JPH0732005A - Rolling method for pure titanium - Google Patents

Abstract

(57) [Summary] [Object] The present invention is intended to provide a cold rolling method for pure titanium in which surface cracks do not occur. [Structure] When cold rolling pure titanium, the rolling load during rolling, work roll speed, strip speed at the rolling mill exit side, rolling mill inlet and outlet tension, rolling mill inlet and outlet plate thickness Measure or calculate the friction coefficient and material deformation resistance based on the data and the rolling conditions such as work roll diameter and strip width, and use the obtained data to calculate the maximum temperature of the interface in the roll bite. A method for cold rolling pure titanium, which comprises rolling at a temperature lower than a limit value determined in advance by experiments and calculations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling pure titanium free from cracks on its surface, and more particularly to a method for cold rolling pure titanium in a tandem cold rolling mill using a large diameter work roll.

[0002]

2. Description of the Related Art Generally, since pure titanium has a high deformation resistance, a rolling speed of 20 using a small diameter roll of φ200 mm or less is used.
Cold rolling at a low speed of 0 m / min or less is performed.

By rolling pure titanium with a cold tandem rolling mill having a work roll with a diameter of 400 mm or more, there are advantages that productivity can be improved and manufacturing cost can be reduced. Since the surface of the plate after rolling is inferior to that of the small diameter roll, such rolling has not been performed.

Another technique is disclosed in Japanese Patent Laid-Open No. 56-1655.
No. 02, a method of controlling the average crystal grain size of a material to prevent seizure, and JP-A-54-145349.
There is a method in which the saponification value of a rolling lubricating oil is specified in order to prevent seizure as in Japanese Patent Publication No.

[0005]

In recent years, the applications of pure titanium products have been expanded, and some products do not necessarily require the gloss equivalent to that obtained by rolling with a small-diameter roll. However, there is a problem that when pure titanium is rolled by a tandem rolling mill with a work roll having a large diameter, cracks perpendicular to the rolling direction are generated depending on rolling conditions.

An object of the present invention is to provide a cold rolling method for pure titanium in which the above-mentioned surface cracks in the rolling direction do not occur.

[0007]

The cold rolling method for pure titanium according to the present invention includes a rolling load during rolling (P, detection by load cells installed on the work side and drive side,
However, in a rolling mill that has a function of applying external force such as work rolls and intermediate roll benders, those loads are detected and only the load required for plastic deformation is calculated).
Work roll speed (V _r , rotation speed of mill motor PL
G, etc., and calculate by using the gear ratio and roll diameter), the strip speed on the delivery side of the rolling mill (V _o , the rotation speed of the roll in contact with the strip is detected using PLG, etc., and the roll diameter is Calculate by using, or measure by using the Doppler effect by irradiating a plate with a laser beam, etc., or if there is a plate thickness meter, detect the plate thickness and calculate the mass flow of the standard stand, and then use that value. And sheet thickness are used to calculate the sheet speed), and the tension on the rolling mill entrance side and exit side (σ _b , σ _f) is detected by the load cell attached to the deflector roll, and the tension per unit area is calculated. ), And if the plate thickness (H, h, plate thickness gauge on the inlet side and the outlet side of the rolling mill can be detected or the plate speed can be detected, find the mass flow of the standard stand, and use that value and the plate speed. Plate by calculation Measures or calculates a seek), the data and the work roll diameter (D), determine the deformation resistance of the original coefficient of friction rolling conditions such as the plate width (mu) and material (sigma _y), obtained data Is used to calculate the maximum temperature (T) of the interface in the roll bite, and the rolling is performed so that the temperature becomes lower than the limit value (T _CR ) obtained in advance by experiments and calculations.

The friction coefficient (μ) and the deformation resistance (σ _y ) are obtained by the following method, for example. For the deformation resistance, a constant a, m, n is obtained by performing a tensile test on a material that has been rolled in advance.

[Equation 1] However, since the effect of the strain rate is not taken into consideration in the above-described equation of deformation resistance, the constant a is corrected as described later.

Formula (2) is used as the rolling load formula, formula (3) is used as the roll flat formula, and formula (4) is used as the friction coefficient formula.

[Equation 2]

Using the above three equations, the friction coefficient (μ)
And the parameter (a) of the deformation resistance is obtained. The calculation flow is shown in FIG. However, P _e is the measured value of the rolling load.
The rolling load (P) thus obtained naturally coincides with the actually measured value (P _e ).

The maximum temperature of the interface inside the roll bite is determined as follows.

[Equation 3] The maximum temperature (T) of the interface in the roll bite is expressed by the following equation. T = T _dmax + T _fmax

The above calculation is carried out, and the maximum temperature (T) of the interface in the roll bite is compared with the limit temperature (T _CR ) obtained in advance by experiments and calculations, and the temperature (T) is the limit temperature (T
_{Roll at a} lower temperature than _CR ). If the temperature (T) is higher than the limit temperature (T _CR ), one or more factors such as rolling speed, rolling reduction and friction coefficient are changed and calculated by the method described above. The maximum temperature of the interface in the obtained roll bite is lower than the limit value. In addition, when operating the friction coefficient by changing one or more factors of the concentration of the rolling lubricant oil, the average particle size of the emulsion, and the supply amount of the rolling lubricant, an experiment or experiment and calculation should be performed in advance. The relational expression between the factor changed by
Based on this relational expression or the influence coefficient, the maximum temperature of the interface in the roll bite obtained by the above-described method is set to be lower than the limit value.

[0013]

When cold rolling of pure titanium, if the maximum temperature of the interface in the roll bite exceeds a certain limit value, a hard and brittle layer similar to that obtained by applying a coil grinder to the surface layer of the material is formed. Further rolling of this material causes cracks due to insufficient ductility of the hardened layer. Therefore, by adopting the rolling method of the present invention, since a hard and brittle layer is not formed on the material during rolling, it is possible to prevent the occurrence of cracks.

[0014]

Example In order to clarify the effect of rolling conditions on microcracks, a strip rolling experiment was conducted. There are four types of rolling lubricants used in the experiment, A to D, and their properties are shown in Table 1. Rolling lubrication was carried out by mixing industrial pure water and rolling lubricating oil in a tank with a volume of 30 l to a concentration of 5% (temperature 55 ° C), stirring with a homogenizer at 8000 rpm for 30 minutes or more, and then rolling at the entrance side of the rolling mill. A method was adopted in which a total of about 2 l / min of rolling lubricant was supplied from the upper and lower sprays to the bite inlet. The average particle size of the emulsion was measured using a Coulter counter after extracting the rolled lubricating oil in a well-stirred tank.

[0015]

[Table 1]

Table 2 shows the rolling conditions. The work roll was polished with # 600 abrasive paper before each rolling experiment. The roll coating was treated by water-lubricated rolling with a rolling reduction of 20 to 30% and repeating rolling until the change in roll roughness was saturated.

[0017]

[Table 2]

Table 3 shows the pass schedule. There are two pass schedules, a strong reduction pattern and a light reduction pattern. The maximum rolling force of the rolling mill used is 80
Since it is tf, the rolling reduction of the strong rolling pattern may differ depending on the rolling lubricant. When microcracks were observed by microscopic observation of the rolled sheet, rolling was stopped at that point.

[0019]

[Table 3]

The experimental results are shown in Table 4. As shown in Table 4, microcracks were generated or not generated depending on the rolling conditions.

The coefficient of friction, the deformation resistance, and the temperature rise at the interface were determined according to the calculations shown above. As a result, it was clarified that the temperature of the interface in the first pass was greatly different under each rolling condition, and that the cause of the microcracks was due to the rolling condition in the first pass. Table 6 shows the temperature rise at the interface in the first pass.
The physical properties used are those shown in Table 5.

[0022]

[Table 4]

[0023]

[Table 5]

[0024]

[Table 6]

Microcracks are generated in the subsequent pass when the temperature rise at the interface of the first pass is about 230 ° C. or more, whereas those where the temperature rise of the interface at the first pass is about 220 ° C. or less are generated. No microcracks occurred in the subsequent pass. Therefore, in this case, the limit temperature is 230 ° C. Thus, by applying the rolling method according to the first aspect of the present invention, microcracks can be prevented.

An example in which the maximum temperature of the interface in the roll bite is higher than the limit value under the condition that the rolling lubricant A is not used for roll coating will be described. When the same lubrication state was used, the temperature of the interface described above was calculated under the same conditions except for the rolling speed, and the rolling speed was changed to a limit temperature of about 200 m / min.

Therefore, as a result of multipass rolling with a rolling pass schedule of 200 m / min and a rolling pass under strong reduction, 6
No microcracks were generated even after the pass. Similarly, except that the conditions other than the reduction rate were the same and only the reduction rate was changed, the reduction rate at the critical temperature was 20%. Therefore, the rolling reduction of the first pass was set to 20%, and from the second pass, multi-pass rolling was performed with a rolling pass schedule of strong reduction. As a result, no microcracks were generated even after 6 passes. The fact that the micro-cracks can be prevented by changing the friction coefficient is apparent from the experimental results of the high-pressure reduction pass schedule without the roll coating of the lubricating oils A and D as described above.

Changing the type of rolling lubricating oil is obviously effective in preventing microcracks in the rolling of pure titanium, but the type of oil cannot be changed depending on the rolling conditions in consideration of actual operation. An example of changing the friction coefficient in such a case will be described with reference to the condition where the rolling lubricant A is used and no roll coating is performed.

Generally, the higher the concentration of the rolling lubricant, the larger the amount of the rolling lubricant supplied, and the larger the average particle size of the emulsion, the greater the amount of oil adhering to the plate and the work roll (plate-out amount). Therefore, the amount of rolling lubricating oil supplied into the roll bite increases, and the friction coefficient decreases. Before operating the coefficient of friction, conduct an experiment in advance to find the relationship between the coefficient of friction, the concentration of rolling lubricant, the amount of rolling lubricant supplied, and the average particle size of the emulsion, and obtain an approximate expression of these relationships or a table of influence coefficients. create. At this time, since the rough rolling schedule is determined by the operating conditions, the above-mentioned experiment is performed based on the standard rolling conditions.

In the case of a strong reduction pass schedule under the condition that there is no roll coating using the rolling lubricant A, the conditions other than the friction coefficient are the same in the above-mentioned temperature calculation of the interface,
When the coefficient of friction was changed and calculated, the coefficient of friction at the limit temperature was about 0.07. Therefore, the friction coefficient is 0.093
From 0.023 to 0.07.

From the results of the above-mentioned experiments conducted in advance, in order to further decrease the friction coefficient by 0.023, the concentration of rolling lubricating oil should be increased by 5% or the amount of smooth lubricating oil supplied per nozzle should be increased. It was found that the amount should be increased to 3.5 l / min or the average particle size of the emulsion should be increased to 10 μm.

Therefore, when the concentration of the rolling lubricating oil is further increased by 5% under the rolling conditions of the first pass (the oil was remade in the experiment, a static mixer may be used,
(Another oil tank may be prepared) If the supply amount of rolling lubricating oil is further increased to 3.5 l / min per nozzle (the supply amount of the pump was changed in the experiment), the average particle size of the emulsion was changed. As a result of further experimenting with an increase of 10 μm (in this experiment, the number of revolutions of the homogenizer was changed, an emulsifier, a dispersant, or a static mixer may be used), no microcracks were generated even after 6 passes. It was

Another embodiment in which the maximum temperature of the interface in the roll bite is higher than the limit value and in which in particular the coefficient of friction is manipulated is described with reference to FIG. The rolling mills used were work rolls 1, 1'having a diameter of 165 mm and a diameter of 4 mm.
It is a 4-high rolling mill consisting of backup rolls 2 and 2'of 00 mm. The material 3 used is a coil of pure titanium with a plate thickness of 3 mm and a plate width of 100 mm. A flying micro type plate thickness measuring device 5 is installed on the output side of the rolling mill, detects the plate thickness, and sends the signal to the calculator 11. The work roll speed of the rolling mill is PLG attached to the motor 4.
The rotation speed is detected by (not shown), calculation is performed using the gear ratio and the work roll diameter, and the result is sent to the calculator 11. The tensions on the inlet side and the outlet side of the rolling mill are detected by the deflector rolls 6 and 7 and calculated by the calculator 9, and the result is sent to the calculator 11. Further, the rotation speed is detected by the PLG attached to the deflector roll 7, the strip speed on the delivery side of the rolling mill is calculated using the gear ratio and the deflector roll diameter, and the result is sent to the calculator 11. The rolling load is detected by the load cell 8 attached to the rolling mill, and the result is sent to the calculator 11. The rolling reduction of the rolling mill is controlled by the electric rolling reduction device 12. The rolling conditions such as the work roll diameter and the plate thickness and plate width of the material are manually input to the external input device 10, and those values are calculated by the calculator 1.
Sent to 1. The rolling lubricant is A rolling lubricant with a concentration of 5%,
At a temperature of 60 ° C., a total of 5 l / min was supplied from the upper and lower two rolling lubricating oil supply nozzles. The rolling speed was 100 m / min, the front tension was 20 kgf / mm ² , the back tension was 15 kgf / mm ² , and the standard reduction rate was 30%.

Experiments and calculations were carried out in advance, and the limit temperature of the interface where microcracks were generated in this rolling mill was 200 ° C.
Was confirmed. As already indicated, rolling is performed while checking the maximum temperature of the interface while analyzing the data during rolling, and if the temperature exceeds the critical temperature of the interface where microcracks occur in this rolling mill, the reduction rate is The method of controlling was adopted.

In order to exceed the limit temperature, the amount of rolling lubricant was intentionally reduced by hand. When nothing was done, microcracks were generated when the supply amount of rolling lubricant was 2 l / min or less. However, this microcrack was judged by taking a rolled plate, applying a tensile elongation of 2% to the sample, and then observing the surface of the plate with a microscope. On the other hand, when the present invention was adopted, microcracks did not occur even when the supply amount of rolling lubricating oil was 1 l / min.

[0036]

According to the method for producing pure titanium of the present invention,
Since it does not cause embrittlement of the surface layer of the material generated in the roll bite and poor ductility, a good product without microcracks can be obtained, and at the same time, for example, the rolling speed can be increased to near the critical temperature, It is possible to improve productivity and reduce manufacturing costs.

[Brief description of drawings]

FIG. 1 is a calculation flowchart of parameters of a friction coefficient and a deformation resistance.

FIG. 2 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1,1 'Work roll 2,2' Backup roll 3 Material 4 Motor 5 Plate thickness gauge 6,7 Deflector roll 8 Load cell 9 Calculator 10 External input device 11 Calculator 12 Electric reduction device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location // B21B 37/00 BBP 37/76 (72) Inventor Kazuhiko Sato Fujimachi, Himeji-ku, Hyogo Prefecture No. 1 Shin-Nippon Steel Co., Ltd. in Hirohata Works (72) Inventor Shinichi Minato No. 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Prefecture Shin-Nippon Steel Co., Ltd. in Hirohata Works (72) Takehiko Ichimoto Wakayama, Wakayama Prefecture Ichinohara 136-16 (72) Inventor Kazuyuki Kamada 2-8-15 Nishihama, Wakayama City, Wakayama Prefecture (72) Inventor Koichi Kawashita 1450 Nishihama, Wakayama City, Wakayama Prefecture Kenichi Miyamoto 1450 Nishihama, Wakayama City, Wakayama Prefecture

Claims (3)

[Claims] 1. When cold rolling pure titanium, rolling load during rolling, work roll speed, strip speed at rolling mill exit side, tension at rolling mill entry side and exit side, rolling mill entry side and exit side Sheet thickness is measured or calculated, and the data and work roll diameter,
The coefficient of friction and the deformation resistance of the rolled material were calculated from the rolling conditions including the strip width, and the maximum temperature of the interface in the roll bite was calculated using the obtained data. A method for rolling pure titanium, which comprises rolling at a temperature lower than the above temperature. 2. When the maximum temperature of the interface in the roll bite is higher than the limit value, one or more factors selected from the rolling speed, the rolling reduction, and the friction coefficient are changed, and the roll is obtained by calculation. The rolling is performed such that the maximum temperature of the interface in the cutting tool is lower than the limit value.
The method for rolling pure titanium described above. 3. One of the concentration of the rolling lubricant oil emulsion, the average particle size of the emulsion, and the supply amount of the rolling lubricant oil.
When manipulating the friction coefficient by changing one or more factors, the relational expression or the coefficient of influence between the coefficient to be changed and the coefficient of friction is obtained in advance by experiments or experiments and calculations, and this relational expression or the coefficient of influence is calculated. The method for rolling pure titanium according to claim 2, wherein the rolling is performed such that the maximum temperature of the interface in the roll bite obtained by the calculation is lower than the limit value.