Features: after the surface of the casting is processed, there are micro concave and convex, and some parts have “shiny” hard spots. The surface hardness of the casting varies greatly, reaching 30-50hb (foreign advanced level 5-10hb). The hardness of the hard spots may exceed the standard. The hardness difference of casting is easy to cause uneven wear of working face, poor machining accuracy of machine tool and high noise of diesel engine.
(1) In order to eliminate the influence of pig iron heredity, it is better to raise the superheat temperature of molten iron, and the temperature of furnace outlet is higher than 1480 ℃.
(2) To prevent the reduction of C and Si content due to the oxidation of molten iron, strictly control the amount of inoculant added and the particle size of inoculant, and the inoculant should be added evenly. It is better to use a vibration feeding device with controllable time to ensure that the inoculation time accounts for more than 70% of the iron production time.
(3) It is better to use scrap less than 20 ° and avoid alloy steel. It is better to remove rust before using scrap. Small, light and thin scrap steel should be pressed into lumps before use.
(4) For the castings with uneven thickness, the pouring system should be designed reasonably to ensure that all parts of the castings are cooled evenly, especially the thick parts can be placed with cold iron or refractory bricks.