Solidification test and mechanical properties test of chromium white cast iron by pressure casting technology

1. Hardness test

(1) Macrohardness

Thbrv-187.5 electric broville hardness tester is mainly used for macro hardness analysis of samples. As the sample is chromium white cast iron, HRC Rockwell hardness should be used to test. Check the hardness meter with standard hardness block, and the hardness value checked shall not exceed 1 ~ 1.5% of the hardness value of standard hardness block. The sample shall be ground or polished and placed on the worktable smoothly, and there shall be no movement during the test. The experimental load is set at 150kgn, the holding time is 5S, and five points are measured for each sample, and the arithmetic mean value is taken.

(2) Microhardness

Hr-150a Rockwell hardness tester is mainly used for micro hardness analysis. The load of the hardness tester is between 10g and 1000g, and it is loaded and unloaded continuously during the experiment. The magnification of microstructure is 100x, 400X, and the maximum measurement length is 200 μ m. The measurement accuracy is 0.5 μ m。 The sample needs to be polished to keep the surface smooth. Five points are measured for each sample, and the arithmetic mean value is taken.

2. Impact toughness

Jb-50b impact toughness testing machine is mainly used for impact toughness analysis. Because the as cast chromium white cast iron belongs to brittle material, there is no need to cut the sample before the experiment. Three samples are selected for each group of impact toughness test, and the average value is taken as the test value to reduce the experimental error and ensure the accuracy of data.

3. Impact wear

Mld-10b dynamic load abrasive wear tester is used for impact wear test of chromium white cast iron, as shown in figure (a) (b). The weight of the hammer is 100N, the impact times is 150 times / min, and the free falling height of the hammer is 0 ~ 50mm. The abrasive used in the experiment is quartz sand purchased by Zhangjiakou Chengxin test equipment manufacturing Co., Ltd. (Fig. C). The particle size is between 10 and 20 mesh, and the flow rate of the abrasive is 50kg / h.

(a) MLD-10 impact wear tester: (b) Test machine schematic diagram; (c) Quartz sand; (d) Specimen size

It has been mentioned in the process of specimen preparation that there is no heat treatment in this study, and the chromium white cast iron samples are all as cast. Therefore, a smaller range of impact energy (1 ~ 2J) should be selected to prevent the sample from breaking and falling off, resulting in larger experimental error. Before the formal test, it is necessary to pre grind each wear sample for 30 ~ 60min, so that the shape of the sample port is completely consistent with that of the lower sample, so as to ensure that the wear contact area is always consistent during impact wear. The time of formal wear test for each sample is 120 min. after every 10 min, the sample is removed and cleaned by ultrasonic cleaning machine, and then weighed by one ten thousandth balance.