JP4580046B2 - Method for straightening rolled shaped steel - Google Patents

Abstract

A steel profile, which at least during straightening has a largely homogeneous temperature distribution over its cross section, is straightened at a temperature within the structural transformation range from Ar1 to Ar3 of the steel.

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for straightening rolled shaped steel.
[0002]
[Prior art]
The rolled section steel, for example double T-section steel, U-section steel or angle material, is generally cooled on a cooling bed. Shape steel is distorted by uneven cooling. This strain has a detrimental effect on the straight and internal stress states of the section steel. As common to these two above-mentioned quality standards, the flatness at the time of sheet steel rolling is compared with this quality standard. When straightness is reduced (i.e., shape warping, twisting and bending warping (distortion caused by bending)), often high internal stresses are induced. Warped shapes must be post-treated. Internal stress reduces the load capacity of the shape steel.
[0003]
The cause of warpage is attributed to the acceptable dimensions of one or many straightening steps at low profile temperatures in the known art. In this regard, roller-type straighteners and press-type straighteners are used.
[0004]
In this case, a roller type straightening machine that continuously corrects the shape steel first sets a new warpage of the shape steel to a certain size. In this case, the existing internal stress is removed by the newly determined internal stress. However, this is not possible in principle over the entire cross section of the section steel. Within the region of neutral fibers outside the station, an unaffected material region remains during the entire correction process. After the first bending stroke, the product is subjected to a constant bending alternation (multiple warping alternations). At that time, the internal stress is deformed so that the shaped steel becomes straight after the straightening process. Residual internal stress remains fundamentally intact. The internal stress remaining in the shape steel with the above-mentioned problems in terms of load capacity as a shape steel is disadvantageous. In addition, severely warped sections cause problems during the straightening process (eg introduction into a straightening machine).
[0005]
In a press-type straightening machine that works discontinuously, the section of the section that is gradually warped to an unacceptable level is corrected by applying a bending that antagonizes as accurately as possible. Interference with internal stress is not possible with press straighteners. The unknown internal stress state, which is discontinuous after the straightening process, adversely affects the load capacity of the section steel. This method impedes material flow in the manufacture of shape steel and takes a lot of time for correction.
[0006]
Furthermore, methods and devices for selectively cooling the shape steel during rolling operations are known from known techniques (see Stahl and Eisen, 109 (1989), pages 171-176). Depending on the mass distribution of the heterogeneous steel, the shaped steel is cooled unevenly. With selective cooling, a sufficiently uniform temperature distribution can be achieved across the cross section of the section. This improves the material properties of the product. In order to provide selective cooling, the rolling line is provided with a cooling device, which enables rolling at a normal rolling speed. These cooling devices are adjustable, so that it is possible to cool various sizes of steel. Similarly, it is known from this known technique that the heat treatment of the shape steel is performed using the heat of rolling in the flow of the rolling operation.
[0007]
[Problems to be solved by the invention]
Based on the above-mentioned known technology, the problem underlying the present invention is that of a structural steel that is excellent in quality and has little warpage and little internal stress without impairing the material flow during the production of the structural steel. It is to provide a method of straightening the rolled shape steel that allows production.
[0008]
[Means for Solving the Problems]
The present invention, so as to have a temperature distribution that varies in a sufficiently uniform and the longitudinal direction in its cross-section by the shaped steel is heated to a temperature of 700 ° C. or less, the structural steel transformation range of the lower limit Ar ₁ It is solved by correcting at the temperature just below .
[0009]
The shape of the cooled section is essentially dependent on the shape and temperature distribution of the section of the section at the point where the hottest region of the section is just below the temperature Ar ₁ (end of transformation). It uses the recognition that it is. The shape occupies at this point of the shape steel remains as it is, with a completely uniform temperature distribution after the shape steel is completely transformed.
[0010]
The present invention is based on the idea that this point in the technical sense of uniform temperature distribution across the cross section of the section steel is used to correct the steel material shape. In this case, the present invention has a sufficiently uniform temperature distribution and corresponds to all temperatures in the transformation region Ar ₁ -Ar ₃ .
[0011]
The straightening of the shape steel is performed by pulling or upsetting. Due to the selection of the uniform temperature distribution as well as the correction temperature according to the invention and the subsequent selection of the correction time point, the section steel is thermally and uniformly transferred into the α region without any internal stress. This ensures that the above conditions are completely cooled to ambient temperature, even if the shape steel is warped and / or elastically tensioned again until it is completely cooled, based on uniform cooling. Will be maintained even after ending.
[0012]
Due to the advantageous configuration according to the invention, the section is at a temperature in the vicinity of the lower limit Ar ₁ of the transformation zone, especially when the temperature is just below Ar ₁ . Is because internal stress sometimes occurs in the phase of tissue remodeling of steel materials (Ar ₁ -Ar ₃₎ is immediately collapsed.
[0013]
Optionally, a uniform temperature distribution across the cross section is obtained by appropriately adjusting the temperature of this section during rolling of the steel.
[0014]
The present invention will be described in detail with reference to the embodiments of the invention shown in the accompanying drawings.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The shape steel HEB 140 has a virtual initial warp with a curvature radius of 200 m. By selective water cooling, a sufficiently uniform temperature distribution was achieved at about 700 ° C. across its entire cross section.
[0016]
FIG. 1 shows the residual warpage expected after cooling the shape steel to ambient temperature depending on the temperature at the time of straightening by tension. It can be clearly seen that no residual warping can be expected at a tensile temperature of 700 ° C.
[0017]
FIG. 2 shows the expected relative maximum values of the pressure internal stress and the tensile internal stress of the section steel depending on the tensile temperature. The upper curves each show the expected relative maximum value of the pressure internal stress of the section steel, while the lower curve shows the respective maximum value of the tensile internal stress of the shape steel . From FIG. 2, it can be clearly seen that for a tensile temperature of 715 ° C., both a slight pressure internal stress and a tensile internal stress occur, and at the same time the expected residual warpage is actually zero (see FIG. 1 for this matter). Please refer.)
[0018]
FIG. 3 of course shows a diagram corresponding to FIG. 1 for a straight section C240 for the moment due to its own weight. Again, selective water cooling on the outside of the flange achieved a uniform temperature distribution across the section of the section at temperatures below 700 ° C.
[0019]
This section steel has no warp at tensile temperatures of 712 ° C, 702 ° C and 570 ° C. However, from FIG. 4 showing a diagram made with respect to the structural steel C240 corresponding to FIG. 2, when trying to eliminate the residual warp, the relatively low pressure internal stress and tensile internal stress of the structural steel only at 570 ° C. Can be expected. A slight internal stress-accepting the occurrence of a slight residual warp-can be achieved when the section steel C240 is pulled at a temperature of 720 ° C or higher.
[0020]
In embodiments of both inventions, it can be said that when a homogenization temperature other than 700 ° C. is selected, other combinations of residual warpage and internal stress occur.
[0021]
The application of the straightening method according to the invention is also possible when the temperature distribution is uniform over the entire cross section, but changes in the longitudinal direction of the section steel. Different flow tensions based on non-uniform temperature distribution across the longitudinal axis of the section steel are equalized due to the different rate of shape change, so a plastic flow is expected along the entire section steel and the basic strength is the highest. You can't expect it only in a few places.
[0022]
【The invention's effect】
By the method according to the present invention, it is possible to produce a shape steel which is excellent in quality and has little warpage and little internal stress without impairing the material flow during the production of the shape steel.
[Brief description of the drawings]
FIG. 1 is a diagram showing straightening of a section steel HEB140.
FIG. 2 is a diagram showing straightening of a section steel HEB140.
FIG. 3 is a diagram showing tension correction of a section steel C240.
FIG. 4 is a diagram showing tension correction of a section steel C240.

Claims (2)

In a method for straightening a rolled shape steel,
The section steel is heated to a temperature below 700 ° C. so that it has a temperature distribution that is sufficiently uniform over its cross section and varies in its longitudinal direction so that the section steel is at a temperature just below the limit Ar ₁ below the transformation zone. A method characterized by correcting . The method according to claim 1, characterized in that the temperature of the section steel is adjusted during rolling so that a uniform temperature distribution is achieved across the section of the section steel .

Images