After heat treatment, the steel parts are deformed under the combined action of thermal stress and structural stress. Only correct straightening can meet the design requirements of the process. According to the temperature difference of parts during straightening, it can be divided into cold straightening and hot straightening. In the straightening process of actual parts deformation, selective straightening should be carried out according to specific conditions.
(1) cold straightening
Cold straightening refers to the process of applying external force to the deformed parts after heat treatment at room temperature to correct the twisted and warped parts. Generally, there are the following processes.
(1) cold pressing straightening method. Put the convex part of the "C" shape deformation upward on the "V" shape iron, apply static pressure to the convex part with a manual press to make it produce appropriate reverse bending, and straighten the deformation after removing the static pressure. Mostly used for parts with hardness below 35HRC or non-ferrous metals;
(2) Cold knocking (knocking) straightening method. Its principle is the same as that of cold-pressing straightening, except that the way of applying external force is hammering;
(3) Cold knock (counterattack) straightening method. The concave part of the deformed part is continuously struck with a high-hardness hammer, so that a small area of plastic deformation occurs, and the concave surface is elongated, so that the deformation is corrected. It is mostly used for high hardness parts with hardness greater than 50HRC.
(2) Thermal straightening method
Thermal straightening refers to the process of straightening steel parts at a certain temperature.
① Hot-pressing straightening method. Local heating or overall heating at the highest protrusion. It should be noted that the heating temperature should be lower than the tempering temperature;
(2) Local drying thermal correction method. Slowly heating the convex part with oxygen-acetylene flame to transform quenched martensite into tempered martensite, and shrinking the convex part to correct deformation;
(3) the hot back (counterattack) correction method. Tap the deformed concave surface to make the concave surface produce plastic elongation;
④ Hot spot correction method. The convex part of deformed steel is heated by a small flame of oxyacetylene, then quenched, and the deformed part is straightened by thermal expansion and cold contraction.