Ferritic Stainless Steel Sheet Deep Drawability via Crystal Orientation Control
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Solution Overview
Problem
Ferritic stainless steel sheets with a thickness of 1.0 mm or more face challenges in developing adequate {111} grains for improved deep drawability due to reduced rolling reduction, and existing methods either compromise productivity or lead to defects like cracks during forming processes.
Innovation Solution
A ferritic stainless steel sheet with a specific chemical composition and production process involving hot-rolling, pickling, and cold-rolling without annealing, followed by controlled annealing to develop {111} and {322} crystal orientations, ensuring high workability and deep drawability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ferritic stainless steel sheet is used for exhaust system components, then cost is reduced compared to austenitic stainless steel, but workability and formability are insufficient
Solution Approach 1:
The invention changes the chemical composition parameters by precisely controlling the content ranges of alloying elements (C: 0.001-0.020%, Si: 0.02-1.50%, Mn: 0.02-1.50%, Cr: 10.0-25.0%, Ti: 0.01-0.30%, Nb: 0-0.10%, and others). This parameter optimization enables ferritic stainless steel to achieve both cost-effectiveness and improved workability, resolving the contradiction between cost and formability
Solution Approach 2:
The invention creates a composite microstructure consisting of ferrite phase with specific crystal orientations ({111} and/or {322} planes) and controlled grain size (5.0-15.0 μm). This composite microstructural design provides both the cost advantage of ferritic steel and the workability characteristics normally associated with more expensive austenitic steels
2Productivity
If rolling reduction is reduced for thick steel sheets (1.0 mm or more), then productivity is maintained, but adequate {111} grains cannot be developed for deep drawability
Solution Approach 1:
The invention changes the chemical composition parameters, particularly increasing Si content (0.02-1.50%) and Cr content (10.0-25.0%), which modify the recrystallization behavior during rolling. This enables {111} grain development even with reduced rolling reduction, maintaining both productivity and deep drawability
Solution Approach 2:
The invention performs preliminary microstructure control through optimized chemical composition before the rolling process. The controlled composition promotes preferential formation of {111} oriented grains during rolling, so that adequate deep drawability is achieved without requiring extensive rolling reduction
3Ease of operation
If conventional annealing processes are applied to improve workability, then deep drawability is enhanced, but productivity decreases due to additional process steps
Solution Approach 1:
The invention merges the composition control and microstructure development into a single integrated rolling process. By optimizing the chemical composition, the desired ferritic microstructure with {111} orientation develops during the rolling operation itself, eliminating the need for separate annealing processes while maintaining deep drawability
Solution Approach 2:
The invention maintains continuous rolling without interrupting for separate annealing steps. The optimized composition enables the rolling process itself to continuously produce the desired microstructure, preserving productivity while achieving the workability improvements normally requiring additional heat treatment steps
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 a ferritic stainless steel sheet with enhanced deep drawability and workability, particularly for exhaust system components, while maintaining productivity and avoiding defects like cracks.
Implementation Method 1
a first crystal orientation intensity of a {111} plane and a second crystal orientation intensity of a {322} plane in a sheet thickness direction of the steel sheet satisfy predetermined relationships, wherein the steel sheet has a recrystallized fine grain
Data Source
AI summary
A ferritic stainless steel sheet is provided that has a chemical composition consisting of, in mass %, C: 0.001 to 0.020%, Si: 0.02 to 1.50%, Mn: 0.02 to 1.50%, P: 0.01 to 0.05%, S: 0.0001 to 0.01%, Cr: 10.0 to 25.0%, Ti: 0.01 to 0.30%, N: 0.001 to 0.030%, and optional elements, with the balance being Fe and unavoidable impurities, wherein: a grain size number is 6 or more; the ferritic stainless steel sheet satisfies the formulas [A+B≥12.0/t], [X+Y≥12.0/(t−0.3)] and [(X+Y)−(A+B)≤5.0] with respect to crystal orientation intensities of a ferrite phase obtained by X-ray diffraction; and the sheet thickness is 1.0 mm or more.