JPS5922633B2 - Low hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-hydrogen coated arc welding rod, and more particularly to a low-hydrogen coated arc welding rod that provides a weld metal with good low-temperature toughness and tensile strength.

The coating of coated arc welding rods used for welding low-temperature steel and high-tensile steel of grade 50 to 9 f/m4 or higher contains Mn, Cr, Mo, etc. in order to give a specified strength to the weld metal. Furthermore, in order to improve toughness, it is customary to contain Ni or the like in the form of metal powder or alloy powder, respectively. However, even when these coated arc welding rods are used, the notch toughness of the weld metal is insufficient, and when large amounts of alloying elements are added to obtain high strength, the weld metal hardens and the notch toughness further deteriorates. death,
In addition, the alloy components solidify without being sufficiently diffused, causing segregation and impairing the uniformity of strength. For example, reference photo 1 is a cross-sectional macro photo showing the state of Ni segregation in the deposited metal obtained using a conventional coated arc welding rod, and segregation is seen in the circled area.

Reference photo 2 shows a 50 times enlarged photo of the segregated area. Moreover, FIG. 1 shows the analysis results of Ni by EPMA, and the state of macro segregation can be confirmed. However, the measurement conditions of EPMA are A
CC, voltage: 20KV, sample current: 0.05μAl chart speed: 20Rm/min, sample speed: 50μm
/minute. The deterioration in the physical properties of weld metal due to the above-mentioned macro-segregation is particularly apparent when a low-hydrogen coated arc welding rod is used. However, the weld metal using this type of welding rod has a high impact value, and since it is the welding rod that exhibits the effect of Ni addition most, the deterioration of the above physical properties due to macro segregation is a particular problem. Also, patterns along the lines of segregation are observed in magnetic particle testing. The inventors of the present invention paid attention to the above-mentioned circumstances and conducted experiments to first investigate the cause of macro segregation.

As a result, it was confirmed that the particle size of the alloy powder of the metal powder mixed in the coating material has a close relationship with macro segregation. That is, if the metal powder or alloy powder transferred from the coating material into the molten pool during the welding process is a fine particle, it will be dispersed into the molten metal by the arc force. However, in the case of coarse particles, solidification is completed before they are uniformly dispersed, and macro segregation appears, and this tendency becomes worse when a low-hydrogen coated arc welding rod with weak arc force is used. Therefore, we thought that macro segregation could be suppressed by making the metal powder or alloy powder mixed in the coating material as fine as possible, and as a result of intensive research along this line, we arrived at the present invention. That is, the low hydrogen-based coated arc welding rod according to the present invention contains a deoxidizing agent, a slag forming agent, and an arc stabilizer, and also contains one or more carbonates selected from the group consisting of CacO3, MgcO3, and BacO3. 25 to 55% in total (weight (fl): same below), C
2-30% aF2, 15% metal powder and/or alloy powder
In a low-hydrogen coated arc welding rod in which a coating material containing a binder as a main component is distributed around the outer periphery of a steel core wire, the particle size of the coating material raw material excluding metal powder and/or alloy powder is 296 μm. Those below and 74μ or less are 25(f
), and the particle size of the metal powder and/or alloy powder is adjusted so that the particle size of 149μ or more becomes 20q6 or less. Based on the knowledge that the particle sizes of Ni, Cr, and MO contained in coating materials have a close relationship with microsegregation, the present inventors conducted experiments to quantitatively confirm these relationships. .

That is, CaCO3: 45%, CaF2: 18%, Si content of 45% Fe-Si: 10%, Mn: 3q6 and Ti
The basic composition is a low hydrogen coating agent consisting of 3% O2, to which 0.5 to 16q6 of Ni powder with different particle size composition is added, water glass is added as a binder, and this is made into a steel core wire (5.
0wmφ) and dried at 400 to 450°C to obtain a test bar. Using this sample rod, we used SM5O material of 100 different thicknesses (6 V grooves, groove angle: 30 degrees, root gap: 10r).
m) was welded downward at a current of 220A. Five test pieces were cut out from the obtained weld metal, polished, and enlarged 50 times to examine the number of segregations in each cross section. In addition, test bars containing 1 to 4.5% of Cr powder and test bars containing 0.5 to 3% of MO alloy powder in terms of MO were prepared in the same manner as above, and similarly the number of segregation I looked into it. The average number of segregated pieces of each test piece is as shown in FIG. As is clear from FIG. 2, when the metal powder content in the coating material is small, the number of segregated particles is extremely small regardless of the particle size of the metal powder.

Moreover, when the content of metal powder increases, segregation cannot be suppressed even if the particle size of the metal powder is adjusted. However, Ni, Cr and MO
There is a clear correlation between the proportion of coarse particles of 149μ or more in the powder and the number of segregated particles, and when the proportion of coarse particles is 2
By reducing the amount to 0% or less, the number of segregated particles can be significantly reduced. CacO3, MgcO3 and BacO3 are all equivalent substances and decompose during welding to produce CO and CO2.
occurs and exerts a shielding effect.

Therefore, in order to obtain a sufficient shielding effect, it is necessary to mix at least 25% of one or more of the above carbonates. However, if it is too large, the penetration becomes deep and spatter tends to occur frequently, so it must be kept at 55% or less. These carbonates also act as arc stabilizers and slag forming agents. CaF2 is a slag forming agent and is an essential component for improving the fluidity and pitting resistance of molten slag.
It is necessary to contain at least 2#) or more.

However, if it is too large, the arc becomes unstable, so it should be kept at 30% or less. As mentioned above, examples of metal powder include Cr, MO, Ni, etc., and these have the effect of improving the physical properties of the weld metal as shown below.

However, if the amount is too high, problems will appear in terms of physical properties and segregation will likely occur. That is, Cr contributes to improving the strength of the weld metal, but care should be taken because if it exceeds 3.5%, the number of segregated particles will increase and the toughness will decrease.

Like Cr, MO also has the effect of increasing the strength of the weld metal, but when it exceeds 2%, the number of segregated particles increases, the toughness decreases, and weld cracks are likely to occur. Ni is an extremely useful element that increases toughness and strength, but if it exceeds 14%, the number of segregated particles increases and weld cracking becomes more likely to occur. The above metal elements may be added as single metals, or in the form of their alloys or iron alloys, but the content of the above metal elements, excluding iron, in the total coating material must be 15% or less. It is desirable to do so. However, if it exceeds 15%, segregation cannot be sufficiently suppressed even if the particle size structure is adjusted.
Note that the metal powder or alloy powder in the present invention should be considered as excluding Fe-Mn, Fe-S1, etc., which can be used in combination as a deoxidizing agent. By the way, as is well known, suitable amounts of a slag forming agent, an arc stabilizer, a gas generating agent, and a deoxidizing agent are required as coating material components, and alloy additives other than those mentioned above may be added as desired. It goes without saying that these agents should be appropriately blended.

Among these, typical examples including the above-mentioned essential components are as follows. [Arc stabilizer] Calcite, toxite, rutile, anatase, illuminite, soft manganite, iron powder, potassium silicate, etc.

[Slag forming agent]

Silicate minerals (silica sand, feldspar, talc, mica, etc.), carbonate minerals (calcite, etc.), oxides (rutile, illuminite, iron ore, soft manganese, etc.), fluorides (fluorite, cryolite, etc.), etc.

[Gas generating agent]

Carbonate minerals, wood chips, starch, etc.

[Deoxidizing agent]

Fe-Mn, Fe-Si, Fe-Ti, Fe-Al, M
n, Si, Ti, At, etc.

[Alloy additive]

Si, Mn, Cu, Cr, CO, Ni, W, etc.

In addition, it is also effective to incorporate iron powder into the coating material to increase welding efficiency, similar to conventional low-hydrogen coated arc welding rods. However, if it exceeds 40%, the arc becomes unstable and welding workability, especially in a vertical position, deteriorates. Furthermore, trace amounts of B, Nb, V, P, or their oxides mixed into the coating material or the steel core material seriously impede the notch toughness of the weld metal.

Therefore, as a result of conducting experiments to quantitatively confirm the damage caused by the contamination of these impurity elements, we found that (B+N・b+
Keep the total content (in the case of oxides, converted to B, Nb, P) of V + P) to 0.035q6 or less, and also keep the content in the steel core wire to 0.015% or less. Ba,
Problems caused by the inclusion of these impurity elements can be suppressed to an almost negligible level. By the way, the coating agent used in the present invention is mixed with the above-mentioned essential ingredients and the above-mentioned agents as necessary, and is kneaded with a binder such as sodium silicate or potassium silicate, and then applied to the outer periphery of the steel core wire. It has been found that the productivity and performance of welding rods are significantly affected by the particle size composition of the coating materials, excluding metal powder.

That is, as a result of various experiments, 7 of the coating material raw materials excluding metal powder
If the content of fine particles of 4μ or less exceeds 25%, the arc force will be weak and the melting rate will decrease, the number of segregated particles will increase, welding workability will decrease, and dry cracking will become significant during welding rod production, resulting in a decrease in yield. Further, if coarse particles exceeding 296 μm are included, the coating material becomes difficult to coat during the coating process, reducing productivity and causing frequent spatter during welding. Therefore, the particle size structure of other coating material raw materials excluding metal powder is 2.
It must be 96μ or less, and 74μ or less is 2
Optimal is one that satisfies the conditions of 5% or less and 74-296μ of 75% or more. By the way, the greatest feature of the present invention is that the coarse particle content of the metal powder and alloy powder blended into the coating material is set below a certain value, thereby reducing the macro segregation of these metals and alloys. As is clear from the results in Figure 2, it is difficult to reduce the number of segregated particles to zero. Therefore, we conducted research to compensate for the decline in weld metal performance due to residual segregation by improving the core wire composition. As a result, it was found that by reducing the carbon content in the core wire as much as possible, the physical properties of the weld metal could be significantly improved even with the same amount of segregation. In other words, areas with a high concentration of Ni, etc. in the weld metal have a lower transformation point than other areas, and during the solidification process, carbon diffuses from the transformation start area to the untransformed area, so carbon is accumulated in the segregated area. Tend. The structure of this carbon accumulation area is extremely hard.
When subjected to impact force, stress concentration occurs and it is easy to break.
However, if a core wire with a low carbon content is used, carbon accumulation will be reduced, and the tendency for local hardness to increase will be suppressed.
As a result, the stress concentration occurring in the macro-segregation area is alleviated, and together with the reduction in the number of segregations, the mechanical properties, especially the low-temperature toughness, of the weld metal are significantly improved. For these reasons, the lower the carbon content in the core wire, the better; however, as is clear from the experimental results shown in Figure 3 below, if a steel core wire with a carbon content of 0.01% or less is used, Hardening of the segregated portion can be sufficiently suppressed. The present invention is constructed as described above, and in particular, by appropriately adjusting the particle size structure of metal powder, alloy powder, and other coating material raw materials, a high-quality weld metal with less segregation can be obtained. It is now possible to provide a hydrogen-based coated arc welding rod.

Next, an experimental example will be shown.

Example 1 A low-hydrogen coated arc welding rod was prepared by coating the outer periphery of a carbon steel core wire (5wr 1nφ x 400mm) with a carbon content of 0.06% with a coating material having the composition shown in Table 1, and each welding The workability and the number of segregated weld metals (measured in the same manner as in FIG. 2) when using a rod were investigated.

Hiroka is shown in Table 1. However, in Table 1 *1
~*5 indicates the following meaning. *1: JISG23
For O2 FSi3 applicable products, the particle size composition is 74μ or less.
0%, 21% of 74-105μ, 14% of 105-149μ, and 5% of 149-250μ.

*2: JISG23ll MMnE applicable product, particle size composition is 73% below 74μ, 11q6 between 74μ and 105μ,
105~149μ is 13C! 11149~250μ is 3
% was used.

*3: JISG2l3 Mcr applicable product.

*4: For JIS G23O7 FMOL applicable products, the numbers in the table are MO conversion values.

*5: At2O3, K2O, Na2O, TiO2, Si
Indicates C2 etc.

From Table 1, it can be considered as follows.

(1) Codes 1 to 3 are conventional bars in which the particle size of Ni powder or the like is not adjusted, and the number of segregated pieces is quite large. (2) On the other hand, code 4
~8 is an example in which the particle size of Ni powder, etc. was adjusted so that the coarse particles of 149μ or more were 20% or less, and a comparison of codes 1 and 4, where the Ni powder, etc. was 2%, and code 2, where the Ni powder, etc. was 8%. When comparing numbers 3 and 7 and 8, which are 14%, respectively, it can be seen that the number of segregated particles can be significantly reduced.

(3) Codes 9 and 10 are Ni powder at 0.50! I, the number of segregated particles is small regardless of the particle size structure, and the number of segregated particles is 1.
In Nos. 1 and 12, the amount of Ni powder is too high at 16%, so even if the particle size is adjusted appropriately, the number of segregated particles does not decrease much.

(4) In case of code 13, the fluidity of the molten slag is poor due to insufficient amount of CaF2 and pit defects appear, and in case of code 14, the arc is unstable due to too large amount of CaF2, and welding workability is poor in both cases.

(5) Since the number 15 has too much carbonate, the penetration tends to be too deep, and the number 16 has insufficient carbonate, so the shielding effect is insufficient.

(6) No. 17 indicates that the proportion of fine particles of 74 μm or less in the coating material raw materials other than metal powders and alloy powders is too large, so the arc becomes weak, the melting rate becomes slow, and the number of segregated particles increases. Further, in the case of No. 18, since the proportion of coarse particles of 296 μm or more in other coating material raw materials is too high, the coating properties during manufacture are poor, and spatters occur frequently during welding. (7) Codes 19-23
is one in which the Cr content and particle size structure are changed, and C
The higher the r content and the larger the amount of coarse particles of 149μ or more in the Cr powder, the more the number of segregated particles increases.

(8) Codes 24 to 28 are obtained by changing the MO content and particle size structure, and the higher the MO content, the more MO
As the amount of coarse particles of 149μ or more in the powder increases, the number of segregated particles increases.

Fig. 3 is a graph showing the relationship between the amount of carbon in the steel core wire and the hardness of the segregated part when coating materials 5 and 7 are used. If a certain core wire is used, even if some macro-segregation occurs, the hardening of the segregated portion is suppressed and crack resistance is improved.

Experimental Example 2 A coating material whose composition and particle size structure all satisfy the requirements of the present invention as shown in Table 2 was applied to the outer periphery of a steel core wire (4.0rmφ×400wr!nl) with a carbon content of 0.0.7%. A low hydrogen-based coated arc welding rod was manufactured by applying the same to

Using this welding rod, welding workability and JIS Z32l2
The tensile strength and impact strength (Sharpy impact value at -20°C) of the weld metal were investigated using Table 2. As is clear from Table 2, when the welding rod of the present invention is used, not only good welding workability can be obtained, but also segregation of metal powder and alloy powder does not occur, and welding with excellent low-temperature toughness and tensile strength can be achieved. You can get metal.

Experimental Example 3 A steel core wire (4
．． 0 starch (φ

In this example, (B+Nb+V+
In order to investigate the influence of the content rate of P), these are also listed. The particle size structure of the coating material raw material was adjusted to meet the requirements of the present invention. Using each obtained welding rod, the second
Welding was carried out under the same conditions as in the table, and the welding workability and physical properties of the weld metal were investigated.

The results are summarized in Table 3. From Table 3, the following can be considered. (1) Reference numbers 36 to 40 are comparative examples in which the blending ratio of carbonate, CaF2, or iron powder is out of the specified range, and welding workability is poor in all of them.

(2) The code 34 is a conventional 60 kg class welding rod (B+
Since the amount of Nb++P) is outside the preferred range, the impact strength is lower than that of No. 35, in which the same content is within the preferred range.

(3) The code 41 is a conventional 80 kg class welding rod (B+
Since the amount of Nb+V+P) is outside the preferred range, the impact strength is lower than that of code 42 in which the same content is within the preferred range.

(4) Reference numeral 43 is an 80kg welding rod containing an appropriate amount of iron powder, which provides high tensile strength and impact strength.

(5) Reference numeral 44 is an 80kg welding rod with a coating material containing a large amount of Ni, which satisfies the requirements of the present invention, and has good strength and
It has toughness. (6) Symbols 45 and 46 are 60 kg class and 100 kg class welding rods that satisfy the requirements of the present invention,
Excellent welding workability and physical properties of weld metal.

Figures 4 and 5 show weld metals before and after heat treatment obtained using conventional rods (numbers 34, 41) or the present invention rods (numbers 35, 42) for 60 kg and 80 kg class welding rods. The shock transition curve is shown for .

As is clear from this figure, by using the welding rod of the present invention, it is possible to obtain a weld metal with superior impact resistance compared to the case where a conventional rod is used.

[Brief explanation of drawings]

Figure 1 shows the EPM of the part where macro segregation of weld metal occurred.
Chart A, Figure 2 is a graph showing the relationship between the particle size structure of Ni, Cr and MO powder and the number of segregated particles, Figure 3 is a graph showing the relationship between the amount of carbon in the core wire and the hardness of the segregated part, 4th, Figure 5 shows the impact transition curves of the weld metals obtained in the experimental examples.

Claims (1)

[Claims] 1. A total of 25 to 10 carbonates selected from the group consisting of CaCO_3, MgCO_3 and BaCO_3.
A low hydrogen-based coated arc made by applying a coating material containing 55% by weight, 2 to 30% by weight of CaF_2, 15% by weight or less of metal powder and/or alloy powder, and a fixing agent to the outer periphery of the steel core wire. In the welding rod, the particle size of the coating material raw material excluding metal powder and/or alloy powder is 296 μ or less and 7
In addition to adjusting the ratio of particles of 4μ or less to 25% by weight or less, the particle size of the metal powder and/or alloy powder is adjusted.
A low-hydrogen-based coated arc welding rod, characterized in that the ratio of electrodes of 149μ or more is adjusted to be 20% by weight or less. 2. In claim 1, the metal powder and/or alloy powder contains 14% by weight or less of Ni, 3.5% by weight or less of Cr, and 2% by weight or less of Mo and/or Fe- A low hydrogen-based coated arc welding rod that is one or more types selected from the group consisting of Mo. 3. A low hydrogen-based coated arc welding rod using a steel core wire having a C content of 0.01% by weight or less, as set forth in claim 1 or 2.