JPH03204196A - Wire for welding two-phase stainless steel having excellent concentrated sulfuric acid corrosion resistance - Google Patents

Abstract

PURPOSE:To allow the use of the welding wire for concd. sulfuric acid with the concd. sulfuric acid of a wide temp. range by specifying the contents of C, Si, Mn, P, S, Cr, Ni, Mo, N, Al, O, and S+O and containing the balance substantially Fe. CONSTITUTION:This wire for welding two-phase stainless steels having concd. sulfuric acid corrosion resistance contains, by weight %, 0.005 to 0.05 C, 0.01 to 1 Si, 0.1 to 2 Mn, <=0.02 P, <=0.005 S, 25 to 30 Cr, 4 to 9 Ni, 1 to 3 Mo, 0.01 to 0.4 N, <=0.05 Al, and <=150ppm O, and the balance substantially Fe and has <180ppm S+O. The C is harmful to corrosion resistance but is necessary in terms of strength. The S is indispensable as a deoxidizing element but deteriorates the corrosion resistance to a high concn. sulfuric acid environment if the S is incorporated at a high ratio into the wire. The Mn is necessary for deoxidizing and desulfurizing but deteriorates the corrosion resistance to the high concn. sulfuric acid environment if the content thereof exceeds 2%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has excellent general corrosion resistance in environments where sulfuric acid is manufactured, stored, and transported, such as sulfuric acid manufacturing plants, sulfuric acid storage equipment, and transportation equipment such as chemical tankers. The present invention relates to a duplex stainless steel welding wire.

[Conventional technology]

Conventionally, equipment that handles sulfuric acid, such as sulfuric acid production plants, sulfuric acid storage equipment, and chemical tankers, has used different materials depending on the concentration of sulfuric acid and temperature conditions (from room temperature to high temperature range of 250°C). In particular, when manufacturing, storing, and transporting high-concentration sulfuric acid, depending on the temperature conditions, acid-resistant brick (near the boiling point) or high-alloy stainless steel (near the 150°C)
, Ni-based alloy (near 60°C), Carbon II (150°C)
The reality is that around C) etc. are used as much as possible. In other words, since the corrosion behavior of metal materials in sulfuric acid changes significantly depending on the concentration and temperature of sulfuric acid, corrosion prevention technology in sulfuric acid from room temperature to high temperature has not been sufficiently studied from the perspective of materials technology. The current situation is that there was no such thing.

On the other hand, ferritic-austenitic stainless steel (hereinafter referred to as duplex stainless steel) has a two-phase structure in which 40 to 65% austenite is finely mixed in a ferrite matrix. In recent years, it has been actively applied as a corrosion-resistant structural material because of its combination of advantages. There are standards such as JIS 5US329, DINl, and 4462 for such duplex stainless steel, and JP-A-56-127 is the standard for stainless steel with excellent base material corrosion resistance and mechanical properties.
753, JP-A No. 57-47852, and welding materials are disclosed in JP-A No. 58-93593, JP-A No. 59-150692, etc. However, although these welded structures have excellent corrosion resistance in chloride and nitric acid environments, when these welded structures are applied to high concentration sulfuric acid environments over a wide temperature range (from room temperature to 250°C), Corrosion resistance becomes a major issue.

[Problem to be solved by the invention]

The present invention is used as a material for equipment that handles high-concentration sulfuric acid, such as sulfuric acid production plants, storage equipment, and transportation equipment, and is intended to extend the lifespan and safety of the equipment over a long period of time. (crude sulfuric acid and pure sulfuric acid 98
% or more), and the operating temperature range is from room temperature to 25%.
The object of the present invention is to provide a duplex stainless steel welding material that has excellent corrosion resistance up to a high temperature range of 0°C.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors conducted a systematic study on the influence of component elements on the sulfuric acid corrosion resistance of duplex stainless steel-like weld metal.

In other words, in a high concentration sulfuric acid environment and at room temperature to 250°C.
In order to ensure excellent corrosion resistance in a wide temperature range up to A weld metal was prepared using a welding wire in which the range of Ni was regulated and an appropriate amount of N was added so that the ferrite to austenite ratio was the same as that of the base metal, and a full-scale corrosion test was conducted. As a result, by performing welding using a welding wire having the following composition, as a result, by performing welding using a welding wire having the following composition, the corrosion rate can be reduced to 0.0% over a wide temperature range from room temperature to 250°C. 12 m
It has been found that the sulfuric acid corrosion resistance is improved below m/year.

That is, in the present invention, in weight %, c: 0.005% or more,
0.05% or less, Si: 0.01% or more, 1.0% or less, Mn: 0.1% or more, 2.0% or less, P: 0.0
2% or less, S: 0.005% or less, Cr: 25.0
% or more, 30.0% or less, Ni: 4.0% or more, 9
．． Less than 0%? 'lo: 1.0% or more, 3.0% or less,
N: 0.01% or more, 0.4% or less, A10.05
% or less, O: 150 ppm or less, the remainder consists of Fe and unavoidable impurities, and the contained components are expressed as 1) l) l [S + O) < 180,
Corrosion rate is 0.12 MA/y in the range of room temperature to 250°C with Cr in the range of 25.0% or more and 30.0% or less
Ni and M that can ensure less than ear.

A duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance, which is characterized by setting an appropriate range of Ca.
, containing one or two types of Ce at 0.001% or more and 0.03% or less, respectively, and containing components in ppmT:
Duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance characterized by the indicated [S+0-0.8Ca-0,3Ce)〈40, and for imparting even higher corrosion resistance to these. , Sn70, 01% or more, 0.1
% or less, Sb: 0.01% or more, 0.1% or less, Nb:
0.01% or more, 1.0% or less, Ti: 0.01% or more, 1.0% or less, Cu: 0.05% or more, 2.0% or less, v: o, ot% or more, 1. 0% or less, Zr: 0.
01% or more, 1.0% or less, W: 0.01% or more, 0,
This is a duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance, which is characterized by containing one or more types of 5% or less.

These wires are applicable to TIG or MIG gas shielded arc welding wires. Further, these wires can be used as core wires of materials for coated arc welding and submerged welding, and also as outer skins of flux-cored welding wires.

[For production]

The reason for limiting the content of each element according to the present invention will be described below.

C: 0.005% or more, 0.05% or less C is harmful to the corrosion resistance of stainless steel, but a certain amount of content is necessary from the viewpoint of strength.

If the carbon content is extremely low, less than 0.005%, the manufacturing cost will be high, and strength cannot be ensured. Moreover, if it exceeds 0.05%, Cr will be present in the as-welded state or when subjected to reheating.

It combines with Mo and the like and precipitates as carbides at grain boundaries, significantly deteriorating the corrosion resistance of these regions. Therefore, 0
．． The content was limited to 0.005% or more and 0.05% or less.

Si: 0.01% or more, 1.0% or less Si is essential as a deoxidizing element, but when contained in a large amount, corrosion resistance in a high concentration sulfuric acid environment is significantly deteriorated.

Furthermore, when the weld metal is reheated, the precipitation of the σ phase is accelerated and the mechanical properties are significantly deteriorated. Therefore, it is limited to 0.01% or more and 1.0% or less so that it is effective as a deoxidizing agent and does not affect corrosion resistance and σ phase precipitation.

Mn: 0.1% or more, 2.0% or less Mn is added as a deoxidizing and desulfurizing element, but at the same time, since it is an austenite stabilizing element, it can be added as a substitute for expensive Ni. Furthermore, it is an effective element for increasing the solid solution amount of nitrogen, which is effective for austenite formation. but,
In the high-concentration sulfuric acid environment targeted by the present invention, if it exceeds 2%, corrosion resistance deteriorates, so it is limited to 0.1% or more and 2.0% or less.

P: 0.02% or less P is an unavoidable impurity that causes grain boundary embrittlement and produces low melting point eutectics at the grain boundaries, causing hot cracking.

Furthermore, since it significantly deteriorates corrosion resistance in a high concentration sulfuric acid environment, it is limited to 0.02% or less.

S: 0.005% or less S is an unavoidable impurity that causes grain boundary embrittlement and produces low melting point eutectics at grain boundaries, causing hot cracking.

Furthermore, since it significantly affects hot workability, 0.00
It was limited to 5% or less.

Cr: 25.0% or more, 30.0% or less Cr is a basic component of the stainless steel of the present invention, and in order to obtain excellent corrosion resistance in a high concentration sulfuric acid environment, it is necessary to coexist with Ni, Mo, and N. It is necessary to add 0% or more. However, 3
Even if it exceeds 0.0%, its corrosion resistance is saturated and sigma phase precipitation is promoted during welding thermal cycles, resulting in a significant decrease in ductility and toughness. Therefore, it was limited to 25.0% or more and 30.0% or less.

Ni: 4.0% or more, 9.0% or less Ni is a main element that forms austenite, and is the most effective element for improving toughness and ductility.

From this point of view, the content must be at least 4.0%.

However, the addition of Ni generally deteriorates corrosion resistance in a high-temperature, high-concentration sulfuric acid environment. In particular, when the content exceeds 9.0%, corrosion resistance deteriorates significantly. Therefore, it was limited to 4.0% or more and 9.0% or less.

Mo: 1.0% or more, 3.0% or less Mo is an essential element to ensure excellent corrosion resistance in a high concentration sulfuric acid environment. From this point of view, at least 1.0%
It is necessary to contain However, if it exceeds 3.0%, 15
Corrosion resistance deteriorates in the high temperature range of 0°C or higher, and in the range of 1.0% to 3.0%, which is the range of this patent, Cr, Ni, and N
It has been found that there is an excellent corrosion resistance region in a wide temperature range from room temperature to 250°C. Therefore, 1.0
% or more and 3.0% or less.

N: 0.01% or more, 0.4% or less N is an austenite-forming element, and is an effective element in suppressing a decrease in the amount of austenite in the weld metal, and is also effective in improving strength. However, if the content is large, nitride precipitation increases and ductility decreases. Therefore, it was limited to 0.01% or more and 0.4% or less.

A/! :0.05% or less AI! is added as a deoxidizing agent, but if it exceeds 0.05%, corrosion resistance and hot workability deteriorate, so it was limited to 0.05% or less.

0: 150 pps+ or less Since O, like S, is an element that significantly affects hot workability, it is limited to 150 ppm or less.

[S + O) (ppm) < 180 Table 1 shows the results of investigating the influence of component elements on the manufacturability of the wire. S and O are elements that significantly affect hot workability, and as shown in Table 1 < [S+0) is 180p.
It has been found that if the temperature exceeds pm, wire breakage occurs during wire manufacture or flaws occur on the wire surface. Therefore, [S +
O) (ppm)<180.

Ca, Ce: 0.001% or more, 0.03% or less Ca, Ce are 0.001% each as deoxidizing and desulfurizing agents
% or more and 0.03% or less. Exceeding this has no effect. In addition, Ca and Ce are present in low S steel.
It coexists with MnS to fix 0, prevents the formation of MnS, and greatly improves hot workability.

0: 200 ppm or less and [S+O-0,8Ca-0,
3Ce) (ppm) < 40 Table 1 shows the influence of Ca and Ce on wire manufacturability. As a result, 0 exceeds 150 ppm, 200
Even if it is less than ppm, Ca and Ce are A1 in low S steel.
In order to fix S and O by coexisting with S and O, Ca
, By adding Ce under the indicated conditions, Cr-Ni
- Hot workability of Mo-Cu-N alloy is significantly improved,
It was found that no wire breaks or surface flaws occurred. Therefore, [S+O-0,8Ca-0,3Ce](ppm
) < 40.

Sn: 0.01% or more, 0.1% or less Sn improves the corrosion resistance of stainless steel in a high concentration sulfuric acid environment, so it is added in an amount of 0.01% or more and 0.1% or less, if necessary. Above 0.1%, the effect is saturated.

Sb: 0.01% or more, 0.1% or less Sb improves the corrosion resistance of stainless steel in a high concentration sulfuric acid environment, so it is added in an amount of 0.01% or more and 0.1% or less, if necessary. Above 0.1%, the effect is saturated.

Nb: 0.01% or more, 1.0% or less Nb increases the strength of stainless steel and fixes C to improve corrosion resistance, so it may be added 0.01% or more as necessary.
Add at 0% or less. If it exceeds 1.0%, the amount of NbC precipitated increases, which deteriorates corrosion resistance and causes hot cracking.

Ti: 0.01% or more, 1.0% or less Ti fixes C and improves corrosion resistance. In addition, since it coexists with Ca and fixes 0 and suppresses the formation of oxides of Si and Mn, it improves corrosion resistance and hot workability. However, 1
．． If it exceeds 0%, hot workability deteriorates.

From these viewpoints, it is added in an amount of 0.01% or more and 1.0% or less.

Cu: 0.05% or more, 2.0% or less Cu is added in coexistence with Cr, Mo, and Ni.
Since it improves corrosion resistance in a high concentration sulfuric acid environment, it is added in an amount of 0.05% or more and 2.0% or less, if necessary. If it exceeds 2.0%, the effect is saturated.

V: 0.01% or more, 1.0% or less (2) improves the corrosion resistance of stainless steel in a high concentration sulfuric acid environment, so it is added as necessary in an amount of 0.01% or more and 1.0% or less. If it exceeds 1.0%, the effect is saturated.

Zr: 0.01% or more, 1.0% or less Zr improves the corrosion resistance of stainless steel in a highly concentrated sulfuric acid environment, so it is added as necessary in an amount of 0.01% or more and 1.0% or less. If it exceeds 1.0%, the effect is saturated.

W: 0.01% or more, 0.5% or less W indicates the corrosion resistance of stainless steel in a high concentration sulfuric acid environment.
, improves by coexisting with N, so add 0.01% as necessary.
It is added in an amount of 0.5% or less. Above 0.5%, the effect is saturated.

〔Example] Hereinafter, the effects of the present invention will be specifically described based on Examples.

Based on the above knowledge, after melting steel with the chemical composition shown in Table 2 by vacuum melting, drawing it by the usual method, TIG
and MIG welding wire.

Next, create a groove as shown in Figure 1 on a steel plate with the composition shown in Table 3. Plate thickness (t): 8 mm, root spacing (g):
1-2mm, root surface (f): 1m, groove angle (θ):
60°), butt welding of the above groove was performed by the TIG method and the MIG method using the welding wire shown in Table 2. Corrosion test pieces shown in FIG. 2 were taken from these butt welds and subjected to a full surface corrosion test. In the same figure, 1 is the base material, 2
is the weld metal, where a is 1.5mm, b is 20mm,
c is 30 mm.

In the general corrosion test, the test piece shown in FIG. 2 was immersed for 24 hours in a highly concentrated sulfuric acid environment set at a constant temperature, and the corrosion weight change before and after immersion was determined. However, in order to avoid the influence of the film formed in the atmosphere on the general corrosion evaluation, each test piece was subjected to activation treatment immediately after being immersed in the environment. Weight loss is 0
．． Measure up to 1■ and calculate the measured weight loss per unit area.
Corrosion rate converted per unit time, mm/ye
Obtained using ar.

Regarding the test temperature, as shown in Figure 3, in the temperature range from room temperature to 250°C, there are two regions where the corrosion rate is maximum. ℃ and 250″C.

Table 4 shows the corrosion rate of each weld at each temperature.

As a result, both TIG welding and MIG welding showed that the welded parts using the welding wire of the present invention had a general corrosion resistance of 0.12 rrm/in the temperature range from room temperature to 250°C compared to comparative materials.
It is clear that it is an extremely excellent material for a year or less. Note that the * marks in Tables 1 and 2 indicate the chemical composition and corrosion rate of comparative materials outside the scope of the present invention.

〔Effect of the invention〕

Conventionally, welding wires for concentrated sulfuric acid have been used depending on the temperature conditions. In contrast, the present invention has excellent corrosion resistance with a corrosion rate of 0.12 an/year or less over a wide temperature range from room temperature to 250°C, which was previously impossible, and has minimal alloy addition. Therefore, it is highly economical and has extremely significant industrial effects.

[Brief explanation of drawings]

FIG. 1 is a side view showing the groove shape. FIG. 2 is a perspective view of a corrosion test piece. FIG. 3 is a diagram showing the temperature dependence of the corrosion rate of stainless steel in high concentration sulfuric acid.

Claims (3)

[Claims] (1) In weight%, C: 0.005% or more, 0.05% or less Si: 0.01% or more, 1.0% or less Mn: 0.1% or more, 2.0% or less P: 0. 02% or less S: 0.005% or less Cr: 25.0% or more, 30.0% or less Ni: 4.0% or more, 9.0% or less Mo: 1.0% or more, 3.0% or less N : 0.01% or more, 0.4% or less Al: 0.05% or less O: Contains 150 ppm or less, the remainder is Fe and unavoidable impurities, and the contained components are expressed in ppm [S + O] (ppm) <1
A duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance characterized by a hardness of 80%. (2) In weight%, C: 0.005% or more, 0.05% or less Si: 0.01% or more, 1.0% or less Mn: 0.1% or more, 2.0% or less P: 0. 02% or less S: 0.005% or less Cr: 25.0% or more, 30.0% or less Ni: 4.0% or more, 9.0% or less Mo: 1.0% or more, 3.0% or less N : 0.01% or more, 0.4% or less Al: 0.05% or less .00
Contains 1% or more and 0.03% or less, and pp.
[S+O-0.8Ca-0.3Ce] expressed in m (p
A duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance, characterized in that pm)<40. (3) Sn: 0.01 or more and 0.1% or less, Sb: 0.
01% or more, 0.1% or less, Nb: 0.01% or more, 1
．． 0% or less, Ti: 0.01% or more, 1.0% or less, C
u: 0.05% or more, 2.0% or less, V: 0.01% or more, 1.0% or less, Zr: 0.01% or more, 1.0% or less, W: 0.01% or more, The duplex stainless steel welding wire with excellent concentrated sulfuric acid corrosion resistance according to claim 1 or 2, characterized in that the wire contains one or more types of 0.5% or less.