High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same

A technology of hot-dip galvanized steel sheet and cold-rolled steel sheet, which is applied in the field of high-strength cold-rolled steel sheet and high-strength hot-dip galvanized steel sheet, which can solve the problems of steel sheet hole expandability and lower bendability, and achieve excellent hole expandability and bendability , Excellent formability, and the effect of ensuring safety

Active Publication Date: 2011-10-26
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] However, in general, the increase in the strength of steel sheets leads to a decrease in the hole expandability and bendability of the steel sheets. Therefore, high-strength cold-rolled steel sheets that have both high strength and excellent formability, and high-strength hot-dip steel sheets that impart corrosion resistance are desired. Zinc steel plate

Method used

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  • High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same
  • High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same
  • High-strength cold-rolled steel sheet having excellent workability, molten galvanized high-strength steel sheet, and method for producing same

Examples

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Effect test

Embodiment 1

[0112] Steel Nos. A to P having the compositions shown in Table 1 were smelted in a converter, and steel slabs were produced by a continuous casting method. These billets were heated to 1200°C, hot rolled at a finishing temperature of 850 to 920°C, and coiled at a coiling temperature of 600°C. Then, after pickling, it was cold-rolled at a rolling reduction rate of 50% to the plate thickness shown in Table 2, and annealed under the annealing conditions shown in Table 2 through a continuous annealing line to produce cold-rolled steel sheets No. 1 to 24. . Then, the area ratio of the ferrite phase of the obtained cold-rolled steel sheet, the area ratio of the martensite phase obtained by combining the tempered martensite phase and the untempered martensite phase, and the martensite The ratio of the area of ​​the ferrite phase to the area of ​​the ferrite phase, the average grain size of the martensite phase, the area ratio of the tempered martensite phase in the entire martensit...

Embodiment 2

[0118] Steel Nos. A to P having the compositions shown in Table 4 were smelted in a converter, and steel slabs were produced by a continuous casting method. These billets were heated to 1200°C, hot rolled at a finishing temperature of 850 to 920°C, and coiled at a coiling temperature of 600°C. Then, after pickling, cold rolling at a rolling ratio of 50% to the plate thickness shown in Table 5, and after annealing in the annealing conditions shown in Table 5 through a continuous hot-dip galvanizing line, some steel sheets were subjected to heat treatment at 400°C. Heat treatment for the time shown in Table 5, followed by immersion in a 475°C zinc plating bath containing 0.13% Al for 3 seconds to form a coating with a deposition weight of 45g / m 2 The galvanized layer was alloyed at the temperature shown in Table 5 to make galvanized steel sheets No.1-26. In addition, as shown in Table 5, some galvanized steel sheets were not alloyed. Then, the same investigation as in Example ...

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Abstract

The invention provides a high-strength cold-rolled steel sheet having a TS of 1,180 MPa or greater and excellent workability, such as stretch flange workability and bendability. Also provided are a molten galvanized high-strength steel sheet, and a method for producing the same. The high-strength cold-rolled steel sheet having excellent workability has a composition that comprises, by mass%, C: 0.05 to 0.3, Si: 0.5 to 2.5, Mn: 1.5 to 3.5, P: 0.001 to 0.05, S: 0.0001 to 0.01, Al: 0.001 to 0.1, N: 0.0005 to 0.01, and Cr: 1.5 or less (including 0) and satisfies formulas (1) and (2), with the balance being Fe and inevitable impurities. The steel sheet has a microtexture wherein there is a ferrite phase and a martensite phase, the percentage of the texture total surface area occupied by martensite phase is 30% or greater, (the surface area occupied by martensite phase)/(surface area occupied by ferrite phase) exceeds 0.45 but is less than 1.5, and the average particle diameter of the martensite phase is 2 microns or larger. [C]1/2*([Mn]+0.6*[Cr])>/=1-0.12*[Si] (1), and 550-350*C*-40*[Mn]-20*[Cr]+30*[Al]>/=340 (2), wherein C*=[C]/(1.3*[C]+0.4*[Mn]+0.45*[Cr]-0.75).

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet and a high-strength hot-dip galvanized steel sheet which are mainly suitable for structural parts of automobiles and which are excellent in formability, and in particular have a tensile strength TS of 1180 MPa or more and are excellent in formability such as hole expandability and bendability High-strength cold-rolled steel sheets and high-strength hot-dip galvanized steel sheets and their manufacturing methods. Background technique [0002] In recent years, in order to ensure the safety of occupants in the event of a collision and to improve fuel efficiency by reducing the weight of the car body, the application of high-strength steel plates with a TS of 780 MPa or more and a thin plate thickness to automotive structural parts has been actively studied. In particular, application of extremely high-strength high-strength steel sheets having a TS of 1180 MPa class or more has recen...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C21D9/46C22C18/00C22C38/38C22C38/58C23C2/02C23C2/06C23C2/28
CPCC21D1/25C21D1/26C21D8/0463C21D8/0473C21D9/48C21D2211/005C21D2211/008C22C38/001C22C38/02C22C38/04C22C38/06C22C38/38C23C2/06C23C2/28C23C2/024C23C2/0224C23C2/02
Inventor 金子真次郎川崎由康中垣内达也松冈才二
Owner JFE STEEL CORP
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