Wind Tower Steel Sheet Composition for Strength Without Normalizing
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Solution Overview
Problem
Existing steel materials for wind towers face challenges in achieving high strength and low-temperature impact toughness, especially when thickened, due to limitations in grain refinement during rolling and the need for costly normalizing heat treatments, which increase manufacturing costs.
Innovation Solution
A steel sheet composition with specific alloying elements (C, Si, Mn, P, S, Al, Nb, V, Ti, N) and controlled manufacturing processes, including heating, hot rolling, and air cooling, to achieve a microstructure with fine ferrite grains and omit normalizing heat treatment, ensuring strength and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of steel material is increased to improve load-resisting capacity, then the strength decreases, but the required thickness is additionally applied creating a vicious cycle
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.20-0.40%, Si: 0.05-0.50%, Mn: 1.00-2.50%, etc.) and processing parameters (heating temperature, rolling temperature, cooling rate) to achieve a microstructure that provides high strength without increasing thickness. This resolves the contradiction by changing the material's internal parameters rather than its dimensional parameters.
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and pearlite phases with specific area fractions (ferrite: 5-30%, pearlite: 70-95%). This composite microstructure provides both high strength and adequate thickness, resolving the vicious cycle between strength and thickness requirements for wind tower applications.
2Strength
If normalizing heat treatment is applied to achieve high strength and low-temperature impact toughness, then the manufacturing cost increases significantly, but as-rolled or TMCP steel materials are more commercially feasible
Solution Approach 1:
The patent extracts and eliminates the normalizing heat treatment step from the manufacturing process while maintaining the desired microstructure and mechanical properties through optimized composition and rolling parameters. This removes the costly heat treatment step, making the steel material more commercially feasible while still achieving high strength and impact toughness.
Solution Approach 2:
The patent enables the steel material to self-form the desired microstructure (ferrite-pearlite with specific fractions) through controlled rolling and cooling processes without requiring additional heat treatment. The composition and processing parameters are designed so that the material automatically achieves the target microstructure during normal production, eliminating the need for separate heat treatment operations.
3Strength
If grain refinement is performed through rolling to achieve high strength and low-temperature impact toughness, then rolling force is limited for thick steel materials, making it difficult to form fine grains toward the central portion
Solution Approach 1:
The patent applies parameter changes by optimizing the chemical composition (adding elements like Ti, Nb, V for microalloying) and processing parameters (heating temperature, rolling temperature, reduction ratio) to achieve uniform fine grain structure throughout the thickness of thick steel materials. This resolves the contradiction by changing parameters that control grain formation and distribution during rolling.
Solution Approach 2:
The patent applies preliminary action by performing controlled heating and rolling processes that pre-establish the microstructure before final cooling. The heating temperature and rolling parameters are carefully controlled to ensure uniform austenite grain formation throughout the slab thickness, which then transforms uniformly during cooling, achieving consistent grain refinement without requiring excessive rolling force.
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 a steel sheet with yield strength of 355 MPa or more, tensile strength of 470 MPa or more, and Charpy impact absorption energy of 100 J or more at -20°C, while reducing manufacturing costs by omitting normalizing heat treatment.
Implementation Method 1
a microstructure of the steel sheet comprises, by area fraction, 60 to 85% of ferrite and a remainder of pearlite and inevitable structures
Implementation Method 2
Charpy impact absorption energy of 100 J or more at -20°C
Data Source
Figure 1(a)~1(b)
Figure 2
AI summary
The present invention relates to a steel sheet having excellent strength and toughness which can be used in offshore and onshore wind power generators, etc., and a method for manufacturing same.