The bucket tooth material is low-alloy wear-resistant steel, which is more suitable for bucket teeth. However, due to the lack of necessary heat treatment, the organization of the bucket teeth is uneven, the insert does not play its due role, and the overall wear resistance of the bucket teeth is poor, leading to early failure.
One: Force analysis The bucket tooth working surface is in contact with the excavated material, and the force is different at different working stages in a complete excavation process. When the tip of the tooth first touches the surface of the material, the tip of the bucket receives a stronger impact due to the faster speed. If the yield strength of the tooth is low, plastic deformation will occur at the tip. As the digging depth increases, the force of the bucket teeth will change. When the bucket tooth cuts the material, the bucket tooth and the material move relative to each other, and a large positive squeezing force is generated on the surface, thereby generating a relatively large frictional force between the working surface of the bucket tooth and the material.
If the material is hard rock, concrete, etc., the friction force will be great. The repeated action of this process produces varying degrees of surface wear on the bucket tooth working surface, which in turn produces deep furrows. Whether the composition of the bucket teeth is good or not affects the service life of the bucket teeth. The positive pressure of the front working face is obviously greater than that of the rear working face. The front working face is seriously worn. It can be judged that the positive pressure and friction are the main external mechanical factors of bucket tooth failure, which play a major role in the process of failure.
Two: Process analysis Take two samples from the front and rear working faces respectively, and grind them for hardness testing. It is found that the hardness of the same sample is very different, and the preliminary judgment is that the material is uneven. The samples were ground, polished, and corroded, and it was found that there were obvious boundaries on each sample, but the boundaries were different. From a macro point of view, the surroundings are light gray and the middle part is darker in color, indicating that the piece is likely to be an inlay casting. On the surface, the enclosed part should also be an inlay. Hardness tests were carried out on both sides of the boundary on the HRS-150 digital Rockwell hardness tester and the MHV-2000 digital micro hardness tester, and the differences were obvious.
The above analysis proves that the tooth is an insert structure. The closed part is the insert, and the surrounding part is the base. The composition of the two is similar, and they are alloyed with elements such as Cr, Mn, Si, and the main alloy composition (mass fraction, %) is 0.38C, 0.91Cr, 0.83Mn, 0.92Si. The mechanical properties of metal materials depend on the composition of the material and the heat treatment process. The composition is similar but the hardness is different, indicating that the bucket teeth were put into use without heat treatment after casting. The following organizational observations also proved this point.
Three: Microstructure analysis. Metallographic observation shows that the matrix is mainly black flake structure, and the inlay structure is composed of white block and black flake, and there are more white block structures far away from the cross-sectional area. Further microhardness test It is proved that the white massive structure is ferrite, and the black flake structure is troostite or a mixed structure of troostite and pearlite. The formation of bulk ferrite in the insert is similar to the formation of part of the phase transition zone in the welding heat-affected zone. Due to the heat of the molten metal during the casting process, this region is in a two-phase region of austenite and ferrite, where the ferrite fully grows, and its structure is maintained to room temperature. Due to the relatively thin wall of the bucket teeth and the large volume of the insert, the temperature in the center of the insert is low, and no large ferrite is formed.
Four: Performance analysis The wear test on the MLD-10 wear tester shows that the wear resistance of the matrix and the insert under the small impact abrasive wear test conditions is better than that of quenched 45 steel. At the same time, the wear resistance of the matrix and the insert is different, and the matrix is more wear-resistant than the insert. The composition on both sides of the base and the inserts are close, and it can be seen that the inserts in the bucket teeth mainly play the role of cold iron. In the casting process, the matrix grains are refined to improve its strength and wear resistance. Because the insert is affected by the casting heat to produce a structure similar to the welding heat-affected zone, it does not play a role in enhancing the wear resistance. If proper heat treatment is carried out after casting to improve the structure of the matrix and inserts, the wear resistance and service life of the bucket teeth will be significantly improved.
One: The bucket tooth material is low-alloy wear-resistant steel, which is more suitable for bucket teeth. However, due to the lack of necessary heat treatment, the organization of the bucket teeth is uneven, the insert does not play its due role, and the overall wear resistance of the bucket teeth is poor, leading to early failure.
Two: It is recommended to properly normalize the castings after casting to improve the structure and performance and increase the service life. After reasonable heat treatment of the casting, under the same working conditions, the service life of the bucket teeth is increased by nearly 2 times.
