For a long time, the cylinder block and cylinder head have been made of gray cast iron. Due to the demand of energy saving and lightweight, some enterprises use Al alloy to manufacture the cylinder block and cylinder head, which greatly reduces the casting quality and reduces the fuel consumption of the engine. However, in recent years, due to the increase of engine power and the increase of working temperature of cylinder block and cylinder head, Al alloy is difficult to meet the requirements, Some enterprises also use vermicular graphite cast iron to produce cylinder block and cylinder head castings.
At present, many factories at home and abroad have used vermicular cast iron to produce cylinder block and cylinder head, and achieved good results. However, due to the unique and excellent properties of gray cast iron and the continuous development of high CE and high strength gray cast iron materials, gray cast iron cylinder block and cylinder head castings are still dominant. In the 1990s, our company cooperated with the internal combustion engine Research Institute of a European company to design 6DL high-power vehicle diesel engine. The other party disagreed with our proposal to use vermicular cast iron and advocated that the cylinder head should use high-grade gray cast iron. The reason is that the hardness, dimensional stability and thermal conductivity of vermicular cast iron are not as good as gray cast iron.
ZHY casting senior engineer team studied the method of producing HT300 cylinder block and cylinder head castings under high CE conditions:
(1) Using the whole scrap induction furnace smelting process, the carburizing agent must be graphitized at high temperature. Its functions are as follows: the amount of W (s) is generally less than 0.05%, or even less than 0.03%; In addition, after high-temperature graphitization treatment, the amount of W (n) in the carburizing agent is greatly reduced, because s, N and h can volatilize only in the high-temperature graphitization stage, which is the key to prevent N2 pores in castings.
(2) The amount of W (c) is controlled at 3.25% ~ 3.35%, and the amount of W (SI) is controlled at 2.10% ~ 2.40%. Such a high CE is very beneficial to reduce the shrinkage of molten iron.
(3) Control the amount of W (s) at 0.08% ~ 0.12%. When w (s) is less than 0.05%, increase s must be carried out.
(4) Strictly control the amount of W (MN). It is found that the properties of the material will decrease with the increase of W (MN). However, it does not mean that the lower the amount of W (MN) in gray cast iron, the better. If the amount of W (MN) is too low, the oxidation tendency of molten iron will increase, the fluidity will deteriorate and the shrinkage tendency will increase.
(5) Appropriate alloying treatment, the alloy addition range is: w (CR) 0.25% ~ 0.30%, w (Cu) 0.5% ~ 0.6%, w (MO) 0.2%, w (SN) 0.02%.
(6) A good inoculant should be selected because some undercooled D-type graphite often appears in the graphite form of ordinary SIFE inoculant. In the production of high-grade gray cast iron, the flow inoculation process is a very common process. The inoculant used with flow must have uniform particle size, no powder, uniform melting point and rapid melting.
(7) The casting can be cooled slowly in the sand box by delaying the unpacking time, so as to reduce the casting stress and improve the casting quality.
Through the above measures, ZHY casting has stably produced the cylinder block and cylinder head castings of heavy-duty truck high-power diesel engine. The material brand reaches HT300, with high performance and small shrinkage tendency.