Steel Sheet Production via P and S Composition Control
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Solution Overview
Problem
Existing methods for producing cold-rolled steel sheets with excellent workability suffer from issues such as increased skinpass rolling reduction, degradation due to oxide inclusions, non-uniform heat transfer, and neglect of planar anisotropy and surface properties.
Innovation Solution
A steel sheet composition with specific elements like P, S, and controlled cold-rolling and heating rates, along with precise annealing processes, is used to achieve a tensile strength of 340 MPa or more, excellent workability, and improved surface properties, while maintaining low planar anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If skinpass rolling reduction ratio is increased to improve surface quality, then surface properties are improved, but workability degrades
Solution Approach 1:
The patent changes the chemical composition parameters of the steel sheet, specifically controlling P content at 0.003-0.015% and S content at 0.003-0.015%, to achieve both improved surface quality and maintained workability without requiring excessive skinpass rolling reduction ratio
2Manufacturing precision
If oxide inclusions are controlled through MnS size, then inclusion quality is improved, but oxygen content must be 60 ppm or more causing large quantities of oxide inclusions
Solution Approach 1:
The patent changes the compositional parameters by precisely controlling P and S content within 0.003-0.015% ranges, which fundamentally alters the inclusion formation mechanism and reduces oxide inclusion quantity while maintaining quality
Solution Approach 2:
The patent converts the traditionally harmful P and S elements, when present in controlled amounts of 0.003-0.015%, into beneficial components that improve surface quality and workability simultaneously, rather than viewing them merely as impurities to be eliminated
3Productivity
If heat transfer is increased during annealing to improve processing speed, then productivity is improved, but heat transfer becomes non-uniform throughout the steel sheet
Solution Approach 1:
The patent changes the chemical composition parameters (P: 0.003-0.015%, S: 0.003-0.015%) that affect the material's thermal and mechanical properties, enabling uniform microstructure development during annealing that ensures both speed and uniformity
4Strength
If cold-rolling reduction ratio is increased to improve strength, then tensile strength is improved, but planar anisotropy increases
Solution Approach 1:
The patent changes the chemical composition parameters, specifically controlling P and S content at 0.003-0.015%, which influences the microstructure formation during cold-rolling to achieve high strength while minimizing planar anisotropy
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 method produces steel sheets with enhanced workability, surface quality, and planar anisotropy, suitable for applications like automobile structural elements, leading to improved fuel efficiency through weight reduction.
Implementation Method 1
cold-rolling a steel sheet at a rolling reduction ratio of 50% or more
Implementation Method 2
regulating the cooling conditions and the overaging conditions after annealing
Data Source
AI summary
A method of producing a hot-rolled steel sheet and a method for producing a cold-rolled full hard steel sheet are provided. The methods comprising heating a steel slab having a composition containing, in terms of mass %, C: 0.010% or more and 0.150% or less, Si: 0.20% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.0500% or less, Al: 0.001% or more and 0.100% or less, N: 0.0100% or less, and the balance being Fe and unavoidable impurities, in which 0.002%≤[% P]+[% S]≤0.070% ([% M] denotes a content (mass %) of M element in steel) is satisfied.