Quenched and tempered gray cast iron, gray cast iron quenched and tempered method and its application

Abstract

The invention discloses a quenched and tempered gray cast iron, a gray cast iron quenching and tempering method and application thereof. The gray cast iron quenching and tempering method includes the following steps: placing a gray cast iron blank in a quenching furnace at 850-950° C. for 0.5-2 h, Immediately after coming out of the furnace, put it into quenching oil at 65~85℃ for 3~6min, control the cooling rate to be 65~85℃ / s, and air-cool to no higher than 200℃ after the oil is discharged; put the grey cast iron blank at 550℃~650℃ The temperature is kept in a tempering furnace at ℃ for 1 to 4 hours, and air-cooled to room temperature after being released from the furnace to obtain quenched and tempered gray cast iron. The invention develops a quenching and tempering process suitable for gray cast iron, which avoids quenching and cracking of gray cast iron, the structure of quenched and tempered gray cast iron is uniform, the shape and size of graphite do not change, and the matrix structure is dominated by fine sorbite (more than 90%). ), the internal stress is the smallest, which can effectively prevent the expansion of thermal fatigue cracks, and improve the mechanical strength and thermal fatigue resistance of the material while ensuring the thermal conductivity.

Description

technical field [0001] The invention relates to the field of heat treatment of gray cast iron, in particular to a tempered gray cast iron, a gray cast iron quenching and tempering method and an application thereof. Background technique [0002] HT250 is the main material for producing low-power engine cylinder heads and flywheels. As the combustion and explosion pressure of diesel engines continues to increase, engine cylinder heads are subjected to higher and higher thermal and mechanical loads. The higher load makes the cracking of the weakest nose bridge area of ​​diesel gray iron engine cylinder head become a more common failure mode. At present, the commonly used technical solution is to add more alloying elements on the basis of gray cast iron to improve the overall strength of the material, but The addition of alloying elements first makes the fluidity of molten iron worse, which leads to more defects when pouring the engine cylinder head with a very complicated desig...

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Problems solved by technology

Quenching is to heat the steel to the quenching temperature (hypoeutectoid steel is Ac3+30~50℃, hypereutectoid steel is Ac1+30~50℃, alloy steel can be slightly higher than carbon steel), and then the steel is put into the quenching medium for rapid Cooling to obtain martensite. It is generally believed that gray cast iron is easy to crack during quenching and loses its own mechanical properties after quenching and tempering treatment, so there is no gray cast iron quenching and tempering process in the prior art

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