JPH07179995A - Refractory cast steel - Google Patents

Abstract

PURPOSE:To produce a refractory cast steel material used for joining of refractory steel material and excellent in refractoriness and joining property by casting a cast steel of specific composition and then applying heat treatment under specific temp. conditions. CONSTITUTION:As joining parts and members to be used for joining refractory steel materials used for various structures in the fields of construction, civil engineering, coastal structure, etc., cast steel parts, having a composition which contains, by weight, 0.09-0.15% C, 0.2-0.8% Si, 0.6-1.4% Mn, 0.2-0.3% Cr, 0.2-0.5% Mo, and 0.01-0.1% V and in which carbon equivalent(CE) represented by equation I is regulated to >=0.45%, are subjected to diffusion annealing at 900-1000 deg.C, to cooling at 0.8 to 80 deg.C/sec cooling rate, and successively to tempering treatment at 600-700 deg.C. By this method, the refractory cast steel member, having about 235 to 315N/mm<2> yield strength at ordinary temp. and 157 to 217N/mm<2> proof stress at 6O0 deg.C, used for joining various refractory steel materials, and excellent in refractoriness and weldability, can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining part or a member including a joining part used for joining refractory steel materials in various structures in fields such as construction, civil engineering and marine structures.
The present invention relates to a fire-resistant cast steel having excellent fire resistance and weldability (for joint parts / members).

[0002]

2. Description of the Related Art In a structure, particularly a building structure, when a steel frame is exposed to a high temperature during a fire, its strength decreases and the yield strength of the building structure decreases. Was obliged. However, in the "new fireproof design method" that was added in 1989, the use of steel materials with excellent high temperature resistance (hereinafter referred to as fireproof steel materials) reduces the amount of fireproof coating materials, or depending on the application and structure The structure without fireproof coating is now accepted. According to the new standard, the refractory steel is required to retain the yield strength of the conventional steel at 350 ° C even at 600 ° C. For example, a refractory steel material is required to have a yield strength at 600 ° C. that is ⅔ or more of a standard lower limit value of yield strength at room temperature.

Therefore, a new refractory steel material has been developed (for example, Japanese Patent Application Laid-Open No. 2-170943), and further, a fire resistant bolt for use in such a structure (for example, Japanese Patent Application Laid-Open No. 2-247355).
Issue) has also been developed. However, in addition to the above refractory steel materials and refractory bolts, the above-mentioned steel structures are made of cast steel from the viewpoint of structural strength and aesthetics at the joints of joints between columns or columns, or the nodes of truss members, etc. Parts / members such as a diaphragm or a metal fitting for a space truss are required. These joint parts / members are usually joined to the refractory steel by welding.

The above refractory steel materials are supplied as rolled steel materials such as steel plates and H-shaped steels, and steel types having these component compositions cannot be diverted to the cast steel for the above-mentioned joint parts / members which is the object of the present invention. This is because the strength of the latter is generally inferior to that of the former when the rolled steel and cast steel have the same composition. As the refractory steel material, the strength at room temperature is JIS G 3
Corresponds to SM400 and SM490 specified in 106, and 6
Steels having a yield strength at 00 ° C of 2/3 or more of the lower limit of the standard of yield strength at room temperature are used relatively often.

[0005]

Conventionally, a joined part / member, for example, a diaphragm (casting diaphragm) is a cast steel product because it has a complicated shape as shown in FIG.
The material is specified in JIS G 5101 (cast carbon steel products).
SC 450 or SCW 480 specified in JIS G 5102 (cast steel products for welded structures) is used.

The yield strength of these cast steel products at 600 ° C. is about 1/3 of the yield point or yield strength at room temperature (100 to 150 N / m).
m ² ), cannot be used as refractory cast steel. On the other hand, as cast steel with excellent high temperature proof stress, chromium-molybdenum cast steel (JIS G
5151). This cast steel product has a yield strength of 600 ° C of about 2/3 of the yield strength at room temperature (for example, 190 N / mm ² for SCPH 21 annealed material).
However, due to the high susceptibility to welding cracks, the resistance to welding cracks is poor, and there are difficulties in welding such as preheating or postheating. Therefore, in order to reduce or omit the fireproof coating construction of the structure, in addition to having high temperature proof stress, it has excellent weldability and base material properties, and steel structures having various shapes that can be applied to any design Fireproof cast steel for joint parts / members is required.

Therefore, in the present invention, as a cast product, the strength equivalent to that of the above steel material, that is, the strength at room temperature is JIS
An object is to provide a refractory cast steel that is equivalent to SM400 and SM490 specified in G 3106, and has a yield strength at 600 ° C of 2/3 or more of the lower limit of the yield strength or the yield strength at room temperature.

[0008] Specifically, as a fire resistant cast steel equivalent to SM400, the yield strength at room temperature is about 235 N / mm ² or more and 600 ° C.
Refractory cast steel having a proof stress of about 157 N / mm ² or more, and S
Yield strength at room temperature is about 315 as a fire resistant cast steel equivalent to M490.
In N / mm ² or more, it is an object of the invention a refractory cast steel yield strength of 600 ° C. has about 217 N / mm ² or more.

[0009]

In view of the above problems, the present inventors have conducted diligent research, and as a result, the chemical component is Mn-C.
It is an invention completed with the knowledge that it is possible to significantly improve the high-temperature yield strength without impairing the weldability by further strengthening the hot strength by V using the r-Mo system as a basic component.

(1) The invention of claim 1 is a refractory cast steel having the following characteristics (component composition is wt%). (A) As a main component, C: 0.09 to 0.15%, Si: 0.2 to 0.8
%, Mn: 0.6 to 1.4%, Cr: 0.2 to 03% Mo: 0.2 to 0.5% V: 0.01 to 0.1%, with the balance being Fe and inevitable impurities,
(B) CE (carbon equivalent) is 0.45% or less.

(2) According to the second aspect of the present invention, the cast steel having the above-described composition is diffusion-annealed at 900 to 1000 ° C., air-cooled, and then 600.
The refractory cast steel according to claim 1, which is tempered at about 700 ° C.

(3) According to the invention of claim 3, 0.8 to 80 ° C./sec is obtained after the cast steel having the above composition is annealed at 900 to 1000 ° C.
The refractory cast steel according to claim 1, characterized in that the refractory cast steel is cooled at 600 ° C. to 700 ° C.

(4) The invention of claim 4 is a joint part / member for a steel structure manufactured from the refractory cast steel according to claim 2 or claim 3.

[0014]

The reason for limiting the chemical components in the present invention will be described below. C is an element that contributes to the strength increase, but if it is less than 0.09%, it is difficult to secure the strength,
Also, if added in excess of 0.15%, the weldability and toughness deteriorate. Therefore, its content is 0.09 ~
The range is 0.15%.

Si is an essential element for ensuring the deoxidizing effect and the castability. If it is less than 0.2%, the deoxidizing effect is small, and it is preferable that it is large in order to secure the castability.
If it is added in excess of%, the weldability is deteriorated. Therefore, the amount of addition is set to the range of 0.20 to 0.80%.

Mn is an element necessary for securing its deoxidizing effect and castability, and securing strength and toughness, but if it is less than 0.6%, such an effect is small, and 1.
If added in excess of 4%, it deteriorates weldability and toughness. Therefore, it is set to 0.6% to 1.4%.

Cr is an element effective for improving the high temperature strength, but if it is less than 0.2%, such an effect cannot be obtained, and if it exceeds 0.3%, the weldability is impaired. Therefore, the added amount is 0.2 to 0.3%.

Mo is an essential element for securing high temperature strength. In particular, Mo is a necessary element because its resistance to temper softening at 600 ° C. is remarkably higher than that of other elements. If the content is less than 0.2%, such an effect cannot be obtained, and if it exceeds 0.5%, the weldability is impaired. Therefore, the added amount is 0.2 to 0.5%.

V is an element effective in increasing the strength by precipitation hardening, but if less than 0.01%, such hardening cannot be expected, and if it is added in excess of 0.1%, weldability deteriorates. To do. Therefore, the amount added is 0.01-0.1
The range is%.

Also, in order to prevent welding defects such as cold cracking during welding, it is necessary to suppress the maximum hardness Hv of the heat affected zone to 350 or less. This maximum hardness can be achieved mainly by keeping the carbon equivalent (CE) below a certain limit. Here, the carbon equivalent (CE) is calculated by the following formula. CE (wt%) = C + Mn / 6 + Si / 24 + Ni / 4
0 + Cr / 5 + Mo / 4 + V / 14 Since welding defects such as cold cracking during welding depend on various welding conditions, the maximum hardness test of the weld heat affected zone under the conditions for welding the joint parts / members which is the object of the invention. I went.

The welding conditions are as follows. Test method: JIS Z3101 Welding condition: Welding material; Shinko LB-490FR 4mmφ Preheating temperature; Room temperature (no preheating) Welding condition: 170A-25V-15cm / min. Heat input for welding: 16.3 kJ / cm Material to be welded: Cast steel of the present invention (A, B, C in Table 1), 120 x 200 x
A 35 mm test material was heated to 950 ° C, cooled with oil, tempered at 600 ° C, and mechanically cut.

Test results: A (CE; 0.45%); Hv295 B (CE; 0.40%); Hv255 C (CE; 0.43%); Hv273 The above test results are the highest in the heat affected zone. Hardness is Hv3
It was 50 or less, and the weldability was good. So CE
Was 0.45%.

Next, the limitation of heat treatment conditions in the present invention will be described. In the second aspect, since the proof stress at 600 ° C. is intended to be about 157 N / mm ² or more, and considering that the structure before quenching is a cast structure, 900-1000 ° C.
Diffusion annealing is carried out with and air cooling is carried out. In this case, a ferrite-pearlite structure is obtained. In claim 3,
Since the proof stress at 600 ℃ is about 217 N / mm ² or more, and considering that the structure before quenching is the cast structure, diffusion annealing is performed at 900 to 1000 ℃, and then water cooling or oil cooling is performed. I do. In this case, the cooling rate is 0.8-80 ℃
/ Sec range, but preferably 10 to 20 ° C /
sec. In this case, the metal composition has a bainite structure. The reason for performing diffusion annealing at 900-1000 ° C is
Below 900 ℃, uniform austenite cannot be obtained,
This is because if it exceeds, anxiety occurs in toughness.

The reason for limiting the tempering temperature to 600 to 700 ° C. is that the effect of tempering hardening by Mo, Cr, Si, etc. is maximized. Therefore, if the temperature is lower than 600 ° C, the product tends to lack in toughness, and if it exceeds 700 ° C, the strength becomes too low.

[0025]

EXAMPLES The present invention will be described below with reference to examples. Using a 500 kg high-frequency electric furnace, the test materials with the chemical composition shown in Table 1 were melted, and 120 × 20 using a carbon dioxide template.
The test materials of 0 × 35 mm and 120 × 200 × 60 mm were cast and subjected to the above heat treatment. Test pieces were sampled from these test materials and subjected to a room temperature tensile test and a 500 ° C, 600 ° C and 700 ° C high temperature tensile test. Inventive materials A to C and comparative material D are shown in Table 1.
The chemical components of ~ G are shown. Here, the comparative material is SM in Table 2.
The strength of the refractory cast steel according to the present invention corresponding to 400 is shown. 600 ° C
The target yield strength is 157 N / mm ² or more. Table 3 shows the strength of the fire resistant cast steel according to the present invention corresponding to SM490. It has been shown that the target yield strength of 217 N / mm ² or more is obtained at 600 ° C.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

EFFECTS OF THE INVENTION The refractory cast steel of the present invention is excellent in high temperature characteristics as described above and also extremely good in room temperature characteristics, and therefore is used for various structures in the fields of construction, civil engineering and marine structures. It can be applied to joint parts and members used for joining existing refractory steel materials. Therefore, even if it is a steel structure that uses steel plates or H-shaped designs,
Can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a shape of a diaphragm as an example of a joining component / member to which a refractory cast steel according to the present invention is applied.

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[Procedure amendment]

[Submission date] June 29, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Front page continuation (72) Inventor Toshihiro Matsuzaka 2-1, Shiraishi-cho, Kawasaki-ku, Kawasaki City Nippon Foundry Co., Ltd. (72) Inventor Takeichi Fujii 2-1-1 Shiraishi-cho, Kawasaki-ku, Kawasaki City Nippon Casting Co., Ltd. Within

Claims (4)

[Claims] 1. The following characteristics (component composition is wt%):
Fire-resistant cast steel with. (A) As a main component, C: 0.09 to 0.15%, Si: 0.2 to 0.8
%, Mn: 0.6 to 1.4%, Cr: 0.2 to 0.3% Mo: 0.2 to 0.5% V: 0.01 to 0.1%, with the balance being Fe and inevitable impurities,
(B) CE (carbon equivalent) is 0.45% or less. 2. The refractory cast steel according to claim 1, wherein the cast steel having the composition of components is diffusion annealed at 900 to 1000 ° C., air-cooled, and then tempered at 600 to 700 ° C. 3. A cast steel having the above composition is annealed at 900 to 1000 ° C. and then cooled at a cooling rate of 0.8 to 80 ° C./sec.
The refractory cast steel according to claim 1, which is then tempered at 600 to 700 ° C. 4. A joint part / member for a steel structure manufactured from the refractory cast steel according to claim 2 or 3.