Composite Tube Composition for Crack-Resistant Welded Joints
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Solution Overview
Problem
Composite tubes composed of different materials experience cracking during butt welding, particularly near the fusion line, due to the influence of elements like Si, P, S, and Sn, which lower the solidus temperature and increase solidification cracking susceptibility.
Innovation Solution
The composite tube is composed of a first tube made of low alloy steel and a second tube made of high alloy steel, with controlled chemical compositions and average values of Si, P, S, and Sn to prevent cracking, ensuring a stable welded joint by adhering to specific relational expressions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-layer welding is performed using welding consumables for austenitic stainless steel or Ni-based alloy without changing consumables for inner tube and outer tube portions, then working efficiency is improved, but cracking occurs in the weld metal near the fusion line boundary between inner tube and outer tube
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the composite tube materials. Specifically, it limits Si to 0.01-1.50%, P to 0.0400% or less, S to 0.0100% or less, and Sn to 0.0005-0.0300%, and establishes relational expressions (i) and (ii) that define the interrelationships between these elements. This compositional control prevents cracking while allowing the use of uniform welding consumables throughout multi-layer welding, thus resolving the contradiction between productivity and weld quality.
2Reliability
If different materials are combined in composite tubes to impart corrosion resistance and wear resistance, then material performance is improved, but welding becomes more difficult due to material incompatibility
Solution Approach 1:
The patent resolves the welding difficulty of composite tubes with different materials by establishing specific compositional parameters. It defines the chemical composition ranges for both the first tube (corrosion-resistant material) and second tube (structural material), and creates relational expressions that control the interaction between elements like Si, P, S, and Sn. This allows different materials to be combined for optimal corrosion and wear resistance while ensuring weldability through controlled compositional relationships.
Solution Approach 2:
The patent inherently uses composite materials by combining a first tube made of corrosion-resistant material with a second tube made of structural material. The invention extends this composite approach to the welded joint itself, creating a multi-layer weld structure where each layer's composition is controlled to be compatible with the underlying material, thus enabling successful welding of composite tube structures.
3Reliability
If elements like Si, P, S, and Sn are present in the material composition, then material properties are enhanced, but solidification cracking susceptibility increases due to lowered solidus temperature
Solution Approach 1:
The patent applies parameter changes by establishing specific concentration ranges and interrelationships between elements that lower solidus temperature. It limits Si to 0.01-1.50%, P to 0.0400% or less, S to 0.0100% or less, and Sn to 0.0005-0.0300%, and defines relational expressions (i) and (ii) that control the combined effect of these elements. This prevents excessive solidus temperature reduction and associated cracking while preserving the beneficial material properties that these elements provide.
Data Source
AI summary
A composite tube includes a first tube and a second tube. A chemical composition of the first tube includes, in mass %, C: more than 0.060% to 0.400% or less, Si: 0.01 to 1.00%, Mn: 0.01 to 1.20%, P: 0.0350% or less, S: 0.0150% or less, Sn: 0.0005 to 0.0400%, Al: 0.040% or less, N: 0.050% or less, O: 0.030% or less, and the balance: Fe and impurities. A chemical composition of the second tube includes, in mass %, C: 0.003 to 0.100%, Si: 0.01 to 1.50%, Mn: 0.01 to 2.20%, P: 0.0400% or less, S: 0.0100% or less, Sn: 0.0005 to 0.0300%, Ni: 7.0 to 52.0%, Cr: 15.0 to 27.0%, Al: 0.001 to 0.600%, N: 0.001 to 0.150%, O: 0.030% or less, and the balance: Fe and impurities. The composite tube satisfies formulas [Siave+6×Pave+20×Save+2×Snave≤1.1000] and [0.0015≤4×Save+Snave].