Maraging Steel Powder Composition for Low Retained Austenite
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Solution Overview
Problem
Additively manufactured maraging steels, such as 18Ni300, face challenges in achieving high hardness and toughness due to micro-segregation and retained austenite, which hinder their ability to reach peak hardness and strength comparable to conventionally processed materials.
Innovation Solution
A tailored powder composition for additive manufacturing, specifically optimized with 13.0-14.5 wt.% Ni, 12.0-14.0 wt.% Co, 7.0-8.0 wt.% Mo, and 0.05-1.00 wt.% Ti, with careful control of Ni, Mo, and Ti content to minimize retained austenite, combined with rapid cooling rates and laser-based additive manufacturing processes, to enhance martensite aging and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional 18Ni300 maraging steel composition is used in additive manufacturing, then the material can be processed by L-PBF, but micro-segregation and retained austenite prevent achieving high hardness and strength
Solution Approach 1:
The patent modifies the chemical composition parameters of maraging steel specifically for additive manufacturing, adjusting Ni (13.0-14.5 wt%), Co (12.0-14.0 wt%), Mo (7.0-8.0 wt%), and Ti (0.05-1.00 wt%) content to optimize the balance between achieving high strength through martensite aging and minimizing retained austenite formation during rapid solidification
Solution Approach 2:
The patent creates a tailored powder composition with specific local concentration ranges of alloying elements to ensure uniform distribution and minimize micro-segregation during the additive manufacturing process, thereby achieving consistent mechanical properties throughout the built part
2Strength
If Ni, Mo, and Ti content is increased to enhance aging capability, then peak hardness can be achieved, but retained austenite formation increases and stabilizes during direct aging
Solution Approach 1:
The patent optimizes the specific parameter ranges of Ni (13.0-14.5 wt%), Mo (7.0-8.0 wt%), and Ti (0.05-1.00 wt%) to achieve the critical balance: sufficient content to provide adequate aging capability and peak hardness, but controlled within limits that prevent excessive retained austenite stabilization during direct aging
Solution Approach 2:
The patent applies a controlled amount of alloying elements that is sufficient to achieve the desired aging response and mechanical properties, but deliberately limited to avoid the threshold where retained austenite becomes excessively stabilized and undermines the maraging mechanism
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 powder composition achieves yield hardness of 700 HV and tensile strength of up to 2500 MPa through direct aging, surpassing existing additively manufactured 18Ni300 and comparable to 13Ni400 grades, while improving ductility and maintaining high strength levels.
Implementation Method 1
Laser Metal Deposition (LMD) and Selective Laser Melting (SLM)
Implementation Method 2
the material (powder) is subjected to melting followed by rapid cooling (cooling rate 104-106 K/s)
Implementation Method 3
Aging of the martensite to peak hardness gives rise to the precipitation of intermetallics within the martensite
Implementation Method 4
martensite aging (heat treatment of the as-built part at 480-530° C. for 2-10 h)
Implementation Method 5
Fast solidification also promotes grain refinement and increased dislocation density within the material
Data Source
AI summary
A powder for additive manufacturing, including, in wt. %, C<0.03; Ni 13.0-14.5; Co 12.0-14.0; Mo 7.0-8.0; Ti 0.05-1.00; and, as optionals Al 0-0.1; Cr 0.0-1.0; N 0-200 ppm; Si 0-0.10; Mn 0-0.10, and a balance of Fe and unavoidable impurities.