Maraging Steel LPBF in Nitrogen for Dense Complex Parts
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Solution Overview
Problem
Existing manufacturing processes for maraging steels are limited in the shapes of parts that can be produced, particularly in additive manufacturing, due to limitations in microstructure and composition.
Innovation Solution
A process for additive manufacturing using a metal powder with specific composition and microstructure, melted in an inert gas atmosphere other than Argon, and optimized laser parameters for Laser Powder Bed Fusion (LPBF) to achieve high-quality parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional hot rolling and cold rolling processes are used to manufacture maraging steel strips, then the elastic limit can be achieved (>1800 MPa), but the part shapes obtainable are limited
Solution Approach 1:
The patent replaces traditional mechanical rolling processes with additive manufacturing technology. The metal powder is selectively melted and deposited layer by layer using laser energy, enabling complex three-dimensional shapes to be manufactured directly without the form limitations of conventional rolling processes. This substitution of manufacturing methodology allows for highly customized part geometries while maintaining the required mechanical properties through controlled microstructure.
Solution Approach 2:
The patent employs precise control of laser parameters (power, scan speed, hatch spacing) and process conditions (inert gas atmosphere, powder composition) to achieve the desired microstructure and mechanical properties. By optimizing these parameters, the additive manufacturing process produces maraging steel parts with elastic limits exceeding 1800 MPa, matching traditional rolling processes but with superior design flexibility.
2Strength
If maraging steel is manufactured with high nickel content (6-14 wt%) to achieve fully martensitic structure, then strength is improved, but retained austenite forms above 14 wt% reducing strength
Solution Approach 1:
The patent precisely controls the nickel content parameter within the optimal range of 6-14 wt% and adjusts other compositional parameters (chromium 5-10 wt%, silicon 0.5-2.5 wt%, titanium 0.5-2 wt%) to achieve complete martensitic transformation. This compositional optimization ensures high strength while preventing retained austenite formation, maintaining microstructural stability during cooling and aging.
Solution Approach 2:
The patent creates a multi-element alloy system combining nickel, chromium, silicon, and titanium in specific proportions to achieve the desired martensitic microstructure. This composite material approach allows for tailored properties where each element contributes specific functions: nickel for martensitic transformation, chromium for hardenability, silicon for precipitation hardening, and titanium for fine precipitate formation.
3Strength
If carbon content is increased to improve strength, then tensile strength increases, but titanium carbides form severely reducing impact strength, ductility and toughness
Solution Approach 1:
The patent strictly controls carbon content at very low levels (C ≤ 0.04 wt%, preferably C ≤ 0.015 wt%) to prevent carbide formation. Instead of relying on carbon for strength, the patent achieves high tensile strength through controlled martensitic transformation and precipitation hardening by titanium and other alloying elements, thereby avoiding the harmful effects of carbide inclusion while maintaining excellent impact strength and ductility.
4Reliability
If additive manufacturing is performed in Argon atmosphere, then oxidation is prevented, but manufacturing precision deteriorates due to porosity and spatters
Solution Approach 1:
The patent uses nitrogen as an inert atmosphere alternative to argon for additive manufacturing. Nitrogen provides effective oxidation protection while producing superior manufacturing precision with reduced porosity and spatter. The nitrogen atmosphere creates a more favorable melting and solidification environment that enhances part density and surface quality without compromising the protective function against oxidation.
Data Source
AI summary
A process for manufacturing an additively-manufactured part from a metal powder having a composition having the following elements, expressed in content by weight: 6%≤Ni≤14%, 5%≤Cr≤10%, 0.5%≤Si≤2.5%, 0.5%≤Ti≤2%, C≤0.04% and optionally containing 0.5%≤Cu≤2%, the balance being Fe and unavoidable impurities resulting from the elaboration, the metal powder having a microstructure including in area fraction more than 98% of a body-centered cubic crystalline phase, the process having a step during which at least a part of the metal powder is melted in an atmosphere substantially composed of an inert gas other than Argon or of a combination of inert gases other than Argon.