JPH0978180A - Steel material excellent in high density energy line cutting property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel material excellent in high density energy line cutting property. SOLUTION: This steel material has a composition containing 0.10-<0.50% Si and 0.08-<0.30% Cr and also has blue scale of 10-60μm thickness, and further, an internally oxidized layer of 1-5μm thickness, in which 0.5-5.0% Si and 0.4-4.0% Cr are concentrated, exists in the interface between the scale and the ferrite. Further, at least one element, selected from a second element group consisting of Nb, V, Ti, Cu, Ni, Cr, Mo, and B and a third element group consisting of Ca and REM, can be incorporated into the steel. This steel material can be produced by subjecting a steel, having a composition where limited amounts of C, Mn, and Al are added besides the above components, to heating at 1,050-1,300 deg.C and then to rolling under specific conditions where temp. and draft are respectively controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material (in particular, a thick steel plate, a steel strip, etc.) using a high-density energy beam and having an excellent thermal cutting property, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In the fields of construction machinery, shipbuilding, bridges, and the like, there are major issues in the entire industry, such as reduction of manufacturing costs, and measures such as automation of manufacturing lines and thoroughness of processing operations are being taken. Under such circumstances, a cutting machine using a high-density energy beam (for example, a laser beam) capable of automatically and efficiently cutting with high precision is remarkably popular in the above fields.

However, steel materials used in large amounts in these fields (for example, thick steel plates having a plate thickness of 12 to 25 mm, and steel strips) are satisfactorily cut only under certain specific cutting conditions during high-density energy beam cutting. Is possible, and since the good cutting conditions vary depending on the steel material,
One of the greatest merits of the cutting method using a high-density energy beam is the automation and the efficiency, which are significantly impaired.

The reason for this is that when a large amount of dross is generated (self-burning) due to an excessive reaction between iron and oxygen gas which is an assist gas at the time of cutting, it is difficult to discharge the dross from the lower part of the cutting groove. In addition to the fact that the cutting conditions that occur depending on the steel material and the use of high-density energy rays, it is possible to perform high-precision cutting with a very narrow cutting groove width, but a slight amount of self-burning causes dross. This is because it cannot be discharged.

This is a phenomenon that can occur with any type of high-density energy beam, as long as oxygen gas is used as an assist gas to perform narrow thermal cutting of the cutting groove width with the high-density energy beam. However, there is a strong demand for a steel material having excellent thermal cuttability that does not cause self-burning regardless of cutting conditions.

However, for example, in laser cutting using a laser beam as a high-density energy ray, good cutting can be achieved under any of various cutting conditions by changing the laser output, cutting speed, etc. A possible steel material and a manufacturing method capable of inexpensively and stably manufacturing the steel material have not been established.

[0007]

The problem to be solved by the present invention is a high density energy ray cuttability which can greatly contribute to the reduction of manufacturing cost, which is a major problem in the fields of construction machinery, shipbuilding, bridges and the like. An excellent steel material and a method for stably manufacturing the steel material at low cost.

[0008]

The present invention has been made to solve the above problems, and the summary thereof is as follows. (1) C: 0.03 to 0.25% by weight%, Si:
0.10 to less than 0.50%, Mn: 0.05 to 1.60
%, Cr: 0.08 to less than 0.30% Al: 0.005
.About.0.10%, the balance being Fe and unavoidable impurities, having a blue scale of 10 to 60 .mu.m, and
0.5 to 5.0% Si at the interface between the scale and the base steel,
A steel material excellent in high-density energy ray cuttability, in which an internal oxide layer having a thickness of 1 to 5 μm in which 0.4 to 4.0% of Cr is concentrated is present.

(A) C: 0.03% by weight (2)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: containing at least one element selected from the group consisting of 0.0003 to 0.003%, the balance consisting of Fe and unavoidable impurities, having a blue scale of 10 to 60 μm in thickness, Moreover, 0.5 to 5.0% Si and 0.4 to 14.0% Cr are present at the interface between the scale and the base metal.
A steel material having a high-density energy ray cuttability, in which an internal oxide layer having a thickness of 1 to 5 μm is concentrated.

(A) C: 0.03% by weight (3)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: 0.0003 to 0.003%, at least one element selected from the group consisting of (c) Ca: 0.
0003 to 0.010%, REM: 0.001 to 0.0
30%, containing at least one element selected from the group consisting of, the balance consisting of Fe and unavoidable impurities, having a blue scale of 10 to 60 μm in thickness, and
0.5 to 5.0% Si at the interface between the scale and the base steel,
A steel material excellent in high-density energy ray cuttability, in which an internal oxide layer having a thickness of 1 to 5 μm in which 0.4 to 14.0% of Cr is concentrated is present.

(4) In% by weight, C: 0.03 to 0.2
5%, Si: 0.10 to less than 0.50%, Mn: 0.0
5 to 1.60%, Cr: 0.08 to less than 0.30%, A
1: 0.005 to 0.10%, the balance Fe and unavoidable impurities, the heating temperature is 1050 to 1300 ° C., and the rolling biting temperature of the final pass of rolling is T
_F (° C), the average rolling reduction of the final 3 passes in finish rolling is R _F
(%), 880 ≦ T _F ≦ 1020 (° C.) 21 ≦ R _F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolled under the conditions that satisfy the three formulas at the same time, and then air-cooled after rolling. A method for producing a thick steel sheet excellent in high-density energy ray cutting property, which comprises cooling at the above cooling rate.

(A) C: 0.03% by weight (5)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: 0.0003 to 0.003%, at least one element selected from the group consisting of, and the balance Fe
And inevitable impurities, and the heating temperature is 1050-1
At 300 ° C., the rolling bite temperature of the final pass of rolling is T _F (° C.), and the average rolling reduction of the final 3 passes of finishing rolling is R.
_F (%), 880 ≤ T _F ≤ 1020 (° C) 21 ≤ R _F ≤ 40 (%) R _F ≥ 155-3T _F / 20 Rolled under the conditions that simultaneously satisfy the following three formulas, and then rolled. A method for producing a thick steel sheet having excellent high-density energy ray cuttability, which comprises cooling at a cooling rate of air cooling or higher.

(A) C: 0.03% by weight (6)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: 0.0003 to 0.003%, at least one element selected from the group consisting of (c) Ca: 0.
0003 to 0.010%, REM: 0.001 to 0.0
It contains at least one element selected from the group consisting of 30%, the balance consists of Fe and unavoidable impurities, the heating temperature is 1050 to 1300 ° C., and the rolling biting temperature in the final pass of rolling is T _F ( ℃), final 3 in finish rolling
The average rolling reduction path when the _{R F (%), 880 ≦} T F ≦ 1020 (℃) 21 ≦ R F ≦ 40 (%) R F ≧ 155-3T simultaneously satisfying condition 3 Expression of _F / 20 The method for producing a thick steel sheet excellent in high-density energy ray cuttability, comprising:

(7) In% by weight, C: 0.03 to 0.2
5%, Si: 0.10 to less than 0.50%, Mn: 0.0
5 to 1.60%, Cr: 0.08 to less than 0.30%, A
1: 0.005 to 0.10%, the balance Fe and unavoidable impurities, the heating temperature is 1050 to 1300 ° C., and the rolling biting temperature of the final pass of rolling is T
_F (° C), the average rolling reduction of the final 3 passes in finish rolling is R _F
(%), 880 ≦ T _F ≦ 1020 (° C.) 21 ≦ R _F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolled under the conditions that satisfy the three formulas at the same time, and after rolling is finished. 5
A method for producing a steel strip having excellent high-density energy ray cuttability, which comprises air-cooling for 30 seconds, winding, and cooling to room temperature.

(A) C: 0.03% by weight (8)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: 0.0003 to 0.003%, at least one element selected from the group consisting of, and the balance Fe
And inevitable impurities, and the heating temperature is 1050-1
At 300 ° C., the rolling bite temperature of the final pass of rolling is T _F (° C.), and the average rolling reduction of the final 3 passes of finishing rolling is R.
_{When F} (%) is set, rolling is performed under the condition that the three formulas of 880 ≦ T _F ≦ 1020 (° C.) 21 ≦ R _F ≦ 40 (%) R _F ≧ 155-3T _F / 20 are simultaneously satisfied, and the rolling is completed. After 5
A method for producing a steel strip excellent in high-density energy ray cutting property, which comprises cooling for 30 seconds with air, winding, and cooling to room temperature.

(A) C: 0.03% by weight (9)
0.25%, Si: 0.10 to less than 0.50%, Mn:
0.05 to 1.60%, Cr: 0.08 to less than 0.30%, Al: 0.005 to 0.10%, and
(B) Nb: 0.001 to 0.20%, V: 0.001
~ 0.30%, Ti: 0.001 to 0.20%, Cu:
0.05 to 1.50%, Ni: 0.05 to 1.50%,
Cr: 0.30 to 1.00%, Mo: 0.05 to 1.0
0%, B: 0.0003 to 0.003%, at least one element selected from the group consisting of (c) Ca: 0.0
003 to 0.010%, REM: 0.001 to 0.03
0%, and at least one element selected from the group consisting of, the balance consisting of Fe and unavoidable impurities, the heating temperature is 1050 to 1300 ° C., and the roll entrapment temperature of the final pass of rolling is T _F (° C), final 3 in finish rolling
The average rolling reduction path when the _{R F (%), 880 ≦} T F ≦ 1020 (℃) 21 ≦ R F ≦ 40 (%) R F ≧ 155-3T simultaneously satisfying condition 3 Expression of _F / 20 Rolling at 5
A method for producing a steel strip excellent in high-density energy ray cutting property, which comprises cooling for 30 seconds with air, winding, and cooling to room temperature.

The inventors of the present invention have conducted a number of experiments to solve the above problems. As a result, in order to widen the range of cutting conditions in which good cutting is possible, the steel material is provided with a blue scale having a thickness of 10 to 60 μm. It is found that it is important to impart, and to impart scale peeling resistance, and further,
By satisfying the above, the present invention succeeded in developing a method for inexpensively and stably producing a steel material excellent in high-density energy ray cutting property.

FIG. 1 shows the effect of scale on the high-density energy ray cutting property. This figure shows the laser cuttability of 16 mm thick steel plates with various scale thicknesses and scale color tones. The scale color of the steel sheet surface is JIS
In conformity with Z 8722 was determined at measured a ^* values at colorimeter, the scale tone when the a ^* value ≦ 0.5 blue,
When 0.5 <a ^* value, the scale color tone was red.

The laser cutting performance is evaluated by laser output,
The number of cutting conditions is set so that cutting can be performed satisfactorily when cutting is performed under 15 conditions in which the cutting speed is changed. The laser output was varied between 1.8 and 3.0 kW and the cutting speed was varied between 0.6 and 1.1 m / min.

FIG. 2 shows specific conditions of the laser output and the cutting speed used for the evaluation of the laser cutting property by using an example of the cutting result. 2 shows the roughness of cut surface (Ra value) is 15μ.
It was as small as m or less and could be cut satisfactorily, and the mark x indicates that it could not be cut well due to occurrence of self-burning or adhesion of dross. The number of circles in FIG. 2 is the numerical value on the vertical axis in FIG. 1, and the larger this numerical value is, the wider the range of cutting conditions in which good cutting can be performed. From FIG. 1, 10 to 60 μm
It can be seen that steel having a blue scale with a thickness of (preferably 20 to 40 μm) has excellent laser cuttability.

Next, FIG. 3 shows the influence of the amounts of Si and Cr at the interface between the scale and the base metal on the laser cutting property. The method for evaluating laser cutting properties is the same as that in FIG. From FIG. 3, 0.5% or more of Si and 0.
It is recognized that the laser cuttability becomes good in steel in which 4% or more of Cr is concentrated.

At this time, at the interface between the scale and the ground iron,
An internal oxide layer having a thickness of 1 to 5 μm is formed. In the steel having such an internal oxide layer, the scale peeling at the time of laser cutting hardly occurs, and the laser cuttability becomes good because Si and Cr are concentrated in the internal oxide layer and the scale peeling resistance is improved. This is to improve.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the effects brought about by the limitation of the components and the heating and rolling conditions in the present invention will be described below. The reasons for limiting the components in the present invention will be described. It is necessary to add 0.03% or more of C in order to secure the strength. Addition of a large amount deteriorates the toughness of the base metal and hardens the weld heat affected zone to deteriorate the weldability, so the upper limit is 0.25.
%.

Si is an essential element in the present invention in order to improve the adhesion of scale, and it is necessary to add Si in an amount of 0.10% or more to obtain the effect. Addition of a large amount deteriorates the descaling property during rolling, makes it easier for scale indentation defects to occur, and raises the cost, so the upper limit is made less than 0.50%.

Mn must be added in an amount of 0.05% or more in order to fix S contained in steel and improve toughness.
Since the addition of a large amount increases the production cost and also lowers the toughness, the upper limit is set to 1.60%.

Cr is an essential element in the present invention in order to improve the adhesion of the scale, and it is necessary to add 0.08% or more to obtain the effect. Addition of a large amount raises the manufacturing cost, so the upper limit is less than 0.30%
And Since Al is deoxidized in steel, it is necessary to add 0.005% or more, and if added in a large amount, the toughness is remarkably reduced, so 0.10% is made the upper limit.

In the present invention, in addition to the above-mentioned elements, the steel used is Nb:
0.001 to 0.20%, V: 0.001 to 0.30
%, Ti: 0.001 to 0.20%, Cu: 0.05 to
1.50%, Ni: 0.05 to 1.50%, Cr: 0.
30-1.00%, Mo: 0.05-1.00%, B:
At least one element selected from the group consisting of 0.0003 to 0.003% can be contained.

Nb, V, and Ti have the effect of precipitating as carbonitrides in the steel and increasing the strength, and by making the microstructure of the steel finer, the strength, the base metal toughness, and the toughness of the heat affected zone of welding are combined. Has the effect of improving. For each element, addition of 0.001% or more is necessary to obtain the effect, and addition of a large amount significantly deteriorates the toughness of the weld heat affected zone. Therefore, the upper limits are 0.20% for Nb and V for V. 0.30%, Ti is 0.
20%.

Cu has the effect of improving strength and corrosion resistance. To obtain the effect, addition of 0.05% or more is necessary. Since addition of a large amount causes hot cracking of the slab, its upper limit is set to 1.50%. Ni has the effect of improving both strength and toughness. To obtain this effect, addition of 0.05% or more is necessary, and addition of a large amount significantly impairs economic efficiency, so the upper limit is made 1.50%.

As described above, Cr is an essential element to be added in an amount of 0.08% or more in the present invention in order to improve the adhesion of the scale. In addition to that effect, the effect of enhancing hardenability and temper softening are also provided. It has an effect of increasing resistance and an effect of improving corrosion resistance. For the purpose of obtaining these effects, even if the addition amount of Cr is 0.30% or more, the effects of the present invention are not impaired. Addition of a large amount deteriorates the toughness of the weld heat affected zone, so the upper limit is made 1.00%.

Mo has the effect of enhancing hardenability and the effect of enhancing temper softening resistance. In order to obtain these effects, addition of 0.05% or more is necessary, and addition of a large amount deteriorates the toughness of the weld heat affected zone, so the upper limit is made 1.00%.

B has the effect of significantly improving the hardenability and increasing the strength. 0.00 to get the effect
It is necessary to add 03% or more, and if a large amount is added, the weld heat-affected zone is hardened and the weldability is greatly deteriorated.

Further, in the present invention, the steel contains Ca: 0.0003 to 0.0100%, and REM: 0. At least one element selected from the group consisting of 001 to 0.030% can be contained.

Ca and REM have the effects of improving the anisotropy of the mechanical properties of steel and improving the lamella tear resistance. In order to obtain these effects, it is necessary to add Ca in an amount of 0.0003% or more and REM in an amount of 0.001% or more. Since the addition of a large amount of both elements deteriorates the toughness, the upper limit of Ca is 0. 0100% and REM 0.030%.

In the present invention, it is essential to form an internal oxide layer in which 0.5% or more of Si and 0.4% or more of Cr are concentrated at the interface between the scale and the base iron.
In order to concentrate a large amount of Si and Cr in the internal oxide layer, it is necessary to add a large amount of Si and Cr to the steel or heat the slab at a high temperature for a long time, which causes an increase in manufacturing cost. . Therefore, the upper limits of the concentration in the internal oxide layer are 5.0% for Si and 4.0% for Cr. However,
When the added amount of Cr in the steel is set to 0.30 to 1.00% for the purpose of enhancing the strength or imparting corrosion resistance, the upper limit of the Cr concentration in the internal oxide layer is set to 14.0%.

Next, a method for manufacturing a thick steel plate having excellent high-density energy ray cuttability will be described. The heating conditions will be described. A heating temperature of 1050 ° C. or higher (preferably 1170 ° C. or higher) is required in order to sufficiently concentrate the amounts of Si and Cr necessary for improving the scale peel resistance at the interface between the scale and the base iron. . The upper limit of the heating temperature is 1300 ° C. in order to suppress the occurrence of scale indentation flaws. Regarding the in-furnace time at the time of heating, the slab temperature should be uniformly 1050
It takes about 120 minutes to set the temperature to not less than 0 ° C., and heating for a long time causes an increase in manufacturing cost.

Regarding the rolling conditions, it is important to control the rolling temperature and the rolling reduction in order to stably produce the blue scale thick steel plate. FIG. 4 shows the influence of the rolling temperature and the rolling reduction on the scale state of the steel sheet. As the rolling temperature, the roll biting temperature of the final pass of finish rolling (hereinafter, referred to as rolling finish temperature T _F ) is the most important factor, and as the rolling reduction, the average rolling reduction of the final three passes of finishing rolling is used. (Hereinafter, referred to as finish rolling reduction R _F ) is the most important factor. For example, 7 pass rolling is 20%, 25%, 3% as finish rolling.
When the reduction ratios of 0%, 30%, 30%, 35%, and 35% are used, the finish reduction ratio R _F is (30 + 3).
5 + 35) /3=33.3%.

The three types of marks (○, Δ, ×) in FIG. 4 are
Each means the scale state shown in Table 1, and the claims relating to the rolling conditions of the present invention are ranges in which ◯ and Δ are surrounded by straight lines. The scale tone of the steel plate surface in Table 1 is JIS Z
Judgment was made based on a ^* value measured by a color difference meter in accordance with 8722.

The effect of the rolling finish temperature T _F on the scale state is large, and the scale color tone becomes blue by increasing the temperature. Conventionally, rolling is performed at a finish rolling reduction R _F of about 20% or less, but in this case, a blue scale thick steel sheet cannot be obtained unless the rolling finishing temperature T _F is 930 ° C. or more. In order to make the scale thickness 60 μm or less, the upper limit of the rolling finishing temperature T _F is 1020 ° C.

The influence of the finishing reduction rate R _F on the scale color tone is further large, and the scale color tone becomes remarkably blue by increasing the finishing reduction rate R _F. Conventional finish reduction R
Rolling finishing temperature T to produce blue scale thick steel plate at _F
F must be 930 ° C. or higher, but among the thick steel plates, a thick steel plate having a relatively thin plate thickness of about 12 to 25 mm causes a rapid temperature decrease of the steel plate surface during rolling, so that the rolling finish temperature T _F is stable. It was difficult to control the temperature to 930 ° C. or higher.

However, by increasing the finishing reduction ratio R _F to about 30%, the rolling finish temperature range in which the blue scale thick steel sheet can be obtained can be greatly expanded to the low temperature side of 880 ° C. or higher. Stable manufacturing is possible.
The upper limit of the finish rolling reduction R _F is set to 40% in view of the rolling capability. As indicated by a circle mark in FIG. 4, 880 ≦ T _F ≦
1020 (° C.), 21 ≦ R _F ≦ 40 (%), R _F ≧
By simultaneously satisfying the three conditions of 160-3T _F / 20, it is possible to manufacture a blue-scale thick steel sheet with almost no red scale.

By performing accelerated cooling after rolling, 10 to 10
It is possible to obtain a thick steel sheet having a desired scale thickness within a range of 60 μm and having excellent heat cuttability. Thick steel plates that are bent after hot cutting may require a thin scale, but accelerated cooling after rolling can meet this demand. Specific methods of accelerated cooling after rolling include water cooling and forced air cooling with a fan.

Next, a method of manufacturing a steel strip excellent in high density energy ray cutting property will be described. With respect to the heating conditions necessary for improving the peeling resistance of the scale and the rolling conditions required for the blue scale, the above-described heating and rolling conditions for the thick steel plate can be applied to the method for manufacturing a steel strip.

However, in the steel strip, the scale thickness tends to be thinner than that of the thick steel plate, and the scale thickness is 1
In order to adjust the thickness to 0 μm or more, it is necessary to perform air cooling for 5 seconds or more after rolling and then wind. If the time from rolling to winding is 30 seconds or more, the scale thickness exceeds 60 μm, so the air cooling time is 5 to 30 seconds.

As a result of intensive studies, it was found that the following four points were the main effects of the scale of the steel surface on the thermal cutting property. If the scale thickness is less than 10 μm, stable burning becomes difficult because self-burning occurs during thermal cutting. Even if the scale thickness is 10 μm or more, stable cutting becomes difficult if the scale is a red scale in which a large amount of crushed hematite (Fe ₂ O ₃ ) fine powder is present. This is because the red scale has a large number of parts where the scale has peeled off when viewed microscopically, so that self-burning occurs during thermal cutting.

The scale thickness is 10 μm or more, and
By making the blue scale with hematite in the form of lumps, and by imparting scale peeling resistance to steel so that scale peeling does not occur immediately before cutting due to assist gas pressure and thermal stress, self-burning does not occur and it is stable Can be cut. If the scale thickness is more than 60 μm, the steel material will be significantly degraded in scale resistance, making it difficult to perform stable thermal cutting.

That is, in order to improve the heat cutting property of the steel material, it is important to impart the steel material with a blue scale having a thickness of 10 to 60 μm and to impart scale peeling resistance. In addition, the steel material mentioned here is a thick steel plate and a steel strip.

Next, the reason why the control of the rolling temperature and the rolling reduction is important for the stable production of the steel material to which the blue scale is applied, and the specific method for imparting the scale peeling resistance will be described. . The reason why the control of the rolling temperature and the rolling reduction is important for stable production of blue scale steel will be described below.

As a result of extensive studies on the cause of the generation of red scale, the red scale is a fine powder of hematite.
Wustite (FeO) crushed to a fine size of about 10 μm and magnetite (Fe ₃ O ₄ ) were oxidized during cooling after rolling into hematite fine powder, and hematite crushed during rolling. It became clear that there is.

Then, as a result of extensive studies on the method of suppressing the crushing of the scale during rolling, the present invention has been achieved, and the gist thereof is the following 6 points. In order to prevent the scale from being crushed during rolling, it is effective to set the rolling finishing temperature T _F to a high temperature. The reason for this is that if the temperature during rolling is sufficiently high, the scale can be plastically deformed before being crushed by having ductility equivalent to that of the base steel.

However, in the conventional rolling with a rolling reduction of about 20% or less, the rolling finishing temperature T _F is 930.
Blue scale steel cannot be obtained unless the temperature is above ℃. Thickness 1
With steel having a relatively thin plate thickness of about 2 to 25 mm, it is difficult to stably stabilize the rolling finishing temperature to 930 ° C. or higher. Therefore, by simply increasing the rolling finishing temperature T _F to a high temperature, stable production of blue scale steel is possible. Is difficult. Increasing the rolling reduction at the time of rolling is very effective for blue scaling.

The mechanism is to increase the rolling reduction by increasing the rolling heat of the steel during rolling, suppress the temperature decrease of the scale on the steel surface, and maintain the ductility of the scale high. Because it can be made thinner and less likely to be crushed during rolling. By increasing the finishing reduction ratio R _F as compared with the conventional one, it is possible to reduce the finishing temperature T _F required for forming the blue scale to about 880 ° C., and thereby the plate thickness 1
It is possible to produce 2-25 mm blue scale steel.

Further, in order to impart scale peeling resistance to the steel material when laser cutting, 0.5% or more Si and 0.4% or more Cr are simultaneously concentrated at the interface between the scale and the base iron. It is effective to provide an internal oxide layer having a thickness of 1 to 5 μm, and in order to form such an internal oxide layer in the steel material, 0.1% or more Si and 0.08% or more Cr in the steel are formed. 1050 ° C. (preferably 1170 ° C.)
It is necessary to perform hot rolling after heating at a temperature of (° C.) Or higher.

[0054]

[Example] The effect of scale thickness on laser cutting
12 to 25 having the chemical composition of steel numbers A to C shown in Table 2
Table 3 shows the results using a thick steel plate having a thickness of mm. Test Steel No. 1-29
All test materials up to were heated at 1200 ° C. After the heating, the rolling temperature and the rolling reduction were changed for each test material, and the test materials with different scale color tone and scale thickness were manufactured, and the laser cutting property was evaluated. Scale tone of Table 3, the scale tone when in the same manner as Table 1 was evaluated by the a ^* value of the steel surface, the scale tone when the a ^* value ≦ 0.5 blue, of 0.5 <a ^* value Was red.

The scale thickness was an average value of 5 points measured from an optical micrograph of the scale cross section. As for the laser cutting property, the laser output and cutting speed were changed as in FIG.
Evaluation was performed based on the number of cutting conditions that allow good cutting when cut under the same conditions.

Specimen steel Nos. 1 to 12 are steels of the present invention, and
Having a blue scale with a thickness of 0 μm or more and 60 μm or less,
Furthermore, since the chemical composition and the heating temperature are within the range of the present invention, 0.5 to 5.0% of Si and 0.4 to 4.0% of Cr are concentrated in the interface between the scale and the base metal. Thickness 1-5
Due to the presence of the internal oxide layer of μm, good laser cutting property can be obtained.

On the other hand, although the sample steels Nos. 13 to 19 are blue scale steels, the scale thickness thereof deviates from the range of the present invention, and therefore good laser cutting property cannot be obtained. Also,
Since the test steel Nos. 20 to 29 are red scale steels, good laser cuttability cannot be obtained.

Next, the effects of the addition amounts of Si and Cr in the steel and the heating temperature on the laser cuttability are shown in Table 2. Steel plates A to H shown in Table 2 have a thickness of 12 to 25 mm and are thick steel plates. And shown in Table 4 using the steel strip. The amounts of Si and Cr in the internal oxide layer in Table 4 are the values obtained by quantitative analysis using an EPMA analyzer, and the thickness of the internal oxide layer is the SEM of the scale cross section.
The average value of 5 points measured from the photograph was used. The evaluation method of the laser cuttability is the same as that of FIG. 1 and Table 3.

All the thick steel plates in Table 4 have rolling finish temperatures T _F
Is 885 to 982 ° C., and the finishing reduction ratio R _F is 29.3 to 3
Since it is manufactured by rolling under the rolling condition of 4.2% and then air cooling or water cooling, it has a blue scale with a thickness of 10 to 60 μm. In addition, all the steel strips in Table 4 have a rolling finish temperature T
_F is 920 to 962 ° C, finishing reduction ratio R _F is 29.5 to 3
Since it is manufactured by rolling under a rolling condition of 2.5%, air-cooling for 5 to 12 seconds, and then winding up, it has a blue scale with a thickness of 10 to 30 μm.

Steel Nos. 1 to 15 of the present invention are the steels of the present invention, and since the amounts of Si and Cr in the steel and the heating temperature are appropriate, the peeling resistance of the scale is improved at the interface between the scale and the base metal. Since an effective internal oxide layer is formed and a blue scale having an appropriate thickness is formed, the laser cutting property is excellent. In the case of the test steel Nos. 16 to 21, since the amount of Cr added in the steel is small, the internal oxide layer is present, but the Cr in the internal oxide layer is present.
The amount is small, the scale peeling resistance is not improved, and good laser cutting property cannot be obtained.

Steel Nos. 22 to 27 under test had a small amount of Si added to the steel and therefore had almost no internal oxide layer, and could not obtain good laser cutting properties. Steel under test No. 28-30
Although satisfying the addition amounts of Si and Cr in the steel, since the heating temperature is low, the internal oxide layer effective for improving the scale peeling resistance cannot be obtained, and the laser cutting property is not good.

Next, the effect of rolling conditions on the scale properties of thick steel plates is shown in Table 5 by using thick steel plates of 12 to 25 mm thickness having the chemical compositions of steel numbers A to C shown in Table 2.
All of the sample steels from sample steel numbers 1-27 are 1050 ° C.
After heating at a temperature of ˜1300 ° C., hot rolling was performed under the rolling conditions shown in Table 5. The scale color tone in Table 5 was evaluated by the a ^* value on the surface of the steel sheet as in Tables 1 and 3. Test steel Nos. 1 to 18 are steels manufactured according to the present invention.
It is a thick steel plate provided with a blue scale having a thickness of 0 to 60 μm.

Specimen Nos. 19 to 24 are red scale steel plates with 0.5 <a ^* value because the rolling conditions deviate from the condition range of the present invention. Since the rolling finish temperatures of the test steel Nos. 25 to 27 are 1020 ° C. <T _F , the scale thickness becomes thicker than 60 μm.

Next, the influence of rolling conditions on the scale properties of the steel strip is shown in Table 6 using steel strips having a chemical composition of steel Nos. A to C shown in Table 2 and having a thickness of 12 to 16 mm. All of the sample steels from sample steel numbers 1 to 24 are 1050 ° C to 1
After heating at a temperature of 300 ° C., hot rolling and subsequent cooling and winding were performed under the conditions shown in Table 6. Sample steel Nos. 1 to 9 are steels manufactured according to the present invention.
It is a steel strip provided with a blue scale having a thickness of 0 to 58 μm.

The test steel Nos. 10 to 15 are red scale steels having 0.5 <a ^* value because the rolling conditions deviate from the condition range of the present invention. For the test steel numbers 16 to 17, the rolling conditions are blue scale within the range of the present invention, but since the air cooling time after rolling is short, the scale thickness is less than 10 μm. Sample steel Nos. 18 to 19 have a rolling finish temperature of 1020.
Since ° C <T _F , the scale thickness becomes thicker than 60 μm.

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

[Table 3]

[0069]

[Table 4]

[0070]

[Table 5]

[0071]

[Table 6]

[0072]

EFFECTS OF THE INVENTION According to the present invention, a steel material excellent in high-density energy ray cutting property, which can greatly contribute to the reduction of manufacturing cost, which is a major problem in the fields of construction machinery, shipbuilding, bridges, etc., can be manufactured at low cost. Since it enables stable supply, it is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is a scale thickness of a thick steel plate, which has an effect on laser cutting properties.
3 is a chart showing the influence of the scale color tone.

FIG. 2 is a chart of a laser cutting property test result.

FIG. 3 is a table showing the influence of the amounts of Si and Cr at the interface between the scale and the base iron on the laser cuttability.

FIG. 4 is a chart showing the effects of rolling temperature and reduction rate on the scale state of thick steel plates.

Claims (9)

[Claims] 1. In weight%, C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to 0.30 % Al: 0.005 to 0.10% The balance is Fe and inevitable impurities, and is 10 to 60 μm.
has a blue scale with a thickness of m, and has 0.5 to 5.0% Si and 0.4 to 4.0% at the interface between the scale and the base metal.
1. A steel material having an internal oxide layer with a thickness of 1 to 5 μm in which Cr is concentrated and having excellent high-density energy ray cutting properties. 2. In weight%, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to Containing at least one element selected from the group consisting of 0.003%, the balance being Fe and inevitable impurities, and
It has a blue scale with a thickness of 60 μm, and 0.5 to 5.0% Si at the interface between the scale and the base metal, and 0.4 to 1
A steel material excellent in high-density energy ray cuttability, in which an internal oxide layer having a thickness of 1 to 5 μm in which 4.0% of Cr is concentrated is present. 3. In weight%, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to At least one element selected from the group consisting of 0.003%, and (c) at least one element selected from the group consisting of Ca: 0.0003 to 0.010% REM: 0.001 to 0.030%. Element and the balance consisting of Fe and unavoidable impurities,
It has a blue scale with a thickness of 60 μm, and 0.5 to 5.0% Si at the interface between the scale and the base metal, and 0.4 to 1
A steel material excellent in high-density energy ray cuttability, in which an internal oxide layer having a thickness of 1 to 5 μm in which 4.0% of Cr is concentrated is present. 4. In% by weight, C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to 0.30 Less than% Al: 0.005 to 0.10% The balance consists of Fe and unavoidable impurities, and the heating temperature is 1
When the rolling biting temperature of the final pass of rolling is _TF (° C.) and the average rolling reduction of the final three passes in finish rolling is R _F (%), 880 ≦ T _F ≦ 1020 ( C.) 21 ≦ R _F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolling is carried out under the condition of simultaneously satisfying the three formulas, and after rolling, cooling is performed at a cooling rate higher than air cooling. A method for manufacturing a thick steel sheet excellent in high-density energy ray cutting property. 5. In weight%, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to Containing at least one element selected from the group consisting of 0.003%, the balance consisting of Fe and unavoidable impurities, the heating temperature to 1050 to 1300 ° C., and the roll entrapment temperature in the final pass of rolling to T _F (° C.), an average reduction rate of the final 3 passes in finish rolling when the _{R F (%), 880 ≦} T F _{1020 (℃) 21 ≦ R F} ≦ 40 (%) was rolled at R _F ≧ 155-3T _F / 20 at the same time satisfying the condition 3 Expressions, and characterized in that cooling by rolling after cooling with a cooling rate higher than A method for producing a thick steel sheet excellent in high-density energy ray cutting property. 6. In% by weight, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to At least one element selected from the group consisting of 0.003%, and (c) at least one element selected from the group consisting of Ca: 0.0003 to 0.010% REM: 0.001 to 0.030%. Element and the balance consisting of Fe and unavoidable impurities, and the heating temperature is set to 1050 to 1300 ° C. Roll biting temperature of the final pass rolling T _F (℃), the average reduction ratio of the final 3 passes in finish rolling when the _{R F (%), 880 ≦} T F ≦ 1020 (℃) 21 ≦ R F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolled under the conditions that simultaneously satisfy the three formulas, and then cooled at a cooling rate higher than air cooling after rolling, high-density energy ray cutting property A method for manufacturing thick steel sheets with excellent heat resistance. 7. In% by weight, C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to 0.30 Less than% Al: 0.005 to 0.10% The balance consists of Fe and unavoidable impurities, and the heating temperature is 1
When the rolling biting temperature of the final pass of rolling is _TF (° C.) and the average rolling reduction of the final three passes in finish rolling is R _F (%), 880 ≦ T _F ≦ 1020 ( 21 ° C.) 21 ≦ R _F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolled under the conditions that simultaneously satisfy the three formulas, and after rolling, 5
A method for producing a steel strip having excellent high-density energy ray cuttability, which comprises air-cooling for 30 seconds, winding, and cooling to room temperature. 8. In weight%, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to Containing at least one element selected from the group consisting of 0.003%, the balance consisting of Fe and unavoidable impurities, the heating temperature to 1050 to 1300 ° C., and the roll entrapment temperature in the final pass of rolling to T _F (° C.), an average reduction rate of the final 3 passes in finish rolling when the _{R F (%), 880 ≦} T F _{1020 (℃) 21 ≦ R F} ≦ 40 (%) was rolled at R _F ≧ 155-3T _F / 20 at the same time satisfying the condition 3 Expression of rolling after the end 5
A method for producing a steel strip having excellent high-density energy ray cuttability, which comprises air-cooling for 30 seconds, winding, and cooling to room temperature. 9. In% by weight, (a) C: 0.03 to 0.25% Si: 0.10 to less than 0.50% Mn: 0.05 to 1.60% Cr: 0.08 to Less than 0.30% Al: 0.005-0.10% is contained, and (b) Nb: 0.001-0.20% V: 0.001-0.30% Ti: 0.001- 0.20% Cu: 0.05 to 1.50% Ni: 0.05 to 1.50% Cr: 0.30 to 1.00% Mo: 0.05 to 1.00% B: 0.0003 to At least one element selected from the group consisting of 0.003%, and (c) at least one element selected from the group consisting of Ca: 0.0003 to 0.010% REM: 0.001 to 0.030%. Element and the balance consisting of Fe and unavoidable impurities, and the heating temperature is set to 1050 to 1300 ° C. Roll biting temperature of the final pass rolling T _F (℃), the average reduction ratio of the final 3 passes in finish rolling when the _{R F (%), 880 ≦} T F ≦ 1020 (℃) 21 ≦ R F ≦ 40 (%) R _F ≧ 155-3T _F / 20 Rolled under the conditions that simultaneously satisfy the three formulas, and after rolling, 5
A method for producing a steel strip having excellent high-density energy ray cuttability, which comprises air-cooling for 30 seconds, winding, and cooling to room temperature.