Cold-Rolled Ferritic Stainless Steel Grain Control
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Solution Overview
Problem
Cold-rolled ferritic stainless steel sheets face challenges in achieving excellent surface appearance quality and formability due to issues like ridging, roping, and surface roughening, which are not adequately addressed by existing methods that either compromise manufacturability or increase costs.
Innovation Solution
Control the average grain diameter of the ferrite phase to 10 µm or less by generating a large amount of dislocations through rolling or a martensite phase, and maintain a specific grain diameter distribution to inhibit deformation-induced defects and enhance formability and surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If long-time annealing is omitted to improve productivity, then manufacturing efficiency increases, but cold rolling manufacturability deteriorates significantly
Solution Approach 1:
The patent applies preliminary action by performing a specific hot-rolled-sheet annealing treatment before cold rolling. The steel sheet is heated to 900-1050°C and held for 10-120 seconds to create an austenite phase, which then transforms to martensite during cooling. This preliminary phase transformation creates a metallographic structure that is more amenable to subsequent cold rolling, thereby improving manufacturability without requiring long-time annealing processes.
Solution Approach 2:
The patent utilizes phase transitions by controlling the transformation from austenite to martensite during the hot-rolled-sheet annealing process. By heating to 900-1050°C to form austenite and then controlling cooling to transform it to martensite, the patent creates a specific metallographic structure that improves cold rolling manufacturability. This phase transition mechanism allows the material to have better formability during cold rolling without requiring extended annealing times.
2Productivity
If cold rolling is performed on hardened hot-rolled steel sheet to improve productivity, then manufacturing time decreases, but formability deteriorates
Solution Approach 1:
The patent utilizes phase transitions by controlling the transformation from austenite to martensite during the hot-rolled-sheet annealing process. By heating to 900-1050°C to form austenite and then controlling cooling to transform it to martensite, the patent creates a specific metallographic structure that improves cold rolling manufacturability. This phase transition mechanism allows the material to have better formability during cold rolling without requiring extended annealing times.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the temperature range (900-1050°C) and holding time (10-120 seconds) during hot-rolled-sheet annealing. These parameter adjustments create an optimal metallographic structure with controlled grain size and phase distribution, enabling the steel to maintain both productivity and formability during subsequent cold rolling operations.
3Manufacturing precision
If grain diameter is reduced to improve surface appearance quality, then surface gloss and ridging resistance improve, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the temperature range (900-1050°C) and holding time (10-120 seconds) during hot-rolled-sheet annealing. These parameter adjustments create an optimal metallographic structure with controlled grain size and phase distribution, enabling the steel to maintain both productivity and formability during subsequent cold rolling operations.
Solution Approach 2:
The patent applies preliminary action by performing a specific hot-rolled-sheet annealing treatment before cold rolling. The steel sheet is heated to 900-1050°C and held for 10-120 seconds to create an austenite phase, which then transforms to martensite during cooling. This preliminary phase transformation creates a metallographic structure that is more amenable to subsequent cold rolling, thereby improving manufacturability without requiring long-time annealing processes.
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 approach results in a cold-rolled ferritic stainless steel sheet with improved surface gloss, ridging resistance, and formability, achieving a balance between aesthetic quality and manufacturability without significant increases in costs.
Implementation Method 1
the average grain diameter of a ferrite phase is 10 µm or less, in which the proportion of ferrite grains having a grain diameter of 10 µm or more and less than 40 µm to the whole metallographic structure is 60% or more in terms of area ratio
Implementation Method 2
generating a large amount of dislocations through rolling or a martensite phase
Data Source
AI summary
Provided is a cold-rolled ferritic stainless steel sheet excellent in terms of surface appearance quality before and after a forming process and having sufficient formability. The chemical composition contains, by mass%, C: 0.01% or more and 0.05% or less, Si: 0.02% or more and 0.75% or less, Mn: 0.1% or more and 1.0% or less, P: 0.04% or less, S: 0.01% or less, Al: 0.001% or more and 0.10% or less, N: 0.01% or more and 0.06% or less, Cr: 16.0% or more and 18.0% or less, and the balance being Fe and inevitable impurities. The metallographic structure includes a ferrite phase, in which the average grain diameter of a ferrite phase is 10 µm or less, in which the proportion of ferrite grains having a grain diameter of 10 µm or more and less than 40 µm to the whole metallographic structure is 60% or more in terms of area ratio, and in which the proportion of ferrite grains having a grain diameter of less than 5 µm to the whole metallographic structure is less than 20% in terms of area ratio.