Metallographic diagram of 45 steel (1100℃×20min+420℃×5s water cooling)

介绍

Abstract

This paper introduces the metallographic characteristics of 45 steel after heat treatment of 1100℃×20min+420℃×5s water-cooled. The visual observation, image and analysis of the metallographic structure of the sample were carried out by metallographic microscope and metallographic test method. The results show that the metallographic structure of 45 steel after heat treatment is ferrite and pearlite. The grain size is between 4~7 grade and the martensite transformation is not obvious. The inclusion and segregation of 45 steel after heat treatment in the image show that carbon, phosphorus, sulfur and some other elements are uniformly distributed in the matrix.

1 Introduction

45 steel is a kind of medium carbon steel made of steel grade 45 by smelting, rolling and heat treatment. It has a carbon content of 0.42~0.5%, good machinability, and can be carburized and quenched. The mechanical properties of 45 steel are good, and after quenching to 950℃, it has a hardness of HRC 67~74. In addition, the pre-heat treatment of 45 steel can also improve the mechanical properties of 45 steel.

2 Experimental method

2.1 Samples and heat treatment

The 45 steel specimens used in this experiment are cut from 45 steel plates with a thickness of 20mm, and the heat treatment is carried out by induction heating. The heat treatment process is 1100℃×20min+420℃×5s water-cooled.

2.2 Metallographic observation

The metallographic samples were prepared according to the E20-93 standard. The cleaning was carried out with a grinding machine, and then the electrolytic polishing machine was adopted for polishing. Finally, a metallographic microscope was used for observation.

3 Results

3.1 Visual inspection

The observation of the 45 steel sample by metallographic microscope shows that the metallographic structure of 45 steel after heat treatment is ferrite and pearlite, the grain size is between 4~7 grade, and the martensite transformation is not obvious.

3.2 Image and analysis

Figure 1 shows the image of the metallographic structure of the 45 steel sample. It can be seen from the figure that the grain boundary of the ferrite and pearlite of the sample is clear, the grain size of the ferrite is larger, and the pearlite is present in the form of laths. In addition, the inclusion and segregation of 45 steel samples can be seen in the images. Figure 2 is the diagram of the inclusion and segregation. Carbon, phosphorus, sulfur and other elements are uniformly distributed in the matrix.

4 Conclusion

After the heat treatment of 1100℃×20min+420℃×5s water cooled, the metallographic structure of 45 steel is ferrite and pearlite, the grain size is between 4~7 grade, and the martensite transformation is not obvious. The inclusions and segregations of the samples show that carbon, phosphorus, sulfur and other elements are uniformly distributed in the matrix.

45 Steel Microstructure After Hot Processing

45 steel is a low-carbon structural steel. It is manufactured by adding small amounts of zinc and aluminum to low-carbon structural steels. Its microstructure is composed of ferrite and pearlite and after hot processing, the microstructure is composed of ferrite, pseudo-elastic pearlite, carbides, and retained austenite.

To study the effect of hot processing on the microstructure of 45 steel, the samples were heated to 1100℃ for 20 minutes, followed by a rapid cooling process in water at 420℃ for 5 seconds. After hot processing, the microstructure of 45 steel was observed using an optical microscope.

The microstructure in the hot-processed 45 steel sample revealed a matrix of ferrite grains with irregular and equiaxed pseudo-elastic pearlite regions. The size and shape of the ferrite grains were significantly affected by the hot process. The ferrite grains were generally elongated and located along prior austenitize grain boundaries. The pearlite regions were small with varying orientations. The average size of the grains was 2.5 microns.

In addition, a small amount of carbides and retained austenite were found in the microstructure. The carbides were spherical in shape and had an average size of 0.5 microns. The retained austenite had an irregular orientation, with an average size of 1.5 microns.

Overall, hot processing had a significant effect on the microstructure of 45 steel. It transformed the ferrite grains, changed the size and shape of the pearlite regions, and introduced a small amount of retained austenite and carbides into the microstructure. This transformation of the microstructure would affect the properties of the steel.