Ferritic Stainless Steel Hot Rolling Coiling Temperature Control
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Solution Overview
Problem
Ferritic stainless steel sheets used in vehicle exhaust systems face challenges with high-temperature strength, workability, and toughness, particularly due to the precipitation of Cu-rich clusters, which lead to decreased toughness and cold cracking issues during processing.
Innovation Solution
Optimizing the coiling temperature and cooling conditions to prevent the precipitation of Cu-rich clusters, such as setting the coiling temperature between 620°C to 750°C and controlling the temperature hysteresis, allows for improved toughness and workability by promoting ε-Cu precipitation and recrystallization textures beneficial for workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Cu is added to increase high-temperature strength through precipitation strengthening, then high-temperature strength is improved, but toughness decreases due to Cu-rich cluster precipitation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the coiling temperature range (620-750°C) and cooling conditions to regulate the precipitation behavior of Cu-rich clusters. This temperature control transforms the harmful effect of Cu precipitation into a beneficial one, achieving both high-temperature strength and acceptable toughness by optimizing the thermal parameters during hot rolling and coiling processes
Solution Approach 2:
The patent utilizes phase transitions by controlling the transformation of Cu from solid solution state to precipitated state during the cooling process. By managing the phase transition timing and conditions through specific coiling temperatures, the patent achieves ε-Cu precipitation that provides strengthening while controlling the morphology and distribution to maintain toughness
2Strength
If Nb or Mo is added to increase high-temperature strength through solid-solution strengthening, then high-temperature strength is improved, but production cost increases due to expensive alloy elements
Solution Approach 1:
The patent replaces expensive long-term strengthening elements (Nb, Mo) with cheaper Cu that achieves strengthening through precipitation. This substitution uses a more economical alloying element to achieve the same functional goal of high-temperature strength enhancement, significantly reducing production costs while maintaining performance
Solution Approach 2:
The patent creates a composite microstructure by combining Cr solid-solution strengthening with Cu precipitation strengthening. This composite approach integrates multiple strengthening mechanisms, where Cr provides baseline strength and Cu precipitation provides additional high-temperature strength, achieving synergistic effects that replace expensive single-element solutions
3Reliability
If coiling temperature is reduced to prevent Cu-rich cluster precipitation, then toughness is improved, but workability deteriorates due to insufficient recrystallization
Solution Approach 1:
The patent applies parameter changes by optimizing the coiling temperature to a specific range (620-750°C) that simultaneously satisfies both toughness and workability requirements. This precise parameter control enables the material to achieve adequate toughness while maintaining sufficient recrystallization for good workability in subsequent processing
Solution Approach 2:
The patent utilizes periodic action through controlled cooling rates and holding times during the coiling process. By managing the thermal cycle characteristics, the patent allows sufficient time for recrystallization to occur while preventing excessive Cu precipitation, thereby balancing toughness and workability through time-temperature processing
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 enhances the toughness and workability of hot-rolled ferritic stainless steel sheets, reducing cold cracking and improving production efficiency, while also reducing the need for expensive alloy elements like Nb and Mo, thus lowering production costs and environmental impact.
Implementation Method 1
The high-temperature strength is increased by utilizing the solid-solution strengthening and the precipitation strengthening of Cu
Implementation Method 2
The high-temperature strength is increased by utilizing the solid-solution strengthening and the precipitation strengthening of Cu
Implementation Method 3
controlling a temperature hysteresis of the hot-rolled steel sheet after the coiling
Data Source
AI summary
This hot-rolled ferritic stainless steel sheet has a steel composition containing, in terms of % by mass: 0.02% or less of C; 0.02% or less of N; 0.1% to 1.5% of Si; 1.5% or less of Mn; 0.035% or less of P; 0.010% or less of S; 1.5% or less of Ni; 10% to 20% of Cr; 1.0% to 3.0% of Cu; 0.08% to 0.30% of Ti; and 0.3% or less of Al, with the balance being Fe and unavoidable impurities, and the hot-rolled ferritic stainless steel sheet has a Vickers hardness of less than 235 Hv.