JPH11314193A - Submark welding method for refractory steel - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain a weld metal excellent in high-temperature yield strength, high-temperature ductility, and toughness in submerged arc welding of fire-resistant steel and weather-resistant fire-resistant steel. SOLUTION: In weight% and weight ppm, C: 0.01 to
0.15%, Si: 0.5% or less, Mn: 0.4-2.
5%, Cu: 0.7% or less, Ni: 0.5% or less, C
r: 1.0% or less, Mo: 0.14 to 0.8%, Nb:
0.01-0.1%, Ti: 400 ppm or less, B: 1
A refractory steel and a weather-resistant refractory steel containing 5 ppm or less, a flux having a basicity of 0.2 to 3.5, and a C: 0.01 to
0.15%, Si: 0.5% or less, Mn: 0.4-2.
5%, Cu: 0.7% or less, Cr: 1.0% or less, N
i: 0.5% or less, Mo: 0.8% or less, Nb: 0.1
%, Ti: 400 ppm or less, B: Combined with a wire containing 50 ppm or less, the heat input is 120 kJ / c.
Weld at m or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel having excellent fire resistance (hereinafter referred to as "fire-resistant steel") used for various buildings in the fields of construction and bridges, and excellent in both weather resistance and fire resistance. The present invention relates to a submerged arc welding method for steel (hereinafter, referred to as weatherable fire-resistant steel).
The present invention relates to a submerged arc welding method for obtaining a weld metal having excellent high-temperature proof stress and high-temperature ductility at 00 ° C. and good toughness, and obtaining a weld metal having good weather resistance in a weather-resistant refractory steel. (Hereinafter, in the text, tables and drawings, ppm means ppm by weight.)

[0002]

2. Description of the Related Art Conventionally, as for submerged arc welding for refractory steel and weatherable refractory steel, for example, Japanese Patent Application No. 1-1969.
No. 1 proposes a submerged arc welding wire and a flux for refractory steel, and obtains proper room temperature strength and good toughness while obtaining sufficient hot metal ductility at high temperatures. Japanese Patent Application No. 1-86991 also proposes a submerged arc welding wire and a flux for weatherable refractory steel. Here, in addition to sufficient high temperature strength and toughness,
A weld metal with good weather resistance has been obtained.

[0003]

In the above-mentioned welding method using a welding material, attention is paid to high-temperature tensile strength and high-temperature proof stress as high-temperature characteristics, but high-temperature ductility is not taken into consideration. However, if the high-temperature ductility is insufficient, the fracture of the steel member at the time of fire proceeds brittlely, which is extremely dangerous for ensuring the safety of the structure.

[0004] An object of the present invention is to provide high toughness and high-temperature ductility without impairing other properties such as high-temperature proof stress at 600 ° C and weatherability at room temperature, and to ensure high-temperature ductility.
Provided is a submerged arc welding method for refractory steel and weatherable refractory steel having improved creep rupture life at this temperature.

[0005]

According to the present invention, C: 0.01 to 0.15%, Si: 0.5% or less, Mn: 0.4 to 2.5%, by weight% and weight ppm, Cu: 0.7% or less, Ni: 0.5% or less, Cr: 1.0% or less, Mo: 0.14 to 0.8%, Nb: 0.01 to 0.1%, Ti: 400 ppm or less , B: 15 ppm or less, with the balance being Fe and unavoidable impurities, the refractory steel and the weather-resistant refractory steel were used as constituents of the flux (% by weight).
The basicity L calculated by the formula of Equation 3 is L = 0.2
With a submerged arc welding bond flux having a C content of 0.01 to 0.15%, Si: 0.5% or less, Mn: 0.4 to 2.5%, Cu: 0.7% or less, Cr: 1.0% or less, Ni: 0.5% or less, Mo: 0.8% or less, Nb: 0.1% or less, Ti: 400ppm or less, B: 50ppm or less Contained, the balance being a submerged arc welding wire consisting of Fe and unavoidable impurities, with a heat input of 120 kJ
/ Cm or more, and the amount of B in the weld metal (weight pp
m): [B] and Ti content in weld metal (weight ppm):
A submerged arc welding method for refractory steel, characterized by obtaining a weld metal having a high hot ductility in which [Ti] satisfies Expression 4.

[0006]

(Equation 3)

[0007]

(Equation 4)

[0008]

The present invention will be described in further detail with the following operation.

In order to solve the above-mentioned problems, the present invention focuses on the amounts of Ti and B in the weld metal. Ti is controlled by austenite grain structure control by Ti oxide.
Since B enhances the toughness of the weld metal by suppressing excessive grain boundary ferrite and fixing nitrogen, conventionally, in the construction of steel structures such as marine structures and ships, welding materials containing Ti and B are often used. I have.

The inventors of the present invention have studied in detail the effects of Ti and B in the weld metal on the high-temperature ductility, and as a result, FIG. 1 is obtained. FIG. 1 is a drawing showing the relationship between the Ti and B contents in the weld metal and the elongation at 600 ° C. As is clear from this figure, the elongation is significantly reduced when the Ti or B content in the weld metal increases. As a result of observing the fracture surface of the tensile test at a high temperature with a scanning electron microscope, this is because the mode of fracture at a high temperature changes from intragranular ductile fracture to intergranular brittle fracture as the amount of Ti or B increases. I found it. FIG. 1 also shows a region where intragranular ductile fracture occurs and a region where grain boundary brittle fracture occurs. Thus, we have:
It has been found that the amounts of Ti and B must be limited in order to ensure high-temperature ductility.

Judging from FIG. 1, in such an oxygen amount, it is possible to prevent the intergranular fracture in the tensile test at 600 ° C., to secure appropriate high-temperature ductility, and to obtain a welding with good toughness. The range of the contents of Ti and B in the metal is shown as a shaded portion in FIG. Here, [B] _max is when Ti does not exist in the weld metal (Ti
<10 ppm), which is an upper limit of B, here 1
It is 0 ppm. [Ti] _max also contains B in the weld metal.
Is the upper limit of Ti that can be tolerated when B does not exist (B <1 ppm), and is 100 ppm here. This hatched portion is represented by Expression 5 when expressed by an inequality expression.

[0012]

(Equation 5)

However, these [B] _max and [Ti] _max
Varies strongly under the influence of gas components in the weld metal, particularly oxygen. The inventors have further determined that [B] _max ,
As a result of examining the effect of oxygen on [Ti] _max in detail, it was found that [B] _max and [Ti] _max can be represented by Equation 6 as a function of the amount of oxygen in the weld metal.

[0014]

(Equation 6)

According to the present invention, Ti and B satisfying the above equation are used.
The present invention relates to a submerged arc welding method characterized by obtaining a weld metal having an amount of Ti,
If the amounts of B and B are limited as in the above formula, a weld metal excellent in high-temperature ductility can be obtained. By ensuring high-temperature ductility by such means, the creep rupture life, which has a positive correlation with high-temperature ductility, also improves. Although sufficient toughness can be obtained only with an amount satisfying the above equation, the T
It is more desirable that the i amount satisfies Expression 7.

[0016]

(Equation 7)

Even if the amounts of Ti and B are limited as described above, since these elements do not contribute to fire resistance and weather resistance at all, these properties are not impaired.

[B], [Ti] and [O] in the equations (1), (2), (3) and (4) are controlled so as to satisfy the equation (1) or the equation (4). The following describes how to do this.

[O] is determined by steel and welding wire
For example, it is uniquely determined by the basicity of the flux. [B]
Used steel and wire with sufficiently low B content
Sometimes, a B source in the flux, for example, 2CaO.3B_Two
O_Three・ 5H_TwoO or Na_TwoB _FourO₇Controlled by the amount of
Is possible, as well as steel and steel with a sufficiently low Ti content.
When ears are used, [Ti] is in flux
Ti source, TiO_TwoCan be controlled by the amount of addition. Also
Conversely, using a flux that does not contain a B source or Ti source
Or controlling [Ti] and [B] with wires
Can also.

Hereinafter, the component elements in the present invention and the added amounts thereof will be described.

First, a steel sheet obtains a sufficient high temperature proof stress by adding Mo and a trace amount of Nb in combination, or further obtains Cu, Ni, Cr
Is characterized in that sufficient weather resistance has been obtained by the inclusion of chromium.

C is for securing the strength at room temperature, and for Mo and Nb.
Is necessary to exhibit the effect of adding, and for that purpose, the lower limit is 0.01%. On the other hand, if the content exceeds 0.15%, the susceptibility to hot cracking increases and the toughness deteriorates. Therefore, the upper limit of C is set to 0.15%.

Si can be added from the welding flux to be combined, and the lower limit of the steel sheet is not particularly defined. However, if it exceeds 0.5%, the toughness of the weld metal decreases, so it is necessary to make the content 0.5% or less.

Mn is an element indispensable for securing strength and toughness, and must be contained at 0.4% or more. On the other hand, if it exceeds 2.5%, the hot cracking susceptibility increases and the toughness deteriorates. Therefore, the upper limit of Mn is set to 2.5%.

Cu is an element necessary for obtaining good weather resistance, but if Cu exceeds 0.7%, the toughness is deteriorated.

Ni also improves the weather resistance similarly to Cu, but if it exceeds 0.5%, the toughness deteriorates.
It is necessary to:

Cr improves the weather resistance similarly to Cu, but if it exceeds 1.0%, the toughness deteriorates.
It is necessary to:

Mo and Nb are added in order to obtain sufficient high temperature proof stress, but Mo is 0.1% or more and Nb is 0.01%.
% Is required. Further, if Mo and Nb are excessive, the room temperature strength becomes too high and the toughness is deteriorated. Therefore, it is necessary to set Mo to 0.8% or less and Nb to 0.1% or less.

If the content of Ti in the steel material is too large, the flux or wire cannot control the excessively high content of Ti in the weld metal, impairing the high-temperature ductility.
i needs to be suppressed to 400 ppm or less.

B also needs to be suppressed to 15 ppm or less for the same reason as Ti.

Next, regarding the welding wire, each specific value is determined in the same manner as in the above steel sheet. However, since Mo and Nb can be added from the flux, the lower limits are not specified.

Next, regarding the bond flux, if the basicity L calculated by the equation (8) according to the constituents (% by weight) of the flux is less than 0.2, the oxygen of the weld metal is too high and the toughness deteriorates. If it exceeds 3.5, the oxygen of the weld metal is too low, so that Ti and B are excessively produced in the weld metal and the high-temperature ductility decreases.

[0033]

(Equation 8)

[0034]

EXAMPLES Two kinds of wires, W1 and W2 shown in Table 1, were used, and ten kinds of bond fluxes shown in Table 2 were produced. The steel plates used were three types of weather-resistant refractory steels P1, P2, and P3 shown in Table 3. These steel plates 1 are shown in FIG.
, And then welded under the welding conditions shown in Table 4. Table 5 shows the combinations of flux and steel plate. After the welding, a tensile test piece, a creep test piece, and a Charpy impact test piece 2 were sampled from the position (a = 7 mm) shown in FIG. 4, and a mechanical test was performed. The creep test was performed at 600 ° C. under a load of 25 kg / mm ² . Table 5 shows the results of these tests.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

No. No. 1 to No. No. 8 is a welding method according to the method of the present invention. 9 to No. 9 13 is illustrated for comparison. No. In No. 1, the contents of Ti and B in the weld metal were small, and sufficient high-temperature elongation and creep rupture life were obtained. No. 2 is No. B. However, since Ti is still sufficiently low, sufficient high-temperature elongation and creep rupture life are obtained. No. No. 3 is No. Although Ti is higher than 1 but B is still low, sufficient high-temperature elongation and creep rupture life are obtained. No. No. 4 is No. 4.
Although Ti is higher than No. 3, oxygen is also sufficiently high, so that sufficient high-temperature elongation and creep rupture life are obtained. No.
5 also has a high B, but has a high oxygen elongation, so that sufficient high-temperature elongation and creep rupture life are obtained. Similarly, even if the steel plate changes from P1 to P2, no. Sufficient high-temperature elongation and creep rupture life can be obtained with Ti and B contents satisfying the formula (1) as shown in FIG. In addition, No. In No. 7, steel plate Ti
And B content is large, but by adjusting the flux,
The amounts of Ti and B in the weld metal are appropriate, and the high temperature elongation and creep rupture life are good. No. At 8, N
o. No. 1 to No. Although the wire W2 having a lower alloy content than the wire W1 used in Example 7 was used, even in this case, since the formula (1) was satisfied, sufficient high-temperature elongation and creep rupture life were obtained. As described above, the weld metal according to the method of the present invention that satisfies the formula (1) exhibits a good high-temperature elongation, is a stable fracture in which the fracture mode is ductile fracture, and has good high-temperature proof stress and toughness. In addition, No. 1,
No. 3, No. 4, no. 7, no. 8 satisfies expression (4) as well, 2, No. 5, no.
As compared with No. 6, the toughness is also improved. On the other hand, in the comparative welding methods, Ti or B are all excessive and do not satisfy the expression (1), grain boundary fracture occurs, and high temperature elongation and creep rupture life are insufficient. In the present embodiment, Ti and B are added from a flux or a steel plate, but the method of the present invention can be applied even when added from a wire.

[0041]

As described above, the welding method of the present invention
It is possible to obtain a weld metal excellent in high-temperature ductility, as a result, to prevent brittle fracture of the welded portion of fire-resistant steel and weather-resistant refractory steel structure at the time of fire, and further improved creep rupture life, Even in a longer-time fire, the weld metal does not break, and safety can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between Ti and B contents in a weld metal and elongation at 600 ° C.

FIG. 2 is a view showing the range of the contents of Ti and B in a weld metal in which good ductility and creep rupture life at 600 ° C. are obtained.

FIG. 3 is a front view showing a shape of a welding groove used in the embodiment.

FIG. 4 is a front sectional view showing a test piece sampling position.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Tensile test piece, creep test piece, and Charpy impact test piece

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Nobuyuki Ohhama 5-10-1 Fuchinobe, Sagamihara City, Kanagawa Prefecture Nippon Steel Corporation

Claims (1)

[Claims] 1. In weight% and weight ppm, C: 0.01 to 0.15%, Si: 0.5% or less, Mn: 0.4 to 2.5%, Cu: 0.7% or less, Ni: 0.5% or less, Cr: 1.0% or less, Mo: 0.14 to 0.8%, Nb: 0.01 to 0.1%, Ti: 400ppm or less, B: 15ppm or less Refractory steel and weather-resistant refractory steel whose balance is Fe and unavoidable impurities are used as flux constituents (% by weight).
The basicity L calculated by the formula of Equation 1 is L = 0.2
A submerged arc welding bond flux having a C content of 0.01 to 0.15%, a Si content of 0.5% or less, a Mn content of 0.4 to 2.5%, Cu: 0.7% or less, Cr: 1.0% or less, Ni: 0.5% or less, Mo: 0.8% or less, Nb: 0.1% or less, Ti: 400ppm or less, B: 50ppm or less Contained, the balance being a submerged arc welding wire consisting of Fe and unavoidable impurities, with a heat input of 120 kJ
/ Cm or more, and the amount of B in the weld metal (weight pp
m): [B] and Ti content in weld metal (weight ppm):
A submerged arc welding method for refractory steel, wherein a weld metal having a high hot ductility in which [Ti] satisfies Expression 2 is obtained. (Equation 1) (Equation 2)