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High-strength cold-rolled steel sheet superior in chemical conversion treatability and manufacturing method thereof

A technology for chemical conversion treatment and cold-rolled steel sheets, applied in the field of cold-rolled steel sheets, can solve the problems of inability to obtain high-strength steel sheets, limited heating time, and inability to ensure chemical conversion treatment, and achieve excellent chemical conversion treatment, easy to manufacture. Effect

Active Publication Date: 2016-08-03
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0010] However, the technology of the above-mentioned Patent Document 1 not only limits the heating time before hot rolling, but also cannot obtain the high strength of 700 MPa or more which is the object of the present invention, especially on the basis of steel having a C content of 0.10% or less and a Si content of 1.0% or less. steel plate
In addition, in the technology of Patent Document 2, in order to ensure good formability, if the addition amount of Si is increased, the composition of the surface oxide is mainly composed of Si, and the atomic ratio [Si / Mn] in the surface oxide exceeds 1, Therefore, sufficient chemical conversion treatability cannot be ensured
It should be noted that the technology of Patent Document 3 is originally a technology for improving the platability, and is different from the production process of the plated steel sheet and the production process of the cold-rolled steel sheet. -The form of the Mn-concentrated layer is different between the plated steel sheet and the cold-rolled steel sheet, and simply making the Si-Mn-concentrated phase on the surface of the steel sheet to be 80% or less cannot ensure sufficient chemical conversion treatability

Method used

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  • High-strength cold-rolled steel sheet superior in chemical conversion treatability and manufacturing method thereof
  • High-strength cold-rolled steel sheet superior in chemical conversion treatability and manufacturing method thereof
  • High-strength cold-rolled steel sheet superior in chemical conversion treatability and manufacturing method thereof

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Embodiment 1

[0046] Steel materials A and B shown in Table 1 were melted in a converter, and slabs were produced by continuous casting. This slab was heated and hot rolled to a thickness of 2.5 mm. Thereafter, pickling was performed, and cold rolling was performed to a thickness of 1.2 mm. After cold rolling, annealing was performed on a continuous annealing line at 850° C. for about 80 seconds, water quenching was performed, pickling was performed under the conditions shown in Table 2, and tempering was performed thereafter. Tempering is held at 200°C for about 140 seconds for the steel material A, and about 140 seconds for the steel material B at 300°C. The ambient gas during annealing and tempering was hydrogen-nitrogen mixed gas (hydrogen concentration: 3 vol%), and the dew point was adjusted as shown in Table 2. As a result of measuring the tensile strength of the cold-rolled steel sheets produced in this way, the steel sheet of the steel type A was about 780 MPa, and the steel shee...

Embodiment 2

[0055] Steel materials 1 to 14 shown in Table 3 were melted in a converter, and slabs were produced by continuous casting. This slab was heated and hot rolled to a thickness of 2.5 mm. Thereafter, pickling was performed, and cold rolling was performed to a thickness of 1.2 mm. After cold rolling, annealing and quenching were performed on the continuous annealing line under the annealing conditions shown in Table 4, and then tempering was performed under the tempering conditions shown in Table 4. The ambient gas during annealing and tempering was hydrogen-nitrogen mixed gas (hydrogen concentration: 3 vol%), and the dew point was adjusted as shown in Table 4. In addition, "WQ" in a table|surface represents water quenching. Furthermore, post pickling was performed under the conditions shown in Table 4, and the tensile strength (TS) was measured. As shown in Table 5, the tensile strengths of all the steel sheets of steel types 1 to 14 were 700 MPa or more. Table 5 also shows YP...

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Abstract

The invention provides a high-strength cold-rolled steel plate which has excellent chemical conversion treatability even in the case that a large amount of Si which is effective for higher strength is added while the formability is maintained, and a preparation method of the high-strength cold-rolled steel plate. The high-strength cold-rolled steel plate provided by the invention contains the following ingredients in percentage by mass: higher than 0.04% of C and not lower than 0.4% of Si, wherein the ratio of the content of Si by mass to the content of Mn by mass is greater than 0.1. According to the high-strength cold-rolled steel plate, the tensile strength is higher than 700 MPa, the percentage of the surface, covered by a Si-based oxide mainly composed of Si, of the steel plate is lower than 20%, and the diameter of a biggest circle, internally connected with a region covered by the Si-based oxide, is smaller than 5 microns.

Description

technical field [0001] The present invention relates to a cold-rolled steel sheet having a high strength of 700 MPa or more, good press formability, and excellent chemical conversion treatability. Background technique [0002] In the context of improving fuel efficiency and reducing the weight of automobiles, high-strength steel is required, and high-strength cold-rolled steel sheets are also required. Since cold-rolled steel sheets are press-formed into parts, it is necessary to ensure sufficient ductility such as stretching when increasing the strength. High strength is mainly achieved by adding alloy elements, but among alloy elements, Si is an element that reduces ductility less and is effective for high strength while ensuring formability. However, when the amount of Si added is large, there is a problem that the chemical conversion treatability is significantly lowered. [0003] For high-tensile steel sheets containing Mn and Si, as a technique for improving chemical...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/04C22C38/00C22C38/54C21D8/02C21D1/18C21D1/26
CPCC23G1/08
Inventor 内海幸博梶原桂村上俊夫野村正裕桥本郁郎大宫良信上妻伸二嘉村学
Owner KOBE STEEL LTD
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