JPH08257791A - Low hydrogen covered electrode - Google Patents

Abstract

PURPOSE: To improve toughness by covering the covering material containing a specific quantity of metal carbonate, metal fluoride, Mg, Si, Mn, Cr, Ti around the steel core wire containing a specific quantity of C, P, S, N. CONSTITUTION: A steel core wire consists of, by weight, <=0.03% C, <=0.01% P, <=0.01% S, <=0.005% N. A covering material consists of, by weight, 30-60% metal carbonate, 8-20% metal fluoride, 0.5-3% Mg, 2.8-5.8% Si, 0.5-4% Mn, 8-14% Ni, <=0.02X Cr, 0.3-0.8% Ti, further arc stabilizer, slag agent and binder. The steel core wire is covered with the covering material. By this method, in welding a high strength steel having >=HT590 class, weld zone having excellent low temp. toughness, excellent toughness after PWHT and CTOD value is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a low hydrogen type coating which is capable of obtaining a high-strength weld metal of 590 N / mm ² grade or more, excellent in low temperature toughness, and excellent in fracture toughness after stress relief annealing (hereinafter referred to as PWHT). It relates to an arc welding rod.

[0002]

2. Description of the Related Art Low-hydrogen coated arc welding rods are widely used for welding highly constrained places and high-strength steel because of their excellent crack resistance and low temperature toughness. On the other hand, recently, with the increase in size of welded structures, the steel materials used tend to become thicker, and the use of high-strength steel materials is increasing due to the reduction in plate thickness. However, in general, increasing the strength of weld metal and ensuring low temperature toughness tend to conflict with each other.
There is a need for new methods to improve toughness as well as strengthening.

As a measure for improving the toughness of weld metal, for example, in Japanese Patent Publication No. 2-42312, the toughness is improved by adding Ni and limiting the total amount of Mn and Ni. However, even if high toughness is obtained, there is a problem that it is difficult to say that it is a sufficient method in terms of stabilization, that is, variation. In addition, Japanese Examined Japanese Patent Publication 60-539
Japanese Patent Publication No. 7 discloses that the addition of titanium oxide and boron oxide to the coating material improves the low temperature toughness, especially the CTOD characteristics, by making the weld metal into a fine grained uniform structure, but with higher strength. However, it is not sufficient to meet the required requirements for high toughness weld metal.

On the other hand, in Japanese Patent Laid-Open No. 63-242491, Mg is added to a Cr-Mo system low hydrogen system coated arc welding rod for high temperature steel to reduce the amount of oxygen in the weld metal and to refine the structure. Although a technique for improving crack resistance and ductility of weld metal has been disclosed, it is insufficient for high strength and high toughness.

[0005]

SUMMARY OF THE INVENTION The present invention is a high strength steel,
For example, the present invention provides a low-hydrogen-based coated arc welding rod from which a weld metal exhibiting low-temperature toughness in welding 590 to 980 N / mm ² class high-strength steel and excellent fracture toughness after PWHT can be obtained.

[0006]

Means for Solving the Problems The present invention is to solve the above problems, and in a low hydrogen system coated arc welding rod, the weight percentage of the steel core wire is C: 0.03% or less, P:
0.010% or less, S: 0.010% or less, N: 0.0
As a coating agent around the steel core wire regulated to 05% or less,
Metal carbonate: 30-60%, metal fluoride: 8-20%,
Mg: 0.5-3.0%, Si: 2.8-5.8%, M
n: 0.5 to 4.0%, Ni: 8 to 14%, Cr: 0.
02% or less, Ti: 0.3 to 0.8%, and if necessary, Mo: 0.9% or less, SiO as an acidic oxide.
₂ , the total content of TiO ₂ and Al ₂ O ₃ : 12% or less, and the steel core wire is coated with a coating agent other than the above, including an arc stabilizer, a slag forming agent, and a binder. It is a low hydrogen type coated arc welding rod.

[0007]

It has been conventionally known that it is effective to reduce the oxygen content of the weld metal in order to improve the toughness of the weld metal.
However, in the covered arc welding rod, oxygen generated by decomposition of the coating agent and oxygen in the atmosphere are caught in the arc during welding and enter the weld metal, so that the oxygen cannot be significantly reduced. Further, it is known that it is effective to reduce impurities in the weld metal in order to improve the toughness of the weld metal after PWHT, but the CTOD value was not significantly improved and stable toughness was not achieved. As a result of various investigations by the present inventors, adding Mg to the coating agent,
Controlling Si and Mn in the coating agent, as well as Ti and C
By limiting r and Mo, and limiting C, P, S, and N in the core wire, a coated arc welding rod that can obtain a weld metal with high strength and high toughness even after PWHT has been developed. The reason for limiting the components in the present invention will be described in detail below.

[Core Wire Component] In the steel core wire of the present invention, when C exceeds 0.03% by weight, martensite is formed to deteriorate toughness and crack resistance. Further, in order to improve low temperature toughness and fracture toughness after PWHT, P, S,
Limit N.

[0009] P and S segregate in the final solidified portion during welding, and the toughness deteriorates. Although it is desirable that P and S of the core wire be reduced as much as possible, the cost of the core wire is increased as the number is decreased.
Therefore, the amounts of P and S are each set to 0.010% by weight or less as a range in which the low-temperature toughness of the weld metal is less affected.

Reducing the amount of N in the weld metal is effective in improving the toughness of the weld metal. The amount of N in the weld metal is not only mixed in from the atmosphere during welding, but also entered from N in the welding rod core wire. Therefore, it is desirable to keep N of the core wire as low as possible, but like P and S, this leads to an increase in manufacturing cost. Therefore, the amount of N is set to 0.005% by weight or less as a range in which the low temperature toughness of the weld metal is less affected.

The core wire used in the welding rod of the present invention is not specified except for C, P, S and N, but the other components are preferably in the range specified in JIS G3523.

[Coating agent] Metal carbonate means CaCO ₃ ,
It refers to MgCO ₃ , BaCO _3, etc., and has a function of decomposing by the heat of the arc to generate a gas and protecting the arc atmosphere from the atmosphere. If the sum of one or more of them is less than 30% by weight, the shield gas is insufficient, and nitrogen in the atmosphere in the weld metal,
A large amount of hydrogen and oxygen dissolve, causing deterioration in toughness and crack resistance. Further, if it exceeds 60% by weight, the arc becomes unstable and the bead shape and the slag removability deteriorate, so the range was set to 30 to 60% by weight.

The metal fluorides are CaF ₂ , MgF ₂ and A.
refers to lF _3, etc., it will be added for fluidity modifier of the molten slag, in which one or more total is less than 8% by weight of the insufficient viscosity of the molten slag becomes poor encapsulation of the slag, bead shape Also deteriorates. If it is added in an amount of more than 20% by weight, the shape of the coated cylinder becomes incomplete and the stability of the arc is deteriorated.

[0014] Mg acts as a deoxidizer and is effective for obtaining a clean weld metal, and is also very effective as an arc stabilizer for securing welding workability. The amount added is 0.5
If it is less than wt%, a sufficient deoxidizing effect cannot be obtained. Meanwhile, 3.
If added in excess of 0% by weight, the arc during 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 is 0.5 to 3.0. It was set to% by weight.

Si is used for the purpose of deoxidizing the weld metal, but it is also necessary from the viewpoint of ensuring welding workability. 2.
If it is less than 8% by weight, pores are easily generated in the weld metal due to insufficient deoxidation, and the welding workability in the vertical position deteriorates. On the other hand, if it exceeds 5.8% by weight, the toughness of the weld metal decreases, and S
Since it causes R embrittlement, the Si content range is from 2.8 to
It was determined to be 5.8% by weight.

Like Si, Mn is important as a deoxidizing agent, must be contained in at least 0.5% by weight, and is a component necessary for maintaining strength. The upper limit is 4.0
The weight% is not preferable in terms of toughness and SR embrittlement if it exceeds this, so the Mn content range of the welding rod is set to 0.5.
Was determined to be 4.0% by weight.

With regard to Ni, it becomes difficult to obtain high toughness when the Ni content of the welding rod is less than 8% by weight in the target high-strength weld metal. On the other hand, if it exceeds 14% by weight, the grain boundaries of the weld metal become embrittled, grain boundary fracture occurs and the toughness decreases, so the Ni content range was made 8 to 14% by weight.

When Cr exceeds 0.02% by weight, quench hardening of weld metal, crystallization of δ ferrite phase occurs, and low-temperature toughness and toughness after PWHT deteriorate remarkably.
It is limited to less than or equal to weight%.

Ti is effective as a part of a strong deoxidizing agent, but if it is less than 0.3% by weight, a sufficient deoxidizing effect cannot be obtained. On the other hand, if it exceeds 0.8% by weight, the precipitation of titanium oxide increases, the hardness increases and the variation in hardness also increases, and the toughness deteriorates.
It was 0.8% by weight.

Although each of the above components is an essential component, Mo and an acidic oxide can be added as other components. Similar to Cr, Mo causes δ ferrite phase to crystallize, and the low temperature toughness and toughness after PWHT are significantly deteriorated.
The content range of is limited to 0.9% by weight or less. The acidic oxide refers to SiO ₂ , TiO ₂ , Al ₂ O _{3 and the} like, and can be added for the purpose of adjusting the viscosity of the molten slag. However, the amount of SiO ₂ , TiO ₂ , Al ₂ O _{3 in} the coating agent If the total amount exceeds 12% by weight, the basicity of the slag is insufficient, and it becomes difficult to reduce the oxygen content of the weld metal to 0.02% or less. Therefore, the total content is set to 12% or less.

The other components mainly consist of a deoxidizer, an arc stabilizer, a slag forming agent, a binder and an alloying agent. The deoxidizing agent may be an ordinary deoxidizing agent. The alloying agent refers to V, Nb, etc., and is added as necessary for the purpose of increasing the strength of the weld metal, improving heat resistance, corrosion resistance, and the like. In addition to the respective metal powders, they are added in the form of alloy powders with iron and other metals. The arc stabilizer and slag forming agent refer to iron, alkali components, rutile and the like.
Further, examples of the binder include potassium silicate, sodium silicate and the like.

The coated arc welding rod of the present invention includes, for example, a steel core wire containing the above-mentioned elements, an arc stabilizer, iron powder, an alkaline component, a slag forming agent such as rutile, sodium silicate, and water glass containing potassium silicate. The coating material obtained by kneading with the binder of No. 1 is coated and coated by a conventional welding rod coating machine, and then baked at 300 to 550 ° C. to remove water, and thus manufactured.

[0023]

EXAMPLES The effects will be concretely shown below by Examples of the present invention. Steel core wire having the chemical composition defined in Table 1 (4.
0 mm diameter) with the coating agent shown in Table 2 at a coverage of 20 to 4
A coated arc welding rod was manufactured by coating so as to be 5%.
Using the various welding rods obtained, a thickness of 25m as the base metal for the test
The X groove was applied to the steel plate of m and arc welding was performed. The welding conditions are welding current 150 A, welding heat input 30 kJ / cm,
A prefabricated / pass-pass temperature of 100 to 200 ° C. and a welded joint were prepared in a vertical posture.

[0024]

[Table 1]

[0025]

[Table 2]

A tensile test and a 2 mmV notch impact test at a test temperature of -60 ° C. were performed on the obtained weld metal. Further, the weld metal prepared under the above welding conditions was subjected to PWHT at 570 ° C. for 3 hours, and then subjected to a tensile test, a 2 mmV notch impact test at a test temperature of −20 ° C., and a CTOD test at a test temperature of −20 ° C. The results are shown in Table 3.

[0027]

[Table 3]

All of A1 to A9 satisfy all the requirements of the present invention, and show good values together with strength and low temperature toughness, and strength, toughness and CTOD value after PWHT are also good values. Further, the amount of diffusible hydrogen was measured by a gas chromatographic method based on JIS Z3118 “Method for measuring hydrogen amount in steel welded portion”. All the welding rods of the present invention are 3 ml / 1
It is about 00 g and is D801 described in JIS Z3212.
The hydrogen content of 6 was 6 ml / 100 g or less.

The welding rods A10 to A20 show comparative examples. The welding rod A10 is poor in welding workability because the metal fluoride and Ti exceed the upper limits. Further, Ni in the coating material was below the lower limit, and the toughness was lowered. Mn, Ni, Ti and Mo in the coating material of the welding rod A11 were out of the range, and the welding workability and toughness were deteriorated.

In welding rod A12, the Ti content in the coating material was below the lower limit, and the total amount of acidic oxides in the coating material exceeded the upper limit, so the amount of oxygen increased. Also, Ni was lower than that, and the toughness was lowered. Some of the welding rods A13 and A14 have C, P, S and N of the used core wires exceeding the upper limit,
Remarkably low low temperature toughness and CTOD value.

In welding rod A15, Ni in the coating material was below the lower limit, and the low temperature toughness was lowered. In the welding rod A16, the metal carbonate exceeded the upper limit, and the welding workability deteriorated. Furthermore, the Cr content in the coating exceeds the upper limit, and the toughness after PHWT and CT
The OD value decreased significantly. The welding rod A18 is N in the coating agent.
i exceeds the upper limit and the toughness is low.

In the welding rod A19, the metal carbonate was below the lower limit, and the Mg content in the coating material was above the upper limit, the welding workability was deteriorated. In the welding rod A20, the metal fluoride exceeded the upper limit, and the Si in the coating material fell below the lower limit, degrading the welding workability. Furthermore, since Cr exceeds the upper limit, P
Low toughness and CTOD value after WHT.

[0033]

As described in detail above, since the core wire and the coating material are regulated in the low hydrogen type covered arc welding rod, the HT
Excellent low temperature toughness and excellent toughness and CTOD value after PWHT are obtained for weld metal with high strength of 590 grade or higher. Therefore, the reliability of the welded joint for various steel structures can be significantly improved.

Claims (2)

[Claims] 1. A low-hydrogen coated arc welding rod, wherein the weight% of the steel core wire is C: 0.03% or less, P: 0.010% or less, S: 0.010% or less, N: 0.005% or less. As a coating material around the steel core wire regulated by the above, metal carbonate: 30 to 60% Metal fluoride: 8 to 20% Mg: 0.5 to 3.0% Si: 2.8 to 5.8% Mn: 0.5 to 4.0% Ni: 8 to 14% Cr: 0.02% or less Ti: 0.3 to 0.8%, arc stabilizers other than the above, slag generators, binders A low hydrogen-based coated arc welding rod, characterized in that the steel core wire is coated with a coating agent containing. 2. The coating material further contains Mo: 0.9% or less, and the total amount of SiO ₂ , TiO ₂ , and Al ₂ O ₃ as an acidic oxide: 12% or less. Low-hydrogen coated arc welding rod.