Steel plate having excellent fine blanking processability and method for manufacture thereof

Abstract

A steel sheet which has excellent suitability for FB and has excellent formability after FB. The steel sheet has: a composition which contains, in terms of mass%, 0.1-0.5% C and 0.2-1.5% Si and Mn and in which Si, P, and S are regulated so as to be in respective proper ranges; ferrite having an average particle diameter of 1-10 [mu]m; and a structure which has a degree of spheroidization of 80% or higher and in which the ferrite grain boundary carbide amount defined by Sgb (%) = {Son / (Son+Sin)} 100 (wherein Son is the total area occupied by carbide present at the grain boundaries, of the existing carbide, per unit area and Sin is the total area occupied by carbide present in the grains, of the existing carbide, per unit area) is 40% or larger. This steel sheet is excellent in suitability for FB, die life, and formability after FB.

Description

technical field [0001] The present invention relates to a steel sheet suitable for applications such as automobile parts, and particularly to a steel sheet with excellent fine blanking properties suitable for fine blanking (hereinafter also referred to as fine blanking or FB processing). Background technique [0002] In the manufacture of complex mechanical parts, it is known that fine blanking is an extremely advantageous processing method compared with cutting processing from the viewpoint of improving dimensional accuracy and shortening the manufacturing process. [0003] In normal punching, the gap between dies is about 5% to about 10% of the thickness of the blanking material metal plate, but fine blanking is different from normal punching in that the gap between dies is set. It is a punching method in which compressive stress is applied to the material near the cutting edge of the die while being extremely small and almost zero (actually less than about 2% of the thick...

AI Technical Summary

Problems solved by technology

[0023] However, each of the technologies described in Patent Document 4 and Patent Document 5 is based on the premise of performing conventional punching, and it is not considered that they can be applied to fine blanking where the clearance is almost zero.

Therefore, after strict fine blanking, it is difficult to ensure the same stretch flangeability, and even if it can be ensured, there is a problem that the life of the die is shortened.

[0024] In addition, the technique described in Patent Document 6 requires a ferrite grain size in the range of 0.5 to 1 μm, and it is difficult to manufacture steel sheets with such a ferrite grain size in an industrially stable manner, resulting in a problem of lower product yield.

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