1, the impact of heating rate
In general, the quenching heating, the heating rate is faster, the greater the thermal stress generated in the mold, easy to cause deformation of the mold cracking, especially for alloy steel and high alloy steel, because of its poor thermal conductivity, particular attention to preheating , For some complex shapes of high-alloy mold, but also need to take multiple preheating.
In some cases, however, the use of rapid heating can sometimes reduce the deformation, but only the surface of the mold is heated while the center is still in a "cold state", thereby reducing the tissue stress and the thermal stress, and the core deformation resistance , Thus reducing the quenching deformation, according to some factory experience, used to solve the hole pitch deformation has some effect.
2, the impact of heating temperature
Quenching the heating temperature of the material affects the level of hardenability, while the composition of austenite and grain size play a role.
(1) From the aspect of hardenability, the high heating temperature will increase the thermal stress, but at the same time make the hardenability increase, so the stress of the structure also increases and gradually dominates.For example, carbon tool steel T8, T10, T12, etc., quenching the general quenching temperature, the performance of the shrinkage of the internal diameter tend to, but if the quenching temperature to ≥ 850 ℃, then due to increased hardenability, the organizational stress gradually dominated, so the inner diameter may be expressed as Bloated tendency.
(2) From the view of austenite composition, the increase of quenching temperature increases the carbon content of austenite and the squareness of martensite increases (specific volume increases) after quenching, so that the volume increases after quenching.
(3) From the point of view of the impact of Ms, quenching temperature is high, the austenite grains coarse, will make the deformation deformation of the part tends to increase.
In summary, for all types of steel, especially some high-carbon medium and high alloy steel, the quenching temperature level will significantly affect the quenching deformation of the mold, so the correct choice of quenching temperature is very important.
In general, the choice of quenching temperature is not good on the deformation of the deformation is not affected in the premise of the use of performance, always use a lower heating temperature.But for some quenched more residual austenite steel (Such as Cr12MoV, etc.), but also by adjusting the heating temperature, change the amount of retained austenite to adjust the deformation of the mold.
3, quenching the impact of cooling rate
In general, increasing the cooling rate above the Ms point results in a significant increase in the thermal stress, resulting in an increase in the deformation due to thermal stress. Increasing the cooling rate below the Ms point tends to predominate the deformation caused by the stress in the tissue Big.
For different types of steel, due to the different levels of Ms, so when using the same quenching medium, there are different deformation trends. The same steel, such as the use of different quenching medium, because of their cooling capacity, and therefore have different deformation trends .
For example, carbon tool steel at the Ms point is relatively low, so the use of water-cooled, the impact of thermal stress often prevail; and when used by the cold, it may be the organizational stress the upper hand.
In actual production, the mold often use grading or grading - Isothermal quenching, usually not fully hardened, it is often the role of thermal stress, so that the cavity tends to shrink, but then the thermal stress is not great, So the total amount of deformation is relatively small.If the water-oil dual-liquid quenching or oil quenching, caused by greater thermal stress, cavity shrinkage will increase.
4, the impact of tempering temperature
Tempering temperature on the deformation, mainly due to the tempering process caused by tissue transformation.If the tempering process to produce 'secondary quenching' phenomenon, the residual austenite into martensite, the resulting horse The specific volume of the body than the large retained austenite will cause the mold cavity swell; for some high alloy tool steels such as Cr12MoV, etc., when the requirements of the red hardness of the main use of high-temperature quenching, multiple tempering, each A fire back, the volume to swollen once.
If tempering in other temperature range, due to quenching martensite to tempered martensite (or tempered sorbite, tempering troostite, etc.) change, the specific volume decreases, therefore, the cavity tends to shrink.
In addition, the tempering, the residual stress in the mold slack, the deformation is also affected.Module quenching, if the surface is in the state of tensile stress, the size will increase after tempering; the other hand, if the surface is in a state of compressive stress, contraction Of the two effects of organizational change and stress relaxation, the former is the main one.