JP2001279323A - Method for producing rolled fire resistant shape steel excellent in material uniformity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing fire resistant rolled shape steel in which the difference in the material of each part in a flange is small and excellent in cross-sectional shape. SOLUTION: A steel having a composition containing, by mass, 0.02 to 0.20% C, 0.05 to 0.7% Si, 0.8 to 1.8% Mn, 0.3 to 0.7% Mo (wherein, in the case one or more kinds selected from Nb, V and Ti are contained, and further, Mo+8.0Nb+2.4V+3.0Ti>=0.3 is satisfied, Mo: 0.1 to 0.7%) and 0.01 to 0.1% Al and moreover containing one or more kinds selected from Cu, Ni, Cr and B, and the balance substantially Fe with inevitable impurities is rolled, subsequently, both sides of a flange are subjected to primary cooling from the temperature range of >=Ar3 point to the surface temperature of (Ar3)-200 deg.C at the average cooling rate of >=2.0 deg.C/s in the flange part, after the temporary interruption of the cooling, the surface temperature is recuperated to >=600 deg.C, and subsequently, both sides of the flange are subjected to secondary cooling to 400 to 600 deg.C by the average temperature of the flange part at the average cooling rate of >=2.0 deg.C/s in the flange part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled steel excellent in fire resistance used for high-rise buildings and the like, and more particularly to a rolled steel having a small difference in material at various parts of a flange.

[0002]

2. Description of the Related Art As for the material of structural steel, in addition to the conventional strength at normal temperature, low temperature toughness, and high strength at high temperature, in building applications, etc., according to the new refractory design method established in April 1987. Is required. In the case of refractory extra thick rolled H-beams used as building pillars,
Since Mo, which is considered to be effective in improving high-temperature strength, is added, deformation resistance during hot rolling increases, and in rolling, it is important to secure a shape.

[0003] Therefore, the heating temperature before rolling is higher than that of a thick steel plate, the austenite has an insufficient cumulative rolling reduction in a low temperature region, and is controlled and cooled from a coarse austenite region. As compared with a thick steel plate capable of sufficiently reducing the thickness, even if the cooling rate is the same, the material difference in the thickness direction tends to increase.

FIG. 1 shows a cooling time when an extremely thick H-section steel is heated to 1250.degree. C., and after hot rolling, the average cooling rate at 500 to 800.degree. This shows changes in the outer surface temperature and the center temperature at the flanges 1 / 4F and 1 / 2F, and the surface temperatures are indicated by the same line without significant difference between the flanges 1 / 4F and 1 / 2F. At 1 / 2F compared to 1 / 4F,
Large temperature difference between surface and center, thickness direction (board thickness direction)
Shows a tendency that the difference in material tends to be large. Furthermore,
Since it has a more complicated shape than a thick steel plate, deformation such as bending is likely to occur at the time of controlled cooling, and it is difficult to adjust cooling conditions only for securing the material.

As a manufacturing technique for suppressing the difference in the material in the thickness direction, for example, Japanese Patent Laid-Open Publication No. Hei 3-188216 is disclosed. After recuperating and softening the area,
A technique for suppressing an increase in surface hardness for performing cooling again is described. However, the present technology is intended for thick steel plates, and in the case of rolled section steel, the heating temperature and cooling rate of rolling are completely different, and the aim is to optimize the material at low temperature heating and high cooling rate Things.

[0006] Refractory rolled section steel for construction is disclosed in, for example, JP-A-2-77525 and JP-A-2-16334.
No. 1 and Japanese Unexamined Patent Publication No. 3-27134, which are applications from the viewpoints of low yield ratio and fire resistance. Is not considered.

[0007]

As described above, in a rolled section steel having excellent fire resistance, it is necessary to add Mo in order to ensure fire resistance. It is difficult to select the conditions from the viewpoint of securing the material in combination. Therefore, the cooling after rolling tends to cause a change in the material of each part of the flange, and the tendency is particularly strong when the thickness of the rolled section steel is large.

An object of the present invention is to provide a method for producing a rolled steel bar having excellent fire resistance, which is cooled after rolling, and which is excellent in material uniformity and cross-sectional shape of each part of the flange.

[0009]

SUMMARY OF THE INVENTION The present inventors have found that when cooling a flange of a rolled section steel excellent in fire resistance from both sides, cooling conditions such that the material of each part of the flange including the fillet portion becomes uniform. Was examined. As a result, the bainite phase formed on the surface of the flange of the rolled section steel can be sufficiently softened by the tempering effect due to recuperation, and can be further softened by adjusting the final stop temperature of cooling, even when the bainite phase is not reversely transformed into a ferrite phase. I've found it to go.

It has been found that when the cooling method is a two-stage cooling of primary cooling after rolling and secondary cooling after recuperation, the above-described effects and excellent cross-sectional shape can be obtained, and the present invention has been completed. It is a thing. That is, the present invention provides: In mass%, C: 0.02 to 0.20%, Si:
0.05-0.7%, Mn: 0.8-1.8%, Mo:
A steel containing 0.3 to 0.7%, Al: 0.01 to 0.1%, and the balance substantially consisting of Fe and unavoidable impurities is heated to more than 1200 ° C and rolled by heating to 1350 ° C or less.
From the temperature range of Ar3 point or more, the surface temperature is Ar3-200 ° C or less. The flange surfaces are primarily cooled at an average cooling rate of 2.0 ° C / s or more at the flange portion, and once cooled, the surface temperature is raised to 600 ° C or more. After reheating, the average temperature of the flange is 400 to 600 ° C. and the average cooling rate of the flange is 2.
A method for producing a rolled refractory section steel excellent in material uniformity, characterized in that both surfaces of a flange are secondarily cooled at 0 ° C / s or more.

2. Further, as a steel component, Cu: 0.02
-1.5%, Ni: 0.02-1.5%, Cr: 0.0
5. The method for producing a rolled refractory section steel having excellent material uniformity according to 1, wherein one or more kinds of 5 to 1.0% are added.

3. As a steel component, Nb: 0.00
5 to 0.1%, V: 0.005 to 0.3%, Ti: 0.
3. The method for producing a rolled refractory section steel having excellent material uniformity according to 1 or 2, wherein one or more kinds of 005 to 0.1% are added.

4. B: 0.000 as a steel component
1 to 3 characterized by adding 5 to 0.003%
4. The method for producing a rolled refractory section steel having excellent material uniformity according to any one of the above.

5. In mass%, C: 0.02 to 0.20
%, Si: 0.05 to 0.7%, Mn: 0.8 to 1.8
%, Mo: 0.1 to 0.7%, Al: 0.01 to 0.1
%, Nb: 0.005 to 0.1%, V: 0.005 to
0.3%, one or two or more of Ti: 0.005 to 0.1%, and Mo + 8.0Nb + 2.4V +
A steel which satisfies 3.0 Ti ≧ 0.3 and whose balance substantially consists of Fe and unavoidable impurities exceeds 1200 ° C. and 135
After heating and rolling to 0 ° C or less, the surface of the flange is primarily cooled at an average cooling rate of 2.0 ° C / s or more from the temperature range of Ar3 or more to the surface temperature of Ar3-200 ° C or less,
Once the cooling is interrupted, the surface temperature is re-heated to 600 ° C or higher, and then the secondary cooling of both sides of the flange is performed at an average flange cooling rate of 2.0 ° C / s or more from 400 to 600 ° C. A method for producing a rolled refractory section steel having excellent material uniformity.

6. Further, as a steel component, Cu: 0.02
-1.5%, Ni: 0.02-1.5%, Cr: 0.0
5. The method for producing a rolled refractory section steel having excellent material uniformity according to 5, wherein one or more kinds of 5 to 1.0% are added.

[7] B: 0.000 as a steel component
5 or 6 characterized by adding 5 to 0.003%
4. A method for producing a rolled refractory section steel having excellent material uniformity according to item 1.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Component composition C C is added in an amount of 0.02% or more in order to secure the strength of steel. However, if contained in a large amount exceeding 0.20%, toughness or weldability deteriorates. , 0.2
0% or less (0.02 to 0.20%).

Si Si is inevitably contained for deoxidation. However, in order to secure strength, the content of Si is set to 0.05% or more in the present invention. 0.
If it exceeds 7%, HAZ toughness and weldability deteriorate, so
0.05 to 0.7%.

Mn Mn is added in an amount of 0.8% or more to improve the strength and toughness of the steel material and suppress the generation of FeS which causes red hot embrittlement. However, if it exceeds 1.8%, the hardenability increases. , A hardening phase occurs during welding and cracking sensitivity increases,
1.8%.

Mo Mo enhances hardenability, temper softening resistance, increases strength,
It is particularly effective in increasing the strength at medium and high temperatures, and is added. As with Mo, the amount of Nb, which is effective for increasing the strength at medium and high temperatures, is
It increases or decreases depending on whether V or Ti is added, and when one or more of these elements are added, the lower limit of Mo is set to 0.1%. On the other hand, when none of Nb, V, and Ti is added, the lower limit is set to 0.3%. In any case, if it exceeds 0.7%, the cost increases and the weldability deteriorates, so the upper limit is made 0.7%.

Al Al is added for deoxidation. If the content is less than 0.01%, the effect cannot be obtained. If the content exceeds 0.1%, the cleanliness of the steel decreases and the toughness of the welded portion deteriorates.
0.1% or less.

In the present invention, the above-mentioned basic component composition can sufficiently obtain the function and effect. However, when the characteristics are further improved, one or more of Cu, Ni, Cr, Nb, V, Ti, and B are used. Can be added.

Cu Cu is very effective in improving the strength and toughness. If the effects are expected, Cu is added in an amount of 0.02% or more. 1.5%
If more than 1.5%, precipitation hardening is remarkable and cracks easily occur on the surface of the steel material.

Ni Ni is effective in improving the strength and toughness. If the effects are expected, Ni is added in an amount of 0.02% or more. If it exceeds 1.5%, the cost increases, so it is set to 1.5% or less.

Cr Cr is effective in improving hardenability, and if that effect is expected, 0.05% or more is added. If it exceeds 1.0%, the weldability and the HAZ toughness deteriorate, so the content is made 1.0% or less.

Nb Nb is effective for improving the strength at room temperature and high temperature and further improving the toughness due to the precipitation effect of fine carbonitrides. If the effect is expected, Nb is added in an amount of 0.005% or more. If it is added in excess of 0.1%, it is difficult to lower the yield ratio due to excessive precipitation hardening.

V V is a small amount that improves hardenability and temper softening resistance.
It is effective in increasing the strength at room temperature and high temperature, and when that effect is expected, 0.005% or more is added. If added over 0.3%, the weldability is degraded, so the content is made 0.3% or less.

Ti Ti is effective in raising the strength at room temperature and high temperature in a small amount due to precipitation strengthening by TiC. In addition, TiN suppresses the coarsening of the crystal grains in the HAZ portion and improves the HAZ toughness. When the effect is expected, 0.005% or more is added. 0.1
%, TiC precipitates during the cooling process of welding and deteriorates the HAZ toughness.

BB is added in an amount of 0.0005% or more in order to improve hardenability, turn the structure into bainite, and increase the strength.
If added in excess of 0.003%, the toughness and weldability deteriorate, so the content is made 0.003% or less.

Mo + 8.0Nb + 2.4V + 3.0Ti This parameter is defined in the case of a component composition in which one or more of Nb, V, and Ti are added as selective elements to the basic component system. To gain sex
This parameter is set to 0.30 or more. (In this parameter, elements that are not contained are treated as 0.) FIG. 3 shows Y at 600 ° C. at the center of the flange thickness of an extremely thick rolled H-section steel 1 / 4F in which the material of each part of the flange is uniform.
The effect of the component composition on the ratio of S to YS at room temperature
The results are summarized by o content and Mo + 8.0Nb + 2.4V + 3.0Ti.

Mo + 8.0Nb + 2.4V + 3.0Ti
≧ 0.30, YS at 600 ° C. becomes Y at room temperature
S is 0.5 or more times that of S, and excellent fire resistance equivalent to that of Mo alone (Mo ≧ 0.30) containing no Nb, V, or Ti is obtained.

However, as described above, when one or more of Nb, V, and Ti are added, the lower limit of the Mo content is 0.10%. When Mo is less than 0.10%, Mo
Even if + 8.0Nb + 2.4V + 3.0Ti ≧ 0.30, the fire resistance is poor.

2. Manufacturing Conditions In the present invention, hot rolling conditions and cooling conditions are defined as follows. These rules need only be satisfied at least in the production of the flange, and the production conditions for the web are not particularly defined.

Slab heating temperature In the production of an extremely thick H-section steel, a pass schedule for finishing rolling at a relatively high temperature range is used from the viewpoint of dimensional accuracy.
It is necessary to increase the slab heating temperature.

When the slab heating temperature is 1200 ° C. or less,
It is difficult to roll into a predetermined shape due to a decrease in temperature during rolling. On the other hand, if the temperature exceeds 1350 ° C., the structure after rolling and cooling is significantly coarsened, and the toughness is significantly deteriorated.
Over 1300C and below 1350C.

Cooling Conditions In the present invention, in order to increase the strength by controlled cooling while suppressing the hardening of the flange surface, two-stage cooling is used, and the primary cooling stop temperature, recuperation temperature, and secondary cooling stop temperature are defined. .

Primary cooling stop temperature The primary cooling stop temperature is set so that the hardness of the steel sheet surface after reheating is reduced and the cooling effect is sufficient.
(r3-200) C or lower. The primary cooling stop temperature is (A
If the temperature exceeds (r3 -200) ° C, high strength cannot be achieved even if the secondary cooling rate is set to a high cooling rate.

Reheating temperature The reheating temperature is set to 600 ° C. or higher in order to soften the bainite phase formed on the surface by the tempering effect. In the case of a flange portion of an extremely thick H-section steel, it does not soften if the reheat temperature is less than 600 ° C.

FIG. 2 shows 0.12C-1.
The 5Mn-0.45Mo steel is heated to 1250 ° C.
After rolling a 0 x 400 x 45 x 65 (mm) refractory extremely thick section steel, the average cooling rate of the flange portion from the inner and outer surfaces was 3.5 ° C /
s, water cooling at a predetermined temperature, temporarily suspending the cooling at a predetermined temperature, changing the recuperation temperature by changing the subsequent holding time, and re-cooling to 550 ° C. at an average cooling rate of 3.5 ° C./s again. 3 shows the relationship between the hardness difference in the thickness direction of / 2F and the first cooling stop temperature and recuperation temperature. When the primary cooling stop temperature is Ar3-200 ° C. or less and the recuperation temperature is 600 ° C. or more on the flange surface, the hardness difference in the flange thickness direction is Hv40 or less, and good uniformity is obtained.

Secondary Cooling Stop Temperature The secondary cooling stop temperature is set to 600 ° C. or less in terms of the average temperature of the steel sheet in order to obtain an effect of increasing strength by cooling. On the other hand, when the cooling stop temperature is lowered, the strength can be easily ensured, but the surface hardness increases and becomes significant below 400 ° C.
C or higher.

[0041]

EXAMPLES (Example 1) Steels having the component compositions shown in Table 1 were rolled into H-shaped steels under various production conditions, and mechanical properties and fire resistance were evaluated. Steel 1 shown in Table 1 is 50 kg class, steel 2
Is an ingredient with a 60 kilo class in mind. Table 2 shows the rolling size, manufacturing conditions, and characteristics of the flange portion. Since all steels satisfy the fire resistance condition of the present invention, 6
YS at 00 ° C has 0.5 times or more of room temperature YS, and the absolute value of YS at 600 ° C, which is a standard of 50 kg class refractory steel, is 217 MPa or more. Y at 600 ° C, which is a guideline for steel equivalent to 60 kilo class refractory steel
S is 293 MPa or more.

In Table 2, Examples 1 and 8 are comparative examples in which the cooling after rolling is not a two-stage cooling.
The hardness difference in the flange thickness direction is large at both positions F and 1 / 2F.

In Examples 2, 3, 9, 10, and 15, two-stage cooling was performed. In Examples 2, 9, the interruption temperature, in Examples 3, 10, the recuperation temperature, and in Example 15, the cooling was stopped. The temperature is outside the range of the present invention and is a comparative example, and the hardness difference in the flange thickness direction is large. In Example 15, the toughness was remarkably deteriorated.

On the other hand, Examples 4, 5, 6, 7, 11, 1
Nos. 2, 13, and 14 are examples of the present invention, and have a small difference in hardness in the flange thickness direction and excellent uniformity.

[0045]

[Table 1]

[0046]

[Table 2]

(Example 2) A steel having the composition shown in Table 3 was rolled, and after rolling, a shaped steel was produced by two-stage cooling. Table 4 shows the rolling size, manufacturing conditions and characteristics of the flange portion.
The test steels 3 to 6 and 8 have a composition of 50 kg steel, and the test steel 7 has a composition of 60 kg steel. Examples 16 to of Table 4
18, 20, 22 to 24 and 26 are all examples of the present invention, and the hardness difference in the flange thickness direction is small at any of the positions of the flanges 1 / 4F and 1 / 2F. Has fire resistance and excellent toughness. On the other hand, in Examples 19, 21, 25 and 27, the chemical composition of the test steel was out of the range of the present invention and was inferior in fire resistance.
The ratio of YS between ° C and room temperature is as low as less than 0.5.

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

As described above, according to the present invention,
After rolling, after primary cooling, recuperate and then secondary cooling, regardless of the flange thickness, the material of each part of the flange is uniform, excellent in fire resistance without deterioration of cross-sectional shape Steel can be manufactured without complicated heat treatment and refining work, and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a diagram showing changes in a flange outer surface temperature and a central part temperature during cooling after rolling.

FIG. 2 is a diagram showing the influence of a primary cooling stop temperature and a recuperation temperature in a two-stage cooling on a difference in hardness in a thickness direction in a flange 1 / 2F.

FIG. 3 shows the effect of M on fire resistance (YS600 ° C./YSRT).
The figure which shows the influence of o, NbV, Ti.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Minoru Suwa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. 4K032 AA01 AA02 AA04 AA05 AA11 AA14 AA15 AA16 AA19 AA21 AA22 AA23 AA24 AA27 AA29 AA31 AA35 AA36 BA00 CA03 CC03 CC04 CD02

Claims (7)

[Claims] 1. A mass% of C: 0.02 to 0.20%,
Si: 0.05 to 0.7%, Mn: 0.8 to 1.8%,
Rolling a steel containing Mo: 0.3-0.7%, Al: 0.01-0.1%, and the balance substantially consisting of Fe and unavoidable impurities is heated to more than 1200 ° C and 1350 ° C or less. Then, from the temperature range of Ar3 point or more, the surface temperature becomes Ar3-200.
Primary cooling of both sides of the flange at an average cooling rate of 2.0 ° C./s or more to below 100 ° C. is performed. After cooling is once suspended, the surface temperature is returned to 600 ° C. or more, and the average temperature of the flange is 400 ° C. A method for producing a rolled refractory section steel excellent in material uniformity, characterized in that both sides of a flange are secondarily cooled at an average cooling rate of the flange portion of 2.0 ° C / s or more to 600 ° C or more. 2. The steel component further comprises Cu: 0.02 to
1.5%, Ni: 0.02 to 1.5%, Cr: 0.05
The method for producing a rolled refractory section steel having excellent material uniformity according to claim 1, wherein one or more kinds of -1.0% are added. 3. The steel component further comprises Nb: 0.005 to 0.005.
0.1%, V: 0.005 to 0.3%, Ti: 0.00
3. The method for producing a rolled refractory section steel having excellent material uniformity according to claim 1, wherein one or two or more of 5 to 0.1% are added. 4. B: 0.0005 to steel component
4. The method according to claim 1, wherein 0.003% is added. 5% by mass, C: 0.02 to 0.20%,
Si: 0.05 to 0.7%, Mn: 0.8 to 1.8%,
Mo: 0.1 to 0.7%, Al: 0.01 to 0.1%,
Nb: 0.005 to 0.1%, V: 0.005 to 0.3
%, Ti: one or more of 0.005 to 0.1%, and further Mo + 8.0Nb + 2.4V + 3.0T.
After the steel satisfying i ≧ 0.3 and the balance substantially consisting of Fe and unavoidable impurities is heated to more than 1200 ° C. and 1350 ° C. or less, the surface temperature is Ar 3 −200 ° C. from the temperature range of Ar 3 point or more. Primary cooling of both sides of the flange at an average cooling rate of 2.0 ° C./s or more to the flange below, after temporarily interrupting the cooling, and returning the surface temperature to 600 ° C. or more,
A method for producing a rolled refractory section steel having excellent material uniformity, characterized in that both surfaces of the flange are secondarily cooled at an average cooling rate of the flange portion of 2.0 ° C./s or more to an average temperature of the flange portion of 400 to 600 ° C. . 6. The steel component further contains Cu: 0.02 to
1.5%, Ni: 0.02 to 1.5%, Cr: 0.05
The method for producing a rolled refractory section steel having excellent material uniformity according to claim 5, characterized in that one or two or more of 1.0% or more are added. 7. As a steel component, B: 0.0005 to
The method for producing a rolled refractory section steel having excellent material uniformity according to claim 5 or 6, wherein 0.003% is added.