The quality of the ring die is related to the material and structural design, but the most important thing is to adopt a suitable heat treatment process to improve the mechanical properties of the ring die, improve its internal and external quality, and prolong the service life of the ring die. The heat treatment process of the ring die is different according to the material of the ring die.
1. Alloy structural steel. (20CrMnTi)
In most cases, the ring die is strengthened and surface carburized to enable it with high hardness, good wear resistance and toughness.
The following is one of the heat treatments:
The ring die is placed in a sealed carburizing furnace, heated to 900-950°C, and carburizing gas is introduced into the furnace.
The ring die undergoes a chemical reaction in the furnace to adsorb carbon atoms on the surface to form a carburized layer.
The thickness of the carburized layer of the ring die can be determined by the holding time of the ring die in the furnace according to the design requirements. For carburizing at 900-950 ℃, the thickness of the carburized layer increases by 0.2-0.3mm for each holding time for 1 hour.
After carburizing, the ring pellet die must be quenched. Generally, a quenching process is used. After the carburized ring die is slowly cooled, it is reheated to above the critical temperature, and then quenched after heat preservation. Due to the high requirements of the core of the ring die, the heating temperature of the first quenching should be slightly higher than the temperature of the core, about 850 ℃, in order to refine the grains of the core and avoid the appearance of ferrite. After die quenching, lath martensite is formed, which has high mechanical properties and has little effect on the carburized surface of the ring die.
In order to eliminate quenching stress, deformation and improve toughness, after quenching, a low temperature tempering treatment of 180-200 ° C is carried out. Therefore, the core area and carbon content of the ring die are low, the texture is soft, and it has high impact toughness and good fracture resistance. The carburized layer on the surface of the ring die has good wear resistance, but poor corrosion resistance.
2.The following is a research on the 4Cr13 material (X46Cr13 stainless steel )pellet die quenching and tempering heat treatment process curve.
The main process is as follows:
①Put the pellet die into the washing machine for continuous cleaning for 4 hours, the purpose is to remove the iron filings, rust and oil stains left by the machining of the ring die. After cleaning, take it out and dry it in a dryer.
②Put a group of ring dies on the grate, and separate the ring dies with a backing plate to prevent the ring dies from wearing each other during heating.
③ Strictly control the heating temperature, heating speed and holding time. First heat at 650°C and hold for 1h, then heat to 850°C for 1.2h, and then heat to 1050°C for oil quenching. After quenching, tempering is performed, and the tempering temperature is 220°C.
④ After heating to the quenching temperature, keep it warm, put it into the oil for quenching immediately after being released from the furnace, try to ensure the uniformity of the cooling speed inside and outside the ring die, and cool it to room temperature.
⑤Tempering is to eliminate the thermal stress generated inside the ring die after oil quenching, and tempering at 220℃ for 3h.
