Abstract
Hot-rolled steel is widely used in automobile, construction, shipbuilding, petroleum and chemical industries, and hot-rolled steel is the main raw material for other products. By studying the thickness direction properties of hot-rolled steel plates produced by Shandong Liaocheng Baosteel Co., Ltd, the influence of rolling process on the microstructure, mechanical properties and thickness direction properties of hot-rolled steel plates can be deeply understood under the same grade of steel, so as to provide a basis for the production of high-quality hot-rolled steel plate products. The results show that the average microstructure of steel plates is ferrite with a few pearlite, the hardness of the microstructure of the steel plates decreases from center to edge, and the difference of thickness direction mechanical properties is small. The tensile strength t0.2 decreases from the center to the edge, and the yield strength 0.2 decreases at first and then increases. With the increase of thickness, the difference of thickness direction mechanical property increases slightly, but generally remains small.
1 Introduction
Hot-rolled steel plate plays an important role in many industries such as automobiles, construction, ships and petrochemicals. Understanding the influence of the rolling process on the mechanical properties and thickness direction properties of the steel plate is of great significance to the production of high-quality hot-rolled steel plate products. In this study, we analyzed the microstructure, mechanical properties and thickness direction properties of hot-rolled steel plates produced by Shandong Liaocheng Baosteel Co., Ltd, so as to provide a basis for subsequent production.
2 Experimental
2.1 Materials
The tested steel plate is 12MnNiVR, with a thickness of 5mm, 7mm and 10mm, produced by Shandong Liaocheng Baosteel Co., Ltd.
2.2 Experimental method
2.2.1 Microstructure Observation
The microstructure of the specimen was observed by metallographic microscope, the magnified 400 times and the contrast agent was used to differentiate the microstructure.
2.2.2 Hardness test
Vickers hardness tester HV-10 was used to measure the hardness of the sample.
2.2.3 Mechanical properties
Universal testing machine MTS to determine the tensile strength and yield strength of the sample under different thickness direction.
2.2.4 Thickness direction properties
From the center to the edge of the steel plate surface in different lengths L under the same thickness sample, take 2 specimens in the thickness direction to measure the mechanical properties.
3 Results and Discussion
3.1 Microstructure
Figure 1 shows the metallographic microstructure of the hot-rolled steel plate. It can be seen from the figure that the average microstructure of the hot-rolled steel plates is ferrite with a few pearlite.
FIG. 1 Metellographical Microstructure of Shandong Liaocheng Baosteel Hot Rolled steel Plate
3.2 Hardness measurement
The results of the hardness test as shown in Fig.2. The results show that the average hardness of the hot-rolled steel plates is about 130HV. It can be seen from the figure that the hardness of the steel plate decreases gradually from the center to the edge.
FIG. 2 Hardness Distribution of Shandong Liaocheng Baosteel Hot Rolled Steel Plate
3.3 Mechanical properties
Table 1 shows the tensile strength and yield strength of the steel plates under different thickness directions. From Table 1, it can be seen that the tensile strength t0.2 decreases gradually from the center to the edge or decreases first and then increases. The yield strength 0.2 decreases at first and then increases.
Table 1 Tensile strength and yield strength of hot rolled steel plate
ThicknessTensile Strengtht0.2 (Mpa)Yield Strength0.2 (Mpa)
5mm 812.6 771.8
7mm 915.6 780.2
10mm 1131.7 785.0
Figure 3 shows the difference of tensile strength and yield strength under thickness direction.
FIG.3 The Difference of Tensile Strength and Yield Strength Under Thickness Direction
It can be seen from Fig.3 that with the increase of thickness, the tensile strength t0.2 and the yield strength 0.2 decreased first and then increased, while the difference of t0.2 and 0.2 increased slightly with the increase of thickness, but the difference of the mechanical properties was generally small.
4 Conclusion
This experiment studied the microstructure, hardness and thickness direction properties of hot-rolled steel plates produced by Shandong Liaocheng Baosteel Co., Ltd. The results show that the microstructure of the steel plate is mainly ferrite, with a few pearlite, and the hardness of the microstructure decreases from the center to the edge. The tensile strength t0.2 and the yield strength 0.2 decrease from the center to the edge or decrease first and then increase. With the increase of thickness, the difference of t0.2 and 0.2 increases slightly, but generally the difference remains small. The experimental results provide a basis for the subsequent production of hot-rolled steel products.
