Precision casting manufacturers how to conduct heat treatment process casting hardware

1. The quenching equipment is high pressure and high flow direct air quenching furnace.

(1) before quenching: use the heat balance method to ensure the consistency of heating and cooling of the moving mold.The thin-walled holes, grooves and cavities that affect this point should be filled and sealed to ensure that the mold can be heated and cooled evenly.Together, pay attention to the furnace method, to avoid casting metal in high temperature due to weight caused by the deformation.

(2) the mould heating: the heating in the process of slowly heating (with 200 ℃ / h temperature), and choose two levels of preheating method, to avoid a rapid increase in the mould of internal and external temperature difference is too big, cause excessive thermal stress, reduce the phase transformation stress together.

(3) quenching temperature and holding time: the lower limit of quenching heating temperature should be selected. The soaking time should not be too short or too long. Generally, the soaking time is determined by the wall thickness and hardness.

(4) quenching and cooling: choose the pre-cooling method, and through the dispatch of air pressure and wind speed, the useful control of the cooling speed, so that the maximum limit of the ideal cooling.Namely: precooling to 850 ℃, the increase cooling speed, fast through the nose "C" curve, die temperature under 500 ℃ cooling rate of decline gradually, to the Ms point changes below, choose the approximate isothermal cooling method, with maximum limit reduce quenching deformation.Mould cooled to about 150 ℃, shut off the cooling fan, make natural cooling mould.

2. Annealing includes the spheroidizing annealing after casting and the stress relief annealing during the mold manufacturing process.Its main intention: to improve the crystallization arrangement in the raw material stage;Easy to process and reduce the hardness;To avoid post-processing deformation and quenching crack and remove the internal stress.

(1) spheroidizing annealing.Die steel after casting, the internal arrangement of steel into unstable crystallization, high hardness difficult to cut, and this kind of steel, the internal stress is large, after processing a brief deformation and quenching, poor mechanical properties, in order to make the carbide crystallization into spheroidizing stable arrangement must be spheroidized annealing.

(2) stress relief annealing.Machining die steel with residual stress will lead to deformation after machining. Assuming that there is still stress after machining, there will be a great deformation or quenching crack during quenching.In order to avoid these problems, it is necessary to conduct stress relief annealing.

Three times of stress relief annealing are generally carried out in the mold manufacturing process:

(1) when cutting away more than 1/3 of the volume of raw materials or deep processing 1/2 of the thickness of raw materials, the processing allowance is left at 5 ~ 10mm and the first stress relief annealing is carried out.

(2) the second stress relief annealing is carried out when there is a margin (2 ~ 5mm) left in the finishing.

(3) after the mold test, the quenching line for the third stress relief annealing.

3, the mold cooling quenching tempering to about 100 ℃, the tempering shall promptly, in order to avoid deformation of sustained attack, and even cracking.Tempering temperature determined by the hardness of the operation, generally three times tempering.

4, nitriding treatment general casting mold after quenching, tempering (45 ~ 47HRC) can be used, but in order to travel the mold wear resistance, corrosion resistance and oxidation resistance, to avoid sticky mold, extending the life of the mold, it is necessary to carry out nitriding treatment.The depth of nitride layer is generally 0.15 ~ 0.2mm.After nitriding, polish is required to remove the bright white layer (about 0.01mm thick).

5. Several clarifications

(1) the heat treatment deformation of precision casting molds is caused by the combined action of phase change stress and thermal stress and is affected by a variety of factors.Therefore, under the premise of the correct selection of materials, but also pay attention to the blank casting, to choose the six-sided casting method, repeated upsetting.Together, in the design stage of the mold is necessary to pay attention to, make the wall thickness as uniform as possible (when the wall thickness is not uniform to open the process hole);For the disordered shape of the mold, to choose the Mosaic structure, rather than all the structure;For the die with thin wall and sharp Angle, we should choose the fillet transition and increase the fillet radius.In the heat treatment to make data records, the length, width, thickness of the upward deformation, heat treatment conditions (furnace loading method, heating temperature, cooling speed, hardness, etc.), for the future heat treatment of mold piling record.

(2) generally there are two kinds of process flow in the processing of casting mold, which are determined according to the actual situation.First kind: general casting die.Forging, spheroidizing annealing, rough machining, first stress relief annealing (with a margin of 5 ~ 10mm), rough machining, second stress relief annealing (with a margin of 2 ~ 5mm), finishing, third stress relief annealing (after mold test and before quenching), quenching, tempering, clamping and nitriding.The second kind: especially messy and quenching very easy to deformation of the mold.Forging, spheroidizing annealing, rough machining, first stress relief annealing (with a residual amount of 5 ~ 10mm), quenching, tempering, mechanical and electrical processing, second stress relief annealing (with a residual amount of 2 ~ 5mm), mechanical and electrical processing, third stress relief annealing (after mold test), clamping and nitriding.