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 the delaying effect of Nb on recrystallization, leading to insufficient workability and increased productivity costs.
Innovation Solution
A ferritic stainless steel sheet with a chemical composition that includes specific elements like Nb, Ti, and Mo, and a production process involving hot-rolling, pickling, cold-rolling, and controlled annealing to promote the development of {111} and {322} crystal orientations throughout the sheet thickness, enhancing deep drawability and workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Nb is added to ferritic stainless steel sheets to improve heat resistance and strength, then material properties are enhanced, but the development of {111} grains during recrystallization is delayed, resulting in insufficient deep drawability and workability
Solution Approach 1:
The invention changes the chemical composition parameters by strictly controlling Nb content to 0.005% or more and less than 0.10%, and combining it with specific amounts of Ti (0.01-0.50%) and other alloying elements. This parameter optimization resolves the contradiction by finding the precise compositional window where both heat resistance and deep drawability are achieved.
Solution Approach 2:
The invention creates a composite alloying system combining Nb with Ti, Cr, Mn, Mo, and other elements in specific proportions. This composite approach allows the synergistic effects of multiple elements to promote {111} grain development while maintaining heat resistance, overcoming the limiting effect of Nb alone.
2Strength
If the sheet thickness is increased to 1.0 mm or more for exhaust system parts, then structural strength and durability are improved, but rolling reduction is reduced, making it difficult to develop adequate {111} grains for improved deep drawability
Solution Approach 1:
The invention changes the compositional parameters with specific alloying ratios that promote grain development during rolling. The controlled addition of Ti (0.01-0.50%) and Nb (0.005-0.10%) along with Cr (13.0-20.0%) creates a microstructure that facilitates {111} grain formation even in thick sheets with limited rolling reduction.
3Ease of manufacture
If conventional ferritic stainless steel sheets are used for exhaust system parts requiring complex forming, then cost is reduced compared to austenitic stainless steel, but workability for complex integral forming is insufficient
Solution Approach 1:
The invention optimizes chemical composition parameters to achieve a mean r-value of 1.20 or more, which significantly improves deep drawability and workability. By controlling C (0.001-0.020%), Si (0.02-1.5%), Mn (0.02-1.5%), Cr (13.0-20.0%), and adding Nb (0.005-0.10%) and Ti (0.01-0.50%), the steel achieves both cost-effectiveness and enhanced formability for complex integral forming applications.
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 achieves excellent deep drawability and workability in ferritic stainless steel sheets with a thickness of 1.0 mm or more, ensuring high productivity and cost-effectiveness for exhaust system parts.
Implementation Method 1
a process of annealing a cold-rolled steel sheet at an annealing temperature Tf (°C.) within a range of 800≤Tf (°C.)≤950
Data Source
AI summary
A ferritic stainless steel sheet is provided that has a predetermined chemical composition, wherein: a grain size number is 6.0 or more; the ferritic stainless steel sheet satisfies the formulas [A+B≥9.0] and [X+Y≥9.0] 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. A represents a {111}<112> crystal orientation intensity at a center portion of sheet thickness, B represents a {111}<112> crystal orientation intensity at a ⅛ portion of the sheet thickness, X represents a {322}<236> crystal orientation intensity at a center portion of sheet thickness, and Y represents a {322}<236> crystal orientation intensity at a ⅛ portion of the sheet thickness.