Fe-36Ni Welding Wire Composition for Cryogenic Strength
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Solution Overview
Problem
Fe-36Ni alloy welding wires fail to achieve overmatching mechanical properties with the base metal, leading to fragile welds and increased sensitivity to martensitic transformation, which is unacceptable in cryogenic applications like pressure vessels.
Innovation Solution
A welding wire with a specific alloy composition of 38.6% ≤ Ni+Co ≤ 45.0%, 2.25% ≤ Ti+Nb ≤ 0.8667 x (Ni+Co) - 31.20%, and limited Co, Nb, Mn, C, and Cr contents to ensure stability and overmatching mechanical properties at both room and cryogenic temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a homogeneous welding wire with identical chemical composition to the base metal is used, then the manufacturing process is simple, but the welded joint does not meet the overmatching requirement and has larger grains than the base metal
Solution Approach 1:
The patent modifies the chemical composition parameters of the welding wire by adding specific alloying elements (Ti: 0.05-0.50%, Nb: 0.05-0.50%, Mn: 0.05-0.30%, Si: 0.05-0.20%, C: 0.01-0.05%) to achieve solid solution hardening and grain refinement, thereby improving the mechanical properties of the welded joint while maintaining manufacturing feasibility
Solution Approach 2:
The patent creates a composite alloy system by combining Fe-36Ni base metal with multiple alloying elements (Ti, Nb, Mn, Si, C) in specific proportions, forming a complex composite material that achieves both grain refinement and solid solution hardening to meet the overmatching requirement
2Strength
If niobium is added to harden the alloy for improving room-temperature tensile strength, then the tensile strength is improved, but the weld becomes brittle and ductility at -196°C decreases by 80%
Solution Approach 1:
The patent precisely controls the niobium content within 0.05-0.50% and combines it with titanium (0.05-0.50%), manganese (0.05-0.30%), silicon (0.05-0.20%), and carbon (0.01-0.05%) to achieve optimal hardening while preventing excessive brittleness, balancing room-temperature strength and cryogenic ductility
Solution Approach 2:
The patent creates a multi-element composite system where niobium works synergistically with titanium, manganese, silicon, and carbon to achieve both solid solution hardening and grain refinement, preventing the formation of large brittle grains while maintaining ductility at cryogenic temperatures
3Strength
If the welding wire is hardened to improve mechanical properties, then the tensile strength increases, but the welded joint becomes more susceptible to martensitic transformation at cryogenic temperatures
Solution Approach 1:
The patent modifies the alloy composition parameters by adding specific amounts of titanium (0.05-0.50%), niobium (0.05-0.50%), manganese (0.05-0.30%), silicon (0.05-0.20%), and carbon (0.01-0.05%) to control the transformation behavior and prevent excessive martensitic transformation at cryogenic temperatures while maintaining strength
Solution Approach 2:
The patent converts the potential harmful effect of alloying element additions (which could promote martensitic transformation) into a beneficial effect by using these elements for grain refinement and solid solution hardening, thereby preventing martensitic transformation through controlled microstructure development
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 welding wire achieves resilience and thermal expansion coefficients similar to the base metal, maintaining stability and overmatching mechanical properties, reducing the risk of fragile rupture and corrosion, and enhancing fatigue resistance.
Implementation Method 1
niobium, which generate a solid solution hardening of the alloy
Implementation Method 2
manganese to trap sulfur and improve resistance to solidification and reheating cracks
Implementation Method 3
achieves resilience and thermal expansion coefficients similar to the base metal
Implementation Method 4
increases its coefficient of thermal expansion at cryogenic temperatures... more susceptible to martensitic transformation when deformed
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention concerns a welding wire intended to be used for welding together portions of parts made from Fe-36Ni alloy. This welding wire is made from an alloy comprising, in % by weight: 38.6% ≤ Ni+Co ≤ 45.0%; traces ≤ Co ≤ 0.50%; 2.25% ≤ Ti+Nb ≤ 0.8667 x (Ni+Co) - 31.20% if 38.6% ≤ Ni+Co ≤ 40.33%; 2.25% ≤ Ti+Nb ≤ 3.75% if 40.33% ≤ Ni+Co ≤ 41.4%; 0.4167 x (Ni+Co) - 15.0% ≤ Ti+Nb ≤ 3.75% if 41.4% ≤ Ni+Co ≤ 45.0%; traces ≤ Nb ≤ 0.50%; 0.01% ≤ Mn ≤ 0.30%; 0.01% ≤ Si ≤ 0.25%; traces ≤ C ≤ 0.05%; traces ≤ Cr ≤ 0.50%, the remainder consisting of iron and inevitable impurities resulting from production.