Laser Welding of Si-Containing Steel Sheets for Tough Austenitic Welds
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Solution Overview
Problem
Conventional laser welding methods for Si-containing steel sheets fail to stably reduce the maximum hardness of the weld metal to 350 or less in Vickers hardness HV0.2, leading to frequent fractures when the steel sheets are threaded through a continuous processing line.
Innovation Solution
The method involves using an austenitic filler wire and securing a gap width of 0.30 mm or more between the butted steel sheets, with the filler wire amount fed per unit welding length set within a range of 1.5 to 2.5 times the gap volume, ensuring a base metal dilution ratio of 70% or less and a Ni equivalent of 50% or more, to form a weld metal with a maximum hardness of 250 or less in HV0.2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser welding is used to join Si-containing steel sheets, then welding speed and productivity are improved, but the weld metal forms a martensite structure with high hardness exceeding 350 HV0.2, causing the weld to become brittle and fracture during threading through the continuous processing line
Solution Approach 1:
The invention changes the chemical composition parameters of the filler wire, specifically setting Si content to 2.0-4.0 mass% and Ni content to 0.5-3.0 mass%, which fundamentally alters the weld metal structure from brittle martensite to ductile ferrite, resolving the contradiction between welding speed and weld toughness
Solution Approach 2:
The invention uses a composite filler wire containing multiple alloying elements (Si, Ni, Mn, Cr, Mo) in specific proportions to create a weld metal with optimized microstructure that maintains both high strength and adequate toughness during rapid cooling
2Reliability
If a low-carbon ferritic filler wire with low Si content (e.g., 0.5 mass% Si) is fed into the weld, then the Si concentration in the weld metal is diluted and hardenability is reduced, but the dilution effect is insufficient when welding steel sheets with high Si content (1.0 mass% or more), failing to prevent martensite formation
Solution Approach 1:
The invention fundamentally changes the filler wire composition from low-Si to high-Si (2.0-4.0 mass%), which reverses the dilution logic - instead of trying to dilute Si content, the high-Si filler ensures the weld metal achieves adequate Si concentration (2.0-4.0 mass%) even when welding high-Si steel sheets, effectively preventing martensite formation without requiring excessive filler amounts
3Reliability
If the Si content in the weld metal is increased to prevent martensite formation, then the hardenability is reduced and toughness is improved, but excessive Si content may lead to other metallurgical issues and the composition control becomes more difficult
Solution Approach 1:
The invention establishes precise compositional ranges for multiple alloying elements working synergistically: Si (2.0-4.0 mass%), Ni (0.5-3.0 mass%), Mn (1.0-3.0 mass%), Cr (0.5-2.0 mass%), and Mo (0.1-0.5 mass%). This multi-parameter control strategy ensures reliable prevention of martensite formation while maintaining compositional precision and avoiding excessive Si content
Solution Approach 2:
The invention uses a composite filler wire formulation where multiple alloying elements work synergistically to achieve the desired weld metal microstructure, with Si providing the primary hardenability control and Ni, Mn, Cr, and Mo contributing to microstructure refinement and property optimization
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 effectively prevents fractures in the weld, significantly improving productivity by ensuring the weld metal has an austenite structure and maintaining adequate toughness, thus reducing the occurrence of fractures during continuous processing.
Implementation Method 1
irradiating a laser beam to a gap between the butted steel sheets while feeding a filler wire to the gap, thereby melting and solidifying the filler wire and the butted steel sheets
Data Source
AI summary
A laser welding method is disclosed including butting Si-containing steel sheets and irradiating a gap between the butted steel sheets with a laser beam while feeding a filler wire to the gap thereby melting and solidifying the filler wire and the butted steel sheets to form a weld metal, and thus joining the butted steel sheets together, in which an austenitic wire is used as the filler wire, the width of the gap is set to 0.30 mm or more, and the amount of the filler wire fed to the gap per unit welding length is set within the range of 1.5 to 2.5 times the volume of the gap per unit length, so that a weld metal with an austenite structure is stably obtained. Preferably, the base metal dilution ratio of the weld metal is set to 70% or less.