Maraging Alloys Research Articles

Precipitation behavior of the G-phase strengthened 7Ni maraging steels

In this study, G-phase strengthened 7Ni maraging alloys were studied using a combination of thermodynamic prediction based on the TCFE-7 database and advanced experimental techniques, including micro-hardness testing, electron backscatter diffraction (EBSD), in-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). The martensite reversion and phase stability of overcooled austenite were precisely determined for a series of Fe–7Ni–2Si-based alloys, validating the effectiveness of thermodynamic predictions in martensite transformation.Based on these theoretical prediction, aging hardness measurements and microstructural observations further revealed that Ni16X6Si7-G (X = Ti, Nb, Ta) precipitates are effective strengthening phases in 7Ni maraging steel, with the exception of Ni16X6Si7 (X = Mn, Zr) due to their significantly different thermal stabilities. Experimental results showed that the Ni16X6Si7-G (X = Ti, Nb, Ta) precipitates remained stable and densely distributed within the martensitic matrix after aging at 500 °C, resulting in high aging hardness values ranging from 350 to 550 HV. Among the studied alloys, the 1Ti alloy strengthened by the Ni16Ti6Si7-G phase exhibited the finest particle radius (estimated at 1.4 nm) and the highest number density (estimated at 1.9 × 1024/m3). Additionally, it is worth noting that the Ni16Zr6Si7-G phase was believed to form through eutectic reaction with α-Fe during solidification and the Ni16Mn6Si7-G phase was only stable at temperatures below 460 °C and was not detected experimentally.These findings enhance our comprehension of G-phase precipitation and strengthening in 7Ni maraging steel and underscore the potential for utilizing thermodynamic calculations and advanced experimental techniques to guide the design and optimization of high-strength alloys.

Production and Characterization of Oxides Formed on Grade 300 and 350 Maraging Steels Using two Oxygen/Steam Rich Atmospheres

The growing process of a spinel-like oxide film can be obtained through different atmospheres; in this sense Air, O2, steam, and nitrogen atmospheres were used in different steps during the aging heat treatment at 490ºC of maraging 300 and 350 alloys. The oxidation layer produced under different atmospheres was chemically, microstructurally and mechanically characterized by means of advanced techniques. The results showed (in both alloys) a non-homogeneous mix oxide formed by magnetite, nickel and cobalt ferrites and MoO3 heterogeneously distributed along the oxide thickness. It was also founded TiO2 in the innermost areas and a particularly important quantify of hematite on the external surface. A nickel-rich austenite phase was produced at the interphase due to the combination of nickel stability and the preference of cobalt, molybdenum, and iron diffuses through the film as ions. The highest thickness values were found in the oxides produced in maraging 300 steels which could indicate greater susceptibility to oxidation comparing with grade 350 maraging steel. The oxide films produced in both maraging alloys using air atmosphere presents excellent adherence, and the results show the capability for being used for tribological applications under sliding contact tests.

Influence of laser shock peening pulse density and spot size on the surface integrity of X2NiCoMo18-9-5 maraging steel

Abstract Maraging alloys are a special class of steels with exceptional mechanical properties, suitable for critical and added value applications in aeronautical, aerospace engineering, and the tooling industry. Researchers have been studying several surface engineering techniques to enhance surface characteristics of maraging and tool steels with the aim of extending service life. The goal of the research presented in this paper was to investigate the influence of laser shock peening (LSP) pulse density and spot size on the surface integrity of X2NiCoMo18-9-5 maraging steel. Different pulse densities and spot sizes were chosen for this purpose. Surface integrity was analysed through roughness, residual stress, and microhardness measurements. The influence of each processing parameter was statistically evaluated using the analysis of variance (ANOVA) confirming a significant influence. LSP without the use of an absorbent coating generated high compressive residual stresses in the surface layer with relatively low surface roughness, a combination of characteristics which may have a beneficial influence on mechanical properties of 18% Ni maraging steel. According to the measurements taken in this research, maximal compressive residual stresses were not achieved using the smallest laser beam spot while maintaining constant pulse energy.

Microstructure and Mechanical Properties of Mn-Containing Maraging Steels

An attempt to the modification of the microstructure and mechanical properties of affordable, Mn-containing maraging alloys is reported. These alloys have demonstrated strong age hardening but suffered with premature intergranular brittleness despite their potential applications in tooling, dies, and machinery industries. An Fe-10Ni-6Mo-3Mn-1Ti (wt.%) alloy was prepared by vacuum melting and processed by homogenization (1250 °C/48 h), cold rolling, solution annealing (950 °C/1 h), and aging treatments (500 °C/4 h). It presented tensile strength of about 2.65 GPa, a few percent of tensile elongation and a mixed ductile-brittle fracture mode. Transmission electron microscopy (TEM) revealed the precipitation of a nearly spherical phase. Crystal symmetry of the second phase precipitates was identified hexagonal close-packed corresponding reasonably to the Fe2Mo Laves phase having lattice parameters of a = 0.4745 and c = 0.7754 nm. Precipitation of a Mo-enriched second-phase particle was occasionally found at prior austenite grain boundaries but the pronounced grain boundary precipitation was never identified. Energy-filtering transmission electron microscopy using the Mo-M4,5 post edge revealed remarkable segregation of Mo at grain boundaries.

Influence of temperature in arc-activated plasma nitriding of maraging steel in solution annealed and aged conditions

Maraging alloys are a group of high performance steels that combine high strength and good fracture toughness. Their excellent combination of properties is due to their microstructure, formed by nanometer-sized intermetallic precipitates embedded in a ductile martensite matrix. Their hardening treatments consist of aging processes that are compatible with thermochemical treatments such as nitriding or nitrocarburizing.An arc-activated plasma nitriding technique has been used in this study to investigate the effect of simultaneous aging and ion nitriding of maraging steel grade 300 at temperatures from 450°C to 510°C. The paper compares the results obtained for solution annealed and aged hardened samples in order to verify the compatibility of both processes, aging and nitriding.Chemical composition and micro-hardness profiling, glancing incidence X-ray diffraction (GIXRD), metallographic tests, corrosion studies and wear resistance tests were carried out. The results demonstrate the feasibility of arc-activated ion nitriding to achieve significant improvements of the surface properties of maraging steels and to merge together thermochemical and aging processes, thus reducing their processing time and energy consumption.

Effect of aging on the microstructure and tensile properties of Fe–Ni–Mn–Cr maraging alloys

Effect of aging on the microstructure and mechanical properties of chromium-containing Fe–Ni–Mn maraging alloys was studied. An Fe–10Ni–7Mn–2Cr (wt.%) alloy exhibited strong age hardenability but suffered from premature intergranular brittleness after aging. Further chromium addition resulted in partial austenite retention in Fe–10Ni–7Mn–6Cr (wt.%) and Fe–10Ni–7Mn–9Cr (wt.%) alloys at ambient temperature. The retained austenite exhibited mechanical instability during tensile loading at ambient temperature and transformed into martensite substantially, aiming at large tensile ductility. Age hardenability of the studied alloys decreased by increasing of retained austenite. In an Fe–10Ni–7Mn–6Cr (wt.%) alloy, transmission electron microscopy studies represented pronounced precipitation of a face-centered tetragonal (fct) θ-NiMn intermetallics in martensite and weak precipitation of a needle-shaped phase in retained austenite. After aging of the partially transformed alloy, yield strength increased moderately while tensile ductility decreased drastically. The ductility loss is mainly attributed to the premature intergranular fracture initiating within the aged martensite.

Evolution of Precipitate Coarsening Reaction in a Nanostructured Fe-Ni-Mn Maraging Alloy

Fe-Ni-Mn maraging alloys show discontinuous coarsening of fct θ-NiMn precipitates along prior austenite grain boundaries (PAGBs) during isothermal aging. Heavy cold rolling of a solution annealed Fe-10Ni-7Mn (wt. %) maraging alloy and subsequent aging treatment at 773 K led to the formation of a nanostructured material. Hardness measurement and transmission electron microscopy were used to study the aging behaviour and microstructural evolution of the nanostructured alloy. At the early stage of aging, an ultrafine grained structure was observed with fine matrix precipitates. However, at later stages of aging, severe coarsening of precipitates was found. At that stage, a lamellar microstructure composed of finely precipitated ferrite laths and ultrafine ferrite grains were identified. Coarse fct θ-NiMn precipitates were identified at the ultrafine ferritic grain boundaries. Development of the coarsening reaction was found to increase the ultrafine grained ferritic regions with prolonged aging.

Structure and properties of titanium-free maraging alloys

The changes in the structure, phase composition, and physicomechanical properties of titanium-free maraging alloys based on the Fe-15–23% Ni-(Co, Mo, V) system after heating to the single-phase α field and two-phase α + γ field have been studied. It has been established that the strengthening of N15K10M5F5-type maraging alloys is caused by the precipitation of fine particles (20–50 nm) of intermetallic phases such as the fcc Ni3(Mo, V) phase and the Fe2(Mo, V) Laves phase (in the N23K9M6 alloys, with the formation of the Ni3Mo and Fe2Mo phases). It has been shown that the two-step aging of the N15K10M5F5 alloy leads to an additional strengthening by 200–250 MPa and provides the achievement of the ultimate tensile strength σu=2400−2500 MPa. The high-strength N15K10M5F5 maraging alloys are obtained with two levels of the coercive force Hc: (a) semihard maraging alloys with Hc=20−50 Oe and σu=2100−2400 MPa; and (b) hard magnetic maraging alloys with Hc=180−230 Oe and σu=1500−1800 MPa. The high-strength titanium-free N15K10M5F5 and N23K9M6 maraging alloys possess many properties characteristic of structural, elastic, and magnetic alloys and are thus multifunctional materials. These alloys can be used for advanced high-tech articles and as high-strength magnetic materials.

Effect of conventional and subzero treating on the mechanical properties of aged martensitic Fe–12wt.% Ni–Xwt.% Mn alloys

Fe–Ni–Mn maraging alloys are suffering from sever embrittlement after aging. Mechanism of the embrittelement has not been well understood yet. Segregation of Mn atoms or formation of Austenite particles at prior Austenite grain boundaries (PAGBs) have been reported as embrittelement mechanisms while it remains controversial now. For better understanding of embrittelement behavior, effect of subzero treating after aging, double aging and modification of alloy composition on the mechanical properties and fracture behavior were investigated. Alloys of chemical compositions Fe–11.9 wt.% Ni–6.3 wt.% Mn and Fe–10.5 wt.% Ni–5.8 wt.% Mo–3 wt.% Mn were studied. Double solution annealing was performed at 1223 and 1093 K for 3.6 ks followed by water quenching. After aging at 723 K for 0.9 ks (under aging) and 172.8 ks (over aging), tensile properties of specimens heat treated conventionally and cryogenically were measured. Double aging was done at 623 K for 3.6 ks followed by a step aging at 753, 783 and 803 K. Aging behavior and tensile properties of Fe–10.5 wt.% Ni–5.8 wt.% Mo–3 wt.% Mn were investigated after aging at 773 K. Results showed that alloy modification yields reasonable tensile properties while subzero treatment and double aging couldn’t improve tensile properties. An insight toward more investigation of the embrittelement mechanism was made on the basis of this study.

Banding of MAR-Aging Steel

MAR-aging steels have gained a respectable position among design engineers who demand ultra-high strength, reasonable ductility, and good fracture toughness, especially where outerspace and aerospace applications are concerned. This specialty steel category of MAR-aging alloys owes its unique properties to a complex hardening reaction, which involves precipitation of uniform intragranular ribbons (Ni3Mo phase) on dislocations during the treatment cycle. Like any other metallurgical process, MAR-aging treatment cycles can become quite difficult, if not impossible. When that condition does exist, the end result is often called a dead heat by MAR-aging technologists. This paper examines a dead heat and makes appropriate comparisons to other live heats. Salient differences and interactive similarities are both studied in terms of microstructure, serial sections, chemical composition, and selected mechanical properties. The intent of this paper is to shed more light on the previously indistinct subject of banding.

Quantification of early stages of age hardening in Fe-12Ni-6Mn maraging type alloy

The effect of heat treatment and composition on the toughness and hardness of mar aging alloys based on Fe-Ni-Mn is first summarised. Age hardening data for an Fe-12Ni-6Mn alloy have been subjected to quantification. In the early stages of aging, the increase in hardness (∆H) has been found, both practically and theoretically, to follow the relationship ∆H = (Kt)n, where t is the isothermal aging time and K a temperature dependent rate constant, giving an activation energy of 79 ± 1.3 kJ mol−1 for the process. This is reasonablefor pipe diffusion of Ni and Mn, as is the value of <disp-formula><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="splitsection2-m1.tif"/></disp-formula> for the effective diffusion coefficient Do for the temperature range 350–425°C.

Strengthening behaviour and embrittlement phenomena in Fe-Ni-Mn-(Ti) maraging alloys

The effects of manganese and titanium on the mechanical properties of Fe-20Ni-(1.0–3.5)Mn-(0–1.0)Ti maraging steels were studied in order to investigate the strengthening behaviour and embrittlement phenomena in Co-free Fe-Ni-Mn maraging steels. Marked changes in tensile properties occurred as a function of ageing time and temperature, and alloy composition. As the amount of Mn and Ti increased, strength increased drastically but suffered from severe embrittlement. The strengthening behaviour of aged specimens was explained by the well-known Orowan mechanism. There was no evidence of second phase precipitation and no segregation of Mn along grain boundaries, which have been suggested as the proofs for the explanation of the embrittlement phenomena by many researchers. It is proposed that the combined amount of (Mn+Ti) should be controlled to below 3.5 wt.% in order to avoid severe embrittlement in Fe-20Ni-Mn-Ti maraging alloys, where the amount of Ti is held to 1.0 wt.%. The best combination of yield strength (1371 MPa) and elongation (18.8%) was obtained after ageing Fe-20.8Ni-2. 13Mn-0.8 Ti alloy for 1 h at 450 °C.

Electron microscopy study of precipitates in FeNiMn maraging alloys

Abstract The age-hardening characteristics of Fe-20wt.%Ni-1.27wt.%Mn (alloy A–O) and Fe-20wt.%Ni-3.23wt.%Mn (alloy B-0) maraging alloys have been studied in detail using analytical electron microscopy and computer simulation of selected-area diffraction patterns (SADPs). Only alloy B-0 showed substantial maraging response and the activation energy of 24.3 kcal mol −1 obtained suggests the nucleation and growth of precipitates along dislocations. An ordered f.c.t. Θ-NiMn precipitate was identified in overaged samples and confirmed by energy-dispersive X-ray analysis and computer simulation of SADPs. The shape of precipitates depends on the aging temperature. Lower temperature aging resulted in rod-shaped precipitates, while disc-shaped precipitates appeared at higher temperatures. Rod-shaped Widmanstatten austenite, having the Kurdyumov-Sachs orientation relationship with the matrix, appeared simultaneously within the lath martensite.

Susceptibility to pitting and stress corrosion cracking of aged 18 wt.% Ni maraging alloy in synthetic sea water

Limited work reported in the literature on free and stress corrosion behaviour of maraging alloys has revealed several controversial findings. An attempt has been made here to clear up some doubt by studying the free corrosion and stress corrosion cracking (SCC) behaviour of 18 wt.% Ni 250 grade commercial maraging alloy in the aged and unaged conditions. The study is confined to a sea water medium only. The pitting characteristics of the alloy as well as the crack initiation and propagation behaviour during stress corrosion have been studied in relation to various microstructures of the alloy. The peak-aged structure (aging for 3 h) exhibited maximum resistance to SCC as well as to pitting as revealed by a maximum threshold stress and a minimum pitting factor respectively. The mechanism of crack growth was also investigated in the light of existing theories.

A comparative analysis of the precipitation phenomena occurring in Ni and Mn maraging alloys using small-angle neutron scattering experiments

Abstract Small-angle neutron scattering experiments with an applied external magnetic field have been performed at 20°C upon Mn and Ni maraging alloys aged in the temperature range 400–500°C. In the Mn alloy aged at 425°C, it has been shown that ageing occurred in two distinct stages as a function of time. The contour plots of constant intensity recorded from aged specimens are always anisotropic. In both ageing stages, magnetic inhomogeneities have been revealed. Taking into account the transverse contribution to the magnetic response, the occurrence of superparamagnetic clusters has been suggested. In stage I, it was not possible to identify the chemical composition of the clusters, while in stage II, magnetic inhomogeneities have been related to Fe2 Mo precipitates revealed by prior transmission electron microscopy (TEM) observations. An increase in Mo content in the Mn maraging alloy also leads to the observation, in stage II of ageing, of a transverse contribution which has been related to superparam...

Effect of T.M.T. on the structures and mechanical properties of martensite in a few Fe‐Mn‐Ni base maraging alloys

Low temperature and room temperature thermomechanical treatment of four Fe‐Mn‐Ni alloys. Mechanical properties and electron microstructures of martensite in worked and unworked alloys. Attempts to correlate properties with structures.

Kinetics of martensite in Fe?Ni?Ta and Fe?Ni?Ta?Co alloys

1. In the initial stage of aging martensite in Fe 18Ni 6Ta and Fe 18Ni 6Ta 10Co alloys the electrical resistivity increases. This is evidently due to the formation of clusters or microregions with ordered distribution of atoms (the precipitation stage). In the second stage of aging the electrical resistivity decreases sharply, which is due to formation of intermetallic phase Ni3Ta. 2. The thermal effect during low-temperature aging of these alloys is far larger than during high-temperature aging, which is not characteristic of well-known maraging alloys. 3. The precipitation stage has a considerable effect on hardening of these maraging alloys. 4. Alloying with cobalt leads to additional hardening, which is due to formation of short- and/or long-range order of the FeCo type.

Mössbauer study of precipitation in FeNiMo and FeNiCoMo maraging alloys

Mössbauer study of precipitation in FeNiMo and FeNiCoMo maraging alloys

Studies on fracture toughness and fractographic features in FeMn base alloys

Fractographic examinations of fracture surfaces of single edge crack plate tension fracture toughness test specimens of some new FeMn base maraging alloys have been conducted. The interrelations between the fractographic features, fracture toughness and other mechanical properties of these alloys have been studied. It is observed that the width of the stretched zone between fatigue and rapid fracture is related to K σ ys of the material where K is either K IC , K Q or the stress intensity for onset of microscopic slow crack growth. The stretched zone width is approximately equal to the average dimple size. Also it is of the order of the process zone size (calculated by modified Krafft's model) and the critical crack opening displacement in plane strain condition. Hahn and Rosenfield's model to estimate K Ic was found to show much higher values in those cases where the fracture mode was predominantly cleavage, quasicleavage or intergranular.

Recrystallization of maraging alloys

In the maraging alloys investigated the α→γ transformation is not accompanied by refining of the original grains. The coarse-grained structure is eliminated by recrystallization of austenite at 900–1000°C, which occurs mainly by means of grain boundary migration.