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CN-121986179-A - Electric resistance welded steel pipe and method for manufacturing same

CN121986179ACN 121986179 ACN121986179 ACN 121986179ACN-121986179-A

Abstract

The purpose of the present invention is to provide a resistance welded steel pipe having excellent weld quality, and a method for producing the same. A resistance welded steel pipe comprising a base material and a resistance welded portion, wherein the base material comprises, in mass%, 0.10 to 0.50% of C, 0.15 to 0.35% of Si, 0.60 to 0.90% of Mn, 0.001 to 0.1% of Al, 0.03% or less of P, 0.03% or less of S, 0.90 to 1.20% of Cr, 0.15 to 0.30% of Mo, 0.25% or less of Ni, and the balance of Fe and unavoidable impurities, and wherein Mn/(Si+Cr) is 0.52 to 0.85 in the composition, and the resistance welded steel pipe satisfies the following formula (1) in a flattening test. h/D is 0.5/1 or less, where h is a crushed crack height (mm) at which an initial crack is observed in the resistance welded portion, and D is an outer diameter (mm) of the steel pipe.

Inventors

  • MATSUMOTO MASASHI
  • KATSUMURA TATSURO

Assignees

  • 杰富意钢铁株式会社

Dates

Publication Date
20260505
Application Date
20241003
Priority Date
20231016

Claims (7)

  1. 1. A resistance welded steel pipe comprising a base material and a resistance welded portion, The base material comprises, by mass%, 0.10 to 0.50% of C, 0.15 to 0.35% of Si, 0.60 to 0.90% of Mn, 0.001 to 0.1% of Al, 0.03% or less of P, 0.03% or less of S, 0.90 to 1.20% of Cr, 0.15 to 0.30% of Mo, 0.25% or less of Ni, and the balance of Fe and unavoidable impurities, In the composition, mn/(Si+Cr) is 0.52-0.85, and the flattening test of the resistance welded steel pipe satisfies the following formula (1), h/D≤0.5······(1) Wherein h is the flattening crack height of initial crack observed in the resistance welding part, and the unit is mm, and D is the outer diameter of the steel pipe, and the unit is mm.
  2. 2. The electric resistance welded steel pipe according to claim 1, wherein the composition further contains, in mass%, 1 or 2 or more selected from the group consisting of 0.5% or less of Cu, 0.05% or less of Ti, 0.005% or less of Nb, 0.005% or less of V, 0.001% or less of B, and 0.001% or less of Ca.
  3. 3. A resistance welded steel pipe according to claim 1 or 2, wherein the hardness of the base material of the resistance welded steel pipe at a position of 0.2 mm.+ -. 0.05mm in the wall thickness direction from the outer surface of the steel pipe and the hardness of the base material at a position of 0.2 mm.+ -. 0.05mm in the wall thickness direction from the inner surface of the steel pipe are 300HV or more, And a difference between the hardness of the steel pipe at a position 0.2mm + -0.05 mm from the outer surface of the steel pipe in the thickness direction and the hardness of the steel pipe at a position 0.2mm + -0.05 mm from the inner surface of the steel pipe in the thickness direction is 100HV or less.
  4. 4. A resistance welded steel pipe according to any one of claim 1 to 3, wherein the difference between the maximum wall thickness and the minimum wall thickness of the steel pipe in the C section of the resistance welded steel pipe is 10% or less of the average wall thickness of the steel pipe, The C-section is a surface parallel to the circumferential direction and the wall thickness direction of the steel pipe.
  5. 5. A method for producing a resistance welded steel pipe according to any one of claims 1 to 4, And heating at a heating speed of 120 ℃ per second or lower and a heating temperature of 850-1200 ℃ and then reducing and rolling.
  6. 6. The method for producing an electric resistance welded steel pipe according to claim 5, wherein the heating rate is 20 ℃ per second or higher, and the average cooling rate after the reducing rolling is 3 ℃ per second or higher.
  7. 7. The method for producing a resistance welded steel pipe according to claim 5 or 6, wherein the heating temperature is 1100 ℃ or lower, and the reduction ratio in the reduction rolling is 25 to 75%.

Description

Electric resistance welded steel pipe and method for manufacturing same Technical Field The present invention relates to a resistance welded steel pipe used for a mechanical structure or the like and a method for manufacturing the resistance welded steel pipe. Background In mechanical structures such as automobiles, the parts using solid steel bars are gradually replaced with hollow materials such as steel pipes in view of environmental protection such as improvement in fuel consumption due to reduction in total weight. In particular, when a steel pipe is used in place of a shaft of a rotating body such as a shaft, not only the strength of the material but also the wall thickness of the steel pipe is required to have uniform cross-sectional dimensional accuracy in the circumferential direction so as to minimize vibration during rotation. The steel pipes used in the machine structure are roughly classified into welded steel pipes having welded portions and seamless steel pipes having no welded portions. In welded steel pipes, the dimensional accuracy of the cross section of the resistance welded steel pipe is excellent, but it is necessary to ensure the quality of the welded portion for the applied components. On the other hand, the seamless steel pipe does not need to ensure the quality of the welded portion, but there is a problem in terms of the cross-sectional dimensions such as the eccentricity of the outer diameter and the inner diameter and the uneven wall thickness of the cross section in the circumferential direction. Therefore, there is an advantage in terms of dimensional accuracy of a cross section in that the use of the electric resistance welded steel pipe for the rotary shaft of the rotary body structure, and when the electric resistance welded steel pipe is used, excellent weld quality is required in order to avoid fracture failure of the weld in use of the rotary machine. In addition, when used for a rotary shaft, it is necessary to reduce abrasion of the surface of the steel pipe, and therefore, the surface hardness is also required to be large as a component performance. In addition, in the case of hollow materials such as steel pipes, it is also required that the variation in material properties in one cross section is small. Forced cooling such as water quenching is difficult to be applied to the inner surface of a steel pipe having a long length, and it is difficult to obtain a steel pipe having a large hardness on both the inner and outer surfaces of the pipe in a general carbon steel. Therefore, by adding an alloy component such as Cr or Mo to the steel pipe blank to improve the hardenability of the steel, a steel pipe having sufficient hardness on the inner and outer surfaces of the pipe can be obtained even when naturally cooled. However, since Cr has a high affinity with oxygen and its oxide is higher than the melting point of steel, if the amount of Cr added is increased, the amount of Cr-based oxide having a high melting point formed on the joint surface during resistance welding increases, the amount of residual in the welded portion increases, and the quality of the welded portion is significantly deteriorated. Therefore, in the case of manufacturing an electric resistance welded steel pipe from a steel material to which Cr is added, it is necessary to adjust the chemical composition of the steel material so as to suppress the formation of Cr-based oxides having a high melting point during electric resistance welding or to promote the discharge of molten steel discharged together with the Cr-based oxides. Patent document 1 proposes an electric resistance welded steel pipe in which Sn is added to a blank containing 0.01 to 0.50% by mass of Cr to reduce the surface decarburized layer. Patent document 2 proposes an electric resistance welded steel pipe in which the difference between the hardness of the surface layer of the base material portion and the hardness of the central portion of the steel pipe wall thickness is small in a steel pipe to which 1.00% or less by mass of Cr is added. Patent document 3 proposes a resistance welded boiler steel pipe characterized in that (Si%)/(Mn% +cr%) is set to 0.005 to 1.5 and that the melting point of a mixed oxide of SiO 2, mnO and Cr 2O3 produced during resistance welding is set to 1600 ℃. Prior art literature Patent literature Patent document 1 International publication No. 2020/230795 Patent document 2 International publication No. 2018/011862 Patent document 3 Japanese patent laid-open No. 2006-77330 Disclosure of Invention In the above patent documents 1 and 2, the addition amount of Cr is 1% or less, and the quality of the resistance welded portion is not mentioned. Therefore, when Cr is added, the composition of the steel material needs to be designed in consideration of the quality of the resistance welded portion. In patent document 3, the adjustment of the composition of Si, mn, and Cr of steel is mentioned, but there is a proble