Quality Analysis of Q195 Trial-produced Thin Billet Continuous Casting and Rolling Steel Plate
the quality problems of the thin slab continuous casting and rolling trial production of Zhuzhou Iron and Steel Co., Ltd. Q195 , and hopes to be resolved as soon as possible.
•Keywords・Quality of steel plate Q195
. the Q195 steel plates sold to Lecong, Shunde were comprehensively tracked.
At the site, a random inspection of the appearance of 30037 coils was carried out, and no major problems were found, only minor edge cracks. According to the situation in the quality assurance certificate, the coil steel plate is 3mm, the steel type is Q195, and the weight is 15.85t. The chemical composition and mechanical properties are shown in the following tables 1 and 2 . '
Hong 1 |
|
chemical composition |
|
|
|
|
|
Yuan beard: |
c |
Si I Mn |
P |
S |
Cu |
al |
Volume % 0.044 ; 0.15 j 0.30 0.016 0.002 0.12 0.039
|
table 2 |
mechanical properties |
|||
|
project |
% |
° b |
-3% |
cold bending |
|
MPa |
345 |
| 420 |
34 |
qualified |
- Sampling situation
1# ～ 5# is continuous sampling, and sample is divided into 5 sections, long 8.7m ; 6# ~ 95 s * Take a large sample every 5.4 meters ( 67* is divided into two samples of 67A and 67 ); 96# ~ 99** is taken continuously, the sample is divided into 5 sections, and the length is 5.6 meters. The actual sampling is 100 large samples with a total weight of 1.65t . According to the sample taken above, the cumulative length of the coil is about 567nio
1# , 4# , 10# , 30\50" , 70# , 90# , 96# , and 99# in the above-mentioned I s -99 s sampling are respectively left, middle and right in the vertical rolling direction Three samples (the left and right samples are taken at 1/4 from the edge , and the middle sample is taken at the center of the steel plate), the sampling is shown in Figure lo
- test
2.1 Surface quality of steel plate
From the appearance, the steel coil has a slight edge crack; when the coil is opened and observed in detail, there are severe wavy horizontal lines of about 15m at the coil end, and the coil head also has a wave shape; regarding the plate shape, the thickness deviation fluctuates by 2.95~3.24mm , the difference between up and down is 0.29, and the width fluctuates
1252 ~ 1248mm .
2.2 Chemical Composition
The analysis samples come from the head, middle and tail of the coil. The sample number is 99 right ( 1), 50 right (2) and 1 middle ( 3) . See Table 3 .
Table 3 Coil Sample Chemical Composition
|
|
C |
S % |
Sn % |
P |
Mn |
Cu % |
Al % |
[0] |
[N] |
|
1 |
0.061 |
0.18 |
0.000 |
0.011 |
0.31 |
0.13 |
0.042 |
75 |
74 |
|
2 |
0.062 |
0.17 |
0.001 |
0.013 |
0.30 |
0.12 |
0.037 |
35 |
72.6 |
|
3 |
0.058 |
0.18 |
0.001 |
0.013 |
0.30 |
0.13 |
0.044 |
49 |
73.5 |
2.3 Mechanical inspection
2 for the yield strength, tensile strength and elongation of the transverse specimen along the length direction from the end of the roll . The average value is q = 320Mpa, a b - 400Mpa, 5=38% .
tensile strength and elongation of samples taken longitudinally and transversely at each sampling point are shown in Figure 3 . Corroded by 5% nitric acid alcohol, the structure is 20% pearlite , 80% ferrite , and the grain size is 7.1 . See Figure 5 .
- analyze
3.1 According to the mechanical properties, it shows that the mechanical properties of the product are stable, especially after a certain aging treatment, the comprehensive performance is better, more ideal, and can better meet the requirements of customers. The yield strength has dropped by 25Mpa, that is, it has dropped by 7.3 % . The tensile strength has dropped by 20Mpa, that is, it has dropped by 4.8%, and the elongation has increased by 11.8% . It is basically on a horizontal line from the head of the coil to the tail of the coil, but the mechanical properties of the vertical and horizontal directions have not been well concentrated on the line. , the degree of dispersion distribution is high, and the quality still has unstable factors.
|
aspect ratio |
Yield Strength |
Breaking strength |
Elongation |
|
maximum |
0.94 |
0.947025 |
0.85 |
|
the smallest |
1.07 |
1.055502 |
1.24 |
|
average |
1.00 |
1.00 |
1.02 |
3.2 The three samples of chemical composition are taken from the head, middle and tail of the coil, which are more representative to reflect the performance of the steel coil. Among them, the change of C is quite different from the original result, and carbon may be added in the continuous casting process. As a result, the quality of the covering agent in the bag should be strictly controlled to ensure the quality of the product. Regarding the gas situation [N] is relatively stable at about 73ppm , but the lowest content of the steel plate is 35ppm in the middle of the coil, followed by 49ppm at the head of the steel coil, and the highest is 75ppm at the end of the steel coil. The reason is probably that the slag radiates into the mold at the end of casting caused by. It is necessary to strengthen the operation and management of continuous casting operators at the end of pouring.
3-3 From the perspective of the structure, it basically meets the requirements of the steel plate. The sulfide and inclusions are relatively good, and the grains are relatively fine, which is 7.1 grade.
3.4 The problem of relative concentration of the steel coil is mainly that when the coil is opened, there are serious wavy horizontal stripes at the tail of the coil about 15 meters away, and the tail also appears, and the deviation of the thickness of the coil fluctuates ( 2.95 ~3.24). 0.29mm, the width also exists 1252 ~ 1248mm .
4. Conclusion
4.1 The Q195 steel plate produced by Zhugang has good mechanical properties, less inclusions and finer grains in metallographic examination. However, there are moderately severe waves and edge cracks in the surface quality, and recently there have been more mild to moderate scratches, pits, lapping and other defects, and the thickness deviation of the steel plate is relatively large.
4.2 The four links of process, production, quality and inspection are not well connected, and there is a lack of strong coordination mechanism and personnel.
4.3 There is no superficial quality inspection personnel and lack of training. The surface quality inspection and sampling were transferred from the steel rolling department to the technical department, but there has been no assigned staff, and no relevant internship or training has been arranged. At present, the surface quality inspection is only carried out by mechanical inspectors (there is also a shortage of mechanical inspectors). It is inevitable to lose sight of one another at work.
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