Heat treatment process of 20 mn2 car chain
Car chain is installed on the car tyres a circular chain, mainly used for automobile driving snow prevented slippery, to ensure safety, is an essential tool for winter elevations are the car, so demand chain wear resistance and fracture, i.e. the chain must have good wear resistance and tenacity. As people's safety consciousness enhancement. Car is becoming more and more wide chain of using electricity.
20 mn2 steel by carburizing and hardening capacity can be good, especially with excellent abrasion resistance, therefore, in addition to used in the manufacture of lifting chain, is also is widely used in the manufacture of the chain of heavy trucks.
In some heavy load below goods GuangFeng chain, for example, within the ring size of 12 mm x 42 mm, wire diameter of 7 mm. Technical requirements: the carburized layer thickness 0.25 ~ 0.35 mm, surface hardness > 54 HRC, heart > 40 HRC hardness, tensile test of not less than 30 kn.
General mills using heat treatment process is shown in figure 1.
1. Before and after the improvement process
The advantages of the process is characterized by: furnace charging to the temperature, heat preservation water directly after carburizing and quenching, fast production, cycle is short, to improve production rate. And small foot is: although permeability layer thickness, surface and hardness are up to par, but when tapping pull test, it is difficult to reach 30 kn, chain drive lean on large fracture easily and can't use, return and exchange happens quite often, detrimental to the enterprise.
Obviously, as shown in figure 1 heat treatment process to focus on the guarantee on the surface hardness and wear resistance, strong toughness have been ignored and central department. Therefore, must be to improve the heat treatment process.
Compared with figure 1 process, the improved heat treatment process (see figure 2) has the following features:
(1) decrease the temperature of carburizing, shorten the carburizing time, to prevent grain increase, improve the mechanical properties.
(2) reduce the quenching temperature. After carburizing for 30 min to cut off the power supply and cooling, this phase is still in a certain dose of drip into the kerosene, ensure no oxidation decarburization during cooling, at the same time also can spread effect, expand the carbonitriding layer depth (relatively short this time 30 min carburization process); Reduce the quenching temperature, also can reduce the residual austenite volume, thus reducing brittleness. ,
(3) improve the tempering temperature. Medium temperature tempering, instead of low temperature tempering for improve the toughness of the chain.
(4) comprehensive performance is improved significantly. Except the permeability layer thickness, surface hardness is the same as the original process, the core hardness partial floor (within the scope of 40 ~ 44 HRC), tapping pull test value can reach more than 30 kn.
(5) and production efficiency has no obvious decline. Through the measured. Two basic process cycle, had no obvious effect on production efficiency.
2. The conclusion
Heat treatment process after the improvement, not only ensure the chain has high wear resistance, and fundamentally solve the chain fracture problems in using, customers are very satisfied with.
