Cold-Rolled Steel Sheet Austenite Refinement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cold-rolled steel sheets face challenges in achieving a fine structure after cold rolling and annealing, particularly when using hot-rolled steel sheets with fine structures, as the conventional annealing methods restrict austenite grain refinement and lead to decreased stretch flangeability due to the loss of preferred nucleus forming sites during recrystallization.
Innovation Solution
The process involves rapid heating to a temperature range that promotes austenitic transformation before completion of recrystallization, utilizing high-angle grain boundaries and fine carbide grains as nucleus sites to refine austenite grains and maintain a fine structure, while controlling the annealing temperature to suppress texture growth and enhance ductility and stretch flangeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional annealing is performed after cold rolling, then recrystallization occurs and austenite transformation occurs after recrystallization completion, but the fine structure cannot be easily obtained and stretch flangeability decreases due to loss of nucleus forming sites
Solution Approach 1:
The patent applies preliminary action by performing austenite transformation before recrystallization completion. The annealing process is controlled to transform austenite while the hot-rolled steel sheet structure is still present, utilizing the high-angle grain boundaries and fine carbide grains as nucleus sites before they disappear during recrystallization. This timing strategy preserves the fine structure that would otherwise be lost in conventional annealing processes.
2Manufacturing precision
If hot-rolled steel sheet with fine structure is used as starting material, then structure refinement is expected, but austenite transformation after recrystallization limits the fine structure retention
Solution Approach 1:
The patent applies parameter changes by controlling the annealing temperature range and heating rate to achieve austenite transformation at specific conditions. By adjusting these parameters, the process transforms austenite before recrystallization completes, preserving the fine structure from the hot-rolled steel sheet. The specific temperature range and timing parameters are critical to maintaining the fine austenite grain structure.
3Strength
If annealing is carried out for single-phase austenite region, then austenite transformation is promoted, but it is difficult to utilize the fine structure of hot-rolled steel sheet for structure refinement
Solution Approach 1:
The patent applies local quality by creating different transformation conditions in different regions of the material. The annealing process is controlled to transform austenite at specific locations where the hot-rolled steel sheet structure provides favorable nucleus sites. This localized transformation approach utilizes the fine structure of the hot-rolled steel sheet to refine the final structure while promoting austenite transformation.
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
This approach effectively refines the structure of cold-rolled steel sheets, improving ductility and stretch flangeability by promoting austenitic transformation before recrystallization, maintaining a fine structure, and preventing crack formation during working, thus achieving a balance between strength and formability.
Implementation Method 1
rapid heating to a temperature range that promotes austenitic transformation before completion of recrystallization
Implementation Method 2
completion of recrystallization
Implementation Method 3
rapid heating to a temperature range that promotes austenitic transformation
Data Source
AI summary
A high-strength cold-rolled steel sheet having excellent ductility and stretch flangeability includes: a chemical composition consisting, in mass %, C: 0.06 to 0.3, Si: 0.6 to 2.5%, Mn: 0.6 to 3.5%, P: at most 0.1%, S: at most 0.05%, Ti: 0 to 0.08%, Nb: 0 to 0.04%, total of Ti and Nb: 0 to 0.10%, sol.Al: 0 to 2.0%, Cr: 0 to 1%, Mo: 0 to 0.3%, V: 0 to 0.3%, B: 0 to 0.005%, Ca: 0 to 0.003%, REM: 0 to 0.003% and the remainder of Fe and impurities; a microstructure having a main phase including at least 40 area % in total of martensite and/or bainite; and a texture in which proportion of an average X-ray intensity in an {100}<011> to {211}<011> orientations relative to an average X-ray intensity of a random structure not having a texture is less than 6.