Flash-Butt Welded Steel Joint Microstructure for Better Workability
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Solution Overview
Problem
Existing flash-butt welding methods for high-strength steel joints in automotive parts face challenges in achieving optimal workability due to brittle structures and microstructure issues, leading to processing cracks and reduced toughness, which hinder mass production.
Innovation Solution
A flash-butt joining member and method that control the average effective grain size difference and width of coarse-grained and fine-grained heat-affected zones, along with specific welding parameters, to enhance joint toughness and workability by minimizing grain size disparities and optimizing microstructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high-strength steel is used for lightweight parts, then weight reduction is achieved, but the joint becomes brittle due to hardening and phase transformation, reducing workability
Solution Approach 1:
The patent applies parameter changes by controlling the carbon equivalent content (Ceq) within specific ranges (0.35-0.45% or 0.40-0.50%) and adjusting alloying element compositions (Si: 1.50-3.00%, Mn: 1.00-3.00%, Cr: 0.50-2.00%, Mo: 0.10-1.00%, B: 0.0005-0.0050%) to modify the steel's microstructure and phase transformation behavior, thereby improving joint workability while maintaining lightweight properties
Solution Approach 2:
The patent applies local quality by creating distinct microstructural zones in the heat-affected area with controlled grain sizes (coarse-grained and fine-grained HAZ regions), where each zone has specific properties optimized for preventing brittle fracture and improving local workability
2Productivity
If flash-butt welding is used for joining, then joining efficiency is improved, but processing cracks occur in the joint after welding, reducing reliability
Solution Approach 1:
The patent applies parameter changes by optimizing welding process parameters including flash time (0.5-5.0 seconds), upset time (0.1-1.0 second), flash pressure (10-50 MPa), and upset pressure (50-150 MPa) to control the welding thermal cycle and minimize processing cracks while maintaining high joining efficiency
Solution Approach 2:
The patent applies feedback by implementing a controlled upset process that applies pressure during and after welding to discharge oxide inclusions and control microstructure formation, with the pressure magnitude and duration adjusted based on the steel composition and welding conditions to prevent crack formation
3Manufacturing precision
If upset is increased to discharge oxide inclusions, then joint purity is improved, but grain size difference between HAZ zones increases, reducing toughness
Solution Approach 1:
The patent applies parameter changes by controlling the carbon equivalent and alloying composition to modify the steel's hardenability and phase transformation characteristics, which balances oxide inclusion discharge with grain size control to maintain joint toughness
Solution Approach 2:
The patent applies local quality by creating a controlled dual-zone microstructure (coarse-grained and fine-grained HAZ) where each zone serves a specific function: the coarse-grained zone facilitates oxide discharge while the fine-grained zone maintains toughness, with the transition between zones optimized for overall joint performance
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
Improves the toughness and workability of high-strength steel joints by reducing embrittlement and softening, enabling the production of lightweight steel wheels with enhanced strength and processing capabilities.
Implementation Method 1
joining accomplished through melting scattering of the joining target surfaces and upset of the melted portion by a flash arc
Implementation Method 2
melting scattering of the joining target surfaces and upset of the melted portion by a flash arc
Data Source
AI summary
A flash-butt joining member and welding method are provided. In the joining member and the welding method with excellent workability, the joining member having excellent workability includes a joint obtained by flash-butt welding a steel plate, and an average effective grain size difference between the coarse-grained heat-affected zone and a fine-grained heat-affected zone formed on either left or right side of the joint is within 10 μm.