Ferritic Stainless Steel Sheet Surface Defect Control
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Solution Overview
Problem
Ferritic stainless steel sheets with Ti as a stabilizing chemical element face challenges in achieving both reduced surface defects and improved toughness while maintaining corrosion resistance, as existing methods either fail to sufficiently address surface defects or toughness issues.
Innovation Solution
Incorporating appropriate amounts of Zr and Nb into the chemical composition of Ti-containing SUS443J1-type stainless steel sheets to alter the precipitation form of TiN, allowing for finely dispersed Ti-based inclusions and controlling the content of Ti, Nb, and Zr to satisfy the relational expression Zr ≤ Nb ≤ Ti, which enhances toughness and reduces surface defects without increasing cold-rolled-sheet annealing temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ti is added as a stabilizing chemical element to improve corrosion resistance and promote texture growth, then workability and corrosion resistance are improved, but coarse TiN forms on the surface causing streaks and deteriorating aesthetic appearance, and toughness decreases
Solution Approach 1:
Nb and Zr are introduced as intermediary elements that mediate the precipitation behavior of TiN. These elements have different precipitation characteristics than Ti alone, and their presence modifies the precipitation sequence and morphology, transforming coarse TiN into fine dispersed precipitates that do not cause surface streaks
Solution Approach 2:
The invention changes the chemical composition parameters by specifying precise ranges for Ti (0.10-0.50%), Nb (0.010-0.150%), and Zr (0.005-0.150%), along with the relational expression Zr ≤ Nb ≤ Ti. This parameter control transforms the precipitation behavior from coarse TiN formation to fine dispersed precipitate formation, eliminating surface defects while maintaining corrosion resistance
2Reliability
If Ti is added as a stabilizing chemical element to improve corrosion resistance and promote texture growth, then workability and corrosion resistance are improved, but coarse TiN forms causing preferential fracturing and low toughness
Solution Approach 1:
Nb and Zr act as intermediary elements that modify the precipitation behavior of Ti-based inclusions. Their presence changes the precipitation sequence and morphology, transforming coarse TiN (which causes fracturing) into fine dispersed precipitates that do not serve as preferential fracture starting points, thereby improving toughness
Solution Approach 2:
By controlling the composition parameters within specified ranges and satisfying the relational expression Zr ≤ Nb ≤ Ti, the invention transforms the nature of precipitates from coarse harmful TiN to fine beneficial dispersoids, simultaneously improving both surface quality and toughness while maintaining corrosion resistance
3Productivity
If cold-rolled-sheet annealing is performed at lower temperature to maintain productivity, then manufacturing efficiency is improved, but insufficient softening occurs in Ti-containing steel
Solution Approach 1:
The invention changes the chemical composition parameters by adding Nb and Zr in specific ranges relative to Ti content. This composition modification alters the precipitation behavior and softening characteristics of the steel, enabling sufficient softening to occur at lower annealing temperatures (700-900°C), thereby maintaining high productivity while achieving the required softening effect
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 ferritic stainless steel sheet with excellent corrosion resistance, minimal surface defects, and improved toughness, while maintaining productivity by allowing sufficient softening during cold-rolled-sheet annealing at conventional temperatures.
Implementation Method 1
controlling the precipitation of TiN when the molten steel is cast... allow nitrides in the steel to exist in the form of ZrN... change the precipitation form of TiN, which causes a deterioration in toughness
Implementation Method 2
cold-rolled-sheet annealing is performed at a lower temperature than that for steel containing Nb... sufficiently softened even in the case where cold-rolled-sheet annealing is performed at a lower temperature... sufficient softening during cold-rolled-sheet annealing at conventional temperatures
Data Source
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AI summary
Provided is a ferritic stainless steel sheet excellent in terms of corrosion resistance with which a decrease in the quantity of surface defects and an improvement in toughness are realized at the same time. The ferritic stainless steel sheet has a chemical composition containing, by mass%, C: 0.020% or less, Si: 0.05% to 0.40%, Mn: 0.05% to 1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% to 0.80%, Cu: 0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr: 0.005% to 0.150%, N: 0.020% or less, and the balance being Fe and inevitable impurities, in which relational expression (1) below is satisfied. Zr≤Nb≤Ti (Here, each of Zr, Nb, and Ti in relational expression (1) denotes the content (mass%) of the corresponding chemical element.)