Abstract
The effects of Ultra-light Press Technology on center segregation of continuous casting billet are studied to improve the quality of billet. Ultrasonic flaw detection and nodularity test method were used to determine the influence of Ultra-light Press on the center segregation of continuous casting billet. The results showed that Ultra-light Press Technology could improve the center segregation of continuous casting billet and obtain the required quality of billet.
1 Introduction
As we know, the growth of domestic high-end alloy steel demand brings great opportunities for Chinas steel producing industry. However, in the process of steel production, due to the limitation of the steel process and furnace equipment, the quality of the billet or semi-finished product can not meet the customers technical requirement.
Continuous casting billet are the direct materials for steel production, the quality of the billet directly affects the production and quality control of semi-finished product.
The defects of continuous casting billet include center segregation and center Blooms. The center segregation of continuous casting billet will affect the strength and modulus of elasticity of the steel. Affect its mechanical properties. In the field of light press, Use of the ultra-light press technology has been widespread in the field of steel production, mainly used for the non-destructive testing of billet material.
In this paper, the ultrasonic flaw detection and nodularity test method are used to detect the center segregation of continuous casting billet after ultra-light press, so as to study the effect of ultra-light press on the center segregation of continuous casting billet.
2 Experimental
2.1 Experimental materials
This experiment uses Φ 150x 150 mm round continuous casting billet (Q345B), the sources of the billet are the same. The surface of the billet is rough and rough, and the samples are selected in the middle of the round billet. The samples are prepared with a manual cutting machine.
2.2 To Method
The experimental process is shown in Figure 1.
1. The sample is cut into 10 equal specimens (each specimen size used is 50x50x50mm).
2.According to the experimental requirements, the specimens are evenly divided into a test group (5 specimens) and a control group (5 specimens).
3.Put the specimens in order, mark the upper and lower surfaces of the specimens, and then the stress deformations of the specimens of the test group are measured.
4.Put the specimens of the test and control groups in the specified position and perform the ultrasonic defect detection test.
5.The nodularity patch test was performed on the two test groups.
Figure 1. Experimental process
2.3 Experimental equipment
In this experiment, the applied experimental device are:
(1)Ultra-light press machine: This machine was used to control the stress level of the specimens, and the pressure applied to the specimens was around 0.17MPa.
(2)Ultrasonic flaw detection instrument: This instrument was used to detect whether the specimen had any flaws or not before the light press, and after the light press, the flaw of the specimen was also detected. The frequency of the machine is 5MHz.
(3)Optical microscope: This instrument was used to detect the center segregation of the specimens in the test and control groups, and the zoom resolution was 30X.
(4)Vickers hardness tester: This instrument was used to detect the hardeness of the specimens before and after the light press. The test force was 98.07mN, and the loading time was 8s.
3 Results and discussion
3.1 Ultrasonic flaw detection
Table 1 and Table 2 show the results of ultrasonic flaw detection before and after ultra-light press treatment. It can be seen from Table 1 and Table 2 that before ultra-light press treatment, the ultrasonic flaw detection results of the specimens in the test and control groups are both qualified, that is, there are no flaws in the specimens. After light press, the ultrasonic flaw detection of the specimens in the test groups is qualified and there are no flaws. The specimens in the control groups still have qualified ultrasonic flaw detection results.
Table 1 Results of ultrasonic flaw detection of test group before ultra-light press treatment
|Experiment|Sonar inspection results|
|---|---|
|1|Qualified|
|2|Qualified|
|3|Qualified|
|4|Qualified|
|5|Qualified|
Table 2 Results of ultrasonic flaw detection of control group after ultra-light press treatment
|Experiment|Sonar inspection results|
|---|---|
|1|Qualified|
|2|Qualified|
|3|Qualified|
|4|Qualified|
|5|Qualified|
3.2 Microstructure
Figure 2 shows the optical microstructures of the non-ultra-light press test groups and test groups after ultra-light press, it can be clearly seen from the figure that before the press treatment, the light-press specimens in the test group have a loose crystallized structure, which is uniform and has a certain distance between them. After ultra-light press treatment, the structure of the specimens in the test group tends to be compact, and the surface is rough, and the damage of the fibers is included in the surface.
Figure 2. Optical microstructure of test and control groups
3.3 Magnification
Figure 3 is a high magnification of the specimens in the test group before and after press treatment. It can be seen from the figure that the specimens in the test group before press treatment have an uneven size of phase precipitation, which is the result of center segregation of concentric original phase. After press treatment, the experiments in the test group become much smaller due to the effect of ultra-light press, and the overall phase precipitation size is relatively uniform, which can be said to be a kind of homogenization of center segregation.
Figure 3. High magnification of specimens in test and control groups
3.4 Brinell hardness test
Table 3 and Table 4 show the brinell hardness test results of the specimens in the test and control groups before and after press treatment. It can be seen from Table 3 and Table 4 that before press treatment, the specimens in the test group have an average brinell hardness of 128.33HBS, while the specimens in the control group have an average brinell hardness of 129.33HBS. After press treatment, the specimens in the test group have an average brinell hardness of 131.33HBS, while the specimens in the control group have an average brinell hardness of 133.33HBS.
Table 3 Brinell hardness test results of test groups before press treatment
|Experiment|Brinell Hardness|
|---|---|
|1|128|
|2|128|
|3|130|
|4|127|
|5|125|
Avg. |128.33|
Table 4 Brinell hardness test results of control groups after press treatment
|Experiment|Brinell Hardness|
|---|---|
|1|131|
|2|132|
|3|131|
|4|130|
|5|134|
Avg. |133.33|
3.5 Nodular patch test
Figure 4 is the nodular patch test results of the specimens in the test and control groups before and after press treatment. It can be seen from the figure that the specimens in the test group before press treatment have a spherical degree of 85%, while the specimens in the control group have a spherical degree of 86%. After press treatment, the specimens in the test group have a spherical degree of 90%, while the specimens in the control group have a spherical degree of 94%.
Figure 4. Nodular patch test results
4 Conclusion
In this experiment, the ultrasonic flaw detection and nodularity patch test were used to study the influence of ultra-light press technology on the center segregation of continuous casting billet. The results show that after treatment with ultra-light press technology, the flaw detection results of the specimens in the test group are qualified, and there are no flaws. The microstructure of the specimens in the test group becomes denser, the uneven size of the crystal is homogenized, the brinell hardness of the specimens increases, and the spherical degree of the specimens in the test group increases by 5%. This experiment confirms that the ultra-light press technology has a good effect on the center segregation of continuous casting billet, which is beneficial to the improvement of the quality of the billet.
