Maraging Steel Composition for High Strength and Fatigue Resistance
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Solution Overview
Problem
Current maraging steels with high tensile strength, such as those around 2,300 MPa, face challenges in maintaining excellent toughness, ductility, and low-cycle fatigue characteristics due to the formation of inclusions like AlN and TiN, and lack the strength boost from the precipitation of NiAl phases.
Innovation Solution
A maraging steel composition is optimized with specific ranges of elements like C, Co, Ni, Mo, Cr, and the absence of Al and Ti to prevent inclusion formation, ensuring high tensile strength, elongation, and fatigue characteristics through the precipitation of carbides such as Mo and Cr carbides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Al and Ti are added to maraging steel to enhance strength, then tensile strength is improved, but inclusions like AlN and TiN form which deteriorate low-cycle fatigue characteristics
Solution Approach 1:
The patent removes Al and Ti elements from the maraging steel composition to prevent the formation of harmful inclusions (AlN and TiN) that deteriorate low-cycle fatigue characteristics. This extraction of problematic elements resolves the contradiction by eliminating the source of inclusion formation while maintaining strength through alternative mechanisms.
Solution Approach 2:
The patent changes the compositional parameters by strictly limiting Al and Ti contents to 0.005 mass% or less, and controlling N content to 0.003 mass% or less. These parameter changes prevent inclusion formation while achieving high strength (2,300 MPa or more) through optimized Co (9.0-20.0 mass%) and Ni (6.0-16.0 mass%) contents combined with controlled carbide precipitation.
2Strength
If Ni content is increased to boost strength through NiAl phase precipitation, then tensile strength is improved, but without Al the precipitation mechanism is lost
Solution Approach 1:
The patent replaces the Al-dependent NiAl precipitation mechanism with a more robust carbide precipitation mechanism involving Mo and Cr. By using readily available Mo (1.0-2.0 mass%) and Cr (1.0-4.0 mass%) to form stable carbides, the patent achieves high strength without relying on Al, which is limited to trace amounts. This substitution provides a reliable precipitation mechanism that operates independently of Al content.
3Strength
If high strength is achieved through conventional maraging steel composition, then tensile strength reaches 2,300 MPa, but toughness and ductility are compromised
Solution Approach 1:
The patent optimizes multiple compositional parameters simultaneously: Co (9.0-20.0 mass%), Ni (6.0-16.0 mass%), Mo (1.0-2.0 mass%), Cr (1.0-4.0 mass%), with strict limits on C (0.20-0.35 mass%) and alloying element contents. These coordinated parameter changes achieve high strength (2,300 MPa or more) while maintaining excellent toughness and ductility (total elongation 8% or more) through controlled martensite formation and carbide precipitation.
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 optimized maraging steel achieves a tensile strength of at least 2,300 MPa with an elongation of at least 8% at room temperature, while avoiding the detrimental effects of AlN and TiN inclusions, thereby enhancing both high-strength and fatigue-resistant properties.
Implementation Method 1
very high strength attributable to precipitation of intermetallic compounds, such as Ni3Mo, Fe2Mo and Ni3Ti, in martensite texture through aging treatment
Implementation Method 2
precipitation of carbides (e.g., Mo carbides and Cr carbides) in appropriate amounts
Data Source
AI summary
The present invention relates to a maraging steel containing, in terms of mass %, 0.20≤C≤0.35, 9.0≤Co≤20.0, 1.0≤(Mo+W/2)≤2.0, 1.0≤Cr≤4.0, and a certain amount of Ni, with the balance being Fe and inevitable impurities, in which in a case where the contents of V and Nb satisfy V+Nb≤0.020 mass %, the amount of Ni is 6.0≤Ni≤9.4, and in which in a case where the contents of V and Nb satisfy 0.020 mass %<V+Nb≤0.60 mass %, the amount of Ni is 6.0≤Ni≤16.0.