Heat Treatment Basic Knowledge of Metal Casting

Heat treatment is very meaningful for metal casting design engineers and mechanical engineers, and heat treatment is a very high value method used to improve the quality of metal materials. Heat treatment can change or influence the organization and the nature of cast iron, and can get higher strength, hardness, and improve the wear resistance and so on.

According to different purposes, there are many types of heat treatment. The basic principal can be divided into two categories.

The first category, the organizational structure will not change by heat treatment or should not be changed.

The second category, the basic organizational structure will be changed by heat treatment.

The first heat treatment process is mainly for the elimination of internal stress. The internal stress is caused in the casting process because of different cooling conditions, and the organization, strength and other mechanical properties will not change significantly due to this heat treatment. For the second heat treatment, the basic organization has an obvious change and this kind of heat treatment can be broadly classified into five categories:

1. softening annealing: The main purpose is the decomposition of carbide, the hardness will be reduced, while improving processing performance, and for ductile iron, its purpose is to get more ferrite.

2. normalizing: The main objective is to obtain pearlite and ferrite. Normalizing can eliminate the cast organization of cast steel, and enhance its strength and toughness.

3. quenching: the main objective is to obtain higher hardness or abrasion strength, and obtain the high wear characteristics.

4. surface hardening treatment: the main objective is to enhance the surface hardness and higher surface wear characteristics.

5. precipitation hardening: The main purpose is to obtain high strength, while the elongation are not been drastic changed.

Casting parts have general mechanical properties, and moreover, have the wear and corrosion resistance, shock-absorbing, and other comprehensive performance. You can not get these performance from other metal forming methods such as forging, rolling, welding, punching, etc. So, casting methods are widely used in the machine manufacturing industry. Metal castings are the largest demand for many areas.

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