Industry information

What should I do if the hardness is insufficient or hard?

2021-08-21
What should I do if the hardness is insufficient or hard?
Mold heat treatment hardness is a very important mechanical performance indicator, and hardness is unqualified is a very serious defect. After the thermal treatment of the mold, the hardness is insufficient or hardness, which will reduce the mold wear resistance and fatigue strength, causing the mold to fail to fail, and severely reduce the life of the mold.
 
1. Cause
(1) The mold is large, the steel is quenching, such as a large-scale steel type with low hardenability.
(2) Due to the primary tissue of mold steel, severe segregation or coarse tissue, graphite and carbide segregation in steel, aggregation.
(3) The mold forging process is incorrect, and no good spheroidization annealing after the forging, making the mold steel ballochemical tissue.
(4) Decarbonation produced during the surface of the mold does not except for net annealing or quenching heating.
(5) The mold quenching temperature is too high, and the residual amount of the residual amount is too much; or the quenching temperature is too low, the heating and holding time is insufficient, so that the phase change of the mold steel is not complete.
(6) The mold is quenched after heating, the cooling speed is too slow, the grading and the isothermal temperature are too high or too long, and the quenching cooling medium is selected.
(7) Too little alkali is too small, or excessive impurities in the quenching cooling medium, or the aging of the quench cooling medium.
(8) The temperature is too high when the mold quenching is low, and the temperature is too high and the cooling is insufficient.
(9) The temper is insufficient and the tempering temperature is too high.

2. Countermeasures
(1) Correctly use mold steel, large molds should be used high alloy mold steel with high hardenability.
(2) Strengthen the examination of raw materials to ensure that the raw materials meet the standards. Reasonable forging of poor raw materials steel, and performs a spheroidal annealing to ensure a good organization. Carbon tool steel is not easy to anneae multiple times to prevent graphitization.
(3) Strictly implement the forging process and the spherical annealing process to ensure a good preparatory heat treatment tissue.
(4) Before the heat treatment, the rust and oxidation of the mold should be thoroughly removed, and the protection is heated when heated, and the salt bath should be carried out when heated is heated.
(5) Correctly formulate the mold quenching heating process parameters to ensure that the phase change is sufficient to quickly cool at a cooling rate greater than the critical cooling speed to obtain a qualified metallographic tissue.
(6) Correctly select the quenching cooling medium and cooling method, strictly control the grading and isothermal temperature and time.
(7) To strictly control the amount of alkali bath, the quench cooling medium for long-term use is often filtered and regularly replaced, and is kept clean, and its quench cooling characteristic curve is regularly detected.
(8) Time to immerse the quench cooling medium is appropriately extended to prevent the temperature of the hardening medium from being immersed in the quench cooling medium.
(9) After the mold is quenched, it should be fully tempered and prevent the tempering temperature from being too high.
(10) For molds with high hardness requirements, deep cold treatment (such as -110 to -196 ° C) can be used.
(11) Surface strengthening treatment.