JPH05337690A - Flux cored wire for submerged arc welding having excellent wear resistance and bead mark resistance - Google Patents

Abstract

PURPOSE:To provide the flux cored wire for submerged arc welding suitable for easily production of build-up rolls, etc., having excellent wear resistance and bead mark resistance. CONSTITUTION:The flux cored wire formed by packing a flux into a steel sheath is constituted by incorporating 0.2 to 0.7% C, 0.2 to 1.5% Si, 0.5 to 3.0% Mn, 8 to 15% Cr and 2.5 to 8.5% W by the total weight of the wire into the wire and suppressing Mo, V, Nb and Ti so as to satisfy the relation (2/3 Mo+V +2Nb+2Ti) <=1.0%. Proper fluxes are usable for the flux to be combined with the wire. This flux cored wire is suitable for production of the build-up rolls, such as blocker rolls and pinch rolls, in a hot rolling line.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a flux-cored wire for submerged arc welding, which is suitable for overlay welding of various rolls such as blocker rolls and pinch rolls in a hot rolling line requiring abrasion resistance and bead mark resistance. It is about.

[0002]

2. Description of the Related Art Blocker rolls, pinch rolls and the like in a hot rolling line are liable to be worn due to repeated contact with a hot metal strip, and are also apt to be corroded by being exposed to cooling water or steam. For this reason, a build-up roll has been applied to these rolls, which is easily imparted with wear resistance, corrosion resistance, and bead mark resistance and can be repeatedly used by repair welding.

Conventionally, submerged arc welding using a flux-cored wire has been mainly applied to the overlay welding of these rolls because it is easy to add alloying elements, and C is 0.15 to 1. A flux-cored wire containing 20%, Cr 2 to 13%, and an appropriate amount of Mo, V, Nb and Ti is widely used.

[0004]

Generally, most of the weld metal obtained by the above-mentioned flux-cored wire and the combined flux is of martensite type because it requires an appropriate hardness. However, in such a weld metal, carbides are selectively precipitated in the heat-affected zone of the weld metal affected by the heat after the next pass, or in some cases, the same effect as the tempering heat treatment is applied to this portion. The structure is likely to become a microstructure different from other parts, such as tempered martensite. Then, there is a problem that abrasion resistance and corrosion resistance are different between this portion and a portion that is not affected by heat, and the heat-affected portion is selectively corroded, which easily causes a bead mark.

In order to prevent this bead mark, the inventors of the present invention first managed the preheating / interpass temperature (Japanese Patent Application No.
245127) and solution treatment (Japanese Patent Application No. 2-26).
2242) and other new construction technologies were proposed.

However, in order to maintain the preheating / pass-pass temperature within a certain range from the start to the end of the overlay welding in the above-mentioned roll having a large diameter or length, a simple furnace other than the normal overlay welding equipment is used. It was necessary for the operator to pay attention to the roll temperature at all times, even if welding was performed in this simple furnace or even if the simple furnace was not used. In addition, solution treatment is not included in the normal build-up roll manufacturing process,
There was a problem that led to an increase in manufacturing man-hours.

An object of the present invention is to solve the above problems of the prior art and to provide a flux-cored wire for submerged arc welding capable of easily manufacturing a build-up roll having excellent wear resistance and bead mark resistance. It is what

[0008]

As a means for solving the above-mentioned problems, the present invention relates to a flux-cored wire obtained by filling a steel sheath with flux, in the weight% of the total weight of the wire, C: 0.2-0.7%, Si: 0.2-1.
5%, Mn: 0.5-3.0%, Cr: 8-15% and W: 2.0.
5 to 8.5%, and Mo, V, Nb and Ti (2
A flux-cored wire for submerged arc welding, which is excellent in wear resistance and bead mark resistance, is characterized in that the relationship of / 3 Mo + V + 2Nb + 2Ti) ≦ 1.0% is satisfied.

The present invention will be described in more detail below.

[0010]

[Action]

As described above, the conventional flux-cored wire contains an appropriate amount of carbide-forming elements such as Mo and V in addition to Cr, and forms carbide in the weld metal. It had an appropriate hardness and contributed to maintaining good wear resistance of the weld metal. However, these carbides are likely to selectively precipitate in the heat-affected zone of the weld metal affected by the heat after the next pass, making the microstructure of the weld metal as-welded or after heat treatment non-uniform, and This has caused a difference in wear resistance and bead mark resistance between other portions.

Therefore, the present inventors can obtain good wear resistance in the entire weld metal without causing a difference in wear resistance and bead mark resistance between the heat-affected zone and other portions in the weld metal. The composition system of the flux-cored wire was examined.

As a result, in the component system mainly composed of C and Cr, Mo is very likely to form M ₂ C type carbides due to the influence of heat, which is a main cause of bead marks, and further V, Nb and Ti. It was found that has a stronger tendency to form carbides than Mo and is likely to cause bead marks. As a result of research on the countermeasures, it was found that bead marks caused by the structural nonuniformity of the heat-affected zone can be prevented by keeping the amount of these alloy elements below a certain value.

However, if the rolls which are required to have abrasion resistance and bead mark resistance as described above do not have an appropriate hardness, significant wear occurs at an early stage of use, and continuous use for a long period cannot be performed. Therefore, an investigation was conducted on alloy elements that can impart appropriate hardness without impairing the bead mark resistance.

As a result, W has a tendency to form carbides higher than Mo and lower than V, Nb, and Ti, but in the iron-based weld metal mainly composed of C and Cr, it is selected as the welding heat affected zone due to the welding heat effect. It was found that it was difficult to form a typical carbide. Moreover, it was confirmed that the addition of an appropriate amount of W has the effect of increasing the temper softening resistance. That is, in order to improve the bead mark resistance and maintain the wear resistance, W is 2.
5 to 8.5% and (2/3 Mo + V + 2Nb +
It has been found that setting 2Ti) ≦ 1.0% is effective.

The reasons for limiting each component of the flux-cored wire of the present invention will be shown below.

C: 0.2-0.7% C increases the hardness of the weld metal and contributes to the improvement of wear resistance, but if it is less than 0.2%, its effect is insufficient and 0.2%.
If it exceeds 7%, high temperature cracking or low temperature cracking tends to occur, so the C content is set to 0.2 to 0.7% with respect to the total weight of the wire.

Si: 0.2-1.5% Si has a deoxidizing effect, but if it is less than 0.2%, the effect is not sufficient, and if it exceeds 1.5%, the effect is saturated and On the contrary, hot cracking may occur. Therefore, the amount of Si is 0.2 to 1.5% with respect to the total weight of the wire.

Mn: 0.5-3.0% Mn has a deoxidizing action similar to Si, and further has an effect of improving hardenability. However, if it is less than 0.5%, the effect is insufficient, and if it exceeds 3.0%, the effect is saturated. Therefore, the amount of Mn is 0.1 with respect to the total weight of the wire.
5 to 3.0%.

Cr: 8-15% Cr is indispensable for maintaining the corrosion resistance and the oxidation resistance, and further forms a carbide to contribute to the improvement of hardness.
If less than%, these effects are not sufficiently obtained, and 15%
If it exceeds, the hardness is lowered and seizure is likely to occur during operation. Therefore, the Cr amount is 8 with respect to the total weight of the wire.
-15%.

W: 2.5-8.5% W is an alloy component that forms the basis of the present invention, and is effective in increasing hardness and temper softening resistance without impairing bead mark resistance. However, if it is less than 2.5%, the effect is not sufficient, and if it exceeds 8.5%, the effect is saturated.
Therefore, the amount of W is set to 2.5 to 8.5% with respect to the total weight of the wire.

(2/3 Mo + V + 2Nb + 2Ti): ≦ 1.0% Mo, V, Nb, and Ti form carbides in the heat-affected zone of the weld metal more easily, and systematically the heat-affected zone and other portions in the weld metal It causes non-uniformity. In order to prevent this effect, it has been found that the amount of (2 / 3Mo + V + 2Nb + 2Ti) (ratio to the total weight of the wire) needs to be 1.0% or less.

Of course, these components can be contained in one or both of the steel shell and the flux filling the shell, and each can be added as a simple metal or in the form of an alloy.

In addition to these, alloy components such as Ni and Cu may be added in order to improve properties such as corrosion resistance. However, excessive addition causes hot cracking. On the other hand, it is better to suppress the content to about 1%, preferably about 0.5%. Furthermore, in order to improve arc stability and bead appearance, various fluorides (CaF ₂ , NaF)
Etc.) and oxides (SiO ₂ , TiO _2, etc.) and the like may be added in an amount of about 0.1 to 5% with respect to the total weight of the wire.

Flux-cored wires containing the above-mentioned components are manufactured by filling the flux into the steel outer sheath at an appropriate filling rate. As the outer sheath, various steel types such as carbon steel and 13Cr type stainless steel can be used. It goes without saying that it is possible.

As the flux to be combined with the above-mentioned flux-cored wire, any of a fusion type, a bond type and a sintering type can be used.

Next, examples of the present invention will be described.

[0028]

[Example] A carbon steel shell was filled with flux and

[Table 1] A flux-cored wire having the composition shown in (1) was manufactured as a prototype. Using this flux-cored wire, build-up by submerged arc welding under the following conditions: 318 mmφ (outer diameter) x 2
A blocker roll having a size of 250 mmL was manufactured.

-Preheating-Temperature between passes: 200 to 350 ° C-Welding conditions: 380A-30V-40cpm (5 layers: 7.0mm finish on one side) -Combination flux: Commercial bond flux (PF-2)
00S) ・ Base material: Blocker roll (304mmφ × 2250mmL)

The blocker roll obtained was used by incorporating it into an actual hot rolling line, and the maximum amount of wall thinning (diameter) after 3 months was used.
Was measured. Good wear resistance was judged when the maximum thickness reduction (diameter) was 1 mm or less. In addition, the state of selective corrosion after 3 months of use was also examined. The results are also shown in Table 1.

As is clear from Table 1, all the examples of the present invention have good bead mark resistance and abrasion resistance. On the other hand, in Comparative Example No. 5, the bead mark was generated because the amount of C was large. No. 6 has a small amount of C,
Due to the large amount, the wear resistance was insufficient and significant wear occurred. In No. 7, the amount of (2 / 3Mo + V + 2Nb + 2Ti) is 2.
As many as 3%, a bead mark occurred early in use. No.
In No. 8, the amount of W was small, wear resistance was insufficient, and large wear occurred.

[0032]

As described in detail above, according to the flux-cored wire for submerged arc welding of the present invention, it is possible to easily manufacture a build-up roll having excellent wear resistance and bead mark resistance.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the shape and dimensions of a build-up roll obtained in an example.

[Explanation of symbols]

 a Overlay layer b Base material

Claims (1)

[Claims] 1. A flux-cored wire obtained by filling a steel shell with flux, in weight% (hereinafter the same), C: 0.2-0.7%, Si: 0.0, relative to the total weight of the wire. 2 to
1.5%, Mn: 0.5-3.0%, Cr: 8-15% and W:
2.5-8.5% and contains Mo, V, Nb and Ti
A flux-cored wire for submerged arc welding, which is excellent in wear resistance and bead mark resistance, characterized by being suppressed so as to satisfy the relationship of (2/3 Mo + V + 2Nb + 2Ti) ≦ 1.0%.