JPH0112595B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention has excellent micro-cracking resistance.
This relates to Ni-base coated arc welding rods. [Prior art] Ni or Ni-based alloys are used as heat-resistant and acid-resistant materials for various reactors, distillation columns, heat exchangers, pressure vessels, etc. used in harsh atmospheres such as hydrochloric acid, sulfuric acid, and hydrofluoric acid. The number of uses has increased year by year, and the number of types has become extremely large. These metals are classified into pure Ni, Ni-Cu (Monel alloy, etc.), Ni-Mo (Hastelloy A, Hastelloy B) depending on their chemical composition.
They are classified into Ni-Cr-Mo series (Hastelloy C alloy, etc.), Ni-Cr series (Inconel, Incoloy alloy, etc.), and are used to take advantage of their respective characteristics. By the way, when welding Ni or Ni-based alloys as mentioned above, Ni-Cu, Ni-Cr, Ni-
Covered arc welding rods whose core wires are made of various alloys such as Mo-based alloys are used, but inconel-based covered arc welding rods, which belong to the Ni-Cr system, can be obtained by welding using these. Since the weld metal has the advantage of having excellent corrosion resistance, heat resistance, and low-temperature toughness, it can be used for welding between Ni-based alloys, welding low-temperature steels such as 9% Ni steel, and dissimilar metals between Ni-based alloys and ferrite steel. Widely used for welding, etc. By the way, when there is a large amount of hydrogen in the core wire or moisture in the coating material, there is a tendency for microcracks to occur in the weld metal or welded area. The same applies to welding alloys, and when the amount of hydrogen in the core wire is large, microcracks occur. On the other hand, as structures have become larger in recent years, multi-layer welding has become more common, but in multi-layer welding, welding heat input is repeatedly applied and micro-cracking occurs due to thermal history. This tendency is particularly noticeable during high heat input welding.
When such microcracks occur, the mechanical strength such as ductility and bending strength of the weld metal and weld heat-affected zone decreases, so research is currently being carried out to suppress such microcracks as much as possible. Therefore, there is a strong desire for a welding rod with excellent microcracking resistance. [Problems to be Solved by the Invention] The present invention has been made focusing on the above-mentioned circumstances, and has excellent micro-cracking resistance.
The purpose of this invention is to provide a Ni-base coated arc welding rod. [Means for solving the problem] The Ni-based coated arc welding rod of the present invention that meets the above objectives includes Ni: 60% or more, Cr: 10-30%, and C: 0.01.
~0.15%, Si: 0.02~0.50%, Nb: 0.3~4.0%,
Cu: 0.001-0.20%, N: 0.001-0.015%, H:
The gist lies in that a core wire containing 0.0005% or less of H, the remainder of which is mainly Fe, is coated with a coating material containing 0.05% or less of H. [Operation] Next, the structure and operation and effects of the present invention will be explained while tracing the research history that led to the completion of the present invention. The present inventors investigated the cause of microcracking in Inconel weld metal and discovered that film-like Ni-Nb-Si-
It was found that the main cause was the C compound (hereinafter sometimes simply referred to as a film-like compound) and the H contained therein. The Ni-Nb-Si-C compound is
C derived from the metal to be welded and the Inconel coated arc welding rod (hereinafter simply referred to as welding rod),
Si and Nb segregate at grain boundaries during the cooling process, and are enriched by being reheated after the next pass during multilayer welding. The film-like compound formed in this way weakens the bonding force between the matrix crystals and is itself very brittle, so that when it is subjected to thermal stress due to subsequent welding passes, the film-like compound opens from the part. ,
Microcracks occur in the weld metal starting from the opening. On the other hand, H is thought to accumulate in the openings of the film-like compound and promote micro-cracks. Therefore, in conducting research on Ni-based coated arc welding rods with excellent micro-cracking resistance, the present inventors took into account the causes of micro-cracking as described above, and proposed the following (1), (2), and (3). We focused our research on this. In other words, (1) What is the appropriate content of Ni and Cr in the core wire of a Ni-based coated arc welding rod? (2)
C, which is an element related to the above film-like compound,
Our research focuses on three points: how to handle Si, Nb, and H, and (3) whether it is possible to add other elements to the core wire to have a positive effect on the crystal formation process. I proceeded. The above (1), (2), and (3) will be explained below. (1) Ni in the core wire of Ni-based arc welding rod,
Regarding the content of Cr: Ni in the core wire is essential for stabilizing austenite in the weld metal and improving low-temperature toughness.If the content is less than 60%, the above effects will not be achieved to a satisfactory extent. I couldn't do it. On the other hand, Cr is effective in strengthening the matrix and increasing the strength of the weld metal, but if it is less than 10%, satisfactory strength cannot be obtained, and if it exceeds 30%, the solidification cracking resistance is significantly reduced. A decrease occurred and the ductility of the weld metal also decreased. (2) Regarding C, Si, Nb, and H, which are elements related to the above film-like compound (a) About C, Si, and Nb In order to suppress the formation of the above-mentioned film-like compound, it is necessary to include these elements in the core wire. The first consideration is to reduce the ratio, but C, Si, and Nb are
Because these elements have a strong deoxidizing effect, they have useful properties such as reducing the amount of oxygen in Inconel weld metal, increasing ductility, and increasing the strength of Inconel weld metal. Because it is
There are limits to reducing the content of the above elements in the core wire. Therefore, the present inventors conducted research based on the viewpoint that it is necessary to define a suitable range that does not form the above-mentioned film-like compound and that can still exhibit the effects shown above.C:
0.01~0.15%, Si: 0.02~0.50%, Nb: 0.3~4.0%
The results show that the production of the film-like compound can be suppressed while making the most of the useful properties of the elements. If the lower limit of these content ranges is not reached, the deoxidizing effect and strength increasing effect described above will not necessarily be sufficiently exerted, while if the above upper limit is exceeded, a large amount of the film-like compound will precipitate. However, the occurrence of microcracks becomes significant, and the solidification cracking performance and low-temperature toughness also decrease. (b) Regarding H As mentioned above, H is thought to accumulate in the openings in the film-like compound and promote micro-cracking, but H that exhibits this effect is mainly supplied from the core wire and the coating material. The present inventors investigated which of the H supplied from the core wire and the H supplied from the coating material is more involved in micro-cracks, and found that the H supplied from the core wire is more important. The conclusion was that it is likely to have an impact. This is because it has been confirmed that the hydrogen yield in the core wire is overwhelmingly higher than that in the coating material. Based on this knowledge, Ni: 60%
Above, Cr: 10-30%, C: 0.01-0.15%, Si:
As a result of various studies of welding rods with Nb: 0.02 to 0.50% and Nb: 0.3 to 4.0%, the H content in the core wire and the H content in the coating material were varied, and the H content in the core wire was 0.0005%.
Hereinafter, it was concluded that microcracks can be suppressed if H in the coating material is 0.05% or less. (3) Possibility of adding other elements to the core wire to have a favorable effect on crystal growth As mentioned above, the Ni and Cr contents in the core wire of Inconel welding rods, the core C, Si, Nb in the wire
We have concluded the research results that by specifying the H content in the core wire and coating material, it should be possible to greatly contribute to suppressing micro-cracks without adversely affecting other performances. However, as a practical matter, it has not been possible to arrive at an optimal Inconel-based welding rod with good micro-cracking resistance by using only the above-mentioned provisions. Therefore, the present inventors have drastically changed the idea of changing the content of elements as described above, and wondered if it would be possible to positively influence crystal growth by actively adding other elements. After much thought and extensive research, we learned that adding Cu and N can strongly prevent the occurrence of microcracks. Regarding N, we obtained the following knowledge. N and Cr added to the core wire become chromium nitride and disperse, and this becomes a nucleus during the cooling process after welding, so crystals grow in a dispersed state around this nucleus, resulting in coarse crystal grains. is prevented. As mentioned above, the film-like compound that causes micro-cracks is formed at the grain boundaries of coarse grains, but by adding N, the coarsening of the crystal grains is prevented, so the film-like compounds are formed at the grain boundaries. Concentration is also prevented, and as a result, the film-like compound is formed in a dispersed manner, thus greatly reducing the occurrence of micro-cracks. A film compound is spheroidized. As a result of examining the content rate of N in the core wire, which has such effects, we found that the above effects are not necessarily satisfactory when the content rate is less than 0.001%.
%, it was found that blowholes occur frequently. Therefore, the lower limit of N content is 0.001%,
The upper limit may be 0.015%, but a more preferable range is 0.002 to 0.010%. On the other hand, Cu has the effect of preventing the segregation of Si and Nb at grain boundaries, and therefore has the effect of N, which disperses these elements within the grains and suppresses the formation of film-like compounds itself. I learned that it has the effect of encouraging. As a result of examining the content of Cu in the core wire, which has such an effect, we found that the above effect is not necessarily sufficient when the Cu content is less than 0.001%, and when it exceeds 0.20%, solidification cracking becomes significant. I understand. But the preferred range is
It was 0.002-0.10%. In some cases, Fe and Mn are added to the core wire to improve its ductility. Fe and Mn are effective in improving the ductility of the weld metal, but if added in excess they reduce low temperature toughness, so the content is preferably 20% Fe or less and 10% Mn or less. In addition to Ee and Mn, Mo, W, Ti, Al,
Zr, V, B, etc. may be added. Mo and W are effective in increasing the strength of the weld metal, but excessive addition reduces ductility, so the preferred ranges are Mo: 5% or less and W: 3% or less. Ti, Al, Zr, V, B,
is effective in reducing oxygen in the weld metal and improving ductility, improving blowhole resistance, but if added in excess, solidification cracking resistance decreases.
The content is preferably 1.0% or less for Ti, Al, and Zr, and 0.03% or less for V, B. Further, from the viewpoint of improving the ductility of the molten metal and reducing the occurrence of blowholes, the content of oxygen in the core wire is preferably 0.015% or less. Next, a description will be given regarding the coating material. The coating materials include carbonates such as calcium carbonate, barium carbonate, and magnesium carbonate, metal fluorides such as fluorite, cryolite, and magnesium fluoride, alumina, magnesium oxide, wollastonite, titanium oxide, and potash glass. It is made by mixing one or more types of agent raw materials, and its purpose is to adjust the fluidity of the slag, improve arc stability, improve the peelability of the slag, and improve the appearance of the bead. Among the above coating material raw materials, carbonate and metal fluoride are the main raw materials necessary to maintain good workability, and the preferred blending range of these is carbonate: 20-50%, metal fluoride: 10-50%. It is 40%. It is known that the carbonate decomposes during welding to generate CO ₂ gas, and the metal fluoride generates HF due to fluorine. By the way, I previously stated that it has been confirmed that the hydrogen yield rate in the core wire is overwhelmingly higher than that in the coating material, but the reason for this is actually the above-mentioned CO ₂ gas and HF generated from the coating material components. This is because it dilutes the hydrogen during welding. Furthermore, the above coating material may contain Si, Mn, Ni, Cr, Mo,
Elements such as W, Nb, Al, and Ti can also be added in the form of metals or alloys. In this case, especially Si, Nb
Excessive addition of will deteriorate the micro-cracking resistance.
It is preferable that Si: 5% or less and Nb: 8% or less. [Example] Next, an example of the present invention will be described. A welding rod was produced by using a core wire having the composition shown in Table 1 and coating it with a coating material having the composition shown in Table 2.

【table】

【table】

[Table] The diameter of the core wire was 4 mm, and the coating material shown in Table 2 was mixed with sodium silicate, applied to the core wire, and dried to obtain a welding rod. At this time, the weight of the coating material was 30% of the total weight of the welding rod. The test plate was a 40mm thick 9% Ni steel plate (JIS G 3127 SL 9N60).
A groove as shown in FIG. 1 was formed in this by using a groove. Before welding, we first performed backside root pass welding in a downward position to check for solidification cracking (welding current 150A, welding speed
20cm/min). Next, after the second pass, welding is performed in a vertical position, and a tensile test (JIS Z 3111), an impact test (JIS Z 3112), and a bending test (JIS Z 3122) are performed.
The mechanical performance of the weld metal and the occurrence of microcracks were investigated (vertical welding conditions: welding current 110-120A, welding heat input 40-50KJ/
cm). These results are shown in Table 3. Welding rod No.1
-4 and 10-13 had good solidification cracking resistance, strength, ductility, toughness, and bending performance. Comparative examples are shown below.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to provide a Ni-base coated arc welding rod having excellent micro-cracking resistance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the metal to be welded used to complete the present invention.

Claims (1)

[Claims] 1 Ni: 60% by weight or more (hereinafter simply referred to as %), Cr: 10-30%, C: 0.01-0.15%, Si: 0.02-0.50%, Nb: 0.3-4.0%, Cu : 0.001 to 0.20%, N: 0.001 to 0.015%, H: 0.0005% or less, and the remainder is mainly Fe, H: 0.05
% or less of a coating agent.