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High-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, and method for manufacturing same

A cold-rolled steel plate and sinter hardening technology, which is applied in the manufacture of tools, furnaces, heat treatment equipment, etc., can solve problems such as unfavorable raw material costs, increased deformation resistance, and delayed austenite recrystallization, so as to contribute to collision safety and lightweight effect

Active Publication Date: 2013-07-10
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

First, Nb is a very expensive element, which is disadvantageous in terms of raw material cost
In addition, Nb significantly delays the recrystallization of austenite, so there is a problem that the load during hot rolling increases.
In addition, the NbC precipitated in the hot-rolled sheet will increase the deformation resistance during cold rolling. Therefore, in the case of cold rolling at a high rolling ratio (65%) disclosed in the examples of Patent Document 7, rolling There are many problems in stable production of steel plates such as increased load, increased risk of failure, reduced productivity, and restrictions on the width of steel plates that can be manufactured.

Method used

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  • High-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, and method for manufacturing same
  • High-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, and method for manufacturing same
  • High-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, and method for manufacturing same

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0153] The steels A to V having the composition shown in Table 1 were melted by a known melting process such as a converter and vacuum degassing, and cast into a slab with a thickness of 260 mm. These billets were heated to 1220° C., and then hot-rolled to obtain hot-rolled sheets with a thickness of 3.8 mm. In addition, the rolling temperature and rolling ratio of the final pass and the pass preceding the final pass in the finish rolling of the above-mentioned hot rolling, the average cooling rate and coiling rate from the start of cooling after finish rolling to 720° C. The temperatures are shown in Table 2, and the time from the completion of finish rolling to the start of cooling was set within 3 seconds.

[0154]

[0155]

[0156] Next, the above-mentioned hot-rolled sheet was pickled, cold-rolled under the conditions shown in Table 2 to make a cold-rolled sheet with a thickness of 1.2 mm, and then continuously annealed under the conditions shown in Table 2, and the...

Embodiment 2

[0170] Steel slabs having the composition of steels D, G, and L described in Table 1 were heated to 1220° C., and then hot-rolled to obtain hot-rolled sheets with a thickness of 3.8 mm. In addition, the finish rolling conditions, cooling conditions, and coiling temperatures in hot rolling are shown in Table 4. In addition, the time from the end of finish rolling to the start of cooling is set within 3 seconds. Next, the above-mentioned hot-rolled sheet was pickled, and cold-rolled under the conditions shown in Table 4 to make a cold-rolled sheet with a thickness of 1.2 mm. Then, similarly, continuous annealing was carried out under the conditions shown in Table 4. Cold-rolled steel sheets (products) are produced by temper rolling with an elongation of 0.5%.

[0171] A test piece was cut out from the cold-rolled steel sheet obtained in the above manner in the same manner as in Example 1, and a microstructure observation and a tensile test were performed to measure the area rat...

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Abstract

The present invention provides a high-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, a tensile strength of 440 MPa or greater, an average r value of 1.20 or greater, and a bake hardening value of 40 MPa or greater by a process in which a steel raw material containing, in terms of mass%, 0.010 to 0.06% C, between 0.5% and 1.5% Si, 1.0 to 3.0% Mn, 0.010 to 0.090% Nb, and 0.015 to 0.15% Ti, and having a component composition satisfying conditions of (Nb / 93) / (C / 12) < 0.20 and a solid-solution C content of 0.005 to 0.025%, is hot rolled and cold rolled, then annealed by heating from a temperature of 700 to 800 DEG C to a temperature of 800 to 900 DEG C at an average temperature increase rate of less than 3 DEG C / s, soaking, and then cooling at 5 DEG C / s or faster from the soaking temperature to a cooling stop temperature of 500 DEG C or below to obtain a formation which includes a ferrite phase having an area ratio of 70% or greater and a martensite phase having an area ratio of 3% or greater.

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet having a tensile strength TS of 440 MPa or more, an average r-value of 1.20 or more, and a BH amount of 40 MPa or more, which is suitable for use as an outer panel of an automobile body and is excellent in deep drawability and sinter hardenability, and its method of manufacture. Background technique [0002] In recent years, from the viewpoint of protecting the global environment, in order to improve the fuel efficiency of automobiles, reduce CO 2 emissions, there is a strong demand for lightweight car bodies. At the same time, from the viewpoint of ensuring the safety of occupants at the time of a collision, there is also a strong demand for an increase in the strength of the vehicle body. In order to meet the above requirements, it is necessary to satisfy both weight reduction and high strength of the automobile body. Therefore, it is effective to reduce the thickness of the s...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/14C22C38/58C21D9/48
CPCC21D8/0226C21D8/0236C21D8/0273C21D2211/005C21D2211/008C22C38/001C22C38/008C22C38/02C22C38/04C22C38/06C22C38/12C22C38/14C22C38/60C21D8/005C22C38/08C22C38/18C22C38/20C22C38/24C22C38/26C22C38/28C22C38/40C22C38/42C22C38/46C22C38/48C22C38/50
Inventor 木村英之长泷康伸
Owner JFE STEEL CORP
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