JP2631756B2 - Hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention has particularly excellent low-temperature toughness and a proof stress of 65 kgf / mm.
^The present invention relates to a low hydrogen coated arc welding rod capable of obtaining ^two or more high-strength weld metals.

(Prior art) A low hydrogen-based coated arc welding rod is widely used for welding a portion having a large constraint or high strength steel because of its excellent crack resistance and low-temperature toughness. On the other hand, recently, with the increase in the size of the welded structure, the steel material used has also tended to be thicker, and the use of high-strength steel material has also increased due to the reduction in the plate thickness.

(Problems to be solved by the invention) However, in general, increasing the strength of the weld metal and securing low-temperature toughness tend to be in conflict with each other. Therefore, a new method for improving toughness with increasing strength is required. Regarding the improvement of toughness of metal, Japanese Patent Application Laid-Open No. 54-11445 discloses a method of adding a titanium oxide or a boron oxide to a coating material to form a fine-grained uniform structure of a weld metal and to provide a low-temperature toughness, particularly
Although it is disclosed that the CTOD characteristics are improved, it is already insufficient for today's severe demands for higher strength and tougher weld metal.

Techniques for reducing the amount of oxygen in the weld metal using SiC are disclosed in JP-A-58-138591 and JP-A-61-2320.
No. 94, there is a former relating to a fillet welding rod with improved pit resistance, and the latter as a Cr-Mo based low-alloy heat-resistant steel welding rod, the embrittlement characteristics during use and low-temperature toughness. However, none of them have significantly improved toughness as welding rods for high-tensile steel.

An object of the present invention is to provide a low hydrogen-coated arc welding rod which can obtain a weld metal exhibiting excellent low-temperature toughness in welding of high-tensile steel, for example, 70-90 kg class high-tensile steel.

(Means for Solving the Problems) The gist of the present invention is as follows: metal carbonate: 30 to 60% by weight (hereinafter, all percentages are by weight). Metal fluoride: 13 to 23% SiC: 0.1 -0.6% Si: 3.2-5.6% Mg: 0.8-5.0% Mn: 2.2-7.4% One or more of Nb and V: 0.02-0.8% In addition, other arc stabilizers, slag generators,
C: 0.02% or less of coating agent consisting of alloying agent and binder, Si:
A low-hydrogen-based coated arc welding rod coated with a steel core wire of 0.05% or less.

Conventionally, it has been known that reducing the oxygen content of a weld metal is effective for improving the toughness of the weld metal. However, in the coated arc welding rod, oxygen generated by the decomposition of the coating agent and oxygen in the atmosphere were caught in the arc during welding and entered the weld metal, so that the oxygen amount did not decrease significantly.

As a result of various studies, the present inventors have found that the combined addition of SiC and Si to the coating agent is effective in lowering the oxygen content of the weld metal, and the increase in C and Si due to these additions is considered as a core. We have developed a welding rod that can be prevented by limiting the contents of C and Si inside, and in addition, a high strength and high toughness weld metal can be obtained by adding a small amount of Nb and V.

(Operation) The present invention has been made based on the above findings, and will be described in detail below together with the operation.

One of the features of the present invention resides in that SiC and Si are added in a composite to the coating agent to greatly reduce the oxygen content in the weld metal.

Conventionally, in low-hydrogen welding rods, Si has been frequently used in the form of Fe-Si mainly as an effective deoxidizing agent and as a component for maintaining the viscosity of a weld metal and maintaining welding workability. While Si lowers the oxygen of the weld metal, the use of Si as a component that coarsens the crystal grains and degrades the toughness requires fine adjustment. However, when a small amount of SiC is further added as a deoxidizing agent, this strong deoxidizing power can significantly reduce the oxygen content of the weld metal after limiting Si in the coating agent, which is extremely effective in improving toughness. And Fe
-Addition of SiC to the coating agent in the form of metallic Si, such as Si, has a greater effect as a deoxidizing agent, but the migration of Si to the weld metal is small, and slag is formed. It is effective in reducing the amount.

Table 1 shows CaCO ₃ 45%, BaCO ₃ 3%, CaF ₂ 18%, rutile 3%, metal Mn 3.0%, metal Mo 2.0%, metal Mg 3.0%, Fe-V
(50% V) 0.2%, Fe-Si (40% Si) 4.0-15%, SiC0-0.
8%, binder 6.8%, balance of iron powder C0.012
%, Si 0.01%, Mn 0.52%, P0.008%, S0.003%, balance of Fe and unavoidable impurities 4.0mm in diameter, 400mm in length, and outer diameter of coating is 6.3mm After coating and drying and firing to produce a welding rod, welding according to JISZ3212,
The impact test and oxygen analysis of the deposited metal were performed.

As a result, welding rod Nos. 7, 8, and 10 in which Fe-Si was less than 8%, that is, Si was less than 3.2%, the oxygen content of the deposited metal did not decrease irrespective of the amount of SiC added, and -40 ° C The absorbed energy was also low. Similarly, welding rod No. 1 without SiC added
In No. 10, the oxygen content of the deposited metal exceeded 0.0300%, and the absorbed energy at −40 ° C. was less than 10 kgfm.

On the other hand, the welding rod N containing 14% Fe-Si,
In No. 6 and No. 6 in which SiC exceeds 0.6%, the amount of oxygen in the deposited metal was significantly reduced, but the absorbed energy at −40 ° C. was low due to embrittlement due to excessive Si and C.

From the above results, if the amount of Si added to the coating agent is less than 3.2%, the decrease in the oxygen content of the weld metal is not sufficient, and if it exceeds 5.6%, embrittlement due to an increase in Si occurs, so that the amount is 3.2 to 5.6%. I decided.

If the amount of SiC added to the coating agent is less than 0.1, the effect of lowering the oxygen content of the weld metal is not sufficient, and if it exceeds 0.6%, C
0.1-0.6% due to large toughness degradation due to increased amount
It was decided. The addition of a small amount of SiC is also effective in improving the strength by lowering the oxygen content of the weld metal and increasing the hardenability due to the yield of the small amount of C.

Still another feature of the present invention is that the effects of SiC and Si added to the coating agent by limiting the amounts of C and Si in the core wire are made effective. C in the core exceeds 0.02% or Si is 0.05%
Above, the C, Si content in the coating agent combined with the yield of C, Si
Is excessive, causing embrittlement of the weld metal.
The amounts of C and Si are set to 0.02 or less and 0.05% or less, respectively.

Subsequently, Mg is added to the coating agent and acts as a deoxidizer to be effective in obtaining a clean weld metal, and is also very effective as an arc stabilizer in securing welding workability. If the added amount is less than 0.8%, a sufficient deoxidizing effect cannot be obtained.
%, The arc at the time of welding becomes unstable, the spatter increases, the viscosity of the slag decreases, and the peelability of the slag deteriorates. Therefore, the addition range of Mg to the coating agent is set to 0.8 to 5%. .

Mn acts as a deoxidizing agent to reduce the amount of oxygen and also to fix S causing embrittlement, and is effective in improving toughness. In addition, it is a component that is indispensable for a high-strength steel welding rod because it significantly improves the hardenability of steel and increases the strength. If the amount added to the coating is less than 2.2%, the effect of improving toughness and strength is not sufficient, and if it exceeds 7.4%, the hardenability of the weld metal becomes excessive and the toughness deteriorates.
Was set to 2.2 to 7.4%.

Nb, V can significantly improve the strength of weld metal by adding a small amount to the coating agent. If the addition amount is less than 0.02%, the strength improving effect is not sufficient, and if it exceeds 0.8%, the toughness deteriorates conversely.
0.02 to 0.8%.

Further, the metal carbonate according to the present invention refers to CaCO ₃ , BaCO ₃ , Mg
It refers to CO ₃ , MnCO _3, etc., and includes CaCO ₃ as an essential component and other components as required, so that the total content is 30 to 60%. These metal carbonates decompose in the arc
It has the effect of generating CO ₂ gas, cutting off the molten metal from the atmosphere, lowering the gas partial pressure of hydrogen and nitrogen in the arc atmosphere, and producing basic slag. When this amount is 30
%, The melting point of the slag decreases, the encapsulation of the slag deteriorates, a good bead cannot be obtained, and the amount of gas generated to cut off the air is insufficient, so that pits and blowholes may occur. The amount of hydrogen in the weld metal increases and the crack resistance deteriorates. On the other hand, if added over 60%, the amount of generated gas becomes excessive, pits are generated frequently, the melting point of the slag increases, the fluidity of the slag deteriorates, the conformity with the welding base metal becomes uneven, and the bead shape is reduced. Deteriorate.

The metal fluoride according to the present invention is CaF ₂ , BaF ₂ , MgF ₂ , A
It refers to lF ₃ , MnF ₂ , LiF, etc., which is required to include CaF ₂ and combine other components as required, so that the total content is 13 to 23%. Each of these metal fluorides lowers the melting point of the slag and forms a slag with good fluidity. In addition, the fluorine decomposed in the arc reacts with hydrogen in the molten metal or molten slag to reduce the hydrogen in the weld metal to produce a weld metal having good crack resistance. If the amount of these additives is less than 13%, appropriate slag fluidity cannot be obtained, resulting in poor bead shape, pit generation, and increase in the amount of hydrogen in the weld metal to cause cracking. On the other hand, if it is added in excess of 23%, the viscosity of the slag will be insufficient and the bead shape will be poor, and the coating cylinder will also be weak and the welding workability will be poor.

Next, other arc stabilizers and slag forming agents to be contained in the coating agent refer to iron powder, alkali components, rutile and the like, and the amount of addition is not particularly specified, but the total amount is 2 to 2.
25% is desirable in terms of welding workability.

The other alloying agents referred to in the present invention are Ni, Cr, Mo, Ti,
It refers to Cu and the like, and is added as necessary for the purpose of increasing the strength of the weld metal, stabilizing the low-temperature toughness and improving heat resistance, corrosion resistance, and the like. These are, in addition to their metal powder,
It is added in the form of alloy powders with iron and other metals. Since the amount of addition varies depending on the purpose, it is not particularly specified. However, the total amount is desirably 30% or less from the viewpoint of welding workability and coatability of the coating at the time of manufacturing the welding rod.

The binder refers to a binder component such as water glass represented by sodium silicate and potassium silicate, and is a mole fraction of SiO ₂ and alkali components such as Na ₂ O and K ₂ O in the water glass. It is desirable to use a water glass having a molar ratio expressed as a ratio in the range of 1.5 to 3.5.

The welding rod of the present invention is coated with the above-mentioned coating agent around the core wire by a usual welding rod coating machine so that the coating agent weight becomes 25 to 40%, and then 350 to 550 ° C to remove moisture.
It is manufactured by firing.

The core of the welding rod of the present invention may be a low-alloy core containing Ni, Cr, Mo, etc., depending on the purpose, in addition to the carbon steel core in which C and Si are within the above-specified range. .

(Examples) Next, the effects of the present invention will be more specifically shown by examples.

Chemical composition of core wire (4mm diameter each) used in Table 2, 3rd
The table shows the coating composition and various test results of the welding rod of the present invention and the welding rod used for comparison.

In Table 3, A-1 to A10 are welding rods of the present invention, and B-1 to B12 are welding rods of comparative examples.

In order to compare the low temperature toughness and proof stress of these welding rods, an impact test and a tensile test of the deposited metal were performed. In other words, based on JISZ3212, welding is performed under the conditions of preheating / interpass temperature of 100 ° C, welding current of 170A, and welding heat input of 20kJ / cm.
According to 3111, the impact test and tensile test of the deposited metal were performed. The impact test is performed at -40 ° C according to JISZ2242,
The absorption energy at −40 ° C. was 10 kgf · m or more. The tensile test was performed at room temperature according to JISZ2241, and the 0.2% proof stress was determined for each. Good 0.2% proof stress of 65 kgf / mm ² or more.

Further, a welding workability test was also performed on these welding rods. The absorbed energy of the deposited metal at −40 ° C. by the welding rod of the present invention all exhibited a good value of 10 kgf · m or more due to the sufficient deoxidizing action of SiC, Si, and Mg. In addition, the 0.2% proof stress was 66 kgf / mm ² or more due to the increase in strength due to the improvement in hardenability by C added from SiC and the improvement in strength due to the addition of Mn, Nb, and V. Furthermore, the welding workability was excellent.

On the other hand, the welding rod B-1 in which SiC is not added to the coating agent, the welding rod B-7 in which less than 0.1%, the welding rod B-4 in which Si is less than 3.2%, and the welding rod B-8 in which Mg is less than 0.8% are: In each case, the absorption energy at -40 ° C was low due to insufficient deoxidizing action. Further, the welding rod B-8 having Mn of less than 2.2% did not sufficiently improve the hardenability and had a low 0.2% proof stress.

The welding rod B-2 containing SiC in excess of 0.6% has low absorption energy at -40 ° C due to excessive yield of C, and the welding rod B-3 containing Si in excess of 5.6% has low absorption energy at -40 ° C due to embrittlement due to excessive Si. Was.

The welding metal test for the welding rod B-6 in which Mg exceeded 5% and metal fluoride exceeded 23% was remarkably inferior in welding workability, so the welding metal test was stopped.

The welding rod B-5 to which Nb and V were not added had no strength improving effect due to these precipitations, and had a low 0.2% proof stress.
Conversely, welding rod B-7, in which Nb and V exceeded 0.8%, had a sufficient 0.2% proof stress, but the absorption energy at -40 ° C was extremely low.

The welding rods B-9 and B-11 in which the C of the core wire exceeds 0.02% and the welding rods B-10 and B-12 in which the Si of the core wire exceeds 0.06% all had sufficient strength. Therefore, the absorbed energy at -40 ℃ was low due to embrittlement due to excessive yield of Si.

Further, the welding rod B-2 was inferior in the amount of gas generated due to the small amount of metal carbonate, and the slag flowability was poor. Conversely, the welding rod B-4 had too much metal carbonate, so that the penetration with the base material was not uniform and the bead shape was poor. Welding rod B-3
However, the slag had poor fluidity due to a small amount of metal fluoride, exhibited a bead shape with severe irregularities, and had poor welding workability.

(Effects of the Invention) As described above, the welding rod of the present invention can provide a welding metal having a high yield strength and extremely improved low-temperature toughness, as compared with a conventional welding rod for 70 to 90 kg steel, for example. With the future increase in demand for high-tensile steel, it will contribute to improving the quality of welding of parts with large constraints and large structures.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoaki Matsutani 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa New Nippon Steel Corporation Second Technical Research Institute (56) References JP-A-59-110495 (JP, A) JP-A-60-213398 (JP, A) JP-A-59-4997 (JP, A) JP-A-61-140399 (JP, A) JP-A-61-180695 (JP, A) JP-A-62 220300 (JP, A) JP 4-62837 (JP, B2) JP 1-55079 (JP, B2) JP 60-59993 (JP, B2)

Claims (1)

(57) [Claims] 1. Metal carbonate: 30 to 60% by weight Metal fluoride: 13 to 23% by weight SiC: 0.1 to 0.6% by weight Si: 3.2 to 5.6% by weight Mg: 0.8 to 5.0% by weight Mn: 2.2 to 7.4% by weight % Nb, V: at least 0.02 to 0.8% by weight In addition, C: 0.02% by weight or less, a coating agent comprising an arc stabilizer, a slag forming agent, an alloying agent and a binder other than the above.
i: A low-hydrogen coated arc welding rod coated on a steel core wire of 0.05% by weight or less.