The carbon content of low-carbon structural steel is generally 0.1% to 0.3%, and commonly used materials include Q235, 20 steel, 20Cr, 16Mn, etc. If heat treatment is not used for strengthening, that is, quenching and tempering treatments, these materials are suitable for galvanizing, hot-dip galvanizing and electro-galvanizing. If low temperature tempering is used after quenching, the tempering temperature is generally 180~220℃. The temperature of sherardizing and hot-dip galvanizing is higher than their tempering temperature. The materials using low-temperature tempering are not suitable for the use of sherardizing and hot-dip galvanizing, otherwise the strength of the material will be reduced. Electro-galvanizing is suitable, but after electro-galvanizing Dehydrogen annealing must be carried out to reduce the tendency of hydrogen embrittlement.
The carbon content of medium carbon structural steel is generally 0.3% to 0.5%, and commonly used materials are 45 steel, 40Cr, 35CrMo, etc. Commonly used to manufacture gears, shafts, pins, high-strength bolts (≥8.8 grade) and other parts. This kind of material is strengthened by quenching + medium temperature tempering heat treatment. The tempering temperature of medium temperature is generally 470~570℃. Sherardizing can be carried out at a temperature lower than the tempering temperature of the medium temperature, without affecting the strength of the parts, and there is no tendency for hydrogen embrittlement. Sherardizing is very suitable for such parts. Although electro-galvanizing does not affect the strength of the material, the higher the strength, the greater the tendency for hydrogen embrittlement. The hot-dip galvanizing temperature should be lower than the tempering temperature, otherwise the strength of the material will be reduced. Take the high-strength bolt hot-dip galvanizing as an example. Some companies even use high-temperature galvanizing above 600℃. Although the time is very short, some of the 8.8-grade bolts cannot meet the tensile strength requirements after the hot-dip galvanizing. Less than the tensile strength requirements.