JPH0920962A - Thick steel plate excellent in laser cuttability and its production - Google Patents

Abstract

PURPOSE: To produce a thick steel plate excellent in laser cuttability by subjecting a steel having a specified compsn. in which the contents of C, Si, Mn, Cu and Cr are prescribed to hot rolling under specified conditions. CONSTITUTION: A steel contg., by weight, 0.03 to 0.06% C, 0.05 to 0.3% Si, 0.5 to 1.5% Mn (where Si+Mn=0.8 to 1.5%), <=0.03% P, <=0.02% S, <=0.03% Al, 0.05 to 1.40% Cu, 0.05 to 0.40% Ni, 0.05 to 0.6% Cr and <=0.006S N, and the balance iron with inevitable impurities is prepd. to form into a slab. This slab is heated at 950 to 1250 deg.C in a heating furnace, and in the process of rolling, the rear side of the steel plate is sprayed with water under >=100kgf/mm<2> , and descaling is executed for >= three times. After the completion of the rolling at 850 to 750 deg.C, it is air-cooled to an ordinary temp., and the luster of the surface of the steel plate is regulated to <=15%. Thus, the thick steel plate (plate thickness : >=20mm) good in laser weldability and applicable to the fields of industrial equipment, bridges, shipbuilding or the like can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet having excellent laser cuttability used in the fields of industrial machinery, bridges and shipbuilding, and a method for producing the same.

[0002]

^2. Description of the Related Art Generally, a thick steel plate of 400 to 490 N / mm ² used in the fields of industrial machines, bridges, etc. is manufactured as an as-roll product in order to reduce the manufacturing cost. . The surface condition of the steel sheet manufactured by such a method varies greatly depending on the manufacturing conditions. That is, a surface of a steel sheet such as a steel sheet on which a black scale is formed and the thickness of the scale exceeds 50 μm, or a steel sheet whose scale is thin but red scale powder is attached to the surface. The state varied greatly depending on the manufacturing conditions.

On the other hand, in this field, as a method for processing a steel sheet, laser cutting is widely used instead of conventional gas cutting. This is a cutting process, environment, precision, efficiency, etc.
This is because laser cutting is superior to gas cutting in any case. However, it is also known that the laser cutting property is greatly influenced by the composition and surface condition of steel, and therefore it is a technical problem to apply laser cutting to the thick steel plate having the above surface condition. there were.

[0004]

The present invention is applied to the fields of industrial machinery, bridges, shipbuilding, etc., which have good laser-cutting properties by defining the steel composition and the steel plate manufacturing conditions in the optimum range. And a method for manufacturing the same.

[0005]

The gist of the present invention is (1) C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% by weight. % (However, the condition of Si + Mn = 0.8 to 1.5% is satisfied) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6 % Ni: 0.05 to 0.40% Cr: 0.05 to 0.6% N: 0.006% or less, and the balance is iron and unavoidable impurities. Excellent thick steel plate (2) By weight%, C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (however, Si + Mn = 0.8 to Satisfies the condition of 1.5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr: 0.05 to 0.6% N: 0.006% or less as a basic component, and Mo: 0.4% or less Nb: 0.04% or less V: 0 Steel plate having excellent laser cuttability, characterized by containing one or more of 0.08% or less, and the balance consisting of iron and unavoidable impurities (3)% by weight, C: 0.03 to. 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (provided that the condition of Si + Mn = 0.8 to 1.5% is satisfied) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr: 0.05 to 0.6% N: 0.006% A slab made of steel containing the following and the balance being iron and unavoidable impurities, and then heated in a heating furnace at 950 ° C or higher and 1250 It was heated at a temperature, during rolling, by spraying water on the steel plate front and back surfaces at 100 Kg / mm ² or more pressure, conducted descaling three times or more, to room temperature to terminate the rolling at eight hundred and fifty to seven hundred fifty ° C. A method for producing a thick steel sheet having excellent laser cuttability, which comprises cooling the steel sheet with a gloss of 15% or less by air cooling. (4) C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (however, Si + Mn = 0.8 to 1.5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr: 0 0.05 to 0.6% N: 0.006% or less as a basic component, and further contains Mo: 0.4% or less Nb: 0.04% or less V: 0.08% or less. Then, after slabs made of steel with the balance being iron and inevitable impurities, 950 in a heating furnace
℃ to 1250 ℃ below the temperature during heating, 1 during rolling
Water is sprayed on the front and back surfaces of the steel sheet at a pressure of 00 kg / mm ² or more, descaling is performed 3 times or more, and rolling is performed at 850 to 850.
A method for producing a thick steel sheet excellent in laser cutting property, which comprises finishing at 750 ° C. and air-cooling to room temperature to make the gloss of the steel sheet surface 15% or less.

[0006]

The concept underlying the present invention will be described below.

In the steel plate having a plate thickness of 20 mm or more, particularly the plate thickness of 20 to 30 mm, which is the object of the present invention, laser light and the heat of oxidation reaction of the steel are used as the energy of laser cutting, and the respective influencing factors differ. That is,
(A) Since the laser beam has the same characteristics as light, it is greatly affected by the surface properties of the steel sheet. (B) In the portion heated during laser cutting, the heat of oxidation reaction of the elements in the steel is large in the cutting performance. (C) The viscosity of the molten steel melted during laser cutting has influence factors such as the quality of the cut surface and the state of dross adhesion.

The present inventors diligently studied these influential factors, and in order to improve the laser cutting property of the steel sheet, it is important to increase the laser absorption rate of the steel sheet surface and make maximum use of the heat of oxidation reaction. I found that.

The present inventors have examined how the surface properties of the steel sheet affect the laser cuttability, and obtained the following findings.

That is, the characteristics of the laser are similar to those of visible light, and the laser is reflected and absorbed on the surface of the steel sheet during laser cutting. Of these, it is the absorbed laser that is converted into heat energy. The laser absorptance is greatly affected by the gloss of the steel sheet surface, and controlling the gloss is important for improving the laser absorptance. Furthermore, we found that the gloss is influenced by the color tone of the scale surface and the roughness of the scale surface. When the color tone is evaluated on the axis of black ← → white, it is possible to suppress the gloss by making it black, and for this reason, rolling below 750 ° C makes the color tone white, so it must be avoided. Further, the rougher the surface roughness, the more effectively the gloss can be suppressed, but practically R
The effect can be exhibited at a of 1 to 4 μm. As a result, the inventors have found that setting the gloss value to 15% or less is the limit value for obtaining good laser cutting property.

Therefore, in a heating furnace, 950 to 1250 ° C
The slab heated to the temperature was rolled, the rolling was completed at 850 to 750 ° C., and the air was cooled to room temperature.

Further, during rolling, water is sprayed onto the front and back surfaces of the steel sheet at a pressure of 100 kg / mm ² or more to perform descaling to 3
The reason for carrying out more than once is to ensure that the scale value and the dust are not left on the surface of the steel sheet, and that the scale is not unnecessarily thickened so that the gloss value is 15% or less.

Further, in order to improve the laser cuttability, it is important to control the influencing factors (b) and (c) by the steel composition. Oxygen is used as an assist gas during laser cutting of a steel sheet, which promotes oxidation with iron and generates heat of oxidation reaction. Therefore, it is known that the purity of oxygen in the assist gas has a great influence on the laser cutting property.

The inventors of the present invention have found that the composition of steel influences the generation of heat of oxidation reaction, which is an influential factor of laser cuttability. Oxidation reaction of iron occurs in the area heated to high temperature during laser cutting, but if the amount of C in the steel is large, C +
The reaction of O occurs and suppresses the oxidation reaction of iron. For this reason,
Heat generation due to the oxidation reaction is reduced and the cutting property is reduced. Therefore, in order to improve the laser cutting property, the lower the amount of C in the steel, the better. However, if the heat of oxidation reaction of the elements in the steel is too large, burning occurs and cutting is interrupted. Therefore, the heat of oxidation reaction is larger than that of Fe such as Si and Mn.
It is important to control the amount within the proper range. If the C content of the steel sheet of the present invention is 0.8 to 1.5% as the sum of Si and Mn
Is an appropriate range.

Further, the addition of Cu and Cr is effective for the viscosity of the molten steel, and it is important in addition to the oxidation heat generation.

The limit range of each alloying element will be described below.

C is required to be 0.03% or more to secure the strength, but if it exceeds 0.06%, the laser cutting property is deteriorated, so 0.06% is made the upper limit.

Although Si increases the viscosity of molten steel at the time of laser cutting and deteriorates the cuttability, it is effective for deoxidation at the time of manufacturing steel, so 0.05 to 0.3% was made the limiting range.

When Mn is excessively large, the upper limit is 1.5% because it deteriorates the laser cutting property. Further, the lower limit is 0.5% in order to secure strength and toughness. Also, as mentioned above,
Since excessive addition of Si and Mn deteriorates the laser cutting property, it is necessary to set Si + Mn = 0.8 to 1.5%.

P and S are preferably as low as possible in terms of material, but if P is 0.03% or less and S is 0.02% or less, the predetermined effect can be exhibited, so the upper limit was made.

Al is necessary for deoxidation, but if it exceeds 0.03%, nonmetallic inclusions increase, which is not preferable.
The upper limit was 0.03%.

Cu has an effect on dross adhesion at the time of laser cutting and is effective, but if less than 0.05%, the effect is small, and if it exceeds 0.60%, the weldability is impaired, so that the proper range is 0. It is 05 to 0.60%.

Ni is effective in reducing the viscosity of molten steel, and Cu
It is also essential to prevent hot cracking of the steel, and the appropriate range is 0.05 to 0.40%.

Cr has an oxidation reaction heat similar to that of Fe, but has a function of lowering the viscosity of molten steel and preventing oxidation of the cut surface. However, addition of a large amount impairs weldability, so 0.05 to 0.60% is an appropriate range.

If N is 0.006% or less, the weldability and the cracking during slab casting are not adversely affected, so the upper limit is set.

Within the range of the above solid steel components, a steel sheet having good laser cuttability can be obtained, but in order to obtain higher strength without deteriorating the characteristics, one or two of the following elements is used.
It is effective to add more than one species.

Mo is a solid solution strengthening element and has a great effect of increasing the strength of the steel sheet. However, addition of a large amount impairs weldability, so the upper limit value is 0.4%.

Nb and V are precipitation hardening elements and have a large effect of increasing the strength of the steel sheet. However, addition of a large amount impairs the weldability and the toughness of the welded portion, so the upper limit value is N
b was 0.04% and V was 0.08%.

[0029]

EXAMPLES Table 1 shows the chemical composition of the steel according to the present invention and the comparative steel, and Table 2 shows the heating and rolling conditions and the results of laser cutting.

[0030]

[Table 1]

[0031]

[Table 2] Steels 1 to 10 are steels according to the present invention, and the surface of the steel sheet has a gloss of 6 to 14 and excellent laser cuttability (piercing property, cut surface quality). On the other hand, Comparative Steel 11 has a low gloss on the surface of the steel sheet, but has a high C content and has a poor laser cutting property (piercing).

Comparative Steel 12 has a low gloss on the surface of the steel sheet,
High C and Si content, laser cutability (piercing, cut surface)
Is bad.

Comparative Steel 13 has a low gloss on the surface of the steel sheet, but M
The amount of n is high, and the laser cuttability (pierce, cut surface) is poor.

Comparative Steel 14 has a low gloss on the surface of the steel sheet,
High C and Mn content, laser cutability (piercing, cut surface)
Is bad.

The steel composition of Comparative Steel 15 is the same as that of the steel of the present invention, but since the rolling end temperature is low, it has a lot of gloss and is poor in laser cuttability (piercing, cut surface).

[0036]

As described above, according to the manufacturing method of the present invention, it is possible to obtain a steel sheet having a good laser cutting property.
Further, the steel sheet of the present invention is the most suitable steel sheet for laser cutting, and can be applied to fields such as industrial machines, bridges, and shipbuilding.

Front Page Continuation (72) Inventor Yasunobu Miyazaki 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Steel Works

Claims (4)

[Claims] 1. C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% by weight% (provided that Si + Mn = 0.8 to 1. Satisfies the condition of 5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr : 0.05 to 0.6% N: 0.006% or less, the balance being composed of iron and unavoidable impurities 2. C .: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% by weight% (provided that Si + Mn = 0.8 to 1. Satisfies the condition of 5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr : 0.05 to 0.6% N: 0.006% or less as a basic component, and Mo: 0.4% or less Nb: 0.04% or less V: 0.08% or less, or one or more kinds thereof. Steel plate with excellent laser cuttability, characterized in that it contains iron and the balance is iron and unavoidable impurities 3. By weight%, C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (provided that Si + Mn = 0.8 to 1. Satisfies the condition of 5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr : 0.05 to 0.6% N: 0.006% or less, with the balance being steel and iron and unavoidable impurities as the slab, and then heated at a temperature of 950 ° C or higher and 1250 ° C or lower in a heating furnace. During heating and rolling, water is sprayed on the front and back surfaces of the steel sheet at a pressure of 100 Kg / mm ² or more, descaling is performed 3 times or more, rolling is completed at 850 to 750 ° C., and air cooling is performed to room temperature. A method for producing a thick steel sheet having excellent laser cuttability, characterized by having a surface gloss of 15% or less. 4. By weight%, C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (provided that Si + Mn = 0.8 to 1. Satisfies the condition of 5%) P: 0.03% or less S: 0.02% or less Al: 0.03% or less Cu: 0.05 to 0.6% Ni: 0.05 to 0.40% Cr : 0.05 to 0.6% N: 0.006% or less as a basic component, and Mo: 0.4% or less Nb: 0.04% or less V: 0.08% or less, or one or more kinds thereof. Slab made of steel containing iron and the balance iron and unavoidable impurities, and then 950 in a heating furnace
℃ to 1250 ℃ below the temperature during heating, 1 during rolling
Water is sprayed on the front and back surfaces of the steel sheet at a pressure of 00 kg / mm ² or more, descaling is performed 3 times or more, and rolling is performed at 850 to 850.
A method for producing a thick steel sheet excellent in laser cutting property, which comprises finishing at 750 ° C. and air-cooling to room temperature to make the gloss of the steel sheet surface 15% or less.