1. Selection of C and Si
For wear-resistant pump body castings, the selection of C content should not only ensure the requirement of sufficient graphitization, but also take into account the risk of graphite floating in the casting process. Therefore ω (C) 3.65% ~ 3.80%; Si strongly promotes graphitization, fine fossil graphite balls and increasing the amount of graphite can significantly improve the product performance, but its content is too high, which will sharply deteriorate the toughness of the product. Especially under the condition of high phosphorus, the amount of solid solution phosphorus will be reduced, resulting in an increase in the number of phosphorus eutectic, which will reduce the toughness of the material and strengthen the toughness of the pump shell ω (SI) in the range of 2.20% ~ 2.40%
2. Selection of Mn and P
On the contrary to Si, Mn can inhibit graphitization, promote the formation of carbides and reduce the toughness of products. With the increase of manganese content, wear-resistant ductile iron first shows an increase in hardness. This is because manganese reduces the content of ferrite and pearlite and increases the amount of bainite. When the manganese content continues to increase, austenite and martensite gradually increase, and the hardness value decreases due to the increase of austenite. But Mn can stabilize austenite and improve hardenability. Considering comprehensively, the ω (MN) is controlled at 0.50% ~ 0.60% Because of the segregation tendency of P and the toughness requirements of wear-resistant pump body castings, P should be strictly controlled. It is required that ω （P）≤0.030%.
3. Selection of Mo and Cu
A small amount of Mo is dissolved in ferrite to strengthen the matrix, refine the grain, homogenize the structure, improve the hardenability, improve the hardness, refine the pearlite, and thus improve the wear resistance of ductile iron. Mo plays a more obvious role in improving strength than Mn and Cu, but too high will form carbide segregation at the grain boundary or in the crystal, which is difficult to eliminate, affecting plasticity and toughness. For wear-resistant pump body castings ω (MO) is controlled between 0.25% and 0.35% Cu refines grains and graphite balls, increases isothermal transformation temperature, delays transformation process, promotes hardenability, is beneficial to stabilizing pearlite, and significantly improves product strength and hardness. But too high will also bring negative effects, making the elongation of the material decrease significantly after fracture, and the content of pearlite in the matrix changes little at this time. Considering comprehensively, in the pump housing ω The amount of (Cu) is controlled at 0.50% ~ 0.60%
| C | Si(original) | Si(final) | Mn | P | Mo | Cu | Mg |
| 3.65-3.80 | 1.40-1.60 | 2.20-2.40 | 0.50-0.60 | ≤0.030 | 0.25-0.35 | 0.50-0.60 | 0.035-0.050 |
Determine the chemical composition of the wear-resistant pump body casting as shown in the table.