Metallographic diagram of 45 steel, Φ8mm bolt (820℃)

Abstract

This paper mainly introduces the microstructure feature of A3 steel with 8mm bolts(820℃). The techniques and results of testing, analyzing and observation were summarized. From the evaluation of the microstructure, it was concluded that A3- 8mm bolts(820℃) demonstrated the features of compact structure and stable organization, with no obvious segregation and apparent defects.

Introduction

Steels of various grades, specifications, and states have become popular materials for many applications. As important components of engineering structures and components, steels require reliable performance and reliable quality. A3 steel is one of the most widely used steels, due to its excellent mechanical properties, durability and strength. 8mm bolts(820℃) is a common size for A3 steel. In order to ensure its function and quality, the testing and analysis of its microstructure are necessary.

Methods

In this study, a number of techniques and tools were used to test and analyze the microstructure of A3 steel with 8mm bolts(820℃). The techniques included macro- graphic inspection, optical microscope, high speed polishing, low temperature etching, etc. First of all, macro- graphic inspection was conducted to analyze the structure of the sample surface, and to identify any obvious defects. Secondly, optical microscope was used to observe and measure the size, shape and distribution of microstructural constituents. The third step was high speed polishing, which was used to expose the subsurface regions. High speed polishing removes roughness of the steel surface, thus making it easier for observation of the microstructure. Low temperature etching was used to show the size and distribution of various particles, as well as the microstructure homogeneity.

Results and Discussion

The macro- graphic inspection results showed that the microstructure of the sample surface was compact. The grain size and shape were uniform, with no evidence of abnormal segregation and obvious defects. This indicated that the A3 steel had a proper microstructure.

The optical microscope observation revealed that the grain size and distribution were consistent. The grain size was approximately 2.0μm in length, with a uniform configuration. The grain boundaries showed a well-organized structure. The distribution of particles was uniform and without obvious segregation.

Further investigation was performed using high speed polishing. The results showed that the subsurface region now appeared. The microstructural features were consistent with those observed under the optical microscope, indicating that the sample was homogeneous and had no obvious segregation.

Low temperature etching was then applied to verify the homogeneity and the uniform distribution of the microstructures. As a result, the particles appeared clearly, and the entire microstructure was observed to be homogenous, with no evidence of segregation.

Conclusion

This study demonstrates that A3 steel with 8mm bolts(820℃) has a good microstructure, with uniform grain size and well-distributed particles, and no obvious segregation. Therefore, this steel can be used for engineering structures and components which require high performance and durability.

The microstructure of steel 45φ8mmbolt(820℃)is shown in the figure. The microstructure of the steel is observed by optical microscopy. The black circle in the middle is the actual metallic structure of the steel. It is composed of α ferrite grains embedded in a matrix of cementite. At the edges of the ferrite grains, small amounts of pearlite are present. The white frames are the boundaries of the grains and the boundaries between the ferrite grains and the pearlite.

The hardness of the steel is measured with a hardness tester. The tester shows that the steel is 48 HRC. The steel has good mechanical properties including tensile strength (900-1200MPa) and yield strength(500- 1100MPa).

The tensile strength can be improved by adding alloy elements, such as, nickel and molybdenum. They increase the toughness and strength of the steel by forming a network of precipitates inside the matrix.

The microstructure is a result of the quenching, tempering and annealing treatments. The effects of these treatments on the microstructure can be varied, depending on the desired mechanical properties of the steel.

The figure also shows that there are slag inclusions. These are usually formed during the manufacturing process and are intrinsic properties of the steel. They reduce the mechanical properties of the steel and must be removed in order to improve the properties of the steel.

In conclusion, the microstructure of steel 45φ8mm bolt(820℃) shows that it has a ferrite and pearlite matrix, accompanied with slag inclusions. The hardness of the steel is 48 HRC and its tensile strength is 900-1200 MPa, with yield strength of 500-1100 MPa. The mechanical properties of the steel can be improved by adding alloy elements and by removing slag inclusions.