JPS6320191A - Surface roughening method for cold rolling roll - Google Patents

Abstract

PURPOSE:To improve the wear of a laser dulled roll and the roughness change of the sheet surface of a material to be rolled by subjecting the roll consisting of the components having the Ms point of a specific temp. or above to laser surface roughening. CONSTITUTION:The roll 1 consisting of the components, the Ms point of which rises to >=200 deg.C at the time of melting and solidifying is used with respect to the roll components to be used prior to the operation. The laser beam outputted from a laser oscillator 3 is projected via plural mirrors perpendicularly to the roll surface. A laser projecting head part 4 is moved in parallel with the axial direction of the roll by the rotation of a driving screw 5 synchronized with the rotation of the roll. The laser beam is pulsed to a for example, frequency by a Q switch. The pattern and depth of the surface roughness are controlled by setting the frequency and output of the pulses, the rotating speed of the roll and the moving speed of the laser projecting head 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for roughening a roll for cold rolling, and more specifically, a method for roughening a roll for cold rolling or temper rolling of metal materials into a desired pattern and roughness. Concerning how to roughen and maintain depth.

[Conventional technology]

Surface quality is an important quality of rolled steel sheets, which are metal materials. Surface quality includes beauty, adhesion of paint and enamel, press workability, corrosion resistance, gloss, etc., and the geometric shape of the board, that is, surface roughness, has an important influence on these properties.

The most common method of obtaining a metal surface with the desired surface roughness for each application is by cold rolling or/and
In this method, the surface of a temper rolling roll is processed to a predetermined roughness, and a steel plate is I'E-rolled using this roll at a predetermined pressure, thereby transferring the roughness of the roll surface onto the plate surface.

Conventionally widely used methods for roughening the roll surface include (1) shot blasting and (2) electrical discharge machining.

Shot blasting is very simple and has the advantage of work-hardening the roll surface and improving the wear resistance of the roll, but it has the advantage of uneven roughness and deep roughness. It has drawbacks such as being difficult to attach.

In electrical discharge machining, roughness is controlled by changing the applied voltage and frequency between a rotating roll and an axially moving electrode, but the range of sparks that determines the size of the crater depends on the shape of the electrode. Since it is determined by the dimensions, it is difficult to obtain fine, small-pitch roughness beyond a certain limit. In addition, the convex parts created by electrical discharge machining are mechanically weak.
The initial wear of the rolls during rolling is severe, and the roughness of the transferred plate surface changes drastically.

In contrast to the above two methods, a processing method using a laser beam (hereinafter referred to as laser dull processing) has recently been proposed.

For example, JP 56-160892, JP 58-255
57, JP-A-54-61043, JP-A-55-9479
0, etc.

- All of them describe in detail how to irradiate laser pulses, but do not mention the characteristics of the irradiated roll.

[Problem that the invention seeks to solve]

The inventors began research to develop roll surface roughening technology based on laser dulling. When temper rolling was carried out using a roll whose surface had been roughened by laser dulling, it was found that the initial wear of the roll was quite large and the effect of this method could not be fully demonstrated.

In order to investigate the cause, we cut the roll into rings and investigated the cross-sectional structure and hardness distribution near the surface. As a result, we found that there was a retained austenite phase that was softer than the base metal near the surface, like the convex parts. .

The present invention focuses on this point, and has little wear even when rolled.
Therefore, it is an object of the present invention to provide a method for roughening the surface of a mill roll using a pulsed laser, which causes less reduction in roughness.

[Means for solving problems]

That is, in the present invention, when roughening a cold rolling roll by laser dulling, (IIL) the roll has a component whose Ms point (starting temperature of martensitic transformation) at the time of melting and solidification is 200°C or higher. to use

(b) 5X104~9X10eW/on the roll surface
The surface is roughened by irradiation with a laser beam having an energy density of cm'.

A method for roughening the surface of a cold rolling roll, characterized by:

[Effect]

The soft portion of the roll surface layer after laser dulling is caused by the metal being quenched once melted by laser irradiation, and the austenite phase remains without sufficient transformation into martensite.

Whether martensite is sufficiently formed after quenching is determined by the Ms point, which depends on the components. The Ms point is expressed by the following equation. (The following formula is expressed in 0F, so convert it to °C) Ms, ('F) = 930-5400
-60Mn-40Cr-3ONi -20Si-20M.

Here, C, Mn, Cr, Ni, Si, and Mo are weight percent of each component.

The Ms point is particularly influenced by C, and the others are Mn.

The influence of Cr is also large.

When the C, Mn, and Cr components are large, the Ms point decreases, and as a result, the Mf point also decreases. The Ms point of roll components commonly used for cold rolling is 100 to 150°C.

Detailed experiments have shown that if the Ms point is 200°C or higher, the Mf point (the temperature at which martensitic transformation ends) is higher than room temperature. Sufficient martensitic transformation can be obtained when the surface is melted and solidified by laser irradiation and cooled to room temperature. I found out. Therefore, by laser irradiating a roll whose composition has a Ms point of 200°C or higher during melting and solidification, it is possible to achieve a state in which the surface layer of the roll has extremely little residual austenite.After laser irradiation, a special hardening treatment is applied. There is no need for

The method of the present invention uses the above-mentioned technical means to provide much superior wear resistance compared to conventional methods, and can suppress changes in plate surface roughness to a small level.

〔Example〕

Hereinafter, a detailed explanation will be given based on examples.

FIG. 1 shows an overall view of a surface roughening apparatus that can be suitably used in carrying out the present invention.

The roll 1 is attached to a roll rotation support device M2 having a configuration similar to that of a machine tool such as a lathe or a grinder, and is rotated at a predetermined speed.

On the other hand, the laser beam output from the laser oscillator 3 is irradiated approximately perpendicularly onto the roll surface via a plurality of mirrors. The laser beam is adjusted to a predetermined beam by an optical device, and further focused and narrowed onto the roll surface. The laser irradiation head section 4 can be moved parallel to the roll axis direction by rotation of the drive screw 5 which is synchronized with the roll rotation. The laser beam can be pulsed to a predetermined frequency by a Q-switch or by a mechanical chopper. The pattern and depth of the surface roughness can be controlled by setting the frequency and output of this pulse, the number of rotations of the roll, and the moving speed of the laser irradiation head.

In the method of the present invention, a roll having a Ms point of 200° C. or higher during melting and solidification is used as the roll component used before this operation. As a result, the roll has a hardness equal to or higher than that of the base material up to the surface, and exhibits excellent wear resistance.

Next, specific processing conditions will be shown based on specific examples.

The rolling mill used in the experiment was a small laboratory rolling mill, and the diameter of its rolls was 70 mm. A hoop-shaped material was continuously rolled using this roll, and roll wear and changes in the roughness of the material surface were investigated.

The chemical composition of the rolls used in the experiment was C: 0.85% by weight Si: 0.8 weight% Mn: 0.4 weight% Ni: 0.15% by weight Cr: 2.9 weight% Mo: 0.29% by weight V: 0.01% by weight This is a commonly used component system.

The Ms point during melting and solidification is 152°C.

The chemical composition of the roll as a comparative material is C: 0.5% by weight, Si: 0.8% by weight, Mn: 0.8% by weight, Ni: 0.2% by weight, Cr: 1.0% by weight, Mo: 5. O weight % V: 0.01 weight %, and the Ms point during melting and solidification is aimed at 200°C or higher, and the Ms point is 232°C.

The manufacturing process of the roll is as follows.

That is, after casting molten steel with the above components, the temperature is 1100.
It was forged at ℃ to a forging ratio of 3.5. Thereafter, a so-called norm treatment of heating to 950° C. and cooling with air was performed. This is heated to 800℃
After carbide spheroidization treatment for ×lθ hours and 700°C × 10 hours, machined to the specified dimensions.After machining, heated to 900°C, quenched in oil, tempered at 650°C, and then Machined to final dimensions. Furthermore, the surface layer was heated to 900° C. by induction heating, quenched in water, tempered at a low temperature of 150° C., and then the final surface was polished.

Rolls subjected to such treatment exhibit a healthy structure in which spherical carbides are uniformly distributed in the martensitic matrix.

Using this apparatus, the surface of this roll was roughened to a predetermined roughness by irradiating a pulsed C02 gas laser beam using a mechanical chopper.

Laser irradiation conditions are: Laser power: 2kW, Pulse frequency: 56kHz, Energy density: 6.4X 10BW/cm” 1
Irradiation time per pulse: 13ILsec Pitch of craters formed on the roll surface after irradiation: Roll circumferential direction,
The resulting roll roughness is 170#Lm in both axial directions, and Rmax is approximately 15ILm.
It is.

FIG. 2 shows the results of measuring the hardness distribution near the roll surface of the conventional component which has been roughened in this way.

Figure 3 shows the results of measuring the hardness distribution near the roll surface of the components whose MS point is 200°C or higher. The melted part during laser irradiation is sufficiently transformed into martensitic material by subsequent cooling, and the surface layer exhibits high hardness.

Using these two sets of rolls, a cold-rolled and annealed plate of low carbon An-killed steel with a plate thickness of 0.8 mm was rolled at a reduction rate of 0.8%.
Figure 4 shows the results of temper rolling and comparison of changes in plate surface roughness.

As is clear from FIG. 4, when rolling is performed using a laser-processed roll having an Ms point of 232° C., the decrease in roughness of the rolled material can be significantly reduced compared to the conventional method.

〔Effect of the invention〕

By performing laser surface roughening on a roll whose Ms point is 200°C or higher, the wear of the laser dulled roll can be reduced.
Roughness changes on the surface of the rolled material are significantly improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a roll surface roughening processing device that can suitably carry out the method of the present invention, FIGS. 2 and 3 are graphs showing the relationship between the depth from the surface of the roll and hardness, and FIG. The figure is a graph showing the relationship between actual machine equivalent pressure extension and average surface roughness. l... Roll 2... Roll rotation support device 3... Laser oscillator 4... Laser irradiation head 5
...Laser drive screw

Claims (1)

[Claims] 1 When roughening the surface of a cold rolling roll,
A method for roughening the surface of a cold rolling roll, comprising using a roll material having an Ms point of 200° C. or higher during melting and solidification, and roughening the surface of the roll by irradiating the surface with a laser beam.