JPS5933441B2 - How to ensure uniform material properties of controlled rolled steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for ensuring uniform material properties of controlled rolled steel sheets.

Line pipes supplied for resource development in cold regions, which have become popular in recent years, are required to have high strength and toughness to accommodate use in extremely cold regions as well as higher pressure and larger diameter pipelines. be done.

When manufacturing steel plates for pipes that meet these requirements by controlled rolling, not only must the material properties meet those requirements, but there should be no variation in material within the same steel plate. The deformation conditions acting on the material can originally be constant over the entire rolling region, but in order to produce a controlled rolled steel sheet that has better material properties in terms of the above-mentioned high strength and high toughness, the controlled rolling conditions have to become even stricter.
As the conditions become more severe, large material non-uniformities occur, especially at the side edges of the steel plate.

This invention advantageously detects such material non-uniformities in all controlled rolled steel plates online using a combination of an infrared camera, etc. and a process computer, and instructs the appropriate cutting amount to the next process. As a result, we have found an appropriate processing method for producing controlled rolled steel sheets that can guarantee the required material properties in all parts of the steel sheet.

By the way, the product cutting position of a rolled steel plate has conventionally been determined by the shape of the steel plate after rolling, with emphasis placed on small stops.

Control-rolled steel sheets generally have uneven material properties at the ends of the steel sheet, but until now the required properties have not been very strict, so by simply cutting out the defective parts, the entire steel plate can be made to have uniform material properties. It was possible to do so.

However, in recent years, applications such as line pipes used in resource development in cold regions have become more demanding than ever before, and in addition to being used in extremely cold regions, transportation costs have also increased. There is a trend toward larger diameter pipes, higher internal pressures in transportation systems, and thicker pipes as a result. Demand for higher strength and toughness has increased.

Therefore, control-rolled steel sheets for pipes used for such purposes are inevitably subjected to strict controlled-rolling conditions.

In this case, the fate of a controlled rolled steel plate is that the temperature of the edge of the rolled steel plate is large during rolling, and the material quality after rolling is also different. Therefore, if the product cutting position of such a steel plate is determined using the same conventional method, a steel plate with uneven material will be produced, and if such a steel plate is welded, it will be difficult to manufacture and lay pipes. The brittle part due to the influence of welding heat and the defective part of the base metal continuously exist, and the pipe is exposed to the risk of destruction.

Further, it can be easily inferred that the material test values of the test material taken from the conventional sample collection position cannot be reliable representative characteristics of the steel plate.

Now, as mentioned above, in general control-rolled steel sheets, material non-uniformities as shown in FIG. 1 occur, although there are some differences depending on the severity of the control conditions.

The figure shows an example of the longitudinal direction of the steel plate, but research has shown that a similar tendency is observed in the width direction as well.

This material non-uniformity area is caused by a significant temperature drop around the steel plate during controlled rolling due to forced cooling, etc., and this area greatly deviates from the planned control conditions, resulting in abnormal yield stress and strength due to subsequent rolling. rise, significant deterioration of toughness (
In particular, this resulted in a sharp drop in impact energy.

The difference between the center and the periphery of the steel plate becomes larger as the thickness of the controlled rolled steel plate increases and as the finishing temperature of the steel plate is regulated lower, and the defective parts tend to become wider.

Based on the idea of detecting this defective part from the surface temperature distribution of the steel plate during the final finish rolling of controlled rolling, the inventors attempted to correlate this temperature distribution with the material test values, and found that it was very successful. We found that there is a correlation.

In other words, Figure 2 is an example of scanning measurement using an infrared camera of the surface temperature distribution of a steel plate that has undergone controlled rolling immediately after finishing, and shows that the surface temperature, which is almost constant in the center area of the steel plate, approaches the edges and side edges of the steel plate. It can be seen that the temperature drops rapidly.

In addition, the longitudinal temperature distribution and yield point (y, s
, ) and tensile strength T, S, ) are shown in Figure 3.

In this example, temperature ~ Y, S, correlation coefficient γ - 0.979 temperature ~ T
,S, A high degree of correlation is observed with a correlation coefficient γ = 0.987, and the temperature distribution in the width direction and Charpy absorbed energy (VE-45) investigated in the same way also have a temperature ~ vE −
There is a high correlation of 45γ=0.968.

(Refer to Figure 4) As a result of investigating many examples in this way, a very high degree of correlation was recognized in all of them, and the surface temperature of each side of the steel plate subjected to controlled rolling was measured immediately after finishing. It was confirmed that it was possible to distinguish between good quality parts and defective parts.

In other words, specifically, the part of the steel plate that is within a specified tolerance range (for example, the average temperature ±15°C) with respect to the average temperature at the center of the steel plate measured using an infrared camera, etc. is considered to be a high-quality part of the steel plate, and that part is commercialized. Alternatively, by collecting samples from the high-quality parts, a steel plate with uniform material properties inside the steel plate can be manufactured, and material test values that can be true representative values for the steel plate can be obtained.

Therefore, this invention makes it possible to manufacture steel plates with uniform material properties by identifying and determining the above-mentioned good quality parts and defective parts using a combination of an online small computer and an infrared camera, etc., and instructing the cutting process with the results in real time. That is.

In this case, it is necessary to guarantee that the material properties in the central region of the steel sheet, that is, the property stability region, satisfy the required performance, and for this purpose, a trial controlled rolling stage is set to satisfy the required performance required for the product steel sheet. In other words, the center of the above required performance range is determined by the distribution of the steel plate surface temperature in the rolling direction and/or width direction during the final finish rolling of the controlled rolled steel plate obtained through at least some rolling steps included in the controlled rolling schedule that matches the material and performance. The relationship between the target surface temperature in the area and the temperature difference with respect to the variation in required performance depending on the temperature distribution in the rolling direction and/or width direction is determined, and based on this, if necessary, the trial control rolling stage is modified as appropriate. In addition, for subsequent steel plates that have been subjected to controlled rolling through similar rolling steps, the surface temperature distribution during final finish rolling is scanned and measured, and areas that deviate from the allowable temperature difference corresponding to the required performance are discarded and cut. This ensures uniform material properties.

In addition, in this method, automatic plate thickness control devices (A, G, C,) are not used at least in some rolling stages during the controlled rolling process,
It goes without saying that by following this controlled rolling step in the controlled rolling of subsequent steel plates, it is possible to more accurately grasp the material distribution.

Hereinafter, embodiments of the method of the present invention will be explained using specific examples.

Chemical component (weight percentage) is C; 0.07%3i;
0.27%, Mn'', 1.61%, P; 0.15%, S
;0.006%.

v; 0.063%, Nb;
,s,)56. Absorbed energy at -40°C (VE-4
0) 7.0'KP-m or more, D, W, T, T, ductile fracture ratio SA at -40°C in the test, -4o 85% or more, thickness 32.0 mm, width 3700 mm .

Controlled rolling was carried out including the following trial controlled rolling steps to obtain a steel plate with a length of 20,000 mm.

Measure the temperature distribution in the rolling direction and/or width direction during the final finish rolling of the obtained control-rolled steel sheet, and investigate the relationship between the temperature difference and the corresponding required performance to determine Y, S, T, and S. Figure 5a and VE-40 Figure 5b (rolling direction) Figure 5C (width direction), 5A-
Figure 5d was obtained for 40.

In this example, the correlation coefficient of Y and S with respect to temperature difference is γY=0.
978, the same < T, the correlation coefficient of S is γ1 = 0.996,
Also, for vE 40, γE=0.990°0.97
A correlation as high as 0 was found.

According to this result, for the controlled rolling of the subsequent slab, the temperature distribution in the rolling direction and width direction during the final finish rolling of the controlled rolled steel plate obtained through controlled rolling including a controlled rolling stage similar to the trial controlled rolling stage described above was measured, In this example, the temperature difference is ±10 to meet the tolerance range for Y and S, which have the most severe requirements.
By cutting off the portions that deviate from ℃, it is possible to easily ensure a high degree of homogeneity in the material properties of the controlled rolled steel sheet.

Note that the trial controlled rolling stage described above must be appropriately selected depending on the characteristics and specifications of the steel plate to be produced, and if the material test results performed on the steel plate obtained thereby meet the required performance. Of course, if this is not the case, it is necessary to modify the controlled rolling schedule.

Next, on the side, the chemical components were C; 0.06%, Si; 0.
26%, Mn; 1.71%, p; 0.01 s%,
S; 0.006%, V; 0.042%, Nb; 0.
Y, 854.0~59.0~, T, S, 60
．． 0~ or more, VE-505, 5Kp-m or more, 5A-5
o Thickness: 19.0mm, width: 3mm, satisfying over 90% of required performance
Controlled rolling including the following trial controlled rolling step was carried out to obtain a steel plate with a length of 740mm and a length of 20.000mm, as shown in Fig. 6a.
Temperature difference correlation of Y, S and T, S shown in Figure 6.
VE-50 shown in c and SA-5o shown in Figure 6 d.
The temperature difference correlation was obtained.

As can be seen from Figure 6 a, b, c, and d, Y and S.

The correlation coefficients for the temperature difference between T and S are γY=0.
951 γT=0.975, γE=0.921, 0.
970, this also exhibits a high correlation.

Other examples are summarized below.

Chemical component (force) C; o, o O7, Si; 0.26, Mn'', 1
．． 68, P, 0.015, S; 0.006, V; 0
．． 038, Nb; o, o4゜Size (=1.-) 27゜0X3720X20,000 Required performanceThe relationship of Y, S, T, S with respect to the longitudinal direction temperature distribution is shown in Figure 7a. E- for the distribution
The relationship between 5o and 5A-50 is shown in FIG. 7c, and the relationship between 5A-50 and longitudinal temperature distribution is shown in FIG. 7d.

As described above, in this invention, the surface temperature of a control-rolled steel plate at the time of finishing is measured using an infrared camera or the like installed in the rolling line, and the average temperature in the center area of the plate surface is determined. Discard parts outside the allowable temperature range as determined by .

In this case, the allowable temperature range is determined by the severity of the chondral roll and the severity of the required characteristics.

This method is particularly effective when the product length tolerance is large, such as double random length steel plates for pipes.

The effects of this invention can be summarized as follows.

1. It is possible to produce controlled rolled steel sheets with uniform and high material properties.

2. Reliable material test values for the steel plate can be obtained by commanding the appropriate sampling location.

3. By using a small online computer to identify and judge good quality parts and defective parts, it is possible to quickly and accurately command the amount of defective parts to be cut.

4. Compared to the case where the amount of defective parts cut is constant in order to obtain uniform material properties, the method according to the present invention in which defective parts are determined for each individual steel plate leads to an improvement in plate reduction.

[Brief explanation of the drawing]

Figure 1 is a graph showing the longitudinal tensile test results of the controlled rolled steel plate, Figure 2 is a graph showing the surface temperature measurement results of the controlled rolled steel plate immediately after finishing, and Figure 3 is the temperature distribution (edge) and tensile test. Graph showing the results (longitudinal direction), Figure 4 is a graph showing the temperature distribution and Charpy impact test results (width direction), a, b, c, d in Figures 5, 6 and 7.
are Y and S with respect to the surface temperature of the controlled rolled steel plate, respectively. T! S, VE-4o or VE-50 and 5
It is a graph showing the correlation of A-5o.

Claims (1)

[Claims] 1. The distribution of the surface temperature of the steel plate in the rolling direction and/or width direction during the final finish rolling of the controlled rolled steel plate obtained through the trial controlled rolling stage set to meet the required performance of the product steel plate to the median value of the above required performance range. A subsequent steel plate that has been subjected to controlled rolling through the same rolling steps as the trial controlled rolling, with the target surface temperature and the relationship between the temperature difference and the variation in required performance according to the rolling direction and/or widthwise temperature distribution being determined. To ensure uniform material properties of controlled-rolled steel sheets, the method scans and measures the surface temperature distribution during final finish rolling, and cuts off areas that deviate from the allowable temperature difference corresponding to the required performance range. Method.