JP3218166B2 - Thick steel plate excellent in laser cutability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

^2. Description of the Related Art Generally, thick steel plates of 400 to 490 N / mm ² used in the fields of industrial machines, bridges and the like are produced as rolled (As-roll) products in order to reduce production costs. . The surface condition of the steel sheet manufactured by such a method is significantly different depending on the manufacturing conditions. That is, the scale of black scale is formed on the surface of the steel sheet, and the thickness of the scale exceeds 50 μm, or the scale of the steel sheet such as a steel sheet having a thin scale of the steel sheet surface but red scale powder adhered to the surface. The state was greatly different depending on the manufacturing conditions.

On the other hand, in this field, the use of laser cutting instead of conventional gas cutting has become remarkable as a steel sheet processing method. This is a cutting process, environment, precision, efficiency, etc.
In any case, laser cutting is superior to gas cutting. However, it is also known that laser cutting properties are greatly affected by the composition and surface condition of steel, and therefore, it is a technical problem to apply laser cutting to thick steel plates with such surface conditions. there were.

[0004]

SUMMARY OF THE INVENTION The present invention is applied to the fields of industrial machines, bridges, shipbuilding, etc. having good laser cutting properties by specifying the steel composition and the manufacturing conditions of the steel sheet in the optimum range. And a method for manufacturing the same.

[0005]

The gist of the present invention is as follows: (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, with the balance being composed of iron and inevitable 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, Mo: 0.4% or less Nb: 0.04% or less V: 0 0.08% or less, and the balance is composed of iron and unavoidable impurities. The steel plate having excellent laser cutting properties. (3) In weight%, C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (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% A steel containing the following, and the balance being iron and unavoidable impurities, was made into a slab, and then heated to 950 ° C. 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 plate having excellent laser cutting properties, wherein the gloss of the steel plate surface is reduced to 15% or less by air cooling. (4) 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 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 Mo, 0.4% or less Nb: 0.04% or less V: 0.08% or less Then, after slabs were made of steel consisting of iron and unavoidable impurities, the remaining amount was 950 in a heating furnace.
At a temperature of not less than 1250 ° C. and not more than 1250 ° C.
Water is sprayed onto the front and back surfaces of the steel sheet at a pressure of 00 kg / mm ² or more, descaling is performed three times or more, and rolling is performed at 850 to 850 mm.
A method for producing a thick steel plate having excellent laser cutting properties, wherein the process is completed at 750 ° C. and air-cooled to room temperature to reduce the gloss of the steel plate surface to 15% or less.

[0006]

The basic concept of the present invention will be described below.

[0007] In a steel plate having a plate thickness of 20 mm or more, particularly a plate thickness of 20 to 30 mm, which is the object of the present invention, the energy of laser cutting uses laser light and the heat of oxidation reaction of steel, and each has a different influencing factor. 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 at the time of laser cutting, the heat of oxidation reaction of elements in the steel is large in the cutting property. (C) The viscosity of the molten steel melted at the time of laser cutting has influential factors such as affecting the quality of the cut surface and the state of dross adhesion.

The present inventors have intensively studied these influential factors, and it is important to increase the laser absorptivity on the steel sheet surface and to maximize the heat of oxidation reaction in order to improve the laser cutting performance of the steel sheet. Was found to be.

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

That is, the characteristics of the laser are very similar to those of visible light, and the laser is reflected and absorbed on the surface of the steel sheet during laser cutting. It is the laser that is absorbed that is converted to thermal energy. The laser absorptivity is greatly affected by the gloss of the steel sheet surface, and it is important to control the gloss to improve the laser absorptivity. Furthermore, it was found that the gloss was affected by the color of the scale surface and the roughness of the scale surface. When the color tone is evaluated on the axis of black ← → white, gloss can be suppressed by making the color black, and for this purpose, rolling at a temperature lower than 750 ° C. must be avoided because the color tone becomes white. In addition, the effect of suppressing the gloss is lower as the surface roughness is higher.
The effect can be exhibited at a of about 1 to 4 μm. As a result, the present inventors have found that a gloss value of 15% or less is a critical value for obtaining good laser cutability.

[0011] Therefore, in a heating furnace 950 ~ 1250 ℃
Was rolled at 850-750 ° C., and air-cooled to room temperature.

In addition, water is sprayed on the front and back surfaces of the steel sheet at a pressure of 100 kg / mm ² or more during rolling to reduce the descaling to 3 times.
The reason for carrying out the process more than once is to secure a gloss value of 15% or less so as not to leave scale or dust peeled off on the surface of the steel sheet and not to make the scale thicker than necessary.

Further, in order to improve the laser cutting property, it is important to control the above-mentioned influential factors (b) and (c) by the steel component. When laser cutting a steel sheet, oxygen is used as an assist gas, which promotes oxidation with iron and serves to generate heat of oxidation reaction. Therefore, it is known that the laser purity is greatly affected by the purity of oxygen in the assist gas.

The present inventors have found that the steel component affects the generation of heat of oxidation reaction, which is an influential factor of laser cutting properties. The oxidation reaction of iron occurs in the region heated to a high temperature during laser cutting, but if the amount of C in the steel is large, C +
O reaction 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 C content in the steel, the better. However, if the heat of oxidation reaction of elements in the steel is too large, burning occurs and cutting is interrupted. For this reason, Si or Mn whose oxidation reaction heat is excessively larger than Fe
It is important to control the amount to an appropriate range. If the C content of the steel sheet of the present invention, the sum of Si and Mn is 0.8 to 1.5%.
Is an appropriate range.

Furthermore, the addition of Cu or Cr is effective for the viscosity of molten steel, which is important together with the heat generated by oxidation.

Hereinafter, the limitation range of each alloy element will be described.

C is required to be 0.03% or more in order to secure the strength. However, if it exceeds 0.06%, the laser cutting property is deteriorated. Therefore, the upper limit is set to 0.06%.

Although Si increases the viscosity of molten steel during laser cutting and degrades the cutting properties, it is effective for deoxidation during steel production, so the limiting range is 0.05 to 0.3%.

When Mn is excessively large, the upper limit is set to 1.5% to deteriorate the laser cutting property. The lower limit is set to 0.5% for securing strength and toughness. Also, as mentioned above,
Since excessive addition of Si or Mn deteriorates the laser cutting property, it is necessary to set Si + Mn = 0.8 to 1.5%.

Although P and S are preferably as low as possible in terms of material, if P is 0.03% or less and S is 0.02% or less, a predetermined effect can be exerted, so the upper limit is set.

Al is necessary for deoxidation, but if it exceeds 0.03%, non-metallic inclusions increase, which is not preferable.
0.03% was made the upper limit.

Cu has an effect on dross adhesion during laser cutting and is effective. However, if it is less than 0.05%, the effect is small, and if it exceeds 0.60%, the weldability is impaired. 05 to 0.60%.

Ni is effective in lowering the viscosity of molten steel.
Is essential to prevent high-temperature cracking, and the appropriate range is 0.05 to 0.40%.

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

[0025] If the N content is 0.006% or less, it does not harm the weldability or cracks during slab casting, so the upper limit is set.

In the above range of the solid steel component, a steel sheet having good laser cutability can be obtained. However, in order to obtain higher strength without deteriorating the properties, one or more of the following elements are required.
It is effective to add more than one kind.

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

Nb and V are precipitation hardening elements and have a great effect of increasing the strength of the steel sheet. However, since the addition of a large amount impairs the weldability and the toughness of the welded portion, the upper limit is set to N
b 0.04% and V 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 results of heating, rolling conditions and laser cutting.

[0030]

[Table 1]

[0031]

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

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

The comparative steel 13 has a low gloss on the surface of the steel sheet,
High n content, poor laser cutting properties (piercing, cut surface).

The 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 the comparative steel 15 is the same as that of the steel of the present invention. However, since the rolling end temperature is low, the gloss is large and the laser cutting properties (piercing, cut surface) are poor.

[0036]

As described above, according to the production method of the present invention, it is possible to obtain a steel sheet having good laser cutting properties.
Further, the steel sheet of the present invention is the most suitable steel sheet to be subjected to laser cutting, and can be applied to the fields of industrial machines, bridges, shipbuilding and the like.

Continuation of the front page (72) Inventor Yasunobu Miyazaki 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works (56) References JP-A-5-112821 (JP, A) JP-A-61-257458 (JP) JP-A-7-155975 (JP, A) JP-A-5-279734 (JP, A) JP-A-7-70649 (JP, A) JP-A-8-3692 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/00-8/10 B21B 45/08

Claims (4)

(57) [Claims] C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% (% by weight) 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 : 0.05-0.6% N: 0.006% or less, the balance being iron and unavoidable impurities, characterized by having excellent laser cutting properties. 2. C: 0.03-0.06% Si: 0.05-0.3% Mn: 0.5-1.5% (% by weight) (Si + Mn = 0.8-1.%) 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 Mo, 0.4% or less Nb: 0.04% or less V: 0.08% or less Steel plate with excellent laser cutability, characterized by containing iron and the balance consisting of iron and unavoidable impurities 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 1.0%). 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 : 0.05-0.6% N: 0.006% or less, and the balance is made of steel consisting of iron and unavoidable impurities. Heating, during rolling, water is sprayed on the front and back surfaces of the steel plate at a pressure of 100 kg / mm ² or more, descaling is performed three times or more, rolling is completed at 850 to 750 ° C., and the steel plate is air-cooled to room temperature. A method for producing a thick steel plate having excellent laser cutability, characterized in that the surface gloss is 15% or less. 4. C: 0.03 to 0.06% Si: 0.05 to 0.3% Mn: 0.5 to 1.5% by weight% (where 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 : 0.05 to 0.6% N: 0.006% or less Mo, 0.4% or less Nb: 0.04% or less V: 0.08% or less Containing steel and the balance consisting of iron and unavoidable impurities was converted into a slab, and then heated to 950 in a heating furnace.
At a temperature of not less than 1250 ° C. and not more than 1250 ° C.
Water is sprayed onto the front and back surfaces of the steel sheet at a pressure of 00 kg / mm ² or more, descaling is performed three times or more, and rolling is performed at 850 to 850 mm.
A method for producing a thick steel plate having excellent laser cutting properties, wherein the process is completed at 750 ° C. and air-cooled to room temperature to reduce the gloss of the steel plate surface to 15% or less.