JPS6057954B2 - Primer-resistant, low hydrogen-based coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a primer porosity-resistant, low hydrogen-based coated arc welding rod.

This invention is the result of the development of a low-hydrogen coating composition for welding rods that is advantageous in solving the problem of pitting that is inevitable in conventional butt or fillet welding, especially when an organic primer is applied. This is what we propose. When welding with conventional low-hydrogen coated arc welding rods is applied to steel plates that have already rusted or have been coated with a primer, pores (bits and blowholes) may occur, especially in butt or fillet welds. There was a problem that holes were likely to occur.

For this reason, JLS stipulates a method for measuring the amount of diffusible hydrogen in weld metal, and welding rods with a diffusible hydrogen amount of 10 (ml/100 y of weld metal) or less when determined by this measurement method are classified as low hydrogen welding. It is well known that welding high-strength steel using these low-hydrogen welding rods is extremely effective in preventing hydrogen-induced embrittlement and cracking.

However, when using these welding rods to manually or gravity weld downward or horizontal fillet welding parts of steel coated with a wash primer or zinc-rich primer, pores may be generated due to the primer. A great deal of effort is required to repair the defective parts, or to polish and remove the primer of the fillet welding member in advance to prevent the formation of pores.

The cause of pores during fillet welding of primer coated steel plates is that the growth of pores generated by the combustion gas of the primer generated in the voids of the fillet welded parts coincides with the progress of solidification of the molten metal. This very same phenomenon can occur in the case of butt welding.

This is caused by rain on the butt groove surfaces, the influence of moisture existing in the gap due to moisture, or moisture in rust based on this, and in such cases, welding of primer-coated steel materials as described above. The same pores as in the case of primers are generated, and therefore, the present invention is also concerned with prevention of these pores. It shall be included in porosity resistance. The inventors previously proposed the invention disclosed in Japanese Patent Publication No. 55-24397 as a measure to prevent the occurrence of such pores.

This method is mainly due to the method of improving the wettability of the weld metal, and has been shown to be quite effective. However, this method does not always satisfy welding workability because it requires the coating material to be basic. There are still some aspects where we are not getting the results we could have. Now, even in the case where a primer or the like is not present in the welding member, there is a close relationship between the amount of diffusible hydrogen and the generation of pores, and the inventors' studies can summarize the results as shown in FIGS. 1 to 3.

To summarize these, as shown in Figure 3, in the low hydrogen content region, there is not enough gas to generate pores in the weld metal, so as a result, no pores are generated in the solidified weld metal. . On the other hand, in the high hydrogen content region, as the weld metal solidifies, supersaturated dissolved hydrogen is extremely actively released into the molten metal, and for this reason, gas bubbles in the weld metal are likely to be released outside the system. As a result, the pores in the solidified metal disappear and no pores are generated. The inventor calls this kind of effect the pulling effect. On the other hand, in the intermediate hydrogen content region, there is enough dissolved hydrogen to generate gas bubbles in the molten metal, and on the other hand, there is not enough hydrogen to cause the bubbling effect mentioned above. Therefore, the timing of the solidification of the weld molten metal and the generation and growth of pores coincide, and as a result, pores are generated in the solidified weld metal.

In general, welding rods for mild steel are non-low hydrogen type welding rods, so they have a strong bubbling effect due to hydrogen and are not affected by primers, etc., and are insensitive to primer-coated parts or rusting materials, and have pores. It can be used without causing any problems.

However, the inventors have discovered that the intermediate hydrogen content region where pores occur in Figure 3 varies slightly depending on welding conditions (welding current, basicity of coating material, chemical composition of base material, etc.) and the presence of primer. I've confirmed it.

The presence of the primer generally exhibits a phenomenon in which the amount of diffusible hydrogen increases by about 3 to 5 ml. 50HTJ11Mg
Regarding the 01 SiO2-TiO2 fillet welding rod, bits occur when the amount of diffusible hydrogen is lower than about 13 ml in fillet welding of parts without primer coating, and when it is higher than that, bits occur. Bit does not occur.
On the other hand, when fillet welding parts are welded using a welding rod with a diffusible hydrogen content of 9.5 m1 and no primer is applied, pores occur, whereas the primer is applied to a film thickness of 20 m1.
Corner welding of parts coated with a thickness of ~30 μm results in no light generation. However, JIS
The standard for D5O26 (fillet welding rod for 50HT) requires that the amount of diffusible hydrogen be 10ml or less, so this condition can be met, and the porosity resistance against primer can be satisfied without using a primer. Fillet welding rods for 50HT, which do not generate pores and have excellent workability, have not yet been developed. This invention focuses on the fact that conventional welding rods with excellent anti-primer pore resistance have a strong bubbling effect, and first solves the lack of bubbling effect when the amount of diffusible hydrogen regulated by JIS is 10 mL or less. Complete primer porosity resistance is achieved by supplementing the molten metal with CO, a gas produced by the reaction of carbon and oxygen, and by adding nitrogen compounds such as manganese nitride and molybdenum nitride to the coating material, welding. We propose an improved coated welding rod that increases the amount of nitrogen dissolved in the molten metal and enhances the bubbling effect by releasing supersaturated nitrogen gas due to the decrease in nitrogen solubility as the molten metal solidifies, making it completely resistant to pores. There are things.

As mentioned above, the relationship between the amount of diffusible hydrogen and the generation of bits is affected by various welding conditions, but as shown in Figure 4, the inventors have determined the limit diffusibility of hydrogen, where pores are generated by deoxidizing components in the weld metal. It was found that the amount varies greatly.

That is, the manganese content in the total weld metal is 1.0% by weight.
In the case of , the limit diffusible hydrogen amount is 14 ml, whereas at 0.35% by weight, it decreases to about 10 ml.

In this case, the standard value for the amount of diffusible hydrogen according to JISD5O26 is 10.
Since it is less than m1, the amount of manganese in the weld metal is set to 0.35.
Although it is almost satisfactory if it is less than % by weight, it is not a fully satisfactory value when considering the dispersion of the measured value of the amount of diffusible hydrogen. The dissolved oxygen concentration in the weld metal is inversely proportional to the deoxidizing agent concentration in the weld molten metal, but by adding oxides such as hematite, magnetite, illuminite, or manganese dioxide to the coating material, the oxygen concentration in the molten steel can be reduced. Although increasing the CO reaction is effective in actively causing the CO reaction, it is not always necessary when carbon is added to the coating material as described below.

In other words, to enhance the bubbling effect, it is also effective to add graphite, activated carbon, or alloys containing carbon, such as medium- and high-carbon ferromanganese (JISG23Ol), high-carbon ferromolybdenum (JISG23O7), cast iron, and pig iron to the coating material. It is true.

The amount of carbon added to the coating material should be regulated by the final carbon and oxygen concentrations in the weld metal, and the amount of carbon in the weld metal is preferably 0.04 to 0.1 slag weight % or less.

If the carbon content in the weld metal is less than 0.04% by weight, the amount of carbon is not sufficient to cause a bubbling effect as a CO reaction,
If it exceeds 0.1% heel weight, it is not good because it increases the hardness of the weld metal and significantly deteriorates the impact performance.

Here, the inventors have discovered that the addition of carbon to the coating material is simple, such as graphite or activated carbon, as well as high carbon ferromanganese,
It was confirmed that there is no difference in the effect even if it is added as an alloy such as medium-charcoal ferromanganese, and that it is sufficient to consider it as the total addition amount of these carbon amounts.

As mentioned above, the amount of carbon added to the coating material must ultimately be controlled by the carbon content in the weld metal, but if this is converted to the amount added to the coating material, the total amount of carbon will be 0.
．． It was confirmed that the content should be in the range of 14% by weight to 0.85% by weight.

The amount of oxygen dissolved in the weld metal is influenced by the above-mentioned oxides in the coating material, but is ultimately determined by the manganese content, which is a deoxidizing component of the weld metal. Therefore, it is necessary that the manganese content in the total weld metal be 0.35% by weight or less. However, the manganese content is 0.
If it is less than 1% by weight, the deoxidizing ability is too insufficient, inclusions in the weld metal increase beyond the limit, the weld metal becomes unclean, and impact performance and ductility are significantly impaired, which is not good. Therefore, in order to satisfy the porosity resistance by setting the amount of hydrogen to 10 ml or less, the amount of Mn added to the coating material should be ultimately controlled by the Mn content in the total weld metal, as described above. As a result of various studies and experiments considering the addition of iron oxides as oxidizing agents as shown below, we found that Fe-Mn, etc.
The Mn content due to the combination of Mn-containing ferroalloys is 1
．． 9-6. It is necessary to keep it within the range of heel weight%.

In addition, the amount of iron oxide added to the coating material as an oxidizing agent must be determined by taking into account the manganese content as a deoxidizing agent in the weld metal as described above. It is preferable that any one scale, or the sum of two or three of them, be 8% by weight or less, and in the case of illuminite, 14% by weight or less. Even if these limits are exceeded, the effect of the present invention will not be diminished if an appropriate amount of deoxidizing agent is added, but this means that a large amount of the expensive deoxidizing metal will be added. Since it is economically expensive, it is better to keep it within the above limits. Furthermore, regarding nitrogen, as shown in Figure 5, nitrogen dissolved in weld metal exhibits almost the same behavior as hydrogen.
A bubbling effect similar to that of hydrogen described above can be expected.

However, since nitrogen in the weld metal forms various metal nitrides and causes embrittlement, its remaining amount must be limited. The amount of nitrogen in the weld metal of a normal fillet welding rod is 0.
However, in the present invention, nitrogen compounds such as ferromanganese nitride (nitrogen content of 4 to 4%) are contained in the coating material.
6% by weight) or ferrochromium nitride (nitrogen content 2~
4% by weight) to increase nitrogen dissolution in welding molten metal,
It was discovered that nitrogen causes a bubbling effect.

However, as mentioned above, nitrogen causes embrittlement, and the nitrogen content in the solidified weld metal is 0.022% by weight.
For this reason, ferromanganese nitride should be limited to 3% by weight or less, and ferrochromium nitride should be limited to 4% by weight or less. Other reasons for limiting the coating composition will be described below.

MgCO3 adjusts the viscosity of the slag and also has a shielding effect from the atmosphere caused by decomposed gas.

If it is less than 8% by weight, the viscosity of the slag will be too high, and the shielding effect will be weakened, impairing the bead shape or mechanical performance of the weld metal, which is not good.

If it exceeds 2% heel volume. This is not good because too much slag flow will cause the bead shape to deteriorate.

Since MgO is originally used for adjusting slag viscosity like MgCO3, the amount of MgO added needs to be limited within the above range in terms of MgCO3.

TiO2+ZrO2 has an effect as a slag forming agent and controls most of the slag viscosity. If it is less than 14% by weight, the amount of slag will be insufficient, and if it exceeds 35% by weight, the slag viscosity will increase too much, and it will become entangled with the end of the welding rod during welding, making the arc unstable and damaging the bead shape, which is not good.

Like TiO2, SiO2 acts as a sludge forming agent and increases slag viscosity.

If it is less than 5% by weight, the slag amount and viscosity will be insufficient and the bead shape will deteriorate.

Also, if the slag weight exceeds 3%, the slag viscosity will increase significantly,
Slag gets entangled in the welding rod, making the arc unstable.
This is not good as it will damage the bead shape. Iron powder can be added according to conventional practice to improve welding efficiency, especially in the case of fillet welding rods.

However, if it exceeds 45% by weight, the amount of slag will be insufficient and the bead shape will be impaired, which is not good. Talc, mica, kaolin, sericite, and clay each have the same effect as minerals containing crystalline water in that they have a direct relationship to the amount of diffusible hydrogen in the weld metal, and one or more of these minerals have the same effect in that they have a total weight of 3. %, the amount of diffusible hydrogen exceeds 10ml and JISD5
It becomes impossible to satisfy the standard value of O26.

Furthermore, if it is less than 0.4% by weight, the amount of dissolved hydrogen is too small, resulting in insufficient bubbling action and the formation of pores. Molybdenum and nickel are added to compensate for the decrease in tensile strength of the weld metal due to the decrease in manganese content in the weld metal and to improve impact performance. The amounts of molybdenum and nickel added must be considered in relation to their respective amounts. In this case, the addition of molybdenum and nickel to the coating material is MO equivalent expressed as MO+blue N1%), and 3. Heel weight% or less, especially 0.7 to 3. It is best to set it within the range of call volume %3. If the saliva content % is exceeded, the tensile strength is too high, which is not good.

The examples shown in Table 1 will be described below.

No. 1 indicates a conventional MgO-SiO2-TiO2 fillet welding rod (JISD5OOO and D5OO3), which has a high amount of diffusible hydrogen exceeding 10 ml.

No. 2 shows a conventional MgO-SiO2-TiO2 based low hydrogen fillet welding rod (JISD5O26), which has poor pore resistance to primer.

No. No. 3 is a comparative example related to the present invention, in which the amount of crystallization water in the coating material was insufficient, the bubbling effect was insufficient, and the pore resistance to the primer was poor.

No. Examples 4 to 7 are adaptations of the present invention, in which the amount of minerals containing water of crystallization (talc, mica, kaolin) added to the coating material is varied, but in these cases, the amount of diffusible hydrogen and the porosity resistance are Of course, satisfactory results can be obtained in all respects.

No. No. 8 is a comparative example in which the amount of the above-mentioned crystalline water mineral added is too large, and the amount of diffusible hydrogen exceeds 10 ml, making it impossible to satisfy the JIS standard. No. 9 to 11 are examples of the present invention in which iron oxide as an oxygen supplying agent is added to the coating material, and by adding a deoxidizing metal corresponding to the amount added, satisfactory results are obtained in accordance with the gist of the present invention. is obtained.

No. 12 is another specific example of the present invention, in which graphite was not used in the coating and the carbon source was only high carbon ferromanganese.

NO13-15 showed an example in which the bubbling effect was particularly promoted by nitride (ferromanganese nitride, nitrogen 5.1, manganese 70% by weight) added to the coating material.

NOl3 and l4 are within the range of this invention, and satisfactory results can be obtained in all respects. However, NO. In l5, the amount of nitride added is large, the nitrogen concentration in the weld metal exceeds the limit value, and the impact performance deteriorates significantly. No. 16 and 17 are examples of the present invention in which the bubbling effect is a combined effect of CO reaction gas and nitrogen.

It is shown that addition amounts within the limits of both are satisfactory without any problems. No. 18 and 19 are examples of the present invention in which chromium nitride was used as the nitrogen source, and satisfactory results were obtained in all respects.

No. 2O, 2L is a comparative example in which the amount of carbon added in the coating material is reduced, and the bubbling effect is weak and the pore resistance is poor.

No. No. 22 is an example in which molybdenum is not added to the coating material, and although the tensile strength of the weld metal is slightly insufficient, it is suitable for applications where this is not necessary.

By using the welding rod of this invention, which satisfies the JIS standard as a low-hydrogen welding rod and exhibits excellent porosity resistance against primers, there is no need to repair the pore-generated area, and it can be used to prevent pores. Significant efficiency improvements can be expected in that time and effort such as primer removal is no longer necessary.

It has also been confirmed that by adding appropriate amounts of Cu, Ni, and Cr to the coating material of this invention, a fillet welding rod having the same principle and excellent weather resistance or corrosion resistance can be produced.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between carbonate (CO2 equivalent) in the coating material, crystal water content, and porosity generation rate; Figure 2 is a diagram schematically showing the test results in Figure 1; Figure 3 is a chart that summarizes the results of Figures 1 and 2 in terms of the amount of diffusible hydrogen in the weld metal and the number of pores generated. Figure 4 shows the generation of pores when the manganese content in the total weld metal is changed. Figure 5 is a graph showing the solubility of hydrogen and nitrogen in pure iron.

Claims (1)

[Claims] 1 MgCO_38-27% by weight, TiO_2 and ZrO
14-35% by weight of one or both of _2, SiO_2
5 to 30% by weight, and a total of 0.4 to 3 of one or more of talc, mica, kaolin, clay, and sericite.
．． 0% by weight, and the carbon source made of graphite, activated carbon, or a ferroalloy containing carbon is 0.14% by weight.
~0.85% by weight, and a manganese source consisting of a ferroalloy containing manganese, including the ferroalloy, with an Mn amount of 1.9~
A primer pore-resistant, low hydrogen-based, coated arc welding rod made by applying a coating agent having a composition of 6.2% by weight around a steel core wire using water glass. 2 MgCO_38-27% by weight, TiO_2 and ZrO
14-35% by weight of one or both of _2, SiO_2
5 to 30% by weight, and a total of 0.4 to 3 of one or more of talc, mica, kaolin, clay, and sericite.
．． 0% by weight, and the carbon source made of graphite, activated carbon, or a ferroalloy containing carbon is 0.14% by weight.
~0.85% by weight, and a manganese source consisting of ferroalloys containing manganese, including the ferroalloy, with an Mn content of 1.9%.
~6.2% by weight of molybdenum and/or nickel or an alloy containing them in addition to Mo+(1/4.5)Ni
Primer pore-resistant, low hydrogen-based, coated arc welding rod made by applying a coating material containing a molybdenum equivalent of 3.0% by weight or less expressed around a steel core wire using water glass. . 3 MgCO_38-27% by weight, TiO_2 and ZrO
14-35% by weight of one or both of _2, SiO_2
5 to 30% by weight, and a total of 0.4 to 3 of one or more of talc, mica, kaolin, clay, and sericite.
．． 0% by weight, and the carbon source made of graphite, activated carbon, or a ferroalloy containing carbon is 0.14% by weight.
~0.85% by weight, and a manganese source consisting of ferroalloys containing manganese, including the ferroalloy, with an Mn content of 1.9%.
~6.2% by weight Furthermore, molybdenum and/or nickel or alloys containing them are added to Mo+(1+4.5)N
A coating material having a composition in which the molybdenum equivalent represented by i is 3.0% by weight or less, and ferromanganese of the above-mentioned ferroalloys is blended with 3% by weight or less and 4% by weight or less of ferrochromium nitride. A porosity-resistant, low-hydrogen, coated arc welding rod made by applying water glass around a steel core wire.