The difference between normalization and annealing

How to obtain a fine wave body structure with excellent performance in the workpiece?

Annealing treatment will make the steel soft, and quenching treatment will make the steel hard. In comparison, if "normalization" treatment is performed, a layered wave iron structure can be obtained, which can effectively improve the cutting performance and wear resistance of the steel. It has the advantages of no cracks, less deformation and easy operation. However, normalization treatment is a relatively difficult heat treatment technology because it uses air cooling, which will be affected by many factors. For example, the cooling effect is different in summer and winter, the size of the workpiece has different air cooling rates, and even wind blowing Also affects cooling rate. Therefore, normalization requires the use of various methods to maintain uniformity, such as shading, screens, potholes, fans, etc.

The difference between normalization and annealing

Normalization treatment is a heat treatment process in which the steel is heated to 40~60°C above the a3 point or acm point for a period of time to turn the steel structure into a uniform Worthfield structure, and then cooled to room temperature in still air. For hypoeutectoid steel, it can achieve the purpose of grain refinement and have good strength and toughness; for hypereutectoid steel, it can prevent snow carbon iron from forming a network precipitation on the grain boundaries of Worthfield iron. , to reduce the toughness of the material.

The main purpose of complete annealing treatment is to soften the steel and improve the machinability of the steel. The heat treatment procedure is to heat to 20~30℃ above the a3 point (hypoeutectoid steel) or 30~50℃ above the a1 point and maintain the temperature for a period of time to form After the Vostian body structure is completed (or the Voss field body plus Schiff carbon body structure), the bollite transformation is fully carried out at 50°C below the a1 point, and a softened steel is obtained. In addition, stress relief annealing is heated at 450~650°C below the transformation point for a period of time and then slowly cooled to room temperature, which can eliminate the residual stress generated inside the steel during the cutting, stamping, casting, and welding processes.

How to eliminate residual stress in the workpiece?

Stress relief annealing is heated at 450~650°C below the transformation point for a period of time and then slowly cooled to room temperature, which can eliminate the residual stress generated inside the steel during the cutting, stamping, casting, and welding processes. For carbon steel, the reference heating temperature is 625±25℃; for alloy steel, the reference heating temperature is 700±25℃. The temperature holding time will also vary. For carbon steel, the holding time is 1 hour per 25mm thickness; for alloy steel, the holding time is 2 hours per 25mm thickness, and the cooling rate is 25mm or more. Cool it at a cooling rate below 275°C/hour.

How to prevent heating deformation?

To prevent the occurrence of heating deformation, it is best to heat slowly and implement preheating treatment. When selecting the preheating temperature for general steel, the preheating temperature can be selected according to the following criteria: (1) Use the temperature below the transformation point as the preheating temperature. For example, ordinary steel is about 650~700°C, and high-speed steel is 800~850°C. Around ℃. (2) Use approximately 500°C as the preheating temperature. (3) Two-stage preheating, first perform the first stage preheating at about 500°C, maintain it for a period of time to fully preheat, and then increase the preheating temperature to below the a1 transformation point. (4) Three-stage preheating. For large steels containing high alloy content, such as high-speed steel, sometimes a third stage of preheating is required at 1000~1050℃.