Abstract
Laser-based powder bed fusion of 300-grade maraging steel allows the production of parts with a high hardness, which improves the service life and wear resistance of tooling or mould insert produced from this material. The material typically consists of a martensitic matrix material, with retained austenite and nano-precipitation. The transformation from austenite to martensite has been linked to compressive stresses at the surface of parts produced in 300-grade maraging steel. In a cantilever beam-type part, this means that after cutting from the base-plate, the part will bend downwards, which is the opposite direction from the deformation found in most other materials after additive manufacturing. One way to gain insight into processing 300-grade maraging steel, while limiting the number of test samples that need to be printed, is by means of a numerical model. Using previously established models, additive manufacturing of a cantilever part in 300-grade maraging steel is simulated. Inclusion of the transformation from austenite to martensite into a numerical simulation of the laser-based powder bed fusion revealed the origin of the compressive stress at the surface of a simple cantilever beam-type sample. Additionally, changing the effective laser power through the laser absorptivity shows that the behaviour of the post-cutting deformation flips as compared to more conventional materials. Information about the laser absorption coefficient is rare, while it can greatly affect the results of a simulation. It is included in the presented result through the effective laser power, which is the product of the input laser power and laser absorption coefficient. When the effective laser power is changed from 95 W to 47.5 W, the cantilever bends upwards rather than downwards after release from the base plate. The results demonstrate the major influence played by the laser absorption coefficient on the simulation, an aspect to which little attention is paid in literature, but is proven to be one of the main factors to determine the component distortions after the laser-based powder bed fusion process.
Highlights
Maraging steels are a type of low-carbon, but nickel-rich steels, which form martensite upon cooling, and exhibit high hardness, wear resistance, weldability, creep resistance and toughness [1,2,3,4]
The results demonstrate the major influence played by the laser absorption coefficient on the simulation, an aspect to which little attention is paid in liter ature, but is proven to be one of the main factors to determine the component distortions after the laser-based powder bed fusion process
This paper aims to investigate the laser-based powder bed fusion (LPBF) process of a cantilever in maraging steel, and more the resulting residual stresses and their effect on the deformation of the beam after release from the base plate, through numerical modelling
Summary
Maraging steels are a type of low-carbon, but nickel-rich steels, which form martensite upon cooling, and exhibit high hardness, wear resistance, weldability, creep resistance and toughness [1,2,3,4]. This makes them suitable for a large number of applications, such as tooling [3], aircraft components [5] and mould production [6]. Pryds and Pedersen [23] investigate microstructure formation during gas atomisation, and identified different cooling rates for different powder sizes They concluded that smaller particles, which are exposed to larger cooling rates, retain less martensite (from 6% to 3.5%). For rolled billet of M300, Antolovich et al [20] found that, if the cooling rate is sufficiently high, the transformation from martensite to austenite is diffusionless
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