Ferritic Stainless Steel Formability via Crystal Orientation Control
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Solution Overview
Problem
Ferritic stainless steel sheets and pipes face limitations in formability, particularly for thick products and components requiring 2D pipe expansion, due to issues with r-value, ridging characteristics, and surface flaws, which existing methods fail to adequately address.
Innovation Solution
A ferritic stainless steel sheet with specific composition and manufacturing process, including controlled crystal orientations, intermediate annealing, and finish annealing, to achieve enhanced r-value and ridging characteristics, enabling improved formability and 2D pipe expansion capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ferritic stainless steel sheet is used for components requiring high formability, then cost is reduced compared to austenitic stainless steel, but formability is insufficient for complex shapes and 2D pipe expansion
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (C: 0.003-0.03%, Si: 0.01-0.9%, Mn: 0.01-1.0%, Cr: 10-20%, Ti: 0.05-1.0%, Nb: 0.05-1.0%) and processing parameters (intermediate annealing temperature, finish rolling reduction ratio) to transform ferritic stainless steel from having insufficient formability to achieving excellent formability with r-value of 1.6 or more and total elongation of 25% or more, while maintaining cost advantage over austenitic stainless steel
Solution Approach 2:
The patent creates a composite microstructure by combining multiple alloying elements (Ti, Nb, Cr, Si, Mn) in specific proportions to achieve a ferritic steel with enhanced formability. The combination of Ti and Nb with Cr in controlled amounts creates a composite material system that exhibits superior formability characteristics compared to conventional ferritic stainless steel
2Manufacturing precision
If rolling reduction is increased during hot rolling to improve formability, then r-value increases, but surface flaws and ridging characteristics deteriorate
Solution Approach 1:
The patent applies preliminary action by performing intermediate annealing before the final cold rolling process. This intermediate annealing treatment, conducted at controlled temperatures with specific holding times, pre-prepares the material microstructure to accommodate subsequent high rolling reduction (40% or more in finish rolling) without generating surface flaws or deteriorating ridging characteristics, while still achieving r-value of 1.6 or more
3Adaptability or versatility
If intermediate annealing is applied to enhance formability, then r-value and total elongation improve, but production time and process complexity increase
Solution Approach 1:
The patent optimizes the intermediate annealing parameters (temperature range, holding time, cooling rate) to achieve the desired formability improvement with minimal process time. By precisely controlling these parameters, the intermediate annealing process enhances r-value and total elongation while keeping the additional production time acceptable compared to conventional processes
4Adaptability or versatility
If carbon content is reduced to improve formability, then total elongation increases, but strength and corrosion resistance may be compromised
Solution Approach 1:
The patent compensates for the strength loss from reduced carbon content by creating a composite alloy system with controlled combinations of Si (0.01-0.9%), Mn (0.01-1.0%), Cr (10-20%), Ti (0.05-1.0%), and Nb (0.05-1.0%). These alloying elements work synergistically to provide solid solution strengthening and precipitation hardening, maintaining strength and corrosion resistance while enabling total elongation of 25% or more through the controlled carbon content (0.003-0.03%)
Solution Approach 2:
The patent changes the compositional parameters by precisely controlling the carbon content range (0.003-0.03%) and coordinating it with specific amounts of other alloying elements. This parameter optimization allows the steel to achieve excellent formability (r-value ≥ 1.6, total elongation ≥ 25%) while maintaining adequate strength and corrosion resistance through the balanced alloy composition
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 solution provides a ferritic stainless steel sheet with excellent formability, capable of efficient manufacturing and 2D pipe expansion, even for thick sheets, by optimizing crystal orientations and annealing processes, thus enhancing the freedom of formation and integral molding without welding.
Implementation Method 1
intermediate annealing, and finish annealing, to achieve enhanced r-value and ridging characteristics
Implementation Method 2
intermediate annealing, and finish annealing, to achieve enhanced r-value and ridging characteristics
Data Source
AI summary
A ferritic stainless steel sheet and a steel pipe as a material suitable for a heat-resistant component that is required to have especially excellent formability are provided. The ferritic stainless steel sheet contains 10 to 20 mass % of Cr and a predetermined amount of C, Si, Mn, P, S, Al and one or both of Ti and Nb, a {111}-orientation intensity being 5 or more and {411}-orientation intensity being less than 3 at a portion in the vicinity of a sheet-thickness central portion of the ferritic stainless steel sheet. Further, with similar composition and by setting {111}<110>-orientation intensity at 4.0 or more and {311}<136>-orientation intensity at less than 3.0, a relationship rm≥−1.0t+3.0 (t(mm): sheet thickness, rm: average r-value) is satisfied, thereby providing a ferritic stainless steel sheet and a steel pipe with excellent formability.