JPH0737657B2 - H-section steel excellent in fire resistance and toughness and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to fire resistance used as a structural member of a building,
The present invention relates to an H-section steel having excellent toughness and a method for manufacturing the H-section steel.

(Conventional technology) Due to the construction of super high-rise buildings and the sophistication of building design technology, the fireproof design was reviewed by the Ministry of Construction comprehensive project, and the "New Fireproof Design Law" was enacted in March 1987. . According to this regulation, the temperature of the steel material should be 350
The restriction that fireproof coating should be kept below ℃ has been lifted, and it has become possible to determine the fireproof coating method suitable for it by the balance between the high temperature strength of steel and the actual load of the building. That is, if the designed high temperature strength at 600 ° C can be secured, the fireproof coating can be reduced accordingly.

In response to such a trend, the present inventors have previously proposed Japanese Patent Application No. 63-1
A low yield ratio steel for construction with limited fire resistance of 43740, a steel material, and a manufacturing method thereof were proposed. The gist of this technology is 60
Mo and Nb are added so that the yield point at 0 ° C is 70% or more of that at room temperature, and the high temperature strength is improved. The reason why the design high temperature strength of steel is set to 600 ° C is based on the finding that it is the most economical due to the balance between the increase of steel cost due to alloying elements and the fireproof coating construction cost.

(Problems to be Solved by the Invention) The inventors of the present invention have made the steel materials produced by the above-mentioned prior art into various shaped steels, particularly, H-shaped steel materials having strict restrictions on rolling shaping and unique shapes. As a result, there were differences in rolling finish temperature, pressure reduction, and cooling rate in each part of web, flange, and fillet, and room temperature / high temperature strength, ductility, and toughness varied, and there were parts that did not meet the criteria. occured.

In order to solve the above problems, the object of the present invention is to achieve high temperature strength characteristics, material characteristics, rolling finishing temperature, rolling reduction ratio,
An object of the present invention is to provide an H-section steel which is less dependent on the steel plate thickness (cooling rate) and is excellent in economical fire resistance, and a method for producing the H-section steel.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and the gist thereof is shown in the following items A to E.

A. % By weight, C: 0.05 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.
4 to 2.0%, Mo: 0.3 to 0.7%, V: 0.05 to 0.20%, N: 0.0070 to 0.
H-section steel with excellent fire resistance and toughness, with a composition of 0150%, Al <0.005%, and the balance being Fe and unavoidable impurities.

I. Dissolved oxygen is 0.003% by weight by preliminary deoxidation of molten iron
Melted to 0.020%, weight% by adding alloy, C: 0.05〜
0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Mo: 0.3 to 0.7
%, V: 0.05 to 0.20%, N: 0.0070 to 0.0150%, Al <0.005%,
The balance is a steel slab consisting of Fe and unavoidable impurities, and the steel slab is reheated to a temperature range of 1100 to 1300 ° C, and hot plastic working is performed to 85
A method for producing an H-section steel excellent in fire resistance and toughness, which ends in a temperature range of 0 to 1050 ° C.

C. % By weight, C: 0.05 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.
4 to 2.0%, Mo: 0.3 to 0.7%, V: 0.05 to 0.20%, N: 0.0070 to 0.
0150%, Al <0.005%, in addition Cr <0.7%, Ni <1.0%, Nb <
H-section steel containing 0.05%, Cu <1.0%, Ca: 0.001 to 0.005%, one or more kinds, and the balance being Fe and inevitable impurities, and having excellent fire resistance and toughness.

D. Dissolved oxygen is 0.003% by weight by preliminary deoxidation of molten iron
Melted to 0.020%, weight% by adding alloy, C: 0.05〜
0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Mo: 0.3 to 0.7
%, V: 0.05 to 0.20%, N: 0.0070 to 0.0150%, Al <0.005%,
In addition, Cr <0.7%, Ni <1.0%, Nb <0.05%, Cu <1.0%, Ca:
Includes 0.001 to 0.005% of 1 or 2 types, with the balance being Fe
And a steel piece consisting of inevitable impurities, and the steel piece is 1100 to
After reheating to the temperature range of 1300 ℃, hot plastic working is performed at 850 to 1050
A method for producing an H-section steel excellent in fire resistance and toughness, which ends in a temperature range of ° C.

(Operation) Hereinafter, the present invention will be described in detail.

The high-temperature strength of steel material is almost the same as the strengthening mechanism at room temperature at a temperature of 700 ° C or lower, which is about half the melting point of iron, and the refinement of ferrite crystal grain size, solid solution strengthening by alloying elements,
It is dominated by dispersion strengthening by the hardening phase and precipitation strengthening by fine precipitates.

Generally, the increase in high temperature strength is achieved by increasing the precipitation strengthening by adding Mo and Cr and increasing the softening resistance at high temperature by reducing the disappearance of dislocations. However, the addition of Mo and Cr remarkably enhances the hardenability, and the ferrite + pearlite structure of the base material is easily transformed into a bainite structure. When a component that easily forms a bainite structure is applied to H-section steel, there are differences in the rolling finish temperature, reduction rate, and cooling rate at each part of the web, flange, and fillet due to its unique shape. The bainite structure ratio changes greatly. As a result, room temperature / high temperature strength, ductility, and toughness vary, and some parts do not meet the standard.

The feature of the present invention is to maximize the effect of promoting the transformation of austenite to ferrite by the precipitation of VN and the effect of precipitation at high temperature in order to reduce the change in the composition ratio of bainite and ferrite in each part of H-section steel. There is a place to utilize.

Next, the reasons for limiting the basic composition range of the steel of the present invention will be described.

First, C is added as an effective component to improve the strength of steel. If it is less than 0.05%, the strength required for structural steel cannot be obtained, and if it is added in excess of 0.20%, the base metal toughness and welding The crack resistance and the weld heat affected zone (hereinafter referred to as HAZ) toughness are significantly reduced, so the upper limit was made 0.20%.

Next, Si is necessary for securing the strength of the base metal, pre-deoxidizing molten steel, etc., but if it exceeds 0.5%, it produces high carbon martensite (hereinafter referred to as M *) with a hardened structure in the heat treated structure, Remarkably reduces toughness. If it is less than 0.05%, the required pre-deoxidation of molten steel cannot be performed, so the Si content is limited to this range.

Mn needs to be added in an amount of 0.4% or more to secure the strength and toughness of the base metal, but the upper limit was set to 2.0% within the allowable range of toughness and cracking of the welded part.

Al is a strong deoxidizing element, and the addition of 0.005% or more of manganese, silicon oxide, etc. that promotes ferrite transformation is not formed, resulting in a decrease in toughness and excessive solid solution.
AI and N combine to form AIN, and in order to reduce the amount of VN precipitation, which is a characteristic of the invention steel, it was limited to less than 0.005%.

N is an extremely important element for the precipitation of VN. If it is less than 0.007%, the amount of VN precipitation is insufficient, a sufficient amount of ferrite structure is not formed, and the high temperature strength at 600 ° C cannot be secured. It was set to 0.007% or more. If the content exceeds 0.015%, the toughness of the base material is reduced and the surface cracks of the steel slab during continuous casting occur, so the content was limited to 0.015% or less.

Mo is an element effective in securing the base metal strength and high temperature strength. If it is less than 0.3%, sufficient high temperature strength cannot be secured due to the combined action with the precipitation strength of VN, and if it exceeds 0.7%, the hardenability increases too much and the base metal toughness and HAZ toughness deteriorate, so 0.3 to 0.7 Limited to%.

V is extremely important as VN in order to generate a ferrite structure, reduce its grain size, and secure high-temperature strength.
The precipitation amount of VN is insufficient, and if it exceeds 0.2%, the precipitation amount becomes excessive and the toughness of the base material decreases, so it was limited to 0.05 to 0.2%.

Although the amounts of P and S contained as unavoidable impurities are not particularly limited, they should be reduced as much as possible because they deteriorate weld crackability and toughness due to solidification segregation.
The amounts of P and S are 0.02% and 0.02% or less, respectively.

The above are the basic components of the steel of the present invention. For the purpose of increasing the strength of the base metal and improving the toughness of the base metal, one of Cr, Ni, Nb, Cu and Ca is used.
It may contain one species or two or more species.

First, Ni is an extremely effective element that enhances the toughness of the base metal, but the addition of more than 1.0% increases the alloy cost and is not economical, so the upper limit was made 1.0%.

Cr enhances hardenability and strengthens the base metal by precipitation hardening,
Effective for high temperature strengthening. However, excessive addition exceeding the upper limit is harmful from the viewpoint of toughness and curability, so the upper limit was made 0.7%.

Nb is effective for the toughness of the base metal, but excessive addition exceeding the upper limit is harmful from the viewpoint of toughness and hardenability, and therefore 0.
It was less than 05%.

Cu is an element effective for strengthening and weathering of the base metal, but considering the temper embrittlement due to stress relief annealing, weld cracking property, hot work cracking, etc., the upper limit was made 1.0%.

Ca has an effect as a deoxidizing material and an effect of subdividing a fluidized material (MnS), improving ductility and toughness of a base material, and suppressing anisotropy. However, less than 0.001% has no effect, and 0.005%
If it exceeds, a coarse Ca-fluxed oxide is formed, and ductility and toughness are deteriorated, so the Ca content was made 0.001 to 0.005%.

In producing the H-section steel of the present invention, after melted iron is melted to 0.003 to 0.020% by weight of dissolved oxygen by preliminary deoxidation, the composition is adjusted by adding an alloy so that the [0] concentration before deoxidation is 0.
If it is less than 003, ferrite-producing nuclei such as manganese and silicon oxide that promote ferrite transformation are reduced, and toughness cannot be improved. If it exceeds 0.020%, the oxide particles become coarse and become the starting point of brittle fracture, even if other conditions are satisfied.
In order to reduce the toughness, the dissolved oxygen content of the molten iron before adding the alloy was limited to 0.003 to 0.020% by weight.

The reheating temperature was restricted to the temperature range of 1100 to 1300 ℃ in order to facilitate plastic deformation in the production of shaped steel by hot working.
Since heating at 1100 ° C or higher is required, and in order to increase the yield point due to V and Mo at high temperature, it is necessary to sufficiently dissolve these elements in solid solution, so the lower limit of reheating temperature was set to 1100 ° C. . The upper limit was set to 1300 ° C due to the performance and economical efficiency of the heating furnace.

The hot working finish temperature is set to 850 to 1050 ° C because the toughness is improved as the rolling temperature is lower, but it is difficult to work below 850 ° C due to the shaping of shaped steel, and the working temperature above 1050 ° C is coarse grained. This is because the structure forms and the toughness decreases.

(Examples) The effects of the present invention will be further illustrated by the following examples.

The trial steels were melted in a converter, cast into 250 to 300 mm thick slabs by continuous casting, and then H-shaped steels of various shapes shown in Table 1 were manufactured by rolling shaping for each flange thickness.

FIG. 1 is a drawing showing the cross-sectional shape and mechanical properties of H-section steel 1, 2 is a flange, 3 is a web, 4 is a fillet, H is the web height, B is the flange width, t ₁ and t. ₂ indicates the web thickness and the flange thickness, respectively.

1 / 4B, 1 / 2B of the flange width B total length at the center of the thickness of the flange 2 (1 / 2t ₂ ), the flange 1/4 lower part and the flange 1 /
2 The lower part was defined, and the test piece was taken from this position. The reason for obtaining the characteristics of these parts is that the flange 1 / 4F part is H
This is because the mechanical properties of the H-section steel can be represented by these two locations because the flanges 1 / 2F part show the most average mechanical properties and the properties of the flange 1 / 2F part are the lowest.

Table 2 shows the chemical composition of the steels of the present invention and comparative steels, and Table 3 shows the rolling conditions and mechanical test characteristics. It is well known that the rolling heating temperature is set to 1280 ° C. Generally, a decrease in heating temperature improves mechanical properties, and it is estimated that high temperature heating conditions show the lowest value of mechanical properties. This is because it was determined that the values can represent the characteristics at heating temperatures below that.

As shown in Table 3, in the steels 1 to 10 of the present invention, the target room-temperature strength, high-temperature strength, and 0-zero strength are large in accordance with changes in rolling finish temperature, reduction rate, flange plate thickness (cooling rate), and flange part.
Satisfy Charpy value of 3.5kgfm or more at ℃.

On the other hand, Comparative Steels 11 to 13 cannot secure high temperature strength at 600 ° C due to reduction of N and Mo and addition of Al. Steels 14 to 17 satisfy normal temperature and high temperature strength, but have zero concentration due to insufficient deoxidation. Increase, M
Due to excessive addition of o, Si and N, the toughness is significantly reduced and the target value cannot be achieved.

That is, when all the requirements of the manufacturing method of the present invention are satisfied, as in Steels 1 to 10 shown in Table 3, a flange plate thickness of 1/2 which is the most difficult to secure the mechanical test characteristics of H-section steel, It is possible to manufacture H-section steel having sufficient strength at normal temperature and high temperature even in the width 1/2 part, excellent toughness, fire resistance and toughness.

(Effects of the Invention) The H-section steel according to the present invention has excellent high-temperature characteristics, and the coating thickness of the refractory material is 20 to 50% of the conventional level, so that the refractory purpose can be achieved. It will be possible. In addition, even in the flange plate thickness 1/2 and width 1/2 part where it is most difficult to secure the mechanical test characteristics of H-section steel, it is possible to manufacture H-section steel with sufficient room temperature and high temperature strength and excellent toughness. It has become possible, and industrial effects such as improved reliability of large buildings, ensuring safety, and economic effects are extremely remarkable.

[Brief description of drawings]

FIG. 1 is a drawing showing the cross-sectional shape of H-section steel, the name of each part, and the sampling position of a mechanical test piece. 1 ... H-section steel, 2 ... Flange, 3 ... Web, 4 ...
Fillet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Oda 1 Shinko Hachiman-cho, Sakai City, Osaka Prefecture, Nippon Steel Co., Ltd. Inside the Sakai Works (72) Inventor Kiyonosuke Yano 5-10-1, Fuchinobe, Sagamihara City, Kanagawa Prefecture Nippon Steel Co., Ltd., Second Research Laboratory (56) Reference JP-A-3-87332 (JP, A)

Claims (4)

[Claims] 1. By weight%, C: 0.05 to 0.20%, Si: 0.05 to 0.5
0%, Mn: 0.4 to 2.0%, Mo: 0.3 to 0.7%, V: 0.05 to 0.20
%, N: 0.0070 to 0.0150%, Al <0.005%, the balance being Fe and inevitable impurities, and H with excellent fire resistance and toughness
Shaped steel. 2. Dissolved oxygen in wt% by preliminary deoxidation of molten iron
Melted to 0.003 to 0.020%, weight% by addition of alloy, C:
0.05 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Mo:
0.3-0.7%, V: 0.05-0.20%, N: 0.0070-0.0150%, Al
<0.005%, the balance is Fe and unavoidable impurities as a steel slab, and after reheating the steel slab to a temperature range of 1100 to 1300 ° C., the hot plastic working ends in the temperature range of 850 to 1050 ° C. A method for producing an H-section steel having excellent toughness. 3. By weight%, C: 0.05 to 0.20%, Si: 0.05 to 0.5
0%, Mn: 0.4 to 2.0%, Mo: 0.3 to 0.7%, V: 0.05 to 0.20
%, N: 0.0070 to 0.0150%, Al <0.005%, in addition Cr <0.7
%, Ni <1.0%, Nb <0.05%, Cu <1.0%, Ca: 0.001 to 0.
An H-section steel containing 005% of one or more kinds and the balance being a composition of Fe and unavoidable impurities and having excellent fire resistance and toughness. 4. Dissolved oxygen in wt% by preliminary deoxidation of molten iron
Melted to 0.003 to 0.020%, weight% by addition of alloy, C:
0.05 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Mo:
0.3-0.7%, V: 0.05-0.20%, N: 0.0070-0.0150%, Al
<0.005%, in addition Cr <0.7%, Ni <1.0%, Nb <0.05
%, Cu <1.0%, Ca: 0.001 to 0.005%, 1 or 2 or more, and the balance is Fe and unavoidable impurities, and the rest is reheated to a temperature range of 1100 to 1300 ° C. , A method for producing an H-section steel having excellent fire resistance and toughness, in which hot plastic working is completed within a temperature range of 850 to 1050 ° C.