JPH0525924B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a high-tensile invert (high tensile strength scalene angle shape steel) having excellent weldability. The applicant is
No. 28577 provides an efficient method for manufacturing an invert, and the present invention is suitable for the above-mentioned invention. (Background of the Invention) Invert is a structural steel section that is mainly used as a material for shipbuilding.In recent years, as efforts have been made to reduce the weight of ship hulls in order to save energy and cost, inverts have become more and more high-strength steel. is requested. Generally, high-strength steel for welded structures is shown in Table 1.
Representative examples are JIS G3106 and SM 50B. The carbon equivalent Ceq (=C+Mn/6+Si/24 +Ni/40+Cr/5+Mo/4+V/14) at the maximum element content shows a very high value of 0.453, but currently it is necessary to lower Ceq to around 0.37 to 0.42. being produced. However, from the viewpoint of weldability, the above carbon equivalent is too high.

【table】

[Table] As a result, when constructing welded structures using these high carbon equivalent steel materials, it is necessary to heat the steel materials before and after welding, or to use special Welding materials must be used, and this is one of the major causes of impeding welding efficiency. Further, the invert has a curved cross section, a thin and long web, and a thick and short flange. For this reason, the web cools easily during rolling, and the flange does not cool easily. Figure 2 shows an example of how it cools. In the figure, L indicates the universal mill assembly rolling process. This example shows universal mill assembly 6 before finish rolling.
(Universal Mill 4 + Edger 5). Normally, the temperature from the start to the end of rolling is 1050
~800℃, but as you can see from the figure, the web cools down much faster. It is not uncommon for the temperature difference between the flange and the web to be 100 to 150°C. As a result, the cross-sectional distribution of typical mechanical properties of the invert is as shown in Figure 3.
In the web, the tensile strength TS and yield point YP are high, and the elongation EL is low, and in the flange,
The trend is opposite to that of the web. For this reason, it is common practice to adjust the chemical composition in order to obtain the tensile strength and yield point of the flange that satisfies the standards. Therefore, the elongation tends to approach the lower limit of the specification, the carbon equivalent becomes higher, and the mechanical properties within the cross section are different. (Conventional method and problems) For inverts with thick flanges and thin webs, a technology was developed in 1973 to cool the flanges by spraying water on both sides of the flanges on a roller table in front of the finishing mill.
This is proposed in Publication No. 31227. This method prevents thermal distortion during the cooling process of inverts (roll inverts) manufactured in a two-hole rolling mill, creates well-shaped sections, and is convenient for refining work such as straightening work and table transfer. This is what I did. However, this method merely improves the shape of the shaped steel after rolling, and high tensile strength inverts with excellent weldability cannot be manufactured by this method alone. In particular, when trying to cool the flanges of channel-shaped steel by spraying water, water also gets on the web, which tends to cool the web. For this purpose, there has been no suitable method or apparatus. (Object of the Invention) In view of the above points, the present invention provides a method for efficiently and economically manufacturing a high tensile strength invert having excellent weldability. (Structure and operation of the invention) The present inventors conducted various tests to achieve the present invention in order to equalize the mechanical properties within the inverted cross section and lower the carbon equivalent, and the summary thereof is as follows. is C; 0.07~0.15, Si; 0.15~
0.35, Mn; 0.90-1.30, P0.025, S0.025,
SolAl; Contains each weight% of 0.010 to 0.035, the balance
Consisting of Fe and unavoidable impurities, and carbon equivalent (Ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/
4+ V/14)<0.36% of the heat-roughened steel slab obtained from the continuous casting slab, when its total cross-sectional temperature is 900°C or less, start rolling with a universal mill set,
After rolling with the universal mill set within the range of 750±40°C to form a channel section, after finish rolling the channel section, cooling and straightening are performed, and then the channel section is longitudinally cut. It is characterized by having two inverts. The present invention will be described in detail below with reference to the drawings. First, regarding the alloying element content, C is an essential element to maintain the strength of the base metal, but too much will impair weldability and toughness, and too little will result in insufficient base metal strength, so the range from 0.07
The rate shall be 0.15%. Si is an effective element for improving strength, but if it is too large, it will reduce the toughness of the weld zone, and if it is too small, the strength of the base material will be insufficient, so the range is set to 0.15 to 0.35%. Mn is an effective element for improving strength and toughness, but if it is too much or too little, it deteriorates the toughness of the base metal and welded part, so the range was set to 0.90 to 1.30%. P and S are unavoidably contained in steel as impurities and deteriorate strength and toughness, so it is desirable to keep them in as small a quantity as possible, but the upper limit, which can be adjusted industrially relatively easily, is set at 0.025%. However, the carbon equivalent Ceq is preferably 0.010 or less, and the carbon equivalent Ceq is also preferably 0.34 or less. SolAl was set at 0.010 to 0.060% for grain refinement.
Other unavoidably contained Ni, Cr, Mo, V
must be reduced so that it does not exceed the range of Ceq<0.36. As shown in FIG. 1, the continuously cast slab 8 having the above-mentioned chemical composition is heated to an appropriate temperature by, for example, a heating device 1, and then converted into a rough shaped steel slab 9 by a first rough rolling mill 2 and a second rough rolling mill 3. Temperature adjustment is performed by providing a cooling means, which will be described later, before (on the upstream side) or before and after the universal mill assembly 6, which will be processed and provided in the next step. 7 is a final finishing mill. Normally, the heating temperature for continuously cast slabs and the finishing temperature for rough shaped steel slabs are approximately 1280℃ and 1050℃, respectively, but if the capacity of the first and second rough rolling mills is large, lower temperatures may be used. . The cross-sectional change of the rolled material is
Approximately in the order shown in FIG. 1 b, c, and d, the first rough rolling mill may be omitted if the cross-sectional dimension is small. Now, Fig. 4 shows the processing procedure for the universal mill assembly 6, which occupies the main part of the modeling, and Fig. 4a
4 shows a universal mill set 6 which is a pair of the well-known universal mill UM4 and edger mill EM5, and FIG. 4c shows a reverse rolling situation by this universal mill set 6. FIG. 4b shows an example of the cooling means used in the present invention, in which a device 22 is installed to cool the flanges 24 of the groove-shaped steel sections 9, 10 with the gutter down to a predetermined temperature. In the conventional method, as mentioned above, due to the difference in cooling rate due to the difference in wall thickness between the web and the flange,
As illustrated in the figure, the temperature of the thin-walled web decreases faster than that of the thick-walled flange, but the web is also cooled by the roll cooling water, and this tendency is magnified. , the difference in mechanical properties between the two is expanded. For example, in order to satisfy the mechanical properties of the flange portion, the carbon equivalent of the steel material must be increased. Web thickness in the diagram: 9-13
mm, indicating flange thickness 14-18 mm. The present inventors discovered the above-mentioned phenomenon by observing the manufacturing conditions in detail, and as a solution to the problem, firstly, in order to equalize the mechanical properties within the cross section, the rolled material We focused on achieving a low carbon equivalent by controlling the rolling temperature within a narrow range. In other words, it was decided to make the processing conditions for the web and flange substantially the same. As shown in the outline in Fig. 4b, a web draining device 21 such as an air blower removes the roll cooling water that has gotten onto the upper surface of the web during rolling, thereby eliminating cooling causes other than those caused by roll contact and radiant heat dissipation. The web 23
keep the temperature high. In the figure, 25 is an air blowing nozzle. Air supply source not shown. Further, the flange 24 is acceleratedly cooled by the flange water cooling device 22 to keep the rolling temperature lower than the conventional rolling temperature, and furthermore, the temperature within the entire cross section of the material to be rolled is accurately controlled. 26 in the figure is a water injection nozzle, and illustration of a water supply unit such as a cooling water supply header is omitted. FIG. 5 is a graph of the cooling progress of the web and flange in the embodiment of the present invention, showing each rolling pass when cooling was performed in the middle of reverse rolling of the universal mill assembly 6 using the cooling device shown in FIG. 4b. Although the temperature progress of the web and flange is shown every (total of 8 passes), the cross-sectional temperature and its distribution are controlled to desired values, and the entire cross-sectional temperature is made uniform. 6th
The figure shows the relationship between the rolling start temperature and finishing temperature in the process. If the rolling start temperature is higher than 900°C, the rolling temperature will become too high, resulting in deterioration of mechanical properties and requiring excessive cooling equipment to keep the processing temperature within a specified value. , impractical. In addition, as shown in Figure 7, which shows the relationship between the rolling end temperature (“processing temperature” in the graph) and mechanical properties in the universal mill set, if the rolling end temperature of the universal mill set exceeds 750 + 40°C, the rolling end temperature after rolling The crystal grains are coarse and the mechanical properties deteriorate. If the rolling end temperature of the universal mill set is less than 750-40℃,
In addition to the abnormally high yield point, there is also a significant deterioration in elongation, which is disadvantageous. In the figure Ceq=0.30~0.34,
Web thickness 9-13 mm and flange thickness 14-18 mm are shown.
Note that if the amount of processing in this step is too small, the effect (grain refinement) will naturally decrease, so the total amount of processing (reduction amount) is preferably 50% or more. In addition,
The main structural requirements of the present invention are that the components and carbon equivalent of the rolled material and the rolling start and end temperatures in the intermediate rolling process are specified, and the rolling conditions of the final finishing mill 7 are not particularly defined. That is, the final finishing mill stage of invert rolling generally involves only light reduction for shaping, and the mechanical properties are built up to the intermediate rolling step. (Example) A to C shown in Table 2 are examples of the present invention, and D and E are conventional examples not based on the present invention. In order to obtain similar tensile strength, in D and E,
Since a large amount of Mn is used and V is added, the carbon equivalent Ceq is high. In contrast, the carbon equivalent of the present invention is low. Furthermore, the temperature difference between the web and the flange is small in both the rolling start (biting) temperature and the rolling end (final) temperature in the universal mill set. For this reason, a product with no difference in mechanical properties between the web and the flange can be obtained.

[Table] The present invention was made regarding high-tensile inverts, which are in high demand in the shipbuilding industry. It is obvious that it can be used as a. (Effects of the Invention) As explained above, according to the present invention, a structural high-tensile invert (usually referred to as a 50 kg class invert) with excellent weldability can be manufactured efficiently, and its economic effects can also be achieved. This is a major contribution to the development of industry.

[Brief explanation of the drawing]

Figure 1 is a layout showing a general example of a section rolling process with universal mill rows and an explanatory diagram of cross-sectional changes of the rolled material. Figure 2 is a diagram showing the cooling of webs and flanges in conventional method rolling of grooved sections. FIG. 3 is a graph showing the relationship between the carbon equivalent and various mechanical properties corresponding to FIG. 2, and FIG. 4 is a schematic diagram for explaining the embodiment of the present invention. is a plan view of the universal mill row and the flange water cooling device, b is a longitudinal cross-sectional view of the flange water cooling device installed at X-X′, Y-Y′ in a, and c is the rolling state of the universal mill and edger in the universal mill row ( FIG. 5 is a graph illustrating the cooling transition of the web and flange in the present invention, FIG. 6 is an explanatory diagram of the relationship between rolling start temperature and processing temperature, and FIG. FIG. 2 is an explanatory diagram of the relationship between various mechanical properties and processing temperature of the invert web and flange manufactured according to the present invention.

Claims (1)

[Claims] 1% by weight, C; 0.07 to 0.15, Si; 0.15 to 0.35, Mn; 0.90 to 1.30, P≦0.025, S≦0.025, SolAl; 0.010 to 0.035, the remainder consisting of Fe and inevitable impurities. , and carbon equivalent (Ceq=C+Mn/6+Si/24+Ni/40
+Cr/5+Mo/4+V/14)<0.36% of the hot rough shaped steel slab obtained from the continuous casting slab is started rolling with a universal mill set when the total cross-sectional temperature is 900℃ or less, and at the same time it is heated to 750±40℃. After finishing rolling with the universal mill assembly to form a channel section within the range of 2. After finishing rolling the channel section, cooling and straightening the channel section, then longitudinally cutting the channel section. A method for manufacturing high-strength inverts with excellent weldability, which is characterized by the fact that they are made with book inverts.