Solid Welding Wire Composition for Back Beads Without Backing Gas
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Solution Overview
Problem
Welding steels with high Cr content using gas shielded arc welding results in poor back bead appearance due to Cr oxide formation, requiring costly and complex continuous backing gas, and existing materials lack consideration for post-weld heat treatment (PWHT) toughness and mechanical performance.
Innovation Solution
A solid wire composition with controlled contents of C, Si, Mn, S, Cr, Mo, Ni, Nb, V, Ti, Al, and optionally Zr, Co, Cu, and N, ensuring excellent back bead appearance and mechanical performance without backing gas, and a welding method using this wire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If continuous backing gas is used to prevent Cr oxide formation on back bead surface, then back bead appearance is improved, but cost increases and work becomes complicated
Solution Approach 1:
The invention extracts and eliminates the backing gas system from the welding process by developing a wire composition that inherently prevents Cr oxide formation through controlled Si content (0.6-1.7 mass %) and S content (0.005-0.030 mass %), thereby simplifying the equipment and reducing operational complexity
Solution Approach 2:
The wire composition is designed to be self-protecting against oxidation through its specific chemical composition, particularly the Si and S content control, which prevents Cr oxide formation without requiring external protective measures like backing gas
2Shape
If wire composition is optimized for back bead appearance, then back bead performance is improved, but mechanical performance and PWHT toughness may be compromised
Solution Approach 1:
The invention applies local quality by differentiating the functional roles of various elements: Si (0.6-1.7 mass %) and S (0.005-0.030 mass %) control back bead oxidation resistance, while C (0.02-0.11 mass %), Cr (4.0-13.0 mass %), and Mo (0.3-1.5 mass %) ensure mechanical strength and PWHT toughness, with each element optimized for its specific function
Solution Approach 2:
The wire composition creates a composite material system where multiple elements work synergistically: the combination of Si, S, C, Cr, Mo, Ni, Mn, and other alloying elements produces a weld metal that simultaneously achieves excellent back bead appearance and superior mechanical properties including high Ac1 transformation point and good toughness
3Strength
If Ac1 transformation point is increased for PWHT, then toughness is improved, but welding parameter control becomes more critical
Solution Approach 1:
The invention changes the chemical composition parameters of the wire, specifically controlling C content (0.02-0.11 mass %) in combination with Cr (4.0-13.0 mass %) and Mo (0.3-1.5 mass %), to raise the Ac1 transformation point of the weld metal, thereby improving toughness and enabling effective PWHT
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
Achieves back beads with excellent appearance and weld metals with superior mechanical properties, including high Ac1 transformation points, tensile strength, and toughness, without the need for backing gas, facilitating efficient PWHT.
Implementation Method 1
in order to prevent poor appearance of beads generated by back bead welding due to formation of Cr oxides with a high melting point on a back bead surface
Implementation Method 2
gas shielded arc welding is performed
Implementation Method 3
welding steel materials, at least one of which contains 4 mass % or more and 10 mass % or less of Cr, with the solid wire
Data Source
AI summary
A solid wire capable of obtaining back beads with excellent appearance and a weld metal with excellent mechanical performance without using a backing gas. The solid wire is used for welding a steel material that contains 4 mass % or more and 10 mass % or less of Cr. The solid wire contains, based on a total mass of the wire, C: 0.02 mass % or more and 0.11 mass % or less; Si: 0.6 mass % or more and 1.7 mass % or less; Mn: 0.2 mass % or more and 1.5 mass % or less; S: more than 0.005 mass % and 0.030 mass % or less; Cr: 4.0 mass % or more and 13 mass % or less; Mo: 0.3 mass % or more and 1.5 mass % or less; P: 0.030 mass % or less; Ni: 1.4 mass % or less; Nb: 0.05 mass % or less; V: 0.05 mass % or less; Ti: 0.05 mass % or less; and Al: 0.05 mass % or less, with the remainder being Fe and unavoidable impurities.