JPS5841957B2 - Highly corrosion-resistant chromium-based stainless steel wire for inert gas arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inert gas arc welding wire made of highly corrosion-resistant chromium-based stainless steel that has excellent corrosion resistance and toughness.

Stainless steel can be broadly classified into ferritic and austenitic stainless steels, but ferritic stainless steels that do not contain Ni as an alloying element contain N, which is at risk of being depleted as a resource.
It has the advantage of not using i and does not cause various types of stress corrosion cracking, but has the disadvantage of poor general corrosion resistance, poor weldability, and low corrosion resistance and toughness of the welded part.

However, recently, many chromium-based ferritic stainless steels have been developed that have improved corrosion resistance compared to conventional ones, taking advantage of the characteristics of ferritic stainless steels that have excellent stress corrosion cracking resistance.

In this way, chromium-based stainless steel is made of Cr to obtain corrosion resistance.
In most cases, the content is 16% or more, and Mo is usually added to further increase corrosion resistance.

Furthermore, there are many examples in which elements such as Ti and Nb are added as elements to stabilize C and N elements, which have a negative effect on corrosion resistance and toughness.

Furthermore, it is known that the toughness and workability of chromium-based stainless steels are improved by lowering C and N, and recent advances in steelmaking technology have led to the development of chromium-based stainless steels with lower C and N than before. Manufacturing of stainless steel is becoming easier.

In the welding of corrosion-resistant chromium-based stainless steel as described above, there are cases in which an austenitic stainless steel wire is used as the welding wire, and a chromium-based stainless steel wire that is of the same type as the base metal is used.

If austenitic material is used, weldability is good, but
On the other hand, it has various problems such as impairing the good stress corrosion cracking resistance that is a characteristic of chromium-based stainless steel, and this is a major drawback.

On the other hand, when a chromium-based wire is used, it has the disadvantage of extremely poor weldability, especially toughness and workability.

The more the amount increases, the more noticeable it becomes, making it difficult to weld using chromium-based wire.

From the above points, there is a strong desire to develop a welding wire that can provide welded parts with high corrosion resistance and high toughness.

As a result of various studies, the present inventors found that C
, Nb while limiting N to lower than conventional chromium-based wires.
, ■, By adding appropriate amounts of Al and, if necessary, a rare earth element with an atomic number of 57 to 71, Y, and Ca as a composite of one or more types, and also adding sufficient amounts of Cr and Mo,
They discovered that it was possible to obtain a welded part with sufficient corrosion resistance and good toughness in the as-welded state, and succeeded in developing a new welding wire.

That is, in the present invention, C+N is in the range of 0.03% (: 0.02%, Cr is 12.0-30.0%, MOo is 2-3%).
5%, (Nb+V)/(C+N)-10 to 40, Nb0.02 to 0.50%, Vo, 05 to 2%, AIo
, 01-1.0%, further including Y and Ca as necessary,
This is an inert gas arc welding wire made of highly corrosion-resistant chromium-based stainless steel and characterized by containing one or more rare earth elements in a total amount of 0.002 to 0.5%.

In the present invention, inert gas arc welding refers to A
Arc welding is performed in an atmosphere of inert gas such as r, He, or a small amount of active gas added to these,
TIG welding, MIG welding, and plasma welding are commonly used.

However, in the case of welding where impact properties are very important, TIG welding is preferable because it can keep the oxygen content in the weld metal low.

The present invention will be explained in detail below.

In order to improve the weld properties of chromium-based stainless steel, especially the toughness, it is desirable to reduce the C and N contents in the welding wire as much as possible.

Figure 1 shows the results of investigating the toughness of TIG welds when the amount of C in the wire was varied based on the basic system of 19% Cr and 2% Mo. It shows the relationship between the toughness of a TIG weld and the amount of (C+N) when the amount is changed.

Base material is C0,006%, NO,009%, Cr19%,
It is a chromium-based stainless steel with a plate thickness of 6 mm containing 2% Mo.

Note that the hatched portions in FIGS. 1 and 2 indicate the width of variation in toughness data.

As is clear from the figure, the influence of C on the weld toughness is large, and when it exceeds 0.02%, the impact value decreases.

On the other hand, when the amount of (C+N) exceeds 0.03%, the toughness begins to decrease, and when it exceeds 0.04%, the toughness rapidly deteriorates.

Based on this knowledge, C≦0.02% was set within the range of (C+N)ζ0.03%.

Cr is a major element that increases the corrosion resistance of welded parts, and as the amount of Cr increases up to 30% as a wire component, the penetration potential, that is, the corrosion resistance increases, but when it exceeds 30%, it reaches saturation.

On the other hand, when the amount of Cr as a wire component exceeds 30%, the toughness of the weld zone deteriorates rapidly.

Therefore, in the present invention, the range of Cr is determined to be 12 to 30% in view of its effect on the corrosion resistance and toughness of the welded part.

Mo is an element that improves corrosion resistance together with Cr, but 5
%, the effect is saturated, so the amount of Mo is 0.2%.
The range was set to 5%.

If C and (C+N) are reduced, the toughness of the welded part can be improved as shown in Figures 1 and 2, but it is not as tough as the chromium-based stainless steel base material manufactured by rolling and heat treatment. , the welded part remains a cast solidified structure, and the toughness may be poor.

In order to improve the toughness of the weld zone, the present inventors conducted various studies and found that the addition of Nb+V is effective.

In welded parts of chromium-based stainless steel with reduced C and N content, brittle carbonitrides precipitate at grain boundaries, which become starting points for cracks and cause significant embrittlement.

In order to prevent such embrittlement of the weld, a method that does not cause grain boundary precipitation of carbonitrides has been considered, and it has been found that combined addition of Nb + V is effective.

Figure 3 shows the effect of N in welding wire on the toughness of TIG welds.
b+V(1) Indicates influence.

Incidentally, Ti was also investigated, but it was confirmed that although it certainly suppresses grain boundary precipitation of carbonitrides, it was not very effective in improving toughness.

The amount of Nb is 0.02 to 0.5%, and the amount of Nb is 0.0%.
At 5 to 2.0%, C1N is sufficiently fixed and weldability is improved, but as shown in FIG. 4, the optimum value exists at <(Nb+V)/(C+N).

In other words, Fig. 4 shows the influence of (Nb + V)/(C + N) in the wire on the corrosion resistance and toughness of TIG welds, but as seen in Fig. 4, (Nb + V)
/(C+N)-10 to 40, the desired characteristics can be obtained.

In addition, in FIG. 4, the hatched area indicates the width of variation in toughness data.

By adding Nb-V in combination according to the present invention, intergranular corrosion resistance and toughness can be maintained at a high level.

As a result of repeated studies regarding the toughness of the weld zone, the present inventors discovered that oxide inclusions have a significant effect on embrittlement.

In other words, oxide inclusions present in the weld zone become the starting point of cracks, causing significant embrittlement.

Such embrittlement is seen when the amount of O in the weld metal is extremely high, and also occurs when the amount of Al is low.

By adding an appropriate amount of AI to the wire, it is possible to prevent the weld from becoming brittle and improve its toughness.

The appropriate amount of AI added to welding wire is 0.01 to 1.00.
%, and if the amount of AI added exceeds the appropriate amount, the toughness of the weld tends to deteriorate.

Rare earth elements with atomic numbers 57 to 71, mainly consisting of ce, I, and a, and one or more of Ca and Y are present in the wire with a total of 0.0
When present in an amount of 2% or more, it is dispersed in the weld metal as ultrafine oxides, prevents the impact value from decreasing due to oxide inclusions, and refines the coarse grain solidification structure of the weld zone, further improving toughness. .

The upper limit was set at 0.50% in consideration of the yield during welding.

Beyond that, the toughness actually decreases.

Among inert gas arc welding methods, in MIG welding, in which welding is performed by adding 02 or CO2 gas to the inert gas to stabilize the arc, the amount of oxygen in the weld metal increases, so rare earth elements are added to the weld metal. This method is not suitable for wires containing rare earth elements.
It is particularly suitable for tick welding using 100% inert gas.

In addition, each component of Si, Mn, and P has an adverse effect on toughness, so Si is preferably 1.0% or less, and Mn is preferably 0.4% or less.
It is preferably 0.5% or less, preferably 0.2% or less, Po, 0.5% or less, preferably 0.03% or less, and S has a negative effect on corrosion resistance, so it is desirable to keep it as low as possible.

The present invention was developed as a wire for inert gas arc welding of chromium-based stainless steel with high corrosion resistance and high toughness, but conventional chromium-based stainless steel, such as SU
S405.5US409.5US410, SUS4
It goes without saying that sufficient corrosion resistance and toughness of the welded part can be obtained even when applied to No. 30, etc., and there is no problem in using it.

Next, Examples according to the present invention are shown in Table 1, Table 2, Table 3, and Table 4.

The first A-1 to A-8 are welding wires according to the present invention, and the first R-1 to R-7 are comparative welding wires.

Table 2 shows welding conditions when welding was performed using each welding wire.

Note that Table 3 shows the components of the welding base material.

Table 4 shows the results of the toughness and corrosion resistance tests of the welds obtained in Table 2.

In addition, the base material size is plate thickness 6m1 x 100myt x 20
0mm, Charpy impact test piece is 2amVJIS
Using a No. 4 sub-size, a 2 mm V notch was placed in the center of the weld metal in the plane perpendicular to the bead in the thickness direction of the plate.

As a result, as shown in Table 4, according to the wire of the present invention,
Welds with excellent corrosion resistance and toughness were obtained, whereas comparative wires R-1, R-2, R-4, R-5, R-6, and R
-7 is not within the appropriate range of (Nb+V)/(C+N), and R-3 has a small amount of Al content, and R-2 and R
-6 had an excessive amount of Nb, so all of the obtained welds had low toughness, and most of them also had poor corrosion resistance.

As is clear from the above examples, according to the present invention, a welded part with excellent corrosion resistance and toughness can be obtained, and the present invention makes an extremely significant contribution to industry.

[Brief explanation of drawings]

Figure 1 shows the influence of C in the welding wire on the Charpy impact value of TIG welds of highly corrosion-resistant chromium stainless steel, Figure 2 shows the influence of <C+N, and Figure 3 Figure 4 shows the effect of Nb + V in the welding wire on vTrS of TIG welds.
/(C+N: vE in FIGS. 1 and 2) represents the JIS No. 4 subsize Charpy 0°C absorbed energy value.

Claims (1)

[Claims] I C≦0.02% in the range of C10N≦0.03%, C
r 12.0-30.0%, Mo 0.2-5.0%,
(Nb +V)/(C+N) - Nb in the range of 10 to 40
0.02-0.50%, Vo, 05-2.0%, Al0
An inert gas arc welding wire made of highly corrosion-resistant chromium-based stainless steel, characterized by containing 0.001 to 10%. 2 C≦0.02% in the range of C + N + 0.03%, C
r 12.0-30.0%, Mo 0.2-5.0%,
(Nb+V)/(C+N) Nb in the range of -10 to 40
O, 02-0.50%, Vo, 05-2.0%, Al
0001 to 1.0% plus one or more rare earth elements with atomic numbers 57 to 71, Y, and Ca in a total amount of 0.0%.
A wire for inert gas arc welding made of highly corrosion-resistant chromium-based stainless steel, characterized by containing 0.02 to 0.50%.