Gray cast iron mainly refers to the cast iron with flake graphite, which can obtain thinner and more complex castings than cast steel, and the cooling rate sensitivity is very great, while gray cast iron in the heat treatment process, mainly using the following three ways.
1. De-stress annealing
In the process of casting cooling, due to the different cooling rates of various parts, it is easy to generate internal stress, which may lead to casting warpage and crack. The specification is generally: heating temperature
500~550℃, heating rate 60~120℃/h, after a certain time of heat preservation furnace cooling to 150~220℃ air cooling.
2. Eliminate annealing of casting white mouth
On the surface of gray cast iron and some thin sections, the cooling rate is faster in the condensation process, which is easy to produce the white mouth structure, which increases the hardness and brittleness of the casting and causes the difficulty of cutting, which needs to be annealed. Heat cast iron to
At 850~890℃, Fe 3 C was decomposed by heat preservation for 2~5h, then it was slowly cooled by the furnace at 400~500℃, and then it was air-cooled.
3. Surface quenching
Some castings, such as machine guide surface and cylinder inner wall, need to improve the surface hardness and wear resistance, often surface quenching treatment, such as high-frequency induction heating surface quenching, contact resistance heating surface quenching.
On 2018-08-08 11:45:46
