Laser Weld Joint Toughness Through Flux-Controlled Oxygen Balance
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Solution Overview
Problem
Existing laser welding methods face issues with increased spatter due to oxygen in shielding gas, reduced penetration, and inadequate suppression of cracking, leading to weld joints with insufficient toughness, particularly at low temperatures.
Innovation Solution
A laser welding method that adjusts the chemical composition of steel materials and flux components to promote acicular ferrite microstructure formation, optimizing the carbon equivalent, oxygen, and flux index to achieve deep penetration and suppress cracking, resulting in a weld joint with excellent toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If oxygen is included in shielding gas to adjust weld metal composition, then low-temperature toughness is improved, but spatter increases and penetration depth decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the shielding gas by specifying precise oxygen content ranges (0.1-5% for argon-based gases, 0.1-20% for carbon dioxide-based gases) and controls the oxygen potential through flux composition (MnO: 20-80 mass%, SiO2: 5-30 mass%, CaO: 5-30 mass%). This parameter control allows achieving adequate toughness while suppressing excessive spatter generation.
Solution Approach 2:
The invention introduces flux as an intermediary substance between the base metal and shielding gas. The flux (containing MnO, SiO2, CaO) acts as a mediator that controls oxygen potential and facilitates controlled oxidation without direct oxygen exposure, thereby reducing spatter while maintaining weld metal quality and penetration depth.
2Strength
If oxygen content is increased to improve toughness, then low-temperature impact energy is improved, but penetration depth is reduced
Solution Approach 1:
The invention optimizes oxygen content parameters within specific ranges (0.1-5% for argon-based shielding gas, 0.1-20% for carbon dioxide-based shielding gas) and controls oxygen potential through flux composition (MnO: 20-80 mass%, SiO2: 5-30 mass%, CaO: 5-30 mass%). This controlled parameter adjustment achieves adequate toughness (vE−20 ≥ 27 J) while maintaining sufficient penetration depth for industrial applications.
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 ensures a weld joint with a Charpy impact test absorption energy of 27 J or more at −20° C., enhancing joint toughness and industrial applicability.
Implementation Method 1
irradiated with a laser beam from above
Implementation Method 2
a weld metal formed by laser welding is obtained by a process of melting the base metal of the weld together with laser beam energy
Implementation Method 3
melting the base metal of the weld together with laser beam energy, and then solidifying the metals
Data Source
AI summary
A laser welding method for preventing cracking and obtaining a weld joint of a weld metal with excellent toughness, and a laser weld joint. The laser welding method includes butting steel material members, the steel material having a chemical composition including, in mass %, C: 0.04 to 0.15%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, Ti: 0.050% or less, O: 0.010% or less, and N: 0.008% or less, and having a carbon equivalent Ceq, represented by the following Expression (1), of 0.30 to 0.45, with the balance being Fe and unavoidable impurities, covering a portion on the surfaces of the steel material members including a weld line with flux having a predetermined composition, and performing laser welding thereon to produce a weld joint.Ceq=[C]+[Mn]/6+[Si]/24+[Cu]/20+[Ni]/40+[Cr]/5+[Mo]/4 (1)