JPH10102212A - Ferritic stainless steel sheet excellent in penetration at welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless steel sheet capable of having stable and excellent penetration at welding. SOLUTION: This steel sheet has a composition containing, by weight, <=0.05% C, <=0.02$ N, <=1.0% Si, <=1.0% Mn, <=0.04% P, <=0.02$ S, 10.0-30.0% Cr, <=1.0% Ni, and <=0.2% Al, also containing oxygen (O), Al2 O3 , and CaO in the steel so that the relation of inequality 0.0005wt.%<=Owt.%-0.5Al2 O3 wt.%-0.3CaOwt.%<=0.021wt.% is satisfied, and having the balance iron with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel sheet having excellent penetration during welding, and
The present invention relates to a ferritic stainless steel sheet having sufficient penetration when TIG welding a steel sheet having a thickness of not more than mm and having excellent welding workability.

[0002]

2. Description of the Related Art Various containers made of stainless steel,
Products such as structures or pipes are generally manufactured by welding. Among the welding methods, when a thin steel plate or a thin steel strip having a thickness of about 4 mm or less is used as a material, TIG welding is often applied. As is well known, these welded products
In addition to the absence of defects such as cracks in the weld,
Since it is required to be able to withstand loads such as compression and impact, a sound welded part having sufficient penetration during welding is required. On the other hand, especially in the welding of ferritic stainless steel sheets, there is a concern about coarsening of the crystal grains in the welded area. Desirably as little as possible. Therefore, when considering the quality and economics of the welded part, excellent penetration during welding enables welding with lower heat input, and stainless steel materials that meet these conditions are stronger. desired.

[0003] In spite of such demands, in practice, for example, when SUS430 is welded under the same welding conditions, the welded portion expressed by the ratio of the penetration search to the bead width or the ratio of the front and back bead widths. There is an example in which the dissolution properties of the steel are greatly different. Several studies have been made on such a penetration phenomenon. For example, there are studies on the effects of oxygen, sulfur and the like on the penetration of general steel materials by paton et al., And studies on the effects of oxygen, sulfur, aluminum and calcium on the penetration of stainless steel by P. Burgardt et al.

[0004]

However, the inventors of the present invention conducted welding of stainless steel sheets with the same chemical components and examined the state of penetration, and found that despite the fact that the chemical components were the same, It often encountered that the amount of penetration fluctuated and stable penetration could not be obtained.
As described above, the amount of penetration is not necessarily determined only by the contents of oxygen, sulfur, aluminum, calcium, etc. in steel, and even if the contents of these components are controlled, stable penetration welding cannot be performed. there were. Moreover, it has not been possible to stably obtain the above-described good penetration.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ferritic stainless steel sheet that has good and stable penetration during welding. Another object of the present invention is to provide a ferritic stainless steel sheet that has good penetration and can be stably obtained, particularly when TIG welding a steel slab having a thickness of 4 mm or less.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors focused on the form of oxygen in ferritic stainless steel and conducted detailed research on the effect of this on the penetration. It has been found that the object can be achieved by controlling the amount of oxygen in consideration of the contents of Al ₂ O ₃ and CaO in the oxide-based nonmetallic inclusions. The present invention has been completed based on this finding, and the gist configuration thereof is as follows.

(1) C: 0.05 wt% or less, N: 0.02 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.04
wt% or less, S: 0.02wt% or less, Cr: 10.0-30.0wt%,
Ni: 1.0 wt% or less, Al: 0.2 wt% or less, oxygen (O), Al ₂ O ₃ and CaO in the steel are represented by the following formula: 0.0005 wt% ≦ O wt% −0.5 Al ₂ O ₃ wt% − 0.3 CaOwt% ≦
A ferritic stainless steel sheet with excellent weld penetration, characterized by containing 0.012 wt% and the balance being iron and unavoidable impurities.

(2) In the above (1), the steel composition further contains one or two kinds selected from Cu: 3.0 wt% or less and Mo: 4.5 wt% or less, with the balance being iron and unavoidable impurities. A ferritic stainless steel sheet with excellent weld penetration characteristics.

(3) In the above (1) or (2), the steel composition further has a relationship of Ti: 5 (Cwt% + Nwt%) 〜1.0 wt% Nb: 5 (Cwt% + Nwt%) 〜1.0 wt% A ferritic stainless steel sheet excellent in weld penetration, characterized by containing one or two kinds of Ti and Nb in a range to be satisfied and the balance being iron and unavoidable impurities.

(4) In the above (1), (2) or (3),
A ferritic stainless steel sheet having excellent weld penetration, wherein the steel composition further contains Ca: 0.0003 to 0.0030 wt%, with the balance being iron and unavoidable impurities.

(5) In the above (1), (2), (3) or (4), the steel composition further contains B: 0.0030% by weight or less, with the balance being iron and unavoidable impurities. A ferritic stainless steel sheet with excellent weld penetration characteristics.

[0012]

Next, the reason why the gist of the present invention is limited to the above range will be described. C: 0.05 wt% or less C has a small solid solubility limit in ferritic stainless steel, and mainly precipitates as Cr carbide to cause intergranular corrosion. In order to improve the toughness of the weld metal, it is desirable that the amount is as small as possible. However, up to 0.05 wt% is acceptable, so the C content is in the range of 0.05 wt% or less.

N: 0.02 wt% or less N has a small solid solubility limit in ferritic stainless steel, precipitates as Cr nitride, and causes intergranular corrosion. Therefore, N is preferably as small as possible. In order to improve the toughness of the weld metal, it is desirable that the amount is as small as possible. However, up to 0.02 wt% is acceptable, so the N content is in the range of 0.02 wt% or less.

Si: 1.0 wt% or less Si is an element useful as a deoxidizing material for ferritic stainless steel, but is also an element that lowers toughness and increases yield strength. When the content of Si exceeds 1.0 wt%, this adverse effect becomes remarkable.
It is particularly desirable to refrain from adding as much as possible except when high strength is required.

Mn: 1.0 wt% or less Mn has little effect on toughness, but Mn is desirably low in content because it forms sulfides in steel and deteriorates corrosion resistance. However, it is also an element generally used as a deoxidizer, and the upper limit is set to 1.0 wt% in consideration of economical efficiency at the time of production.

P: 0.04 wt% or less P is an element that lowers toughness and hot workability.
A smaller amount is desirable, but up to 0.04 wt% is acceptable.

S: 0.02 wt% or less S is an element which lowers hot workability and corrosion resistance. It is desirable that S is small, but it is acceptable up to 0.02 wt%.

Cr: 10.0 to 30.0 wt% Cr is an element that improves corrosion resistance, particularly pitting corrosion resistance, and is indispensable when stable corrosion resistance is required over a long period of time in an environment where chlorine ions are present. . Such an effect can be obtained by adding 10.0 wt% or more,
If added in excess of wt%, the productivity will deteriorate.
Add in the range of ~ 30.0 wt%.

Ni: 1.0 wt% or less Ni improves pitting corrosion resistance, but a large amount of Ni significantly increases the mechanical strength, so Ni is added in a range of 1.0 wt% or less.

Al: 0.2 wt% or less Al has the effect of detoxifying C and N remaining as impurities during steel melting and preventing intergranular corrosion, in addition to acting as a deoxidizing agent. On the other hand, Al is also an element that selectively oxidizes during annealing to form a dense surface oxide film and deteriorates descalability. Considering these, the amount of Al added is 0.2 wt.
% Or less. In addition, from the point of descalability, it is desirable to set the content to 0.02 wt% or less.

Cu: 3.0 wt% or less Cu improves corrosion resistance, but when added in a large amount, impairs hot workability and increases the susceptibility to hot cracking. Therefore, the upper limit of the content is set to 3.0 wt%.

Mo: 4.5 wt% or less Mo is an element effective for improving corrosion resistance, particularly pitting corrosion resistance and repassivation ability, and is stable for a long time in an environment where chloride ions are present. It is essential when corrosion resistance is required. To achieve this effect, use 0.
Addition of 5 wt% or more is desirable. However, if a large amount of Mo is added, not only does the corrosion resistance improving effect become saturated, but rather the workability is reduced, so that Mo is added in a range of 4.5 wt% or less.

Ti: 5 (Cwt% + Nwt%) to 1.0 wt% Nb: 5 (Cwt% + Nwt%) to 1.0 wt% Both Ti and Nb detoxify C and N remaining as impurities during steel melting. , Is an element effective in suppressing intergranular corrosion, particularly intergranular corrosion in the weld heat affected zone. Such an effect can be obtained by adding 5 times or more of the total content of C and N (Cwt% + Nwt%). However, if it is too much, it impairs the workability. % +
N wt%) to 1.0 wt%.

Ca: 0.0003-0.0030wt% Ca is an element effective for preventing nozzle clogging during continuous casting and preventing the occurrence of defects such as swollen steel strips. Of inclusions and deteriorate the corrosion resistance. Therefore, Ca is added in the range of 0.0003 to 0.0030 wt%.

B: 0.0030 wt% or less B is an element for improving corrosion resistance. However, if added in a large amount, hot workability is impaired, so B is added in an upper limit of 0.0030 wt%.

0.0005 wt% ≦ O wt% −0.5 Al ₂ O ₃ wt% −0.2
3 CaO wt% ≦ 0.012 wt% The inventors of the present invention have pursued the phenomenon mentioned above that causes a difference in the penetration performance even though the chemical components are almost the same. A detailed study was done on the impact. As a result, they found that the form of oxygen in the base material had a great effect on the penetration. That is, although aluminum in steel is considered to exist in the form of Al ₂ O ₃ , AlN, etc., particularly, Al ₂ O ₃ has a high melting point and is not easily decomposed even in a molten pool formed during welding. It is considered that the oxygen effective for the penetration is the dissolved oxygen in the molten pool, and the oxygen existing as Al ₂ O ₃ does not substantially contribute to the penetration. Al ₂ O ₃ for CaO
Is considered to be the same as

FIG. 1 shows an experiment based on this concept.
(11-23wt%) Cr- (0-2wt%) Mo on the penetration amount when a 2mm thick ferritic stainless steel cold-rolled steel plate based on Mo is tanned (in the state of bead-on-plate) by TIG welding It is an investigation of the effects of oxygen and the above oxides. Here, welding conditions were such that welding was performed with a positive polarity using a welding power source having a DC drooping characteristic. The tungsten electrode used had a diameter of 3.2 mm, and the shield was argon gas 15 liter / min on the front side and 10 liter / min on the back side.
And The welding position was downward, the welding current was 200 A, the welding voltage was 16 V, and the welding speed was 0.6 m / min. As the obtained weld penetration properties, the ratio of the front and back weld bead widths (= back bead width / front bead width) was measured for each of five cross sections and evaluated using the average value. For the determination of Al ₂ O ₃ and CaO, the ICP emission spectral analysis value of the oxide extracted by the bromine-methanol method was used. The method of extraction and analysis of oxide is as follows: First, immerse the sample in a 10% bromine-methanol solution at 60 ° C,
The product was decomposed with ultrasonic shaking, and the residue was filtered and washed. The product was reduced and melted in a platinum crucible, dissolved in acid, and analyzed by ICP.

As is apparent from FIG. 1, the penetration is Owt.
% -0.5Al ₂ O ₃ can be organized by wt% -0.3 CaOwt%, this value it can be seen that penetration is significantly improved when the above 0.0005wt%. However, even if the amount of oxygen becomes excessive, not only does the penetration become saturated, but also the corrosion resistance decreases.
Therefore, the value of _{Owt% -0.5Al 2 O 3 wt%} -0.3 CaOwt% is more than 0.0005wt%, it is necessary to control the range of 0.012 wt% or less.

[0029] It should be _{noted, Owt% -0.5Al 2 O 3 wt} % -0.3 CaO
As a specific control method of the wt% value, in order to increase the value, for example, a decrease in the addition amount of Al or Ca, an increase in the addition amount of Si, a decrease in the basicity of VOD slag, or the like, In order to decrease the amount, for example, treatments such as an increase in the amount of Al or Ca added and an increase in the basicity of VOD slag may be performed, and these may be appropriately combined. Other manufacturing conditions for manufacturing the ferritic stainless steel sheet according to the present invention may be in accordance with a conventional method.As preferable conditions, for example, hot rolling is performed by heating at 1035 to 1300 ° C., followed by rough rolling. The total rolling reduction is 95% or less, the total rolling reduction is 97% or less in finish rolling, and the cold rolling is performed with a total rolling reduction of 90% or less using a Sendzimir rolling mill or the like, and the annealing is performed at a temperature of 700 ° C or more. Is mentioned. After the annealing, the scale removal treatment is usually performed by solely or in combination of pickling using sulfuric acid, hydrochloric acid, a mixed acid of nitric acid and hydrofluoric acid, and electrolytic treatment.

[0030]

EXAMPLES Steel having the chemical composition shown in Table 1 was melted in a 50 kg high-frequency vacuum melting furnace, heated to 1250 ° C., and reduced to a total reduction rate of 90%.
%, Followed by cold rolling at a total reduction of 35%,
After annealing at 880 to 950 ° C. for 3 minutes, the scale was removed using a mixed acid of nitric acid and hydrofluoric acid to produce a cold-rolled annealed pickled plate having a thickness of 2 mm. At this time, the addition amount of deoxidizing elements, the order of addition, by changing the deoxidation time and stirring conditions, OWT% of various values -0.5Al ₂ O ₃ wt% -0.3
A steel sheet of CaO wt% was used.

[0031]

[Table 1]

These steel sheets were tanned and welded, and the penetration amount was evaluated. Here, welding conditions were such that welding was performed with a positive polarity using a welding power source having a DC drooping characteristic. The tungsten electrode used had a diameter of 3.2 mm, and the shield was argon gas at 15 liter / min on the front side and 10 liter / min on the back side. The welding position is downward, welding current is 200A, welding voltage is 16
V, the welding speed was 0.6 m / min. As the obtained weld penetration properties, the ratio of the front and back weld bead widths (= back bead width / front bead width) was measured for each of five cross sections and evaluated using the average value. For the determination of Al ₂ O ₃ and CaO, the ICP emission spectral analysis value of the oxide extracted by the bromine-methanol method was used. The method of extraction and analysis of oxide
After being immersed in a 10% bromine-methanol solution at 60 ° C. and decomposed with ultrasonic shaking, the residue was filtered and washed, reduced and melted in a platinum crucible, dissolved in acid, and analyzed using ICP. . The results obtained are shown in Table 1.

[0033]

[Table 2]

As is clear from Table 1, the ratios of the back bead width / the front bead width of each of the invention examples are 0.7 or more, indicating excellent penetration. Moreover, although not shown in the table, it was found that even if these values were repeatedly measured, the fluctuation range was small and extremely stable penetration was obtained. On the other hand, in the comparative example, sufficient penetration was not obtained.

[0035]

As described above, according to the present invention,
It is possible to provide a ferritic stainless steel sheet capable of obtaining a sufficient and stable penetration during TIG welding. Therefore, according to the present invention, in TIG welding of a ferritic stainless steel sheet, it is possible to obtain a sound weld having no weld defects, and to perform sound welding even at a lower heat input than before. It greatly contributes to improving the quality of welds and improving economic efficiency.

[Brief description of the drawings]

[1] OWT% on penetration amount -0.5Al ₂ O ₃ wt% -
It is a graph which shows the influence of 0.3 CaOwt%.

Claims (5)

[Claims] C: 0.05 wt% or less, N: 0.02 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.04 wt% or less, S: 0.02 wt% or less, Cr: 10.0 330.0 wt%, Ni: 1.0 wt% or less, Al: 0.2 wt% or less, and oxygen (O), Al ₂ O ₃ and CaO in the steel are represented by the following formula: 0.0005 wt% ≦ O wt% −0.5Al ₂ O ₃ wt% -0.3 CaOwt% ≦
A ferritic stainless steel sheet with excellent weld penetration, characterized by containing 0.012 wt% and the balance being iron and unavoidable impurities. 2. The steel composition according to claim 1, wherein the steel composition further contains one or two selected from Cu: 3.0 wt% or less and Mo: 4.5 wt% or less, with the balance being iron and unavoidable impurities. A ferritic stainless steel sheet that has excellent weld penetration characteristics. 3. The steel composition according to claim 1, wherein the steel composition further satisfies the relationship of Ti: 5 (Cwt% + Nwt%) to 1.0 wt% Nb: 5 (Cwt% + Nwt%) to 1.0 wt%. A ferritic stainless steel sheet having excellent weld penetration, characterized by containing one or two of Nb and Nb, with the balance being iron and unavoidable impurities. 4. The ferrite according to claim 1, wherein the steel composition further comprises 0.0003 to 0.0030 wt% of Ca, with the balance being iron and unavoidable impurities. Stainless steel sheet. 5. The steel according to claim 1, wherein the steel composition further comprises: B: 0.0030% by weight or less, with the balance being iron and unavoidable impurities, and having excellent weld penetration. Ferritic stainless steel sheet.