JP4592173B2 - Martensitic stainless steel welded structure with excellent fire resistance - Google Patents

Description

【００３３】
【表２】

【００３４】
【表３】

【００３５】
【発明の効果】
以上述べたように、本発明によって、母材および溶接金属の成分を最適化することにより、耐火性に優れたマルテンサイト系ステンレス鋼溶接構造体が得られる。
【図面の簡単な説明】
【図１】溶接部の断面を示す図である。
【図２】Ａ値と高温耐力／常温耐力比の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a martensitic stainless steel welded structure excellent in fire resistance, in which building steel materials such as plates, shaped steel, and steel pipes made of martensitic stainless steel excellent in fire resistance are assembled by welding.
[0002]
[Prior art]
High-temperature strength is required for steel for building structures because of the demand to prevent the collapse and deformation of buildings during a fire. General structural carbon steel suddenly loses its strength when exposed to high temperatures of 300 ° C or higher, so it has been necessary to apply heavy fireproof coating to the steel surface. However, construction costs increase for fireproof coating. As a result, there has been a demand for a steel material that does not require a fire-resistant coating or that requires only a small amount of construction, and that has excellent fire resistance. Low alloy steel materials such as those disclosed in Japanese Patent Application Laid-Open No. 2-77523 having a yield strength standard value of 2/3 or more and a normal temperature tensile strength of 490 MPa or 570 MPa have been put into practical use.
[0003]
From the viewpoint of high-temperature strength, this low alloy refractory steel can provide the desired fire resistance, but because it is a low alloy rust resistance and corrosion resistance, it is difficult to use barely, and rust prevention coating is difficult. It is essential. That is, even if the fireproof coating can be omitted, the rust-proof coating cannot be omitted, which increases the construction cost.
[0004]
Various stainless steels are assumed as steel materials that can be applied to building structures without painting. However, as steel materials that are actually used in building structures such as columns and beams, design is important. It is rarely seen except for austenitic stainless steel (for example, SUS304) in extremely limited applications. The biggest reason is that there is no steel grade that satisfies the balance of strength, toughness, and weldability essential for the structure, but recently, as disclosed in JP-A-11-323507, it is harmful to weldability. Techniques have been proposed for developing martensitic stainless steel with Ni added and reducing mar C to building structural materials. However, it has not yet reached a technology that can sufficiently meet the above-mentioned demand for fire resistance.
[0005]
Further, in fields other than architectural uses, for example, in line pipes, martensitic stainless steel materials having excellent weldability and corrosion resistance and sufficient high-temperature strength as pipelines are disclosed, as disclosed in JP-A-9-316611. Has been proposed. However, the high temperature defined in the pipeline is about 100 to 150 ° C., which is much lower than 600 ° C. defined in the construction fireproof steel.
Therefore, in low-C martensitic stainless steel that can be applied to building structures without painting, the strength and toughness at room temperature are, of course, steel materials that can obtain sufficient strength at high temperatures of 600 ° C have not yet been proposed. There is no situation.
[0006]
Furthermore, when it is completed as a structure, not only the base material but also the high-temperature strength at the welded part is a problem, and the welded metal part is particularly important. In the cross section of the welded structure shown in FIG. 1, the weld metal is formed by melting a part of the welding material and the base material, and naturally has a component composition different from that of the base material. If the weld metal is insufficient even if the base metal has sufficient high-temperature strength, sufficient high-temperature strength cannot be obtained for the entire structure. And when the welding material for stainless steels described in the conventional JIS Z3321 etc. is used, there exists a problem that sufficient high temperature strength cannot be obtained in a weld metal part.
[0007]
[Problems to be solved by the invention]
The present invention overcomes the above-described problems, and in particular, provides a martensitic stainless steel welded structure in which the proof stress at 600 ° C. is 2/3 or more of the minimum proof stress standard value at room temperature. For the purpose.
[0008]
[Means for Solving the Problems]
The inventors first designed the components in terms of the strength, toughness, corrosion resistance, and high-temperature strength of the martensitic stainless steel base material, and then repeated welding tests using various welding materials to determine the high-temperature strength of the welded portion. I have evaluated it.
As a result, the component conditions of the weld metal to obtain the high temperature proof stress equivalent to the base metal were clarified. The present invention is constructed based on the above findings, and the gist thereof is as follows.
[0009]
(1) In mass%,
C: 0.005 to 0.1%, Si: 0.50% or less,
Mn: 1.5% or less, Cr: 10.0 to 15.0%,
Ni: 0.5-6.0% , Mo: 0.3-3.0% ,
N: 0.03% or less, Al: 0.15% or less,
Ti: 0.003 to 0.050%
The content of Ni and Mo satisfies the relationship of the following formula (1), the balance is composed of Fe and inevitable impurities, and the proof stress at 600 ° C. is 2/3 or higher than the proof strength at normal temperature. The martensitic stainless steel base material and the components within the same range as the base material, and the B value and C value defined by the following formulas (2) and (3) are 14.0 to 17.0, respectively. A martensitic stainless steel welded structure excellent in fire resistance, characterized by having a weld metal in a range of −11.8 or more.
A = [Mo] −4.41 [Ni] + 22.94 ≧ 0 (1)
B = [Ni] +0.5 [Mn] +30 [C] +0.8 [Cr] +0.8 [Mo] +1.2 [Si] (2)
C = [Ni] +0.5 [Mn] +30 [C] −1.1 [Cr] −1.1 [Mo] −1.6 [Si] (3)
[0010]
(2) Furthermore, in mass% ,
P ≦ 0.030%, S ≦ 0.0050% ,
And if necessary
Cu: 3.0% or less, W: 1.0% or less,
Sn: 1.0% or less, Nb: 0.05% or less,
V: The martensitic stainless steel welded structure having excellent fire resistance as described in (1) above, containing one or more of 0.1% or less .

(3) Furthermore, in mass%,
P ≦ 0.030%, S ≦ 0.0050%,
and
Ca: 0.0005-0.005%, B: 0.0005-0.0050% 1 type or 2 types are contained, The fireproof in any one of said (1) or (2) characterized by the above-mentioned. Martensitic stainless steel welded structure with excellent properties.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the reasons for limiting the components of the base material in the present invention will be described.
C: C is an element necessary for securing high temperature strength like Mo, and if the content is less than 0.005%, the high temperature proof stress at 600 ° C. becomes insufficient. However, if too much is included, the toughness of the weld heat affected zone deteriorates. For this reason, the optimal range was made into 0.005%-0.1% from both balance.
[0012]
Si: Si is added and left for deoxidation in the refining process, and is an element that forms a ferrite phase that is harmful to toughness in the weld heat affected zone. Therefore, Si is required for deoxidation. The minimum content should be 0.5% or less.
[0013]
Mn: Mn is an element detoxified by fixing S, which is harmful to hot workability, which is important in the molding process of the base material, as a sulfide, and is also an austenite stabilizing element, which is harmful to heat affected zone toughness. It is contained because it has an action of suppressing the formation of ferrite, but the effect is saturated if it is contained too much, so the upper limit was made 1.5%.
[0014]
Cr: Cr is an essential element for ensuring corrosion resistance and needs to be contained in an amount of 10.0% or more. On the other hand, it is also a ferrite stabilizing element. If the content is large, the ferrite phase deteriorates the toughness of the weld heat affected zone. Therefore, the upper limit was made 15.0%.
[0015]
Ni: Ni is an element effective for improving corrosion resistance, and has an effect of stabilizing austenite and preventing the formation of ferrite. For this reason, 0.5% is contained as a lower limit. However, since a high temperature proof stress at 600 ° C. is reduced when a large amount is contained, the upper limit is made 6.0%. The Ni content is optimized in relation to the Mo content described later.
[0016]
Mo: Like Cr, Mo is an element effective for corrosion resistance, and is an essential and indispensable element for maintaining high-temperature proof stress. For this reason, although 0.3% is contained as a lower limit, since it is an element having strong ferrite forming ability, the upper limit of content was set to 3.0% in consideration of weld toughness.
[0017]
N: N is an element that increases the hardness of the heat affected zone and decreases the toughness, and does not have the effect of improving the high temperature strength like C. Therefore, the upper limit is set to 0.03%.
[0018]
Al: Like Si, Al is an element necessary for deoxidation, and is included in order to promote desulfurization and ensure the above S content stably, but if included excessively, oxide inclusions In addition to the increase in the number of nitrides, nitrides are generated and the toughness decreases. For this reason, the upper limit of content was made into 0.15%.
[0019]
Ti: Ti exists as an oxide or nitride and has an effect of suppressing toughness by suppressing grain growth in the weld heat affected zone. In addition, like Mn, it also has the effect of detoxifying S, which is harmful to hot workability, as a sulfide. For this reason, 0.003% is contained as a lower limit. However, if excessively contained, coarse nitrides appear and hot workability is lowered, and carbides are formed and toughness is deteriorated. %.
[0020]
A value (= [Mo] −4.41 [Ni] + 22.94 ≧ 0): FIG. 2 shows the influence of the amounts of Mo and Ni on the high temperature proof stress. Thus, the necessary condition is a range where A ≧ 0 from the viewpoint of high temperature proof stress with the Ni content of the present invention.
[0021]
Based on the above composition, one or more of the elements described below can be selectively added in order to further improve the high temperature proof stress, corrosion resistance, weldability, toughness, and hot workability.
Cu: Like Ni, Cu is an element effective for improving corrosion resistance, and is an element having an effect of preventing the formation of ferrite. However, if excessively contained, hot workability deteriorates, so the upper limit is 3.0. %.
[0022]
W: W, like Mo, is an element effective for improving the high-temperature proof stress, so if the Mo content is low, it may be supplementarily contained, but since it is also an expensive element, the content of The upper limit was 1.0%.
[0023]
Sn: Since Sn has the effect of improving the high-temperature yield strength, it may be supplementarily added when the Mo content is low, as with W, but if included excessively, hot workability and weldability are obtained. Since it deteriorates, the upper limit was made 1.0%.
[0024]
Nb, V: Both Nb and V have an effect of slightly improving the high-temperature proof stress, and are effective in reducing the hardness of the weld heat affected zone. However, since the effect is saturated even if it is contained in a large amount, the upper limit of the content is set to Nb: 0.05% and V: 0.1%, respectively.
[0025]
Ca: 0.0005 to 0.005%, B: 0.0005 to 0.0050%
Ca: Ca is an element effective for improving hot workability, and is contained in an amount of 0.0005% or more as necessary. However, if the content is too large, toughness deterioration due to coarse oxides is caused, so the upper limit of the content Was 0.005%.
B: B is also an element effective for improving hot workability, and 0.0005% is contained as the lower limit. However, if contained over 0.0050%, weld cracking occurs, so the appropriate range is 0.0005-0. .0050%.
[0026]
P, S: P and S are inevitably contained impurity elements that do not directly affect the high-temperature proof stress, but it is desirable to make them as low as possible because they have an adverse effect on toughness and hot workability. . P: 0.03% or less and S: 0.005% or less are desirable as ranges that are industrially and economically reachable with the current refining technology.
[0027]
Next, the reason for limitation regarding the components of the weld metal will be described.
Based on the premise that the base material and the component system with the above composition and the yield strength at 600 ° C. are 2/3 or more of the normal temperature yield strength are the same, and further defined by the above formulas (2) and (3) It is necessary that the component index B value and C value to be within a predetermined range.
[0028]
These B and C values are indices related to the metal structure that affects the high temperature proof stress of the weld metal. The metal structure of the weld metal of the component system is either a martensite single phase, a martensite + austenite two phase, a martensite + ferrite two phase, or a martensite + austenite + ferrite three phase, Martensite is advantageous for securing high-temperature strength, but has poor toughness. Austenite is excellent in toughness, but lowers high-temperature strength. Ferrite has a function similar to martensite, and also helps prevent cracking of weld metal. Therefore, as a weld metal applied to a fireproof building structure, it is necessary that these three phases coexist in a balanced manner under optimum conditions.
[0029]
Since the weld metal is in a solidified state, the phase fraction in the metal structure can be approximated with the component content, and the optimum conditions were determined as follows with the B and C values.
B value: If it is too low, the austenite phase does not appear and the weld metal has low toughness. On the other hand, if it is too high, the austenite fraction becomes too high and the high-temperature proof stress is significantly lower than that of the base material. For this reason, the range of 14.0 to 17.0 was set as an appropriate range.
C value: If it is too low, ferrite will not appear and cracks will occur in the weld metal.
[0030]
【Example】
The invention is explained in more detail on the basis of examples.
After the steel having the composition shown in Table 1 was melted and cast by the ingot-making method, the slab was heated to 1200 ° C., subjected to plate rolling with a plate thickness of 10 mm, cooled to room temperature, and then tempered. To give a base material. Groove processing was performed on this base material, and TIG welding was performed using welding materials having the components shown in Table 2. A normal temperature tensile test according to JIS Z2241 and a high temperature tensile test at 600 ° C. according to JIS G0567 were performed on the welded part and the base metal part.
[0031]
The test results are shown in Table 3. In the present invention of Nos. 1 to 9, a 600 ° C. proof stress that is 2/3 or more of the target normal temperature proof stress can be obtained in the weld zone. On the other hand, in Comparative Examples No. 10, 11, and 12, since the base material is outside the component range of the present invention, the fire resistance characteristics of the entire welded portion are determined by the fire resistance characteristics of the base material portion. In Comparative Example No. 13, since the B value is also outside the scope of the invention even in the weld metal part, the desired fire resistance characteristics cannot be obtained. Moreover, since the C value of the weld metal part is outside the scope of the present invention in Comparative Example No. 14, a weld crack occurs.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
[Table 3]

[0035]
【The invention's effect】
As described above, according to the present invention, a martensitic stainless steel welded structure having excellent fire resistance can be obtained by optimizing the components of the base material and the weld metal.
[Brief description of the drawings]
FIG. 1 is a view showing a cross section of a welded portion.
FIG. 2 is a diagram showing the relationship between A value and high temperature yield strength / normal temperature yield strength ratio.

Claims (3)

% By mass
C: 0.005 to 0.1%, Si: 0.50% or less,
Mn: 1.5% or less, Cr: 10.0 to 15.0%,
Ni: 0.5-6.0% , Mo: 0.3-3.0% ,
N: 0.03% or less, Al: 0.15% or less,
Ti: 0.003 to 0.050%
The content of Ni and Mo satisfies the relationship of the following formula (1), the balance is composed of Fe and inevitable impurities, and the proof stress at 600 ° C. is 2/3 or higher than the proof strength at normal temperature. The martensitic stainless steel base material and the components within the same range as the base material, and the B value and C value defined by the following formulas (2) and (3) are 14.0 to 17.0, respectively. A martensitic stainless steel welded structure excellent in fire resistance, characterized by having a weld metal in a range of −11.8 or more.
A = [Mo] −4.41 [Ni] + 22.94 ≧ 0 (1)
B = [Ni] +0.5 [Mn] +30 [C] +0.8 [Cr] +0.8 [Mo] +1.2 [Si] (2)
C = [Ni] +0.5 [Mn] +30 [C] −1.1 [Cr] −1.1 [Mo] −1.6 [Si] (3) Furthermore, in mass% ,
P ≦ 0.030%, S ≦ 0.0050% ,
And Cu: 3.0% or less, W: 1.0% or less,
Sn: 1.0% or less, Nb: 0.05% or less,
The martensitic stainless steel welded structure excellent in fire resistance according to claim 1 , characterized in that it contains one or more of V: 0.1% or less. Furthermore, in mass% ,
P ≦ 0.030% , S ≦ 0.0050% ,
and
It contains 1 type or 2 types of Ca: 0.0005-0.005% and B: 0.0005-0.0050%, The fire resistance of any one of Claim 1 or 2 characterized by the above-mentioned . Excellent martensitic stainless steel welded structure.

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