38CrMoAl Steel Research Articles

High-speed laser directed energy deposition of Ni60 on 38CrMoAl steel: Crack inhibition and microstructure performance modulation via inductive preheating

High-speed laser directed energy deposition of Ni60 on 38CrMoAl steel: Crack inhibition and microstructure performance modulation via inductive preheating

Tribological properties of the modified layers prepared on 38CrMoAl steel by plasma nitrocarburized and post-sulfurized method

The tribological properties of the different modified layers of plasma nitrocarburized and post-sulfurized on 38CrMoAl steel under oil lubrication were investigated, and the wear mechanism was proposed. The modified layers were prepared by the plasma nitrocarburized at 520 °C for 5 h and post-sulfurized at 160 °C for 1, 3, and 5 h. The morphology, phase structures, and composition were characterized by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, three-dimensional white light interferometry, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The sliding-wear characteristics were investigated by ball-on-disk wear tests against GCr15 steel counterparts. The results show that the nitrocarburized layer mainly comprises ε-Fe2-3(N, C) and γ ′-Fe4(N, C), with a surface hardness of 1250 HV0.1. The nitrocarburized treatment significantly improved the wear resistance of the 38CrMoAl steel. For the plasma nitrocarburized and post-sulfurized samples, a sulfurized layer mainly consisting of FeS and FeS2 was formed on the nitrocarburized layer. The wear mass loss and friction coefficient of the duplex samples are significantly reduced due to the thin FeS layer acting as a solid lubricant. A two-step method, plasma nitrocarburized and post-sulfurized duplex treatment, further improves tribological performance, which is crucial for engineering applications.

In-situ synthesis and wear mechanism of Ni- based self-lubricating composite coating with a dense continuous metal sulfide layer prepared by laser cladding

The friction and wear of bearing cages, sealing rings and other transmission components working in harsh environments such as high vacuum and heavy load directly affect the operational stability and safety reliability of the equipment. Therefore, it is vitally important to improve the tribological properties of machine components. In this paper, NiCrBSi alloy coating, NiCrBSi-30 wt% WS2 coating and double-layer NiCrBSi-30 wt% WS2 coating were prepared on 38CrMoAl steel by laser cladding. The results show that a metal sulfide layer is formed on the double-layer NiCrBSi-30 wt% WS2 coating compared to NiCrBSi-30 wt% WS2 coating. The NiCrBSi-30 wt% WS2 coating consists of γ-(Ni,Fe) solid solution, (Fe,Ni)9S8, Cr7S8 and M7C3 phases. The metal sulfide layer consists of γ-(Ni, Fe) solid solutions, Fe3S4, CrxSy and M7C3 phases. The double-layer NiCrBSi-30 wt% WS2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS2 coating. The average microhardness values of NiCrBSi coating, NiCrBSi-WS2 coating and double-layer NiCrBSi-WS2 coating are 412.6 ± 15.2HV0.3, 383.9 ± 14.5HV0.3, and 368.6 ± 13.3HV0.3, respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS2 coating is 1.51 × 10−5 mm3/(N·m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 × 10−5 mm3/(N·m)) and NiCrBSi-30 wt% WS2 coating (2.32 × 10−5 mm3/(N·m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS2 coating has the best wear resistance and friction reduction performance at room temperature. A more continuous lubricating film was formed on the surface of the double-layer NiCrBSi-30 wt% WS2 coating, which explains its lowest coefficient of friction and wear rate.

Effect of Rare‐Earth Oxides Containing Refractories on the Cleanliness of Al‐Killed Steels

Refractories have a significant impact on the cleanliness of molten steel, especially when utilized as ceramic filters. To explore the feasibility of applying rare‐earth oxides in ceramic filters, the interactions between CeO2/CeAlO3 functional refractories and steels with different Al contents are explored, and compared with the microporous magnesia refractory. In the test of CeO2 refractory, the total oxygen (T.O) content significantly increases, while the dissolved Al content obviously decreases in 38CrMoAl steel (0.876 wt% [Al]). Furthermore, the T.O contents in 38CrMoAl and X70 steel (0.040 wt% [Al]) in the test of CeAlO3 refractory are 22.9% and 70.9% of that in the test of microporous magnesia refractory, respectively. Meanwhile, the loss of dissolved Al in steel caused by the interaction between CeAlO3 refractory and steel is relatively small. Therefore, CeAlO3 is relatively stable after contact with molten steel and promising to be applicated in the ceramic filter for improving the cleanliness of molten steel.

The diffusion behavior and surface properties of catalytic nitriding with LaFeO3 film prepared by the sol-gel method

In the present work, LaFeO3 film prepared by the sol-gel method was applied to realize the catalytic plasma nitriding for 38CrMoAl steel. The plasma nitriding treatments were conducted at 520 °C for 4, 8 and 12 h. The plasma nitriding without LaFeO3 film was set as a normal group. The microstructure, phase structure, mechanical and tribological properties of the plasma nitrided layers with and without the LaFeO3 film were investigated in comparison. The LaFeO3 was proved to be effective for accelerating plasma nitriding because it suppresses the formation of the compound phase and layer. Moreover, the LaFeO3 has a positive effect on the surface mechanical and tribological properties. Interestingly, the effect mechanism was varied during the nitriding process, which was discussed based on the experimental results.

Study of the microstructure and tribological property of CoNiAlB coating with FeB phase reinforced

In this work, the CoNiAlBx coatings were successfully prepared on 38CrMoAl steel by laser cladding technology. The effects of B content addition on the microstructure, phase composition, microhardness, and tribological properties of the coatings were systematically analyzed. We found that CoNiAlB coatings were composed of β,γ,and FeB phase. TEM results shown that the orientation relationships between FeB phase and γ phase were [—112]FeB//[12]γ. With the addition of B, the microstructure changed from cellular morphology to dendritic morphology, then generated FeB phase, the transformation of microstructure led to the improvement of the coating: The microhardness improved from 380 Hv0.3 to 790 Hv0.3, the friction coefficient reduced from 0.75 to 0.45, wear rate decreased from 3.59·10−14 m3 N−1 m−1 to 1.34·10−14 m3 N−1 m−1. The wear mechanism of CoNiAlB coatings was changed from only oxidation wear to only abrasive wear, exhibited excellent tribological property.

Change of Spinel in High Ca Treament at 38CrMoAl Steel

Change of Spinel in High Ca Treament at 38CrMoAl Steel

Numerical simulation on recrystallization behavior and microstructure evolution during hot continuous rolling process of 38CrMoAl steel rod

Numerical simulation on recrystallization behavior and microstructure evolution during hot continuous rolling process of 38CrMoAl steel rod

Research on Surface Quality of 38CrMoAl Polished Based on Abrasive Water Jet

Because the screw surface is slender and complex, it is difficult to process by traditional polishing methods. In order to improve the surface quality of screw, the abrasive water jet polishing (AWJP) technology was used to polish 38CrMoAl steel, which is commonly used in screw. The effects of different inlet pressure, target distance and abrasive particle size on surface roughness are analyzed. The experimental results show that with the increase of inlet pressure, the surface roughness first decreases and then increases. With the increase of target distance, the surface roughness first decreases and then increases. The smaller the abrasive particle size, the better the polishing effect.

Interaction between microporous magnesia castable and 38CrMoAl steel

Interaction between microporous magnesia castable and 38CrMoAl steel

Dynamic fracture toughness and damage mechanism of 38CrMoAl steel under salt spray corrosion

Under the environmental conditions of the aircraft carrier surface, the structure of the carrier aircraft has to withstand the interaction between the takeoff and landing impact load and the corrosion of the marine environment. 38CrMoAl steel is the main material of a carrier aircraft structure which is frequently subjected to impact load. In order to obtain its dynamic fracture toughness under corrosive conditions, it was tested by a experimental–numerical method. The dynamic constitutive model parameters of the corroded 38CrMoAl steel were obtained through dynamic mechanical tests, which were imported into the established finite element model to obtain the dynamic fracture factor time history curve of the material under corrosive conditions. Then, the dynamic crack initiation time of the corroded 38CrMoAl steel was obtained by the three-point bending dynamic fracture toughness test device. Combined with the dynamic fracture factor time history curve, the dynamic fracture toughness of the corroded 38CrMoAl steel was determined. Finally, the fracture mechanism of 38CrMoAl steel under the interaction between corrosion and high strain rate loading was analyzed according to the fracture morphology and EDS energy spectrum of specimens with different loading rates and corrosion cycles. This method provides a new idea for testing the dynamic fracture toughness of corroded materials.

Optimizing mechanical and tribological properties of DLC/Cr3C2-NiCr duplex coating via tailoring interlayer thickness

A top DLC film was deposited on the surface of Cr3C2-NiCr coated 38CrMoAl steel substrate, and the effect of Cr3C2-NiCr cermet interlayer thickness on the mechanical and tribological properties of the duplex coating was investigated by experimental analysis and finite element modeling (FEM). Results shown that, compared with single DLC film, the load-bearing capacity and tribological performance of DLC/Cr3C2-NiCr duplex coating were significantly improved, especially its anti-wear performance was nearly ten times higher than that of the single DLC film. Moreover, the duplex coating with an optimum cermet interlayer thickness of 100 μm showed the best comprehensive performance. FEM analysis also shown that the presence of Cr3C2-NiCr cermet interlayer limited the stress concentration area within the interlayer, which made the stress concentration area far away from the interface of DLC film and cermet interlayer, thus improved duplex coating durability. What's more, the cermet interlayer thickness increase resulted in the contact stress on DLC film increase, which contributed to the improvement of its tribological performance.

Acceleration of Plasma Nitriding at 550 °C with Rare Earth on the Surface of 38CrMoAl Steel

In order to explore the effect of the addition of rare earth (RE) to a steel microstructure and the consequent performance of a nitrided layer, plasma nitriding was carried out on 38CrMoAl steel in an atmosphere of NH3 at 550 °C for 4, 8, and 12 h. The modified layers were characterized using an optical microscope (OM), a microhardness tester, X-ray diffraction (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electrochemical workstation. After 12 h of nitriding without RE, the modified layer thickness was 355.90 μm, the weight gain was 3.75 mg/cm2, and the surface hardness was 882.5 HV0.05. After 12 h of RE nitriding, the thickness of the modified layer was 390.8 μm, the weight gain was 3.87 mg/cm2, and the surface hardness was 1027 HV0.05. Compared with nitriding without RE, the ε-Fe2-3N diffraction peak was enhanced in the RE nitriding layer. After 12 h of RE nitriding, La, LaFeO3, and a trace amount of Fe2O3 appeared. The corrosion rate of the modified layer was at its lowest (15.089 × 10−2 mm/a), as was the current density (1.282 × 10−5 A/cm2); therefore, the corrosion resistance improved.

Study on surface alloying of 38CrMoAl steel by electron beam

TiN/Ni alloying of 38CrMoAl steel surface was carried out by continuous scanning electron beam. The effect of electron beam process parameters on the surface microstructures and mechanical properties of 38CrMoAl steel was studied. The results shows that the sample surface was divided into three regions: alloying layer, heat affected zone and substrate. Alloying layer made up with equiaxed crystals and short columnar crystals, microstructure of the heat affected zone was acicular and lath martensite, microstructure of substrate was tempered sorbate. The microhardness of the sample section first increased and then decreased, at a depth of 400 μm, the microhardness reached a maximum of 817.9 HV. When the beam current reached 12 mA and the moving speed reached 5.5 mm/s, the surface microhardness of the sample reached the highest 1209HV and the abrasion loss reached the lowest 4.6 mg.

Dissolution behavior of Al2O3 into tundish slag for high-al steel

Tundish slag composition is of vital importance to the control of steel cleanliness. In the present study, computation of phase diagram, accompanied with steel–slag reaction, was performed to preliminarily determine the tundish slag composition for high-Al steel 38CrMoAl, and the rotating cylinder method was, then, applied to further clarify the influence of slag composition on Al2O3 dissolution into tundish slag. Thermodynamic analysis suggested that SiO2-minimized CaO–Al2O3 (wt%CaO/wt%Al2O3 = 1.0–1.4) slag with MgO<6 wt% was suitable for tundish operation of 38CrMoAl steel. The results of rotating experiment indicated that the mass transfer in the liquid slag was the rate-limiting element of Al2O3 dissolution into the CaO–Al2O3 based slag and hence the dissolution rate was strongly related to the slag viscosity. The Al2O3 dissolution rate was found to be improved by increasing the wt%CaO/wt%Al2O3 ratio as well as adding small amounts of CaF2 and Na2O. The optimal slag composition for Al2O3 dissolution was put forward: wt%CaO/wt%Al2O3 = 1.1, MgO = 5 wt%, CaF2 = 6 wt%, Na2O = 5 wt%, and SiO2 content should be minimized. Results from plant trials demonstrated the benefit of inclusion removal for present tundish slag.

Influence of surface pores on selective laser melted parts under lubricated contacts: a case study of a hydraulic spool valve

ABSTRACT Hydraulic valve spools can be produced with hollow structures using SLM to increase dynamic response. The contact between the valve spool and body is crucial and relates to the performance of a hydraulic valve, which has not been studied. This paper investigates the reciprocating contact of an SLM-fabricated spool valve from a tribological aspect. By varying the process parameters, porous and standard spool samples (18Ni-300 steel) were produced using SLM. The lubricating behaviours of 18Ni-300 samples under various contact pressures and reciprocating frequencies were investigated in comparison to a real spool sample (hardened 38CrMoAl steel) using conventional manufacturing. The results indicate that the standard SLM 18Ni-300 spool sample has comparable tribological performance compared to the conventional manufactured 38CrMoAl sample. The SLM fabricated sample, with a number of large pores, has the highest friction coefficient under a wide range of contact conditions due to rough surfaces and cracks. Compared to the standard sample, the presence of a few small pores positively affects lubrication by providing local extra lubrication and serving as debris containers. Such an effect becomes very notable under low pressure, reducing the friction coefficients by half.

EFFECT OF NITROGEN HYDROGEN RATIO ON PLASMA NITRIDING FOR 38CrMoAl

Critical nitrogen hydrogen ratio in plasma nitriding was primarily investigated to get enhanced performance for 38CrMoAl steel. The modified surface layer was characterized by optical microscopy (OM), X-ray diffraction (XRD) and micro-hardness tester. The results showed that the critical nitrogen hydrogen ratio was 1: 5 while plasma nitriding at 540℃ for 6 h. Under this condition, no compound layer was formed, and accompanied with high surface hardness, while the compound layer was formed accompanied with lower surface hardness with nitrogen hydrogen ratio higher than the critical value.

Effect of Nitrogen Hydrogen Ratio on The Characteristics and Combined Properties of Plasma Nitriding Layer for 38Crmoal

Critical nitrogen hydrogen ratio in plasma nitriding was primarily investigated to get enhanced performance for 38CrMoAl steel. The modified surface layer was characterized by optical microscopy (OM), X-ray diffraction (XRD), micro-hardness tester and wear tester. The results showed that the critical nitrogen hydrogen ratio was 1:5 while plasma nitriding at 540℃ for 6h. Under this condition, no compound layer was formed, and more importantly, brittleness was significantly decreased, accompanied with high surface hardness, while the compound layer was formed accompanied with lower surface hardness and serious brittleness upon nitriding with nitrogen hydrogen ratio higher than the critical value.

Corrosion Behavior of Active Screen Plasma Nitrided 38CrMoAl Steel under Marine Environment

The 38CrMoAl steels were nitrided at different temperatures for 7 h using active screen plasma discharge. The analysis showed that the thick compound layer composed of ε-Fe2–3N and γ′-Fe4N was formed on the surface. The corrosion behavior was evaluated by measuring the anodic polarization curves in natural sea water (similar 3.5% NaCl solution), and observation of corroded surface were conducted. The electromechanical measurements indicated that the corrosion potential of the nitrided specimens shifted to a nobler value compared to that of untreated specimens. Passive regions were also observed in the polarization curves for all the nitrided specimens. These results indicate that active screen plasma nitriding can enhance the corrosion resistance of the 38CrMoAl steel under marine environment.

Effect of scanning speeds on microstructure and wear behavior of laser-processed NiCr–Cr3C2–MoS2–CeO2 on 38CrMoAl steel

Self-lubricating wear-resistant NiCr–Cr3C2–MoS2–CeO2 layers were fabricated on 38CrMoAl extruder screws by laser processing. The effect of scanning speeds on microstructure, phases, microhardness, and wear behavior was investigated. The obtained results indicate that the laser-processed layers had fine and nonuniform microstructures with undissolved MoS2 particles distributed on the matrix. With an increase of the laser-scanning speeds, the microstructures changed from hypoeutectic to hypereutectic, volume fraction of martensite increased, microhardness increased, and thickness and friction coefficients of the layers decreased. Wear resistance of the optimized layer was increased by 29.76 times compared with that of the substrate. The undissolved MoS2 was separated from the matrix on loading. In addition to the grain-refining and solution-strengthening effects, oxide films formed on the surface of the layers shielded them and enhanced their wear resistance. The crack or fracture behavior of the laser-processed layers on loading was determined by its toughness, which also had an important effect on the wear behavior of the processed layers.