Strip Casting 700 MPa Steel via Austenite Recrystallization
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Solution Overview
Problem
The continuous strip casting process for high-strength atmospheric corrosion-resistant steel faces challenges in achieving a balance between strength and plasticity due to inhomogeneous austenite grains, leading to low elongation and increased manufacturing costs, energy consumption, and equipment damage.
Innovation Solution
A manufacturing method involving continuous strip casting with a specific chemical composition and process parameters, including rapid solidification, controlled cooling, online hot rolling at 1,050–1,250°C, and recrystallization of austenite to produce a steel strip with a homogeneous microstructure of bainite and acicular ferrite, enhancing both strength and elongation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional hot rolling process is used to manufacture 700 MPa-grade atmospheric corrosion-resistant steel, then strength can be improved through multi-pass rolling and cooling, but manufacturing cost increases, energy consumption increases, and equipment damage increases
Solution Approach 1:
The patent changes the key parameters of the rolling process: performing online hot rolling at high temperature (950-1250°C) with high deformation rate (>20 s⁻¹) and controlled reduction rate (20-50%) to achieve austenite recrystallization. This parameter optimization allows single-pass rolling to replace traditional multi-pass processes, reducing energy consumption while maintaining 700 MPa-grade strength through refined homogeneous microstructure
Solution Approach 2:
The patent applies preliminary action by controlling the chemical composition before rolling, specifically adding microalloying elements (Nb: 0.01-0.1%, V: 0.01-0.1%, Ti: 0.01-0.1%, Mo: 0.1-0.5%) and controlling carbon content (0.03-0.1%) to prepare the steel for online recrystallization during hot rolling, enabling the single-pass process to achieve the strength that traditionally required multiple passes
2Strength
If traditional hot rolling process is used to manufacture 700 MPa-grade atmospheric corrosion-resistant steel, then strength can be improved through multi-pass rolling and cooling, but manufacturing cost increases
Solution Approach 1:
The patent optimizes process parameters to enable single-pass online hot rolling instead of traditional multi-pass offline rolling. By controlling deformation rate (>20 s⁻¹), reduction rate (20-50%), and temperature (950-1250°C), the process achieves austenite recrystallization and homogeneous microstructure in one pass, significantly reducing manufacturing cost while maintaining 700 MPa-grade strength
Solution Approach 2:
The patent prepares the steel composition in advance with optimized microalloying element content (Nb, V, Ti, Mo) and carbon content (0.03-0.1%) to enable online recrystallization during the single-pass hot rolling process, replacing costly traditional multi-pass processes while achieving the required strength level
3Strength
If microalloying technology is used to improve strength, then yield strength increases, but elongation decreases due to inhomogeneous austenite grains
Solution Approach 1:
The patent changes the deformation rate to >20 s⁻¹ and performs hot rolling at high temperature (950-1250°C) with controlled reduction rate (20-50%). These parameter changes promote uniform austenite recrystallization throughout the steel strip, creating homogeneous grain structure that simultaneously achieves high strength (700 MPa) and high elongation (≥18%), resolving the contradiction between strength and microstructure homogeneity
Solution Approach 2:
The patent applies dynamic hot rolling with high deformation rate (>20 s⁻¹) to promote uniform austenite recrystallization. The dynamic deformation process ensures homogeneous grain refinement throughout the steel strip, creating uniform microstructure that enables both high strength and high elongation, overcoming the inhomogeneity problem of traditional static rolling processes
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 method achieves a yield strength of 700 MPa or above, tensile strength of 780 MPa or above, elongation of 18% or above, and qualified 180° bending properties, while reducing manufacturing costs and energy consumption by optimizing the microalloy element content and process conditions.
Implementation Method 1
The cast strip undergoes rapid solidification and controlled cooling
Implementation Method 2
online austenite recrystallization occurs during the hot rolling of the cast strip
Implementation Method 3
online austenite recrystallization occurs during the hot rolling of the cast strip
Data Source
AI summary
A manufacturing method for strip casting 700 MPa-grade high strength atmospheric corrosion-resistant steel, comprising the following steps: 1) smelting, where the chemical composition of a molten steel in terms of weight percentage is that C is between 0.03-0.1%, Si≦0.4%, Mn is between 0.75-2.0%, P is between 0.07-0.22%, S≦0.01%, N≦0.012%, Cu is between 0.25-0.8%, Cr is between 0.3-0.8%, and Ni is between 0.12-0.4%, additionally, also comprised is at least one micro-alloying element among Nb, V, Ti, and Mo, where Nb is between 0.01-0.1%, V is between 0.01-0.1%, Ti is between 0.01-0.1%, and Mo is between 0.1-0.5%, and where the remainder is Fe and unavoidable impurities; 2) strip casting, where a 1-5 mm-thick cast strip is casted directly; 3) cooling the cast strip, where the cooling rate is greater than 20° C./s; 4) online hot rolling the cast strip, where the hot rolling temperature is between 1050-1250° C., where the reduction rate is between 20-50%, and where the deformation rate is >20s−1; austenite online recrystallizing after hot rolling, where the thickness of the hot rolled strip is between 0.5-3.0 mm; and, 5) cooling and winding, where the cooling rate is between 10-80° C./s, and where the winding temperature is between 520-670° C. The microscopic structure of a steel strip acquired is primarily constituted by evenly distributed bainite and acicular ferrite.