Electron Beam Welded Steel Joint Composition
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Solution Overview
Problem
The challenge lies in achieving a balanced fracture toughness between the welded metal, heat-affected zone, and base metal in electron-beam welded joints for ultra-thick steel plates, particularly in wind power generator tower foundations, where conventional methods fail to optimize hardness and cleanliness effectively.
Innovation Solution
A steel material composition with Mn ≥ 1.8% and addition of Mg and/or Ca for deoxidation, along with Ni as an insert metal, is used to balance fracture toughness values by dispersing fine oxides and controlling hardenability indices CeEBB and CeEBW, ensuring appropriate CTOD values and microstructural refinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional electron beam welding is used for ultra-thick steel plates, then welding efficiency is improved, but the fracture toughness balance between welded metal, heat-affected zone, and base metal deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the steel material by specifying precise ranges for C (0.02-0.10%), Si (0.03-0.30%), Mn (1.8-2.5%), Ti (0.005-0.015%), N (0.0020-0.0060%), O (0.0010-0.0035%), Mg (0.0003-0.0027%), Ca (0.0003-0.0027%), and other alloying elements. These parameter changes optimize the fracture toughness balance while maintaining welding efficiency for ultra-thick steel plates
Solution Approach 2:
The invention creates a composite microstructure in the welded joint by controlling the formation of different phases (ferrite, bainite, martensite) through the specified chemical composition and welding process, achieving a balanced fracture toughness across the base metal, heat-affected zone, and welded metal regions
2Speed
If high-energy-density beam welding is used to weld ultra-thick steel plates, then welding speed is improved, but the equipment complexity and vacuum chamber requirements worsen
Solution Approach 1:
The invention changes the steel material composition parameters to enable successful electron beam welding with reduced vacuum requirements, making it feasible to weld ultra-thick steel plates (100mm or more) without requiring excessively large or complex vacuum chamber systems
3Reliability
If Mn content is increased to improve hardenability, then fracture toughness is improved, but manufacturing cost worsens
Solution Approach 1:
The invention optimizes the Mn content parameter to a specific range (1.8-2.5%) that provides sufficient hardenability and fracture toughness while controlling manufacturing costs. This parameter is balanced with other alloying elements to achieve the desired performance at reasonable cost
Solution Approach 2:
The invention combines multiple alloying elements (Mn, Si, Ti, Mg, Ca, and others) that work synergistically to improve fracture toughness and hardenability, allowing for cost-effective composition design where each element contributes to multiple performance aspects
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 enhances the fracture toughness of electron-beam welded joints, maintaining balance between the base metal, welded metal, and heat-affected zone, while reducing manufacturing costs and improving the structural integrity of wind power generator towers.
Implementation Method 1
Mg and/or Ca, which are strong deoxidation elements, are added to the steel material together to generate fine oxide containing Mg, which is used as a pinning grain for suppressing grain growth
Implementation Method 2
The electron-beam welding method is a method employing energy of the electron beam to once melt and solidify the base material of a weld target portion to weld
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
A steel material for electron-beam welding including at least: C: 0.02% to 0.10%; Si: 0.03% to 0.30%; Mn: 1.5% to 2.5%; Ti: 0.005% to 0.015%; N: 0.0020% to 0.0060%; O: 0.0010% to 0.0035%; Mg: 0.0003% to 0.0027%; Ca: 0.0003% to 0.0027%; Al: limited to not more than 0.015%; P: limited to not more than 0.015%; and S: limited to not more than 0.010%, with a balance including iron and inevitable impurities, in which the steel material satisfies 0.0006% ≤ Mg + Ca ≤ 0.0040%, an index value CeEBB obtained by substituting the composition of the steel material into the following Formula 1 is not less than 0.42% and not more than 0.65%, the number of oxides having an equivalent circle diameter of not less than 1.0 µm is not more than 20 pieces/mm2 at a thickness center portion in cross-section along a thickness direction of the steel material, and the number of oxides containing Mg of not less than 7% and having an equivalent circle diameter of not less than 0.05 µm and less than 0.5 µm is 1 × 103 to 1 × 105 pieces/mm2 at the thickness center portion. CeEBB=C+1/4Mn+1/15Cu+1/15Ni+1/5Cr+1/5Mo+1/5V