Ferritic Stainless Steel High-Temperature Strength Workability
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Solution Overview
Problem
Current ferritic stainless steels face challenges in achieving optimal workability and high-temperature strength due to inadequate understanding of crystal grains and precipitates' influence on high-temperature properties, particularly in exhaust manifold applications where high-temperature exposure is common.
Innovation Solution
A ferritic stainless steel composition with specific weight percentages of C, N, Si, Mn, P, Cr, Mo, Nb, and W, along with a manufacturing method involving reheating, rough rolling, and controlled holding times to manage precipitate distribution and size, ensuring a high number of fine precipitates and sufficient solid solution W, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloy elements such as Mo, Nb are added to improve high-temperature properties, then high-temperature strength is improved, but workability deteriorates due to excessive precipitate formation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content ranges of alloy elements (C: 0.0005-0.02%, N: 0.005-0.02%, Si: 0.01-1.0%, Mn: 0.01-1.2%, P: 0.001-0.05%, Cr: 10.0-25.0%, Mo: 1.5-3.0%, Nb: 0.3-0.7%, W: 0.5-2.0%) and manufacturing parameters (reheating temperature: 1000-1300°C, holding time: 8000/(RHT-1000) to 120 seconds) to optimize the balance between high-temperature strength and workability. This systematic parameter optimization ensures sufficient solid solution W content while controlling precipitate formation.
Solution Approach 2:
The patent applies preliminary action by implementing a controlled holding time period between rough rolling and finishing rolling, where the holding time is calculated as 8000/(RHT-1000) to 120 seconds. This preliminary holding period allows controlled precipitate formation and solid solution W content adjustment before the final rolling process, preventing excessive precipitate formation that would deteriorate workability while ensuring sufficient high-temperature strength.
2Ease of manufacture
If reheating temperature is increased to improve workability, then workability is improved, but precipitate coarsening occurs which reduces high-temperature strength
Solution Approach 1:
The patent applies continuity of useful action by maintaining a controlled thermal-mechanical process sequence: reheating at 1000-1300°C followed by rough rolling, then a controlled holding time of 8000/(RHT-1000) to 120 seconds, and finally finishing rolling. This continuous controlled process prevents precipitate coarsening while ensuring sufficient solid solution W content, achieving both good workability and high-temperature strength.
Solution Approach 2:
The patent applies preliminary action by implementing a controlled holding time period between rough rolling and finishing rolling, where the holding time is calculated as 8000/(RHT-1000) to 120 seconds. This preliminary holding period allows controlled precipitate formation and solid solution W content adjustment before the final rolling process, preventing excessive precipitate formation that would deteriorate workability while ensuring sufficient high-temperature strength.
3Strength
If the number of fine precipitates is increased to improve high-temperature strength, then high-temperature strength is improved, but workability deteriorates due to excessive precipitation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content ranges of alloy elements (C: 0.0005-0.02%, N: 0.005-0.02%, Si: 0.01-1.0%, Mn: 0.01-1.2%, P: 0.001-0.05%, Cr: 10.0-25.0%, Mo: 1.5-3.0%, Nb: 0.3-0.7%, W: 0.5-2.0%) and manufacturing parameters (reheating temperature: 1000-1300°C, holding time: 8000/(RHT-1000) to 120 seconds) to optimize the balance between high-temperature strength and workability. This systematic parameter optimization ensures sufficient solid solution W content while controlling precipitate formation.
Solution Approach 2:
The patent applies preliminary action by implementing a controlled holding time period between rough rolling and finishing rolling, where the holding time is calculated as 8000/(RHT-1000) to 120 seconds. This preliminary holding period allows controlled precipitate formation and solid solution W content adjustment before the final rolling process, preventing excessive precipitate formation that would deteriorate workability while ensuring sufficient high-temperature strength.
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 enhanced workability and high-temperature strength, with room temperature elongation of 27% or more and 900°C tensile strength of 45 MPa or more, while preventing coarsening and excessive precipitate formation.
Implementation Method 1
reheating the slab including, in percent (%) by weight of the entire composition, C: 0.0005 to 0.02%, N: 0.005 to 0.02%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.2%, P: 0.001 to 0.05%, Cr: 10.0 to 25.0%, Mo: 1.5 to 3.0%, Nb: 0.3 to 0.7%, W: 0.5 to 2.0%
Implementation Method 2
control the composition and distribution of precipitates in the final material
Implementation Method 3
a holding time (seconds) before the start of finishing rolling of the rough rolled bar satisfies the following equation (1)
Data Source
AI summary
Disclosed is a ferritic stainless steel with improved workability and high temperature strength through control of component composition and precipitate distribution, and a manufacturing method thereof. The ferritic stainless steel excellent in workability and high temperature strength according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, C: 0.0005 to 0.02%, N: 0.005 to 0.02%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.2%, P: 0.001 to 0.05%, Cr: 10.0 to 25.0%, Mo: 1.5 to 3.0%, Nb: 0.3 to 0.7%, W: 0.5 to 2.0%, the remainder of iron (Fe) and other inevitable impurities, and the number of precipitates with an average diameter of 0.5 μm or less is 105 pieces/mm2 or less.