Fracture analysis of 45 steel (quenched and tempered)

45 Steel (Heat Treatment and Fault Analysis)

The 45 steel is a kind of structurally and functionally important steel, which is widely used in various aspects of design and engineering applications. The purpose of this paper is to study the microstructure and mechanical properties of 45 steel after heat treatment and to analyze the fracture of the steel.

First of all, the 45 steel is a carbon steel alloy containing manganese, silicon, and phosphorus. It has relatively low carbon content and is fairly malleable, making it ideal for various forging and machining operations. The 45 steel generally requires heat treatment to obtain desired characteristics, including improved machinability, edging, and strength. Heat treatments are usually carried out at temperatures ranging from 930 degrees Celsius to 1080 degrees Celsius, although treating some components at different temperatures may have an influence on the final properties.

After heat treatment, the 45 steel specimens were quenched in heated oil and air, respectively. By using optical microscopy, structure of the specimens was examined and the grain size was determined. Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) were used to examine the material. The hardness of the specimens was evaluated by Rockwell hardness test.

Finally, a fracture analysis was conducted on the specimens. A crack propagation test was performed on the samples, which revealed that the fracture plane of the 45 steel was perpendicular to the direction of load, indicating a cohesive-type breakage. It is concluded that the heat treatments were effective in enhancing the strength and hardenability of the 45 steel. Cross-sectional analysis of the fracture revealed that the fracture originated from the central part of the specimens.

In conclusion, the heat treatment and microstructure of the specimens were effectively examined and the fracture analysis of the 45 steel was conducted to determine its fracture behavior. The heat treatment was found to have improved the microstructural and mechanical properties of the 45 steel. The fracture plane showed that the fracture was a cohesive type, indicating a higher strength of the material compared to other steel grades.

The fracture analysis of 45 steel (heat treatment) refers to the mechanical properties of the fracture surface of 45 steel after heat treatment, which is an important basis for analyzing the mechanical properties and using performance of structural parts and components. A typical fracture process consists of four stages: fatigue cracks occur, cracks propagate, micro-cracking, and brittle fracture.

At the early stage of crack development, fatigue cracks generated from the surface of 45 steel. With the continuous development of fatigue cracks, the cracks will penetrate into the material along the 45 steel substrate, which is usually accompanied by a large amount of grain tearing, obvious shear bands and dimples. This stage is called crack propagation period.

In the crack propagation stage of 45 steel after heat treatment, the micro-cracking forms in the forefront of the crack propagation. During this period, many small micro-cracks appear in the mating crack section during the crack propagation process. Its characteristics are that the surface of the micro-crack has obvious feathery and irregular stripes and large area of mirror surface. In the crack propagation process, the toughness of the material decreases accordingly.

In the final stage of fracture process, due to the difficulties of 60CrSi steels plastic deformation, 45 steel would fracture. Under normal circumstances, the fracture is characterized by nearly perpendicular to the tensile force direction, and the fracture surface is smooth and bright.