Continuous Casting 700MPa Weather-Resistant Steel
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Solution Overview
Problem
The traditional manufacturing processes for high-strength atmospheric corrosion-resistant steel face challenges such as high costs, energy consumption, macroscopic segregation of elements, low yield, and limited thickness range due to the segregation of P and Cu, and difficulties in maintaining microalloy elements in a solid solution form during hot rolling, which affects the steel's strength and elongation.
Innovation Solution
The continuous strip casting process is employed with a rational composition and process design to achieve online recrystallization of austenite, refining austenite grains and promoting a homogeneous microstructure of bainite and acicular ferrite, using a chemical composition with optimized levels of C, Si, Mn, P, Cu, Nb, V, Ti, and Mo, and controlling cooling and hot rolling temperatures and rates to enhance strength and elongation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional hot rolling process is used to manufacture high-strength atmospheric corrosion-resistant steel, then the steel can achieve high strength through microalloying, but the elements P and Cu undergo macroscopic segregation, reducing yield and limiting thickness range
Solution Approach 1:
The patent changes the temperature parameter during hot rolling, specifically controlling the finishing rolling temperature to be above the Ar3 transformation point. This temperature parameter change prevents macroscopic segregation of P and Cu elements while maintaining microalloying effects, thereby resolving the contradiction between achieving high strength and maintaining element distribution uniformity
Solution Approach 2:
The patent applies preliminary austenite recrystallization before final rolling by controlling the temperature schedule. This preliminary action ensures uniform element distribution is established early in the process, preventing subsequent segregation during cooling and finishing rolls
2Strength
If traditional manufacturing process with multiple heating and rolling stages is used, then the steel can achieve required mechanical properties, but the manufacturing cost and energy consumption increase
Solution Approach 1:
The patent merges the heating and hot rolling operations into a more integrated process. By controlling the finishing rolling temperature to be above Ar3 and combining the hot rolling with online recrystallization, the process eliminates separate heating and cooling stages, thereby reducing energy consumption while maintaining the required steel strength through microalloying and controlled microstructure development
3Strength
If microalloy elements are added to improve strength, then the steel achieves high strength, but the elements难以 remain in solid solution form during hot rolling, affecting elongation
Solution Approach 1:
The patent changes the temperature parameter during hot rolling to above the Ar3 transformation point, which maintains microalloy elements in solid solution form during the rolling process. This parameter change prevents premature precipitation of microalloy elements, allowing them to remain soluble and contribute to strength through solid solution strengthening while preserving elongation properties
Solution Approach 2:
The patent applies preliminary austenite recrystallization at controlled temperatures before final rolling. This preliminary action ensures microalloy elements are properly dissolved and distributed in the austenite matrix before transformation, preventing segregation and maintaining both strength and elongation
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 results in a high-strength, high-elongation steel strip with a microstructure of refined bainite and acicular ferrite, achieving superior strength and plasticity matching while reducing manufacturing costs and energy consumption, and increasing the content of P and Cu for improved corrosion resistance.
Implementation Method 1
achieve online recrystallization of austenite, refining austenite grains
Implementation Method 2
controlling cooling and hot rolling temperatures and rates
Implementation Method 3
promoting a homogeneous microstructure of bainite and acicular ferrite
Data Source
AI summary
A method for manufacturing thin strip continuously cast 700 Mpa grade high strength weather-resistant steel, the method comprising the following steps: 1) casting a 1-5 mm thick cast strip in a double roller continuous casting machine, the cast strip comprising the following chemical compositions by weight percent: C 0.03-0.1%, Si≤0.4%, Mn 0.75-2.0%, P 0.07-0.22%, S≤0.01%, N≤0.012%, and Cu 0.25-0.8%, further comprising more than one of Nb, V, Ti and Mo: Nb 0.01-0.1%, V 0.01-0.1%, Ti 0.01-0.1%, and Mo 0.1-0.5%, and the balance being Fe and unavoidable impurities; 2) cooling the cast strip at a rate greater than 20° C./s; 3) hot rolling the cast strip under a temperature of 1050-1250° C. at a reduction rate of 20-50% and a deformation rate greater than 20 s−1; then conducting austenite online recrystallization, the thickness of the hot rolled strip being 0.5-3.0 mm; 4) cooling at a rate of 10-80° C./s; and 5) rolling up under a temperature of 500-650° C. The obtained steel strip microstructure mainly consists of uniformly distributed bainites and needle-shaped ferrites.