JP6938361B2 - Lime titania-based shielded metal arc welding rod - Google Patents

Description

The present invention relates to a lime titanian shielded metal arc welding rod suitable for ensuring various performances such as welding workability and improving slag peelability particularly even in welding of thin steel sheets.

Non-low hydrogen-based shielded metal arc welding rods are more excellent in welding workability than various shielded metal arc welding rods, and are therefore often used for welding mild steel and 490 MPa class high-strength steel. Among them, the lime titanian shielded metal arc welding rod is widely used for general structures such as vehicles and buildings because it has a good bead appearance, a small amount of spatter generation, and a good re-arc property.

However, when lap joints and T joints of thin steel plates with a thickness of 1.2 to 6 mm are welded with a lime titanian shielded metal arc welding rod, the slag peelability becomes poor and the welding work efficiency deteriorates. There is a problem.

Therefore, various proposals have been made conventionally in order to improve the slag peelability of the non-low hydrogen shielded metal arc welding rod. For example, Patent Document 1 defines the contents of MgO and water of crystallization in the coating agent for lime titanian shielded metal arc welding, and diffuses hydrogen generated from the water of crystallization into the slag while maintaining the viscosity of the slag by MgO. A technique for improving slag removability by making the slag porous is disclosed. According to this technique, it is possible to improve the slag peeling property of a lime titanian shielded metal arc welding rod, but there is a problem that sufficient slag peeling property cannot be obtained by welding a lap joint portion or a T joint portion of a thin steel plate. was there.

Further, Patent Document 2 describes a technique for improving slag peelability by suppressing the total amount of iron oxide in a coating agent for a non-hydrogen-based shielded metal arc welding rod as much as possible and increasing the difference between thermal expansion and contraction of slag. Is disclosed. Further, Patent Document 3 discloses a technique for improving slag peelability by reducing _{Nb 2} O ₅ and V ₂ O _{5 and the} like in a coating agent for illuminant-based shielded metal arc welding. However, all of the disclosed techniques of Patent Documents 2 and 3 have a problem that sufficient slag peelability cannot be ensured by welding a lap joint portion or a T joint portion of a thin steel plate.

Japanese Unexamined Patent Publication No. 56-71597 Japanese Unexamined Patent Publication No. 6-262391 Japanese Unexamined Patent Publication No. 2004-243351

Therefore, the present invention has been devised in view of the above-mentioned problems, and while ensuring various performances such as welding workability, sufficient slag peeling is also performed in welding of lap joint portions and T joint portions of thin steel plates. It is an object of the present invention to provide a lime titanian-based shielded metal arc welding rod capable of ensuring properties.

The gist of the present invention is that in a lime titanian-based coated arc welding rod in which a steel core wire is coated with a coating material, the coating material is one or more types of metal carbonates in mass% with respect to the total mass of the coating material. Total: 8 to 18%, Total of Ti oxide _{converted to TIO 2} : 10 to 25%, Total of Si oxide _{converted to SiO 2} : 10 to 25%, Al oxide converted to _{Al 2} O ₃ Total: 1-5%, Total of one or more organic substances: 2-6%, CaO: Over 1.50 to 4.55%, MgO: 1-5%, Mn: 2-8%, Ti : 0.03 to 0.50%, iron powder: 20 to 40%, iron sulfide: 0.01 to 0.05%, _{total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: A lime titanian-based coated arc welding rod containing 0.5 to 3.5% and having a balance composed of a coating agent, Fe content from an iron alloy, and unavoidable impurities.

According to the lime titanian shielded metal arc welding rod of the present invention, various performances such as good welding workability can be ensured, and slag peeling property is excellent especially in welding of lap joints and T joints of thin steel plates. It can greatly contribute to the improvement of welding work efficiency.

In order to solve the above problems, the present inventors have prepared a lime titanian-based shielded metal arc welding rod and investigated in detail welding workability such as slag peeling property at the time of welding a thin steel plate. As a result, in the welding of thin steel sheets, the steel sheet heated by the welding heat is difficult to cool, so that the molten slag that encloses the molten pool is unevenly encapsulated, and the molten slag easily seizes on the bead surface, resulting in slag peeling. I found out that the sex was bad. Therefore, slag peeling occurs even when welding thin steel plates while maintaining the excellent bead shape and appearance, re-arcability, welding workability such as arc stability, and mechanical performance of weld metal, which are the characteristics of lime titanian coated arc welding rods. As a result of various studies on methods for improving the properties, the necessary mechanical performance of the weld metal was ensured by adding appropriate amounts of Mn and Ti to the coating agent, and Ti oxide, Si oxide, Al oxide, CaO, and Na were obtained. By adding an appropriate amount of compound and K compound, arc stability is improved and the amount of spatter is reduced, by adding an appropriate amount of Ti oxide, the bead shape and appearance are improved, and by adding an appropriate amount of organic matter and iron powder. It has been found that the re-arc property, the bar burning resistance and the coating chipping resistance are improved, and welding defects such as blow holes can be prevented by adding an appropriate amount of metal carbonate and Mn. On the other hand, regarding the slag peelability, the surface tension of the molten slag can be lowered by adding an appropriate amount of Si oxide, MgO, and iron sulfide, and the molten slag can uniformly cover the entire surface of the molten pool. It was found that slag seizure can be prevented and sufficient slag peeling property can be obtained.

Hereinafter, the component composition of the coating agent for the lime titanian-based shielded metal arc welding rod in the present invention and the reason for limiting the component composition will be described in detail. The content of each component composition shall be expressed in mass% with respect to the total mass of the coating agent, and when the mass% is expressed, it shall be simply described as%.

[Total of one or more metal carbonates: 8-18%]
Metal carbonate is added from calcium carbonate, magnesium carbonate, barium carbonate, manganese carbonate, lithium carbonate, etc., _{and has the effect of decomposing in an arc to generate CO 2} gas to shield the weld metal from the atmosphere and protect it. .. If the total of one or more of the metal carbonates is less than 8%, the shielding effect is insufficient and blow holes are likely to occur. On the other hand, when the total of one or more of the metal carbonates exceeds 18%, the arc becomes unstable and becomes a convex bead, and the slag peeling property also deteriorates. Therefore, the total of one or more metal carbonates in the coating is 8-18%.

_{[Total TiO 2} conversion value of Ti oxide: 10 to 25%]
Ti oxide is added from rutile, titanium oxide, sodium titanate, titanium slag and the like, acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and bead shape and appearance. If the total value of the Ti oxides _{converted to TIO 2} is less than 10%, the arc becomes unstable, the slag fluidity deteriorates, and the bead shape and appearance become poor. On the other hand, when _{the total of the TIO 2} conversion values of the Ti oxide exceeds 25%, the slag becomes dense and the slag peelability becomes poor. _{Therefore, the total TiO 2} conversion value of the Ti oxide in the coating agent is set to 10 to 25%.

_{[Total SiO 2} conversion value of Si oxide: 10 to 25%]
Si oxide is added from silica sand, feldspar, water glass and the like, acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and slag exfoliation property. _{If the total SiO 2} conversion value of the Si oxide is less than 10%, the arc becomes weak and unstable, and the slag produced becomes less vitreous, resulting in poor slag peelability, especially when welding thin steel sheets. .. On the other hand, when _{the total SiO 2} conversion value of the Si oxide exceeds 25%, the viscosity of the slag becomes high and the bead shape becomes poor. Therefore, the total value of Si oxides in the coating material in _{terms of SiO 2} is set to 10 to 25%.

_{[Total Al 2} O ₃ conversion value of Al oxide: 1 to 5%]
Al oxide is added from alumina, feldspar, silica sand, mica and the like, and has the effect of stabilizing the arc. _{If the total Al 2} O ₃ conversion value of Al oxide is less than 1%, the arc becomes weak and unstable. On the other hand, _{if the total Al 2} O ₃ conversion value of Al oxide exceeds 5%, the slag peelability becomes poor, especially when welding a thin steel sheet. _{Therefore, the total Al 2} O ₃ conversion value of Al oxide in the coating agent is 1 to 5%.

[Total of one or more organic substances: 2-6%]
Organic substances are added from cellulose, dextrin, wheat flour, starch, cornstarch and the like to improve rearcability and also to improve coating chipping resistance. If the total of one or more organic substances is less than 2%, good rearcability cannot be obtained and coating chipping is likely to occur. On the other hand, if the total of one or more organic substances exceeds 6%, the arc becomes too strong and the bead shape becomes poor. In addition, the coating material becomes reddish and stick burning is likely to occur. Therefore, the total of one or more organic substances in the coating is 2 to 6%.

[CaO: Over 1.50 to 4.55%]
CaO is added from wollastonite, calcium titanate and the like to stabilize the arc and is effective in reducing spatter. If CaO is 1.50% or less, the effect cannot be obtained, the arc becomes unstable, and the amount of spatter increases. On the other hand, when CaO exceeds 4.55%, the arc becomes weak and unstable, and welding defects such as fusion defects are likely to occur. Therefore, CaO in the coating agent is set to more than 1.50 to 4.55%.

[MgO: 1-5%]
MgO is added from magnesia clinker or the like and has an effect of improving slag exfoliation property. If MgO is less than 1%, the effect cannot be obtained, and the slag peelability becomes poor especially when welding a thin steel sheet. On the other hand, when MgO exceeds 5%, the slag itself becomes hard and the bead shape becomes convex. Therefore, MgO in the coating agent is set to 1 to 5%.

[Mn: 2-8%]
Mn is added from metals Mn, Fe-Mn, Fe-Si-Mn and the like, is added as a deoxidizer, and is effective in improving the strength and toughness of the weld metal. If Mn is less than 2%, deoxidation is insufficient and blow holes are likely to occur. In addition, the strength and toughness of the weld metal are reduced. On the other hand, when Mn exceeds 8%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, Mn in the coating agent is set to 2 to 8%.

[Ti: 0.03 to 0.50%]
Ti is added from metals Ti, Fe-Ti, etc., is effective as a deoxidizer, and has a function of staying in the weld metal to refine the microstructure of the weld metal and improve toughness. If Ti is less than 0.03%, deoxidation is insufficient and the toughness of the weld metal is lowered. On the other hand, when Ti exceeds 0.50%, the precipitation of Ti oxide in the weld metal increases and the toughness of the weld metal decreases. Therefore, the Ti content in the coating agent is 0.03 to 0.50%.

[Iron powder: 20-40%]
Iron powder has the effect of improving rearcability. If the iron powder content is less than 20%, good re-arcability cannot be obtained. On the other hand, when the iron powder exceeds 40%, the coating cylinder becomes short and the arc becomes unstable, and the electrical conductivity of the coating becomes excessively high, so that a side arc is likely to occur. Therefore, the iron powder in the coating agent is 20 to 40%.

[Iron sulfide: 0.01-0.05%]
Iron sulfide lowers the surface tension of the molten slag to improve its compatibility with the molten pool, and evenly covers the entire surface of the molten slag to prevent slag seizure on the weld bead surface and prevent slag peeling. Has the effect of improving. If the amount of iron sulfide is less than 0.01%, the effect cannot be obtained, and especially in the welding of thin steel sheets, slag seizure occurs on the bead surface and the slag peelability becomes poor. On the other hand, when iron sulfide exceeds 0.05%, the toughness of the weld metal is lowered and high-temperature cracking is likely to occur. Therefore, the iron sulfide in the coating agent is 0.01 to 0.05%.

_{[Total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: 0.5 to 3.5%]
The Na compound and the K compound are added from sodium silicate, potassium silicate, potassium feldspar, potassium glass, soda feldspar and the like in water glass, and have an effect of improving arc stability. _{If the sum of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound is less than 0.5%, the arc becomes unstable. _{On the other hand, if the total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound exceeds 3.5%, the rearc property becomes poor. _{Therefore, the total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound in the coating agent is 0.5 to 3.5%.

The remainder of the coating agent of the lime titanian-based coated arc welding rod of the present invention can contain at least one kind of coating agent such as sodium alginate and mica in a total of 6% or less, and the others are Fe-Mn and Fe. Fe content and unavoidable impurities from iron alloys such as −Si−Mn.

Further, it is preferable to use JIS G3523 SWY11 as the mild steel core wire to be used. Further, C in the mild steel core wire is 0.05 to 0.08% by mass with respect to the total mass of the mild steel core wire, and C is mass% with respect to the total mass of the shielded metal arc welding rod. It is preferably 0.06 to 0.20%, and P is preferably 0.010% or less because the toughness is lowered. The coverage of the coating material on the mild steel core wire (mass% of the coating agent with respect to the total mass of the arc welding rod) is preferably 25 to 40%.

The effects of the present invention will be specifically described with reference to Examples.

The coating agents having various component compositions shown in Table 1 have a diameter of 3.2 mm and a length of 350 mm. Mass%, Mn: 0.48% by mass, P: 0.009% by mass, S: 0.005% by mass) by coating with a coverage rate of 36% and then dried to dry and various lime titanian-based coated arc welding rods. Was prototyped.

Using the prototype welding rod shown in Table 1, welding workability such as slag peelability and mechanical performance were investigated.

To evaluate the welding workability, a JIS G 3131 SPHC steel plate with a plate thickness of 3.2 mm is assembled in a T shape, and a small welding machine with a secondary side no-load voltage of 60 V is used. Fill welding was performed, and the arc stability, spatter generation state, slag peelability, bead shape and appearance, and the presence or absence of welding defects were evaluated. The presence or absence of this welding defect was investigated for the presence or absence of coating chipping, bar burning, high temperature cracking, and side arc generation.

As for the re-arcability, those in which an arc was immediately generated after welding for 10 seconds were regarded as acceptable, the number of tests was set to 20, and those in which 16 out of 20 were passed were considered to be good.

For the evaluation of mechanical performance, a welding metal test was performed with an AC welder according to JIS G 3111 using JIS G 3106 SM490A with a plate thickness of 16 mm, and a tensile test piece (A2) and an impact test piece (V notch test piece) were used. It was sampled and subjected to a tensile test and an impact test.

In the evaluation of the tensile test, the tensile strength was good at 400 to 560 MPa. In addition, the toughness was evaluated by performing a Charpy impact test at a test temperature of 0 ° C., and the average value of absorbed energy three times each was set to be good at 60 J or more.

For the evaluation of welding defects, the test piece after the weld metal test was subjected to an X-ray transmission test according to JIS Z 3106, and the presence or absence of blow holes, fusion defects, etc. was investigated. The results of these surveys are summarized in Table 2.

In Tables 1 and 2, the welding rod No. 1-No. 9 is an example of the present invention, welding rod No. 10-No. 18 is a comparative example.

Welding rod No. which is an example of the present invention. 1-No. 9 is the total of metal carbonates in the coating agent, the total of TiO ₂ conversion values of _{Ti oxide, the total of SiO 2} conversion values of Si oxide, the total of Al ₂ O ₃ conversion values of Al oxide, and organic substances. _{Since the total, Na 2} O conversion value and K ₂ O conversion value of CaO, MgO, Mn, Ti, iron powder, iron sulfide, Na compound and K compound are appropriate, the arc is stable and the amount of spatter is small. , Re-arcability, slag peelability, and bead appearance / shape were good. In addition, welding defects such as coating chipping, bar burning, and side arcs did not occur, there were no blow holes, fusion defects, high temperature cracks, and the tensile strength and absorption energy of the weld metal were good, which was an extremely satisfactory result. ..

Welding rod No. in the comparative example. In No. 10, since the total amount of metal carbonate was small, blow holes were generated in the welded portion. In addition, since the TiO ₂ conversion value was small, the arc was unstable and the bead appearance and shape were poor. Further, since the amount of MgO was small, the slag peelability was poor.

Welding rod No. In No. 11, since the amount of metal carbonate was large, the arc was unstable, the slag peelability was poor, and the bead shape was also convex. In addition, since there was a large amount of iron sulfide, crater cracking occurred and the absorbed energy of the weld metal was low.

Welding rod No. No. 12 had a _{large TiO 2} conversion value, and therefore had poor slag peelability. Moreover, since the amount of Ti was large, the absorbed energy of the weld metal was low. Furthermore, since there was a lot of iron powder, the arc was unstable and a side arc was generated.

Welding rod No. In No. 13, _{since the value converted to SiO 2} was small, the arc was weak and the slag peelability was poor. Moreover, since there is a large amount of MgO, the beads are convex. Further, since the amount of iron powder was small, the re-arcability was poor.

Welding rod No. In No. 14, the bead shape was poor because the value converted to _{SiO 2 was large.} In addition, since there is a large amount of CaO, the arc becomes weak and fusion failure occurs. Further, since the amount of Ti is small, the absorbed energy of the weld metal is low.

Welding rod No. In No. 15, the arc was weak because _{the Al 2} O _{3 conversion value was small.} In addition, since the amount of organic matter is small, the re-arcing property is poor and the coating is chipped. Further, since the amount of Mn is large, the tensile strength of the weld metal is high and the absorbed energy is also low.

Welding rod No. No. 16 had a _{large Al 2} O ₃ conversion value, and therefore had poor slag peelability. Moreover, since the amount of Mn was small, the tensile strength and absorption energy of the weld metal were low. Furthermore, the arc was unstable because the sum of _{the Na 2} O conversion value and the K _{2 O conversion value was small.}

Welding rod No. In No. 17, since there were many organic substances, the arc was strong, the bead appearance was poor, and stick burning occurred. In addition, _{since the sum of the Na 2} O conversion value and the K ₂ O conversion value was large, the rearcability was also poor.

Welding rod No. In No. 18, since the amount of CaO was small, the arc was unstable and the amount of spatter generated was large. Moreover, since the amount of iron sulfide was small, the slag peelability was poor.

Claims (1)

In a lime titanian-based shielded metal arc welding rod in which the steel core wire is coated with a coating agent,
The coating agent is a mass% based on the total mass of the coating agent.
Total of one or more metal carbonates: 8-18%,
Total of TiO ₂ conversion values of Ti oxide: 10 to 25%,
_{Total SiO 2} equivalent of Si oxide: 10-25%,
_{Total Al 2} O ₃ conversion value of Al oxide: 1-5%,
Total of one or more organic substances: 2-6%,
CaO: Over 1.50 to 4.55%,
MgO: 1-5%,
Mn: 2-8%,
Ti: 0.03 to 0.50%,
Iron powder: 20-40%,
Iron sulfide: 0.01-0.05%,
_{Total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: Contains 0.5 to 3.5%.
A lime titanian-based shielded metal arc welding rod characterized in that the balance is composed of a coating agent, Fe content from an iron alloy, and unavoidable impurities.