JPH0673449A - Production of high strength fire resistant steel sheet for building - Google Patents

Abstract

PURPOSE:To produce steel combining high yield point and good weldability and low in yield ratien and to reduce or obviate fireproof covering. CONSTITUTION:A slab contg. 0.05 to 0.15% C, <=0.60% Si, 0.50 to 1.80% Mn, <=0.03% P, <=0.03% S, <=0.003% sol. Al, 0.10 to <0.40% Mo, 0.005 to 0.060% Nb, 0.005 to 0.030% Ti, 0.0020 to 0.0070% N and 0.0005 to 0.0050% Ca as well as <=0.24% PCM value and the balance Fe with inevitable impurities is heated to >=1050 deg.C and is thereafter rolled at <=1000 deg.C and at >=50% draft, and the rolling is finished in the temp. range of >850 to <950 deg.C. If required, one or >=two kinds selected from 0.05 to 0.50% Cu, 0.05 to 0.50% Ni, 0.10 to 0.60% Cr and 0.005 to 0.060% V can be incorporated therein. In the same compsn., PCM=C+C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fire-resistant steel plate, and more specifically, it has a high tensile strength of 490 N / mm ² and a high strength for construction, which has a high yield strength of 216 N / mm ² or more even at a high temperature of 600 ° C. The present invention relates to a method for manufacturing a fireproof steel plate.

[0002]

2. Description of the Related Art Architectural steel sheets are designed and manufactured to have various properties at room temperature, but their strength generally decreases with increasing temperature. Published by Japan Steel Structure Association
In JSSC Vol.4 No.33 1968, the yield point or 0.2% proof stress of SM50B at high temperature gradually decreases as the temperature becomes higher, and the decrease at 500 ° C or more is remarkable. The temperature down to 3 is stated to be 400-500 ° C.

As high temperature steel sheets, Cr-Mo steel sheets for boilers and pressure vessels, which are specified in JIS, ASTM, etc., are widely used. These are steel plates used for a long time of several hundreds of thousands of hours, and the guaranteed temperature is 350 to 400 ° C.

In the conventional Si-Mn-based 490 N / mm ² class steel sheet for construction, when the temperature exceeds 350 ° C, the long-term proof strength (2/3 of room temperature proof strength) of 216 N / mm, which is the proof stress required for structural members during a fire. ^Since it is less than ² , it is obligatory to apply fireproof coating, which is a shackle from the viewpoint of construction cost and construction period, so that the temperature of the steel frame does not exceed 350 ℃. However, in the recently added "new fireproof design method", the steel plate has a normal yield strength at room temperature of 600 ° C.
Depending on the strength at high temperature, such as when it has more than 2/3, the reduction of the amount of refractory coating has been recognized.

[0005]

At present, as a steel sheet having excellent high temperature proof stress, there is the above-mentioned steel sheet for boiler / pressure vessel, but this steel sheet has a proof stress at 600 ° C. of 216 N / mm ² or more. Due to the high composition of weld cracking susceptibility (P _CM ), the weld cracking resistance is poor and there are problems in welding such as pre-heating and post-heating. Furthermore, when large heat input welding such as electroslag welding or submerged arc welding, which is used to improve welding work efficiency, is performed, the toughness of the heat affected zone (HAZ) is significantly reduced, so small heat input welding is unavoidable. ing.

[0006] Therefore, in order to reduce or omit the construction of fireproof coating for building steel, it has a high-temperature proof stress and excellent weldability, large heat input welded joint toughness, and base metal characteristics, and is the same as the conventional one. Steel plates that can be designed and constructed are needed. Moreover, the demand for the yield ratio of 80% or less is increasing for the building steel from the viewpoint of the deformability of the building during an earthquake.

The present invention has been made to solve the above problems, and by controlling the rolling of a steel slab having a controlled chemical composition, a high yield strength of 216 N / mm ² or more can be achieved even at a high temperature of 600 ° C. It is an object of the present invention to provide a method for producing a high-strength refractory steel sheet for construction having.

[0008]

SUMMARY OF THE INVENTION The present invention has been carried out by the inventors of the present invention in view of the above problems in conventional building steels, and as a result, the chemical composition, particularly the sol.Al amount was limited. By adding a small amount of Mo and precipitating Nb to strengthen the weldability, the high-temperature yield strength can be significantly improved, and by utilizing TiN, excellent large heat input welded joint toughness can be secured. The first invention was completed with C:
0.05 to 0.15%, Si: 0.60% or less, Mn: 0.50 to 1.80%, P:
0.03% or less, S: 0.03% or less, sol.Al: 0.003% or less, Mo:
0.10% or more but less than 0.40%, Nb: 0.005 to 0.060%, Ti: 0.005
~ 0.030%, N: 0.0020-0.0070%, Ca: 0.0005-0.0050
%, And the value of P _CM specified by the following formula is 0.24
%, The steel slab consisting of the balance Fe and unavoidable impurities is heated to a temperature of 1050 ° C or higher, and the rolling reduction of 1000 ° C or lower is set to 50% or higher, and rolling is completed in the temperature range of 850 ° C to less than 950 ° C. And a yield strength at 600 ° C. of 216 N / mm ² or more. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B
(%)

The second aspect of the present invention further comprises, as chemical components of the steel sheet, Cu: 0.05 to 0.50%, Ni: 0.05 to 0.50%, Cr: 0.10 to
The method for producing a high-strength refractory steel sheet for construction according to claim 1, which contains one or more selected from 0.60% and V: 0.005 to 0.060%.

[0010]

The reason for limiting the chemical components in the present invention will be described below. The inventor has found that the sol.
Was investigated. The result is shown in FIG. Figure 1
Is 0.10% C-0.35% Si-1.00% when sol.Al is changed
Mn-0.015% P-0.005% S-0.025% Nb-0.012% Ti steel 600
The change in proof stress at ° C is shown.

As shown in FIG. 1, it can be seen that the yield strength is remarkably improved when sol.Al is 0.003% or less. Therefore, the content of sol.Al should be 0.003% or less. In addition,
Since Al is not used for deoxidation of molten steel, deoxidation of molten steel is Si, M
It is preferable to use n, Ti, and Ca, and to limit the amount of FeSi 2 having a high Al content used, and to deoxidize molten steel, use of vacuum carbon deoxidation during molten steel treatment.

C is an element that contributes to the increase in strength,
If less than 0.05%, it is difficult to secure the strength, and if more than 0.15% is contained, the toughness and weldability of steel deteriorate. Therefore, the amount of C added is 0.05
The range is to 0.15%.

Si is an element effective for deoxidizing,
Since the present invention contains Mn and does not necessarily need to be added, the lower limit is not limited. Further, Si is an element effective for solid solution strengthening, but if it is contained in a large amount exceeding 0.60%, the weldability is deteriorated. Therefore, the addition amount of Si is 0.60%
Below.

Mn is an element necessary to secure the strength and toughness of steel, but if it is less than 0.50%, such an effect is small, and if it is contained in a large amount exceeding 1.80%, weldability and toughness are improved. Deteriorates and exceeds the upper limit of SM490 strength. Therefore, the addition amount of Mn is set to the range of 0.50 to 1.80%.

Since P deteriorates HAZ toughness, base metal toughness and weld crack resistance due to microsegregation, P is made 0.03% or less.

S forms MnS which is a non-metallic inclusion and deteriorates the toughness and workability of the base material, so S is made 0.03% or less.

Mo is an indispensable element for ensuring high temperature strength and significantly increases the yield strength at 600 ° C.
However, if it is less than 0.10%, such an effect cannot be obtained, and if it is 0.40% or more, the weldability is impaired. Therefore, the addition amount of Mo is set to a range of 0.10% or more and less than 0.40%.

Nb is an element effective in increasing the strength by precipitation strengthening and transformation strengthening and improving the toughness by grain refinement. To obtain such an effect, 0.005% or more must be added. However, when added in excess of 0.060%, the weld joint toughness deteriorates. Therefore, the amount of Nb added should be in the range of 0.005 to 0.060%.

Ti is an element effective in reducing the deterioration of the high heat input welded joint toughness because TiN suppresses the coarsening of the austenite grains of the HAZ and produces intragranular ferrite. However, if it is less than 0.005%, such an effect cannot be exhibited, and if it exceeds 0.030%, the weld joint toughness deteriorates. Therefore, the amount of Ti added is 0.005
The range is to 0.030%.

N improves the large heat input welded joint toughness when combined with the above Ti. But 0.0020%
If it is less than 0.007%, such an effect cannot be exhibited, and if it exceeds 0.0070%, the toughness of the welded joint is deteriorated. Therefore, the amount of N 2 added is in the range of 0.0020 to 0.0070%.

[0021] Ca is an element that improves the properties in the plate thickness direction with a trace amount, but if it is less than 0.0005%, such an effect cannot be obtained, and if it exceeds 0.0050%, such an effect is saturated. At the same time, large inclusions are generated, and ultrasonic defects are likely to occur. Therefore, the addition amount of Ca is 0.0005 to 0.00
The range is 50%.

In the second aspect of the present invention, one or more selected from Cu, Ni, Cr and V can be added in addition to the above elements, if necessary.

Cu is an element effective for increasing strength by solid solution strengthening, but if it is less than 0.05%, such an effect is small,
Further, if it exceeds 0.50%, surface cracking occurs during hot working and weldability deteriorates. Therefore, the amount of Cu added is in the range of 0.05 to 0.50%.

Ni is an element effective for improving toughness,
If it is less than 0.05%, such an effect cannot be obtained, and 0.50%
If it exceeds, such effects will be saturated and it will be economically wasteful. Therefore, the addition amount of Ni is set to the range of 0.05 to 0.50%.

Cr is an element effective in improving the high temperature strength, but if it is less than 0.10%, such an effect cannot be expected, and 0.60
If it exceeds%, the weldability is deteriorated. Therefore, the addition amount of Cr is set to the range of 0.10 to 0.60%.

V is an element effective for increasing strength by precipitation strengthening, but if less than 0.005%, such an effect can hardly be expected, and if it exceeds 0.060%, weldability deteriorates. Therefore, the amount of V added should be in the range of 0.005 to 0.060%.

In both the first and second inventions, P _CM (welding crack susceptibility composition) is limited to 0.24% or less in order to prevent cold cracking during welding.

Next, the reasons for limiting the heating and rolling conditions in the present invention will be described. The present invention, after heating the steel slab containing the chemical components to a temperature of 1050 ℃ or more, 10
The rolling reduction at 00 ° C or lower should be 50% or higher, and the rolling should be completed within the temperature range of 850 ° C to less than 950 ° C.

The reason why the heating temperature is limited to 1050 ° C. or higher is as follows.
This is because Nb, which is necessary for ensuring room temperature strength and high temperature strength, is dissolved in steel. Further, the rolling reduction of 1000 ° C. or less is required to be 50% or more in order to obtain excellent base material toughness due to the refinement of austenite grains. Further, regarding the rolling end temperature, when the rolling end temperature is 850 ° C or lower, the yield ratio becomes high due to the ferrite grain refinement and the work hardening of the ferrite by the two-phase rolling, and it is required for building steel materials.
A yield ratio of 80% or less cannot be obtained. When the rolling end temperature is 950 ° C or higher, the austenite becomes coarse grains and the toughness of the base material deteriorates. Therefore, the rolling end temperature is
Limit to the temperature range above 850 ℃ and below 950 ℃.

[0030]

EXAMPLES The present invention will be described below with reference to examples. The test steel plates are steel pieces containing the chemical components shown in Table 1.
After heating to 1150 ° C, in order to secure a reduction of 50% or more at 1000 ° C or less, during rolling, the temperature is adjusted at a temperature of 920 to 950 ° C with a thickness of 60 mm, and the rolling end temperature is 890 to 910 ° C. Plate thickness
It is finished to 25 mm. Test pieces were taken from these steel sheets, and a room temperature tensile test, a Charpy impact test, a high temperature tensile test at 600 ° C, a maximum hardness test, and a Charpy impact test after a simulated thermal cycle were performed. The results are shown in Table 2.
The highest hardness test is performed in accordance with JIS Z 3101, and the reproducible heat cycle conditions are 1350 ° C × 5 seconds heating, 800 to 500 ° C.
It takes 220 seconds to cool.

Table 1 shows the present invention methods AF and comparative examples HJ.
The chemical composition of PCM, P _CM , and Table 2 show the tensile properties, impact properties, high temperature tensile properties, weldability and HAZ toughness, respectively.

As is apparent from Table 2, according to the method of the present invention.
A to G is P _cmIs less than 0.24%, and the yield strength at 600 ° C is
216N / mm²Excellent tensile strength at high temperature and tensile properties at room temperature
Is 490 N / mm²Class value (proof strength 314N / mm²Above, tensile strength 490
~ 610N / mm²) Is satisfied, and the yield ratio is required for steel for construction.
We are fully satisfied with less than 80%. Also,
Fracture transition temperature (vTrs) in lupi impact test is also below -25 ℃
Is. Maximum hardness of less than HV350 shows good weldability
In addition, the HAZ toughness (vE
₂₀) Is also good at 27J or more.

[0033]

[Table 1]

[0034]

[Table 2]

On the other hand, Comparative Example H has a proof stress at 600 ° C.
216N / mm ² and higher, but Ti is less than 0.005%, so HA
Z toughness is low and, because the Cr, Mo, is P _CM deviates to increase from the limited range of the present invention, the maximum hardness is HV350 or more, is bad, even higher still fracture appearance transition temperature of the base metal weldability . In Comparative Example I, the HAZ toughness is good, but since Mo that is effective for ensuring high temperature strength is less than 0.10%, the yield strength at 600 ° C. does not satisfy 216 N / mm ² or more. Comparative Example J is an example of a conventional 490 N / mm ² grade steel sheet for construction, but since Mo and Nb are less than 0.10% and less than 0.005% respectively, the yield strength at 600 ° C does not satisfy 216 N / mm ² or more. Moreover, since the Ti content is less than 0.005%, the HAZ toughness is also poor.

[0036]

As described above, according to the present invention,
0N / mm ² class high-strength refractory steel plate for construction is manufactured by limiting the chemical composition, especially sol.Al amount, adding a small amount of Mo, and precipitating Nb to strengthen the high-temperature yield strength without impairing the weldability. Has been significantly improved, and by utilizing TiN, excellent toughness of large heat input welded joints has been secured, so steel with a high yield strength at 600 ° C and good weldability as well as a low yield ratio can be obtained. It is possible to manufacture, and it is possible to significantly reduce or omit the conventionally required refractory coating,
Further, it has an excellent effect that the safety of the structure can be enhanced in terms of welding work and seismic resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of sol.Al on a proof stress at 600 ° C.

Claims (2)

[Claims] 1. C: 0.05 to 0.15%, Si: 0.60% or less, Mn:
0.50 to 1.80%, P: 0.03% or less, S: 0.03% or less, sol.Al:
0.003% or less, Mo: 0.10% or more and less than 0.40%, Nb: 0.005〜
0.060%, Ti: 0.005-0.030%, N: 0.0020-0.0070%,
Ca: 0.0005 to 0.0050% is contained, and the value of P _CM specified by the following formula is set to 0.24% or less, and a steel slab composed of the balance Fe and inevitable impurities is heated to a temperature of 1050 ° C or higher, and then 1000 The reduction rate below ℃ shall be 50% or more, and above 850 ℃ 9
A method for producing a high-strength refractory steel sheet for construction, characterized in that rolling is completed in a temperature range of less than 50 ° C and the yield strength at 600 ° C is 216 N / mm ² or more. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B
(%) 2. The chemical composition of the steel sheet is Cu: 0.05.
~ 0.50%, Ni: 0.05 ~ 0.50%, Cr: 0.10 ~ 0.60%, V:
The method for producing a high-strength refractory steel sheet for construction according to claim 1, which contains one or more selected from 0.005 to 0.060%.