When it comes to heat-resistant steel castings, we have to mention the heat treatment industry; when it comes to heat treatment, we have to talk about the three industrial fires, annealing, quenching, and tempering. So what are the differences between the three?
(One). Types of annealing
1. Complete annealing and isothermal annealing
Complete annealing is also called recrystallization annealing, generally referred to as annealing. This annealing is mainly used for castings, forgings and hot-rolled profiles of various carbon steels and alloy steels with hypoeutectoid compositions, and is sometimes used for welded structures. It is generally used as the final heat treatment of some unimportant workpieces, or as the pre-heat treatment of some workpieces.
2. spheroidizing annealing
Spheroidizing annealing is mainly used for hypereutectoid carbon steel and alloy tool steel (such as steel types used in manufacturing cutting tools, measuring tools, and molds). Its main purpose is to reduce hardness, improve machinability, and prepare for subsequent quenching.
3.Stress relief annealing
Stress relief annealing is also called low-temperature annealing (or high-temperature tempering). This kind of annealing is mainly used to eliminate residual stress in castings, forgings, welding parts, hot-rolled parts, cold-drawn parts, etc. If these stresses are not eliminated, it will cause the steel parts to deform or crack after a certain period of time or during subsequent cutting processes.
(Two). Quenching
The main methods used to improve hardness are heating, heat preservation, and rapid cooling. The most commonly used cooling media are brine, water and oil. The workpiece quenched in salt water is easy to obtain high hardness and smooth surface, and is not prone to soft spots that are not quenched, but it is easy to cause serious deformation of the workpiece and even cracking. The use of oil as the quenching medium is only suitable for quenching some alloy steels or small-sized carbon steel workpieces where the stability of supercooled austenite is relatively large.
(Three). Tempering
1. Reduce brittleness and eliminate or reduce internal stress. After quenching, steel parts will have great internal stress and brittleness. If they are not tempered in time, the steel parts will often deform or even crack.
2. Obtain the required mechanical properties of the workpiece. After quenching, the workpiece has high hardness and high brittleness. In order to meet the different performance requirements of various workpieces, the hardness can be adjusted through appropriate tempering, reducing the brittleness and obtaining the required toughness. Plasticity.
3． Stable workpiece size
4. For some alloy steels that are difficult to soften by annealing, high-temperature tempering is often used after quenching (or normalizing) to properly gather carbides in the steel and reduce the hardness to facilitate cutting.
Post time: Apr-10-2024