During annealing, how should we solve process problems when we encounter them?

The preservation time of stress-relieving annealed castings is lowered, and the icing progress is controlled at (20-50) ℃/h. Only when it is cooled to 300 ℃ or below can it be air-cooled. Due to the high heating intensity, long time and fine grain size of dispersed annealing, thorough annealing or normalizing is performed after dispersed annealing to re-refine the structure. Normal softening layer depth δ=(10~20)%D. The normalizing process is relatively complicated, which is conducive to the use of intermittent thermal normalizing for casting, which can save energy and shorten the production cycle. Normally, the furnace is fed into the furnace at high temperature, and then heated to a specified temperature at a heating rate of 100°C/h or above. The steel is heated to 20~30℃ above Ac1, kept fresh for a period of time, and then freezes rapidly, losing the structure of spherical or granular carbides evenly distributed on the ferrite matrix.

The heating measurement for thorough annealing is generally Ac3+ (30~50℃) for carbon steel; Ac3+ (500~70℃) for alloy steel; the preservation time depends on the type of steel, the size of the workpiece, the amount of furnace loading, and the equipment selected. Determined by various factors such as model number. 1. Equivalent annealing Equivalent annealing is to heat steel parts or blank parts to a level higher than Ac3 (or Ac1), and after maintaining it for an appropriate period of time, freeze quickly to a certain level in the pearlite measurement range and maintain it at the same level. An annealing process that transforms austenite into a pearlite structure and then freezes in the air. • Performance after induction surface quenching 1. Surface angle: The surface angle of workpieces surface quenched by high and medium frequency induction heating is often 2 to 3 parts (HRC) higher than that of ordinary quenching. is the effective diameter of the workpiece. • Varieties of annealing process 1. Uniform annealing (dispersion annealing) Uniform annealing is to reduce the chemical segregation and structural irregularity of non-metal ingots, castings or forgings, by heating them to low temperatures and shortening them. The time is maintained, and then rapid freezing is carried out, and the annealing process is based on chemical composition and structural uniformity. During spheroidizing annealing, austenization is "incomplete", but the flaky pearlite changes into austenite, and a large amount of excess carbides dissolve. The main method for normalizing the casting and standard parts of medium and high carbon steel is to refine the mechanism. In addition, spheroidizing annealing can sometimes be used for some hypoeutectoid steels that need to improve cold plastic deformation (such as stamping, cold heading, etc.). In order to ensure that the supercooled austenite completely stops the transformation of pearlite, the freezing of thorough annealing must be rapid, and the furnace should be air-cooled with the furnace freezing to 500°C. 2. Refine the grains, eliminate structural defects caused by casting, forging, and welding, balance the structure and composition of the steel, improve the performance of the steel, or prepare the structure for future heat treatment operations. Therefore, it is impossible to eliminate reticular carbides. If hypereutectoid steel has reticular carbides, it must be properly normalized before spheroidizing annealing to eliminate them to ensure that spheroidizing annealing proceeds normally. It is conducive to exerting the potential of materials, reducing material consumption and improving the service life of the whole machine. 3. Fatigue strength: High and medium frequency surface quenching greatly improves the fatigue strength and reduces the sensitivity of the crack. Because the angle of high carbon steel is too low after annealing, the phenomenon of knife sticking occurs during cutting and the cutting performance is poor. Increasing the angle by normalizing can improve the cutting performance. Some medium carbon structural steel parts can be replaced by normalizing and tempering to simplify Thermal solution process. Thorough annealing is mainly used for hypoeutectoid steel, usually medium carbon steel and low and medium carbon alloy structural steel standard parts, castings and cold-rolled profiles, and is sometimes used for their riveted components. Equivalent spheroidizing annealing is the same as the general spheroidizing annealing process. After heating and preservation, the furnace freezes to a measurement slightly lower than Ar1 for equalization. The equivalent time is 1.5 times the heating and preservation time. After equalizing, it is then cooled in the furnace to 500℃ or outside the furnace and air-cooled.

What is lost after spheroidizing annealing is the spherical pearlite structure. The cementite in it is in the form of spherical particles, dispersed on the ferrite matrix. Compared with flaky pearlite, it not only has a lower angle and is easier to cut and process, but also During quenching and heating, austenite grains are not easy to grow, and the deformation and cracking of the workpiece tend to be small when freezing.