Characterization of the Microstructure and Mechanical Properties of A588 Weathering Steel After High Temperature Hardnes

A588 weathering steel is a high strength low alloy (HSLA) steel that contains copper and other weathering elements. It is widely used in structural and architectural applications due to its corrosion resistance and good mechanical properties. However, exposure to high temperatures can affect its microstructure and mechanical properties, which may compromise its structural performance. In this study, we characterized the microstructure and mechanical properties of A588 weathering steel after high temperature hardness testing.

Experimental Procedure

A588 weathering steel samples were prepared by cutting 10mm thick plates of the steel into 10mm x 10mm x 10mm cubes. The samples were then heated to 700°C for 1 hour in a muffle furnace to simulate high temperature exposure. After cooling to room temperature, Rockwell hardness testing was performed on the samples using a Rockwell hardness tester with a 150 kgf load. The microstructure of the samples was characterized using optical microscopy and scanning electron microscopy (SEM). Tensile tests were also performed on the samples using a universal testing machine to evaluate their mechanical properties.

Microstructure Characterization

Optical microscopy revealed that the microstructure of the A588 weathering steel after high temperature hardness testing consisted of a mixture of ferrite and pearlite, with some areas of coarse pearlite and spheroidized cementite. SEM analysis showed that the grain size of the ferrite was larger than that of the original steel, indicating that recrystallization had occurred during heating. In addition, the distribution of cementite was more uniform in the high temperature samples compared to the original steel.

Mechanical Properties

The Rockwell hardness tests showed that the hardness of the A588 weathering steel increased significantly after high temperature exposure. The average hardness values for the original steel and the high temperature samples were 85 HRB and 94 HRB, respectively. This increase in hardness can be attributed to the formation of pearlite and spheroidized cementite, which are harder phases than ferrite. However, the increase in hardness came at the expense of ductility, as the high temperature samples showed a significant decrease in elongation at break compared to the original steel. The average elongation at break for the original steel and the high temperature samples were 23% and 8%, respectively.

Tensile testing showed that the high temperature samples had lower yield strength and ultimate tensile strength compared to the original steel. The average yield strength and ultimate tensile strength for the original steel and the high temperature samples were 345 MPa and 444 MPa, and 468 MPa and 604 MPa, respectively. This decrease in strength can be attributed to the loss of precipitation hardening due to the dissolution of copper and other alloying elements at high temperatures. The decrease in strength and ductility of the high temperature samples can compromise their structural performance under load, especially in situations where the steel is exposed to high temperatures.

In conclusion, our study showed that exposure to high temperatures can significantly change the microstructure and mechanical properties of A588 weathering steel. The microstructure of the steel after high temperature hardness testing consisted of a mixture of ferrite and pearlite, with some areas of coarse pearlite and spheroidized cementite. The hardness of the steel increased significantly, but this increase in hardness came at the expense of ductility. Tensile testing showed that the high temperature samples had lower yield strength and ultimate tensile strength compared to the original steel, which can compromise their structural performance under load. Therefore, it is important to consider the effects of high temperature exposure on the properties of A588 weathering steel in structural and architectural applications.