Heat treatment is an indispensable process in the manufacture of 304 stainless steel tubes
1. Annealing of 304 stainless steel pipes
Annealing refers to the process of heating stainless steel pipe to a certain temperature, maintaining that temperature for a period of time, and then allowing it to slowly cool.
Annealing steel involves heating the material to a temperature where phase change or partial phase change occurs, followed by slow cooling after a period of holding the temperature.
The objective of annealing is to eliminate structural defects, improve the homogeneity of the composition and refine the grains, improving the mechanical properties of the steel and reducing residual stresses.
Simultaneously, it can reduce hardness, improve plasticity and toughness, and increase machinability.
Therefore, annealing not only rectifies and improves structural defects and internal stresses left by previous processes, but also prepares for subsequent operations.
Therefore, annealing is considered a semi-finished heat treatment, also known as heat pretreatment.
2. Standardization of 304 stainless steel pipes
Normalizing is a heat treatment method that involves heating steel above a critical temperature, transforming the steel entirely into a uniform austenite structure, and then allowing it to cool naturally in air.
This process eliminates the cementite network in hypoeutectoid steel, refines the grain structure and improves overall mechanical properties.
For parts with less stringent requirements, normalizing can be a more economical alternative to the annealing process.
3. Quenching of 304 stainless steel pipes
Quenching is a heat treatment method in which steel is heated above a critical temperature, held at that temperature for a period of time, and then quickly immersed in a quenching medium, causing a sudden drop in temperature.
This rapid cooling at a rate greater than the critical cooling rate results in a predominantly martensitic and unbalanced structure.
Quenching increases the strength and hardness of steel, although at the expense of its plasticity.
Commonly used quenching media include water, oil, brine, and saline solutions.
4. Quenching of 304 stainless steel pipes
Tempering involves reheating already quenched steel to a certain temperature and then cooling it using a specific method.
The objective is to eliminate internal stresses caused by quenching, reduce hardness and brittleness and achieve the desired mechanical properties.
Tempering is categorized into high, medium and low temperature tempering and is often used in conjunction with quenching and normalizing.
a) Quenching and tempering treatment:
The heat treatment process of high temperature tempering after quenching is known as quenching and tempering treatment.
High temperature tempering refers to tempering carried out between 500-650 ℃.
The quenching and tempering treatment substantially adjusts the properties of the steel, providing it with good strength, plasticity, toughness and general mechanical performance.
b) Aging treatment:
To avoid changes in the size and shape of precision tools or molds and stainless steel pipe components during long-term use, workpieces are often reheated to 100-150°C for 5-20 hours before machining. accuracy, after low temperature tempering (low temperature). quenching temperature 150-250℃).
This treatment, known as aging, is essential to stabilize the quality of precision parts.
Aging treatment of steel components under low temperature or dynamic loading conditions is especially important to eliminate residual stresses and stabilize the steel structure and dimensions.
