JPH0829431B2 - Low-hydrogen coated arc welding rod - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a low-hydrogen coated arc welding rod, and particularly to 60
The present invention relates to a low-hydrogen coated arc welding rod that can obtain good fracture toughness as a solvent for high-strength steel of Kgf / mm ² grade or higher and low Ni steel.

(Prior art and problems to be solved) In recent years, introduction of elasto-plastic fracture mechanics to ensure safety of steel structures, particularly high-pressure tanks and pressure vessels, and higher fracture toughness of welded parts accompanying it The demand for value is noted as a trend in design concept. The required characteristic values are the fracture surface transition temperature (vTrs) in the Charpy impact test, which is related to the brittle fracture initiation temperature, and the fracture toughness value (K
_IC ) is a typical example.

Conventionally, it has been difficult to secure the toughness of the welded portion, and therefore, these structures are mostly manufactured from low-strength materials, but there is a greater demand for high-strength steel that can increase the allowable stress. It is rising.

The present invention has been made to meet such a demand, and an object of the present invention is to provide a welding material which can obtain good fracture toughness particularly for welding high-strength steel and the like.

(Means for Solving the Problems) In order to solve the above problems, the inventors of the present invention have focused on the fracture toughness value (K _IC ) and have been able to obtain a high-strength steel coated arc welding rod with good fracture toughness. Added earnest consideration.

As is well known, in the field of low strength weld metal, toughness is improved by using a Ti-B type weld metal. But,
Since the high-strength weld metal has a mixed structure of martensite and bainite, the approach for improving the toughness is different from that of the former.

Therefore, the inventors of the present invention have clarified the following important matters as a result of earnest studies to find a method effective for improving the toughness of the high-strength weld metal, based on a new viewpoint.

That is, it was found that good fracture toughness can be obtained by applying the following (1) to (5) in the weld metal.

(1) N which is harmful to toughness is 0.008% or less, (2) C is 0.06% or less to form a low carbon structure, (3) Oxygen content is 0.02% or less (conventional covered arc welding). For rods, 0.03% is the limit as shown in Fig. 7), (4) toughen the matrix by adding Ni to 1.5% or more, and (5) reducing P to 0.010% or less to reduce embrittlement in the reheat zone. (See FIG. 8).

As a result of further research on concrete means for achieving these matters, it was found that the following means are particularly effective.

In order to keep N in the molten metal at 0.008% or less, CO ₂ in the coating material should be 8% or more (see Fig. 2), and N in the core wire should be 0.005% or less (see Fig. 1). , Coverage 2
6 to 45% (see Fig. 3), in order to keep C of molten metal at 0.06% or less, C of core wire
Of 0.05% or less, and in order to keep the oxygen content of the weld metal at 0.02% or less, Mg should be contained in the coating agent at 1.3% or more (see Fig. 4),
Set the Mn of the entire welding rod to 0.3% or more, and similarly set Al to 0.1%.
0% or less (see Fig. 5), total 12% or less of acidic oxides in the coating (see Fig. 6), and P of the entire welding rod to 0.010% or less.

The present invention has been completed through more detailed experiments based on the above findings.

That is, according to the present invention, metal carbonate is 8 to 28% in terms of CO ₂ and metal fluoride is 4 to 9 in terms of fluorine around a steel core wire regulated to C: 0.05% or less and N: 0.005% or less. %, Mg 1.3
~ 3.5% content, the balance mainly deoxidizing agent, alloy, iron,
It consists of a slag agent and a binder. Of these, as acid oxides, 9% or less of SiO ₂ , 3% or less of TiO ₂ , 2% or less
Al ₂ O ₃ , 2% or less of ZrO ₂ is regulated to 12% or less in total so that the coating rate (% of coating weight relative to the total weight of the bar) is 26 to 45%. Moreover, as a whole welding rod, Mn: 0.3 to 2.1%, Ni: 1.5 to 6.0%, Al: 0.10% or less, P: 0.010% or less, 60 Kgf / m
The gist is a low-hydrogen coated arc welding rod for welding high-strength steels of m ² or more and low-Ni steels.

 The present invention will be described in more detail below.

Component metal carbonates (action) coatings, primarily to the N in the weld metal to 0.008% or less, the content in the coating in terms of CO ₂ 8-28
The range is%. This is because the N content in the weld metal is less than 8%.
Is increased and the toughness is reduced (see FIG. 2), and if it exceeds 28%, the viscosity of the slag increases and vertical welding becomes difficult, which is not desirable. In addition, as metal carbonate
CaCO ₃ , BaCO ₃ , MgCO _{3 and the} like can be mentioned.

The content of the metal fluoride in the coating agent is 4-9% in terms of fluorine in order to adjust the viscosity of the slag and maintain workability. This is because if it is less than 4%, the viscosity of the slag increases and the bead shape deteriorates, and if it exceeds 9%, the arc becomes unstable and upward welding becomes difficult, which is not desirable. The metal fluorides are CaF ₂ , NaF, BaF.
₂ , AlF _{3 and the} like.

Mg is an element that has an extremely large effect of reducing oxygen in the weld metal, and in order to keep the oxygen content in the weld metal at 0.02% or less,
The content in the coating agent is set to 1.3 to 3.5%. this is,
If it is less than 1.3%, it is difficult to reduce the amount of oxygen to 0.02% or less and the toughness is not improved (see Fig. 4). If it exceeds 3.5%, the spread of the arc deteriorates and welding becomes difficult, which is not desirable. Is. In view of productivity, Mg is mainly added in the form of an alloy, and it is preferable that the amount of Mg in the form of a metal having a high reactivity with a binder is 1% or less.

As components of the coating agent, each of the above components are essential components, but other components are mainly deoxidizing agents, alloys, iron,
It is composed of a slag agent and a binder.

The deoxidizing agent may be an ordinary deoxidizing agent. The alloy is added to improve strength, and examples thereof include alloys of Mo, Cu, Nb, V, etc., but may be added as a simple metal.

As the slag agent, SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , MgO, etc. can be added for the purpose of adjusting the viscosity. Examples of the binder include potassium silicate, sodium silicate and the like.

However, among these, it is necessary to regulate the amount of each component of the acidic oxide and the total amount thereof as follows.

That is, if SiO ₂ exceeds 9%, it becomes glassy slag and deteriorates the peelability, so the content is made 9% or less. Ti
If O ₂ exceeds 3%, the viscosity of the slag decreases and the workability deteriorates, so the content is made 3% or less. If each of ZrO ₂ and Al ₂ O ₃ exceeds 2%, glassy slag is generated and the peelability is deteriorated. Furthermore,
If the total amount of these acidic oxides (SiO ₂ , TiO ₂ , ZrO ₂ and Al ₂ O ₃ ) exceeds 12%, the basicity of the slag will be insufficient and the oxygen content of the weld metal will be 0.02% or less. Since it will be difficult (see Fig. 6), the total amount should be 12% or less.

The coating material having the above composition is coated around the steel core wire with a suitable binder.

Components of the core wire In the steel core wire of the present invention, when C exceeds 0.05%, C of the weld metal exceeds 0.06%, high carbon martensite is generated, and toughness deteriorates.

Further, when N exceeds 0.005%, N of the weld metal is 0.008
%, The internal strain increases and the toughness deteriorates.

Therefore, it is necessary to use the steel core wire in the present invention that contains C: 0.05% or less and N: 0.005% or less.

Although such a core wire is usually carbon steel, S
Deoxidizing elements such as i, Mn, Ti, Al, NiCr, Mo, Cu, Nb,
An element such as V can be added if necessary.

Coverage The coating material having the above composition uses the steel having the above composition as the core wire,
It is necessary to coat so that the coverage A (%) represented by the following formula is 26 to 45%.

However, if the coverage is less than 26%, even if a large amount of metal carbonate is contained in the coating agent, the shield will be insufficient, N in the weld metal will increase and the toughness will decrease, and if it exceeds 45%, the arc length will increase. Becomes longer, the arc becomes short, the shield becomes insufficient, and N in the weld metal increases, which is not desirable (see FIG. 3).

In the present invention, in addition to the above-mentioned conditions, it is necessary to adjust Mn, Ni, Al, P and the like as components of the entire welding rod in the present invention, as described below. In this case, taking the case of Mn as an example, the amount of each component of the entire welding rod is
It is an amount expressed by the following formula.

First, the [Mn of the welding rod] is in the range of 0.3 to 2.1%. If it is less than 0.3%, it becomes difficult to make the oxygen content of the weld metal 0.02% or less, and if it exceeds 2.1%, the upper bainite structure is crystallized and the toughness deteriorates, which is not desirable. Incidentally, Mn can be added from the core wire or the coating agent or both, and as the Mn source in the coating agent, metal Mn, Fe-
Mn, Si-Mn, etc. are usually used.

[Ni of welding rod] is in the range of 1.5 to 6.0%. In the target high-strength weld metal, it is difficult to obtain high toughness when [Ni of the welding rod] is less than 1.5%, so it is necessary to set it to 1.5% or more. The upper limit is 6.0% in consideration of application to 5% Ni steel. Ni can also be added from the core wire or the coating agent or both, and metallic Ni or an alloy is usually used as the Ni source in the coating agent.

[Al of welding rod] is 0.10% or less. Al acts as a deoxidizer, but if [Al of welding rod] exceeds 0.10%, a large amount of Al ₂ O ₃ in the deoxidation product remains in the weld metal, and the deoxidizing effect disappears. Is not desirable because it deteriorates the toughness (see FIG. 5). Although Al can be added from the core wire or the coating agent or both, metal Al, Fe—Al, etc. are usually used as the Al source in the coating agent.

[P of welding rod] is 0.010% or less. This is 0.010%
If it exceeds, the reheat zone generated by the multi-layer welding thermal cycle becomes extremely brittle and the toughness deteriorates, which is not desirable. Since P is an impurity, it is important to use a highly pure raw material as the coating agent.

Note that [Si of welding rod] is 1.0 to 2.5%, [Ti of welding rod]
Is preferably 0.8% or less. Si is effective as a normal deoxidizer, but if it is less than 1.0%, workability in vertical welding deteriorates, and if it exceeds 2.5%, it becomes excessively viscous and workability deteriorates, which is not desirable. Ti is also effective as a part of the deoxidizing agent, but if it is more than 0.8%, seizure of slag is caused and workability is deteriorated, which is not desirable.
When these Si and Ti are added, they can be added from the core wire or the coating agent or both, but Si in the coating agent can be added.
An alloy such as Fe-Si is usually used as the source, and an alloy such as Fe-Ti is usually used as the Ti source in the coating agent.

 Next, examples of the present invention will be described.

(Example) A core wire having the chemical components shown in Table 1 and a coating material having the chemical components shown in Tables 2 and 3 or a coating material having the chemical components shown in Tables 4 and 5 Use, rod diameter 4m
A welding rod of m was prepared. The welding rod of the present invention is the second
The welding rods of the comparative examples are shown in Tables 3 and 4, and Tables 4 and 5 show the comparative welding rods.

Welding tests were performed using these welding rods. In the welding test, a steel plate having a plate thickness of 25 mm (steel material shown in Table 6) was taken with an X groove, and welding was performed with a heat input of 25 KJ / cm in a vertical position, and after welding, a Charpy impact test piece from the weld metal ( 2 mmV notch), tensile test pieces and fracture toughness test pieces (according to ASTM E813) were sampled and various tests were carried out. The workability of welding and the oxygen content of the weld metal were also examined. The results are shown in Table 6.

 From Table 6, the following is considered.

The invention examples (E1 to E8) all had good workability, and exhibited good strength and toughness.

On the other hand, in Comparative Examples (T1 to T17), neither workability nor toughness can be satisfied at the same time.

That is, in Comparative Example T1, since CO ₂ is as small as 6.2%, N
, And showed low toughness. Comparative Example T2 has CO ₂ of 29.5
%, And in Comparative Example T3, F was 2.5%, which was too small, resulting in a convex bead, and the mechanical test was stopped.

Comparative Example T4 has good strength and toughness, but F is 11.3%.
The arc was unstable because it was contained.

In Comparative Example T5, since the Mg content was as small as 0.9%, the oxygen content of the weld metal was high, and good toughness was not obtained. Comparative Example T6
The content of Mg was 4.1%, which was too large, making welding difficult and stopped the test.

Since Comparative Example T7 has too much SiO ₂ of 12%, Comparative Example T8 has
The ZrO ₂ content was 3%, which was too large, and the slag releasability deteriorated. In all cases, the relaxation of acid oxides exceeded 12%, so the weld metal had a high oxygen content and exhibited low toughness.

Since the coverage of T9 and T10 of Comparative Examples was less than 26% or more than 45%, workability was poor and N was increased to show low toughness.

Comparative Example T11, the Mn of the whole welding rod is too small as 0.23%, the oxygen content of the weld metal is high, while Comparative Example T12 is
Since the Mn of the whole welding rod was 2.30%, which was too large, a large amount of upper bainite structure was crystallized, and all exhibited low toughness.

In Comparative Example T13, Ni in the entire welding rod was less than 1.5%, so good toughness was not obtained.

In Comparative Example T14, the Al content of the welding rod is 0.15%, which is too high.
In Comparative Example T15, the P content of the entire welding rod was as large as 0.014% and the reheat zone was significantly embrittled. Therefore, in Comparative Example T16, the C of the core wire was 0.08%.
%, A large amount of high martensite was crystallized, so that Comparative Example T1
No. 7 had a low N toughness of 0.008%, and thus all exhibited low toughness.

(Effects of the Invention) As described in detail above, according to the present invention, the composition of the core wire and the coating agent and the composition of the entire welding rod in the low-hydrogen-coated arc welding rod, and the coating rate are regulated, so that it is particularly 60 Kgf / mm ²
Excellent toughness can be obtained for the above high-strength steels and high-strength weld metals of low Ni steels. Therefore, the effect of contributing to the high tensile strength steel structure is remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the N content of the core wire and the N content of the weld metal,
Fig. 2 is a diagram showing the relationship between the amount of CO ₂ in the coating material and the amount of N in the welding rod metal, Fig. 3 is a diagram showing the relationship between the breaking rate and the amount of N in the welding metal, and Fig. 4 is the coating material Fig. 5 shows the relationship between the amount of Mg in the weld metal and the amount of oxygen in the weld metal. Fig. 5 shows the relationship between the amount of Al in the entire welding rod and the amount of oxygen in the weld metal. Fig. 6 shows the amount of acidic oxide in the coating and welding. Fig. 7 shows the relationship between the oxygen content of the metal, Fig. 7 shows the relationship between the oxygen content of the weld metal and vTrs (fracture transition temperature in Charpy impact test) and K _IC (fracture toughness value) of the weld metal. FIG. 8 is a diagram showing the relationship between the P content of the entire welding rod and the weld metal zone vTrs and K _IC .

Claims (1)

[Claims] 1. A metal carbonate around a steel core wire regulated to C: 0.05% or less and N: 0.005% or less by weight% (the same applies hereinafter), containing 8 to 28% of metal carbonate in terms of CO ₂ and metal fluoride. 4 to 4 in terms of fluorine
9%, 1.3-3.5% Mg, balance is mainly deoxidizer,
It consists of alloy, iron, slag agent, and binder. Of these, as acid oxides, 9% or less of SiO ₂ , 3% or less of Ti
O _2, 2% or less of Al ₂ O _3, 2% or less of the coating agent obtained by regulating the 12% or less ZrO ₂ in total, the coverage (ratio of the coating agent by weight with respect to rod total weight) 26-45 %, And the entire welding rod is Mn: 0.3-2.1%, Ni: 1.5-6.0
%, Al: 0.10% or less, P: 0.010% or less, a low-hydrogen coated arc welding rod for welding high-strength steel of 60 Kgf / mm ² or more and low Ni steel.