Failure analysis of 90mm low chromium casting ball cracking (1)

LU Weidong , SHEN Maolin , ZHOU Yuanxing (Institute of Ningguo Wear Resistant Materials General Plant Anhui Province, Ningguo 242300 , China)

Abstract: The cracking of the 90mm low chromium casting ball occurred too early in the drop ball test. The casting ball material was analyzed by chemical composition, mechanical properties, and metallographic structure. The results show that the content of inclusion is high, the hardness is high, and there are serious shrinkage porosity and plenty of austenite transformation products in the as-cast structure; the casting ball cracked prematurely during the drop test. Through the improvement of technological measures, the premature cracking phenomenon of cast ball is solved.

Keywords: 90mm low chromium casting balls, Split failure, inclusions, shrinkage porosity, as-cast structure

1.Introduction

Ball drop test is a destructive method to detect grinding ball quality, simulating the actual working state of grinding ball in the ball mill, testing the quality of products by the length of ball impact fatigue life.

Fig. 1 is the fracture surface of 90 mm low chromium cast ball after aging treatment (heating to 600 ± 10 °C in a reverberatory furnace, holding for 6 hours, cooling to room temperature). The fracture surface is a crystalline, brittle fracture with coarse columnar crystal. The average number of ball drop is more than 11,000, while the actual number is only 8,320. In order to find out the cause of early failure, chemical composition analysis, hardness test, inclusion, grain size, metallographic structure, and low-power structure were carried out.

low chromium casting ball

2.Physical and chemical examination and results

2.1 Chemical Composition Analysis

The samples were drilled from the cross-section of the sphere for chemical composition analysis. The results are shown in Table 1. The chemical composition of the low chromium casting ball conforms to the requirements of the standard value.

low-Cr casting ball chemical composition

2.2 Hardness Test

A sample of 10mm × 10mm was made by EDM perpendicular to the fracture surface, and the hardness of its core and surface was measured. The hardness of the heart is 47. 548. The surface hardness is 50. 050.15 HRC, which is higher than the normal hardness (core hardness is 46.547.0HRC; surface hardness is 48.549.0HRC), the higher hardness will reduce the impact toughness and increase the brittleness tendency.