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EP-4324939-B1 - HIGH NICKEL ALLOY EXCELLENT IN HIGH WELDING TEMPERATURE CRACKING RESISTANCE

EP4324939B1EP 4324939 B1EP4324939 B1EP 4324939B1EP-4324939-B1

Inventors

  • NISHIDA, YUKIHIRO
  • TSUGE, SHINJI
  • OSUKI, TAKAHIRO

Dates

Publication Date
20260506
Application Date
20220412

Claims (3)

  1. A high-Ni alloy having an excellent weld hot cracking resistance, comprising: in mass%, C: 0.15% or less, Si: 0.05 to 2.0%, Mn: 0.05 to 2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 16 to 30%, Ni: 18 to 50%, Al: 0.01 to 1.0%, Ti: 0.01 to 1.5%, N: 0.35% or less, O: 0.003% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0003 to 0.0050%, Mg: 0.0060% or less, optionally further comprising: in mass%, one or more of B: 0.0002 to 0.0030%, Sn: 0.05% or less, Zn + Pb + Bi: 0.0010% or less, Zr: 0.5% or less, Hf: 0.5% or less, La + Ce + Nd: 0.0050% or less, W: 3% or less, V: 0.01 to 0.5%, Nb: 0.002 to 1.0%, and Ta: 0.002 to 1.0%, and a balance consisting of Fe and impurities, wherein a relationship between a number density of TiC precipitates each having 1.0 µm or more of an equivalent circle diameter and a Mg content in steel satisfies a formula (1) below, number density of TiC (number of pieces/mm 2 ) ≤ 463 - 9.5 × Mg concentration in steel in mass ppm ...(1), wherein the number density of TiC is measured as set out in the description.
  2. The high-Ni alloy having an excellent weld hot cracking resistance according to claim 1, further comprising: in place of a part of the Fe, in mass%, one or more of B: 0.0002 to 0.0030%, Sn: 0.05% or less, Zn + Pb + Bi: 0.0010% or less, Zr: 0.5% or less, Hf: 0.5% or less, La + Ce + Nd: 0.0050% or less, W: 3% or less, V: 0.01 to 0.5%, Nb: 0.002 to 1.0%, and Ta: 0.002 to 1.0%.
  3. A welded structure comprising the high-Ni alloy having an excellent weld hot cracking resistance according to claim 1 or 2, wherein the weld hot cracking resistance is measured as set out in the description and is considered excellent if the average value of the total crack lengths is 0.4 mm or less.

Description

TECHNICAL FIELD The present invention relates to a high nickel (Ni) alloy having an excellent weld hot cracking resistance and used as a high-temperature material. BACKGROUND ART A high Ni alloy is suitably used as a high-temperature material. Alloys 800 and 825 are representative commercial alloys of high Ni alloys containing Al and Ti. In recent years, demands have been expanding in developing countries and there is a need for technical development to supply inexpensive products with favorable surface quality and usability. For this reason, a manufacturing method has been converted from a conventional steel ingot method to continuous casting. Meanwhile, it is known that a high-Ni alloy manufactured by continuous casting is highly susceptible to internal slab cracks during casting, edge cracks during hot working, and surface defects of the product. Accordingly, from a viewpoint of improving productivity of a high-Ni alloy in continuous casting, improvement and development of design of chemical compositions, refining, casting, and hot working techniques of alloys have been promoted. As patent literatures related to continuous casting techniques, for instance, Patent Literature 1 discloses a technique related to a component system and a manufacturing method in which contents of Ti, N, and Si are reduced to a low level as a method of suppressing generation of surface defects. Patent Literature 2 discloses a manufacturing method of preventing nozzle clogging and surface defects by no addition of a Ca alloy. This Literature describes disadvantages that addition of a Ca alloy causes bonding with oxygen in molten alloy to form oxide-based non-metallic inclusions, which agglomerate and increase in size, leading to generation of linear defects on a surface of an alloy sheet that is the final product. In Patent Literature 3, in order to prevent coarse agglomeration of TiN inclusions that cause generation of surface defects, CaO-MgO-Al2O3 inclusions, which are oxide inclusions, are included as essential components, and a percentage of the number of pieces of CaO and MgO in the total number of pieces of the inclusions is defined as 50% or less. Patent Literature 4 discloses an Fe-Cr-Ni-Mo alloy having superior surface properties and a method for producing the same using a commonly used apparatus at low cost. The related arts described above define the component system and the composition of inclusions from the viewpoint of productivity, especially, suppression of surface defects. CITATION LIST PATENT LITERATURE(S) Patent Literature 1 JP2003-147492 A Patent Literature 2 JP2014-189826 A Patent Literature 3 JP2018-59148 A Patent Literature 4 US2017058384 A1 SUMMARY OF THE INVENTION PROBLEM(S) TO BE SOLVED BY THE INVENTION In practical use of a high Ni alloy, the inventors have found that a high Ni alloy is not only disadvantageous in productivity but also exhibits high weld hot cracking susceptibility because the high Ni alloy is austenitic single phase steel, easily causing cracks during welding work. An object of the invention is to stabilize weld hot cracking susceptibility, especially HAZ cracking susceptibility, which have not been conventionally studied, at a low level in an Al- and Ti-containing high-Ni alloy with slight amount(s) of one or both of Ca and Mg alloys. The Al- and Ti-containing high-Ni alloy is said to have a relatively favorable hot workability. However, since a cast piece has a solidified structure, if a S content is several ppm or more, hot workability of the cast piece becomes insufficient in hot working. Accordingly, it is necessary to improve hot workability by adding a slight amount of one or both of Ca and Mg alloys. However, in a case where a high Ni alloy, which is an object of the invention, is subjected to continuous casting with addition of Ca or Mg alloy, the high Ni alloy in a form of slab, bloom or billet is processed into a steel product, and the steel product is used for manufacturing a structure by welding work, weld hot cracks may occur due to thermal stress generated by heat input. Liquefaction cracking in HAZ is sometimes raised at issue, especially, in a high-Ni alloy containing Al and Ti. An object of the invention is to provide a high Ni alloy having an excellent weld hot cracking resistance and used as a high-temperature material. MEANS FOR SOLVING THE PROBLEMS In order to clarify and solve the cause of the above issue, the inventors performed laboratory vacuum melting in which variable amounts of Ca and Mg are added to an Al- and Ti-containing high-Ni alloy of the invention as a basic composition; applied hot rolling, annealing, and heat treatment to the obtained cast piece (i.e., material) to provide a steel product; and evaluated the obtained steel product in terms of HAZ cracking susceptibility during welding according to Varestraint test. In addition, the inventors investigated non-metallic inclusions and precipitates in the alloy using FE-SEM-EDS, and studied to solve