JP3388085B2 - Manufacturing method of thick steel plate with good scale adhesion - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thick steel plate having good scale adhesion used in the field of industrial machinery and the like.

[0002]

^2. Description of the Related Art Generally, a thick steel plate of 400 to 590 N / mm ² used in the field of processing such as industrial machines is as-rolled (As-roll), normalized (Norma), and rapidly quenched in the transformation region after rolling. It is manufactured by controlled cooling (TMCP), reheating quenching and tempering (QT).

However, in such a manufacturing method, since the point of manufacturing is to secure materials such as strength and toughness, the steel plate scale has a result that greatly differs depending on its steel composition and manufacturing method. It was On the other hand, in this field, the scale peels off during cold working of the steel sheet to cause dust and harm the environment, and in the coating after cold working, there is a part where the scale is peeled off and a part that is not peeled off, The quality of the finished product after painting was a problem.

In order to solve these problems, it is not a problem if the scale of the steel sheet is removed and then cold working is carried out. However, in view of the cost and the construction period for removing the scale of the steel sheet, the scale adhesion is eliminated. A steel sheet having good properties was desired.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a thick steel sheet having good scale adhesion by limiting the steel composition and manufacturing conditions to the optimum range.
The steel produced by the present invention has good scale adhesion, and can be applied to the fields of industrial machinery and the like.

[0006]

That is, the gist of the present invention is as follows. (1) Mass%, C: 0.06 to 0.20%, S
i: 0.15% or less, Mn: 1.0 to 1.6%, P:
0.03% or less, S: 0.02% or less, Al: 0.03
% Or less and N: 0.006% or less, and the balance is iron and unavoidable impurities.
℃ to 1150 ℃ below the temperature, 100 during rolling
Descaling is performed 3 times or more by spraying water on the front and back surfaces of the steel sheet at a pressure of kg / cm ² or more, and rolling is performed at 760 to 800.
A method for producing a thick steel sheet having good scale adhesion, which comprises terminating at 0 ° C, air-cooling, further holding the temperature of the steel sheet from 500 ° C to 300 ° C for 80 minutes or more, and then allowing to cool.

(2) C: 0.06 to 0.
20%, Si: 0.15% or less, Mn: 1.0 to 1.6
%, P: 0.03% or less, S: 0.02% or less, Al:
0.03% or less, N: 0.006% or less, and Ni: 0.05 to 0.30%, Cu: 0.05 to
0.30%, Cr: 0.05-0.30%, Mo: 0.
05-0.30%, Nb: 0.005-0.04%,
V: 0.005-0.06%, Ti: 0.005-0.
A steel containing 02% of 1 or 2 or more and the balance of iron and inevitable impurities is used as a slab, and then 950 ° C.
100k during rolling by heating to a temperature above 1150 ° C
Descaling is performed 3 times or more by spraying water on the front and back surfaces of the steel sheet at a pressure of g / cm ² or more, and rolling is performed at 760 to 800 ° C.
The method for producing a thick steel sheet having good scale adhesion, which comprises cooling with air, further maintaining the temperature of the steel sheet from 500 ° C. to 300 ° C. for 80 minutes or more, and then allowing to cool.

(3) C: 0.06 to 0.
20%, Si: 0.15% or less, Mn: 1.0 to 1.6
%, P: 0.03% or less, S: 0.02% or less, Al:
Steel containing 0.03% or less and N: 0.006% or less, the balance of which is iron and unavoidable impurities, is made into a slab, which is then heated to a temperature of 950 ° C. or more and 1150 ° C. or less and 100 kg / Descaling is performed 3 times or more by spraying water on the front and back surfaces of the steel plate at a pressure of cm ² or more, and rolling is performed at 76
Finishing at 0 to 800 ° C., immediately cooling with water to a temperature of 620 ° C. or lower, further keeping the temperature of the steel sheet from 500 ° C. to 300 ° C. for 80 minutes or more, and then allowing to cool, the scale adhesion is characterized. A good method for manufacturing thick steel plates.

(4) C: 0.06 to 0.
20%, Si: 0.15% or less, Mn: 1.0 to 1.6
%, P: 0.03% or less, S: 0.02% or less, Al:
0.03% or less, N: 0.006% or less, and Ni: 0.05 to 0.30%, Cu: 0.05 to
0.30%, Cr: 0.05-0.30%, Mo: 0.
05-0.30%, Nb: 0.005-0.04%,
V: 0.005-0.06%, Ti: 0.005-0.
A steel containing 02% of 1 or 2 or more and the balance of iron and inevitable impurities is used as a slab, and then 950 ° C.
100k during rolling by heating to a temperature above 1150 ° C
Descaling is performed 3 times or more by spraying water on the front and back surfaces of the steel sheet at a pressure of g / cm ² or more, and rolling is performed at 760 to 800 ° C.
The steel plate with good scale adhesion, characterized in that it is immediately cooled with water to a temperature of 620 ° C. or lower, and then the temperature of the steel plate is kept from 500 ° C. to 300 ° C. for 80 minutes or longer, and then allowed to cool. Manufacturing method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The basic idea of the present invention will be described below. The conventional knowledge about scale adhesion is to use the selective oxidation method, which increases the unevenness of the base steel / scale interface to improve the adhesion between base steel and scale.
When the steel containing i is heated to a temperature of 1150 ° C. or higher,
Grain boundaries with a high Si content are selectively oxidized, and roots are extended into the base iron (anchors) to improve adhesion, and strain is added by cold working in a thin scale method. In this case, the thin scale has excellent deformability and is difficult to peel off. The composition of the scale is Fe ₂ O _{3 which has} higher strength than FeO.
And Fe ₃ O ₄ are used, and Fe at 600 to 300 ° C.
A method utilizing the transformation of O to Fe ₃ O ₄ is known.

However, applying these principles as they are has been a very difficult problem for thick steel plates on the assumption that the material is secured. The present inventors have paid attention to scale thinning, blackening, and Fe ₃ O ₄ scale composition, and have obtained the following findings as the most effective method. First, at the start of rolling, it is necessary to eliminate the scale (primary scale) generated during heating. For this reason, it is important to avoid selective oxidation during heating, and it is essential to reduce the content of Si, which is easily oxidized selectively. Further, the slab heating temperature also needs to be 1150 ° C. or lower at which Si starts selective oxidation. Further, if the heating temperature is lower than 950 ° C., the rolling load becomes excessive and a predetermined rolling temperature cannot be secured, so 950 ° C. or higher is essential. In the present invention, since the slab heating temperature is low and the Si content is low, the primary scale is almost eliminated by injecting high-pressure water to the front and back surfaces of the steel sheet at the start of rolling. However, the scale continues to be generated during the subsequent rolling, and particularly in the temperature range of 800 ° C. or higher, the scale is remarkable.

In the present invention, rolling plays a large role in order to obtain a healthy thin scale. That is, in the high temperature region of rolling, the scale is softer than that of the base steel, and therefore is elongated by rolling, but in the low temperature region, transformation of the steel occurs and the base iron becomes softer than that of the scale. Is easily peeled off. Furthermore, the peeled scale is crushed by rolling to form a layer in which the scale is pressure-bonded to the surface of the steel sheet, the surface of the steel sheet turns red, and the scale is easily peeled off during cold working.

Therefore, the following two points are important. Setting of steel components for lowering the transformation start temperature of steel (making sure that the transformation start temperature does not reach a temperature of 800 ° C. or higher at which scale formation is remarkable). The rolling is finished at the temperature above the transformation start temperature of the steel. In the present invention, the content of Si which raises the transformation start temperature of steel is reduced as much as possible, and rolling is performed at a temperature higher than the transformation start temperature of steel by 76%.
The problem was solved by finishing at 0 to 800 ° C. The transformation start temperature of steel can be lowered by the addition of Mn, Cu, Ni, Cr, Mo, etc., but at the strength level of the steel of the present invention, the large addition of these alloying elements loses economic efficiency. Therefore, the scope of the present invention is appropriate.

Further, the reason for performing descaling during rolling is to lower the temperature of the steel sheet surface to suppress scale formation and to clean the steel sheet surface and eliminate foreign substances even during mixing. Is. To obtain this effect industrially, the water pressure for descaling is 100 kg.
/ Cm ² or more is required, and it is necessary to carry out three or more times during rolling.

Further, the reason for water cooling to a temperature of 620 ° C. or lower immediately after rolling is to reduce the scale and improve the strength. This makes it possible to achieve a healthy thin scale,
The composition of the scale is mainly FeO, and the adhesion is not good. Therefore, the FeO-based scale composition is F
5 after rolling (including controlled cooling) to convert to e ₃ O ₄
It is important to keep heat in the temperature range of 00 ° C to 300 ° C. Since the scale transformation is delayed if the heat retention temperature is lower or higher than this temperature, 500 to 300 ° C. is optimal. As an economical method, a method of inserting the steel sheet into the heat retention pit before the temperature of the steel sheet after rolling is excellent, but other methods can be sufficiently achieved.

As described above, there is no steel sheet other than the steel of the present invention, which has the characteristics of excellent scale adhesion obtained by controlling the steel composition and the manufacturing conditions within an appropriate range. The reasons for limiting each element will be described below. C needs to be added in an amount of 0.06% or more to secure the strength, but if it exceeds 0.20%, toughness and weldability are deteriorated, so 0.06 to
The range was 0.20%.

Although it is better for Si to have a low selective oxidation at a high temperature and a low transformation start temperature of steel, Si has a deoxidizing function, so the upper limit was made 0.15%. Mn exhibits excellent effects such as improvement in strength and toughness and reduction in transformation start temperature, but if it exceeds 1.6%, it deteriorates weldability and 1.0%.
If it is less than 1.0, the effect is small, so 1.0 to 1.6% is set as the limit range.

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, a predetermined effect can be exhibited, so these values were made the upper limits.
Al is necessary for deoxidation, but if it exceeds 0.03%, nonmetallic inclusions increase, which is not preferable, so 0.03% was made the upper limit. If N is 0.006% or less, it does not affect the weldability and cracking during slab casting, so 0.0
The upper limit was 06%.

Within the range of the steel components described above, a steel sheet having good scale adhesion can be obtained, but it is effective to add the following elements in order to obtain high strength without impairing the properties. Ni, Cu, Cr and Mo are solid solution strengthening elements,
It has a large effect of increasing the strength of the steel sheet and also has a function of lowering the transformation start temperature during rolling, and is an effective element in the present invention. However, addition of a large amount impairs weldability, so the upper limit value was set to 0.30%. In addition, the lower limit value is 0.
It was set to 05%.

Nb and V are precipitation hardening elements, which have a great effect of increasing the strength of the steel sheet, but have a negative factor of increasing the transformation start temperature during rolling.
b: 0.005-0.04%, V: 0.005-0.0
The range was 6%. Ti fixes N as TiN, and H
It improves AZ toughness, but if it exceeds 0.02%, TiC
Therefore, 0.02% was made the upper limit in order to impair the toughness. If less than 0.005%, the effect is small, so T
The lower limit of i was 0.005%.

[0021]

EXAMPLES Tables 1 and 2 (continued from Table 1) show the chemical compositions of the steels according to the present invention and comparative steels, and Tables 3 and 4 (continued from Table 3) show steel plate manufacturing conditions and steel sheet properties ( The color tone, strength, and scale adhesion of the steel sheet are shown.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

Evaluation Criteria Color tone of steel plate surface (CIE1
976, L ^* a ^* b ^* display system) Evaluation by a ^* display value (green ← → red) ◎: <0 ○: 0 to 0.5 △: 0.5 to 1.0 ×:> 1.0 Scale adhesion Adhesive steel sheet was added with 15% tensile strain and evaluated by the amount of scale peeled off ◎: <1.0 mg / cm ² ○: 1.0 to 2.0 mg / cm ² Δ: 2.0 to 3.0 mg / cm ² ×:> 3.0 mg / cm ² Steels 1 to 15 are steels according to the present invention, and have excellent steel sheet color tone and scale adhesion.

On the other hand, steels 16 to 20 are comparative steels. Comparative steel 16 has the same manufacturing conditions as the present invention,
Since the Mn content is low, the color tone and scale adhesion of the steel sheet are both poor. Steel 17 has the same manufacturing conditions as in the present invention, but the steel plate has a poor color tone because of the high Si content.

The steel 18 has the same steel composition as that of the present invention, but since heat retention is not carried out, the scale adhesion is poor. Steel 19 has the same steel composition as that of the present invention, but the color tone of the steel plate is poor because descaling is not performed.
The steel 20 has the same steel composition as that of the present invention, but the steel plate has a poor color tone because the rolling end temperature is low.

[0029]

According to the present invention, it is possible to provide a thick steel sheet having excellent scale adhesion. The steel produced by the present invention has good scale adhesion, and can be applied to the fields of industrial machinery and the like.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI B21B 45/08 B21B 45/08 F C22C 38/00 301 C22C 38/00 301A 38/06 38/06 38/58 38/58 ( 72) Inventor Seiji Isoda 1 Kimitsu, Kimitsu City Nippon Steel Co., Ltd. Inside the Kimitsu Works (56) References JP-A-7-252593 (JP, A) JP-A-5-112821 (JP, A) JP Japanese Unexamined Patent Publication No. 8-218119 (JP, A) Japanese Unexamined Patent Publication No. 59-215208 (JP, A) Japanese Unexamined Patent Publication 60-77922 (JP, A) Japanese Unexamined Patent Publication No. 9-272917 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C21D 8/00-8/02 B21B 1/00-3/02 B21B 45/00-45/08 C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. Mass%, C: 0.06 to 0.20%, Si: 0.15% or less, Mn: 1.0 to 1.6%, P: 0.03% or less, S: 0 0.02% or less, Al: 0.03% or less, N: 0.006% or less, and the balance made of steel consisting of iron and unavoidable impurities is used as a slab, and then heated to a temperature of 950 ° C or higher and 1150 ° C or lower. Then, water is sprayed on the front and back surfaces of the steel sheet at a pressure of 100 kg / cm ² or more during rolling to perform descaling three times or more, rolling is finished at 760 to 800 ° C., air cooling is performed, and the temperature of the steel sheet is further increased. A method for producing a thick steel sheet having good scale adhesion, which comprises heat-retaining from 500 ° C. to 300 ° C. for 80 minutes or more, and then allowing to cool. 2. Mass%, C: 0.06 to 0.20%, Si: 0.15% or less, Mn: 1.0 to 1.6%, P: 0.03% or less, S: 0 0.02% or less, Al: 0.03% or less, N: 0.006% or less, and further Ni: 0.05 to 0.30%, Cu: 0.05 to 0.30%, Cr: 0.05-0.30%, Mo: 0.05-0.30%, Nb: 0.005-0.04%, V: 0.005-0.06%, Ti: 0.005-0. After slab made of steel containing 02% of 1 type or 2 types and the balance of iron and unavoidable impurities, 950 ° C or higher 1
100kg / c during rolling by heating to a temperature below 150 ℃
Descaling is performed 3 times or more by spraying water on the front and back surfaces of the steel sheet at a pressure of m ² or more, rolling is finished at 760 to 800 ° C., air cooling is performed, and the temperature of the steel sheet is further changed from 500 ° C. to 300 ° C.
A method for producing a thick steel sheet having good scale adhesion, which comprises keeping the temperature at 80 ° C. for 80 minutes or more and then allowing it to cool. 3. Mass%, C: 0.06-0.20%, Si: 0.15% or less, Mn: 1.0-1.6%, P: 0.03% or less, S: 0. 0.02% or less, Al: 0.03% or less, N: 0.006% or less, and the balance made of steel consisting of iron and unavoidable impurities is used as a slab, and then heated to a temperature of 950 ° C or higher and 1150 ° C or lower. Then, water is sprayed on the front and back surfaces of the steel sheet at a pressure of 100 kg / cm ² or more during rolling to perform descaling 3 or more times, rolling is completed at 760 to 800 ° C, and immediately 620 ° C.
A method for producing a thick steel sheet having good scale adhesion, comprising water cooling to the following temperature, further holding the temperature of the steel sheet from 500 ° C. to 300 ° C. for 80 minutes or more, and then allowing to cool. 4. Mass%, C: 0.06 to 0.20%, Si: 0.15% or less, Mn: 1.0 to 1.6%, P: 0.03% or less, S: 0. 0.02% or less, Al: 0.03% or less, N: 0.006% or less, and further Ni: 0.05 to 0.30%, Cu: 0.05 to 0.30%, Cr: 0.05-0.30%, Mo: 0.05-0.30%, Nb: 0.005-0.04%, V: 0.005-0.06%, Ti: 0.005-0. After slab made of steel containing 02% of 1 type or 2 types and the balance of iron and unavoidable impurities, 950 ° C or higher 1
100kg / c during rolling by heating to a temperature below 150 ℃
Descaling is performed three times or more by injecting water on the front and back surfaces of the steel sheet with a pressure of m ² or more, rolling is completed at 760 to 800 ° C., water cooling is immediately performed to a temperature of 620 ° C. or less, and the temperature of the steel sheet is 500. A method for producing a thick steel sheet having good scale adhesion, which comprises heat-retaining from 80 ° C to 300 ° C for 80 minutes or more, and then allowing to cool.