JPS649919B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a coated arc welding rod for austenitic stainless steel, particularly for forming high-strength and high-toughness welds in welded structures used at extremely low temperatures such as superconducting magnet containers. The present invention relates to a suitable coated arc welding rod. [Background of the Invention] In the present invention, temperatures near absolute zero, such as liquid hydrogen temperature (20.2K) and liquid helium temperature (4.2K), are referred to as extremely low temperatures. 9% for containers used to transport and store low-temperature liquids such as liquid nitrogen, liquid oxygen, and liquid natural gas.
Ni steel is used relatively often. Although 9% Ni steel has sufficient toughness at the above-mentioned cryogenic liquid temperature, it is insufficient at extremely low temperatures near absolute zero. For this reason, even higher toughness austenitic stainless steel is used in cryogenic structures. D308, D308L, D316 and D316L series coated arc welding rods are used for welding. In order to prevent weld cracking, these welding rods generally have their composition adjusted so that a few percent or more of delta ferrite crystallizes out, but welding rods that hardly crystallize delta ferrite have also been developed. There is. delta·
Crystallization of ferrite impairs toughness at extremely low temperatures,
This is because structures for superconducting applications in particular require non-magnetism, which cannot be satisfied. However, conventional fully austenitic welding rods have the drawbacks of high welding hot cracking susceptibility and insufficient toughness at extremely low temperatures. [Object of the invention] The object of the present invention is to provide a welding material with low susceptibility to hot weld cracking.
Another object of the present invention is to provide a coated arc welding rod for austenitic stainless steel that has high toughness at extremely low temperatures. [Summary of the Invention] The present invention is characterized in that C0.05 to 0.10% and Si 0.1 to 0.4% by weight.
%, Mn5~7%, Ni15~25%, Cr16~18%,
A coated arc welding rod for austenitic stainless steel characterized by having a metal component of Mo2 to 4%, P 0.02% or less, S 0.005% or less, and the balance Fe. That is, in the present invention, the Ni equivalent in the weld metal is made larger than the Cr equivalent by taking advantage of the effect of Ni to improve the stability and toughness of the austenite structure at extremely low temperatures, and the ratio of Ni equivalent to Cr equivalent (Ni equivalent/Cr It is preferable to set the equivalent weight) to 1.1 to 1.5 using the Delong equation calculated by the following equation, and adjust it so that it becomes an entirely austenite phase. [Ni equivalent = 30 x C (weight %) + Ni (weight %) + 0.5 x Mn (weight %) Cr equivalent = Cr (weight %) + Mo (weight %) + 1.5 x Si (weight %)] This invention When welding metal using a coated arc welding rod is used in structures for superconducting applications, non-magnetic properties and high toughness at extremely low temperatures are required, and an alloy composition with a fully austenitic structure should be selected. C is set to 0.05% or more in order to stabilize austenite and obtain strength at extremely low temperatures. 0.1%
If it exceeds 0.05, the toughness at extremely low temperatures will be impaired.
Set at 0.1%. Si is effective as a deoxidizing element when added in an amount of 0.1% or more, but if it exceeds 0.4%, the toughness at extremely low temperatures decreases, so the content is set at 0.1 to 0.4%. In particular, 0.25
~0.35% is preferred. Mn must be added in an amount of 5% or more as an element that stabilizes austenite, which is important in the present invention, and suppresses welding hot cracking. However, if it exceeds 7%, the toughness at extremely low temperatures decreases, so %. Ni is 15% or more to stabilize austenite and improve toughness at extremely low temperatures. twenty five%
15 to 25, as no significant effect will be obtained even if the
%. Particularly preferred is 20 to 25%. Cr should be at least 16% to increase corrosion resistance and strength at extremely low temperatures and to stabilize austenite. If it exceeds 18%, the toughness at extremely low temperatures will decrease, so it should be set at 16 to 18%. Mo improves corrosion resistance and tensile properties at extremely low temperatures,
It is added in an amount of 2% or more to suppress welding hot cracking.
If it exceeds 4%, delta ferrite is generated and the toughness at cryogenic temperatures is reduced, so the content is set at 2 to 4%. P and S are contained in the weld metal as unavoidable impurities, but when they solidify, they form low melting point eutectics at the grain boundaries, which causes cracks under the action of shrinkage strain.
This causes weld hot cracking. In particular, the present invention contains a large amount of Mn and reacts with S to form MnS, which becomes inclusions and impairs toughness at extremely low temperatures. Therefore, P
shall be 0.02% or less and S shall be 0.005% or less. In addition, it is used as a deoxidizer for coated arc welding rods.
Al, Ti, and Zr, and rare earth elements are added as deP and deS agents. These small additions are effective in improving the toughness of the weld metal at extremely low temperatures and preventing weld hot cracking, but excessive addition of these will actually impede the above performance, so the total amount in the total weld metal is The amount shall be 0.1% or less. On the other hand, if the ratio of Ni equivalent to Cr equivalent is less than 1.1, the toughness at 4.2K will decrease in those containing delta ferrite, and the susceptibility to welding hot cracking will increase even in those without delta ferrite. Furthermore, even if the ratio is set to 1.5 or more, the absorbed energy value will be saturated and no significant results will be obtained. Therefore, the ratio of Ni equivalent to Cr equivalent is 1.1 to 1.5
is preferred. [Example] Table 1 shows the chemical composition (wt%) of the deposited metal and the ratio of Ni equivalent to Cr equivalent in the coated arc welding rods of the present invention and the conventional one. The Ni equivalent and Cr equivalent in the table are values calculated using the Delong formula described above. Ni
The ratio of equivalent to Cr equivalent is 0.64 to 1.09 for the comparative welding rod and 1.10 to 1.49 for the welding rod of the present invention. The covered arc welding rod for comparison is commercially available JIS standard.
D308 rod, D316 rod, 18Cr-13Ni-7Mn-1Mo rod and 19Cr-16Ni-5Mn-3Mo rod. The present invention consists of D316 rod and 18Cr−15Ni−7Mn−1Mo
Each core wire of the rod is coated with a lime titania flux to coat C, Mn, Ni, and Mo.
This is a coated arc welding rod made by mixing powder of The chemical composition of the deposited metal in Table 1 is almost the same as the chemical composition of the metal components of the coated arc welding rod. JIS standard SUS304 steel plate (16×125
×200mm) After two-layer overlay welding on the end face with each welding rod,
A butt welded joint was manufactured with a groove gap of 10 mm and the overlay weld facing the 45-degree V groove. Therefore, the deposited metal in the butt weld is not diluted by the base metal at all. The welding rod is 4 mm in diameter, the welding conditions are 140 A current, 24 V voltage, and welding speed 140 mm/min.
For polarity, positive-rod DC welding was used. The chemical composition and delta ferrite content of the weld metal thus obtained were measured, and a Charpy impact test at 77K and 4.2K and a tensile test at 4.2K were conducted. In the impact test at a test temperature of 4.2K,
A No. 11 test piece specified in JISZ3172 was sealed in a double glass container, and an impact load was applied while the container was filled with liquid helium to determine the absorbed energy. In the impact test at a test temperature of 77K, a test piece of the same shape as above was immersed in liquid nitrogen for 30 minutes or more, then the test piece was taken out and an impact load was applied. In the tensile test, a test piece with a diameter of 4.5 mm and a parallel length of 20 mm was immersed in a cryostat filled with liquid helium, and the 0.2% proof stress and tensile strength were determined. Furthermore, a weld hot cracking test was conducted.
Three layers of overlay welding are performed on the end face of a SUS304 steel plate (12 x 120 x 200 mm) using each welding rod, and after the overlay welds are mechanically finished, the groove gap is 2.5 with the overlay welds facing each other.
mm, and a C-type jig restraint butt weld cracking test was conducted as specified by JIS Z3155. The diameter of the welding rod used, welding conditions, and polarity were the same as those described above. Table 2 shows the amount of delta ferrite in the deposited metal, the welding hot cracking rate, the absorbed energy at 77K and 4.2K, and the absorbed energy at 4.2K in the coated arc welding rods of the present invention and the conventional coated arc welding rod.
These are the measurement results of 0.2% yield strength and tensile strength. The symbols in the table indicate the symbols of the welding rods shown in Table 1. All weld hot cracks were weld crater cracks. Among the comparative welding rods, those containing delta ferrite have 0% weld hot cracking, but the absorbed energy at 4.2K is extremely low, and those that do not contain delta ferrite have low weld hot cracking susceptibility of 5 to 6%. The absorbed energy at 4.2 K is 5 Kgf・m or less, and those with a high absorbed energy of 7.2 Kgf・m at 4.2 K exhibit high welding hot cracking susceptibility with a hot cracking rate of 20% or more. On the other hand, the welding rod of the present invention is a fully austenitic welding rod that does not contain any delta ferrite, but it has a low welding hot cracking rate of 0 to 5%, and has a low welding hot cracking susceptibility, and the absorbed energy at 77K and 4.2K is low. It has a higher absorbed energy than the conventional one, especially at 4.2 K, of 6 to 8 Kgf·m. Further, according to the embodiments of the present invention, the 0.2% yield strength and tensile strength at 4.2K are equal to or higher than those of the conventional ones, and a cryogenic welded structure with high strength and high toughness can be obtained.

【table】

【table】

〔Effect of the invention〕

As described above, the weld metal obtained by the coated arc welding rod for austenitic stainless steel according to the present invention has a completely austenitic structure, has low weld hot cracking susceptibility, and has high toughness at extremely low temperatures. It is suitable for cryogenic welding structures such as superconducting magnet containers that require non-magnetism.

Claims (1)

[Claims] 1 By weight, C0.05-0.10%, Si0.1-0.4%, Mn5
~7%, Ni15~25%, Cr16~18%, Mo2~4%,
A coated arc welding rod for austenitic stainless steel characterized by having a metal component of P0.02% or less, S0.005% or less, and the balance consisting of Fe.