Heat treatment process for cold-drawn round bars
I. Introduction. Cold-drawn round steel is a kind of steel made by cold-drawn process, which has the characteristics of high strength, high hardness and excellent wear resistance, and is widely used in machinery, construction, automobile and other fields. Heat treatment is an important part of the processing process of cold-drawn round steel, which can improve the mechanical properties, processing properties and corrosion resistance of steel. This article will introduce the heat treatment process of cold-drawn round steel in detail.
Second, the heat treatment process.
1.Pre-heat treatment.
Pre-heat treatment is the first step of heat treatment, the purpose of which is to eliminate the internal stress of the steel, improve the plasticity and toughness of the steel, and prevent cracking or deformation during high temperature treatment. The temperature of preheat treatment is generally 30 -50 below the AC1 point, which varies according to the type and thickness of the steel. Pre-heating can be carried out by means of furnace heating or electric induction heating.
2.Heating.
Heating is one of the key aspects of heat treatment, the purpose of which is to make the steel reach the desired austenitization temperature and hold it for a certain period of time to make the steel fully austenitized. Heating temperature and time are important factors affecting the effect of heat treatment. The choice of heating temperature is determined according to the type of steel and the purpose of heat treatment, generally higher than AC3 point to obtain a complete austenitic structure. The heating time is determined according to the thickness of the steel and the heating temperature to ensure that the steel is fully austenitized.
3.Cooling.
Cooling is another key part of heat treatment, the purpose of which is to improve the properties of the steel by controlling the cooling rate to obtain the desired metallographic structure. There are many cooling methods, such as air cooling, water cooling, oil cooling, etc. Depending on the type of steel and the purpose of heat treatment, it is important to choose the right cooling method. For cold-drawn round steel, air cooling or slow cooling is generally used to avoid excessive internal stress, resulting in deformation or cracking of the steel.
4.Tempering treatment.
Tempering treatment is the last step of heat treatment, the purpose of which is to eliminate internal stress, stabilize the structure, and improve the mechanical properties and corrosion resistance of steel. The temperature of tempering treatment is generally 30 -50 below the AC1 point, and the time is determined according to the thickness of the steel and the tempering temperature. The tempering treatment can be carried out by means of furnace heating or electric induction heating. In the tempering process, it is necessary to pay attention to controlling the temperature and time to avoid over-burning or tempering brittleness.
3. Process parameter selection.
The selection of heat treatment process parameters directly affects the effect and quality of heat treatment. In actual production, it is necessary to select appropriate process parameters according to specific production conditions and requirements. For cold-drawn round steel, it is necessary to comprehensively consider the type, size, shape, use and other factors of steel, and choose the appropriate temperature and time for preheating, heating, cooling and tempering treatment. At the same time, attention should also be paid to controlling the speed and uniformity in the heating and cooling process to ensure the performance and quality of the steel.
Fourth, quality control and testing.
Quality control and testing of heat treatment is an important means to ensure the performance and quality of steel. In actual production, strict quality control and testing should be carried out on all aspects of heat treatment. For example, the temperature and time of preheating, heating, cooling and tempering are precisely controlled and recorded; The properties of the steel should be tested, such as hardness, tensile strength, impact toughness, etc.; It is also necessary to observe and analyze the structure of the steel, such as metallographic structure, grain size, etc. Through these quality control and testing methods, the problems in the heat treatment process can be found and solved in time to ensure that the performance and quality of the steel meet the requirements.