JPH0446643B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a slab for continuous hot thin plate rolling using a blooming method using a cylindrical titanium ingot without forging. [Conventional technology] As a method for producing hot-rolled titanium sheets, continuous hot rolling equipment is used to roll titanium slabs in a heating furnace to 700 to 950
A method of transporting the sheet into a furnace while heating it to ℃, then hot rolling, and winding the hot rolled sheet while adjusting the temperature to 450 to 750℃ is known from Japanese Patent Publication No. 54-029458. This method is a method for manufacturing hot coils using as a starting material a slab whose casting structure has already been destroyed and processed in the previous process. A method for manufacturing slabs for rolling hot-rolled thin sheets by blooming after a forging process is disclosed in Japanese Patent Publication No. 16858/1983. Another method is to use titanium ingots of 700 to 980
℃, with a reduction of 1 to 25% and a rolling temperature of
A method of blooming rolling at 400 to 900℃ was published in Japanese Patent Application Laid-Open No. 1986-
It is disclosed in Publication No. 163001. however,
Those that require a forging process have the disadvantage of complicating the process and increasing costs, and currently methods that do not involve forging have not reached a satisfactory level in terms of surface flaws and the shape and dimensions of the slab. [Problems to be solved by the invention] Since titanium is a metal that is highly reactive with oxygen and nitrogen in the atmosphere, ingots are manufactured under vacuum, and cylindrical ingots are widely produced by vacuum arc melting. It is used. In the method of manufacturing a slab by forging a cylindrical ingot or by blooming and rolling after forging, the forging operation has low productivity, and the forged material has many surface defects, making the cost of titanium material very high. The method was to do so. On the other hand, if an attempt is made to form a slab by only blooming and rolling without forging, there is a problem that the width expansion during rolling is small and a wide material cannot be obtained.
Vacuum arc melting equipment for cylindrical titanium ingots is generally for small diameter ingots, and when heating for forging or blooming, uniform heating up to the center is quick.
Due to less oxidation and nitridation of the surface in the heating furnace, the diameter
Many have dimensions of around 700mm. That is, it is easy to expand the width of a cylindrical titanium ingot by forging, but it is difficult to expand the width by rolling it in the axial direction. A, B, and C of FIG. 3 show the rolling process from the cylindrical ingot 1 to the slab 2, and the rolling is intended to be applied only from part a, that is, from the center. The second problem that occurs when a titanium ingot is bloomed at 450 to 850° C. without forging is wrinkles that occur on the entire surface of the slab. These wrinkle defects occur in the form of countless vertical stripes with a depth of 2 to 5 mm on the surface of the slab, and are conspicuous on the side surface corresponding to section b in FIG. 3. Since this impairs the quality of the hot coil produced by continuous hot thin plate rolling, it is necessary to remove the entire amount by grinding the surface of the slab in advance, resulting in a large loss in terms of cost and yield. [Means for Solving the Problems] The present invention is a method for manufacturing a slab for continuous hot thin plate rolling using a blooming method without forging a cylindrical titanium ingot. In the process of successively reducing the thickness, blooming is performed at a temperature of 900°C or higher and 1100°C or lower until the thickness becomes 40% or less of the diameter of the ingot, and then widthwise rolling is performed during adjustment rolling. 883℃ or higher using a grooved roll
This method is performed in the β-phase temperature range of 1100°C or less, and produces a slab with good shape and dimensional accuracy by achieving good widening rolling and reducing wrinkles that occur frequently, especially at the slab corners. Most cylindrical titanium ingots are manufactured by the consumable electrode vacuum arc melting method. As a heating furnace for blooming rolling, a heating furnace for steel (soaking furnace) may be used, but a heating furnace that can maintain a vacuum inside the furnace or a It is recommended to use a furnace suitable for heating cylindrical titanium ingots, such as a frequency induction heating furnace. The temperature of the heating furnace may be set so as to ensure the rolling temperature of the ingot. In blooming rolling, the rolling time required to plastically process the ingot into a slab is short, so the temperature drop during this time is also small. That is, for example, as described later in Tables 2 and 3, rolling of a cylindrical ingot with a diameter of 701 mm is started at 950°C, and a slab of 200 mm in pass 11 is rolled by 70% or more without intermediate heating. Even when manufactured, the finishing temperature of rolling is 880°C. Therefore, it is unnecessary to raise the rolling start temperature excessively, and a rolling start temperature of 1100°C or less is sufficient. Therefore, in the present invention, the upper limit of the blooming rolling temperature and the adjustment rolling temperature is set to 1100°C. Furthermore, if the temperature exceeds 1100℃,
The increased intake of oxygen from the air hardens the surface layer of the titanium slab, and also increases the amount of scale generated due to oxidation, which is also unfavorable from a thermoeconomic standpoint. For ordinary heating furnaces, the appropriate temperature is 960 to 1000℃, but for heating furnaces that can maintain a vacuum inside the furnace or low-frequency induction heating furnaces that can soak the ingot in a short time, the temperature should be within the range of 950 to 1100℃. Retention heating or finishing heating may be performed. As the blooming equipment, a rolling mill suitable for destroying the coarse grain casting structure of the cylindrical titanium ingot can be used, such as a normal high-lift blooming mill, a universal rolling mill, and a plate rolling mill. The purpose of rolling the slab until its thickness is 40% or less of the diameter of the ingot at a temperature of 900°C or higher and 1100°C or lower is to prevent wrinkles from occurring and to facilitate width expansion. Thickness 40% of ingot diameter
The reason why rolling was limited to the following is based on the results of the present inventors' analysis of records of manufacturing slabs using cylindrical titanium ingots with a diameter of 700 mm. This is because a more desirable result was obtained when performed within this range.
As a result of research into the causes of wrinkle defects, the present inventors found that
The casting structure of cylindrical titanium ingots is generally very coarse-grained, about -10 (the average diameter of one piece is about 11 mm), and this coarse-grained structure is destroyed by forging, so it is not necessary to use it through forging. There are no wrinkles on the surface of the slab, but rolling at 450 to 850℃, which is the normal hot working temperature for titanium materials, i.e., alpha titanium (883℃ or less), does not break down sufficiently and causes wrinkles. We obtained the knowledge that it remains on the slab surface. The present inventors further studied the relationship between rolling conditions and wrinkle defects regarding this coarse-grained structure, and the results are illustrated in Table 1. This test was conducted using a rectangular ingot with a thickness of 55 mm, a width of 240 mm, and a length of 240 mm. In the table, R ₀ indicates the initial state before rolling, and R ₁ to _{R 4}
indicates the state after each rolling pass. As a result, it is clear that the wrinkles of test specimens 2, 4, and 6, which were rolled in the same temperature range as normal titanium materials that do not have a cast structure, i.e., in the alpha titanium state, were deep, but the wrinkles were deep at temperatures above 900°C and 1100°C. In the following temperature range, that is, in the state of β titanium

[Table] The wrinkles on the rolled test specimens 1, 3, and 5 are shallow. Table 1 shows an example of a rolled material with a rectangular cross section, but in the case of blooming rolling of a cylindrical titanium ingot, the left and right sides of the cylindrical rolled material are At the initial stage of rolling, the end part b does not come into contact with the rolling rolls, but is deformed by the tensile stress that follows the stretching of the upper and lower ends part a, and therefore the coarse grain structure is not destroyed in parts a and b. Unlike the results shown in Table 1 regarding the rolled material having a rectangular cross section, this is also a major reason why rough skin and wrinkles are more likely to occur on both side edges. Furthermore, the present inventors have researched a rolling method that increases the rolling width using a cylindrical titanium ingot, and the results are shown in Table 2. The pass schedule at that time is shown in Table 3. FIG. 1 is an explanatory diagram schematically showing the state of width expansion when a cylindrical titanium ingot is made into a slab by blooming rolling. 1 indicates an ingot, and 2 indicates a slab. As is clear from Table 2, when rolling is started at 950°C and the thickness is 40% of the ingot diameter at 900°C or higher, blooming occurs in the β titanium region.

【table】

〔Effect of the invention〕

The present invention shows a method for practically producing slabs for continuous hot rolling of thin sheets with excellent properties using the blooming method without forging cylindrical titanium ingots. This study reveals a method for reducing wrinkles caused by the inherent coarse-grained structure and a method for manufacturing wide slabs suitable for continuous hot thin plate rolling from cylindrical ingots, which are unique to titanium ingots. This makes it possible to manufacture expensive titanium materials without wasting them, and is extremely useful industrially.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram schematically showing the state of width expansion when a cylindrical titanium ingot is made into a slab by blooming rolling, and Fig. 2 is a cross-section of the main part showing an example of the shape of a grooved roll. 3 are explanatory diagrams showing the process of manufacturing a slab from a cylindrical titanium ingot. 1: titanium ingot, 2: slab, 3, 4: grooved roll.

Claims (1)

[Claims] 1. A method for producing slabs for continuous hot rolling by sequentially reducing the thickness from a cylindrical titanium ingot by blooming without forging, until the thickness becomes 40% or less of the ingot diameter. A cylinder characterized in that the blooming rolling is performed at a temperature of 900°C or more and 1100°C or less, and the rolling in the width direction is performed in the β phase temperature range of 883°C or more and 1100°C or less using grooved rolls in the subsequent adjustment rolling. A method for producing titanium slabs with less wrinkles from ingots.