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High-strength steel sheet and its production method

A technology of high-strength steel sheets and manufacturing methods, which can be applied to the manufacture of high-strength steel sheets and high-strength steel sheets for automobiles, and can solve problems such as low ductility, insufficient characteristics, and reduced production efficiency.

Inactive Publication Date: 2009-06-17
HONDA MOTOR CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0015] The first problem is that the higher the strength of the steel plate, the lower the ductility, so the lower the press forging formability, it is limited to the use of single-shaped parts
The second problem is that the parts break during the collision
Therefore, this structure is not suitable for steel sheets for press working
[0026] The second disadvantage is that when the cumulative rolling is carried out in the industrial process, the production efficiency is reduced, resulting in a substantial increase in production costs
In the invention example of Patent Document 6, the amount of C is as low as 0.13%, and the addition amount of alloy elements is small, which is excellent, but the tensile strength is 870 MPa and the elongation is 21%, so the characteristics are not good. insufficient

Method used

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  • High-strength steel sheet and its production method
  • High-strength steel sheet and its production method
  • High-strength steel sheet and its production method

Examples

Experimental program
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Effect test

no. 2 Embodiment approach

[0246] The high-strength steel plate produced by the present invention presents a metal structure composed of a ferrite phase and a hard second phase dispersed in the above-mentioned ferrite phase, and the area fraction of the hard second phase in the metal structure is 3%. ~30%, the area fraction of nano-grains in the ferrite phase is 15%-90%, in the ferrite phase, the average particle size dS of nano-grains and the average particle size dL of micro-grains satisfy the following (31) formula.

[0247] dL / dS≧3 (31)

[0248] Such a high-strength steel sheet is preferably on a cross section parallel to the rolling direction of the steel sheet. When nine or more square lattices of 3 μm square are randomly selected, the area fraction of the hard second phase in each lattice is set to is Ai (i=1, 2, 3, ...), at this time, the average A(ave) and standard deviation s of said Ai satisfy the following (32) formula, meanwhile, the average particle diameter of the hard second phase dp a...

Embodiment

[0408] 1. First Embodiment

[0409] Slabs having the chemical compositions shown in Table 4 (invention slabs 1 to 8 and comparative slabs 1 to 9) were melted. Next, using these slabs, hot-rolled sheets were produced under the conditions shown in Table 5, and then cold-rolled and annealed under the conditions shown in Table 6 to obtain steel sheets having the annealed structure and the like shown in Table 7. Then, cut out from each steel plate so that the direction parallel to the rolling direction becomes the drawing axis. Figure 14 Pull test pieces of the shape shown for tensile testing. From the obtained nominal stress and nominal strain curves, the yield point, tensile strength, bake hardening amount (BH amount) and total elongation were obtained, and the product of tensile strength × elongation was calculated at the same time. These results are recorded together in Table 5. In Comparative Example 4, as in Comparative Example 3, both sides of the hot-rolled sheet were ma...

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Abstract

A high-strength steel sheet which has a metallic structure comprising a ferrite phase and a second hard phase dispersed in the steel sheet. In the metallic structure, the areal proportion of the second hard phase is 30-70%. In the ferrite phase, the areal proportion of ferrite having a crystal grain diameter not larger than 1.2 [mu]m is 15-90% and the average grain diameter of ferrite having a crystal grain diameter not larger than 1.2 [mu]m (ds) and the average grain diameter of ferrite having a crystal grain diameter exceeding 1.2 [mu]m (dL) satisfy the relationship dL / ds=3. The size of the ferrite crystal grains has been reduced by reducing the amount of alloying elements to be added. The steel sheet hence has an increased strength. The steel sheet has an excellent balance between strength and ductility, which is important for press molding. It is excellent in energy absorption in high-speed deformation. Also provided is a process for producing the steel sheet.

Description

technical field [0001] The invention relates to a cold-rolled high-strength steel plate for automobiles and a manufacturing method thereof. The cold-rolled high-strength steel plate has both high strength and high ductility, and has excellent press forging formability and impact energy absorption capacity. In addition, the present invention relates to a method for manufacturing a high-strength steel sheet, and in particular to a technology for manufacturing a high-strength steel sheet for automobiles. Ductility during high-speed deformation, low strength during press forging, high strength and high ductility during impact, and excellent impact energy absorption capacity. Background technique [0002] In recent years, steel sheets used for automobile bodies have been required to have both higher strength and higher ductility in response to contradictory demands for improved automobile crash safety and reduced vehicle body weight. Regarding high-strength steel sheets satisfyi...

Claims

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Application Information

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IPC IPC(8): C22C38/00C21D9/46B21B3/00C22C38/58
Inventor 兴津贵隆
Owner HONDA MOTOR CO LTD
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