Maraging steel

About: Maraging steel is a research topic. Over the lifetime, 1728 publications have been published within this topic receiving 19886 citations. The topic is also known as: martensitic ageing steel.

Influence of delta ferrite on the impact toughness of a PH 13-8 Mo maraging steel

Abstract: Due to the fact that maraging steels are widely utilized as structural parts for the aerospace industry, high and consistent impact toughness is crucial to ensure reliability under extreme mechanical loads. The toughness of maraging steels is heavily influenced by the martensitic structure and reverted austenite. Another microstructural constituent is residual delta ferrite that originates from non-equilibrium solidification. This work focuses on the effect of delta ferrite on the impact toughness of a PH 13-8 Mo maraging steel, while keeping other toughness-influencing factors as constant as possible. Three-step heat treatments were applied to samples for adjusting different phase fractions of delta ferrite. Charpy impact testing revealed that the impact toughness decreases with an increasing phase fraction of delta ferrite. However, no significant influence on the lower energy shelf, i.e. the impact energies below the ductile-to-brittle transition temperature range, was found. In addition, no decrease in hardness at room temperature was measured when delta ferrite is present in the microstructure. Particle analysis by APT measurements revealed that delta ferrite contains Ni- and Al-rich precipitates. It is assumed that those precipitates in combination with effective solid solution hardening by Cr, Mo and Al significantly contribute to the hardness of delta ferrite, which is in the range of martensite. Furthermore, EDS analysis showed a depletion in Ni in delta ferrite, presumably resulting in a lower cleavage fracture resistance compared to martensite, and, therefore, causing embrittlement. Moreover, the interface between delta ferrite and martensite possibly plays an additional role for crack initiation due to amplified local stresses.

Numerical investigation into laser-based powder bed fusion of cantilevers produced in 300-grade maraging steel

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.

Destructive Tests of Full-Size Rocket Motor Cases and Their Application to Lightweight Design

Abstract: This paper describes experimental stress investigations of burst-tests under internal pressure of three full-size rocket motor cases made of Ladish D6AC steel. Two full-size cases made of 18% Ni maraging steel were also burst-tested for strength evaluation. Fifteen subscale vessels were also tested to destruction. Electric strain gages (SR-4) were used in all tests. Strain data in the plastic region were reduced by a digital computer. The results indicated that 1) a biaxial ultimate strength equal to 343 ksi has been achieved in 18% Ni maraging steel rocket motor cases; 2) within the range of radius-to-thickness ratios between 40 and 300, the subscale vessels behave essentially in the same way as the full-size cases with respect to the biaxial gains and the total elongation of the vessel at failure; 3) in a 2:1 stress field, the experimental biaxial gains in the elastic range vary from 15.5 to 16.5%, which are in close agreement with values predicted by Huber-Hencky-Von Mises theory of constant energy of distortion; 4) the experimental biaxial gains in the cylinder at fracture are in the range of 13 to 16%; and 5) the total elongadons in the cylindrical vessels at failure are approximately one-fifth of those obtained from the uniaxial specimens.

Model for fracture toughness alteration due to cyclic loading

Abstract: A new model that is capable of predicting and explaining the effect of cyclic loading on the apparent fracture toughness of materials was developed. The model combines macroscopic fracture criteria with the assumption that transient flow properties of material in the cyclic plastic zone can be simulated by those of macroscopic low cycle fatigue specimens, tested in reversed strain control. Little or no changes in the cleavage fracture toughness due to cyclic loading is predicted or observed for materials that cycle strain harden (e.g., rail steel) and in the fracture toughness of other materials that cycle strain harden (e.g., the commercial 2000 series Al-Cu alloys) and fracture by rupture. However, an increase in the fracture toughness is predicted and observed for materials that cycle strain soften (e.g., 1Cr-Mo-V and 18 Ni 300 maraging steels), irrespective of fracture mode (cleavage or rupture). The changes in the fracture toughness are predicted and observed to increase with both the number of cycles of applied load and the reversed plastic strain range (or stress intensity range for precracked specimens).

Space group and atomic structure determination of a nano-sized ordered phase derived from a f c c structure in maraging steel 12Cr-9Ni-4Mo-2Cu using transmission electron microscopy.

Abstract: The unique properties of maraging steel Sandvik 1RK91 were attributed to unique precipitation: a nano-sized L phase in addition to the quasi-crystalline R' phase, which differs from any precipitation system in conventional maraging steels. The L phase was observed after ageing at either 748 or 823 K. It has flake morphology with dimensions approximately 100 x 500 x 500 A. In the present study the structure of the L phase was examined using convergent-beam electron diffraction (CBED), energy-dispersive X-ray analysis (EDX) and high-resolution electron microscopy (HREM). The L phase could be described as Ti(19)Fe(9)Mo(9)Al(8)Cr(5)Ni(50) or simply M(50)Ni(50) (M = Ti, Fe, Mo, Al and Cr). The L phase is isostructural to FeNi. Its crystal structure was determined to have the ordered structure of the uAu-I type (L1(0), P4/mmm, a = 3.52, c = 3.63 A and Z = 2) with two Ni atoms at (1/2) 0 (1/2) and 0 (1/2) (1/2), and two M atoms at 0 0 0 and (1/2) (1/2) 0. The crystal structure of the L phase can also be described using a primitive tetragonal cell and lattice parameters: a = 2.49 and c = 3.63 A, Z = 1. The Volume of the primitive tetragonal unit cell is 22.5 A(3) and the density is approximately 6.98 g cm(-3). The present study has demonstrated the possibility of determining the structure of an extremely small crystal by utilizing the information from CBED, EDX analysis and HREM.