Reasons and preventive measures for the low surface hardness of gears after carburizing and quenching.

The low hardness of the gear carburized surface will lead to a decrease in the wear resistance and fatigue resistance of the gear, and negatively affect the friction and wear properties of the gear surface. Why does this happen! Let's take a look at the box-type carburizing furnace manufacturers below.

1. Cause analysis

(1) The decarburization of the surface and the decarburized layer in the metallographic examination is caused by the poor protection during normalizing or quenching after carburizing.

(2) The cooling rate is too low. Under the microscope, the surface structure is not martensite but sorbite. The corrosion resistance of acicular martensite is obvious, and the corrosion resistance of sorbite is poor (easy to corrode). Microhardness varies widely.

(3) The carburizing temperature and quenching temperature of the gear are too high, and there is too much residual austenite on the surface after quenching.

(4) The hardenability of the gear material is poor, and the cooling capacity of the quenching medium is insufficient.

(5) The tempering temperature after quenching is too high, and the holding time is too long.

2. Preventive measures

(1) Carburizing treatment should be appropriately increased for the surface of low carbon gears.

(2) Select materials with appropriate hardenability and cooling medium with appropriate cooling capacity, and quench and cool them.

(3) Measures should be taken in advance to reduce the amount of retained austenite after quenching. Tempering at 650-670 ℃ for more than 3h, the carburized gear with too much retained austenite will precipitate some carbides, reduce the stability of austenite during reheating and quenching, and promote the transformation of austenite to martensite. change.

(4) Gear carburizing cooling or reheating quenching should be carried out in a protective atmosphere. For oxidized gears, the oxide scale should be removed and surface carburized before quenching.

(5) If the surface hardness of the gear is too low due to the high tempering temperature, it is necessary to re-quench and select a suitable tempering temperature.

Well, we have introduced the reasons for the low surface hardness of gears after carburizing and quenching and the relevant introduction of preventive measures, hoping to help you.