Influence of Heat Treatment on Structure and Properties of High Chrome Cast Iron Grinding Ball (1)

Abstract: The effects of heat treatment on the hardness, impact toughness, and casting high chrome grinding ball’s microstructure have been investigated. The results show that the hardness of the ball quenched at 980 ℃and then tempered at 400 ℃ is up to 60. 5 HRC; meanwhile, the impact toughness of that ball is 6. 8J/ cm2.

Keywords :high chrome grinding ball; heat treatment; hardness; impact toughness

High Chrome Grinding ball is an indispensable grinding body of all kinds of ball mills; the most basic requirement is not broken in wear-resistant use. High Chromium grinding ball is the most suitable material for these requirements, its chemical composition CR content is more than 12%, the eutectic carbide characterizes this material is M7C3 type, broken, continuous network distribution, and through a specific heat treatment processing, can be obtained by Mahalanobis, body-based Matrix structure, and therefore has much higher than the General White Iron, toughness and wear resistance.

Scholars at home and abroad have carried out much fruitful research on chromium-based wear-resistant materials in recent years. Given the low hardness and impact toughness of the high chromium cast iron used in the production of metal mold casting grinding balls, which led to the problems of high breakage rate and increased wear of the grinding balls in the course of use, from heat treatment technology, to improve the performance of high chrome grinding ball and improve the quality of high chrome grinding ball, a suitable technological scheme was studied.

1.Test Content

1.1Specimen preparation

The raw materials used in the test are pig iron P08, low carbon scrap steel, electrolytic copper, chromium iron, Molybdenum Iron, and manganese iron. Molten iron is smelted in 150 kg SCR medium frequency induction furnace, the temperature is measured by double platinum Rhodium fast thermocouple, the furnace temperature is 1500ー1550 °c, the pouring temperature is 1400ー1450 °C, and the furnace front is incubated with 0.8% rare earth alloy, the final chemical composition (mass fraction,%) is 2.8 ~ 2.9 c, 0.6 ~ 0.8 SI, 0.8 ~ 1Mn, 12 ~ 14Cr, < 0.08 P, < 0.1 s, 0.1 ~ 0.2 Mo, 0.2 ~ 0.4 Cu.

The high chromium grinding balls are cast in the metal mould, the size of which is 40 ~ 70mm, the size of which is 80mm or above is made of one mould and one mould. The heat treatment of the grinding balls is carried out in a box-type resistance furnace.

1.2Test method

The experiments mainly focus on the 80mm size grinding ball, and two groups of heat treatment process design, see Table 1. The impact specimens were cut by wire cutting in the body of the grinding ball and processed into 10mm × 10mm × 55mm non-notched specimens. HR-150A Rockwell hardness tester was used to measure the hardness of the impact sample after the ball impact.

2.Test results and analysis

The results of the impact test and hardness test are shown in Table 1

2.1Effect of heat treatment process on hardness and impact toughness of high chrome grinding ball

As shown in Table 1, the hardness and impact toughness of as-cast grinding balls are low. When tempered at 260 °c, the ball’s hardness and impact toughness increased slightly with the increase of quenching temperature, but the impact toughness did not increase obviously. When the temperature is 980 °c, the hardness of the high chrome grinding ball is the highest. As the quenching temperature continues to increase, the hardness begins to decrease, while the impact toughness increases significantly with the quenching temperature, as shown in figure 1.