JPH05138216A - Surface roughening method for cold rolling roll - Google Patents

Abstract

(57) [Abstract] [Purpose] It is intended to provide a surface roughening method for cold rolling rolls capable of obtaining rolls having excellent wear resistance. [Method] A method of roughening a cold rolling roll by beam irradiation of a laser beam, an electron beam or the like, or electric discharge machining, wherein the roll surface is roughened by beam irradiation or electric discharge machining. Liquid nitrogen is blown to the chemically processed portion within 60 minutes immediately after the processing to reduce the roll surface temperature to −50 ° C. or lower. Also, preferably by controlling the flow rate of the spray of liquid nitrogen,
The amount of retained austenite in the surface layer of the roughened portion is 2.
5 to 16%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of roughening a cold rolling roll by irradiating a beam such as a laser beam or an electron beam, or by electric discharge machining.

[0002]

2. Description of the Related Art As a method of roughening a cold rolling roll, there is known a method of irradiating a beam such as a laser beam or an electron beam or an electric discharge machining. However, the rough surface obtained by these methods forms a white layer with a large amount of retained austenite and a hardness lower than that of the base metal near the surface layer of the crater-shaped convex portion generated by beam irradiation or electric discharge machining, and wear resistance Has the disadvantage of being inferior to. For this reason,
This type of processing roll has a problem that the roll life is shorter than that of the conventional roughening processing roll by shot blasting or the like. 5 to 7 show hardness distributions from the surface layer of each roll after electron beam machining (FIG. 5), laser beam machining (FIG. 6) and electric discharge machining (FIG. 7).

In order to solve such a problem, Japanese Patent Laid-Open No.
No. 3-20192 and Japanese Patent Laid-Open No. 63-20193 propose a method of hardening the roll by subjecting the roll to sub-zero treatment such as spraying with liquid nitrogen after laser processing to improve wear resistance. In this proposal, in particular, the amount of retained austenite in the surface layer of the roughened portion is 15 to
It is said that 30% is effective in improving the wear resistance of the roll.

[0004]

However, the residual austenite amount of the base material of a general forged steel roll is in the range of 11 to 16%, and the wear resistance is improved as the residual austenite amount is smaller. According to the experiments conducted by the inventors, the roll having a smaller amount of retained austenite has a higher hardness and a smaller decrease rate of roughness. Therefore, as shown in JP-A-63-20192, etc., when the residual austenite amount in the surface layer of the roughened portion is about 20%, which is larger than the residual austenite amount in the base material, the reduction rate of roughness becomes the minimum. Is doubtful.

Further, according to the study by the present inventors, the timing of the sub-zero treatment by spraying liquid nitrogen is important, and sufficient abrasion resistance can be obtained even if the treatment is performed at a later time. Turned out not to. That is, roll roughening requires about 1 hour with a roll having a normal size of, for example, a roll diameter of 600 mm and a roll length of about 2100 mm. However, when sub-zero treatment is carried out after completion of such roughening, it is sufficient. It was found that excellent abrasion resistance cannot be obtained.

[0006]

As a result of further studies based on the above facts, the inventors of the present invention have found that the spraying of liquid nitrogen must be carried out within 60 minutes after the roughening process to obtain sufficient durability. It was found that wear resistance is not obtained, and that particularly excellent wear resistance is obtained by setting the amount of retained austenite in the surface layer of the processed portion to 2.5 to 16% by such treatment, and the present invention is completed. It was made. That is, the present invention has the following configurations.

(1) In a method of roughening a cold rolling roll by irradiating a beam such as a laser beam or an electron beam, the roll surface is irradiated with a beam to be roughened, and then the roughening is performed. A method for roughening a cold-rolling roll, characterized in that liquid nitrogen is blown to the portion within 60 minutes immediately after processing to lower the roll surface temperature to −50 ° C. or lower.

(2) In the method of roughening a cold-rolled roll by electric discharge machining, the roll surface is roughened by electric discharge machining, and the roughened portion is treated within 60 minutes immediately after machining. A method of roughening a cold-rolling roll, comprising spraying liquid nitrogen onto the surface of the roll to reduce the roll surface temperature to −50 ° C. or lower.

(3) In the above method (1) or (2), the amount of residual austenite in the surface layer of the roughened portion is controlled to 2.5 to 16% by controlling the flow rate of liquid nitrogen sprayed. A characteristic method for roughening a cold rolling roll.

[0010]

The details of the present invention will be described below. The soft portion of the roll surface layer after the roughening process cannot be sufficiently transformed into martensite because the metal once melted by beam irradiation or electrical discharge machining is instantaneously cooled in the atmosphere and reaches room temperature,
The austenite phase remains. In the present invention,
To control the residual amount of such austenite phase,
After roughening by beam irradiation or electric discharge machining, liquid nitrogen is blown to the roughened portion within 60 minutes immediately after the processing to reduce the roll surface temperature to -50 ° C or lower.

FIG. 1 shows that C: 0.93 wt%, Si: 0.
53 wt%, Mn: 0.89 wt%, Cr: 5.08w
t%, Mo: 0.33 wt% composition roll (hardness Hv
(800) is subjected to surface roughening by laser beam irradiation, and then liquid nitrogen is sprayed onto the surface roughened portion after various times, so that the roll surfaces are each-
196 ° C, -120 ° C, -50 ° C, -40 ° C, -20
The effect of the cooling time of cooling to 6 levels of 0 ° C. and 0 ° C. and the effect of the time from the irradiation of the beam until the start of the cooling process on the hardness of the beam irradiation part was investigated. The cooling temperature was adjusted by controlling the amount of liquid nitrogen sprayed. FIG. 2 shows a temperature change in the vicinity of the surface layer of the roll from the start of spraying liquid nitrogen when cooled to −196 ° C.

According to FIG. 1, the cooling temperature of the roll surface layer is −
At a temperature of more than 50 ° C, for example, -40 ° C, a hardness of Hv800 or higher, which is the base material hardness, cannot be obtained unless cooling is performed almost instantaneously after processing. Despite the length of time, a hardness of Hv 800 or higher, which is the base metal hardness, cannot be obtained. Even if the cooling temperature is -50 ° C or less, if the time from the roughening processing to the liquid nitrogen spraying exceeds about 60 minutes, Hv800
It is understood that the above hardness cannot be obtained. Therefore, in the present invention, it is a requirement that the roughened portion is subjected to a treatment of spraying liquid nitrogen within 60 minutes immediately after the processing to reduce the roll surface temperature to −50 ° C. or lower.

Further, the present inventors investigated the influence of the amount of retained austenite in the surface layer of the surface-roughened portion on the hardness and roll roughness reduction rate. FIG. 3 shows the results. When the retained austenite amount is 16% or less, the surface layer hardness becomes equal to or higher than the base material hardness, so that the rough surface reduction rate tends to decrease, and the surface roughness is almost 5 to 10%. In the range of 1, the roll roughness reduction rate is reduced most. On the other hand, when the amount of retained austenite is less than 2.5%, the hardness is high, but the melted portion becomes brittle, so that the roughness reduction rate is large. From the above results, it is preferable that the amount of retained austenite in the surface layer of the roughened portion is 2.5 to 16% by the cooling treatment. Such adjustment of the amount of retained austenite can be performed by adjusting the spraying amount of liquid nitrogen and controlling the cooling temperature. FIG. 4 shows the relationship between the amount of liquid nitrogen sprayed and the amount of retained austenite.

FIG. 8 and FIG. 9 show a surface roughening apparatus used for practicing the present invention and a practical situation of the present invention by the roughening apparatus. The roughening apparatus is provided with a rotation holding mechanism 1 for holding a roll and rotating the roll, a movable table 2 movable along the longitudinal direction of the roll, and a parallel arrangement on the movable table. It comprises a laser irradiation head 3 and a liquid nitrogen spraying device 4. The movable table 2 can move in parallel with the roll axis direction in synchronization with the rotation of the roll by the rotation of the drive screw shaft 5. Further, the liquid nitrogen spraying device 4 has a liquid nitrogen injection nozzle 8 facing the roll surface. In addition, in other drawings, 6 is a laser oscillator, 7 is a guide shaft of the moving base 2, and 9 is a flow rate adjusting valve.

According to such a surface-roughening apparatus, the roll A is set on the rotation holding mechanism 1 and is rotated at a predetermined rotation speed. On the other hand, the laser beam output from the laser oscillator 6 is irradiated from the laser irradiation head 3 to the surface of the roll A substantially perpendicularly through a plurality of mirrors. The laser irradiation head 3 can irradiate a laser beam in pulses by a mechanical chipper.
Further, the pattern depth of the surface roughness can be controlled by setting the frequency and output of this pulse, the roll rotation speed, and the moving speed of the laser irradiation head 3. In addition, roll roughening by this device is usually 600 m
It takes about 1 hour with a roll of m and a roll length of 2100 mm.

During the roughening process by the laser irradiation head 3 as described above, liquid nitrogen is sprayed from the jet nozzle 8 of the liquid nitrogen spraying device 4 to the roughened part to perform the cooling process. In such an apparatus, for example, roll rotation speed: 200 rpm, moving speed of moving table: 50 mm / min, roll-axis-direction distance between laser irradiation section and liquid nitrogen spraying section: 4
When a roll having a roll diameter of 600 mm and a roll length of 2100 mm as described above is roughened under the condition of a roll axial pitch of a 00 mm crater of 300 μm, the roughened portion is subjected to approximately 8 minutes immediately after processing. Liquid nitrogen can be sprayed within.

The amount of liquid nitrogen sprayed is controlled by the flow rate adjusting valve 9. By controlling the cooling temperature of the roll surface and changing the heat treatment level by adjusting the flow rate of the liquid nitrogen, the amount of retained austenite can be arbitrarily controlled, and thus a desired roll surface hardness can be secured. ..

FIGS. 10 to 12 show another embodiment of the apparatus used for carrying out the method of the present invention. A movable table 2 is provided on a base 13 so as to be movable in the roll longitudinal direction, and this movement is performed. A laser irradiation head 3 and a liquid nitrogen spraying device 4 are provided in parallel on the table 2. The movable table 2 can move in parallel with the roll axis direction in synchronization with the rotation of the roll by the rotation of the drive screw shaft 5.

The liquid nitrogen spraying device 4 has a cold insulation ring 10 which surrounds the roll and which has an annular groove 100 for fluid circulation on the inner circumference of the ring. This cool ring 10
Inside the nozzle, the nozzle header 11
Are provided and the injection nozzles 12 are attached at appropriate intervals in the longitudinal direction of the nozzle header 11. Each injection nozzle 12 is positioned in the annular groove 100 with its tip close to the roll surface. is doing. A liquid nitrogen supply pipe 19 is connected to the nozzle header 11.

Further, the inner diameter of the cold insulating ring 10 is constructed so that a slight gap is formed between the cold insulating ring 10 and the outer surface of the roll A.
The cooling effect in the annular groove 100 is enhanced.
The inside of the cold insulation ring 10 is filled with a heat insulating material 17 for cold insulation. The cold insulating ring 10 has a half-split structure for inserting a roll therein, and both half split parts are detachably connected by a connecting fitting 18. Although not shown, the roll rotation holding mechanism, the laser oscillator, and the like in this embodiment also have the same configurations as those in the embodiment shown in FIG. Further, in the other drawings, 14 is a gas-liquid separator for liquid nitrogen, 15 is a flow rate adjusting valve, and 16 is a flow meter.

[0021]

EXAMPLE A temper rolling roll having a roll diameter of 600 mm was subjected to surface roughening by the method of the present invention and the comparative method, and the change in roughness of the strip to be rolled due to abrasion of the roll surface was examined. The component composition of this roll is C: 0.90w
t%, Si: 0.50 wt%, Mn: 0.90 wt%,
Cr: 5.0 wt%, Mo: 0.30 wt%, V: 0.
The content is 01 wt%, which is a commonly used component type forged steel roll. In general, this type of roll is forged after casting and subjected to heat treatment such as quenching and tempering, and has a sound structure in which spherical carbides are uniformly distributed in the martensite matrix.

[Comparative Example 1] CO on the roll surface₂Guthray
The ZaBeam method can be used under the following laser beam irradiation conditions.
Surface treatment was applied. The hardness distribution near the surface of this roll
It shows in FIG. Laser output: 1.4 kW Pulse frequency: 50 kHz Energy density: 6.0 × 10⁶W / cm²  Crater pitch: 300 in both roll and axial directions
Roughness of roll: Ra 2.0 μm

Comparative Example 2 A roll was roughened by laser beam irradiation under the same conditions as above, and 240 minutes after the roughening, 200 g of liquid nitrogen was applied to the roll surface.
Sprayed at a spraying rate of / min. The amount of retained austenite in the surface layer of the roughened portion of this roll was about 30%, and the surface hardness was Hv680.

[Invention Example] Using the apparatus shown in FIGS. 10 to 12, the roll is roughened by laser beam irradiation under the same conditions as described above, and the roughened portion is processed by 200g / min of liquid nitrogen within 8 minutes
The amount of residual austenite in the surface layer of the roughened portion was about 10% and the surface hardness was about 1000 Hv.

Using the rolls of the comparative example and the example of the present invention obtained as described above and the conventional surface-roughening roll obtained by shot blasting, SPCC after annealing was performed.
The cold-rolled steel sheet (0.7 mm in plate thickness) was subjected to temper rolling (rolling length: 50 km) with a rolling reduction of 1.0%, and the degree of decrease in plate surface roughness (ΔRa) was examined. The result is shown in FIG. According to this, in the rolls of Comparative Example 1 and Comparative Example 2, the roughness is significantly lower than that of the conventional surface-roughening roll, whereas in the roll roughened by the method of the present invention, Roughness reduction is suppressed more than the conventional rough surface processing roll.

[0026]

According to the present invention described above, it is possible to obtain a surface-roughening roll for cold rolling which causes less wear and less surface roughness than rolls obtained by the conventional method.

[Brief description of drawings]

FIG. 1 is a drawing showing the relationship between the time until the start of spraying liquid nitrogen after roll roughening and the hardness of the roll surface layer.

FIG. 2 is a drawing showing an example of a temperature change in the vicinity of a roll surface layer from the start of spraying liquid nitrogen.

FIG. 3 is a drawing showing the relationship between the amount of retained austenite in the surface layer of the surface roughened by beam irradiation, the hardness of the roll, and the rate of decrease in roughness.

FIG. 4 is a drawing showing the relationship between the amount of liquid nitrogen sprayed onto the roughened portion and the amount of retained austenite on the surface layer of the roughened portion.

FIG. 5 is a drawing showing a hardness distribution in the vicinity of a roll surface layer of a roughened portion (as-processed) by an electron beam.

[Fig. 6] Surface roughening processing part by laser beam (as-processed)
Drawing showing hardness distribution near the roll surface

FIG. 7 is a drawing showing a hardness distribution in the vicinity of a roll surface layer in a surface-roughened portion (as-machined) by electric discharge machining.

FIG. 8 is a front view showing an example of an apparatus used for practicing the present invention and an implementation state of the method of the present invention.

9 is a sectional view taken along line IX-IX in FIG.

FIG. 10 is a side view showing another example of an apparatus used for carrying out the present invention.

11 is a partially cutaway front view partially showing a liquid nitrogen spraying device of the device shown in FIG.

12 is a sectional view taken along line XII-XII in FIG.

FIG. 13 is a drawing showing the hardness distribution in the vicinity of the surface layer of the roughened portion of the roll of Comparative Example 1 processed in Example.

FIG. 14 is a drawing showing changes in the surface roughness of a steel sheet when temper rolling is performed on the steel sheet by each roll of the comparative example and the example of the present invention obtained in the example and the roll of the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rotation holding mechanism, 2 ... Moving stand, 3 ... Laser irradiation head, 4 ... Liquid nitrogen spraying device, 5 ... Drive screw shaft, 6 ... Laser oscillator, 8 ... Injection nozzle, 9 ... Flow control valve, 10 ... Cooling Ring, 11 ... Nozzle header, 12 ... Jet nozzle, 1
3 ... Base, 15 ... Flow control valve, A ... Roll

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication C21D 1/09 MB 9/38 A (72) Inventor Hideji Kanto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Shoji Mitsukawa Maruuchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (Inventor) Toshinori Mori 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A method of roughening a cold rolling roll by irradiating a beam such as a laser beam or an electron beam, wherein the roll surface is irradiated with a beam to roughen the surface, and the roughened portion. The method for roughening a cold rolling roll is characterized in that, within 60 minutes immediately after processing, liquid nitrogen is sprayed to reduce the surface temperature of the roll to −50 ° C. or lower. 2. The cold austenite according to claim 1, wherein the amount of retained austenite in the surface layer of the roughened portion is controlled to be in the range of 2.5 to 16% by controlling the flow rate of liquid nitrogen sprayed. Surface roughening method for rolling rolls. 3. A method of roughening a cold rolling roll by electric discharge machining, wherein the roll surface is roughened by electric discharge machining, and the roughened portion is processed within 60 minutes immediately after machining. Blow liquid nitrogen to reduce roll surface temperature
A method of roughening a cold rolling roll, which comprises performing a treatment for reducing the temperature to 50 ° C. or lower. 4. The cold rolling roll according to claim 3, wherein the residual austenite amount in the surface layer of the roughened portion is controlled to 2.5 to 16% by controlling the flow rate of liquid nitrogen sprayed. Roughening method.