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CN-122029295-A - High-strength hot dip galvanized steel sheet and method for producing same

CN122029295ACN 122029295 ACN122029295 ACN 122029295ACN-122029295-A

Abstract

The present invention provides a high-strength hot-dip galvanized steel sheet excellent in coating appearance, coating adhesion during working, and LME crack resistance. A high-strength hot-dip galvanized steel sheet comprising a zinc coating layer having a coating adhesion amount per one surface of a steel sheet composed of a predetermined steel component, ((Si+Cr)/Mn) of 0.25 or more, (Si/Mn) less than 0.25 and the balance of Fe and unavoidable impurities of 20g/m 2 to 120g/m 2 or less, wherein the highest temperature T of the steel sheet in an annealing furnace is higher than 700 ℃ and 900 ℃ or less, the dew point of the furnace atmosphere in a temperature range of 700 ℃ to T ℃ is-20 ℃ or more, and the furnace atmosphere contains not only 3.0% by volume but also one or more selected from the group consisting of 0.1 ppm by volume to 3.0 ppm by volume of SO 2 and 0.5 ppm by volume to 10.0 ppm by volume of HCl.

Inventors

  • HOSHINO KATSUYA
  • TAHARA DAISUKE

Assignees

  • 杰富意钢铁株式会社

Dates

Publication Date
20260512
Application Date
20240828
Priority Date
20231016

Claims (6)

  1. 1. A method for producing a high-strength hot-dip galvanized steel sheet having a zinc coating layer on the surface of the steel sheet, the zinc coating layer having a coating adhesion amount per single surface of 20g/m 2 to 120g/m 2 , wherein the steel sheet comprises, in mass%, 0.060 to 0.250% of C, 0.10 to 0.80% of Si, 1.50 to 3.50% of Mn, 0.020% or less of P, 0.0100% or less of S, 0.100% or less of Al, 0.0060% or less of N, 1.0% or less of Cr, the mass ratio ((Si+Cr)/Mn) of (Si+Cr) to Mn) being 0.25 or more, the mass ratio (Si/Mn) of Si to Mn being less than 0.25, the balance being Fe and unavoidable impurities, When annealing and hot dip galvanizing a steel sheet in a continuous hot dip galvanizing facility, the highest temperature T of the steel sheet in an annealing furnace is higher than 700 ℃ and lower than 900 ℃, the temperature of the steel sheet is higher than 700 ℃ and lower than T ℃, the dew point of the internal heating furnace atmosphere is higher than-20 ℃, and the internal heating furnace atmosphere contains not only 3.0-20.0% hydrogen but also one or more selected from the group consisting of 0.1-3.0 ppm by volume of SO 2 and 0.5-10.0 ppm by volume of HCl.
  2. 2. The method for producing a high-strength hot-dip galvanized steel sheet according to claim 1, wherein the steel sheet further comprises one or more groups selected from group A to group E, Group A contains Ti, nb, V, W and at least one of Zr, wherein the total content is below 0.200%; Group B comprising at least one of Mo, cu, co and Ni, in total of 0.01% to 0.5%; group C, B is more than 0.0003% and less than 0.0050%; The group D is one or more of Sb and Sn, and the total of the group D is more than 0.001% and less than 0.200%; And group E comprising at least one of Ca, mg and REM in an amount of 0.0001% to 0.0005%.
  3. 3. The method for producing a high-strength hot-dip galvanized steel sheet according to claim 1 or 2, wherein the steel sheet further comprises one or more groups selected from the group consisting of groups F to I as the component composition in mass%, Group F, ta, less than 0.10% (excluding 0%); Group G is one or more selected from Te 0.10% or less (excluding 0%), as 0.10% or less (excluding 0%), and Hf 0.10% or less (excluding 0%); Group H is at least one selected from Bi below 0.20% (excluding 0%), pb below 0.20% (excluding 0%); Group I is one or more selected from Zn 0.10% or less (excluding 0%), ge 0.10% or less (excluding 0%), sr 0.10% or less (excluding 0%), and Cs 0.10% or less (excluding 0%).
  4. 4. A high-strength hot-dip galvanized steel sheet having a zinc coating layer having a coating adhesion amount per one surface of 20g/m 2 or more and 120g/m 2 or less, wherein the steel sheet comprises, in mass%, 0.060% or more and 0.250% or less of C, 0.10% or more and 0.80% or less of Si, 1.50% or more and 3.50% or less of Mn, 0.020% or less of P, 0.0100% or less of S, 0.100% or less of Al, 0.0060% or less of N, 1.0% or less of Cr, a mass ratio ((Si+Cr)/Mn) of 0.25 or more of Si to Mn, a mass ratio (Si/Mn) of Si to Mn of less than 0.25, and the balance of Fe and unavoidable impurities, The oxygen content of the surface layer portion of the steel sheet immediately below the zinc plating layer, which is within 100 mu m in depth from the surface of the base steel sheet toward the center of the sheet thickness, is 0.030g/m 2 to 0.40g/m 2 per one surface, In the cross section of the steel sheet, the maximum length of the internal oxides present in the steel sheet surface layer portion is 6.0 [ mu ] m or less, and the number of internal oxides having a length of 1.0 [ mu ] m or more present in the steel sheet surface layer portion is 20 or less per 100 [ mu ] m of the length in the steel sheet width direction of the steel sheet surface layer portion.
  5. 5. The high-strength hot-dip galvanized steel sheet according to claim 4, further comprising one or more groups selected from the group consisting of groups A to E, Group A contains Ti, nb, V, W and at least one of Zr, wherein the total content is below 0.200%; Group B comprising at least one of Mo, cu, co and Ni, in total of 0.01% to 0.5%; group C, B is more than 0.0003% and less than 0.0050%; The group D is one or more of Sb and Sn, and the total of the group D is more than 0.001% and less than 0.200%; And group E comprising at least one of Ca, mg and REM in an amount of 0.0001% to 0.0005%.
  6. 6. The high-strength hot-dip galvanized steel sheet according to claim 4 or 5, wherein the steel sheet further comprises one or more of the group F to group I selected from the group consisting of, Group F, ta, less than 0.10% (excluding 0%); Group G is one or more selected from Te 0.10% or less (excluding 0%), as 0.10% or less (excluding 0%), and Hf 0.10% or less (excluding 0%); Group H is at least one selected from Bi below 0.20% (excluding 0%), pb below 0.20% (excluding 0%); Group I is one or more selected from Zn 0.10% or less (excluding 0%), ge 0.10% or less (excluding 0%), sr 0.10% or less (excluding 0%), and Cs 0.10% or less (excluding 0%).

Description

High-strength hot dip galvanized steel sheet and method for producing same Technical Field The present invention relates to a high-strength galvanized steel sheet which is excellent in workability and is suitable for use as a building material and a collision-resistant member for automobiles, the importance of which is higher as the tensile strength is higher, and a method for producing the same. Background Recently, improvement in collision safety and fuel efficiency of automobiles has been strongly demanded, and steel sheets as component materials are being advanced to have higher strength. Further, the popularity of automobiles has been expanding worldwide, and automobiles are used in various fields and climates, and in this case, high rust resistance is required for steel sheets as component materials. In general, a hot dip galvanized steel sheet is produced by using a thin steel sheet obtained by hot rolling and cold rolling a slab as a base material, and subjecting the base steel sheet to recrystallization annealing and hot dip galvanizing in an annealing furnace of a continuous hot dip galvanizing line (Continuous Galvanizing Line; hereinafter referred to as CGL). In the case of galvannealed steel sheet, the galvannealed steel sheet is produced by further carrying out an alloying treatment after the hot dip galvanizing treatment. Examples of the type of heating Furnace of the CGL annealing Furnace include a direct Furnace (DIRECT FIRED Furnace; DFF), a non-oxidizing Furnace (Non Oxidizing Furnace; NOF), and a radiant Furnace (Radiant Tube Furnace; RTF). In recent years, the construction of CGL including a full radiant tube type heating furnace in which the heating furnace is entirely of a radiant furnace type has been increasing, because, for example, a high quality plated steel sheet can be produced at low cost due to ease of handling and difficulty in occurrence of sticking (pick-up) or the like. On the other hand, in the case of a steel sheet containing easily oxidizable elements such as Si, mn, cr, etc., it is preferable to oxidize under appropriate conditions immediately before the reduction annealing. The full radiant tube type annealing furnace is different from an annealing furnace provided with a direct furnace and a non-oxidizing furnace in the front section of the annealing furnace, and has no oxidizing step immediately before the reduction annealing. Therefore, steel sheets containing easily oxidizable elements such as Si, mn, and Cr are disadvantageous in ensuring the plating properties. As a method for producing a hot dip galvanized steel sheet using a high strength steel sheet containing a large amount of Si and Mn as a base material, patent documents 1 and 2 disclose techniques for oxidizing the inside of a steel base surface layer by increasing the dew point in a heating step in an annealing furnace. However, in the technologies described in patent documents 1 and 2, the area for controlling the dew point is premised on the whole furnace, and thus the dew point is difficult to control and the stable operation is difficult. In addition, when an galvannealed steel sheet is produced under unstable dew point control, fluctuations in the distribution state of internal oxides formed in the base steel sheet are observed, and defects such as uneven plating wettability (fluctuations) and uneven alloying (fluctuations) may occur in the longitudinal and width directions of the steel sheet. Patent document 3 discloses a technique of not only defining H 2O、O2 as an oxidizing gas but also defining CO 2 concentration to thereby oxidize the steel-based surface layer immediately before plating internally, suppress external oxidation, and improve the appearance of the plating. However, when a particularly large amount of Si is contained as in patent document 3, cracks are likely to occur on the surface of the base steel sheet during processing due to the presence of internal oxides, and the plating peeling resistance is deteriorated. Further, deterioration of corrosion resistance was also confirmed. Further, CO 2 causes problems such as furnace contamination, carburization of the steel sheet surface, and the like, and there is a concern that the mechanical properties may be changed. Further, recently, high-strength hot-dip galvanized steel sheets and high-strength galvannealed steel sheets are being applied to parts where working is strict (hereinafter referred to as "strong working"), and the plating peeling resistance in man-hours has been paid attention to. Specifically, it is required to suppress the peeling of the plating layer at the processing portion when the plated steel sheet is subjected to bending processing exceeding 90 ° and further bent at an acute angle, or when the steel sheet is subjected to processing by applying impact. In addition, when a large amount of Si is added to a steel sheet, in a state where residual stress is generated in the vicinity of a welded portion during resistanc