Effect of reducing residual stress in mold insulation of high strength cylinder head casting on tensile strength and hardness

The structure of 11 l engine cylinder head casting is shown in Figure 1, and the overall dimension of the casting is 1 002 mm × 420 mm × The average wall thickness is about 5 mm. It is required that the tensile strength of the body is more than 270 MPa, and the residual stress is less than or equal to 50 MPa. The test points are shown in Figure 2.

According to the production experience of 13 l cylinder head, the process of heat preservation annealing after pouring was selected. Statistics of residual stress of castings after different holding time in mold. The results show that the residual stress of cylinder head can be reduced by in mold heat preservation. The stress of cylinder head decreases gradually with the increase of pressing time, and the change of stress is not obvious when the pressing time increases from 7 h to 10 h; However, the time of pressing box decreased from 7 h to 6 h, and the stress increased obviously; Five rounds of tests were carried out, and the stress at 2-3 points of each cylinder head exceeded 50 MPa in each round; In order to ensure that each measuring point meets the requirements, it needs a longer pressing time.

The effect of holding time in mold on the tensile strength and hardness of castings was observed under the condition of keeping the main chemical composition and alloy content relatively stable. The results show that the in mold insulation has a great influence on the tensile strength and hardness under the same conditions; In order to meet the requirements of casting acceptance standard, it is necessary to increase the amount of alloy. If the amount of alloy is increased, the cost will be increased and the shrinkage tendency of hot spot will be increased.

Considering the effect of in mold heat preservation and stress relief process on residual stress, tensile strength and hardness of the casting, the in mold heat preservation and stress relief process is not suitable for the casting.