Cold-rolled steel sheet excellent in spot weldability and manufacturing method thereof
A technology of cold-rolled steel sheets and hot-rolled steel sheets, which is applied in the field of cold-rolled steel sheets and its manufacturing, can solve problems such as stress concentration, reduced fracture strength of spot welds, and discontinuous strength, so as to reduce environmental load, improve manufacturing efficiency, and reduce fuel consumption. The effect of improving efficiency
Active Publication Date: 2018-09-11
JFE STEEL CORP
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Problems solved by technology
In general, since the welded part becomes a discontinuous shape different from the base metal, stress concentration tends to occur, and the generation of residual stress due to the influence of welding heat cannot be avoided.
Therefore, especially for high-strength steel sheets, the discontinuity of strength becomes remarkable in the region covering the range of weld metal-weld heat-affected zone-base metal, and the fracture strength of spot welds tends to decrease compared with the base metal. reduce
Method used
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Embodiment
[0126] The steels with the compositions shown in Table 1 were smelted in a converter, then ladle refined, and cast into steel slabs by continuous casting. Next, the steel slabs were hot-rolled under the conditions shown in Table 2 to produce hot-rolled steel sheets. Thereafter, the hot-rolled steel sheets were cold-rolled and continuously annealed under the conditions shown in Table 2 to obtain cold-rolled steel sheets to be product sheets.
[0127]
[0128]
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Abstract
To provide cold-rolled steel sheets with excellent spot weldability suitable for automobiles, electric motors, etc., having the following steel composition: by mass %, C: 0.05-0.13%, Si: 0.05-2.0%, Mn: 1.5-4.0%, P: 0.05% or less, S: 0.005% or less, Al: 0.01 to 0.10%, Cr: 0.05 to 1.0%, Nb: 0.010 to 0.070%, Ti: 0.005 to 0.040%, and N: 0.0005 to 0.0065%, Ti and N The mass ratio of Ti / N is 2.5 or more and 7.5 or less, the rest is composed of Fe and unavoidable impurities, more than 70% by mass of Ti in the steel exists in the form of precipitates, and 70% by mass of the Nb in the steel exists in the form of precipitates. 15% by mass or more exists in the form of solid solution Nb, and the tensile strength is 980 MPa or more.
Description
technical field [0001] The present invention relates to a cold-rolled steel sheet having a thickness of 0.4 mm to 3.0 mm suitable for use in automobiles, electric motors, etc., and particularly relates to a cold-rolled steel sheet having a tensile strength of 980 MPa or more and excellent spot weldability, and a method for producing the same. Background technique [0002] In recent years, improvement in fuel efficiency of automobiles has become important from the viewpoint of global environmental protection, and weight reduction of automobile bodies has been promoted. In response to this, increasing the strength of the steel sheet used and reducing the thickness of the sheet are the most effective means. In addition, technology to improve the safety of passengers is also an important issue, and increasing the strength of the steel plate used is an effective countermeasure against this. For the purpose of increasing the strength of the above-mentioned steel sheet, convention...
Claims
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IPC IPC(8): C22C38/00C21D9/46C22C38/38C22C38/58
CPCC22C38/00C22C38/38C22C38/58C21D9/46C21D1/26C21D8/0205C21D8/0226C21D8/0236C21D8/0263C22C38/001C22C38/002C22C38/02C22C38/06C22C38/20C22C38/22C22C38/24C22C38/26C22C38/28C22C38/42C22C38/48C22C38/50
Inventor 植田圭治金子真次郎岩崎正美杉原玲子横田毅濑户一洋
Owner JFE STEEL CORP