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High-strength hot-dip galvanized steel sheet with low yield strength and with less material quality fluctuation and process for producing the same

A technology of hot-dip galvanized steel sheet and manufacturing method, applied in the direction of chemical instruments and methods, manufacturing tools, hot-dip coating process, etc., can solve problems such as surface deformation, trunk lid appearance, design damage, etc., and achieve material change Small, excellent surface deformation resistance, low YP effect

Active Publication Date: 2012-08-01
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] However, if it is desired to increase the strength by adding solid solution strengthening elements such as Mn and P based on 340BH with yield strength YP: 230 MPa and IF with YP: 270 MPa, and to make the steel plate thinner, the problem of surface deformation will arise.
Here, surface deformation refers to minute wrinkles and wavy patterns on the press-formed surface caused by an increase in YP. If this surface deformation occurs, the appearance and design of the door, trunk lid, etc. will be significantly impaired.

Method used

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  • High-strength hot-dip galvanized steel sheet with low yield strength and with less material quality fluctuation and process for producing the same
  • High-strength hot-dip galvanized steel sheet with low yield strength and with less material quality fluctuation and process for producing the same
  • High-strength hot-dip galvanized steel sheet with low yield strength and with less material quality fluctuation and process for producing the same

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Experimental program
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Effect test

Embodiment 1

[0093] Steels of steel numbers A to CC shown in Table 1 were melted, and then continuously cast into billets with a thickness of 230 mm. After heating the steel slab to 1180-1250°C, at 830°C (steel numbers A~D, G~U, X~CC), 870°C (steel numbers E, V), 900°C (steel numbers F, W) Hot rolling is performed at the finish rolling temperature. Then, cooling was performed at an average cooling rate of 20°C / sec, and coiling was performed at a coiling temperature of 640°C. The obtained cold-rolled sheet was cold-rolled at a rolling reduction of 67% to obtain a cold-rolled sheet having a thickness of 0.75 mm. The obtained cold-rolled sheet was annealed on the CGL at the average heating rate, annealing temperature AT, and cooling temperature in the temperature range of 680 to 740°C shown in Tables 2 and 3, and hot-dip galvanized during cooling. Here, the cooling step from the annealing temperature AT to the plating solution temperature of 460°C is regarded as the primary cooling, and the...

Embodiment 2

[0102] The slab with the composition of steel number C shown in Table 1 was heated to 1200°C, and after hot rolling at a finish rolling temperature of 830°C, the cooling start time was adjusted for each time shown in Table 4. Each cooling rate was cooled to 600 degreeC, and coiling was performed at the coiling temperature CT shown in Table 4. The obtained hot-rolled sheet was cold-rolled at a rolling reduction rate of 77%, heated at a heating rate of 1.5°C / sec on the CGL, annealed at 775°C, and averaged once at 4°C / sec. After cooling at a cooling rate, hot-dip galvanizing was performed, alloying treatment was performed at 520° C. for 20 seconds, and cooling was performed at an average cooling rate of 30° C. / second twice. JIS No. 5 tensile test pieces were taken from the obtained steel sheets in a direction perpendicular to the rolling direction (direction C) and a direction at 45 degrees to the rolling direction (direction D), and a tensile test was performed.

[0103] The re...

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Abstract

A high-strength cold rolled steel sheet of low YP with less material quality fluctuation, comprising, by mass, 0.01 to 0.12% C, 0.2% or less Si, less than 2% Mn, 0.04% or less P, 0.02% or less S, 0.3% or less sol. Al, 0.01% or less N and more than 0.3 to 2% Cr so that the relationships 2.19<([%Mn]+1.3OE%Cr))<3 and 0.24=[%Cr] / [%Mn] are satisfied ([%Mn] and [%Cr] represent the contents of Mn and Cr, respectively) and comprising the balance iron and unavoidable impurities, which steel sheet has ferrite and the second phase of 2 to 25% area ratio. In the second phase, the area ratio of pearlite or bainite is less than 20%, and the average grain diameter of the second phase is in the range of 0.9 to 7 [mu]m. In the second phase, the area ratio of grains of less than 0.8 [mu]m grain diameter isless than 15%.

Description

technical field [0001] The present invention relates to a high-strength hot-dip galvanized steel sheet for press forming used in applications such as automobiles and home appliances through a press forming process, and a method for producing the same. Background technique [0002] For a long time, for automotive panels that require dent resistance, such as hoods, doors, trunk lids, rear doors, and fenders, it is possible to apply carbonitrides such as Nb and Ti to form carbonitrides based on ultra-low carbon steel. TS: 340MPa grade BH steel plate (sinter hardened steel plate, hereinafter referred to as 340BH), TS: 270MPa grade IF steel plate (Interstitial Free steel plate, hereinafter referred to as 270IF). In recent years, due to the further increase in the demand for vehicle body weight reduction, studies have been advanced to further increase the strength of the above-mentioned covering to improve the dent resistance and to reduce the thickness of the steel plate. In add...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/00C21D9/46C22C38/38C22C38/58C23C2/06C23C2/28
CPCC23C2/02C22C38/14C21D9/46C22C38/002C23C2/28C23C2/06C22C38/12C21D2211/005C22C38/04C22C38/22C22C38/02C21D8/0247C22C38/28C22C38/001C22C38/18C22C38/32B32B15/013C22C38/06C22C38/24C22C38/38C22C38/42C22C38/48Y10T428/12799C23C2/29C23C2/0224C21D1/18C21D8/0226C21D8/0236
Inventor 小野义彦木村英之奥田金晴藤田毅樱井理孝
Owner JFE STEEL CORP
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