Centrifugal casting isothermally quenched ductile iron bushing test process and method

1. Test materials

Figure 1 shows the wear of excavator bushing. It can be found that the bushing has been worn through and there is no obvious wear at the mounting hole, which benefits from the protective effect of the bushing. The shaft was partially worn after one month of service, as shown in Fig. 1C.

(a) Wear bushing (b) Bushing hole (c) Axis

The chemical composition of nodular cast iron is shown in Table 1. Adding a certain amount of Cu into the material will help to improve the density of the material, make the distribution of graphite spheres more uniform, and improve the overall mechanical properties of the material.

2. Test scheme

The outer diameter, inner diameter and height of the bushing are < 95, < 80 and 70mm respectively. The blank size of the casting is determined as < 105mm according to four pieces × 70mm × 350mm, mass 13kg. The molten iron is melted in a 500kg medium frequency induction furnace with a discharge temperature of 1540 ~ 1560 ℃, and the molten iron is poured into a quantitative insulation ladle preheated to more than 500 ℃. The thermal insulation ladle is transferred to the spheroidizing station and inoculated and spheroidized at the same time. The inoculant is si-25fe and the spheroidizing agent is rare earth magnesium. After the spheroidization reaction in the ladle is completed, the molten iron in the quantitative ladle is poured into the centrifugal mold; The mold rotation speed is 1000 R / min and the pouring temperature is 1400 ~ 1420 ℃. In order to prevent spheroidization recession, the pouring process is controlled within 2.5min. Spray water for 4 ~ 6min after pouring. After water cooling, the mold continues to rotate for 30s, the centrifugal casting machine stops and automatically ejects the casting.

(a) Bush after isothermal quenching (b) Bush after machining

Reheat the bushing and conduct austenitizing treatment. The heating temperature is 900 ℃. After holding for 1.5h, it is quenched into 100 ℃ oil. When the workpiece is cooled to 230 ~ 280 ℃, it is transferred to the isothermal furnace at 260 ℃. After isothermal treatment for 100min, it is discharged for air cooling. The bushing obtained after cutting is shown in Figure 2. Cut 6 groups of samples on different bushings, and the sample size is 10mm × 10mm, observe the metallographic structure through mck-50mc metallographic microscope, and measure the hardness with HR150 hardness tester. The size of the cut sample is 50mm × 50mm, the friction and wear test is carried out with rtec wear tester, and the comparison sample is 45 steel. The ball disc friction pair is adopted, in which the upper sample is a steel ball with a diameter of 10mm and the material is GCr15 alloy steel; The lower sample is isothermally quenched ductile iron test block or 45 steel. The steel ball runs in a reciprocating straight line on the surface of the test block. The test load is 30n, the sliding speed is 10mm / s, the sliding stroke is 10mm, and the test time is 1800s. It is carried out under dry friction and oil lubrication to simulate the lubrication condition of bushing under actual working conditions.