JPS6347521B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing titanium slabs. Conventionally, titanium slabs have been produced by forging titanium ingots (using a press, hammer, etc.). Titanium ingots are made by casting titanium melted in a vacuum melting furnace in round molds or by casting titanium melted in a plasma beam furnace in flat molds. A round titanium ingot made by vacuum melting is formed into a slab by forging. but,
This method requires reheating the material two or three times during the forging process, and has the disadvantage that it is difficult to obtain a product that is satisfactory in terms of dimensional accuracy, shape, surface defects, etc. Flat titanium ingots produced by plasma beam furnaces are formed into slabs by forging or press blooming. This method has the drawbacks of low yield due to poor dimensions and shape, and high operating costs due to poor efficiency. SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome the drawbacks of conventional methods and to produce titanium slabs at low cost. The method for manufacturing titanium slabs of the present invention involves heating a titanium ingot to a temperature of 700 to 980°C, reducing the rolling amount per pass by 1 to 25%, and finishing at a final rolling temperature of 400 to 980°C.
It is characterized by blooming in a temperature range of 900℃. The titanium ingot is heated using a conventional soaking furnace or heating furnace. However, since soaking furnaces in general blooming plants are used to heat steel ingots, the heating temperature is usually
The temperature is around 1300℃. Therefore, when heating a titanium ingot, it is necessary to control the furnace temperature so that the heating temperature is 700 to 980°C. The reason why the heating temperature was limited to 700 to 980°C is as follows. If the heating temperature is below 700°C, as will be described later, the hot workability of titanium decreases significantly, surface flaws (cracks) increase, and hot deformation resistance increases, making rolling difficult. On the other hand, the heating temperature
When heated for a long time at 980℃ or higher (particularly at the α-β transformation point of titanium, 883℃ or higher), the surface of the titanium ingot is oxidized and a hardened layer of titanium oxides, nitrides, etc. is formed, which causes problems during rolling. This causes surface flaws due to abnormal growth of crystal grains, and the hot deformation resistance is small at high temperatures, causing indentation and oyster flaws. FIG. 1 shows the amount of oxidation on the outer surface of a titanium material, and shows that the rate of increase in hardness due to an increase in the oxidized layer increases as the heating temperature increases and the heating time increases. In Figure 1, the test material is a titanium material with a diameter of 5 mm heated in the atmosphere, and A is for a low temperature heating material (100 to 600℃), and B is for a high temperature heating material (700 to 1000℃). The experimental results are shown respectively. The relationship between the symbols in FIGS. 1A and 1B and the heating conditions is shown in the following Tables 1 and 2, respectively.

【table】

【table】

[Table] Figure 2 shows the number of twists of titanium material at high temperatures. As can be seen from FIG. 2, it is preferable to roll at the α-β transformation point (883°C) or higher, that is, in the β phase region of 883 to 930°C. However, in order to complete rolling within this temperature range, the heating temperature becomes too high, which increases the oxide film on the ingot and causes surface flaws on the slab. Blossoming is carried out in a conventional universal mill or plate mill. In the case of blooming rolling using a universal mill, horizontal rolls and vertical rolls reduce the thickness and width of the material almost simultaneously. In the conventional forging method and press blooming method, reductions in the thickness and width directions were carried out alternately, resulting in inferior quality such as surface flaws, dimensional accuracy, and shape of the slab. However, when using a universal mill, this These shortcomings are greatly improved. On the other hand, when using a thick plate mill, rolling down in the width direction is not possible, so
Although it has disadvantages such as poor width accuracy and easy occurrence of side defects, it has great advantages such as being able to perform tenter rolling.
The reason why the final finish rolling temperature was limited to 400 to 900°C is as follows. If the final finish rolling temperature is below 400°C, rolling will be difficult, dimensional accuracy and shape will deteriorate, and surface flaws will increase. More specifically, while reversing the steel ingot in a one-stand rolling mill, rolling is completed at 600°C or higher to form a slab of a predetermined thickness, and then smoothing rolling is performed to correct the shape. It is important to control the end temperature so that it does not fall below 400°C. The upper limit of the final finish rolling temperature of 900° C. is limited by the upper limit of the heating temperature as described above. FIG. 3 shows the hot deformation resistance of titanium material, and shows that the hot deformation resistance decreases as the temperature decreases. FIG. 4 shows the hot workability of titanium materials, and shows that at low temperatures, the elongation and drawing properties deteriorate, and the hot workability decreases. Table 3 below shows the components of the titanium materials shown in FIGS. 3 and 4.

[Table] The reason why the reduction amount was set to 1 to 25% per pass is as follows. If the reduction amount is less than 1%, it is difficult to control the dimensions using a large-scale blooming mill, and the rolling efficiency is significantly reduced. Surface flaws (cracks) occur when the reduction amount is 25% or more.
occurs frequently, so the reduction amount per pass is 1~
It was set at 25%. FIG. 5 shows the relationship between the reduction amount per pass and the slab surface flaws, and the vertical axis represents the degree of flaw occurrence in five grades. In the figure, the symbol ,, represents the following items. : Economically unviable area: Good slab surface area: Slab surface, poor shape area: Unrollable area If the rolling reduction exceeds 25%, the slab surface will deteriorate;
This indicates that slab defects will occur. Next, examples of the method of the present invention will be described. Example 1 Thickness created by plasma beam furnace
Flat titanium ingot of 300mm and width 100mm (pure titanium
Equivalent to JISH4600 type. H: 0.013% or less, O: 0.15% or less, N: 0.05%
Below, Fi: 0.20% or less, C: 0.01% or less, remainder
Ti) was heated and soaked at a soaking temperature of 900℃ for a furnace time of 10 hours and 50 minutes, and a soaking time of 5 hours and 30 minutes, followed by blooming using a universal mill and a plate mill according to the method of the present invention, and a conventional method. A slab with a thickness of 150 mm and a width of 1000 mm was manufactured by forging using a press according to the method described below under the following conditions. The results are shown in Table 4. (1) Universal mill and plate mill rolling temperature: Rolling start temperature 850℃ Finishing temperature of thinning rolling 600℃ Shape correction rolling finishing temperature 520℃ Reduction amount: Rolling temperature 1 to 4 passes (light reduction) 3.3 to 1 pass 3.7%
(850℃) 5-6 passes (under strong pressure) 14.8-17.8% per pass
(850℃) 7-10 passes (under light pressure) 5.3-6.3% per pass
(600℃) Shape correction rolling (0 reduction) (520℃) Total reduction: 50% (2) Press forging Forging temperature: Forging start temperature 850℃ Forging end temperature 500℃ Reduction amount: 7 times Pressing amount per time 6.6~11.7% Total reduction: 50%

[Table] Example 2 The test material was a flat titanium alloy ingot (ASTM, B265 Gr2, equivalent to B265 Gr2, with a thickness of 300 mm and a width of 1000 mm, made using a plasma beam furnace in the same manner as in Example 1. O: 0.20) % or less, N: 0.05 or less, Fe: 0.30%
Below, C: 0.10% or less, Mn: 0.015% or less, V:
3.5 to 4.5%, Al = 5.5 to 6.75%, balance Ti) was heated at a soaking temperature of 900°C for 7 hours in the furnace for 3 hours and 30 minutes. The following results are obtained by blooming using a plate mill and forging using a conventional press. Slabs with a thickness of 150 mm and a width of 1000 mm were manufactured under each condition. The results are shown in Table 5. (1) Universal mill and thick plate mill rolling temperature: Rolling start temperature 850℃ End thickness reduction rolling temperature 650℃ Shape correction rolling end temperature 530℃ Reduction amount: Rolling temperature 1 to 4 passes (light reduction) 3.3 to 3.7 per pass %
(850℃) 5-6 passes (under strong pressure) 21.7-25% per pass
(850℃) 7-9 passes (under light pressure) 5.3-6.3% per pass
(650℃) Shape correction rolling (0 reduction) (530℃) Total reduction: 50% (2) Press forging Forging temperature: Forging start temperature 850℃ Forging end temperature 550℃ Reduction amount: 5 times Pressing amount per time 10.0~17.0% Total reduction: 50%

[Table] As is clear from the above description, according to the method of the present invention, it is possible to improve the surface quality and to efficiently produce titanium slabs at low cost.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the outer surface and hardness of titanium materials. Figure 2 is a graph showing the relationship between the number of twists of titanium material and temperature. FIG. 3 is a graph showing the relationship between the deformation resistance of titanium material and temperature. FIG. 4 is a graph showing the relationship between the tensile strength and elongation of titanium materials and temperature. FIG. 5 is a graph showing the relationship between the rolling reduction amount per pass and the slab surface score.

Claims (1)

[Claims] 1 Heating a titanium ingot at a temperature of 700 to 980℃,
A method for producing a titanium slab, characterized by performing blooming at a rolling reduction of 1 to 25% per pass and at a final finish rolling temperature of 400 to 900°C.