Ⅰ. Cold forging process characteristics of stainless steel forging
Cold forging is a general term for plastic processing such as cold die forging, cold extrusion, and cold heading. Cold forging is the forming process below the recrystallization temperature of the material, and the forging performed below the recovery temperature. In production, it is customary to call forging without heating the blank as cold forging. Cold forging materials are mostly aluminum and some alloys, copper and some alloys, low-carbon steel, medium-carbon steel, and low-alloy structural steel with low deformation resistance and good plasticity at room temperature. Cold forgings have good surface quality and high dimensional accuracy, which can replace some cutting processes.
1. The quality of cold forging products is good. Processed at room temperature, the product has high dimensional accuracy, smooth surface and good mechanical properties. It can also process forgings with complex shapes, reducing the cutting processing of stainless steel forging, saving material consumption and reducing costs.
2. Large deformation resistance. Measures must be taken to reduce the deformation resistance: adjust the chemical composition of raw materials, pre-treatment of blanks, improve the deformation process, increase the hardness and smoothness of the mold, and control the pressurization speed of the equipment.
3. Cold deformation strengthening and thermal effect. During the cold forging process, as the degree of deformation increases, a cold deformation strengthening phenomenon occurs in which the strength and hardness of the metal also increase. Cold deformation strengthening can be used to strengthen the strength and hardness of the product and improve the mechanical properties. As the mechanical energy of stainless steel forging is converted into heat energy, the temperature of the blank will increase, which is called the thermal effect.
4. Greater friction. Cold forging has a large deformation force and a large unit pressure, and the friction between the metal and the mold surface is also high. It is necessary to improve the lubrication conditions and reduce the friction.
5. Mechanization and automation. Processing at room temperature, good working conditions, easy to realize mechanization and automation, suitable for mass production.
Ⅱ. Preparation of blanks before cold forging of stainless steel forging
The size and quality of the blank for cold forging must be controlled accurately, and the forging surface must be flat. For high requirements, the surface of stainless steel forging should be stripped, which can be turned or ground.
The purpose of softening annealing heat treatment is to reduce the strength of the raw material of stainless steel forging, to ensure uniform performance of stainless steel forging, and to improve the plasticity of stainless steel forging. General annealing treatment is adopted for low carbon steel, and spheroidizing annealing treatment is adopted for medium carbon steel and low alloy steel.
Lubrication of cold forging is very important. It can reduce the load of cold forging of stainless steel forging, improve die life and quality of cold forgings. Usually lubrication treatment is to generate a firm film on the surface of the blank, which reduces the friction resistance and cold forging force of stainless steel forging during the cold forging process. Before lubrication, the surface of the blank should be cleaned including alkaline washing to remove oil, pickling or shot peening to clean the oxide scale, and water washing to keep the surface of the blank clean.