Discussion on Mechanical Properties of SS330 and SS4O0 Continuous Casting and Rolling Coil Wipers
pick Summary : Through the research on the mechanical properties of SS330 and SS4O0 continuous casting and rolling strip strips and the representativeness of test samples , it is concluded that the thin slab continuous casting and rolling control process system of Tangshan Iron and Steel Co., Ltd. is reasonable , and the mechanics of hot rolled strip strip strips The performance and metallographic structure are uniform . The properties of the sample at 4m from the end of the finished strip are very representative of the properties of the entire coil .
Keywords : Thin slab continuous casting and rolling ; coil ; mechanical properties of strip ; metallographic structure
The production of hot-rolled thin plate is strip rolling, and the uniformity of the mechanical properties of the product has a great relationship with the temperature of the rolling process and the controlled cooling process, especially the controlled cooling process has a great influence on the uniformity of the mechanical properties of the product . The thin slab continuous casting and rolling production line of Tangshan Iron and Steel Co., Ltd. adopts the laminar flow cooling process. The cooling water volume is adjusted according to the rolling speed and thickness of the strip steel to achieve the required cooling rate, so that the entire length of the strip steel can be cooled uniformly and achieved at the expected coiling temperature. coiled . At present , Tangshan Iron and Steel Co., Ltd. takes samples 4m away from the end of the steel strip , and its properties represent the mechanical properties of the entire steel coil . The representativeness of the production samples and the uniformity of the performance of the entire coil cleaning rod are demonstrated through the test method .
17 groups of samples were selected for the test , including 6 groups of SS330 samples and 11 groups of SS400 samples . For each group of samples, select one piece from the head , middle and tail of the same steel coil .
2 Mechanical properties of cleaning rods for SS400 and SS330 coils
2.1 SS400 coil
Among the 11 groups of SS400 steel coil samples , the product thickness is 2.5-3.6mm , which is very representative of SS400 products . The average distribution value of the mechanical properties of each group of samples is obtained by sampling the head , middle and tail of each coil of strip steel for mechanical performance inspection , as shown in Figure 1 , and compared with the production samples taken at 4m from the tail end of the strip steel ( below Refer to Figure 2 for comparison .
It can be seen that for SS400 strip steel with a thickness of 2.5-3.6mm , the distribution of the mechanical properties of the cleaner is :
- Tensile strength : 476MPa at the end of the strip , 480MPa at the middle , and 496MPa at the head , increasing in turn , but the strength values at the tail and the middle of the strip are closer .
- Yield strength : 340MPa at the end of the strip , 346MPa at the middle , and 351MPa at the head , increasing sequentially .
- Elongation : The elongation of the highest end of the middle strip near the tail is the same as the elongation of the production sample .
- Yield strength ratio : The yield strength ratio of the strip steel head , middle and tail is basically the same .
Since the location of production sampling is 4m away from the strip tail , Therefore, the test data obtained at the end of the strip and the production sample data
It fits perfectly , no aging phenomenon occurs . This shows two points : first, the performance of the coil cleaner is relatively stable and uniform ; second, the strength of the head and middle of the coil is higher than that of the tail , and the data of the production sample inspection can meet the mechanical performance requirements of the entire coil . Therefore , the production data of the sample at 4m from the end of the strip is very representative . The reason for the difference in the mechanical properties of the head , middle and tail of the strip is that the cooling strength of the head and middle of the thicker steel strip is the same , but the head of the coil is close to the mandrel of the coiler , and is affected by the cooling water of the mandrel. Influence , the temperature drops faster , so the strength of the head is higher , and the tail is in order to compensate the influence of the temperature drop of the outer layer after coiling , the cooling temperature is controlled higher, so the performance is lower . But overall , the strength value of SS400 is higher than the standard ( standard 400MPa< Ob <510MPa) o
2.2 SS330 coil
6 groups of SS330 samples collected in this test are
13mm, which is very representative of the production products . and
SS4O0 coil is the same , and the test data and production sample data of different parts performance of SS330 coil head , middle and tail are obtained . The results show that the mechanical properties of the tail and the middle of the SS330 coil are the same , and the tensile strength is 404MPa, while the performance of the head is relatively low , 384MPa . This is consistent with the fact that when rolling thin-gauge strip steel in actual production , in order to ensure that the strip steel runs smoothly on the roller table and prevent the strip steel head from buckling , laminar flow cooling is not performed at the strip steel head for more than ten meters . The mechanical properties of the tail and the middle of the strip are similar, which indicates that the mechanical properties of the strip are better . In addition , the test results show that the tensile strength and elongation of the test strip steel are equivalent to the tensile strength and elongation of the production sample data , indicating that the tensile strength and elongation of the strip steel production data can represent the entire coil Strip tensile strength , elongation . Although the head of the strip is not cooled by water , its strength is 20MPa lower than that of the tail ( the length of this part of the strip is more than ten meters, accounting for about 2 % of the total length ) , but according to the test data , the head of the strip with lower strength is stronger than the standard Also higher than 50MPa . Therefore, it can be concluded that the mechanical properties of Tangshan Steel's SS330 strip steel can meet the standard requirements . In order to make the mechanical properties of the coil more uniform , under the condition of ensuring the normal threading of the thin strip , the head of the strip can be properly cooled with water to improve the strength of the head of the strip and improve the mechanical properties of the middle and tail of the strip. more consistent . .
- Metallographic structure of SS330 and SS400 strip steel
The metallographic structure of SS330 and SS400 steel strips is shown in Figure 5. From Figure 5 , it can be seen that the metallographic structure of the strip coil is uniform, and the structure of SS400 is composed of pearlite and ferrite . The ferrite is needle-shaped and the grain size is 6 ~ 11m . _ The microstructure of SS330 is ferrite and pearlite , the microstructure is equiaxed grains , and the grain size is 6-12 % .
The cold process system is reasonable , which can well meet the requirements for the stability and uniformity of the mechanical properties of the product .
- The average strength of SS330 and SS400 steel strips is relatively high , but the coiling temperature is not low , which shows that the contents of C and Mn in the chemical composition are relatively high .
- The performance of the sample taken at 4m from the end of the finished strip during production is very representative of the performance of the entire coil .
- and properties of the hot-rolled strip are uniform , and the grain size is 6 ~ 11mm , which can meet the requirements of users .
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