Steel sheet and plated steel sheet

Abstract

This steel sheet has a specific chemical composition and is provided with a structure represented by, in terms of area ratio, 0 - 30% ferrite and 70 - 100% bainite. When a crystal grain is defined asa region which is surrounded by grain boundaries having a misorientation of 15 DEG or higher and for which the equivalent circle diameter is 0.3 mu m or larger, the proportion of crystal grains havingan intragranular misorientation of 5 - 14 DEG relative to all of the crystal grains is 20 - 100% in terms of area ratio. The grain boundary number density of a solid solution of C, or the total grainboundary number density of a solid solution of C and a solid solution of B is 1 particle / nm<2> to 4.5 particles / nm<2> inclusive. The average particle size of cementite precipitated in the grain boundaries is no larger than 2 mu m.

Description

technical field [0001] The present invention relates to steel sheets and plated steel sheets. Background technique [0002] In recent years, there has been a demand for reducing the weight of various components for the purpose of improving the fuel economy of automobiles, the thinning of steel plates such as iron alloys used in components due to the increase in strength, and the use of light metals such as Al alloys in various components The application in is progressing. However, when compared with heavy metals such as steel, light metals such as Al alloys have the advantage of high specific strength, but have the disadvantage of being significantly expensive. Therefore, the application of light metals such as Al alloys is limited to special applications. Therefore, in order to reduce the weight of various members more cheaply and apply them in a wide range, it is required to reduce the thickness of the steel plate by increasing the strength. [0003] If the strength of ...

AI Technical Summary

Problems solved by technology

However, when the inventors of the present invention conducted additional tests on the steel sheets to which the techniques disclosed in Patent Documents 2 and 3 were applied, steels having the compositions described in Patent Documents 5 and 6 were found to be Also produces "peeling"

Therefore, it can be said that among the techniques disclosed in Patent Documents 2 and 3, there is no disclosure of techniques for suppressing flaws and microcracks on the end faces formed by shearing and punching.

[0011] On the other hand, when the weight is reduced by thinning the wall as described above, the service life of the automobile tends to be shortened due to corrosion.

Images