JPH05117744A - Production of 490n/mm2 class refractory steel products for building - Google Patents

Abstract

PURPOSE:To obtain the refractory steel products for buildings which have high yield strength at a high temp., have good weldability and excellent toughness of a large heat input welded joint in combination and has a low yield ratio. CONSTITUTION:A billet contg., by weight, 0.05 to 0.15% C, 0.05 to 0.60% Si, 0.50 to 1.80% Mn, <=0.02% P, <=0.005% S, 0.10 to 0.40% Mo, 0.030 to 0.150% Ti, 0.0020 to 0.0070% N, and 0.0005 to 0.0050% Ca, and having <=0.24% value of PCM regulated by the following equation is heated to >=100 deg.C and is then rolled at >=50% draft at <=1000 deg.C. As a result, the rolling is ended in a 850 to 950 deg.C range. The 490N/mm<2> class refractory steel products for buildings having >=217N/mm<2> yield strength at 600 deg.C and having the excellent weldability and the toughness of the large heat input welded joint are produced where, PCM =C+Si/30+Mn/2O+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 refractory steel material, and more particularly, it has a high yield strength even at a high temperature of 600 ° C., and has a good weldability and an excellent large heat input welded joint toughness. The present invention relates to a method for manufacturing a 490 N / mm ² class refractory steel material for use.

[0002]

2. Description of the Related Art In a building structure, when a steel frame is exposed to a high temperature during a fire, the strength of the building is lowered and the yield strength of the building is lowered.

In the conventional Si—Mn-based building steel, 3
If it exceeds 50 ° C, it will fall below 217 N / mm ² which is the proof stress required for structural members at the time of fire (2/3 of room temperature proof strength), which is 217 N / mm ² , so that the steel frame temperature should not exceed 350 ° C. From the aspect of construction period, etc., it is covered with a fireproof coating. However, in the recently added "new fireproof design method",
Reduction of the amount of refractory coating has come to be recognized by using steel materials (fire-resistant steel materials) having excellent high-temperature resistance.

[0004]

At present, as a steel material excellent in high temperature proof stress, there is a Cr-Mo steel sheet which is widely used for boilers and pressure vessels. This steel sheet has a proof stress at 600 ° C of 217 N / mm ² or more, but its weld crack susceptibility composition (P _CM ) is high, so the weld crack resistance is poor, and preheating and postheating are performed during welding. There are difficulties.
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 weld heat affected zone (HAZ) decreases significantly, so small heat input welding is unavoidable. It has been lost.

For this reason, in order to reduce or eliminate the fireproof coating work for building steel materials, it has a high-temperature proof stress, excellent weldability, large heat input welded joint toughness and base metal characteristics, and is the same as the conventional one. Steel materials that can be designed and constructed are needed. In addition, in terms of the deformability of a building during an earthquake, a yield ratio of 80% or less [(proof stress / tensile strength)
X 100] requirements are increasing.

As an improved manufacturing method of the above-mentioned construction steel material, JP-A-2-77523 and JP-A-3-6322 have been proposed.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted various studies from the viewpoint different from the above-mentioned prior invention in order to achieve the above-mentioned requirements for the steel materials for construction, and as a result, the chemical composition, particularly Ti The present invention was completed based on the finding that the formation of the carbonitrides in Example 1 improves the high-temperature yield strength of the steel material without impairing the weldability, and that it can secure excellent high heat input welded joint toughness. It was

That is, the first aspect of the present invention is the weight ratio.
C: 0.05 to 0.15%, Si: 0.05 to 0.60%, Mn: 0.50 to 1.80
%, P: 0.02% or less, S: 0.005% or less, Mo: 0.10-0.
40%, Ti: 0.030 to 0.150%, N: 0.0020 to 0.0070%,
Ca: 0.0005 to 0.0050% is contained, the balance is Fe and unavoidable impurities, and the value of P _CM defined by the following formula is 0.
After heating a steel slab that is 24% or less to a temperature of 1100 ° C or higher, the rolling reduction at 1000 ° C or lower is set to 50% or higher, and
Rolling is completed within the temperature range of ℃
It is 217 N / mm ² or more, and the gist is a manufacturing method of a 490 N / mm ² class refractory steel for construction having good weldability and excellent large heat input welded joint toughness. 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 V: 0.005-0.060%, Cu: 0.05-0.50%, and Ni: by weight ratio to the first aspect.
It is intended to provide a manufacturing method of a construction-use 490 N / mm ² class refractory steel material containing one or more selected from 0.05 to 0.50% and Cr: 0.10 to 0.40%.

[0010]

The structure and operation of the present invention will be described. The reasons for limiting the chemical composition of the steel material targeted by the present invention are as follows. C
Is an element that contributes to the increase in strength, but if it is less than 0.05%, it is difficult to secure the strength, and if it is added in excess of 0.15%, the weldability and toughness deteriorate. Therefore, the amount added is in the range of 0.05 to 0.15%.

Si is an essential element for deoxidation,
If it is less than 0.05%, the deoxidizing effect is small, and if it is added in excess of 0.60%, the weldability deteriorates. Therefore, the addition amount is set to the range of 0.05 to 0.60%.

Mn is an element necessary to secure the strength and toughness of steel. If it is less than 0.50%, such an effect is small, and if it is added in excess of 1.50%, the weldability is deteriorated. In addition, it also deteriorates toughness. Therefore, the amount added is in the range of 0.50 to 1.50%.

If P exceeds 0.020%, microsegregation deteriorates the toughness of the high heat input welded joint, the toughness of the base metal and the resistance to weld cracking. Therefore, P is made 0.020% or less.

If S exceeds 0.005%, coarse A-type inclusions are likely to be formed and the toughness of the base material is deteriorated.
% Or less.

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

Ti has the effect of forming carbonitrides and improving the high temperature proof stress of steel, and by refining the austenite grains in the heat-affected zone of the welding and promoting the formation of ferrite,
Although it is an element effective in improving the toughness of the heat affected zone,
If it is less than 0.1%, such an effect is small, while if it exceeds 0.150%, the weldability deteriorates. Therefore, the amount added is
The range is 0.030 to 0.150%.

By combining N with the above Ti,
Improve the toughness of large heat input welded joints. However, if it is less than 0.0020%, such an effect cannot be exhibited, and if it is 0.
If it is added in a large amount exceeding 0070%, the weld joint toughness is deteriorated. Therefore, the addition amount is set to 0.0020 to 0.0070%.

[0018] Ca is an element that improves the properties in the plate thickness direction in a trace amount, but if less than 0.0005%, such an effect cannot be obtained, while if added in excess of 0.0050%, such an effect is obtained. Is saturated, and large inclusions are generated to easily cause ultrasonic defects. Therefore, the amount added is 0.0005-
The range is 0.0050%.

In the present invention, in addition to the above chemical components, V, Cu, N
One or two or more selected from i and Cr can be added.

V is an element effective in increasing the strength by precipitation strengthening, but if less than 0.005%, such an effect can hardly be expected, and if more than 0.060% is added excessively, the weldability deteriorates. To do. Therefore, the amount added is 0.005
The range is to 0.060%.

Cu is an element effective in increasing the strength by solid solution strengthening, but if it is less than 0.05%, such an effect is small,
If added in excess of 0.50%, hot workability and weldability will be impaired. Therefore, the addition amount is set to the range of 0.05 to 0.50%.

Ni is an element effective in improving toughness,
If it is less than 0.05%, such an effect cannot be obtained. Also, 0.
Even if added in excess of 50%, such an effect is saturated and it is economically wasteful. Therefore, the amount added is 0.05-0.
The range is 50%.

Cr is an element effective for improving the high temperature strength, but if it is less than 0.10%, it is difficult to expect such an effect, and if it is added in excess of 0.40%, the weldability deteriorates. Therefore, the addition amount is set to 0.10 to 0.40%.

Further, both the first invention and the second invention,
In order to prevent cold cracking during welding, P _CM (weld crack sensitive composition) is limited to 0.24% or less.

Next, the reasons for limiting the heating / rolling conditions in the present invention will be described. The reason for limiting the heating temperature to 1100 ° C. or higher is that Ti, which is necessary for securing room temperature strength and high temperature strength, is solid-soluted in steel. And after this 1000 ℃
The rolling reduction below is required to be 50% or more in order to secure good base metal toughness due to refinement of austenite grains.

Regarding the rolling end temperature, when the rolling end temperature is lower than 850 ° C., the yield ratio becomes high due to the grain refinement of ferrite and the work hardening of ferrite by the two-phase region rolling, and the yield ratio of 80% or less is obtained. I can't. Also,
If the rolling end temperature exceeds 950 ° C, the austenite becomes coarse grains and the toughness of the base material deteriorates. Therefore, the rolling finish temperature is limited to the range of 850 to 950 ° C.

[0027]

EXAMPLES Examples of the present invention will be described, but the present invention is not limited thereto. The test steel materials are shown in Table 1.
After heating the steel slab containing the chemical composition shown in 1150 ℃,
In order to secure a reduction of 50% or more at 00 ℃ or less, the temperature is adjusted during rolling at a temperature of 920 to 950 ℃ at a plate thickness of 60 mm, and the plate thickness is 25 mm at a rolling end temperature of 890 to 910 ℃. It is finished.

[0028]

[Table 1]

Test pieces were taken from these steel sheets, and subjected to normal temperature tensile test, Charpy impact test, high temperature tensile test at 600 ° C.,
The maximum hardness test and the Charpy impact test after the simulated thermal cycle were performed. The results are shown in Table 2. In addition, the conditions of the simulated heat cycle are as follows:
The cooling time to 500 ° C was 220 seconds. The highest hardness test was performed according to JIS Z3101. Table 1 shows the chemical components, P _CM , of the invention steels A to E and the comparative steels F to I.
Shows tensile properties, impact properties, weldability, high temperature properties and HAZ toughness, respectively.

[0030]

[Table 2]

As is clear from Table 2, the steels A to E of the present invention.
Has a P _CM of 0.24% or less and a proof stress at 600 ° C of 217 N /
It exhibits excellent high temperature proof strength at mm ² or more, and the tensile properties at room temperature satisfy the 490 N / mm ² class values (proof strength 315 N / mm ² or more, tensile strength 490 to 610 N / mm ² ), and the yield ratio is We are fully satisfied with the 80% or less required for building steel products. The fracture surface transition temperature in the Charpy impact test is also -35 ° C or lower. The maximum hardness is less than Hv 350, which shows good weldability, and HAZ by the repeated heat cycle test.
The toughness (vE ₂₀ ) is also good.

On the other hand, the comparative steel F has a proof stress at 600 ° C.
Although it is as high as 217 N / mm ² or more, the HAZ toughness is low because Ti is not added, and the maximum hardness is Hv 350 or more because the Mo and Cr contents and P _CM are out of the range of the present invention. And the weldability is poor.

Comparative Steel G is a Ti-added material and has a P _{CM of} 0.24% or less, which is excellent in high temperature characteristics and weldability, but has a high HAZ toughness because N is out of the range of the present invention. bad.

Comparative Steel H has a Ti content less than the limit range of the present invention, so that the yield strength at 600 ° C. is 217 N / mm.
Not satisfied with ² or more.

Further, Comparative Steel I is 490 N / for conventional construction.
This is an example of a mm ² class steel sheet, but since Mo, Ti, and Cr are not added, the yield strength at 600 ° C. does not satisfy 217 N / mm ² or more, and the HAZ toughness is also poor.

Next, comparative steels A1 to A4 were manufactured under the heating and rolling conditions shown in Table 3 using the steel pieces of the invention steel A shown in Table 1, and the tensile properties of the obtained comparative steels A1 to A4. , Impact properties and high temperature properties were investigated. The results of this investigation are also shown in Table 3.

[0037]

[Table 3]

As is clear from Table 3, the comparative steel A1 has a heating temperature lower than the limited range of the present invention, so that Ti does not form a solid solution sufficiently and both the room temperature strength and the high temperature strength are low.

The comparative steel A2 has a rolling reduction smaller than the limited range of the present invention, so that the austenite grains are not sufficiently refined and the base material toughness is poor.

In Comparative Steel A3, the rolling end temperature is lower than the limit range of the present invention, so the ferrite becomes fine grains and the yield ratio at room temperature exceeds 80%. On the other hand, in Comparative Steel A4, the rolling end temperature deviates higher than the limited range of the present invention, so that the austenite grain refinement is insufficient and the base metal toughness is poor.

[0041]

EFFECT OF THE INVENTION Since the present invention is constituted as described above, the steel obtained has improved high-temperature yield strength without impairing weldability due to the formation of carbonitrides of chemical composition, especially Ti.
Because of the excellent toughness of large heat input welded joints,
It is possible to manufacture steel materials that have a high yield strength at 00 ° C, good weldability, and high toughness heat input welded joint toughness, and a low yield ratio. In addition, it has an excellent effect that the safety of the structure can be enhanced in terms of welding work and earthquake resistance, which is extremely useful in industry.

Claims (2)

[Claims] 1. A weight ratio of C: 0.05 to 0.15%, Si: 0.05.
~ 0.60%, Mn: 0.50 to 1.80%, P: 0.02% or less, S:
0.005% or less, Mo: 0.10 to 0.40%, Ti: 0.030 to 0.150
% N: from 0.0020 to .0070% Ca: containing 0.0005 to 0.0050%, and the balance Fe and unavoidable impurities, and the steel strip values of P _CM is equal to or less than 0.24% which is defined by the following formula 1100
After heating to a temperature above ℃,
50% or more, rolling is completed in the temperature range of 850 to 950 ° C, and the yield strength at 600 ° C is 217 N / mm ² or more,
A method for producing a 490 N / mm ² class refractory steel for construction, which has good weldability and excellent toughness with a high heat input welded joint. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 +
Mo / 15 ＋ V / 10 ＋ 5B (%) 2. The weight ratio is further V: 0.005 to 0.060.
%, Cu: 0.05 to 0.50%, Ni: 0.05 to 0.50%, Cr: 0.10 to
The method for producing a 490 N / mm ² class refractory steel material for construction according to claim 1, which contains one or more selected from 0.40%.