Search

KR-20260064536-A - High heat input welding steel for LPG or ammonia carrier and method for manufacturing the same

KR20260064536AKR 20260064536 AKR20260064536 AKR 20260064536AKR-20260064536-A

Abstract

High heat input welding steel for LPG or ammonia carriers is disclosed. The high heat input welding steel for LPG or ammonia carriers according to the present invention contains, on a weight percent basis, C: 0.05~0.085%, Si: 0.05~0.35%, Mn: 1.30~1.60%, Al: 0.005~0.040%, Nb: 0.015% or less, Ca: 0.001% or more, Ni: 1.0% or less, and the remainder may consist of Fe and impurities.

Inventors

  • 이현준
  • 김병철
  • 장길수

Assignees

  • 에이치디한국조선해양 주식회사
  • 현대제철 주식회사

Dates

Publication Date
20260507
Application Date
20251017
Priority Date
20241031

Claims (12)

  1. As high-heat input welding steel for LPG or ammonia carriers, The above welding steel is based on weight percent, C: 0.05~0.085%, Si: 0.05~0.35%, Mn: 1.30~1.60%, Al: 0.005~0.040%, Nb: 0.015% or less, Ca: 0.001% or more, Ni: 1.0% or less, High heat input welding steel for LPG or ammonia carriers, characterized by containing [subject] and the remainder consisting of Fe and impurities.
  2. In paragraph 1, High heat input welding steel for LPG or ammonia carriers, characterized in that the carbon equivalent (Ceq) calculated by the above composition satisfies the relationship of the following mathematical formula 1. [Mathematical Formula 1] (Note: Ceq is a dimensionless value, and C, Mn, Cr, Mo, V, Ni, and Cu all represent content in weight percent.)
  3. In paragraph 2, High heat input welding steel for LPG or ammonia carriers, characterized in that the composition of the above welding steel satisfies the following mathematical formula 2. [Mathematical Formula 2] (However, the content of each element is based on weight percent, and Ti refers to titanium in the steel, Al to aluminum, Si to silicon, and Nb to niobium.)
  4. In any one of paragraphs 1 through 3, The above welded steel is, High heat input welding steel for LPG or ammonia carriers, characterized by a tensile strength of 440 MPa to 630 MPa, a yield strength of 315 MPa or more, and an impact toughness of 27 J or more of the base material under -60℃ conditions.
  5. A method for manufacturing high-heat input welded steel for LPG or ammonia carriers, Step of reheating the slab; A step of performing rough rolling on the above-mentioned reheated slab; A step of performing finish rolling on the above rough-rolled slab; A step of performing controlled rolling on the above finish-rolled slab; and, A method for manufacturing high-heat input welded steel for LPG or ammonia carriers, comprising the step of cooling the above-mentioned controlled rolled steel to manufacture a steel plate.
  6. In paragraph 5, A method for manufacturing high-heat input welding steel for LPG or ammonia carriers, characterized in that the thickness of the manufactured welding steel is 8 mm to 40 mm.
  7. In paragraph 5, The above reheating step is, A method for manufacturing high heat input welding steel for LPG or ammonia carriers, characterized in that when the thickness of the welding steel being manufactured is greater than 12 mm, the reheating temperature is 1,040℃ to 1,150℃.
  8. In paragraph 5, The above reheating step is, A method for manufacturing high heat input welding steel for LPG or ammonia carriers, characterized in that when the thickness of the welding steel being manufactured is 12 mm or less, the reheating temperature is 1,060℃ to 1,220℃.
  9. In Article 7 or Article 8, A method for manufacturing high-heat input welded steel for LPG or ammonia carriers, characterized in that the above-mentioned rough rolling end temperature is 850℃.
  10. In Paragraph 9, A method for manufacturing high-heat input welded steel for LPG or ammonia carriers, characterized in that the finishing rolling temperature is 790℃.
  11. In Paragraph 10, A method for manufacturing high heat input welded steel for LPG or ammonia carriers, characterized in that when the thickness of the welded steel is 15 mm to 40 mm, the controlled rolling thickness is 2 mm or more and the cooling stop temperature is 650℃ or less.
  12. In Paragraph 10, A method for manufacturing high heat input welded steel for LPG or ammonia carriers, characterized in that when the thickness of the welded steel is 8mm to 20mm, the controlled rolling thickness is 2.5mm or more, and the cooling stop temperature is 620℃ or lower or air-cooled to room temperature.

Description

High heat input welding steel for LPG or ammonia carrier and method for manufacturing the same The present invention relates to a high-heat input welding steel for LPG or ammonia carriers and a method for manufacturing the same. More specifically, the invention relates to a welding steel in which the composition and rolling process are optimized to ensure weldability and productivity required in an automatic high-heat input welding process while maintaining sufficient impact toughness under cryogenic conditions of -60°C or lower, and a manufacturing method including controlled rolling and cooling conditions for manufacturing the same. Generally, since the hull and tank structures of LPG or ammonia carriers must maintain stability even in cryogenic environments, high-quality welding is essential for joining these components. Various welding methods are used for these vessels, including Flux Cored Arc Welding (FCAW), Submerged Arc Welding (SAW), Electro Gas Welding (EGW), and Electro Slag Welding (ESW). In particular, at shipbuilding sites, the use of automated high-heat input welding processes such as SAW and EGW, which can be automated, is gradually expanding to ensure work efficiency and quality. However, due to the high heat input required in automated high-heat input welding processes, using standard manganese-carbon steel results in a slow cooling rate in the Heat Affected Zone (HAZ), leading to the formation of a coarse microstructure and consequently a decrease in low-temperature impact toughness. In particular, securing toughness at cryogenic temperatures below -60°C is essential for LPG or ammonia carriers, yet existing steels often fail to meet classification society standards under these conditions. For this reason, welding of cryogenic areas has historically relied on manual FCAW processes; consequently, this multi-layer, multi-pass operation leads to reduced productivity and increased labor costs. Against this backdrop, there is a demand for welding steel capable of securing cryogenic impact toughness even when applying automated high-heat input welding processes. In particular, there is a need to develop technology that can suppress microstructure coarsening in the HAZ and secure low-temperature impact toughness in both the weld zone and the base material by optimizing compositional design and rolling process conditions. The present invention aims to solve these technical challenges by providing welding steel and a method for manufacturing the same, which are compatible with automated high-heat input welding processes while ensuring sufficient toughness and mechanical properties at -60°C or below. FIG. 1 is a flowchart showing the manufacturing process of high heat input welding steel for LPG or ammonia carriers according to one embodiment of the present invention. FIG. 2 is an image of a table showing the results of improved impact toughness of a base material, which is a high-heat input welding steel for LPG or ammonia carriers according to one embodiment of the present invention. FIG. 3 is an image of a table showing the results of an improved yield ratio (YR) of the base material of high heat input welding steel for LPG or ammonia carriers according to one embodiment of the present invention. FIG. 4 is an image of a table comparing the difference in impact toughness of the heat-affected zone according to the difference in calcium (Ca) content of high-heat input welding steel for LPG or ammonia carriers according to one embodiment of the present invention. FIG. 5 is a table image comparing and analyzing the changes in mechanical properties according to the carbon equivalent (Ceq) of high heat input welding steel for LPG or ammonia carriers according to one embodiment of the present invention. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art. Throughout the specification, the same reference numerals indicate the same components. FIG. 1 is a flowchart showing the manufacturing process of a high heat input welding steel for an LPG or ammonia carrier according to one embodiment of the present invention, FIG. 2 is an image of a table showing the results of improved impact toughness of the base material, which is a high heat input welding steel for an LPG or ammonia carrier according to one embodiment of the present invention, FIG. 3 is an image of a table showing the results of improved yield ratio (YR) of the base material, which is a high heat input welding steel for an LPG or ammonia carrier according to one embodiment of the present invention. FIG. 4 is an image of a table com