Analysis of the Characteristics and Examples of Quenching Cracks and Non-Quenching Cracks
In the process of heat treatment of steel, the occurrence of cracks in the workpiece will affect the quality of the product. Quenching and non-quenching cracks are common in the process of heat treatment. In this article, the characteristics of quenching cracks and non-quenching cracks are analyzed, and examples are given for a comprehensive understanding.
1. Definition
Crack is a kind of form defect that affects the appearance and performance of the product, which is a common form of workpiece defect in heat treatment. Quenching cracks refer to cracking of workpieces due to physical deformation or thermal deformation caused by rapid cooling or heating in heat treatment. Non-quenching cracks refer to brittle fracture of workpieces due to metallurgical structural changes caused by rapid cooling or heating in heat treatment.
2. Characteristics
(1) Quench crack
The quenching process causes physical stress and thermal stress in the workpiece. If the cooling rate is too fast, the energy released by the physical and thermal stresses is not enough to transform the plastic change into elastic change in time, causing cracks or sub-cracks in the workpiece. Quenching cracks usually happen in the quenching process.
For example: In 50CrV4 steel, the martensite start temperature (Ms) is normally 648°C. When tempering the 50CrV4 steel in an oil bath at 800°C, the quenching cracks were observed at the surface of the steel material. It is believed that 2.6% of chromium solutions in ms steels reduce the austenite area, resulting in an increase of the Ms temperature and causing quenching cracks.
(2) Non-quench crack
In the heat treatment of steel, the non-quench process refers to the destruction of the workpiece at a certain temperature due to continuous heating and cooling for a certain time. Non-quench cracks are caused by the destruction of the structural balance of the workpiece, which is caused by the uneven molecular structure of the workpiece.
For example: In 1Cr13 steel, the non-quench process is performed by heating the steel to 670-690°C for about 8 minutes, then quenching it in oil at about 250-280°C for about 30 minutes, and then tempering it at about 350-400°C. In this case, non-quench cracks can be observed on the surface, which may be caused by the destruction of the structural balance of the workpiece due to improper heat treatment.
3. Examples
(1) Quench crack
Quench cracking occurs in the quenching process of steel workpieces. Such cracking is usually caused by rapid cooling or heating. For example, when quenching a steel shaft in oil and water, the quench cracking may be observed if there is a large temperature difference between hot heat and quenching medium. In this case, the risk of quench cracking can be reduced by controlling the temperature of the quenching medium.
(2) Non-quench crack
Non-quench cracks occur in the heat treatment of steel workpiece, which may be caused by improper heat treatment and is usually related to thermal fatigue. The stress caused by the repeated heating and cooling of the workpiece can cause non-quench cracking. For example, when a thin-walled steel pipe is treated, the heat treatment process should avoid temperature differences between different parts. Otherwise, the non-quench cracking of the steel pipe may occur due to thermal fatigue.
In summary, the characteristics and examples of quenching and non-quenching cracks are analyzed in this article, which can provide a reference for the understanding of quenching and non-quenching cracks. As long as the correct methods and methods are used in the process of heat treatment of workpieces, it can be avoided or reduced effectively to improve the quality of products.
