JP2689801B2 - Method for removing surface defects from hot rolling rolls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rolling roll, and more particularly to surface flaws method for removing high hardness roll for hot <br/> rolling.

[0002]

2. Description of the Related Art Recent improvements in the wear resistance of rolling rolls are
There are some amazing things. For example, JP-A 1-240634,
2-25205, 2-88745, 3-126838, 3-1938
High carbon type high speed steel (high speed tool steel) rolls used as work rolls for hot rolling as disclosed in Japanese Patent No. 48, 3-219047, etc. contain high hardness carbide and high hardness matrix. Therefore, superior wear resistance is expected.

However, when such a high hardness roll is ground, there arises a problem that it is difficult to grind due to its excellent wear resistance and the grinding efficiency is significantly lowered.

Therefore, a special grindstone is being developed in order to enhance the grinding efficiency of the high hardness roll.

[0005]

However, even if the grinding speed can be improved by using the above-mentioned grindstone, in the conventional grindstone grinding method, the maximum depth of the roll body is 20.
Since scratch-like surface flaws of about μm are generated, the surface flaws are transferred to the product during rolling, and the product quality is significantly deteriorated. Although the cause of occurrence of the scratch-shaped surface flaw is not clear, it is presumed that the abrasive grains are separated from the grindstone during the grinding and are sandwiched between the grindstone and the roll, resulting in a suppressed flaw.

Moreover, when the scratch-like surface flaw is generated, it remains because it has not been erased even during the rolling of 40 to 50 steel materials due to the excellent wear resistance characteristic of the high-hardness roll for rolling. Is a major cause of lowering.

Therefore, an object of the present invention is to provide a surface flaw removing method for a hot rolling roll which can easily remove only a surface layer portion including a scratch-like surface flaw that occurs during grinding of a high hardness rolling roll. .

[0008]

Therefore, the present inventor has made diligent studies in order to remove the scratch-like surface flaws as described above, and has found the following facts: Only the surface layer including surface flaws having a maximum depth of about 20 μm should be softened and worn before the roll is used. 2. For that purpose, it is only necessary to subject only a large amount of austenite having a low hardness to the hardened structure by subjecting only the surface layer including the surface flaw of the high-hardness roll for rolling to ultra-rapid quenching. 3. Furthermore, for the heat treatment of such a thin layer, the irradiation of laser light, which has been conventionally used exclusively for the purpose of increasing the hardness and adding unevenness to the surface, can be unexpectedly used. The present invention was accomplished by finding the above.

That is, the present invention relates to a rolling roll body .
By irradiating a laser beam to the surface layer portion including a scratch-shaped surface flaw by polishing with a whetstone to leave austenite, after converting the surface layer portion into a surface softened layer, the surface by abrading the surface softened layer It is characterized by removing flaws.

[0010]

According to the present invention, the roll body for hot rolling has a
By irradiating the surface layer portion including scratch-shaped surface flaws by polishing with a grindstone with a laser beam to leave austenite having a low hardness in the structure, the surface layer portion can be transformed into a surface softened layer.

Then, the surface defects can be easily removed by abrading the surface softening layer whose abrasion resistance is lowered.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to the embodiments shown in the drawings. In general, the surface structure of a high hardness roll for rolling represented by a high carbon type high speed steel roll has a matrix structure in which austenite that is low hardness and structurally unstable is reduced as much as possible, such as martensite, bainite and pearlite tempered. It is an organization. That is, it is a common technical idea in the production of high hardness rolls for rolling to reduce the retained austenite as much as possible from the surface structure of the roll.

However, the surface layer portion of the high hardness roll having such a hardened structure is irradiated with laser light and rapidly heated and rapidly cooled, so that incompletely hardened state, that is, austenite having low hardness remains in the structure. It is possible.

Therefore, in the present invention, a laser beam oscillated by a laser oscillator is applied to a surface layer portion including a scratch-shaped surface flaw generated during grinding of a high hardness rolling roll.
By forming a large amount of retained austenite having a low hardness only in the surface damage layer having a maximum depth of about 20 μm, the surface damage layer is transformed into a surface softening layer having low wear resistance. Then, the surface softened layer is rapidly worn at the initial rolling stage or is ground by an in-line / on-line grinder before rolling to remove the scratch-like surface flaws. As the laser oscillator, a CO ₂ gas laser or a YAG laser is preferable from the viewpoint of the softening depth. The laser output, the energy density, and the like, which are laser irradiation conditions, may be selected in consideration of the thickness of the surface layer portion where the surface flaw is generated. Further, the effect of the present invention does not change even if laser light is radiated by continuous oscillation parallel to either the axial direction of the roll body or the circumferential direction.

Further, it is also possible to rapidly heat and melt only the surface layer of the roll by irradiating it with laser light, and then rapidly cool and solidify it by self-cooling.

The surface flaw removal method of the present invention is applied to rolling rolls such as hot steel plates, shaped steels, wire rods and pipes ,
In combination with a roll profile measuring instrument, it can be used for in-line and offline roll profile management.

Roll materials to which the present invention can be preferably applied include high-Cr cast iron (C: 2.0 to 3.
0%, Si: 0.4 to 1.0%, Mn: 0.5 to 1.5%, Ni: 0.5
~ 2.0%, Cr: 13-20%, Mo: 2.0% or less) and high alloy grain cast iron (C: 2.8-3.5%, Si: 0.5-1.2%, Mn:
0.5 to 1.0%, Ni: 3.5 to 5.0%, Cr: 0.5 to 2.5%,
The effect of the present invention is not particularly changed as long as it has a chemical component with good hardenability such as Mo: 1.0% or less).

Experimental Example 1 Next, the effect of the present invention will be clarified by an experimental example. A disk-shaped test piece (φ100 mm × 30 mm) was prepared from a high-carbon high-speed steel having the chemical composition shown in Table 1, and the side surface was polished with a grindstone to generate scratches of about 15 μm at maximum. Then, the side surface is CO ₂
It was rapidly heated and rapidly cooled by a gas laser. Laser irradiation conditions are laser output 450W, irradiation processing speed 30m / min
Continuous oscillation was carried out at 30 l / min as a shield gas.

[0019]

[Table 1]

As shown in FIGS. 1 and 2, the test pieces obtained as a result have scratch-like surface flaws.
It was found that the hardness decreased to about μm. It was also confirmed that the base area was not thermally affected.

(Experimental Example 2) A rolling type abrasion tester shown in FIG. 3 is used by using a test piece (Example 1) which is laser-treated as described above and a test piece (Comparative Example 1) which is not laser-treated. The hot wear test was carried out. In addition, in FIG.
1 is a roll test piece, 2 is a mating material, 3 is a high frequency coil, 4
Is cooling water and 5 is draining air.

As a result, as shown in FIG. 4, in Comparative Example 1, the scratch-like surface flaws did not disappear easily, whereas in Example 1, the depth from the surface to 15 μm was rapid after the test was started. It was found that the surface was abraded and the surface flaw was removed. Further, after the surface softening layer is worn, Comparative Example 1
It was also confirmed that the wear rate was the same.

Further, from a cross-section metallographical microscopic observation after abrasion at a depth of 15 μm, it was confirmed that the surface softening layer having scratch-like surface flaws softened by the laser was completely removed and the roll surface was also cracked. It was confirmed to be very good without any problems.

[0024]

As described above, according to the present invention, the hot pressure
It is possible to easily remove only the surface-damaged layer having scratch-shaped surface flaws by polishing with a rolling high-hardness roll, and to improve product quality.

[Brief description of the drawings]

FIG. 1 is a graph showing a hardness distribution in a depth direction of a roll obtained by the method of the present invention.

FIG. 2 is a metallurgical micrograph (magnification: 100 times) of the surface softening layer.

FIG. 3 is an explanatory diagram showing a procedure of a hot friction test.

FIG. 4 is a graph comparing the wear rates of Example 1 and Comparative Example 1.

[Explanation of symbols]

1 ... Roll test piece, 2 ... Counterpart material, 3 ... High-frequency induction coil, 4 ... Cooling water, 5 ... Draining air

Claims (1)

(57) [Claims] 1. A grinding roll for grinding a roll roll body .
By irradiating the surface layer portion including the clutch-shaped surface flaw with laser light to leave austenite, the surface layer portion is transformed into a surface softened layer, and then the surface flaw is removed by abrading the surface softened layer. Heat characterized by
Surface defect removal method between the rolling rolls.