JPS62110802A - Production of differential thickness steel plate - Google Patents

Abstract

PURPOSE:To obtain a differential thickness steel plate having mechanical properties uniform over the entire length by rolling a thin-walled part and thick-walled part to the plate thickness larger than the target plate thickness without interruption in a pass before the final pass and continuously rolling the thin-walled part and thick-walled part to the target plate thickness in the final pass. CONSTITUTION:A hot rolling material 1 rolled to a uniform thickness is rolled to t+b thickness in the thin-walled part 11 and t+a thickness in the thick- walled part 12 in the pass n-k before the K-th times of the final pass n. The thin-walled part 11 of the material 1 is rolled to the thickness 4+b larger than the target thickness (t) in the pass n-1 just before the fine pass. The thick- walled part 12 of the material 1 is rolled to the thickness t+a larger than the target thickness T. The thin-walled part 11 and the thick-walled part 12 are finish-rolled to the target thickness t and T in the final pass n.

Description

DETAILED DESCRIPTION OF THE INVENTION (→Industrial Field of Application) The present invention relates to a method for manufacturing a steel plate with different thicknesses, in which the thickness of a single steel plate changes along the length thereof.

(b) Prior art In structures that are subject to static pressure, such as ships, pressure responders, and water gates, the thickness of the steel plate used in the lower part is increased and the thickness of the steel plate used in the upper part is decreased due to the difference in pressure. Designed. Therefore, conventionally, two types of steel plates with different thicknesses were joined by full welding.

In order to save this effort, steel plates with different thicknesses are required, and various methods have been proposed. For example, a method of reversing the rotation of the rolls during rolling (JP-A-48-38262, JP-A-48-60059), a method of rolling by cooling only one side of the rolled material during rolling ← Kaisho 49-2855
(No. 2), there is a method in which the roll gap of the rolling mill is increased during rolling to perform mid-way release.

However, in these methods, the rolled material is divided into a portion where rolling is applied and a portion where rolling is not applied in the final rolling pass from the leading end to the trailing end. As is well known, in hot working, the processed part
Recrystallization occurs due to processing strain. Then, recrystallized grains generated according to the temperature grow.

For this reason, when producing differential thickness steel plates, if there are areas where reduction is applied and areas where reduction is not applied in the differential thickness forming path of the liquid junction, recrystallization occurs at iK[ in the area where reduction is applied. In addition, in areas where rolling cannot be applied, recrystallized grains from the previous rolling pass grow, resulting in differences in crystal grain size or in the crystal structure itself. As a result, differences appear in mechanical properties such as tensile strength, Charvi test value, and hardness.

Furthermore, in the method of cooling one side of the rolled material, the temperature of the entire rolled material is lowered, which becomes a cause of poor flatness.

C. Problems to be Solved by the Invention The problems to be solved by the present invention are as follows:
An object of the present invention is to obtain a method for manufacturing a steel plate with different thicknesses, which can provide substantially equal mechanical properties to the entire steel plate.

B) Means for Solving the Problems The method for manufacturing differential thickness steel plates of the present invention involves rolling a hot-rolled material by changing the roll gap. In the passes, the thin and thick parts of the hot rolled material are continuously rolled to a thickness greater than the target plate thickness, and in the final pass, the thin and thick parts are continuously rolled to the target plate. The above problem is solved by rolling it thickly.

(E) Example A method for manufacturing a differential thickness steel plate according to the present invention will be described with reference to FIGS. 1 to 6.

As shown in FIGS. 1(c) and 0) and FIG. 2, in the series of differential thickness forming passes, the target thickness it of the thin wall portion 11 of the hot rolled material 1 is set, and the target thickness of the thick wall portion 12 is Let T be the target plate thickness.

Therefore, in the method of the present invention, after normal rolling is performed with a uniform thickness, in pass n-K before the final pass nOK times in a series of differential thickness forming passes, the thickness of the thin section 11 is t+bn- Also, the thickness of the thick part 12 is T+a
-K (Fig. 1 (A)), and in the pass n-1 immediately before the final pass n, the thickness of the thin section 11 of the hot-rolled material 1 is greater than the target thickness t. rolled to t + bnl, and
Thick wall part 120 target plate thickness T is also larger plate thickness T + an 1
(Fig. 1)).

Next, in the final pass n, the thin part 11 and the thick part 12 are finish rolled to [I mark thickness t and T, respectively (
Figure 2).

In the explanation in FIGS. 1 and 2, rolling is performed from the thin wall portion 11 to the thick wall portion 12 of the rolled material 1, but rolling may be performed in the opposite direction as shown in FIG. 6. . Further, as in the case of K=1, it is sufficient to provide only one stage of differential thickness forming path.

In addition, in order to compare with the conventional method, the rolling half-chewing method, which is a typical example of the conventional method, will be explained with reference to FIGS. 4 and 5. In this method, a pass 11--
1, the thin-walled portion 11 of the hot-rolled material 1 is rolled to the target thickness T of the thick-walled portion (FIG. 4)0. Then, in the differential thickness forming pass n or subsequent passes, the thin-walled portion 11 is rolled to the target thickness T of the thick-walled portion. The plate is rolled to a thickness of t (Fig. 5).At this time, the rolling of the thick wall [12] is not performed.

(f) Specific examples Steel materials with the components shown in Table 1, thickness 212cm x width 1
80C1a+X length from 2850th slab to thickness (22
,0m+25.0■) x Width 2150 dew x Length 8.5m
+10. '7n) differential thickness steel plates were manufactured.

The rolling pass schedule at that time is shown in Table 2.

Table 3 shows the test results regarding the mechanical properties of the product according to this example.

Table 6 As can be seen from Table 6, according to the method of the present invention, the difference in test values between the different thickness sections is small.

Furthermore, the length Lo of the differential thickness step portion 21 (sixth drawing) of the product 10 was 242 sa++ in the conventional method, whereas in the method of the present invention, LO=210 baskets, which is shortened by 32 m+. The reason for this is that in the conventional method, the chewing is done mid-way.
This is because it is necessary to remove the logic within the computer for AGC, which causes a time delay and increases the LO.

In addition, when collecting the test piece TP, in the conventional method (Fig. 6), it cannot be collected from the step part 21 of different thickness (because of the difference in mechanical properties), and the crop length is larger than LO. Become. On the other hand, according to the method of the present invention, since the material can be harvested from the stepped portion 21 of different thickness, the crop length becomes LO and the yield is improved (FIG. 7).

(g) Effects According to the method of the present invention, nearly uniform mechanical properties can be obtained over the entire length of the steel plate. For this purpose, the collection of test pieces can also be carried out at a lower yield rate. Furthermore, AGC (Automatic Gage Con
trol) is used in the differential pressure forming pass, it is possible to obtain uniform board thicknesses in the thin and thick parts.

[Brief explanation of drawings]

FIG. 1 to FIG. 6 are process explanatory diagrams showing the method of the present invention. FIG. 4 and FIG. 5 are explanatory diagrams showing the steps of the conventional method. FIG. 6 is an explanatory diagram of collecting a test piece from a product using a conventional method. FIG. 7 is an explanatory diagram when a test piece is collected from a product according to the method of the present invention. 1: Hot rolled material 11: Thin wall portion 12: Thick wall portion 10: Product 21: Differential thickness step portion TP: Test piece Patent applicant Sumitomo Metal Industries, Ltd. (5 others)

Claims (1)

[Claims] In a method of manufacturing differential thickness steel plates by rolling hot-rolled materials by changing the roll gap, the thin and thick portions of the hot-rolled materials are made larger than the target thickness in passes before the final pass. A method for producing a differential thickness steel plate, which comprises successively rolling the steel plate to the desired plate thickness, and rolling the thin-walled portion and the thick-walled portion to the target thickness in a final pass.