Flux-Cored Welding Wire for High-Strength Steel
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current flux-cored arc welding processes face challenges with poor weld metal toughness, hydrogen cracking, and hot cracking in high-strength structural steels, particularly when aiming for yield strengths above 100 ksi, due to limitations in available filler metals that can achieve both high strength and impact toughness at low temperatures.
Innovation Solution
A consumable welding wire with a steel sheath and fluxed core containing Co, Mn, Ni, Ti, and B, which controls weld metal morphology to produce ferrite-bainite welds, reducing hydrogen diffusion and minimizing cracking risks through the use of fluoride and oxide compounds, and a shielding gas mixture like Ar/CO2 to stabilize the arc and protect the weld pool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional filler metals are used for welding high-strength structural steels, then high deposition rates are achieved through FCAW process, but poor weld metal toughness, hydrogen cracking, and hot cracking occur
Solution Approach 1:
The invention changes the chemical composition parameters of the filler metal by adding specific amounts of Co (3-10 wt%), Mn (1-3 wt%), Ni (1-3 wt%), Ti (0.1-0.5 wt%), and B (0.05-0.2 wt%) to the conventional filler metal composition. These parameter changes transform the weld metal microstructure to ferrite-bainite morphology, improving toughness and cracking resistance while maintaining high deposition rates in the FCAW process
Solution Approach 2:
The invention creates a composite filler metal composition combining multiple alloying elements (Co, Mn, Ni, Ti, B) with base metals (Fe, C). This composite material approach produces a synergistic effect where each element contributes specific properties: Co controls microstructure, Mn provides strength, Ni improves toughness, Ti refines grains, and B enhances hardenability, collectively resolving the contradiction between productivity and reliability
2Strength
If filler metals are designed for high strength (yield strength > 100 ksi), then strength requirement is met, but impact toughness at low temperatures deteriorates
Solution Approach 1:
The invention changes the microstructural parameters of the weld metal by adding Co (3-10 wt%) which promotes ferrite-bainite morphology formation. This parameter change in microstructure allows the weld metal to achieve both high yield strength (>100 ksi) and acceptable impact toughness at low temperatures, as the ferrite-bainite structure provides a balance between strength and ductility that retains toughness at cryogenic conditions
3Reliability
If Co is added to control weld metal morphology, then ferrite-bainite structure is produced with improved properties, but manufacturing complexity increases
Solution Approach 1:
The invention changes the chemical composition parameters by adding Co in a specific range (3-10 wt%) which naturally promotes ferrite-bainite morphology during the welding process. This parameter change achieves reliable weld metal morphology control without requiring complex manufacturing processes or additional equipment, as the microstructural transformation occurs in-situ during welding through the alloying effect of Co
Solution Approach 2:
The Co addition enables the weld metal to self-organize into ferrite-bainite morphology during the welding process itself, without requiring external intervention or complex process control. The alloying element Co performs the function of microstructure control automatically as the metal solidifies and cools, reducing the need for complex manufacturing procedures
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 solution effectively produces welds with minimum yield strength of 100 ksi and acceptable impact strength, while minimizing the risk of hot and cold cracking, achieving low hydrogen concentrations and maintaining weld integrity at low interpass temperatures, thus addressing the limitations of existing filler metals in high-strength steel welding.
Implementation Method 1
the heat is generated by an arc between a tubular wire electrode continuously fed into a welding machine and work piece
Implementation Method 2
the fluxed core heats up and melts faster, transferring and depositing the filler metal on the work piece faster
Implementation Method 3
Molecules of water present in the fluxed core dissociate in the welding arc into hydrogen and oxygen
Implementation Method 4
Some amount of dissociated hydrogen and oxygen will diffuse into the molten weld pool during the welding process
Implementation Method 5
Shielding of the arc is provided either by the flux contained in the tubular wire electrode or by an externally provided shielding gas
Data Source
AI summary
A weld wire of the present invention comprises a steel sheath encapsulating a fluxed core having a combination of fluxing compounds and alloying elements. The fluxing compounds comprise up to 2% Wt of fluoride compounds and up to 49% Wt of oxide compounds. The alloying elements comprise Mn, Ni, Co, Ti and up to about 0.98% Wt of C. The amount of Co is sufficient to produce a ferrite-bainite weld metal morphology of a resulting weld. A yield strength of the resulting weld was measured from about 95 ksi to about 111 ksi.