JPH04193907A - Production of 50kgf/mm2 class refractory steel plate for construction use - Google Patents

Abstract

PURPOSE:To improve yield strength at high temp. without deteriorating weldability and to secure superior toughness at a large heat input welded joint by heating a slab of steel in which the value of Pcm and chemical components are specified, respectively, and performing rolling while specifying temp. and reduction of area, respectively. CONSTITUTION:A steel having a composition which consists of 0.05-0.15% C, <=0.60% Si, 0.50-1.80% Mn, <=0.03% P, <=0.03% S, 0.002-0.10% solAl, 0.10-<0.40% Mo, 0.005-0.060% Nb, 0.005-0.030% Ti, 0.0020-0.0070% N, 0.0005-0.0050% Ca, and the balance Fe with inevitable impurities and in which the value of Pcm represented by <=0.24% is used. A slab of this steel is heated up to >=1050 deg.C and reduction of area at <=1000 deg.C is regulated to >=50%, and rolling is finished at >850 to <950 deg.C. By this method, a 50kgf/mm<2> class refractory steel plate for construction use having >=22kgf/mm<2> yield strength at 600 deg.C 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 manufacturing a fire-resistant steel plate.
50kg for architectural use with high proof strength even at high temperatures of 0℃
The present invention relates to a method for manufacturing f/mm class 2 fire-resistant steel plate.

(Prior Art) Architectural steel plates are designed and manufactured to have strong properties at room temperature, or the strength of the film surface decreases as the temperature rises. JSSC Vol published by Japan Steel Construction Institute
, 4 No. 331968 states that the yield point or 0.2% yield strength of 5M50B at high temperatures gradually decreases as the temperature increases, and the decrease is significant at temperatures above 500°C, reaching the value of 273 at room temperature. It is noted that the decreasing temperature is 400 to 500°C.

As high-temperature steel plates, Cr-Mo steel plates for foilers and pressure vessels, which are specified by J[S, ASTM, etc., are widely used. These are steel plates that can be used for long periods of time, such as hundreds of thousands of hours, and their guaranteed temperature is 350 to 40.
It is 0°C.

With conventional Sj-Mn-based 50kgf/mm2 class steel plates for construction, when the temperature exceeds 350℃, the long-term yield strength (273 of room temperature yield strength), which is the strength required for structural members in the event of a fire, is 22kg.
f/mm2, it is mandatory to install a fireproof covering to prevent the temperature of the steel frame from exceeding 350℃ due to construction costs and construction schedules. However, under the recently added new fire-resistant design method, if the steel plate has a standard yield strength of 273 or higher at room temperature at 600°C, it is permitted to reduce the amount of fire-resistant coating depending on its strength at high temperatures. It looks like this.

(Problem to be solved by the invention) Currently, the above-mentioned boiler and steel sheets with excellent high-temperature yield strength are
Is there a steel plate for pressure vessels? This steel plate has a yield strength of 22 to 2 f/mm2 or more at 600°C, and has a high weld cracking susceptibility composition (PC), so it has poor weld cracking resistance, and it has poor weld cracking resistance after preheating. There is a problem with welding if you do not apply heat. Furthermore, when performing high heat input welding such as electroslag welding and subman arc welding, which are used to increase welding efficiency, the toughness of the weld heat affected zone (HAZ) decreases significantly, so we have no choice but to use dwarf heat welding. has been done.

For this reason, in order to reduce or eliminate the need for fire-resistant coating construction on architectural steel, we have developed a system that has high high-temperature yield strength, excellent weldability, high heat input weld joint toughness, and base metal properties, and is designed to reduce or eliminate the need for fire-resistant coating construction. Steel plates that can be constructed are needed.

Furthermore, from the viewpoint of the deformability of buildings during earthquakes, there is an increasing requirement for architectural steel to have a yield ratio of 80% or less.

(Means for Solving the Problems) In view of the above-mentioned problems in conventional architectural steel, the present inventors have conducted intensive research, and as a result, the present invention has been developed based on the chemical components, particularly the addition of a small amount of Mo and Nb. The precipitation strengthening of Ti significantly improves high temperature yield strength without impairing weldability.
This was completed based on the knowledge that superior high heat input weld joint toughness can be secured by utilizing N.
Invention: Coo, 05-0.15%, Si: 0.60
% or less, Mn: 0.50-1.80%, P: 0.0
3% or less, S: 0.03% or less, sol, Al: 0
．． 002~0.10%, Mo:O, 10% or more 0.40
%, Nb: 0.005-0.060%, Ti・0
．． 005~0.030%, N:0.0020~0゜0
070%, Ca: 0.0005 to 0.0050%, and the PCMO value defined by the following formula is 0.24%
As below, after heating a steel billet consisting of the remainder Fe and unavoidable impurities to a temperature of 1050°C or higher, the rolling reduction at 1000°C or lower is set to 50% or more, and rolling is completed in a temperature range of more than 850°C and less than 950°C, 50kgf/m for construction with proof stress of 22kgf/mm2 or more at 600℃
This is a method for manufacturing m' class fireproof steel plate.

Pex=C+Si/30+Mn/20+Cu/20+N
i/60+Cr/2019iO/+5+V/10+5B
(%) The second invention has V: 0.005 to o, oe%, Cu: 0.
05-0°5%, Ni: 0.05-0.50%, Cr
: 50 kgf/mm for construction according to claim (1), which contains one or more selected from 0.10 to 0.60%.
This is a method for manufacturing second grade fireproof steel plate.

(Function) Below, the reason for limiting the chemical components in the present invention will be explained.

C is an element that contributes to increasing strength, but if it is less than 0.05%, it is difficult to ensure strength;
When the content exceeds 5%, the toughness and weldability of the steel deteriorate. Therefore, the amount of C added is 0.05~
The range is 0.15%.

Although Si is an effective element for deoxidation, the present invention uses M
n, contains AI and does not necessarily require addition, so the lower limit is not limited. Further, Sl is an effective element for solid solution strengthening, and if contained in a large amount exceeding 0.60%, it deteriorates weldability. Therefore, the amount of Si added is 0.60% or less.

Mn is an element necessary to ensure the strength and toughness of steel; if it is less than 0.50%, this effect will be small, and if it is contained in a large amount exceeding 1.80%, it will deteriorate weldability. It deteriorates toughness and exceeds the upper limit of 5M50 strength. Therefore, the amount of Mn added is 0.50 to 1.80%.
The range shall be .

Since P deteriorates HAZ toughness, base metal toughness, and weld cracking resistance due to micro-segregation, it should be kept at 0.03% or less.

S forms MnS, which is a nonmetallic inclusion, and deteriorates the toughness and workability of the base material, so the content is set to 0.03% or less.

sol, AI are essential elements for deoxidation, and
0.00 to contribute to grain refinement as AIN
It is necessary to add 2% or more, and if it is added in a large amount exceeding 0.10%, the number of oxide inclusions increases and the toughness deteriorates. Therefore, the amount of sol and Al added is 0,0
The range is 0.02% to 0.10%.

Mo is an essential element for ensuring high-temperature strength, and significantly increases yield strength at 600°C.

However, if it is less than 0.10%, such an effect cannot be obtained, and if it is more than 0.40%, weldability is impaired. Therefore, the amount of Mo added is in the range of 0.10% or more and less than 40%.

Nb is an element effective in increasing strength through precipitation strengthening and transformation strengthening, and improving toughness through grain refinement, and in order to obtain such effects, it is necessary to add 0.005% or more. However, when added in a large amount exceeding 0.060%, the toughness of welded joints deteriorates. Therefore, the amount of Nb added is in the range of 0.005 to 0060%.

Ti suppresses the coarsening of austenite grains in the HAZ due to TiN, and also generates intragranular ferrite, so it is an effective element for reducing deterioration of the toughness of high heat input welded joints. However, if it is less than 0.005%, such an effect cannot be exhibited, and if it exceeds 0.030%, the toughness of the welded joint will deteriorate. Therefore, the amount of T1 added is 0.
The range is 0.005% to 0.030%.

N improves the toughness of high heat input welded joints by combining with the above Ti. However, if it is less than 0.0020%, such an effect cannot be exhibited;
If it exceeds 0.070%, the weld joint toughness will deteriorate. Therefore, the amount of N added is in the range of 0.0020 to 0.0070%.

Ca is an element that improves properties in the thickness direction in a trace amount, or if it is less than 0.0005%, such an effect cannot be obtained.
Moreover, when it exceeds 0.0050%, such an effect is saturated and large inclusions are generated, which tends to cause ultrasonic defects. Therefore, the amount of Ca added is 0.00
The range is 0.05% to 0.0050%.

In addition, in the second aspect of the present invention, in addition to the above-mentioned elements, one or more selected from among V, Cu, Ni, and Cr may be added as necessary.

Is ■ an element effective in increasing strength through precipitation strengthening?
If it is less than 0.005%, such an effect can hardly be expected, and if it exceeds 0.060%, weldability will deteriorate.

Therefore, the amount of addition of (1) should be in the range of 0.005 to 0.060%.

Is Cu an effective element for increasing strength through solid solution strengthening?
．． If it exceeds 5%, surface cracks will occur during hot working and weldability will deteriorate. Therefore, the amount of Cu added is in the range of 0.05 to 0.5%.N1 is an effective element for improving toughness, or if it is less than 0.05%, such an effect will not be obtained. Furthermore, if the content exceeds 0.5%, this effect will be saturated and it will be economically wasteful. I want to, N1
The amount added is in the range of 0.05 to 0.5%.

Is Cr an element effective in improving high temperature strength?
If it is less than 0.6%, such an effect cannot be expected, and if it exceeds 0.60%, weldability will deteriorate. Therefore, the amount of Cr added is in the range of 0.10 to 0.60%.

In both the first invention and the second invention, in order to prevent cold cracking during welding, P (composition susceptible to welding cracks) is limited to 0.24% or less.

Next, the reasons for limiting the heating and rolling conditions in the present invention will be explained.

In the present invention, the above-mentioned steel slab containing the chemical components is heated to 1050°C.
After heating to the above temperature, it is necessary to set the rolling reduction rate at 1000°C or less to 50% or more and finish the rolling in a temperature range of more than 850°C and less than 950°C.

The reason why the heating temperature is limited to 1050° C. or higher is to dissolve Nb, which is necessary for ensuring room-temperature strength and high-temperature strength, into the steel. Further, the rolling reduction ratio 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. Furthermore, when the rolling end temperature is below 850°C, the yield ratio increases due to grain refinement of ferrite and work hardening of ferrite due to two-phase region rolling, resulting in a yield ratio of 80% or less. I can't do anything.

Further, when the rolling end temperature is 950° C. or higher, the toughness of the base material deteriorates because it becomes austenite or coarse grains. I wanted to,
The rolling end temperature is limited to a temperature range of more than 850°C and less than 950°C.

(Example) The present invention will be described below with reference to Examples.

The test steel plates were 11 pieces of steel containing the chemical components shown in Table 1.
After heating to 50°C, in order to ensure a rolling reduction of 50% or more at 1000°C or less, a 60mm thick 920-95
The temperature was adjusted at 0℃, and the rolling end temperature was 890~9.
It was finished to a thickness of 25 mm at a temperature of 10°C. Test pieces were taken from these steel plates and subjected to a normal temperature tensile test, a Charvi impact test, a high temperature tensile test at 600°C, a maximum hardness test, and a Charvi impact test after a simulated thermal cycle. The results are shown in Table 2. The highest hardness test is J.
It was carried out in accordance with IS Z 3101, and the reproducible thermal cycle conditions were heating at 1350°C for 5 seconds, and cooling time from 800 to 500'C was 220 seconds.
Table 2 shows the chemical composition and PCM of comparative method H-J, tensile properties, impact properties, high-temperature tensile properties, weldability, and H, A.
, respectively indicate Z toughness.

(Left below) As is clear from Table 2, A to G according to the method of the present invention are
PCM is 0.24% or less, yield strength at 600℃ is 2
It shows excellent high temperature yield strength at 2kgf/'mm2 or more, and the tensile properties at room temperature are 50kgf/mm' class value (proof strength 32k
gf/mm2J), tensile strength 50 to 62 kgf/mm
2) is of course satisfied, and the yield ratio fully satisfies the 80% or less required for architectural steel materials. Further, the fracture surface transition temperature (vTrs) in the Tsuyarubi impact test is also -35°C or lower.

The maximum hardness is less than HV350, indicating good weldability, and the HAZ toughness (VLO) in a simulated thermal cycle test
2.8 kgf-m or more is also good.

On the other hand, Comparative method H has a yield strength of 22 kgf at 600°C.
H
AZ toughness is low, and Cr, MO, and PCM are highly outside the limited range of the present invention, so the maximum hardness is H.
V350 or higher, weldability is poor, and the fracture surface transition temperature of the base metal is also high. Comparative method I has good HAZ toughness and contains less than 0.10% Mo, which is effective in ensuring high-temperature strength, so the yield strength at 600° C. does not satisfy 22 kgf/mm 2 or more. Comparative method J is the conventional architectural 5゜kll! f
/mm2 class steel plate, Mo and Nb are less than 0.10% and less than 0.005% respectively, so the yield strength at 600°C does not satisfy 22kgf/mm2 or more, and Ti is less than 0.005%. %, HAZ toughness is also poor.

(Effect of the invention) As explained above, the construction of 50kgf according to the present invention
/mm' class fireproof W4 board manufacturing method is based on chemical components, especially:
A small amount of auxiliary addition and Nb precipitation strengthening greatly improves high-temperature yield strength without impairing weldability, and the use of TiN ensures excellent high-heat-input weld joint toughness. It is possible to manufacture steel with a low yield ratio that combines high yield strength and good weldability at 600°C, and it is possible to significantly reduce or omit the conventionally required fireproof coating, and furthermore, This has the excellent effect of increasing the safety of the structure in terms of welding work and earthquake resistance.

Patent applicant: Kobe Steel Ori Co., Ltd. Representative Patent Attorney Complete History Chapter-

Claims (2)

[Claims] (1) C: 0.05-0.15%, Si: 0.60% or less, Mn: 0.50-1.80%, P: 0.03% or less, S: 0.03% or less, sol ．． Al: 0.002~0
．． 10%, 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:
Contains 0.0005 to 0.0050%, and the value of P_C_M defined by the following formula is 0.24% or less,
A steel billet consisting of the balance Fe and unavoidable impurities was heated to 1050°C.
After heating to a temperature above, the rolling reduction at 1000℃ or less is set to 50% or more, and the rolling is finished in a temperature range exceeding 850℃ and below 950℃, and the yield strength at 600℃ is 22kgf.
/mm^2 or more for architectural use 50kg
Method for producing f/mm^2 class fire-resistant steel plate. P_C_M=C+Si/30+Mn/20+Cu/20
+Ni/60+Cr/20+Mo/15+V/10+5
B (%) (2) V: 0.005-0.06%, Cu: 0.05-0.05%
0.5%, Ni: 0.05-0.5%, Cr: 0.10
50 kgf for construction according to claim (1), characterized in that it contains one or more selected from ~0.60%.
/mm^Method for manufacturing class 2 fire-resistant steel plate.