Steel Sheet Fine Blanking Microstructure Control
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Solution Overview
Problem
Conventional steel sheets used in fine blanking working face challenges in maintaining excellent fine blanking performance and mold life, while also experiencing inferior fabrication performance, especially under severe working conditions and in applications like stretch flanging and bulging for automobile parts.
Innovation Solution
A steel sheet with a composition of 0.1-0.5% C, 0.2-1.5% Mn, and a microstructure of 100% pearlite with a spheroidization ratio of 80% or more for cementite, and a ferrite grain size of 1-10 µm, combined with hot rolling and annealing processes to control cementite distribution, resulting in improved fine blanking performance and mold life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fine blanking working is performed with tool-to-tool clearance of substantially zero, then fine blanking performance is improved with smooth worked surface and dimensional precision, but mold life is shortened due to excessive load on mold
Solution Approach 1:
The invention changes the material parameters (chemical composition and microstructure) of the steel sheet to enable fine blanking working with zero clearance while extending mold life. Specifically, it controls C content at 0.15-0.90% and Mn at 0.3-1.0%, creates a microstructure with spheroidized cementite (80% or more spheroidization ratio) with average grain size of 0.4-1.0 μm in a ferrite matrix, and achieves notch tensile elongation of 20% or more, allowing the material to withstand severe working conditions without excessive load on the mold
2Manufacturing precision
If high carbon content steel sheet is used to improve fine blanking performance and mold life, then fine blanking performance is improved, but fabrication performance after fine blanking working becomes inferior
Solution Approach 1:
The invention optimizes the chemical composition parameters by limiting C content to 0.15-0.90% (not excessively high) and Mn to 0.3-1.0%, and controls the microstructure parameters (spheroidization ratio of 80% or more, average grain size of 0.4-1.0 μm, notch tensile elongation of 20% or more). This balanced parameter control achieves both excellent fine blanking performance and good fabrication performance after working, avoiding the problem of inferior fabrication performance associated with high carbon content steel
3Manufacturing precision
If tool-to-tool clearance is reduced to substantially zero for fine blanking working, then crack generation is inhibited and fracture surface is reduced, but working ratio on material becomes extremely severe
Solution Approach 1:
The invention changes the material parameters (chemical composition and microstructure) to enable the material to withstand extremely severe working ratios. By controlling C at 0.15-0.90%, Mn at 0.3-1.0%, creating spheroidized cementite structure (80% or more spheroidization ratio, 0.4-1.0 μm grain size), and achieving notch tensile elongation of 20% or more, the material gains sufficient ductility and strength to undergo severe plastic deformation without cracking, thus maintaining smooth worked surface even under zero clearance conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The steel sheet exhibits excellent fine blanking performance, reduced surface roughness, extended mold life, and enhanced productivity, with improved stretch flanging properties after fine blanking working, addressing the limitations of previous technologies.
Implementation Method 1
a microstructure with a cementite having a spheroidization ratio of 80 % or more and an average grain size of from 0.4 to 1.0 μm scattered in a ferrite matrix
Implementation Method 2
proper hot rolling to a billet containing from 0.08 to 0.19 % of C and proper amounts of Si, Mn and Al
Data Source
Figure 1~2
Figure 3~4
AI summary
A steel sheet excellent in FB performance and also excellent in fabrication performance after FB working and a manufacturing method of the same are provided. The steel sheet is a steel sheet having a composition containing from 0.1 to 0.5 % of C, not more than 0.5 % of Si and from 0.2 to 1.5 % of Mn in terms of % by mass, with P and S being adjusted at proper ranges, and having a structure in which a ferrite has an average grain size of from 1 to 10 µm, a cementite has a spheroidization ratio of 80 % or more, and of the cementites, an amount Sgb of a ferrite intergranular cementite which is defined by the following expression (1) : Sgb (%) = {Son/(Son + Sin)} × 100 (wherein Son represents a total occupied area of a cementite present on the ferrite grain boundary of the cementites present per unit area; and Sin represents a total occupied area of a cementite present in a ferrite grain of the cementites present per unit area) is 40 % or more. In this way, the steel sheet becomes a steel sheet excellent in FB performance, mold life and performance after FB working.