Heat Treatment of Screws
Heat treatment of screws is a process that improves the strength, ductility, wear resistance and service life of screws. It is the process of changing the physical and chemical properties of screws through the heating and cooling process. Heat treatment of screws can be divided into two categories: surface hardening and bulk hardening. In this article, we will discuss the detailed process of heat treatment for screws.
Surface Hardening:
Surface hardening is a heat treatment method that increases the surface hardness of the screws without changing its core properties. It is usually done to deliver improved wear resistance and longer service life. In surface hardening, temperatures that range from 600 to 1200 ℃ (1100 to 2200 °F) are used. This process is suitable for small parts with complex shapes.
There are several types of surface hardening methods for screws, such as carburizing, induction hardening and flame hardening. Carburizing is a form of surface hardening in which the screws are heated to a high temperature and then cooled. The inner layer of the screws is heated to its austenitizing temperature and then immersed in a carburizing atmosphere containing carbon. This causes the carbon to diffuse into the surface layers of the screws and harden the surface.
Induction hardening is the process in which temperatures between 800 and 1300 ℃ (1470 to 2370 °F) are used. This process is generally suitable for large screws with simple shapes. In this case, induction coils are used to produce heat that is continuously distributed over the surface of the screws. The parts of the screws that are heated by induction hardening will become harder and stronger due to the formation of martensite.
Flame hardening is a process in which intense heat is produced by a flame and directed onto the screws. The temperature of the flame is usually between 500 and 1000 ℃ (930 and 1830 °F). This process is suitable for screws with complex shapes. The intense heat that is produced by the flame results in a surface that is harder and more wear-resistant than the core of the screw.
Bulk Hardening:
Bulk hardening is a heat treatment method that is used to harden and strengthen the entire screws. In this method, the screws are heated to a temperature between 750 and 900 °C (1380 and 1650 °F) and then cooled at a controlled rate. This process is suitable for large and small screws.
The purpose of this heat treatment method is to convert austenite into martensite and other forms of hard micro-structure. Martensite is a type of micro-structure that has superior mechanical properties such as high hardness, wear resistance and strength. There are two types of bulk hardening methods, namely tempering and austempering.
Tempering is a type of bulk hardening process in which the metal is heated to a temperature below its transformation point and then cooled to room temperature. Temper is a form of hardening that is used to raise the ductility and toughness of the metal. Austempering is a bulk hardening process in which the metal is heated to a temperature slightly above its transformation point and is then cooled in a salt bath. This process is used to improve the strength and wear resistance of the metal.
Heat treatment of screws is a complex process that requires close attention to detail. The type of heat treatment that is the most suitable for screws depends on the size of the screws, their shape, and the desired properties. Surface hardening methods such as carburizing, induction hardening and flame hardening are suitable for screws with complex shapes, while bulk hardening methods such as tempering and austempering are suitable for large and small screws.
