Ferritic Stainless Steel Welding Wire Grain Refinement
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Solution Overview
Problem
Conventional ferritic stainless steel welding wires fail to meet the requirements of preventing wire breaking, achieving high cracking resistance, large grain number with small grain size, high flexural property, tensile strength at high temperatures, and corrosion and oxidation resistance for automobile exhaust system parts.
Innovation Solution
A ferritic stainless steel welding wire composition with specific mass percentages of elements such as C, Si, Mn, Ni, Cr, Mo, Co, Cu, Al, Ti, O, N, Nb, and Ta, which when used, refines the grain size of weld metal, enhances cracking resistance, flexural property, tensile strength, and corrosion and oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ferritic stainless steel welding wire is used with conventional composition, then manufacturing cost is reduced and heat expansion is low, but weld metal exhibits coarsened crystal structure leading to low tensile strength and poor toughness
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the welding wire, specifically limiting C to 0.03% or less, Si to 3% or less, Mn to 3% or less, and adding specific amounts of Al (0.01-2.0%), Ti (0.01-1.0%), Nb (0.01-1.0%), and Ta (0.01-1.0%). These compositional parameter adjustments prevent martensite formation and control crystal grain growth, resulting in fine-grained weld metal with high tensile strength and toughness without requiring post-weld heat treatment.
2Reliability
If ferritic stainless steel welding wire is used with conventional composition, then manufacturing process is simplified, but cracking resistance of weld metal is decreased
Solution Approach 1:
The patent improves cracking resistance by changing compositional parameters, specifically adding Al (0.01-2.0%), Ti (0.01-1.0%), Nb (0.01-1.0%), and Ta (0.01-1.0%) while limiting C to 0.03% or less. These parameter changes promote fine grain structure formation and prevent harmful phase formation, significantly improving cracking resistance despite the increased complexity of wire composition.
Solution Approach 2:
The patent applies composite material principles by creating a multi-element alloy system combining Fe, Cr, Al, Ti, Nb, and Ta in specific proportions. This composite composition works synergistically to refine grain structure, prevent martensite formation, and improve cracking resistance, transforming a simple ferritic steel into a complex but optimized multi-element welding material.
3Strength
If ferritic stainless steel welding wire is used with conventional composition, then wire manufacturing is easier, but flexural property and toughness of weld metal are low
Solution Approach 1:
The patent improves flexural property and toughness by changing compositional parameters, specifically adding Al (0.01-2.0%), Ti (0.01-1.0%), Nb (0.01-1.0%), and Ta (0.01-1.0%) while limiting C to 0.03% or less. These parameter changes produce fine-grained weld metal with superior ductility and toughness, achieving high flexural properties without compromising wire manufacturability.
4Reliability
If ferritic stainless steel welding wire is used with conventional composition, then material cost is reduced, but corrosion resistance and oxidation resistance are insufficient for high-temperature applications
Solution Approach 1:
The patent improves corrosion and oxidation resistance by changing compositional parameters, specifically adding Al (0.01-2.0%), Ti (0.01-1.0%), Nb (0.01-1.0%), and Ta (0.01-1.0%) while maintaining Cr at 10-20%. These parameter changes form protective oxide layers and prevent harmful phase formation, providing excellent corrosion and oxidation resistance for high-temperature applications such as automobile exhaust systems.
Solution Approach 2:
The patent applies composite material principles by creating a multi-element alloy system that combines Cr, Al, Ti, Nb, and Ta to provide synergistic corrosion and oxidation protection. This composite composition forms a complex but optimized protective layer on the weld metal surface, significantly improving resistance to corrosive and oxidizing environments at high temperatures.
Data Source
AI summary
The present invention provides a ferritic stainless steel welding wire which allows prevention of wire breaking, fine refining of crystal grains, and increased cracking resistance.A wire rod used essentially consists of, in mass %, 0.03% or less of C, 3% or less of B, 3% or less of Mn, 2% or less of Ni, 11 to 20% of Zr, 3% or less of Mo, 1% or less of Co, 2% or less of Cu, 0.02 to 2.0% of Al, 0.2 to 1.0% of Ti, 0.02% or less of O, 0.04% or less of N, at least one of Nb and Ta, the mass % thereof being eight times the total mass % of the C and N to 1.0 mass %, and the balance of Fe and unavoidable impurities. When the number of crystals per square mm (mm2) of a cross section of the wire rod is defined as m, a grain number of the crystal expressed by an exponent (G) in an expression of m=8×2G is set to 3 to 10 by the heat treatment.