KR100340641B1 - Submerged arc welding flux containing TiO2 for Heat resistant steel - Google Patents

Abstract

PURPOSE: A titanium dioxide containing flux for submerged arc welding of heat-resistant stainless steel with high strength is provided, which has no disadvantage that oxidation occurs on welding bead, has excellent surface roughness and slag delamination. CONSTITUTION: The titanium dioxide containing flux for submerged arc welding comprises SiO2 16 to 22 wt.%, CaF2 20.5 to 25 wt.%, MgO 37 to 44 wt.%, Al2O3 6 to 12 wt.% TiO2 6 to 12 wt.% and (Na2O+K2O+MnO+FeO) 0.5 to 5.0 wt.%, wherein not less than 90 % of flux particle in the total flux particle is in the range of 0.3 to 1.0 mm.

Description

Submerged arc welding flux containing TiO2 for Heat resistant steel}

The present invention relates to an oxide-based flux for fusing or butt welding by submerged arc welding, and more particularly, to a flux having excellent welding properties by containing a small amount of titanium dioxide (TiO ₂ ). will be.

Submerged arc welding is one of the excellent welding methods that are widely applied to you all over the industry because of the excellent refining of weld metal and the possibility of automatic and semi-automatic welding. Flux is an important welding material that has an absolute effect on weldability such as refining properties of slag metal, slag peelability and inclusions in welding. In particular, slag peelability is a property directly connected to welding workability. When slag peelability is degraded, a lot of time and effort are removed to remove the slag, thereby reducing work efficiency. In addition, since the slag is not completely removed from the deposited metal, the inclusion of the inclusions in the weld metal due to the continuous welding operation deteriorates the properties of the weld metal.

The oxide fluxes for improving slag peelability have been disclosed in Japanese Patent Laid-Open Nos. 62-34659, (Pyeong) 2-151393 and Korean Patent Publication No. 96-412.

Flux proposed in Japanese Patent Application Laid-Open No. 62-34695 improves the shape of the weld bead and improves slag peelability by increasing the solidification temperature and viscosity of the flux by appropriately adjusting the contents of Al ₂ O ₃ , ZrO ₂ and MgO. We are trying to improve. However, this flux has a disadvantage of containing a large amount of MgO and Al ₂ O ₃ to cause inclusions into the deposited metal. Incorporation of slag is a phenomenon that occurs when the solidification temperature of the flux is high, especially when Al ₂ O ₃ is large.

Japanese Patent Application Laid-Open No. Hei 2-151393 examines the composition and softening temperature of the flux and proposes a flux that can reduce the inclusion of inclusions in the deposited metal and reduce the flux consumption. However, since the flux contains more than 35% of SiO ₂ , defects such as fork marks during welding are high and the appearance of beads deteriorates. The fork mark is generated by the gas generated at the melting of the flux located at the interface between the deposited metal and the slag.

Korean Patent Publication No. 96-412 proposes a flux capable of removing slag incorporation and fork marks by adding 25-30% of TiO ₂ compound. However, this flux has a disadvantage in that a large amount of TiO ₂ forms a strong oxide layer on the weld bead surface.

Accordingly, the present inventors have developed a flux that satisfies all the characteristics of the flux as a result of evaluating various welding characteristics by manufacturing a variety of flux to solve the above problems, has proposed this.

An object of the present invention is to provide a flux for welding a server-merged arc of high-strength heat-resistant stainless steel excellent in surface roughness, in particular, oxidation of the weld bead surface and excellent surface roughness and slag peelability.

1 is a low magnification stereoscopic optical micrograph showing the appearance of the weld bead and the surface oxidation in the comparative material and the inventive material,

Figure 1 (a) is a weld bead surface of the invention material,

Figure 1 (b) is the weld bead surface of the comparative material.

Flux of the present invention for achieving the above object, by weight ratio SiO ₂ : 16-22%, CaF ₂ : 20.5-25%, MgO: 37-44%, Al ₂ O ₃ : 6-12% TiO ₂ : 6 -12% and (Na ₂ 0 + K ₂ 0 + MnO + FeO): 0.5-5.0%.

Hereinafter, the present invention will be described in detail.

In order to prevent oxidation of the weld bead surface, TiO ₂ is suitably contained, and MgO is contained 37-44% in order to secure surface roughness and slag peelability due to the addition of TiO ₂ .

According to the present invention, the compound composed of MgO, Al ₂ O ₃ and TiO ₂ in the flux component shows excellent slag peeling properties, but when the Al ₂ O ₃ is large, the viscosity of the flux increases to cause the incorporation of slag into the deposited metal. There is a tendency. To prevent this, a significant amount of Al ₂ O ₃ can be replaced with MgO, but an excessive amount of MgO increases the melting temperature, thereby increasing the viscosity to narrow the width of the weld bead and roughen the surface. In order to lower the melting temperature of the slag, it is essential to add a compound having a low melting point such as SiO ₂ and CaF ₂ . However, excessively adding SiO ₂ has the disadvantage of decreasing the physical properties of the deposited metal by increasing the oxygen content in the deposited metal. CaF ₂ also protects the deposited metal from the atmosphere, but when added excessively, CaF ₂ forms many bubbles and defects in the deposited metal. The present invention optimizes the flux components in consideration of the action and the relationship between each of these flux components. In other words, the optimum composition of the flux was observed to slightly change the optimum composition of other compounds such as SiO ₂ , CaF ₂ , MgO, Al ₂ O ₃ by addition of TiO ₂ .

First, SiO ₂ in the flux component is an acidic oxide which affects the basicity of the slag depending on the component content as one of the slag forming agents, and is preferably limited to 16-22%. The reason is that when the SiO ₂ is less than 16%, since the viscosity decreases due to the increase of the solidification temperature, the flow of the slag is increased to roughen the surface of the weld bead. If it exceeds 22%, the slag fluidity deteriorates, which causes defects such as fork marks on the deposited metal surface. SiO ₂ contained in this manner controls the flow of slag to more efficiently enclose molten metal, and consequently plays a decisive role on the surface and shape of the deposited metal.

CaF _{2, which} is a basic component, mainly serves as a gas forming agent and functions to shield the surface of the molten metal by forming a protective atmosphere. In the present invention, the addition range is limited to 20.5-25%. If the CaF ₂ content is lower than 20.5%, the effect of shielding the molten metal is insufficient and the solidification temperature and fluidity increase, thereby deteriorating the appearance of the weld bead. On the other hand, if the content exceeds 25%, the amount of gas is rapidly increased to reduce the stability of the arc, as well as to generate a large amount of defects due to gas formation such as pit and blow hole. have.

MgO is a compound having a relatively high solidification temperature and can be used to control the melting temperature of the flux to maintain an appropriate viscosity. In particular, MgO plays a role of reducing oxygen of the deposited metal as a basic component, and secures the surface roughness or slag peelability in the flux of the present invention containing 6-12% TiO ₂ . For this purpose, it is necessary to contain 37-44% of MgO. The reason is that when the content is reduced to less than 37%, the viscosity becomes high, resulting in poor slag peelability, resulting in rough working efficiency or appearance of weld beads. In addition, if it exceeds 44%, the melting temperature of the slag is too high to narrow the weld bead width, because there is a disadvantage that the inclusion of inclusions in the weld metal is encouraged.

Al ₂ O ₃ has a similar function to MgO but is a weakly acidic compound that affects the basicity of the flux and is preferably contained at 6-12%. The reason is that when the content is less than 16%, the slag melting temperature is relatively low, thereby increasing the viscosity, thereby reducing slag peelability. And, if the content exceeds 22%, the slag temperature becomes high, resulting in poor appearance of the weld bead and incorporation of the slag into the weld metal during high speed welding, such as the server-merged arc welding.

TiO ₂ has a problem of surface oxidation when contained in a large amount as indicated in the Korean Patent Publication No. 96-412, the present invention optimizes the TiO ₂ content in consideration of advantages. That is, TiO ₂ is a weakly acidic component similar to Al ₂ O ₃ , which enhances slag peelability and arc stability. It is preferable to limit the amount thereof to 6-12%. The reason is that when TiO ₂ is added below 6%, the effect is insignificant, and when added above 12%, surface oxidation of the deposited metal is greatly promoted.

The Na ₂ O, K ₂ O, MnO, FeO is regarded as an impurity contained in a binder added to agglomerate the component powders in the manufacture of fluxes or raw materials such as SiO ₂ , CaF ₂ , MnO, and Al ₂ O _3. It is a component which does not have a big influence on the flux characteristic of this invention. However, when the binder content is too small, the caking force is so weak that it is difficult to prepare a flux having an appropriate particle size. When excessive addition of Na ₂ O, K ₂ O, MnO, FeO content is increased to more than 5%, not only makes the arc unstable, but also increases the fluidity of the coagulation powder, making it difficult to perform normal coagulation.

And as for the flux particle size of this invention, it is more preferable that 90% or more of particle | grains have a range of 0.3-1.0 mm. The reason is that when the particles smaller than 0.3 mm or particles larger than 1.0 mm become 10% or more, the arc generation becomes unstable and thus does not exhibit optimal weldability.

The flux of the present invention can be used for welding a variety of metals by submerged arc welding, particularly useful for the growth welding of high strength heat resistant stainless steel.

Hereinafter, the present invention will be described in detail through examples.

Example 1

In the present invention, in order to evaluate the welding properties of the flux suitable for the server-merged arc welding, SiO ₂ , Al ₂ O ₃ , MgO, CaF ₂ was prepared by adjusting TiO ₂ as a basic component. The raw powder was mixed to a desired composition and then dry mixed at a rotation speed of 30-150 rpm for 10 minutes or more in a shake mixer. The mixed powder was agglomerated by adding an appropriate amount of sodium silicate solution. And in order to give uniform composition and strength to the mixed powder for flux, it was sintered at 1050 degreeC for 10 minutes or more. The sintered flux was crushed in the mill and adjusted to have a particle size range of approximately 0.3-1.0 mm. The chemical composition of the flux used in the present invention is shown in Table 1.

Weldability evaluation was performed on the surface of SCM440 steel with 450mm diameter and 70mm thickness by using the manufactured fluxes. Cr: 13%, Ni: 2%, W: 1 Martensitic stainless steels composed of%, Mo: 0.5%, Nb: 0.3%, V: 0.3%, Cu: 0.4%, C: 0.13%, and the remaining Fe were grown and welded. Welding conditions were 570-590A, 26-34V using metalcored wire (MCW). Weldability was evaluated by qualitatively evaluating slag peelability and weld bead shape and surface condition, and measuring arc stability at this time. In addition, the cross section of the weld metal was examined to determine whether the slag was mixed and the internal defects.

Flux SiO ₂ CaF ₂ MgO Al ₂ O ₃ TiO ₂ Etc Comparative Material 1 14.0 20.5 24.0 8.5 28.0 Remainder Comparative Material 2 17.0 29.0 19.0 7.5 23.0 Remainder Invention 19.0 22.0 40.0 9.0 9.0 Remainder The rest are Na ₂ O, K ₂ O, MnO, FeO

Flux Arc stability Slag peelability Weld Bead Form Surface oxidation state Inclusion Comparative Material 1 ++ ++ + Severe radish Comparative Material 2 xx xx xx Severe radish Invention ++ ++ ++ radish radish ++ very good, + very good, x bad, xx very bad

As shown in Table 2, the surface of the comparative material shows a severely oxidized state (Fig. 1 (b)). On the other hand, the flux of the present invention containing TiO ₂ is not only excellent in arc stability, slag peelability and weld bead appearance, but also exhibits excellent welding characteristics that show the gloss of the deposited metal as it is (Fig. 1 (a)). ).

As described above, according to the present invention, unlike the conventional flux, welding bead surface oxidation does not occur, and further, there is an effect of providing a flux having excellent slag peelability and surface roughness. The flux of the present invention is useful as a flux material to be grown into wet welding wires and strips.

Claims (2)

SiO ₂ : 16-22%, CaF ₂ : 20.5-25%, MgO: 37-44%, Al ₂ O ₃ : 6-12% by weight ratio TiO ₂ : 6-12% and (Na ₂ O + K ₂ O + MnO + FeO): Titanium dioxide-containing flux for submerged arc welding of high-strength heat-resistant stainless steel consisting of 0.5-5.0%. The flux of the titanium dioxide-containing flux for submerged arc welding of high-strength heat-resistant stainless steel according to claim 1, wherein the flux has a particle size of 90% or more of the total particles.

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