JPH03240918A - Production of wide flange shape excellent in refractoriness and reduced in yield ratio - Google Patents

Abstract

PURPOSE:To inexpensively produce a wide flange shape excellent in refractoriness and reduced in yield ratio by subjecting a bloom of a steel having a specific composition consisting of C, Si, Mn, Mo, Nb, Al, N, Ni, Cu, Cr, V, Ti, and Fe to specific reheating and then to hot rolling. CONSTITUTION:A bloom of a steel having a composition which consists of, by weight, 0.03-0.15% C, <=0.6% Si, 0.2-1.0% Mn, 0.7-1.5% Mo, 0.005-0.04% Nb, <=0.1 % Al, 0.001-0.0060% N, one or more kinds among 0. 05-0.50% Ni, 0.05-0.50% Cu, 0.05-0.50% Cr, 0.005-0.04% V, and 0.005-0.03% Ti, and the balance Fe with inevitable impurities and in which the value of DI represented by an equation DI=0.316C<0.5>(1+0.7Si) (4.1Mn+0.35) (1+3Mo) (1+0.36Ni) (1+2.2Cr) (1+0.365Cu) is regulated to <0.8 is reheated at 1200-1350 deg.C. Then, hot rolling is finished at 750-1050 deg.C. By the above procedure, the microstructure of the bloom is formed into a structure composed essentially of ferrite. By this method, the amount of expensive additive elements can be reduced, and the wide flange shape excellent in refractoriness and reduced in yield ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a low yield ratio H-section steel with excellent fire resistance for use in various buildings in the fields of architecture and civil engineering.

[Conventional technology]

As is well known, rolled steel for shell structures (JIS G3101) is used as a construction material for various buildings in the fields of architecture and civil engineering.
, Rolled steel materials for welded structures (JIS G 3106), Weather-resistant hot rolled steel materials for welded structures (JIS G 3114)
, highly weather resistant rolled steel (JIS G 3125), carbon steel pipes for shell structures (JIS G 3444), rectangular steel plates for shell structures (JIS G 3466), etc. are widely used.

The above-mentioned well-known steel materials are usually made by removing S from hot metal obtained in a blast furnace.
After dephosphorization, the steel is refined in a converter furnace and made into a steel billet in a continuous casting or blooming process, followed by hot plastic working to produce a product with desired properties.

By the way, when using the well-known steel materials in buildings such as buildings, offices, and residences that are closely connected to daily life, it is not mandatory to provide sufficient fireproof coating to ensure safety in the event of a fire. Construction-related laws and regulations stipulate that the temperature of steel materials should not exceed 350°C in the event of a fire. In other words, when the above-mentioned well-known steel materials are used in buildings, the yield strength at about 350°C is 60 to 70% of that at room temperature, which may cause the building to collapse. In the case of buildings whose columns are made of steel sections specified in G 3101), in addition to spreading sprayed wood or felt based on slag wool, glass wool, asbestos, etc. on the surface, fire prevention mortar is applied. A fire-resistant coating is carefully applied, such as encasing the heat insulating material layer with a thin metal plate, such as aluminum or stainless steel plate, to prevent the steel material from losing its load-bearing capacity due to thermal damage in the event of a fire. Use it in such a way that it doesn't. Therefore, the cost of fireproof coating becomes higher than the cost of steel materials, and it is unavoidable that construction costs will rise significantly.

Therefore, a technology has been proposed that uses round or square steel pipes as construction materials to allow cooling water to circulate, which prevents temperature rise in the event of a fire and does not reduce load capacity. is being expanded.

For example, Japanese Utility Model Publication No. 52-16021 discloses a fire-resistant building in which a water tank is placed on the top of the building and cooling water is supplied to pillars made of hollow steel pipes. Also,
In Japanese Patent Application No. 01-139328, a considerable amount of Mo and Nb are added in combination as the basic components of the steel material, and the microstructure is changed to a relatively large ferrite-based structure by a high-temperature heating-high-temperature rolling method, and the steel is heated at a high temperature of 600°C. Strength is room temperature strength 7
It is proposed that it is possible to secure 0% or more.

However, with this method, it is not possible to industrially satisfy the strength characteristics of both the web and the flange of an H-section steel having a complicated shape at room temperature and 600°C. That is, because the thickness of the web and the flange are different and the effect of cooling water during rolling is different between the two parts, the actual rolling end temperature differs by about 100°C, which affects the strength. In addition, for thin materials, the absolute value of the rolling end temperature must be low, and since ferrite is generated during rolling, the ferrite is processed and the yield ratio at room temperature tends to be significantly high. Not practical.

Furthermore, in Japanese Patent Application No. 01-139329, by using a method of water cooling steel containing a certain amount of Mo from a certain temperature in the austenite and ferrite regions after rolling, the microstructure is reduced by 20 to 50%. By creating a mixed structure of relatively large ferrite and bainite, the yield ratio at room temperature was kept low and strength at 600°C was ensured. However, it is not easy to water-cool the H-section steel from a constant temperature after rolling, and it is not possible to secure a sufficient shape considering the temperature difference between the web and the flange.

[Problem to be solved by the invention]

As a result of research on the strength of steel materials in the event of a fire, the present inventors found that when uncoated use is targeted, the maximum temperature reached in the event of a fire is 1000'C. It was learned that in order to provide the above-mentioned yield strength, a large amount of expensive metal elements must be added, resulting in a loss of economic efficiency. In other words, the unit price of the steel material becomes higher than the cost of the well-known steel material and, in addition, the cost of constructing the fireproof coating, and such steel material cannot be practically used. As a result of further research, we found that the most economical steel material had a high-temperature yield strength at 600°C that was 70% or more of that at room temperature. If possible and the fire load is small,
We have developed a manufacturing method for H-section steel that can be used without coating.

[Means to solve the problem]

The present invention overcomes the aforementioned problems and achieves the objectives.
The specific means is, in terms of weight ratio, C0.03 to 0.15%, Si 0.6% or less, Mn0.
2-1.0%, Mo 0.7-1.5%, Nb 0.
005-0.04%, A10.1% or less, N 0.00
1-0.0060% plus Ni 0.05-0.5
0%, Cu 0.05~0.50%, Cr 0.05~
0.50%, V 0.005-0.04%, Ti
One or more of 0.005 to 0.03%, the remainder containing Fe and unavoidable impurities, and the following (1)
) After reheating a steel piece having a composition with a DI value of less than 0.80 in the temperature range of 1200 to 1350°C,
This is a method for producing a low yield ratio H-beam steel with excellent fire resistance, characterized in that hot rolling is completed in a temperature range of 750 to 1050°C, and the microstructure is made mainly of ferrite.

(1) Formula: DI ~0.316. /”il: (1+0
．． 7Si) (4,1Mn+0.35) (1+3Mo
) (1+0.36Ni) (1+2.2Cr) (1+
0.365Cu) (component unit; weight%) [Function] Now, the feature of the present invention is that 0.70% or more of Mn is added to low Mn steel.
When O and Nb are added, the DI value given by equation (1) is 0.
After reheating a steel slab with a composition of less than 80 at a high temperature, rolling is finished at a relatively high temperature.The H-beam steel produced by the method of the present invention has appropriate room temperature yield strength and low yield for both the web and flange. In addition to having a high temperature ratio, it also has the characteristics of high high temperature yield strength. In other words, the room temperature yield strength is 60
The percentage of yield strength in the temperature range of 0°C is large. The reason for this is that the microstructure mainly consists of ferrite because alloy components are added to the low-Mn base component to suppress hardenability. In addition, since the hardenability is suppressed, it can be heated at both room temperature and 600°C.
M of 0.70% or more to ensure strength.

is added to compensate for this. Furthermore, the addition of 0.70% or more of Mo has the effect of lowering the transformation start temperature during rolling, and is effective in cases where the rolling temperature is likely to drop, such as in H-section steel. That is, rolling at a temperature below the transformation temperature processes the ferrite portion, resulting in a significant increase in YR at room temperature, resulting in a high yield ratio. Addition of 0.70% or more of Mo has the effect of lowering the transformation start temperature by about 60° C. or more, and is effective as a means for obtaining a low yield ratio.

Next, the characteristic constituent elements of the steel of the present invention and their addition amounts will be explained.

Mo and Nb form fine carbonitrides, and Mo increases high-temperature strength through solid solution strengthening, but it is difficult to obtain sufficient yield strength in the high-temperature region of 600°C by adding Mo alone. As a result of their research, they found that the combined addition of Mo and Nb is extremely effective in increasing the yield strength in the high-temperature N range. However, Mo.

If the amount of Nb is too high, weldability will deteriorate, so M o
.

The upper limit of the Nb content needs to be 1.5% and 0.04%, respectively, and the lower limit of Mo is 0.7%, which is the minimum amount to ensure the above-mentioned effect of lowering the transformation temperature and high-temperature strength. did. The lower limit of Nb was set at 0.005% as the minimum amount to obtain a composite effect. The use of Mo to increase high-temperature strength is known in conventional heat-resistant steels, but as mentioned above, steel materials with a compound addition of a small amount of Nb in addition to Mo are used as fire-resistant steel materials for construction. is not known.

Next, the reason for limiting components other than Mo and Nb in the present invention will be explained in detail.

C ensures the strength of the base metal and welded part, and Mo.

Necessary to exhibit the effect of Nb addition, and 0.0
If it is less than 3%, the effect will be weakened, so the lower limit is set at 0.03%. Furthermore, too much C deteriorates the toughness of the base material, so
The upper limit is 0.15%.

Si is an element contained in deoxidized steel, and an increase in Si impairs weldability, so the upper limit was set at 0.6%. In the steel of the present invention, AI deoxidation is sufficient, and Ti deoxidation may also be used.

Next, Mn is an essential element for ensuring strength and toughness, and its lower limit is 0.2%. However, if the amount of Mn is too large, the hardenability increases and the microstructure becomes bainite, making it impossible to obtain a base material strength that meets the target specifications. Therefore, the upper limit of the Mn content was set to 1.0%.

AI is generally an element contained in deoxidized steel, but since deoxidation is also performed by Si and Ti, the present invention does not limit the lower limit of AI. However, if the amount of AI increases, the cleanliness of the steel will deteriorate and the toughness will deteriorate, so the upper limit was set at 0.1%.

N is generally contained in steel as an unavoidable impurity, but it combines with Nb to form carbonitride Nb (CN 2 ), which is effective in improving high-temperature yield strength. For this reason, a minimum amount of 0.001% is required, but if the amount of N increases, it will promote the occurrence of surface flaws during continuous casting, so the upper limit should be set at 0.001%.
006%.

In addition, the steel material of the present invention contains P and S as inevitable impurities.
Contains. Since P and S have a small effect on high temperature strength, their amounts are not particularly limited, but generally the properties of steel materials such as toughness improve as the amounts of P and S decrease. Desirable amounts of P and S are 0.02% and 0.0, respectively.
It is 10% or less.

The basic components of the steel material of the present invention are as described above, and the purpose can be fully achieved, but the following elements, namely Ni,
By selectively adding Cu, Cr, V, and Ti, more favorable results can be obtained in terms of improvement in strength and toughness. Next, the additive elements and their amounts will be explained.

Ni improves the strength and toughness of the base metal, but if it is less than 0.05%, the effect is weak, and if it is added more than 0.5%, it becomes extremely expensive for construction steel, so it loses economic efficiency, so the upper limit is set. was set at 0.5%.

In addition to having almost the same effect as Ni, Cu also has the effect of increasing high-temperature strength and improving corrosion resistance and weather resistance due to Cu precipitates. However, if it is less than 0.05%, the effect is weak, so the amount of Cu is limited to 0.05 to 0.5%.

Cr is an element that increases the strength of the base material, and is also effective in improving weather resistance, but the effect is weak in 0.05% Azumari. Therefore, the amount of Cr is set to 0.05 to 0.5%.

(2) is effective in improving high temperature strength like Nb, but 0.
If it is less than 0.005%, the effect is weak, so the amount is 0.0.
05-0.04%.

When the amount of AI is small, Ti is effective as a deoxidizing element and improves HAZ toughness, but it is not effective when it is less than 0.005%, and it is preferable because it has a negative effect on weldability etc. when it exceeds 0.03%. do not have.

Next, a method for manufacturing steel materials according to the present invention will be explained.

Rolled steel materials for welded structures (JIS G3106
In order to satisfy the performance stipulated in ) and maintain high yield strength at a high temperature of 600°C, the conditions for heating and rolling the steel are important as well as the steel composition. In order to increase the high-temperature yield strength through the combined addition of Mo and Nb, which are characteristic of the steel components of the present invention, it is necessary to sufficiently dissolve these elements during heating. The lower limit of the heating temperature is 1200°C. Furthermore, if the heating temperature is too high, the steel piece will be significantly oxidized or deformed, so the upper limit must be 1350°C.

Next, the heated steel slab is hot rolled, and the rolling end temperature is set to a high temperature of 750° C. or higher. The reason is that M during rolling
This is to prevent carbonitrides of o and Nb from precipitating, and if these elements precipitate in the T region, the precipitate size increases and the high temperature yield strength decreases significantly. Furthermore, the steel of the present invention has 0.
Although 70% or more of Mo is added to lower the transformation start temperature during rolling, rolling at a temperature below 750° C. is not preferable because it processes the ferrite. In the present invention, the upper limit of the rolling end temperature is set to 1050° C., and the reason for this is to ensure toughness as a construction steel. After hot rolling, the product is allowed to cool to room temperature.

In addition, after manufacturing the steel material of the present invention, A c
Even if the steel material is reheated to a temperature below one transformation point, the characteristics of the steel material of the present invention are not impaired in any way.

〔Example〕

H of the steel components shown in the table in the well-known converter, continuous casting, and section steel processes.
A shaped steel was manufactured and its strength at room temperature and at 600°C was investigated.

In Table 1, chemical compositions of the present invention steel are shown in kl to Na2O, and chemical compositions of comparative steels are shown in N1121 to Na2O. Next, Table 2 shows the mechanical properties of the steel of the present invention and the comparative steel according to heating and rolling conditions. The examples No. 1 to No. 1120 in Table 2 all have good strength at room temperature and at high temperature.

On the other hand, in NtL21 to Tsui 25, the heating and rolling temperatures are low, so the YR at room temperature exceeds 80%, and the ratio of 600°C strength to room temperature strength (hereinafter referred to as strength ratio) is 70% or less. , is an insufficient characteristic.

Further, in No. 26 to Na35, although the heating and rolling conditions meet the requirements of the invention, the component compositions do not satisfy the requirements of the invention, so the properties are insufficient. That is, N(126, N
No. o, 32, No. 33, the amount of Mo is low, so the strength ratio is insufficient. In Nα27, No, 28,
Since the DI value is too high, both the YR at room temperature and the strength ratio are insufficient. In Nα29, the Mn content is too low, so the intensity ratio is insufficient. Nα30, No, 34
, Nα35 has an insufficient intensity ratio because Nb is not added. No. 31 has a small amount of C, so
Insufficient strength ratio.

Blank space below [Effects of the invention] The H-beam steel manufactured using the chemical composition and manufacturing method of the present invention has a yield strength at 600°C of 70% or more of the yield strength at room temperature for both the web and the flange, and the yield ratio at room temperature (YR:YS /TS) is a completely new steel material that also has the characteristics of low resistance.

Claims (1)

[Claims] 1) Weight ratio of C0.03 to 0.15%, Si 0.6% or less, Mn0.
2-1.0%, Mo0.7-1.5%, Nb0.005-
0.04%, Al 0.1% or less, N0.001~0.0
060% plus Ni0.05-0.50%, Cu0.05-0.50%
, Cr0.05-0.50%, V0.005-0.04
%, Ti 0.005 to 0.03%, the remainder contains Fe and unavoidable impurities, and the DI value given by the following formula (1) is less than 0.8. A low yield ratio with excellent fire resistance characterized by having a microstructure mainly composed of ferrite by reheating the steel billet in a temperature range of 1200 to 1350°C and then finishing hot rolling in a temperature range of 750 to 1050°C. Method for manufacturing H-beam steel. Equation (1): DI=0.316√C(1+0.7Si)(4.1Mn
+0.35)(1+3Mo)(1+0.36Ni)(1
+2.2Cr) (1+0.365Cu) (component unit; weight %)