Wheel Rim Flash Butt Welding for Weld Hardness and Formability
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Solution Overview
Problem
Existing flash butt welding methods for high-strength steel in automotive wheel rims fail to effectively control the hardness and formability of the weld portion, leading to reduced toughness and increased crack formation, limiting mass production and application in lightweight vehicle parts.
Innovation Solution
A flash butt welding method involving pre-heating, upset-heating, and post-heating processes to control the hardness of the weld portion between 220 Hv and 270 Hv, supplemented by fine-grained heat affected zones to improve toughness and formability, while minimizing coarse-grained zones that degrade toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength steel with tensile strength of 780 MPa or more is used for weight reduction, then strength increases, but formability of the weld portion deteriorates due to hardening and brittle structure development
Solution Approach 1:
The patent applies pre-heat, upset-heat, and post-heat treatment parameters to control the microstructure and hardness of the weld portion. By adjusting heating temperature, holding time, and cooling rate, the weld portion achieves optimal microstructure (acicular ferrite, bainite, or martensite with tempered carbides) that provides both high strength and good formability, preventing the brittle structure that would otherwise develop in high-strength steel welds
Solution Approach 2:
The pre-heat treatment is applied before welding to prevent rapid cooling and martensite formation that would cause brittleness. The upset-heat treatment during welding further controls the microstructure development. These preliminary thermal actions ensure the weld portion develops a ductile microstructure before final cooling, maintaining formability while achieving the required strength
2Productivity
If flash butt welding is performed without optimized heat treatment, then welding speed is maintained, but the weld portion develops a coarse-grained heat affected zone that degrades toughness and increases crack formation
Solution Approach 1:
Pre-heat treatment is applied before the main welding operation to prevent rapid thermal cycling that would create coarse-grained HAZ. This preliminary heating action prepares the material to undergo phase transformation to fine-grained structures during upset-heat, ensuring toughness is maintained even with high welding speed
Solution Approach 2:
The patent utilizes controlled phase transitions during upset-heat treatment where austenite transforms to acicular ferrite, bainite, or tempered martensite. This phase transition, controlled by specific heating temperature (700-950°C) and holding time, produces a fine-grained microstructure that prevents coarse-grained HAZ formation and maintains high toughness despite rapid welding speeds
3Device complexity
If the weld portion hardness is not controlled, then the welding process is simple, but the weld portion develops a brittle structure with Vickers hardness of 300 Hv or more, reducing formability
Solution Approach 1:
The patent controls weld portion hardness by adjusting pre-heat temperature (50-150°C), upset-heat temperature (700-950°C), and holding time (0.1-5 seconds). These parameter changes ensure the microstructure consists of acicular ferrite, bainite, or tempered martensite with carbides, achieving Vickers hardness of 200-300 Hv that provides both strength and formability, preventing the brittle structure that would result from uncontrolled hardening
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 method enhances the toughness and formability of high-strength steel welds, preventing cracks and ensuring excellent mechanical properties, thereby enabling mass production of lightweight automotive wheel rims.
Implementation Method 1
Flash butt welding, mainly used for assembling a wheel rim of a vehicle, is a process of joining through melting and scattering of a joint target surface and upsetting a fusion zone by a flash arc
Implementation Method 2
capable of controlling hardness of a weld portion to 220 Hv or more 270 Hv or less by adopting pre-/upset-/post-heat optimization patterns at the time of flash butt welding
Implementation Method 3
joining through melting and scattering of a joint target surface and upsetting a fusion zone by a flash arc
Data Source
AI summary
Provided are a flash butt welding member and a flash butt welding method for providing a wheel rim weld part with excellent formability. The flash butt welding member of the present invention satisfies that a weld part has a hardness of 220-270 Hv, and d<0.25T, when d is the closest distance between fine-grained heat affected zones (HAZ) formed at the left and right of the weld part while facing each other and T is the thickness of a weld base metal, and satisfies L/T>2, when the total length of an upset part constituting the weld part is L.