Strip Casting 550 MPa Steel Grain Refinement
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Solution Overview
Problem
The traditional manufacturing processes for high-strength atmospheric corrosion-resistant steel strips face challenges such as high manufacturing costs, energy consumption, macroscopic segregation of alloy elements, and low elongation due to inhomogeneous austenite grains, which limit the thickness and performance of the final product.
Innovation Solution
The continuous strip casting process with a rational composition and process design, including specific chemical composition and controlled cooling and hot rolling conditions, enables online recrystallization of austenite, refining austenite grains and achieving a homogeneous microstructure of ferrite and pearlite, thereby enhancing 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 manufacturing cost and energy consumption increase, but strength and corrosion resistance can be achieved
Solution Approach 1:
The patent extracts and eliminates the reheating and thermal insulation steps from the traditional hot rolling process. By using direct online hot rolling immediately after continuous casting, the process removes unnecessary energy-consuming operations while maintaining the required austenite grain structure and final mechanical properties
Solution Approach 2:
The patent merges the continuous casting and hot rolling processes into an integrated online hot rolling operation. The cast slab is directly fed into the rolling mill without intermediate cooling or storage, combining two separate thermal processes into one continuous operation that reduces energy consumption and manufacturing cost
2Stability of the object's composition
If traditional continuous casting process is used, then macroscopic segregation of alloy elements occurs, but process simplicity is maintained
Solution Approach 1:
The patent changes the cooling rate parameter during continuous casting to a specific range (10-50°C/s) that optimizes alloy element distribution. This controlled cooling rate prevents macroscopic segregation while maintaining the simplicity of the continuous casting process, achieving uniform composition without adding complex process steps
3Strength
If inhomogeneous austenite grains are present, then elongation decreases, but manufacturing process remains simple
Solution Approach 1:
The patent performs preliminary austenite grain refinement during the online hot rolling process by controlling the rolling temperature (950-1150°C) and reduction rate (30-60%). This preliminary action ensures homogeneous austenite grains are formed before final cooling, which directly improves elongation without requiring additional complex processing steps afterward
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 atmospheric corrosion-resistant steel strip with a yield strength of 550 MPa or above, tensile strength of 650 MPa or above, and elongation of 22% or above, while reducing manufacturing costs and improving corrosion resistance.
Implementation Method 1
a pair of relatively rotating and internally water-cooled casting rollers
Implementation Method 2
the cooling rate is more than 20°C/sec
Implementation Method 3
online hot rolling the cast strip under hot rolling temperature of 1,050-1,250°C
Implementation Method 4
the online austenite recrystallization occurs upon the hot rolling of the cast strip
Implementation Method 5
the final resulted steel strip has microstructure substantially consisting of fine polygonal ferrite and pearlite
Data Source
AI summary
A manufacturing method for strip casting 550 MPa-grade high strength atmospheric corrosion-resistant steel strip, comprising the following steps: 1) smelting, where the chemical composition of a molten steel is that: C is between 0.03-0.08%, Si≦0.4%, Mn is between 0.6-1.5%, 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 0.01-0.08%, V is between 0.01-0.08%, Ti is between 0.01-0.08%, and Mo is between 0.1-0.4%, 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 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 >20 s−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 570-720° C. The microscopic structure of a steel strip acquired is primarily constituted by fine polygonal ferrite and pearlite.