Cold-Rolled Steel Sheet Composition for Crack-Free Press Forming
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Solution Overview
Problem
Existing low-carbon-based steel materials used in electronic products and frames face challenges with crack occurrence and distortion during forming, necessitating a solution that enhances press workability and strength while minimizing surface defects.
Innovation Solution
A cold-rolled steel sheet with a specific composition of 0.010 to 0.025% carbon, 0.10 to 0.25% manganese, 0.002 to 0.011% sulfur, 0.0006 to 0.0026% boron, 0.0010 to 0.0034% nitrogen, and 0.006 to 0.028% aluminum, along with precipitates of MnS and BN, is developed. This composition and microstructure are achieved through a manufacturing process involving reheating, hot rolling, cold rolling, annealing, and temper rolling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional low-carbon-based steel material is used, then material cost is low and manufacturing process is simple, but crack occurrence and distortion occur during forming
Solution Approach 1:
The patent optimizes the chemical composition parameters of steel, specifically controlling carbon content at 0.010 to 0.025%, manganese at 0.10 to 0.25%, sulfur at 0.002 to 0.011%, boron at 0.0006 to 0.0026%, nitrogen at 0.0010 to 0.0034%, and aluminum at 0.006 to 0.028%. This precise parameter control achieves excellent formability and strength without requiring extremely low carbon content or complex alloying, thus resolving the contradiction between reliability and ease of manufacture
Solution Approach 2:
The patent creates a composite microstructure containing ferrite as the matrix phase with precipitates of MnS and BN distributed within it. This composite structure at the micro level provides both the ductility needed for formability and the strength to prevent cracking and distortion, while maintaining a relatively simple overall material composition and manufacturing process
2Reliability
If extremely low-carbon-based material with solid solution strengthening and precipitation strengthening is used, then strength and formability are secured, but manufacturing process is complicated and material cost increases
Solution Approach 1:
The patent adopts a moderate carbon content range of 0.010 to 0.025%, which is higher than extremely low-carbon materials but lower than conventional low-carbon steel. This parameter adjustment, combined with controlled amounts of Mn, S, B, N, and Al, achieves the desired press workability without requiring the extreme carbon reduction or complex multi-element alloying of ultra-low carbon steels
Solution Approach 2:
The patent utilizes relatively inexpensive elements (C, Mn, S, B, N, Al) in controlled amounts to achieve the desired properties, avoiding the need for expensive rare earth elements or complex alloying systems. The straightforward hot rolling and cold rolling processes also reduce manufacturing complexity compared to more elaborate processing routes
3Reliability
If existing low-carbon-based material is used, then material cost is competitive, but surface defects occur during product production
Solution Approach 1:
The patent converts potentially harmful sulfur, which typically causes surface defects and inclusions, into beneficial MnS precipitates that are controlled in size and distribution. By adding manganese (0.10 to 0.25%) to react with sulfur (0.002 to 0.011%), the patent transforms sulfur from a harmful impurity into a useful precipitate phase that actually improves formability while maintaining surface quality
Solution Approach 2:
The patent precisely controls the composition parameters, particularly keeping carbon at 0.010 to 0.025% and sulfur at 0.002 to 0.011%, with controlled amounts of Mn, B, N, and Al. This parameter optimization ensures that precipitates form uniformly without causing surface defects, achieving high surface quality without requiring extremely complex composition control
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 resulting steel sheet exhibits excellent press workability with no defects during forming, high strength, and improved elongation rate, effectively addressing the challenges of crack occurrence and distortion in existing materials.
Implementation Method 1
including a precipitate of at least one of MnS and BN
Implementation Method 2
including a precipitate of at least one of MnS and BN
Implementation Method 3
annealing the cold-rolled steel sheet
Data Source
AI summary
A cold-rolled steel sheet, according to one embodiment of the present invention, may comprise in percentage by weight: carbon (C): 0.010-0.025%; manganese (Mn): 0.10-0.25%; sulfur(S): 0.002-0.011%; boron (B): 0.0006-0.0026%; nitrogen (N): 0.0010-0.0034%; aluminum (Al): 0.006-0.028%; and the balance being Fe and unavoidable impurities, and may comprise precipitates of at least one of MnS and BN, wherein the average particle diameter of the precipitates may be 40-250 nm, the area fraction of the precipitates in the cold-rolled steel sheet may be 1-10%, and the yield strength may be 150-220 MPa.