Studies Of The Crack Defects In High Performance Engineering Machinery Axle Housing

In the21st century, steel is still the most important engineering material, its wide scope of application, is more than any other engineering materials can match. Carbon steel and low alloy steel with high strength, high toughness and good weld ability, and their mechanical properties can be adjusted in a fairly wide range of different heat treatment processes, is the most widely use of engineering structure material. Cast steel is the combination of casting process and steel material metallurgy. It not only has the complex shape that other forming process is difficult to obtain but also can maintain the performance of the various steel unique. Because of this cast steel establish the important position in engineering structure materials.The rear axle is one of the main components of the heavy trucks. And it plays an indispensable role in the normal operation. The rear axle not only can bear the load of the truck but also is the shell of the main reducer, differential and drive wheel gear. In practice, in addition to satisfy certain requirements bridge shell strength and stiffness requirements, and try to reduce its weight. Considering the cost factors, it also requires bridge shell has simple structure, easy to ensure that the main reducer, dismantling, adjustment and maintenance, etc. At present there are mainly three types of automobile axle housing options:split, monolithic, combined. This thesis mainly studies the object is the integral of the heavy car bridge shell.In the factory’s daily production, there is a special kind of brittle fracture. In the later process of finishing casting we find the cracks. Looking from the fracture, it is the intergranular brittle fracture and has the smooth crystal face, sometimes it also can meet the characteristics of the dendritic crystal, so it is called "stone fracture". There are no signs before fracture, so, if were broken in the car driving, It will cause serious consequences.To cast steel "rock-candy fracture" defect of the research has been on for a long time, but the reasons of this defect and the corresponding measures have not been a unified point of view. This paper to a factory produced during daily production of "rock-candy fracture" as the starting point, according to the general method of fracture analysis, the fracture test and analysis take place on the "rock-candy fracture". Through the analysis of experimental results, the aluminum nitride may be due to the defects in grain boundaries enrichment appear. According to the guess, designing a process validation tests, artificially improve the addition amount of aluminum and nitrogen. Process validation test results was consistent with the guess, the casting produced the "rock-candy fracture" defects. Aim at the process validation test produced "rock-candy fracture" for inspection and analysis, test and analysis results confirmed the guess. We conclude that the defect is due to the join of rare earth, and a mass of the deoxidizing aluminum residual in the molten steel, the residual aluminum product a chemical reaction with the nitrogen in the molten steel, and the reactions that produce aluminum nitride and enrichment in grain boundaries, the "rock-candy fracture" defect production. According to the cause of "rock-candy fracture" defects, and combined with the characteristics of the foundry production, put forward the corresponding process improvement measures.