JP2594623B2 - Welding wire for refractory steel - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a welding wire for welding refractory steel used in the fields of construction, civil engineering and marine structures. The present invention relates to a gas-shielded arc welding wire which provides a weld metal having excellent high-temperature yield strength and good toughness.

(Prior art) As is well known, welding wires for various structures in the fields of construction, civil engineering and marine structures are solid wires for MAG welding mild steel and high-strength steel (JIS Z 3312), and carbon dioxide arc welding for weathering steel. Solid wire (JIS Z 3315) is widely used.

For example, Japanese Unexamined Patent Publication No. 55-109592 discloses a crude Ar-5
Mixed gas arc welding wire using to 50% CO ₂ is, JP 57-58994 and JP Sho 61-159296 and JP 61-159297, and the sputtering reduce the purpose wire JP-A-63-72498 discloses a wire component for a galvanized steel sheet.

By the way, among various structures, in particular, buildings such as buildings and offices and dwellings that are in close contact with daily life, a welded portion constructed using the welding wire has a sufficient fireproof coating to ensure fire safety. It is obligatory to apply it, and according to architectural laws and regulations, the weld temperature should be 350 ° C in the event of a fire.
It doesn't get any more.

This is because the proof stress at about 350 ° C is reduced to 60 to 70% of that at normal temperature, which may cause the building to collapse.

For this reason, slag wool, rock wool, spraying and felt having a base material such as glass wool are spread on the surface of the welded portion, and a method of covering with fireproof mortar and the heat insulating material layer, Careful fireproof coating, such as protection with thin metal sheets, such as aluminum or stainless steel sheets, is used to prevent thermal damage in the event of a fire.

Therefore, the refractory coating construction cost is higher than the welding material price itself, and it cannot be avoided that the construction cost increases significantly.

(Problems to be Solved by the Invention) As described above, when a well-known welding wire is used for a building, it is inexpensive, but cannot be used without coating or light coating due to low high-temperature characteristics, and is expensive. Since fireproof coating must be applied, there is a problem that the construction cost is increased, the space used for the building is narrowed, and the economic efficiency is reduced.

On the other hand, a well-known MAG-welded solid wire for heat-resistant steel (JIS Z 3317) and JP-A-57-100892 and JP-A-
According to the wire for heat-resistant steel disclosed in Japanese Patent Application Laid-Open No. 58-100994, the high-temperature properties are good, but the price is very high, and it is very difficult to use it for welding work.

In addition, in recent years, the height of buildings has been increasing, and from the improvement of design technology and its high reliability, fireproof design has been reviewed, and in 1987 a new fireproof design law for buildings was enacted, The above-mentioned 350 ° C temperature limitation allows the ability of the fireproof coating to be determined by the high-temperature strength of the weld and the load actually applied to the building, and in some cases it can be used without coating Became.

However, there is currently no welding wire for obtaining a weld metal having excellent fire resistance.

An object of the present invention is to provide a gas-shielded arc welding wire that provides a weld metal having excellent high-temperature characteristics at 600 ° C. and excellent impact toughness.

(Means for Solving the Problems) The present invention overcomes the above-mentioned problems and achieves the object, and specific means thereof are shown in the following items a to a.

A. By weight ratio, C: 0.03-0.12%, Si: 0.40-1.00%, M
n: 0.90 to 2.50%, Mo: 0.10 to 0.50%, Nb: 0.005 to 0.025
%, Cu: 0.50% or less, P: 0.030% or less, S: 0.030% or less,
N: 0.0100% or less, (0.5Mo + 10Nb) is 0.1 to 0.4%, and the balance consists of iron and inevitable impurities.

I. By weight ratio, C: 0.03-0.12%, Si: 0.40-1.00%, M
n: 0.90 to 2.50%, Mo: 0.10 to 0.50%, Nb: 0.005 to 0.025
%, Cu: 0.50% or less, P: 0.030% or less, S: 0.030% or less,
N: 0.0100% or less, (0.5Mo + 10Nb) is 0.1 to 0.4%, and further contains one or two kinds of Ti: 0.05 to 0.35%, B: 0.0005 to 0.0080%, and the balance is from iron and inevitable impurities. A welding wire for refractory steel, comprising:

(Action) The present inventors have studied the strength of the weld metal during a fire. As a result, if the target is uncoated, the maximum temperature at the time of the fire is about 1000 ° C. In order to have a proof stress of 70% or more, a large amount of expensive metal elements must be added to known welding wires,
It cannot be used from the economical aspect.

Therefore, what is currently being developed as refractory steel,
Components are designed and manufactured so that the high temperature proof stress at 600 ° C is 70% or more of that at normal temperature.

A typical component of the refractory steels targeted by the present invention is% by weight.
And C: 0.09%, Si: 0.38%, Mn: 0.88%, P: 0.006%, S:
0.004%, Al: 0.024%, Mo: 0.54%, Nb: 0.019%, Cr: 0.1
5%, Ti: 0.009%, N: 0.0023%, including those usually used in the fields of architecture, civil engineering and offshore structures.

For this reason, if the welded part has a high temperature resistance value of this refractory steel material or more, it is economical even from the viewpoint of the whole building, furthermore, only a small amount of expensive additive elements is required, and the fireproof coating of the welded part must be thin. We have developed a welding wire with excellent fire resistance that can be used without coating when the fire load is small.

By the way, the feature of the present invention is that a trace amount of Nb and Mo are added in combination,
The object is to limit the sum of (0.5Mo + 10Nb) to 0.1 to 0.4%.

Here, the characteristic component elements according to the present invention and the added amounts thereof will be described.

Nb and Mo form fine carbonitrides, and Mo increases the high-temperature strength by solid solution strengthening.
It is difficult to obtain sufficient proof stress in the high temperature range of 600 ° C.

The present inventors have conducted test research using various prototype wires,
It has been found that the composite addition of Nb and Mo is extremely effective in increasing the proof stress in the high temperature region. However, if the amounts of Nb and Mo are too high, the weldability deteriorates and the toughness deteriorates, so the upper limits of the Nb and Mo contents are each 0.025.
% And 0.50%, and the lower limit is 0.005% and 0.10%, respectively, as the minimum amount that can achieve the combined effect.

Further, the amounts of Nb and Mo are within the range described above (0.5 M
o + 10Nb) is 0.1 to 0.4%, the high-temperature proof stress at 600 ° C is equal to or higher than that of refractory steel, and the impact toughness is good. Therefore, the sum of (0.5Mo + 10Nb) is 0.1%.
Limited to the range of ~ 0.4%.

In order to increase the high-temperature strength, the use of Mo is known in conventional heat-resistant steel welding wires,
As a welding wire used for construction, there is no known welding wire for refractory steel in which Nb is added in addition to a small amount of Mo.

Next, the reasons for limiting the components other than Nb and Mo in the present invention will be described in detail.

C is necessary to ensure the strength and to exert the effect of adding Nb and Mo. If less than 0.03%, it is difficult to secure the strength.
Since the effect of adding Nb and Mo is weakened, the lower limit is made 0.03%.
On the other hand, if it exceeds 0.12%, the hot cracking susceptibility increases and the toughness deteriorates, so the upper limit is made 0.12%.

Si is an indispensable element as a main deoxidizing agent. If the content is less than 0.40%, insufficient deoxidation causes welding defects such as blowholes in a weld metal, so the lower limit is set to 0.40%. Also, 1.00
%, It causes solid solution hardening of ferrite and lowers toughness, so the upper limit is made 1.00%.

Mn is a deoxidizing agent similar to Si, and is an indispensable element for securing strength and toughness. It must be contained at 0.90% as the minimum amount that can secure strength and toughness, and the lower limit is 0.90%
And On the other hand, if it exceeds 2.50%, the sensitivity to hot cracking increases and the toughness deteriorates, so the upper limit is made 2.50%.

Cu is generally applied to the wire by plating, etc. for the purpose of improving rust resistance, corrosion resistance and wire feedability. However, if it exceeds 0.50%, the hot cracking sensitivity increases and the toughness deteriorates, so the upper limit is 0.50%. %.

Although P and S are contained as unavoidable impurities, they segregate at the grain boundaries, embrittle the grain boundaries and cause a decrease in toughness. Therefore, the upper limits are set to 0.030% or less and 0.030% or less, respectively.

N is generally contained in the wire as an unavoidable impurity, and combines with Nb to form carbonitride Nb (CN) and exerts hardening to improve high-temperature strength. However, as the amount of N increases, toughness decreases. In addition, welding defects such as blowholes are generated in the weld metal, so the upper limit is made 0.0100% or less.

The basic components of the wire of the present invention are as described above, and the object can be sufficiently achieved.However, in order to further improve the properties, the following elements, namely, Ti and B, are selectively added to improve the strength and toughness. , More preferable results are obtained.

Next, the above-mentioned additional elements and the amounts thereof will be described.

Ti forms Ti oxides, refines the microstructure of the weld metal, and is effective for improving toughness. However, if the content is 0.05% or less, this effect cannot be expected, and the lower limit is 0.05%. On the other hand, if it exceeds 0.35%, the toughness is significantly impaired, so the upper limit is made 0.35%.

Since B is a strong deacidified carbide-forming element, its addition to the wire promotes the nucleation action of the weld metal, thereby preventing the growth of columnar crystals.
The crystal grains are refined. In addition, it has the effect of enhancing the hardenability of the weld metal.
A B content of 0.0005% is required, and if it is less than that, there is no effect, and if it is too large, hot cracks are easily generated in the weld metal, so the upper limit is made 0.0080%.

(Example) Table 1 shows typical refractory steel materials used in the test, and Table 2 shows welding wires for the refractory steel used in the test.

After processing the steel sheet shown in Table 1 with a thickness of 25 mm into the groove shape (T = 25 mm, D = 7 mm, φ = 45 °) shown in FIG.
Using the wires shown in the table, welded joints were produced under the welding conditions shown in Table 3.

After the welding was completed, a tensile test piece and a Charpy test piece were sampled from the test material and subjected to a mechanical test. The test results are shown in Table 4.

As is clear from Table 4, the wires according to the present invention all have good room-temperature and high-temperature strengths and also show high values of impact toughness, whereas the comparative wires have too high strength at room temperature. Alternatively, the high-temperature strength is insufficient, and the impact toughness value is low.

In addition, the wire of the present invention was changed to Ar-
Even if the gas is changed to CO ₂ mixed gas, good fire resistance can be obtained without affecting performance.

(Effects of the Invention) As described above, a wire within the composition range of the present invention not only has excellent high-temperature properties and good impact toughness, but also has good welding workability at the time of welding work, and has excellent weldability. It is possible to drastically reduce the cost of fireproof construction.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a groove shape used in the embodiment.

Claims (2)

(57) [Claims] [Claim 1] C: 0.03 to 0.12% Si: 0.40 to 1.00% Mn: 0.90 to 2.50% Mo: 0.10 to 0.50% Nb: 0.005 to 0.025% Cu: 0.50% or less P: 0.030% or less S : 0.030% or less N: 0.0100% or less (0.5Mo + 10Nb) is 0.1 to 0.4%, the balance consisting of iron and unavoidable impurities, the welding wire for refractory steel. 2. C: 0.03 to 0.12% Si: 0.40 to 1.00% Mn: 0.90 to 2.50% Mo: 0.10 to 0.50% Nb: 0.005 to 0.025% Cu: 0.50% or less P: 0.030% or less S : 0.030% or less N: 0.0100% or less (0.5Mo + 10Nb) is 0.1 ~ 0.4%, and Ti: 0.05 ~ 0.35% B: 0.0005 ~ 0.0080% contains one or two kinds, the balance being iron and inevitable A welding wire for refractory steel, comprising an impurity.