Mold manufacturing process - heat treatment of parts

(1)what is the heat treatment?

Heat treatment refers to a metal thermal processing technology that changes the chemical composition and structure of the surface or interior of a material by heating, heat preservation and cooling in a solid state to obtain the desired properties. Heat treatment generally includes three processes: heating, heat preservation and cooling, and sometimes only two processes: heating and cooling.

(2)what is the type of heat treatment?

• Quenching

It is a heat treatment method that heats iron to a red-hot state of 800℃~850℃, leaves it for a while, and then puts it into water or oil for rapid cooling. It is written as HQ in the JIS symbol table. After implementing this process, the steel will become very hard. However, there is also a problem of becoming brittle. For this reason, "tempering" is required after quenching. In addition, when cooling during quenching, due to the expansion and contraction of the organizational structure, the parts may crack and deform, so you need to pay attention. In addition, because the parts will become very hard during quenching, quenching is usually performed after cutting and other processing is completed, near the last process.

• Tempering

This is a process in which a quenched part is heated and cooled again. It is represented by the JIS symbol HT. During tempering, the hardness of the part will be slightly reduced, but the brittleness will be eliminated, and hardness and toughness can be obtained at the same time. Tempering can also be used to remove the internal stress (stress inside the part due to uneven shrinkage, etc.) generated during rapid cooling. Tempering is divided into low-temperature tempering and high-temperature tempering. Low-temperature tempering is to keep the temperature at 150℃~200℃ for one hour and then air cool. On the other hand, high-temperature tempering is to heat to 550℃~650℃, keep it for about an hour, and then cool it rapidly.

• Annealing

Annealing is the opposite of quenching and is used to soften steel to make it easier to process or to soften the structure that has been hardened by processing. It is to homogenize the structure inside the part by heating and to spheroidize the sharp structure. There are several types of annealing. Depending on the type of annealing and the structure of the steel, the required temperature range is around 550℃ to about 950℃. In all cases, the heating and heat preservation are carried out for one hour, and then the steel is slowly cooled in the furnace.

• Normalizing

Normalizing is mainly to make the uneven iron structure produced in the manufacturing stage of steel materials uniform and adjust it to a state suitable for subsequent machining and stamping. It is marked as HNR in the JIS symbol table. It heats the iron to about 800℃~900℃ and then air cools it.

(3)When do parts need heat treatment?

• reduce the difficulty of processing
• improve the comprehensive performance of parts (especially mechanical properties)
• improve the impact resistance of parts (wear resistance and hardness)
• a large number of welding on important components