Die heat treatment defect - Kunshan cold die steel
A quenching crack
The following reasons and preventive measures of cracks:
1, the shape effect, is the main design factors, such as the round R is too small, hole position is set properly, the transition section is not good.
2, overheating (burning), which is mainly caused by the temperature control is not accurate or running temperature, high temperature, temperature setting process and other factors, preventive measures including maintenance, checking temperature control system, temperature correction technology, in between the workpiece and the furnace floor mat iron.
3, decarbonization, mainly by overheating (or burning), air heating furnace without protection, machining allowance, caused by forging or pre heat treatment factors of residual decarburized layer, preventive measures for controllable atmosphere heating, bath heating, vacuum furnace, box type furnace adopts packing protection or use of anti oxidation coating; machining allowance increase from 2 to 3mm.
4, improper cooling, is mainly caused by improper selection of coolant or cold, should grasp the cooling characteristics of quenching mediums or tempering treatment.
5, mold steel bad organization, such as the serious segregation of carbide, the forging of poor quality, pre heat treatment method is improper, preventive measures is the use of the forging process of correct and reasonable preparatory heat treatment system.
Two, the lack of hardness
The following hardness is insufficient, causes and preventive measures:
By 1, or into the furnace cooling tank method due to improper maintenance check should be amended to process temperature, temperature control system, furnace, workpiece spacing reasonable placed evenly dispersed into the groove, prohibit accumulation or bundled into the slot cooling.
2, the quenching temperature is too high, which is caused by the process of setting temperature or improper temperature control system error, the amendment should be process temperature, temperature control system maintenance check.
3, this is tempered by tempering temperature is too high, temperature control system temperature is too high in error or fault caused by furnace, process temperature should be corrected, maintenance check is not higher than the set temperature control system, temperature load.
4, the reason is improper cooling, cooling time, cooling medium choice, quenching medium temperature and high cooling performance gradually decreased, stir the bad or out of the slot temperature too high, measures, etc.: released into the groove to quickly grasp; cooling characteristics of quenching medium; the temperature of 60~80 DEG C, the water temperature below 30 DEG C, when quenching due to the large cooling medium during heating, cooling or quenching medium should be added to other cooling tank for cooling and stirring; strengthen the coolant out at Ms+50 DEG C.
5, decarburization, which is caused by the residual raw materials or decarburization quenching, preventive measures for controllable atmosphere heating, bath heating, vacuum furnace, box type furnace adopts packing protection or use anti oxidation coating; machining allowance increased from 2 to 3mm.
In machinery manufacturing, quenching heat treatment deformation is absolute, not only is the relative deformation. In other words, only a deformation of the size of the problem. This is mainly due to martensite in the heat treatment process of transformation with surface relief effect. The prevention of heat treatment deformation (change in size and shape change) is a very difficult task, in many cases, have to rely on experience to solve. This is not only because the steel and die shape on heat treatment deformation effect, improper distribution of carbides and forging and heat treatment method also can cause or exacerbate, but also in the heat treatment of many conditions, as long as the change of a certain condition, the extent of the deformation of steel will have very big change. Despite a long time mainly depends on the experience and trial method to resolve the problem of deformation of heat treatment, but the correct relation of die steel forging, the module orientation, shape of the mould, heat treatment and heat treatment deformation, to grasp the heat treatment deformation from actual data has been accumulated in the establishment of data files about heat treatment deformation and a very meaningful job is.
Is due to decarburization of steels in heating or insulation, because of the atmosphere, the surface layer part of the carbon loss of all or part of the phenomenon and reaction. Steel decarburization will not only cause the lack of hardness, the quenching crack and deformation of heat treatment and chemical heat treatment defects, but also has a great influence on fatigue strength, wear resistance and mold performance.
Five, the crack caused by electrical discharge machining
In die manufacturing, electrical discharge machining (electric pulse and wire cutting processing method) is more and more commonly adopted, but with the wide application of electric discharge machining, the defect caused by a corresponding increase. The electrical discharge machining with high temperature is generated by the discharge and the processing method, thus forming the mold surface melting, EDM metamorphic layer of white on its surface, and produce about 800MPa tensile stress, so often appear in the process of deformation or crack defects in mold edm. Therefore, mold using electrical discharge machining, we must fully grasp the influence of EDM on die steel, and take appropriate preventive measures in advance. To prevent overheating during heat treatment and decarburization, and fully tempered to reduce or eliminate the residual stress; in order to fully eliminate the stress produced during the quenching and tempering to steel used, should therefore be able to withstand high temperature tempering (such as DC53, ASP - 23, high speed steel, processed to discharge conditions) stable discharge; after processing, for stabilization of relaxation treatment; set up process, reasonable hole groove; fully eliminate the resolidified layer for use in sound condition; using vector translation principle, the internal stress of the cutting part has concentrated sentinel cut through release of disperse drainage.
Six, lack of toughness
The reason may be the lack of toughness and high quenching temperature, heat preservation time caused by long grain coarsening caused, or due to not avoid tempering brittleness area.
Seven, grinding cracks
When the workpiece in the large amount of residual austenite, the grinding heat under the action of backfire change, resulting in tissue stress, resulting in cracking of workpiece. The preventive measures are: quenching after cryogenic treatment or repeated tempering (die tempering is generally 2 to 3 times, even low alloy tool steel for cold working), minimizing the amount of retained austenite.