At present, the commonly used screw materials in China are 45 # steel, 40Cr, ammoniated steel, 38CrMOAl, superalloy and so on.
1 and 45 steels are cheap and machinable, but poor in wear resistance and corrosion resistance. Heat treatment: tempering HB 220-270 and high-frequency quenching HRC45-48.
The performance of 2.40Cr is better than that of 45 steel, but a layer of chromium is often plated to improve its corrosion resistance and wear resistance. However, the requirements for chromium plating are high. The coating is easy to wear if it is too thin, and it is easy to peel off if it is too thick. Stripping will accelerate corrosion, which is rarely used. Heat treatment: tempering HB 220-270 and plating hard chromium HRC & gt55.
3. Nitrided steel and 38CrMoAl have excellent comprehensive properties and are widely used. Usually, the nitride layer is 0.4-0.6 mm. However, this material has low hydrogen chloride corrosion resistance and high price.
4. Superalloy materials are superior to other materials. This material does not need electroplating, and is mainly used to produce halogen-free screws of injection molding machines. This material has high oxidation resistance and corrosion resistance and is heat-treated at HRA 55 ′ 60.
Heat treatment of screws:
Quenching and tempering HB 220-270, nitriding HRC >；; Titanium carbide coating is used abroad to improve the corrosion resistance of screw surface, but it is reported that its wear resistance is not good enough.
A series of measures have been taken abroad to improve the wear resistance and corrosion resistance of screws. One way is to use alloy steel with high wear resistance and corrosion resistance. Such as 34CrAlNi, 3 1CrMo 12, etc. Another method is to spray Xaloy alloy on the surface of the screw. This Xaloy alloy has high wear resistance and corrosion resistance.