be heat treatment, then die steel chemical heat treatment process is what?
Die steel heat treatment usually consists of four processes.
1, die steel reaction in the medium. Die tool steel reaction or evaporation of the components in the medium at a certain temperature, the formation of the active component of the infiltrating element.
2, infiltrant diffusion. The active component diffuses inward on the mold surface, and the reaction products leave the interface to diffuse outward.
3、Phase interface reaction. The active component collides with the mold surface, resulting in physical adsorption or die tool steel adsorption, incorporation or formation of compounds, and other products resolve away from the surface.
4, adsorbed and incorporated and infiltrated elements to the mold internal diffusion. When the concentration of infiltrating elements exceeds the solid solution degree of the base metal, the resulting diffusion, resulting in a new phase.
According to the physical state of the medium, die tool steel heat treatment process can be broadly divided into solid method, liquid method, gas method and glow ion method. Specific classification.
Solid method, powder method; coating infiltration method, paste method; melt infiltration method; electroplating electrophoresis or spraying + diffusion annealing; liquid method, hot dipping method; molten salt method, molten salt impregnation; molten salt electrolysis; electroplating electrophoresis or spraying + diffusion annealing; aqueous solution electrolytic heating; gas method, vacuum evaporation method; fluid particle method; gas or liquid compound decomposition, reduction or replacement.
The quality of the carburized layer of die steel has three requirements.
1, carburizing layer surface carbon concentration
Carburizing layer surface carbon concentration is usually required to be 0.80%~1.05%. At this time, the torsional force is the maximum, the requirement of wear resistance to choose the upper limit, the requirement of strong and a certain degree of wear resistance to take the lower limit.
The depth of the seepage layer depends on the working conditions of the mold and the strength of the heart. When the surface carbon content is the same, the layer depth increases can improve the bending strength, and the bending strength increases, the mold bending fatigue resistance is also improved, but too much to increase the depth of the carburizing mold surface compressive stress will decline, fatigue resistance is also reduced. In the carburizing mold surface quenching does not appear a large number of residual austenite and carbide, properly increase the depth of the carburizing layer, can improve the mold contact fatigue strength and multiple impact resistance, when the depth of the carburizing layer is equal to about 20% of the radius of the specimen section, the best multiple impact resistance.
3、Carburization layer carbon concentration gradient
Carburizing layer carbon concentration gradient reflects the indicator of carbon concentration along the carburizing layer down, the greater the gradient of carburizing layer concentration, the quenching of the carburizing layer in the transition zone residual tensile stress is also higher, often making the mold carburizing layer peel, the more gentle the carbon concentration down, the more firmly combined with the substrate, it can improve the mold bending strength and bending fatigue strength, for this reason, often specify the thickness of the co-precipitation layer plus the co-precipitation layer for the total depth of the carburizing layer 50%~75%.
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