The structure of special alloy gray cast iron frame gray cast iron used in the power system of high-speed railway traction locomotive is shown in the figure, the material requirements are between gg30 and gg35, and the alloy addition requirements are special (as shown in the table), which is higher than the conventional gray cast iron. Gray iron castings are mainly composed of pearlite matrix structure. The mechanical properties require that the tensile strength of the key thick wall section of the gray iron castings body is greater than 258 MPa, the hardness is required to be 170~269hbw, the metallographic structure requires that A-type graphite ≥ 90%, the graphite morphology grade is 4 or finer, and the carbide volume fraction is <2%. At the same time, gray iron castings have complex structure, large wall thickness deviation (the maximum and minimum wall thickness are 120 mm and 15 mm respectively), poor casting processability and high difficulty. Due to its performance requirements, all machined surfaces and key areas of the rack after processing are not allowed to have any casting defects, and the quality control requirements for theare extremely high.
In the early stage of process design, the casting risk should be identified as much as possible and preventive measures should be taken in advance; In the whole production process of gray cast iron, SPC statistical process control method should be applied in advance to monitor the fluctuation of key parameters, so that when abnormal points or abnormal trends occur, measures can be taken immediately to reduce the probability of batch quality problems, so as to effectively reduce the cost of quality control and quality loss.