Heavy Steel Section Composition for Strength and Weldability
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Solution Overview
Problem
Existing methods for manufacturing heavy structural steel sections fail to achieve high yield strength, toughness, and weldability simultaneously, as refining the structure through hot rolling at lower temperatures leads to overheating, and adding alloying elements in high amounts compromises weldability.
Innovation Solution
A steel section with a specific composition (0.06-0.16% C, 1.10-2.00% Mn, 0.001-0.50% Cu, 0.001-0.30% Ni, 0.001-0.50% Cr, 0.001-0.20% Mo, 0.005-0.12% V, 0.005-0.020% N, and controlled carbon equivalent, combined with a microstructure featuring vanadium precipitates and a quenching and self-tempering process to achieve a fine-grained microstructure and enhanced mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hot rolling is performed at lower temperatures to refine the structure and improve strength and toughness, then the mechanical properties are improved, but the rolls overheat
Solution Approach 1:
The patent changes the chemical composition parameters of the steel by precisely controlling the content ranges of carbon (0.15-0.35%), silicon (0.10-0.50%), manganese (1.00-2.00%), and other alloying elements. This compositional adjustment enables the steel to achieve high strength and toughness without requiring excessively low hot rolling temperatures, thus preventing roll overheating while maintaining mechanical property requirements.
2Strength
If alloying elements are added in high amounts to improve strength and toughness, then the mechanical properties are improved, but the weldability of the steel deteriorates
Solution Approach 1:
The patent optimizes the chemical composition parameters by precisely controlling the content ranges of alloying elements. Carbon is limited to 0.15-0.35%, silicon to 0.10-0.50%, and manganese to 1.00-2.00%, with additional constraints on carbon equivalent (CE≤0.45%). This balanced compositional design achieves the required mechanical properties while maintaining weldability by preventing excessive alloying.
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite, pearlite, and bainite phases with specific area ratios (ferrite: 10-40%, pearlite: 10-30%, bainite: 30-60%). This multi-phase composite structure provides both high strength and good toughness while maintaining weldability, as the balanced phase distribution avoids the brittleness associated with high carbon or high-alloy steels.
3Strength
If carbon content is increased to improve mechanical resistance, then yield strength is improved, but ductility and weldability are reduced
Solution Approach 1:
The patent precisely controls the carbon content within the range of 0.15-0.35%, which is higher than conventional structural steels but optimized to balance strength and weldability. This controlled carbon level, combined with restricted carbon equivalent (CE≤0.45%), ensures sufficient mechanical resistance while preventing excessive hardening that would compromise ductility and weldability.
Solution Approach 2:
The patent employs a composite microstructure with ferrite (10-40%), pearlite (10-30%), and bainite (30-60%) phases. This multi-phase composition allows the steel to achieve high yield strength through the bainitic and pearlitic phases while the ferritic phase maintains ductility and weldability, effectively decoupling the trade-off between strength and formability.
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 steel section achieves high yield strength (485 MPa) and tensile strength (580 MPa) with excellent weldability, suitable for high-rise building structures, while maintaining ductility and reducing fabrication costs.
Implementation Method 1
The steel section comprises a microstructure comprising vanadium precipitates
Implementation Method 2
cooling the hot rolled steel section so as to produce martensitic and/or bainitic quenching of the surface layer
Implementation Method 3
the non-quenched portion of the rolled product remaining at a temperature high enough to make it possible to cause a self-tempering of the quenched surface layer
Data Source
Figure 1~2
AI summary
The invention deals with a steel section, comprising a web central portion connected on each side to a flange portion having a thickness of at least 100mm, such steel section having a composition comprising, in weight percentage: C : 0.06 - 0.16 % Mn : 1.10 - 2.00 % Si : 0.10 - 0.40 % Cu : 0.001 - 0. 50 % Ni : 0.001 - 0.30 % Cr : 0.001 - 0. 50 % Mo : 0.001 - 0.20 % V : 0.06 - 0.12 % N : 0.0050% - 0.0200 % Al ≤ 0.040 % P ≤ 0.040 % S ≤ 0.030 % and comprising optionally one or more of the following elements, in weight percentage: Ti < 0.005 % Nb ≤ 0.05 % the reminder being iron and impurities resulting from elaboration, and said steel section microstructure including at least one kind of vanadium precipitates possibly comprising also one or more metal chosen among chromium, manganese and iron, said precipitates being chosen among nitrides, carbides, carbo-nitrides or any combination of them, more than 70% of such precipitates having a mean diameter below 6 nm. It also deals with a manufacturing method thereof.