KR20020096446A - Flux cored wire for ferritic stainless steel - Google Patents

Abstract

PURPOSE: A flux cored wire for welding ferritic stainless steel is provided, which shows low welding cracks such as brittleness cracks and high temperature cracks as well as obtains stable welding bead at welded part of stainless steel. CONSTITUTION: The flux cored wire includes a sheath comprising C<=0.03 wt.%, Si<=0.03 wt.%, Mn 0.15 to 0.45 wt.%, P<=0.02 wt.%, S<=0.02 wt.%; a core comprising C<=0.02 wt.%, N<=0.02 wt.%, P<=0.02 wt.%, S<=0.01 wt.%, Cr 14.5 to 25.0 wt.%, Ti 0.3 to 4.0 wt.%, Mo+W 0.1 to 3.0 wt.%, TiO2 1.0 to 5.0 wt.%, SiO2 0.3 to 3.5 wt.%, Mn 0.5 to 3.0 wt.%, based on the total weight of the flux cored wire, wherein compounding ratio (A) of TiO2, SiO2 and Mn is controlled within the range of 0.5 to 23.3 according to the below equation: A=((TiO2/2)+SiO2)/(1.2912xMn).

Description

Flux cored wire for ferritic stainless steel

The present invention relates to a flux cored wire for welding ferritic stainless steel, and more particularly, to a flux cored wire for welding ferritic stainless steel, which is excellent in oxidation resistance and has a significant reduction effect of welding crack generation.

As exports of automobiles spread to various parts of the world with various climates, the physical properties required for the exhaust system of automobiles are becoming more stringent, and the production of raw materials with high chromium content is increasing according to these demands. In addition, ferritic stainless steel is superior to austenitic stainless steel in terms of high temperature oxidation resistance, thermal fatigue resistance, and high temperature strength. Therefore, the ferritic stainless steel is oxidized or heated and cooled at a high temperature of about 800 to 1000 ° C. It is used a lot in the situation. Accordingly, there is a demand for development of a welding material having excellent physical properties at high temperatures and excellent workability, suitable for welding such high chromium-containing steel or ferritic stainless steel.

On the other hand, ferritic stainless steel welding materials are generally used for thin plate welding for single pass, and in thin plate welding, welding is often performed under low current and low voltage conditions in order to prevent the welding part from falling down. However, the conventional ferritic welding material has a large amount of spatters generated under low current and low voltage conditions, and an arc is unstable, resulting in poor welding workability.

In view of the above problems, Japanese Laid-Open Patent Publication No. 06-000691 uses ferritic stainless steel containing neobium (Nb) specified in JIS SUS 430LX, SUS 444, etc. as the shell of the wire, and the filled flux is chromium. The content of 16 to 25% by weight was intended to improve the physical properties and workability of the wire. However, when ferritic stainless steel is used as the outer shell, not only the shell itself is expensive, but also heat treatment at about 1100 ° C must be accompanied to reduce the work hardening that occurs during drawing. The problem of increased production costs could not be solved.

In Japanese Patent Application Laid-Open No. 09-085491, an attempt was made to obtain a cost reduction effect by using a mild steel outer shell instead of using ferritic stainless steel as an outer shell, but it was not sufficient to maximize the effect of freshness by simply using a mild steel outer shell. . In other words, it was not possible to solve the problem that must be accompanied by heat treatment to alleviate the work hardening occurs during the drawing.

Therefore, the present inventors limited the outer shell of the flux cored wire to ultra-soft steel and at the same time studied the composition of the internal flux by inclining the cardioids. A flux cored wire for welding ferritic stainless steel is disclosed.

It is an object of the present invention to provide a flux cored wire for welding ferritic stainless steel, which has a low manufacturing cost and improved oxidation resistance, corrosion resistance, and welding workability by filling flux optimized for the outer steel sheet.

1 is a schematic view showing a method for measuring the chemical composition of the deposited metal.

2 is a schematic diagram illustrating a method of evaluating arc stability.

The above object of the present invention is an electrode according to the JIS G3141 standard that the shell of the flux cored wire contains C ≤0.03%, Si ≤0.03%, Mn 0.15 ~ 0.45%, P ≤0.02%, S ≤0.02% Flux is 0.1 to 3.0 by adding C ≤0.02%, N ≤0.02%, P ≤0.02%, S ≤0.01%, Cr 14.5-25.0%, Ti 0.3-4.0%, Mo and W based on the total weight of wire %, TiO ₂ 1.0 ~ 5.0%, SiO ₂ 0.3 ~ 3.5%, Mn 0.5 ~ 3.0%, but TiO ₂ , SiO ₂ and Mn have a combination ratio (A) of the formula (1) in the range of 0.5 to 23.3 It is achieved by a flux cored wire for welding ferritic stainless steel characterized by its satisfactory.

‥‥‥ Formula (1)

Hereinafter, the role of each component and the reason of numerical limitation according to the above structure of this invention are demonstrated.

In the present invention, the manufacturing cost was lowered by using mild steel instead of stainless steel as the shell of the flux cored wire. In particular, mild mild steel specified in JIS G3141 is used among mild steel to minimize the problems that may occur during drawing. The extreme mild steel stipulated in JIS G3141 refers to steel satisfying C ≦ 0.03%, Si ≦ 0.03%, Mn 0.15 to 0.45%, P ≦ 0.02%, and S ≦ 0.02%.

In the present invention, the reason for using the ultra-mild steel that satisfies the above specification is as follows. The reason why C is set to 0.03% or less is to make the transition form of arc even in the condition of low current and low voltage. In addition, when the content of C is high, it is preferable to define C in the shell to 0.03% or less because it combines with Ti, Mo, N, Cr, and the like to form carbides or carbonitrides to reduce toughness and cause cracking. Si controls the Si content contained in the weld metal during welding and improves workability by generating a small amount of SiO ₂ , but in order to beautify the appearance of the beads, it is defined as 0.03% or less. It is preferable. Mn plays a role as a deoxidizer and contributes to the improvement of arc stability together with TiO ₂ and SiO ₂ , but MnO is preferably 0.15 to 0.45% because it may affect the appearance of beads. In the case of P and S, there is a problem in that toughness is reduced and cracks are generated as impurities, but considering the manufacturing cost, it is preferably 0.02% or less.

Next, the flux composition of this invention is demonstrated.

Japanese Patent Laid-Open No. 7-124785 discloses a method of adding Nb as a method of reducing brittle cracks, high temperature cracks, and the like, which are commonly generated in welds. However, the inventors of the present invention consider the solid solution limits of C and N in the body-centered cubic structure of ferrite, and therefore, do not add Nb when limiting the contents of C and N and controlling extremely small amounts of impurities such as P and S. It has been found that it is possible to significantly reduce the occurrence of weld cracking. Thus, the present invention has been completed, and the effects will be fully described below. On the other hand, it is noted that all% described below is% by weight unless otherwise specified.

Since C in the flux combines with Ti, Mo, N, Cr and the like to form carbides or carbonitrides to reduce toughness and cause cracking, the C content in the flux is preferably 0.02% or less. In addition, the content of N was also limited to 0.02% or less for the same reason as in the case of C. By limiting the content of C and N to 0.02% or less in this way it is incidentally obtained the effect of stabilizing the ferrite structure. Since P and S in the flux are impurities, the toughness is lowered and cracks are generated. Therefore, the content is preferably limited to P 0.02% or less and S 0.01% or less.

Cr is an element that expands the ferrite region and at the same time forms Cr ₂ O ₃ to improve corrosion resistance. Since the content of Cr is related to the content of other flux constituents, the content of Cr may vary slightly depending on the content of Ti, C, and N. In this specification, the minimum value of the content is 14.5%. As the content of Cr increases, the effect of corrosion resistance also increases, but when it exceeds 25%, the ductility decreases, and the Cr content is higher than that of the base metals such as SUS 430LX, SUS436L, and SUS444. This causes coarse grains in the heat-affected zone (HAZ) which rises to a temperature of 1100 ° C. or higher, resulting in a significant decrease in ductility and toughness. On the other hand, Cr may be added in the form of Cr oxide or Cr alloy, wherein the content of Cr should be converted to Cr conversion value.

Ti, as a ferrite stabilizing element, has an effect of miniaturizing crystal grains when bonded with N and improving corrosion resistance. If the content of Ti is 0.3% or less, the desired degree of corrosion resistance cannot be obtained. If the content of Ti is more than 4.0%, it helps the microstructure of the tissue but causes brittleness. Therefore, the content of Ti is preferably 0.3 to 4.0%.

Mo and W are elements for improving high temperature strength and high temperature salt resistance, but have a problem of coarsening due to a slow precipitation rate of the Laves phase, but have an effect of reducing heat resistance deterioration. In addition, Mo has an effect of improving the high temperature corrosion resistance because it performs the repair action when the corrosion resistant film such as Cr oxide is destroyed. If the total content of Mo and W is 0.1% or more, heat resistance and corrosion resistance are improved in proportion to the content, but the total content of Mo and W is preferably 3% or less. If it exceeds 3%, it not only inhibits the ductility of the weld metal but also increases the cost in terms of economy.

Since the welding conditions of ferritic stainless steel are mainly low current and low voltage, the addition of iron alloy to improve the arc stability under these conditions has resulted in the tendency of the arc to become strong and the smoothing of the welding. The problem with the increase in the amount of data was shown. As a result of examining and testing various methods to improve this phenomenon, it was possible to secure stability of arc and dropping by appropriately adjusting the combination ratio of oxides.

In the present invention, TiO ₂ and SiO ₂ are used as oxides, and both of them serve as slag formers and arc stabilizers. In the present invention, since the TiO ₂ , SiO ₂ and Mn are added to stabilize the arc, the combination ratio (A) of TiO ₂ , SiO _2, and Mn becomes an important factor. The combination ratio A represented by the following formula (1) must satisfy the range of 0.5 to 23.3.

‥‥‥ Formula (1)

TiO ₂ is a component that plays a role of a slag forming agent and an arc stabilizer together with SiO _2, and improves the appearance of the beads after welding and improves the concentration of the arc to suppress spatter generation. At this time, the contents of TiO ₂ and SiO ₂ preferably satisfy the above formula (1) while satisfying the ranges of 1.0 to 5.0% and 0.3 to 3.5%, respectively. This is because if the TiO ₂ is less than 1.0%, it is impossible to secure a sufficient amount of slag, and if it exceeds 5.0%, the arc becomes unstable and the welding workability is deteriorated. In addition, when SiO ₂ is less than 0.3%, it is difficult to secure stability of the arc, and when it exceeds 3.5%, there is a problem in that slag peelability is lowered. Therefore, the desired effect can be obtained only when TiO ₂ and SiO ₂ satisfy the respective ranges and satisfy the combination ratio of the above formula (1).

Mn is added not only for deoxidation of the weld metal, but also in order to sufficiently secure the tensile strength required in ferritic stainless steel. The content of Mn must satisfy 0.5 to 3.0% and at the same time satisfy the condition of Formula (1). When Mn meets the combination ratio according to Equation (1) together with TiO ₂ and SiO ₂ , the stability of the arc is sufficiently secured to maintain uniformity of arc transition even at low current and low voltage, and the amount of spatter generated is also reduced. Will appear.

On the other hand, the flux described so far should be filled in 15 ~ 30% in the ultra-fine steel shell having a specific specification above. If the amount of the flux is less than 15%, the content of Cr, Mo, etc. is insufficient, so that the corrosion resistance is lowered. Therefore, the filling rate of the flux is preferably 15 to 30%.

Hereinafter, the present invention will be further embodied by the following examples, but the present invention is not limited by the following examples.

Table 1 shows the contents of the flux constituents applied to the invention examples and comparative examples, the filling rate of the flux was limited to 21% of the total weight of the wire, the final wire diameter was 1.2mm.

division Flux component (% by weight of wire total) TiO ₂ SiO2 Cr Mo Mn Si Ti C Combination Ratio (A) Comparative example One 0.36 0.11 13.45 0.08 0.47 0.30 0.24 <0.01 0.48 2 0.23 0.12 14.27 0.07 0.45 0.42 0.11 <0.01 0.40 3 4.20 3.29 26.30 0.07 0.15 0.42 0.28 <0.01 27.83 Inventive Example 4 1.32 0.56 15.80 0.89 0.52 0.15 0.86 <0.01 1.82 5 1.97 0.65 16.45 1.02 0.80 0.31 1.27 <0.01 1.58 6 2.50 1.20 18.00 1.02 0.88 0.45 1.75 <0.01 2.16 7 3.52 1.78 19.03 1.37 0.90 0.33 2.33 <0.01 3.05 8 3.98 2.03 22.45 1.67 1.10 0.33 2.69 <0.01 2.83 9 4.00 2.10 23.10 1.67 1.10 0.33 2.69 <0.01 2.89 10 4.00 2.10 23.10 2.00 0.52 0.28 2.69 <0.01 6.11

Welding current 180 ~ 240A, welding voltage 25 ~ 32V, welding speed 20 ~ 30cm / min, shielding gas 100 on 12mm thick SUS 436 steel plate using ferritic stainless steel welding flux cored wire manufactured as described above. Welding was performed under the condition of% CO ₂ . After welding, the components of the weld metal are shown in Table 2, and the results of welding workability evaluation are shown in Table 3. The weld metal chemistry of Table 2 was measured according to JIS Z 3183. Referring to FIG. It is measured after.

division Result of chemical composition analysis of weld metal (wt%) C P S Si Mn Cr Mo Ti Comparative example One 0.032 0.015 0.008 0.319 0.617 13.019 0.085 0.077 2 0.038 0.022 0.009 0.447 0.591 13.813 0.078 0.082 3 0.040 0.024 0.012 0.447 0.197 25.458 0.078 0.151 Inventive Example 4 0.034 0.018 0.007 0.160 0.683 15.294 0.994 0.091 5 0.034 0.026 0.005 0.330 1.050 15.923 1.139 0.095 6 0.035 0.028 0.005 0.479 1.155 17.423 1.139 0.104 7 0.036 0.025 0.012 0.351 1.181 18.421 1.530 0.110 8 0.036 0.023 0.014 0.351 1.444 21.731 1.865 0.129 9 0.037 0.026 0.009 0.351 1.444 22.360 1.865 0.133 10 0.037 0.022 0.015 0.298 0.683 22.360 2.233 0.133

division Welding workability evaluation result Arc stability Amount of fume Weld Crack Generation Bead appearance Comparative example One △ △ △ △ 2 △ △ △ △ 3 X △ X X Inventive Example 4 △ O O O 5 O O O O 6 O O O O 7 O O O O 8 O O O O 9 O O O O 10 △ O △ O

In Table 3, the arc stability was evaluated by the method of FIG. 2, and welded under the conditions of a welding voltage of 24 to 28V and a welding current of 160 to 260A.

As can be seen from the above examples, the invention examples manufactured to satisfy the combination ratio (A) of the formula (1) while satisfying the content of each component of the flux, the arc is stable, and the amount of fume generated was small. Also, no crack was generated after welding, and beautiful welding beads could be obtained. On the other hand, the comparative example had a large volume and the arc was somewhat unstable, and in Comparative Example 3, a slight welding crack was generated.

The use of the flux cored wire for welding ferritic stainless steel according to the present invention not only significantly reduces the occurrence of welding cracks such as brittle cracks and high temperature cracks in the welded portion of the ferritic stainless steel, but also provides excellent welding beads even under low current and low voltage conditions. You can get it. In addition, corrosion resistance and oxidation resistance are of course secured.

In particular, the use of mild steel as an outer sheath improves productivity at high drawing speeds during drawing, and reduces the degree of hardening of the wire, which greatly increases die life and reduces manufacturing costs.

Claims (1)

In the flux cored wire for welding ferritic stainless steel, The shell of the flux cored wire is an ultra mild steel according to JIS G3141 standard containing C ≤0.03%, Si ≤0.03%, Mn 0.15-0.45%, P ≤0.02%, S ≤0.02%, The flux is 0.1% to 3.0% by adding C ≤0.02%, N ≤0.02%, P ≤0.02%, S ≤0.01%, Cr 14.5-25.0%, Ti 0.3-4.0%, Mo and W based on the total weight of the wire , TiO ₂ 1.0 ~ 5.0%, SiO ₂ 0.3 ~ 3.5%, Mn 0.5 ~ 3.0%, The TiO ₂ , SiO ₂ and Mn is a flux cored wire for welding ferritic stainless steel, characterized in that the combination ratio (A) of the following formula (1) satisfies a range of 0.5 to 23.3. ‥‥‥ Formula (1)