Ferritic stainless steel welding wire

Abstract

To provide a ferritic stainless steel welding wire excellent in high-temperature strength and antioxidation property.SOLUTION: A ferritic stainless steel welding wire includes C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.50%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ti: 0.001 to 0.150%, O: 0.020% or less, and N: 0.05% or less in mass%, further includes one kind or two or more kinds selected from Nb: 0.01 to 1.80%, Mo: 0.01 to 3.60%, or W: 0.01 to 3.60%, and satisfies the following expression (1), expression (2), and expression (3), the remaining part having a composition of Fe and inevitable impurities: expression (1) which is [Nb]+[Mo]+[W]+0.25[Si]≥2.2; expression (2) which is [Mo]+[W]≤3.6; and expression (3) which is [Ti]+[Al]≤0.15, [ ] in the expressions showing content mass% of elements in [ ].SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a ferritic stainless steel welding wire.

Background Art

[0002] Ferritic stainless steel is less expensive than austenitic stainless steel, has a low coefficient of thermal expansion so that thermal distortion can be suppressed, and is also excellent in high-temperature oxidation resistance. Therefore, it is widely used in automotive exhaust system parts used in a high-temperature corrosive gas environment. For example, an exhaust manifold for collecting exhaust gas from an engine and sending it to an exhaust pipe, and a case of a converter for purifying exhaust gas by using an oxidation-reduction reaction in the presence of a catalyst can be mentioned. These parts having complex shapes are assembled by welding members made of ferritic stainless steel. Usually, a welding wire made of ferritic stainless steel is used for welding ferritic stainless steel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, as described in Patent Document 1 above, in a conventional ferritic stainless steel welding wire, Nb, Mo, W, etc. are added for the purpose of improving high-temperature strength. In addition, Ti is added to suppress the formation of Nb carbonitrides, which is a factor in the decrease in high-temperature strength due to long-term exposure. However, the addition of Mo, W, and Ti deteriorates the oxidation resistance required for the welding wire.

[0005] The present invention is based on the above circumstances, and an object thereof is to provide a ferritic stainless steel welding wire having excellent high-temperature strength and oxidation resistance.

Means for Solving the Problems

[0006] In the present invention, the effects of various additive components in the ferritic stainless steel welding wire on high-temperature strength and oxidation resistance are investigated, and the degree of influence on high-temperature strength and the degree of influence on oxidation resistance in various additive components are considered, and by appropriately balancing their addition amounts, the high-temperature strength is effectively ensured to be a desired value or more as an overall effect, and at the same time, oxidation resistance is ensured.

[0007] In the present invention, the addition amounts of Nb, Mo, W, and Si, which are effective for improving high-temperature strength, are defined by the following formula (1). However, since the oxidation resistance deteriorates when Mo and W are added in excess, the total amount of Mo and W is defined by the following formula (2). Further, since suppressing the deterioration of weldability is also effective for improving high-temperature strength, the total amount of Ti and Al that affects weldability is defined by the following formula (3).

[0008] Thus, the gist of the present invention is as follows.

[0009] [1] In mass %, C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.50%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ti: 0.001 to 0.150%, O: 0.020% or less, N: 0.050% or less, and furthermore, it contains one or more selected from Nb: 0.01 to 1.80%, Mo: 0.01 to 3.60%, W: 0.01 to 3.60%, and satisfies the following formulas (1), (2), and (3), A ferritic stainless steel welding wire characterized by having a composition in which the balance is Fe and unavoidable impurities. [Nb]+[Mo]+[W]+0.25[Si]≧2.2 ·· Formula (1) [Mo]+[W]≦3.6 ·· Formula (2) [Ti] + [Al] ≤ 0.15 ·· Formula (3) However, in the formula, [ ] represents the mass percentage of the element within [ ].

[0010] [2] By mass, it further contains one or more of Cu: 0.1 to 3.0%, B: 0.01% or less, V: 0.1 to 2.0%, Ta: 0.05 to 0.50%, Zr: 0.001 to 0.010%, Y: 0.001 to 0.010%, and is characterized in that it is the ferritic stainless steel welding wire according to [1].

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a ferritic stainless steel welding wire excellent in high-temperature strength and oxidation resistance.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] The ferritic stainless steel welding wire according to the present embodiment contains C, Si, Mn, P, S, Cr, Ti, O, N, and further contains one or two or more selected from Nb, Mo, and W, and the balance consists of Fe and unavoidable impurities. It may further contain Al, Cu, B, V, Ta, Zr, and Y.

[0014] The reasons for limiting each chemical component in the ferritic stainless steel welding wire of the present embodiment will be described in detail below. In the following description, unless otherwise specified, "%" means "mass %".

[0015] C: 0.001 to 0.050% C is contained in an amount of 0.001% or more from the viewpoint of enhancing the strength of the welded part. However, excessive addition may cause embrittlement of the welded part due to martensite formation and a decrease in ductility and toughness, so the upper limit is set to 0.050%. A more preferable upper limit is 0.042%.

[0016] Si: 0.01 - 2.00% Si is an element effective for suppressing grain boundary precipitation of Nb carbonitride and preventing welding cracks. Also, by containing 0.01% or more, the oxidation resistance characteristics can be enhanced. However, excessive addition may cause deterioration of toughness and suppression of solid solution of Mo, leading to a decrease in mechanical strength, so the upper limit is set to 2.00%. The preferable Si content is 0.30 - 1.95%. Further, a more preferable Si content is 0.30 - 1.00%.

[0017] Mn: 0.01 - 1.50% Mn is used as a deoxidizer during melting. However, excessive addition may generate sulfides and cause a decrease in toughness, so the Mn content is in the range of 0.01 - 1.50%. The preferable Mn content is 0.30 - 0.90%. Further, a more preferable Mn content is 0.40 - 0.80%.

[0018] Cr: 16.0 - 25.0% Cr enhances the strength of the weld metal and forms a dense oxide film on the surface to improve oxidation resistance and corrosion resistance. To exhibit such characteristics, in the present invention, it is contained in an amount of 16.0% or more. However, excessive addition may cause embrittlement, hardening, and a decrease in toughness, so the upper limit is set to 25.0%. The preferable Cr content is 16.5 - 21.0%. Further, a more preferable Cr content is 17.0 - 19.2%.

[0019] Ti: 0.001 - 0.150% Ti forms carbonitrides and refines the crystal grains of the weld metal. Also, it promotes solid solution strengthening by Nb. However, excessive addition may impair weldability, so the Ti content is in the range of 0.001 - 0.150%.

[0020] O: 0.020% or less O forms oxides such as SiO2 and Al2O3, which reduce toughness. Therefore, the amount of O needs to be 0.020% or less.

[0021] N: 0.050% or less N precipitates Cr nitrides and forms a Cr-deficient layer at the grain boundaries. This reduces the corrosion resistance of the welded part, so the amount of N needs to be 0.050% or less. More preferably, it is 0.049% or less.

[0022] P: 0.030% or less, S: 0.010% or less When the amounts of P and S are excessive, welding cracks are likely to occur and the toughness of the welded part decreases. Therefore, the amount of P needs to be 0.030% or less and the amount of S needs to be 0.010% or less.

[0023] Nb: 0.01 - 1.80% Mo: 0.01 - 3.60% W: 0.01 - 3.60% In this embodiment, one or more of Nb, Mo, and W that contribute to the improvement of high-temperature strength are contained.

[0024] Nb is an element effective for improving oxidation resistance and high-temperature strength. However, excessive addition reduces weld crack resistance, so the Nb content is in the range of 0.01 - 1.80%. The preferred Nb content is 0.20 - 1.72%. A more preferred range is 0.20 - 0.80%. Mo improves strength by solid solution strengthening. However, excessive addition saturates the properties and increases the material cost, so the Mo content is in the range of 0.01 - 3.60%. The preferred Mo content is 0.01 - 2.40%. A more preferred range is 1.00 - 2.30%. W improves strength by solid solution strengthening. However, excessive addition causes saturation of the properties and cost increase, so the W content is in the range of 0.01 - 3.60%. The preferred W content is 0.01 - 2.60%. A more preferred range is 0.80 - 2.50%.

[0025] Al: 0.001 - 0.150% Al has the effect of forming nitrides and refining the crystal grains of the weld metal. However, excessive addition will lead to a decrease in toughness and an increase in spatter, so its preferred content is 0.001 - 0.150%.

[0026] Cu: 0.1 - 3.0% Since Cu is effective in improving the tensile strength and corrosion resistance, it can be contained as needed. However, excessive addition will cause a decrease in ductility, so its preferred content is 0.1 - 3.0%.

[0027] B: 0.01% or less Since B is effective in improving the strength by refining the crystal grains of the weld metal, it can be contained as needed. However, excessive addition will cause saturation of the properties, so the preferred content of B is 0.010% or less.

[0028] V: 0.1 - 2.0% Since V improves the strength by solid solution strengthening, it can be contained as needed. However, excessive addition will cause saturation of the properties, so the preferred content of V is 0.1 - 2.0%.

[0029] Ta: 0.05 - 0.50% Ta is a stabilizing element of C and is effective in rust prevention strengthening, so it can be contained as needed. However, excessive addition will cause saturation of the properties, so the preferred content of Ta is 0.05 - 0.50%.

[0030] Zr: 0.001 - 0.010% Since Zr is effective in improving the strength by refining the crystal grains of the weld metal, it can be contained as needed. However, excessive addition will cause saturation of the properties, so the preferred content of Zr is 0.001 - 0.010%.

[0031] Y: 0.001 - 0.010% Since Y is effective for grain refinement, high-temperature oxidation suppression, and improvement of mechanical strength, it can be contained as needed. However, excessive addition causes saturation of properties, so the preferred Y content is 0.001 to 0.010%.

[0032] [Nb] + [Mo] + [W] + 0.25[Si] ≥ 2.2 ·· Equation (1) Nb, Mo, W, and Si have the effect of increasing the high-temperature strength of the welded part. The coefficients of Nb, Mo, W, and Si in Equation (1) represent the contribution degrees to the high-temperature strength respectively. When the value on the left side of Equation (1) is excessively small, the strength improvement by solid solution strengthening becomes insufficient. Therefore, the component adjustment is carried out so that the value on the left side of Equation (1) becomes 2.2 or more. A more preferred value on the left side of Equation (1) is 2.4 or more.

[0033] [Mo] + [W] ≤ 3.6 ·· Equation (2) Mo and W have the effect of increasing the high-temperature strength while deteriorating the oxidation resistance of the welded part. When the total amount of Mo and W, that is, the value on the left side of Equation (2) is excessively large, there is a possibility of forming low-melting point and high-volatility oxides and causing abnormal oxidation. Therefore, the component adjustment is carried out so that the value on the left side of Equation (2) becomes 3.6 or less. A more preferred value on the left side of Equation (2) is 3.4 or less.

[0034] [Ti] + [Al] ≤ 0.15 ·· Equation (3) Ti and Al affect the weldability. Excessive addition of Ti and Al increases the surface tension of the molten metal, so the droplet becomes larger and the droplet transfer is inhibited. Such deterioration of weldability causes welding defects and reduces the strength of the welded part. Therefore, in this example, the component adjustment is carried out so that the value on the left side of Equation (3) becomes 0.15 or less. A more preferred value on the left side of Equation (3) is 0.10 or less.

[0035] The welding wire of this embodiment having the above chemical composition has a ferrite single-phase structure as the main phase. The diameter and length of the welding wire are not particularly limited, and values according to the purpose can be selected. Further, the welding wire of this embodiment may be a solid wire composed only of a ferritic stainless steel, or may be a flux-cored wire containing a flux.

Example

[0036] Next, examples of the present invention will be described below. Here, evaluations of oxidation resistance characteristics and high-temperature strength were performed on weld metals formed using welding wires having the chemical compositions of the examples and comparative examples shown in Table 1 below. Furthermore, in the following, Examples 1 to 14, 28, 37, and 38 are to be read as Reference Examples 1 to 14, 28, 37, and 38, respectively.

[0037]

Table 1a

[0038]

Table 1b

[0039] 1. Preparation of test pieces An alloy having the chemical composition shown in Table 1 above was melted, and hot working and cold working were performed on the obtained ingot to produce a welding wire having a diameter of φ1.2 mm.

[0040] Next, as shown in FIG. 1, a commercially available SUS430 steel plate with a thickness of 20 mm that was buttering welded to the groove surface using the welding wire was used as the test base material, and MIG welding was performed on the groove portion using the welding wire under the conditions shown below to form a weld metal. Welding conditions: welding current 200 A, arc voltage 3.5 V, welding speed 60 cm / min, Interpass temperature 150 to 250 °C, and Ar + 2 vol% O2 was used as the shielding gas.

[0041] Then, as shown in Fig. 1, in accordance with JIS Z 3111, a round bar tensile test piece for high-temperature strength evaluation was taken from the welded part (weld metal) along the welding line direction so that the entire test piece was made of weld metal. Also, a test piece for oxidation resistance evaluation was taken from this welded part.

[0042] 2. Evaluation 2-1. Oxidation Resistance Using the test piece (size: 1.5×15×25 mm) taken from the welded part, a continuous oxidation test was carried out at 900 °C × 200 hr in air in accordance with JIS Z 2281, and the oxidation weight gain was measured. The judgment criteria were as follows. ◎: Oxidation weight gain 2.5 mg / cm 2 Below ○: Oxidation weight gain over 2.5 to 4.0 mg / cm 2 ×: Oxidation weight gain over 4.0 mg / cm 2 Over Here, considering the oxidation resistance required for the welding wire of ferritic stainless steel, when the oxidation weight gain was 4.0 mg / cm 2 or less, that is, in the case of the above "◎" or "〇", it was judged as qualified. The results are shown in Table 2 below.

[0043] 2-2. High-temperature Strength Using the round bar tensile test piece taken from the welded part, a high-temperature tensile test was carried out at 900 °C in accordance with JIS G0567, and the tensile strength was measured. The judgment criteria were as follows. ◎: Tensile strength 40 MPa or more ○: Tensile strength 35 to less than 40 MPa ×: Tensile strength less than 35 MPa Here, in order to ensure that the welded part does not become the weakest part even when SUS444 is used as the base material, when the tensile strength was 35 MPa or more, that is, in the case of the above "◎" or "〇", it was judged as qualified. The results are shown in Table 2 below.

[0044]

Table 2a

[0045]

Table 2b

[0046] From the evaluation results in Table 2, the following can be understood. Comparative Example 1 is an example where C is added in excess of the upper limit of 0.05% of the present invention and does not satisfy the conditions of formula (1) regarding high-temperature strength. In this Comparative Example 1, the tensile strength at high temperatures is low.

[0047] Comparative Example 2 is an example where C is added in excess of the upper limit of 0.05% of the present invention and Cr is below the lower limit of 16.0% of the present invention. There is a large increase in oxidation and the oxidation resistance characteristics are low. Also, this Comparative Example 2 does not satisfy the conditions of formula (1) regarding high-temperature strength, and the value of the tensile strength at high temperatures is also low.

[0048] Comparative Example 3 is an example where Si is added in excess of the upper limit of 2.00% of the present invention. Excessive Si reduces the toughness of the welded part. Therefore, in Comparative Example 3, the value of the tensile strength at high temperatures is low.

[0049] Comparative Example 4 is an example where Al is added in excess of the upper limit of 0.15% of the present invention and does not satisfy the conditions of formula (3) regarding weldability. Adding an appropriate amount of Al contributes to grain refinement, but when excessive Al is added and does not satisfy the conditions of formula (3) regarding weldability, welding defects are likely to occur, and in this Comparative Example 4, the value of the tensile strength at high temperatures is low.

[0050] Both Comparative Example 5 and Comparative Example 6 are examples where Cu is added in excess of the upper limit of 3.0% of the present invention. Excessive addition of Cu reduces the toughness ductility of the welded part. Therefore, in Comparative Example 5 and Comparative Example 6, the value of the tensile strength at high temperatures is low.

[0051] As described above, in each comparative example, the evaluation of at least one of the oxidation resistance characteristics and high-temperature strength is unqualified (「×」).

[0052] In contrast, in Examples 1 to 38 where the chemical composition of the welding wire is within the scope of the present invention, both the oxidation resistance characteristics and the high-temperature strength evaluations are qualified (either "◎" or "○"). For example, when paying attention to Examples 1 to 7, it can be seen that when the value on the left side of formula (1) regarding high-temperature strength is large, the value of the tensile strength is large, indicating that the high-temperature strength is improved. In Examples 8 to 14 to which Al is added, the value of the tensile strength is larger than that in Examples 1 to 7 without Al addition, and the effect of improving the high-temperature strength by adding Al is recognized. In Examples 15 to 18 to which Cu is added, both the oxidation resistance characteristics and the high-temperature strength are improved compared to Examples 1 to 7 without Cu addition. Regarding Examples 19 to 36 to which any one of Cu, B, V, Ta, Zr, and Y is added together with Al, both the oxidation resistance characteristics and the high-temperature strength are improved compared to Examples 1 to 7.

[0053] Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

Claims

1. By mass percentage, C: 0.001 to 0.050%, Si: 0.01 to 2.00%, Mn: 0.01 to 1.50%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ti: 0.001 to 0.150%, O: 0.020% or less, N: 0.050% or less, and furthermore, Nb: 0.01 to 1.80%, Mo: 0.01 to 3.60%, W: containing one or more selected from 0.01 to 3.60%, furthermore, Cu: 0.1 to 3.0%, B: 0.01% or less, V: 0.1 to 2.0%, Ta: 0.05 to 0.50%, Zr: 0.001 to 0.010%, Y: 0.001 to 0.010%, including any one or more of them, and furthermore optionally, Al: 0.001 to 0.150%, and satisfying the following formulas (1), (2), and (3), A ferritic stainless steel welding wire characterized in that the balance has a composition of Fe and inevitable impurities. [Nb] + [Mo] + [W] + 0.25[Si] ≥ 2.2 ··· Formula (1) [Mo] + [W] ≤ 3.6 ··· Formula (2) [Ti] + [Al] ≤ 0.07 ··· Formula (3) However, in the formula, [ ] represents the mass percentage of the element within [ ].

2. In Claim 1, by mass percentage, Cu: 0.1 to 2.20%, B: 0.006% or less, V: 0.1 to 1.20%, Ta: 0.05 to 0.30%, Zr: 0.001 to 0.006%, Y: 0.001 to 0.006%, A ferritic stainless steel welding wire further containing any one or more of them.

3. In any one of Claims 1 and 2, A ferritic stainless steel welding wire characterized in that the N is 0.049 mass% or less.

4. In any one of Claims 1 to 3, A ferritic stainless steel welding wire characterized in that the Cr is 17.0 to 19.2 mass%.

5. In any one of Claims 1 to 4, A ferritic stainless steel welding wire characterized in that the C is 0.042 mass% or less.

6. In any one of Claims 1 to 5, A ferritic stainless steel welding wire characterized in that the Ti is 0.001 to 0.03 mass% and the Al is 0.001 to 0.06 mass%.

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