Do you know the types of annealing heat treatments for steel and their application ranges?

Everyone knows that the same material can obtain different organizational properties after different heat treatments to meet different needs. Today, this article will take the most commonly used steel for workpieces as an example to describe the types of heat treatment of steel and its application range.

Homogenization annealing. After the steel is homogenized and annealed, the composition is homogenized. The homogenized annealing of steel is mainly suitable for steel castings and forged and rolled parts with composition segregation.

Stress Relief Annealing. The purpose of stress relief annealing is to eliminate internal stress and bring it to a stable state. It is often used in the annealing of castings, welded parts, forged and machined parts.

Isothermal annealing. Isothermal annealing can refine the structure, reduce hardness and prevent white spots. Forgings and stampings of carbon steel, alloy steel and high alloy steel should be isothermal annealed. Compared with fully annealed steel, the structure and properties of steel are more uniform, and the process cycle is shortened.

Completely annealed. After the steel is completely annealed, its fine structure changes and its hardness decreases. This annealing method is suitable for hypoeutectoid steel forging, welding, and rolling.

Incomplete annealing. Incomplete annealing can refine the structure and reduce the hardness. Forged and rolled parts of medium and high carbon steel and low alloy steel are annealed using this annealing method.

Spheroidizing annealing. After the steel is spheroidized annealed, the carbon-like compounds spheroidize, the hardness is reduced, and the plasticity is improved. This annealing method is often used for eutectoid steel or hypereutectoid steel parts.

Carburizing (containing carbon and nitrogen) is generally used in situations where the core has a certain strength and good toughness and the surface requires high hardness (58~64HRC). It is also used to improve wear resistance and fatigue performance. It is mainly used for gears, For pin and shaft parts, carburizing increases the carbon content of the surface layer, improving surface hardness, wear resistance and fatigue resistance.

Carburized steel needs to be normalized in order to eliminate the network carbides in the carburized layer.

For high carbon steel and high alloy steel, in order to eliminate network carbides and prepare for spheroidizing annealing, the workpiece needs to be normalized and heat treated.

Normalizing low carbon steel can increase the hardness, improve processing performance, prevent "tool sticking" during machining, and reduce surface roughness values.

Parts with complex shapes and strict deformation requirements, including alloy steel and carbon steel parts with smaller sizes, larger parts or steel types with poor hardenability. In order to make the parts meet the requirements, graded quenching is often used to quench the workpiece first. Put it into the bath to make the temperature inside and outside the part reach the temperature of the bath medium, and then quench into another medium that cools more slowly to reduce deformation and cracking.

Medium and high carbon steel parts and large alloy steel parts often use dual-media quenching to ensure that the hardened layer of the workpiece meets the requirements, avoid quenching cracks, and reduce deformation.

Single-medium quenching is the most commonly used quenching method, which is to quench steel in a single cooling medium (such as oil, water, air, etc.) to achieve hardness, strength and other requirements.

Medium-temperature ultra-high-strength steel, springs, and hot forging dies are tempered at 350-500 degrees to obtain a troostite structure. The purpose is to obtain high elasticity and sufficient hardness to maintain a certain toughness.

Ultra-high strength steel, tool and die steel, measuring tools, cutting tools, and carburized parts are usually tempered at low temperatures between 150 and 250 degrees to obtain a tempered martensitic structure. The purpose is to improve plasticity and toughness while maintaining high hardness.

Structural steel parts and nitrided parts are tempered at high temperatures between 500 and 650 to obtain a sorbite structure, in order to achieve a good combination of higher strength and toughness.

This article briefly describes the types of heat treatment of steel and its application range. If you still have questions, you can call us for more information.