JPS583704A - Production of extra thick steel plate - Google Patents

Abstract

PURPOSE:To facilitate press sticking in the parts which are not press-stuck such as porosities in the stage of hot rolling and to improve the productivity of extra thick steel plates by differentiating the cooling rates on the front and rear surfaces of an ingot in a spraying zone, and displacing the final solidifying region of the ingot in the thickness direction of said ingot. CONSTITUTION:In a spraying zone, an ingot 5 is cooled by decreasing the flow rate of cooling water on the curved outside surface side thereof and increasing the flow rte of cooling water on the curved inside surface side. Then, solidification progresses earlier on the inside surface side where the flow rate of cooling water is larger than on the outside surface side where said flow rate is smaller and this makes the coefft. of the solidification larger on the curved inside surface side than on the curved outside surface side, thereby making the curved inside surface side larger than the outside surface side. The final solidification region 6 inevitably moves to the curved outside surface side. If it is desired to move the region 6 to the curved inside surface side, the ingot is cooled reverse from the above. As a result, the compressive stress in the thickness direction in the stage of rolling increases and the internal defects such as nonpress-stuck porosities, etc. in the extra thick steel plate are improved considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION When manufacturing extra-thick steel plates using a continuous casting method, the present invention aims to reduce the final solidification region of a slab, that is, the area where defects such as center segregation and procity are likely to occur, in the thickness direction of the slab. The present invention relates to a method for producing an extra-thick steel plate, which aims at obtaining an extra-thick steel plate with excellent internal quality by making it easier to penetrate the final solidification zone during rolling of the thick plate by displacing *-1 to □.

When slabs for extra-thick steel plates are manufactured using the continuous casting method, a final solidification region where defects such as center segregation and porosity are likely to occur occurs on the thickness center line of the slab, which is a major material defect in extra-thick steel plates. It is known. This occurs because the final solidification zone is located on the center line of the plate thickness of the slab, making it difficult to penetrate the slab through rolling, resulting in no compression bonding, and this phenomenon becomes more pronounced as the plate thickness increases. Measures to improve defects such as unbonded porosity include (1) a method of reducing the final solidification itself in the steelmaking stage, and (2) a method of compressing the final solidification region in the rolling stage.

Methods for (2) include dehydrogenation in the steel through degassing treatment, but unlike the case of steel ingots, the final solidification region of continuous slabs is determined only by metallurgical factors, and is unique to continuous casting machines. Since many grains are also affected by mechanical factors, it is extremely difficult to find a grain that suppresses the occurrence of the final coagulation zone. In addition, as the method (2), there are known methods such as strong reduction rolling using a large diameter roll, increasing compressive stress in the thickness direction using a large forging press, and applying pressure for a long time using a large forging press. Strong reduction rolling using large-diameter rolls is economically problematic because the cost of the rolling mill itself and manufacturing costs are high, and large forging presses are expensive and have low productivity.

This invention was made in view of the current situation,
This paper proposes a method for manufacturing extra-thick steel plates that can produce extra-thick steel plates with better internal quality than continuous cast slabs.

The gist of this invention is to manufacture slabs for 6 extra-thick steel plates by a continuous casting method, and to displace the final solidification zone in the thickness direction of the slab by varying the rate of solidification on the front and back surfaces of the slab in the spray zone. The method is characterized in that after the rolling process is carried out, normal hot rolling is carried out.

When manufacturing extra-thick steel plates from steel ingots or slabs, the compressive stress in the thickness direction during rolling increases as it approaches the surface of the rolled material, and the compressive stress in the thickness direction increases when heavy reduction rolling is performed. It is also known that the amount of increase is larger on the surface side than in the center. Therefore, the inventors increased the crimping effect of the final solidification zone in the rolling stage by displacing the final solidification zone of the continuous slab toward the surface layer, and obtained the same effect as the increase in compressive stress caused by strong rolling. This is what we are trying to do.

In continuous casting, a solidified shell is formed in the mold,
Solidification progresses through forced cooling in the spray zone, but in conventional operations, for example, in the case of curved continuous casting, the cooling rate on the curved inner surface and the curved outer surface of the slab is the same.
The final solidification zone is located approximately on the center line of the thickness of the slab. The inventors focused on this point and developed a method of varying the cooling rate on the curved inner surface side and the curved outer surface side of the slab in the spray zone, as a method of displacing the final solidification zone of the continuous slab toward the surface side. I took it.

According to this method, it is possible to vary the rate of solidification progress on the curved inner surface side and the curved outer surface side of the slab in the spray zone, so it is possible to displace the final solidification region in the thickness direction of the slab, and the end Since the solidification zone can be moved to the surface layer side where it is easy to permeate during rolling, center segregation and
It becomes easy to press the uncrimped parts such as porosity, and as a result, an excellent extra-thick steel plate without internal defects can be obtained.

FIG. 111 is an example of a cooling pattern showing a specific example for carrying out the method of this invention. ! In Il, (Ri is mold,
(Ri is the spray band, (11 is the guide roller, (4) is the drawing roller, Sono is the slab, +11 is the final solidification area, respectively, ξζ is the curve of the slab - the inner side is strongly cooled, and the curved outside side is An example of a cooling pattern when weakly cooling is shown.

In other words, in the spray band, the curved outer surface of the slab is cooled with a small amount of cooling water, and the curved inner surface is cooled with a large amount of cooling water.As a result, the inner and outer surfaces of the curved section The length of the solidifying shell on the side is that the inner surface, where there is a large amount of cooling water, solidifies faster than the outer surface, where the amount of cooling water is small. The inner surface of the curve is closer to the outer surface, so the final solidification region (・) will inevitably move toward the outer surface of the curve.If you want to move the final solidification region toward the inner surface of the curve, do the above. The slab may be cooled by the opposite method.

Like Jin, according to @11k of ξ, the spray zone is ζ
By cooling the slab with appropriate differences, it is possible to shift the position of the final solidification zone in the thickness direction, so it is possible to produce a slab in which the final solidification zone is located in the surface layer S. This makes it possible to increase the compressive stress in the thickness direction during rolling, which is expected to have a great effect on crimping defects such as procities. The resulting internal defects can be greatly improved.

Next, embodiments of the invention will be described.

〔Example〕

Steel having the components shown in Table 1 was continuously cast in a two-strand curved slab continuous casting machine at a casting temperature of 1535°C and a drawing speed of 0.B IIl/mln, with cross-sectional dimensions of 2005w x 1600mm. A slab of (2) was manufactured.

At the time of ξ, the slab of the first strand is cooled by the cooling pattern shown in Table S2 in each zone shown in Fig. 1 by implementing Jin's invention, and the final solidification area of the slab is displaced toward the outside of the curve. I let it happen. At that time, the changes in the solidified shell thickness depending on the strip position were as shown in Table 3.

The thickness of the solidified shell was measured by driving a stud into the slab. The other second strand slab is solidified in the usual manner.
It was covered.

The dimensions of the slab obtained in this way are 200 x 160
After cutting to 0 x 3500 x and heating to a predetermined temperature, a thick steel plate with a piezoelectric rolling reduction of 10 to 30% in one pass was produced using a normal hot piezoelectric method. As a result of inspecting each thick steel plate using sonic flaw detection, it was found that unbonded porosity was found in slabs produced by the conventional method using the second strand.
However, in the slab manufactured by the method of the present invention using the first strand, there were no defects caused by unbonded porosity. This can be inferred to be due to the fact that the final solidification zone of the slab underwent surface JIK displacement, which prevented penetration of the reduction during rolling and crimped the center porosity.

Table 1 1 @*Acid formation Minute 12 Table Cooling Pattern

[Brief explanation of drawings]

The drawings are explanatory diagrams showing one embodiment of the present invention. l-mold, 2-spray band, 3-guide roller,
4-drawing roller, 5-slab, 6-final solidification zone.

Claims (1)

[Claims] When manufacturing slabs for extra-thick steel plates using the continuous casting method, the solidification cooling rate of the front and back surfaces of the slab in the spray zone is varied.
A method for producing extra-thick steel plates, which comprises displacing the final solidification zone in the thickness direction of the slab and then performing normal hot rolling.