JPH09225680A - Welding wire for ferritic stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding wire capable of obtaining a ferritic stainless steel welded metal having more excellent ductility and toughness than before in the case of welding ferritic stainless steels using the welding wire. SOLUTION: The welding wire for ferritic stainless steels is specified to contain one or more kinds of 0.001-0.08% C, 0.01-1.0% Si, 0.01-2.0% Mn, 10.5-32.0% Cr, 0.005-0.5% Al, 0.001-0.05% Mg, 0.001-0.04% N, 0.001-0.02% O, further if necessary, 0.1-4.0% Ni, 0.1-4.0% Mo, 0.01-0.5% Nb, 0.01-0.5% Ti.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a ferritic stainless steel wire used for welding various ferritic stainless steels.

[0002]

2. Description of the Related Art Ferritic stainless steels are less expensive than austenitic stainless steels, and are also excellent in strength and resistance to stress corrosion cracking in a chloride environment. When applied to welded structures, there are cases where welding is performed without adding welding material and cases where welding is performed by adding welding material.In both cases, due to coarsening of crystal grains in the weld structure A major problem is that the ductility and toughness of the welded part deteriorate.

In order to improve the decrease in ductility and toughness of such a ferritic stainless steel weld, for example, Japanese Patent Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 5-47102 and Japanese Patent Application Laid-Open No. 2-107744, restrictions on the amounts of C and N, Ti, N
addition of stabilizing elements such as b, and the above Japanese Patent Publication No. 55-47
In addition to Japanese Patent Laid-Open No. 102-102, as disclosed in Japanese Patent Laid-Open No. 50-109809, techniques such as addition of Al have been invented. In these inventions, since C and N are harmful to the toughness and ductility in ferrite, C and N are kept low from the beginning (high purification), or C and N are reduced to T in the solid phase.
It is intended to be fixed by i, Nb and Al.
On the other hand, even if these conventional techniques are used, in the case where a member including a welded part is subjected to strong working, insufficient ductility of the welded part often remains a problem. That is, the fundamental problem is that the solidification structure of the welded portion is significantly coarser than that of the base metal.

[0004]

On the other hand, the ductility of the welded portion is further increased with the expansion of the application of ferritic stainless steel for automobile exhaust systems and home appliances, and the diversification of the design and design of the welded structure. -There is a strong demand for ferritic stainless steels with excellent toughness. The present invention has been made from such a background, and when welding ferritic stainless steel with a welding wire, a welding wire capable of obtaining a ferritic stainless steel weld metal superior in ductility and toughness compared to the prior art is provided. To aim.

[0005]

Means for Solving the Problems The present invention is to solve the above problems, and in% by weight (hereinafter the same), C: 0.0
01-0.08%, Si: 0.01-1.0%, Mn:
0.01-2.0%, Cr: 10.5-32.0%, A
1: 0.005-0.5%, Mg: 0.001-0.0
5%, N: 0.001 to 0.04%, O: 0.001 to
0.02%, and if necessary, Ni: 0.1-4.
0%, Mo: 0.1-4.0%, Nb: 0.01-0.
5%, containing at least one of Ti: 0.01 to 0.5%,
A ferritic stainless steel welding wire characterized in that the balance consists of iron and unavoidable impurity elements.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have used a ferritic stainless steel welding wire of various component systems and have a plate thickness of 3 mm.
Of SUS430 ferritic stainless steel sheet by TIG welding, and the weld metal structure, ductility and toughness of the welded portion are examined.
The effects of the constituent elements of the welding wire on them were investigated. As a result, it has been newly revealed that the inclusion of Mg and Al in the welding wire achieves equiaxed crystallization and grain refinement of the weld metal structure, thereby significantly improving the weld ductility. It was

That is, with the ferritic stainless steel welding wire having the above composition range, the fineness of the welded portion was achieved, and the toughness and ductility of the welded portion were improved accordingly. The reasons for limiting each component in the present invention will be described below.

If the amount of C: C is extremely low C of less than 0.001%, the wire manufacturing cost becomes high, and if it exceeds 0.08%, the toughness and corrosion resistance of the welded portion are significantly lowered. Therefore, it is limited to 0.001 to 0.08%.

Si: Si is added as a deoxidizing agent and a strengthening element, but if it is less than 0.01%, its effect is not sufficient, while if it exceeds 1.0%, the impact toughness of the welded portion is greatly reduced and , Reduces melt penetration during welding. Therefore, it is limited to 0.01 to 1.0%.

Mn: Mn is also added as a deoxidizing element,
If less than 0.01%, the effect is not sufficient, while 2.0%
If it exceeds the above range, the workability during the production of the welding wire will deteriorate. Therefore, it is limited to 0.01 to 2.0%.

Cr: Cr is a ferrite-forming element,
It is the main element that imparts corrosion resistance to the weld metal. 10.5
%, Sufficient corrosion resistance cannot be obtained, while 32.0%
If it exceeds the limit, the workability of the wire rod for the welding wire in the hot or cold is poor, and the production is extremely difficult. Therefore, 10.5 to 32.
0%.

Al: Al is a deoxidizing element and is also effective for hot workability of the wire. Further, it co-exists with Mg to refine the weld metal structure. It is necessary to add 0.005% or more, but if it exceeds 0.5%, the melt penetration of the welded portion is reduced and the ductility of the welded portion is reduced. Therefore, it is limited to 0.005 to 0.5%.

Mg: Mg is a strong deoxidizing element, and particularly during welding, coexists with Al in the molten base to form an oxide, which plays a major role in atomizing the weld. From experiments using various alloy components, the effective Mg amount for grain refinement of the weld is 0.0
Although it is 01% or more, if it exceeds 0.05%, there are problems such as reduction of melt penetration in the welded portion and generation of slag on the weld bead.
It was limited to 0.001 to 0.05%.

N: N is an extremely low N content of less than 0.001%, which increases the manufacturing cost of the welding wire, while 0.04%.
If the content exceeds the above value, the ductility of the welded portion is reduced and at the same time, Cr is also bonded in the welded portion to reduce the corrosion resistance. Therefore, it is limited to 0.001 to 0.04%.

O: O is mainly Mg and A in the molten pool during welding.
Combines with l and contributes to grain refinement of the weld. 0.001%
Although the above contents are required, if the O content exceeds 0.02%, the ductility and toughness of the welded part are impaired due to excessive oxide formation.
Therefore, it is limited to 0.001 to 0.02%.

The welding wire of the present invention may contain one kind or two or more kinds of Ni, Mo, Nb and Ti, if necessary. Ni: Ductility of welded part due to addition of Ni of 0.1% or more
It is effective for toughness, but if it is added in an amount of 4.0% or more, ferrite becomes unstable at any Cr level, and brittleness during hot production easily occurs during wire production.
4%.

Mo: Mo is an element that improves the corrosion resistance especially in a chloride environment, and addition of 0.1% or more is effective, but if it exceeds 4.0%, the ductility and toughness of the welded portion deteriorate.

Nb: Nb combines with C to suppress the precipitation of carbides in the weld metal and improve the corrosion resistance. The addition of 0.01% or more is effective, but the addition of more than 0.5% reduces the ductility and toughness of the base material and the weld.

Ti: Ti combines with C to suppress the precipitation of carbides in the weld metal and improve the corrosion resistance. The addition of 0.01% or more is effective, but the addition of more than 0.5% reduces the manufacturability of the welding wire and the ductility / toughness of the welded portion.

The welding wire of the present invention is TIG welding, M
In addition to being used as a welding wire in welding methods such as IG welding, plasma welding, laser welding, and submerged arc welding, it can also be used as a core wire of a coated arc welding rod. These are applicable not only to welding of ferritic stainless steel, but also to repair of those structures, welding of dissimilar materials between ferritic stainless and ordinary steel / low alloy steel, or overlaying.

[0021]

EXAMPLES The effects of the present invention will be specifically described below based on examples. Ten kinds of ferritic stainless steel welding wires shown in Table 1 were subjected to the test. In the table, No. 1 to No.
No. 6 is the welding wire of the present invention, 7-No. 10 is a wire for comparison. Using these welding wires, a typical ferritic stainless steel, SUS4
30 3 mm thick steel plates were welded by the TIG welding method. Table 2 shows the chemical composition of the steel sheet. The welding groove shape is a Y groove (angle 80 °, root face 0.5 mm, no root interval), TIG welding uses Ar as a shield gas, welding current 150 A, voltage 15 V, welding speed 10
It was performed at cm / min.

[0022]

[Table 1]

[0023]

[Table 2]

After TIG welding was performed, the average grain size equivalent to a circle was calculated from the cross-section mirror of the weld, and the Charpy impact test and bending test of the weld metal were performed as the mechanical properties of the weld. . Charpy impact test
A sub-size test piece with a thickness of 3 mm was taken from the direction perpendicular to the welding direction (3 mm thickness x 10 mm width x 55 mm length, notch weld metal center), and three test pieces were repeatedly tested at 0 ° C.
The absorbed energy was calculated. The bending test is a test piece (3 mm thickness x 30 mm width x
250 mm long) was sampled, the welded part was bent from the back (bending radius 6 mm), and the ductility of the weld bead surface was evaluated.

Table 3 shows the evaluation results. The structure of the weld metal is such that when the comparative welding wire is used, ferrite crystal grains coarsely extend from the boundary of the molten portion and are so-called butt-solidified at the center of the weld metal, whereas when the welding wire of the present invention is used, it melts. Grain growth from the part boundary is suppressed, and most of the weld metal consists of equiaxed ferrite crystal grains. Therefore, in the former case, the ferrite sometimes stretches by 1 mm or more, and as a result, the average crystal grain size is considerably large, whereas in the latter case, it is isotropic and isotropic, and is 100 to 200 μm.

[0026]

[Table 3]

Further, the Charpy absorbed energy of the welded portion using the welding wire of the present invention is a stable value above the transition temperature, but the welded portion using the comparative welding wire has a low value which is considered to be due to brittle fracture. It can be seen that the toughness improvement at the welded portion by the welding wire of the present invention is clear. Further, even in the surface bending test of the welded portion, all of the welded portions using the welding wire of the present invention bent without any problem, whereas in the welded portion using the comparative welding wire, cracking was observed during bending, Inventive welding wires have been shown to improve ductility at the weld. The cracking during the bending test of the weld metal using the comparative welding wire occurs along the line of butt solidification in the center of the welded portion, the effect of the grain refinement of the welded portion by the welding wire of the present invention, and the coarseness in the comparative welded portion. The negative impact of grain-butt solidification on ductility is now shown.

[0028]

As described above, the welding wire of the present invention makes it possible to provide a ferritic stainless steel weld metal having improved ductility by suppressing coarse grains in the welded portion, which has been a problem in the past. Therefore, it can be said that the industrial effect is extremely large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Fuji, 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. By weight%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, Cr: 10.5 to 32. 0%, Al: 0.005-0.5%, Mg: 0.001-0.05%, N: 0.001-0.04%, O: 0.001-0.02%, A ferritic stainless steel welding wire characterized in that the balance consists of iron and unavoidable impurity elements. 2. Ni: 0.1-4.0%, Mo: 0.1-4.0%, Nb: 0.01-0.5%, Ti: 0.01-0.5%. The ferritic stainless steel welding wire according to claim 1, containing at least one of the above.