Ni-Based Welding Material Oxide Control for Fusion
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Solution Overview
Problem
Ni-based heat resistant alloys used in high-temperature applications, such as power generation boilers, face issues with poor weldability and a lack of fusion during multi-layer welding, leading to defects like stress relaxation cracking and reduced creep strength.
Innovation Solution
A welding material with a specific chemical composition (C: 0.08-0.12%, Si: 0.10% or less, Mn: 0.02-1.50%, P: 0.008% or less, Ni: 56.0-60.0%, Co: 8.0-12.0%, Cr: 18.0-22.0%, Mo: 6.0-10.0%, Ti: 0.01-0.50%, Al: 0.50-1.00%, and O: 0.010% or less) and a controlled oxide layer thickness of 30 µm or less, which reduces oxides and improves weldability and creep strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional welding materials are used for Ni-based heat resistant alloy, then creep strength and stress relaxation cracking resistance can be achieved, but weldability deteriorates and lack of fusion occurs during multi-layer welding
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the welding material. Specifically, it limits Si content to 0.10% or less, O content to 0.010% or less, and Al content to 0.50-1.00%, while controlling oxide layer thickness to 30 μm or less. These parameter adjustments prevent excessive oxide formation that causes lack of fusion, thereby improving weldability while maintaining the creep strength and stress relaxation cracking resistance required for high-temperature service.
2Reliability
If low heat input welding is used to prevent hot cracking, then cracking resistance is improved, but lack of fusion occurs due to insufficient melting of welding slag
Solution Approach 1:
The patent applies preliminary action by controlling the oxide layer thickness on the welding material surface to 30 μm or less before welding. This preliminary control prevents the formation of thick, hard-to-melt oxide layers that would cause lack of fusion. By preparing the welding material with controlled oxide content in advance, the patent enables low heat input welding to proceed without generating lack of fusion defects, thus maintaining both cracking resistance and fusion quality.
Solution Approach 2:
The patent changes the oxide layer thickness parameter to 30 μm or less and controls Si content to 0.10% or less. These parameter changes reduce the melting point and quantity of welding slag, enabling sufficient melting even with low heat input welding processes. This resolves the contradiction between using low heat input to prevent cracking and achieving adequate fusion.
3Strength
If Al content is increased to improve creep strength, then high-temperature strength is improved, but stress relaxation cracking susceptibility increases
Solution Approach 1:
The patent applies parameter changes by optimizing the Al content to a specific range of 0.50-1.00%. This controlled parameter adjustment balances two competing requirements: sufficient Al content to form precipitates for creep strength, but limited Al content to prevent excessive oxide formation that would increase stress relaxation cracking susceptibility. The patent also controls O content to 0.010% or less to minimize oxide formation, thereby achieving both creep strength and stress relaxation cracking resistance through precise parameter control.
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 enhances weldability, prevents lack of fusion, and provides excellent creep strength and stress relaxation cracking resistance in Ni-based heat resistant alloys, ensuring reliable high-temperature performance.
Implementation Method 1
Patent Document 6 proposes a welding material for Ni-based alloy that achieves high strengthening by taking advantage of solid-solution strengthening by Mo and W
Implementation Method 2
Patent Document 6 proposes a welding material for Ni-based alloy that achieves high strengthening by taking advantage of solid-solution strengthening by Mo and W and a precipitation strengthening effect by Al and Ti
Implementation Method 3
Oxides agglomerate in welding to remain on a weld bead in the form of welding slag, the oxides including those formed by the reaction in a molten pool between Al, Si, and the like, and oxygen (O)
Data Source
AI summary
There are provided: (1) A welding material for Ni-based heat resistant alloy has a chemical composition of: C:0.08 to 0.12%; Si ≤ 0.10%; Mn ≤ 1.50%; P ≤ 0.008%; S ≤ 0.002%; Ni: more than 56.0% to 60.0%; Co: 8.0 to 12.0%; Cr: 18.0 to 22.0%; Mo: 6.0 to 10.0%; Ti: 0.01 to 0.50%; Al: 0.50 to 1.00%; N ≤ 0.010%; O ≤ 0.010%; Nb: 0 to 0.50%; B: 0 to 0.0050%; Ca: 0 to 0.050%; Mg: 0 to 0.050%; and REM: 0 to 0.20%, with the balance: Fe and impurities, wherein the thickness of an oxide layer formed on the surface of the welding material is 30 µm or less; (2) a weld metal formed using the above welding material for Ni-based heat resistant alloy; and (3) a welded joint formed of the above weld metal and a base metal of a Ni-based heat resistant alloy excellent in high temperature strength.