AF1410 Steel Research Articles

Influence of Electron Beam Welding with Multiple Beams on Stress Corrosion Properties of AF1410 Steel

Electron beam welding (EBW) with multiple beams is a new technology simultaneous with preheating or postheating, which contributes to reducing residual stresses. To improve corrosion resistance in marine, EBW with multiple beams is employed on AF1410 steel. The weld is uniform, with a width of 7.3–8.4 mm, which is wider than that of conventional welding. To evaluate susceptibility to stress corrosion cracking (SCC), the welding stresses and slow strain rate tests (SSRT) are studied. The longitudinal stresses on the front weld with preheating and postheating are 25% and 15% lower than conventional welding. The transversal stresses also, respectively, decreased by 15% and 6%. The tensile properties of EBW from SSRT present a susceptibility to SCC. Compared with conventional welding, the loss of elongation I δ with preheating and postheating decreases to 0.9–1.5%, and the area reduction rate I R lowers to 7–10%. EBW with multiple beams presents a low susceptibility, attributed to reducing welding stresses related to a temperature gradient.

Test Study on Strength of Laser Additive Manufacture AF1410 Steel I-Shaped Beam

The static and fatigue strength of laser additive manufactured AF1410 steel I-beam were tested by a four-point bending test, and the same method was used to test the conventional forged, machined AF1410 short steel beams. The fatigues test data of both short beams were analyzed by DFR method. The test and analysis results show that the static strength of laser additive short beams is close to conventionally fabricated short beams, and the fatigue performance is weaker than that of forged, machined short beams.

Microstructures and mechanical properties of AF1410 steel processed by vacuum electron beam welding with multiple beams

Abstract Electron beam welding (EBW) with multiple beams is an advantageous technology to weld parts, as it contributes to decreasing welding distortions and improving mechanical properties. EBW with multiple electron beams was applied to welding simultaneously with auxiliary heating, in a rhombus scanning design, and the energy ratio was 1:1 for AF1410 steel welding. The welds of EBW with multiple beams were nail shaped with a width of 2.54 mm, which were more uniform than those of conventional EBW, and the transversal and longitudinal distortions were lower. The microstructures of specimens processed by EBW with multiple beams contained martensite and a small amount of austenite, and the martensite laths were smaller and more homogeneous than those of conventional EBW. The microhardness values were also more uniform than those of conventional EBW specimens. The tensile strengths of the joints were above 1754 MPa, equivalent to those of conventional EBW, and the percentage elongations were above 9.7 %, which were higher than those of conventional EBW. The microstructure homogeneity and refinement of EBW with multiple beams contributed to improving the mechanical performance.

Experimental and Numerical Investigation of Stress and Distortion in AF1410 Steel Under Varying Quenching Conditions

Experimental and Numerical Investigation of Stress and Distortion in AF1410 Steel Under Varying Quenching Conditions

Residual stress and distortion in thick-plate weld joint of AF1410 steel: finite element simulations and experimental studies

The quantification of the residual stress and distortion in the thick-plate weld joint of AF1410 steel has great significance, which is the basis for the safety and process design of the component. Therefore, this paper systematically investigated the welding residual stress and distortion distribution in the 10 mm thick welded plate for AF1410 steel by tungsten inert gas welding. The residual stress measurements were carried out by the X-ray diffraction method and advanced contour method, and the distortion was determined by coordinate measuring machine. The developed thermo-metallurgical-mechanical finite element model was applied to predict the residual stress and distortion in multi-pass welding considering solid-state phase transformation (SSPT) and transformation plasticity. The measured residual stress and distortion distribution were in good agreement with the finite element simulation results. The comparison results revealed that the residual stresses in the upper and lower parts of the welding plate were small, and there was apparent stress concentration in the center of the welding joint. SSPT and the subsequent thermal cycle had a significant influence on the magnitude of final residual stress. The accurate finite element model and the understanding of stress formation mechanism are helpful to control the residual stress and distortion distribution of aviation parts reasonably.

Transformation plasticity of AF1410 steel and its influences on the welding residual stress and distortion: Experimental and numerical study

Welding residual stresses and distortions have significant consequences on the final quality and service life of high Co–Ni ultra-high-strength steel structural parts. This paper sought to understand and explain the role of transformation plasticity on the welding residual stress and distortion for AF1410 steel. The transformation plasticity was firstly measured by experimental methods. Subsequently, the influence of transformation plasticity on the welding residual stress and distortion was investigated using numerical simulation and experimental methods. The simulated residual stress considering the transformation plasticity had good agreements with experimental results measured by the contour method and XRD. Meanwhile, transformation plasticity decreased the magnitude of stress variation, but its influence on the distortion was not apparent for AF1410 steel. The results contribute to improving the prediction accuracy of welding residual stress and distortion in AF1410 steel and laying a theoretical foundation for the accurate manufacturing of aerospace components.

Influence of last stage heat treatment on microstructure and mechanical properties of laser additive manufactured AF1410 steel

In order to optimize the mechanical properties of laser additive manufactured (LAM) AF1410 steels, two temperatures of 505°C and 515°C were selected for the last stage tempering treatment. Microstructure and compositions were observed by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The mechanical properties were examined by tensile tests and fracture toughness. Results showed that after heat treatment, the microstructure of LAMed AF1410 steels mainly consisted of fine dispersion carbides, lath martensite and film-like reversed austenite. The increase of tempering temperatures from 505°C to 515°C caused the coarsening of carbides and increasing amount of reversed austenite. Consequently, the ultimate tensile strength (UTS) and yield strength (YS) dramatically decreased about 9% and 8% respectively. While the elongation (EL) and the reduction in area (RA) slightly increased from 13.3% and 66.3% to 15.0% and 67% respectively. What's more, the change of tempering temperatures only had small impact on fracture toughness of steels due to the opposite effect of the coarsened carbides and increase number of reversed austenite. In consideration of tensile properties and fracture toughness, the optimum comprehensive mechanical properties were obtained when tempering temperature was 505°C.

The Influence of High‐Temperature Deformation and Heat Treatment on Microstructure of AF1410 Ultra‐High Strength Steel

Hot compression tests of AF1410 ultra‐high strength steel are studied on a Gleeble‐3800 thermo‐mechanical simulator. The dynamic recrystallization behavior and microstructure evolution are analyzed with compression tests at deformation temperatures of 850–1150 °C and strain rates of 0.001–1 s−1. The results suggest that dynamic recrystallization grains of AF1410 steel grow with deformation temperature rising and strain rate decreasing. The coarse dynamic recrystallization grains are obtained at high temperature with low strain rate. The fine grains are obtained at low temperature with high strain rate, while recrystallization is incomplete in this situation. Fine equiaxed grains are obtained at deformation temperatures of 950–1050 °C and strain rates of 0.1–1 s−1, when dynamic recrystallization occurs completely. Then, the hot compression specimens are normalized at 900 °C for 1 h and tempered at 680 °C for 6 h. Compared with the compression specimens, it is found that there are relatively uniform fine grains after the heat treatment, and the grain size ranged from 14 to 23 µm. TEM analysis results show that coarse precipitates mainly include needle‐shaped M2C carbide and square‐shaped M23C6 carbide. There is no coherent relationship between the carbides and the martensite matrix.

Fatigue Properties of AF1410 Steel Welded Joint by Electron Beam Welding

Fatigue test of AF1410 steel and two thickness of electron beam have been done, and fatigue properties of the base metal and EB-welded joints have been studied. The results showed that fatigue limit of electron beam welded joints was close to that of base metal under this test conditions, and the welded thickness has little effect on S-N curves of electron beam welded samples under this test conditions. From SEM fracture morphology, it can be seen that fracture morphology of the welded samples was not obvious different form base metal. In the instant-off area of electron beam welded sample, there was dimple-like morphology showing good ductility.

Influence of Radial Depth of Grinding and Finishing Process on Surface Residual Stresses in Grinding AF1410 Ultrahigh Strength Steel

AF1410 steel is a kind of high alloy secondary hardening ultrahigh strength steel, which is developed for structural applications where the combination of high strength and high fracture toughness is required. The distribution of residual stresses affects the fatigue life and stress corrosion resistance of the components in service. The distribution of surface residual stresses on the components should be controlled by the machining process. Little investigation about the residual stresses on AF1410 steel had been studied previously. In this study, two AF1410 cylindrical workpieces were machined by cylindrical grinding with a white alumina (WA) grinding wheel and under water base cooling fluid. Two groups of experiments were set to investigate the influences of different radial depths of grinding and the finishing process on the residual stresses. The residual stresses along grinding and feed directions were measured respectively using X-ray method. The rule of the residual stresses variety with the radial depth of grinding (ap) was studied. The reasons causing the distinctions of the residual stresses between two groups of experiments were analyzed and the optimized grinding parameters were obtained.

The Influence of Milling Parameters on Surface Residual Stresses during Milling AF1410 Ultrahigh Strength Steel

AF1410 steel is a kind of high alloy ultrahigh strength steel with perfect hardness, strength and fracture toughness after secondary hardening heat treatment. The distribution of residual stresses affects the fatigue life and stress corrosion resistance of the components in service. Little investigation about the residual stresses on AF1410 steel had been studied previously. The distribution of surface residual stresses on the components should be controlled by the machining process. In this study, two AF1410 workpieces machined by the orthogonal end-milling experiment of AF1410 were performed. The axial depth of cut, cutting speed, feed rate per tooth and radial depth of cut were involved in to the experimental factors. The residual stresses were measured by X-ray diffraction method. The influence of milling factors on distribution of surface residual stresses was studied with range analysis method. The influence sequence of the factors on surface residual stresses were obtained and the optimum value of cutting parameters were selected.

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that corrosion-induced surface roughness has on the fatigue life of high-strength steel aircraft components. The steels of interest produce general corrosion in patches as well as localized material loss similar to pitting. In addition, this type of corrosion has characteristic features over a wide range of scales. Consequently, traditional finite element analysis approaches are not well suited to this problem, since the mesh required to accurately reflect the fine details distributed over the entire corrosion patch make computation unrealistic. Therefore, approximate methods were developed that allow localized regions of interest of high stress to be identified. Subsequently, a simple notch metric formula is employed to approximate the stress riser in these regions of interest. Finally, an extension of Peterson’s fatigue notch sensitivity theory is applied to these small “notches” that has the result of suppressing the effect of smaller notches compared to larger notches in the prediction of life. Each region of interest is assigned a probability of crack initiation as a function of fatigue cycles, based on a probabilistic strain–life analysis using the predicted notch factor. The net life (to crack initiation) for the component is then the product of the survivabilities of all of the individual regions of interest on the component surface. Tests on corroded fatigue specimens have been conducted to both calibrate the parameters in the Peterson model as well as to test the life prediction capability of the approach. Predictions from the resulting model have demonstrated that an empirical approach to corrosion surface damage can be utilized to generate probabilistic life predictions that have substantial engineering value in assessing the residual fatigue life of corroded AF1410 steel components, and that the modeling technique can capture the significant corrosion features that cause fatigue cracking in most cases, especially for more severely corroded surfaces.

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model: Part I: Test development and results

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. As part of a NAVAIR High Strength Steel Corrosion–Fatigue Assessment Program, methods were studied to predict the impact that corrosion-induced surface roughness has on the fatigue life of high-strength steel aircraft components. In order to adequately capture the corrosion damage features that cause fatigue cracking, a representative set of well-characterized corrosion–fatigue test results were generated to be used for model development. The test specimens fabricated for this program consisted of bare, unnotched AF1410 steel flat plates with a 25.4 mm diameter corrosion patch on one side. Two sets of test specimens were fabricated and tested, with one set abrasive blasted after heat treatment, and the other set hand polished after heat treatment. A method of growing corrosion in the laboratory was developed that consisted of filter paper soaked in a 3.5% NaCl solution and placed at the center of the test plate gage section, with a voltage applied across the filter paper to accelerate corrosion growth. High-resolution 3D surface topography data was collected from the corroded region on each test plate prior to fatigue testing using a commercial white-light interference microscope. Constant-amplitude fatigue tests were performed on corroded and uncorroded test plates at several different stress levels, for three different corrosion exposure levels. Post-test fractographic analysis of the corroded specimens indicate that all of the critical cracks originated from small corrosion notches on the order of 10–200 μm in width, 10–120 μm in height and 2–100 μm in depth. These notches were not considered to be pits in that the depth dimension was less than the surface dimensions. The repeatability of the fatigue initiating mechanism for corrosion damaged surfaces in this material indicates that it should be possible to develop a single modeling approach that reasonably captures the effects of corrosion notches in reducing fatigue life.

Hydrogen Transport Conditions and Effects in Cathodically Polarized AF1410 Steel

Hydrogen permeation of AF1410 steel membranes due to cathodic polarization using the Devanathan and Starchurski double cell (DSDC) with 0.1M H2SO4 + 1 g/L Na2HAsO4·7H2O, and 0.1M NaOH media in the input and exit cells, respectively, under Galvanostatic conditions depended on the polarization current density, membrane thickness, and surface roughness. For a 0.35-mm-thick membrane, the steady-state hydrogen permeated using increasing polarization currents from 1.00 to 10.00 mA varied correspondingly from 0.6 × 10−5 (mol H/m2s) to 1.03 × 10−5 mol H/m2s, with accompanying transient rates or permeation rates of 1.07 × 10−4 A/m2s to 4.40 × 10−4 A/m2s. With a constant polarization current density of 20 A/m2, the steady-state permeated hydrogen was in the range of 1.00 × 10−5 (mol H/m2s) to 3.50 × 10−5 (mol H/m2s), for 0.30-mm and 0.09-mm-thick membranes, respectively. The breakthrough times decreased from 2130 to 300 seconds with decreasing membranes thickness from 0.30 to 0.09 mm. The formation of blisters was observed more on the input side surface than on the exit-side surface and occurred for polarization charging current densities greater than 30.0 A/m2. The tendency for blister formation increased with decreasing material’s surface roughness. Cracks accompanying blisters tended to form on both the input and exit-side surfaces only with continued charging following the attainment of steady-state permeation, though they were generally lower on the potentiostated exit side. The average effective permeation coefficient of hydrogen was determined to be 2.89 × 10−12 m2/s for membrane thicknesses ranging from 0.09 to 0.30 mm based on the slope method.

Influence of Sizes of Inclusions and Voids on Fracture Toughness of Ultra-High Strength Steel AerMet100

Abstract Mechanical properties of the ultra-high strength steel AerMet100 aged at 454°C∼510°C were studied, and relationship between the critical crack tip opening displacement δIC and X0 (RV/RI)|R0 was calculated, where X0 was an average inclusion spacing and (RV/RI)|R0 was the void radius RV divided by the radius of the inclusion RI nucleating the void evaluated at the average inclusion size R0. The results showed that high fracture toughness could be reached after aging at 510 °C, and aging temperature affected fracture toughness apparently. δIC was in linear relationship with X0 (RV/RI)|R0 in the range of 8μm∼50μm. R0 was 0.53μm, X0 was 6.39μm for the tested steel, and the values of (RV/RI)|R0 were different for varied microstructures. The fracture toughness of AerMet100 steel was influenced by microstructures and inclusions greater than that of AF1410 steel.

Effect of Hydrogen and Hold Time on the Lifetime of AF1410 Steel

Fatigue lifetime of model AF1410 ultrahigh-strength steel as a function of fatigue hold time (time expended at peak loads) and type and severity of environment is presented. Results indicate significant reduction in lifetime as a function of rising hold time for specimens charged with hydrogen, whereas a parabolic trend was observed in the case of specimens tested in air and in the presence of simulated marine environment. Compared with baseline tests in air, a gradual reduction in lifetime was observed as a function of increasing concentration of hydrogen in the specimens. Micrographic, atomic force microscope, and scanning electron microscope analysis is performed to study the various aspects of AF1410 lifetime.

Fatigue and hydrogen embrittlement evaluation of AF1410 steel

AF1410 steel subject to lateral one-sided electrolytic hydrogen-charging and tested under fatigue at a stress ratio of 0.4 and at 1 Hz loading frequency displayed up to four times higher crack growth rate than specimens evaluated without exposure to hydrogen. Additionally, the hydrogen-attacked side underwent a change in the fracture mode from ductile to brittle, which can be either of intergranular, transgranular or quasi-cleavage nature. Scanning electron microscope and atomic force microscope studies as well as fracture surface analysis were conducted to correlate the fracture modes with the hydrogen embrittlement effects on the steel. Since hydrogen did not permeate the entire thickness of the specimens, the experiments provided a more realistic approach to the study of large aircraft components in marine service conditions.

Corrosion Fatigue of High-Strength Aircraft Structural Alloys

Results of corrosion fatigue characterization of AA7075-T6 and AF1410 steel under different simulated marine environments and loading conditions are presented. In comparison with baseline tests conducted in laboratory air, corrosion fatigue experiments performed at 1-Hz frequency in the presence of 1% NaCl environment indicated a substantial reduction in fatigue lifetime in the case of AA7075-T6, whereas AF1410 corrosion fatigue life was found to be statistically unaffected at 1-Hz frequency in the presence of 1% and 3.5%NaCl. However, a reduction of frequency to 0.5 Hz significantly reduced the lifetime of AF1410 steel. On the other hand, Cd-plated AF1410 tested to study fatigue characteristics in a hydrogen-rich metal surface environment yielded minimal change in the lifetime. Atomic force microscope analysis was performed to discern features in fracture surface morphology leading to changes in lifetime of AF1410 and AA7075-T6 alloys.

The effects of titanium additions on AF1410 ultra-high-strength steel

The mechanical properties and microstructure of two heats of AF1410 steel were compared. The first heat, heat 811, contained a titanium addition of 0.02 wt pct, while the second heat, heat 91, contained no titanium, manganese, or other strong sulfide formers. The sulfur in heat 811 was gettered as titanium carbosulfide, while in heat 91 the sulfides were chromium sulfide. The toughness of heat 811 was found to be much enhanced compared to heat 91, with Charpy impact energies of 176 J and 79 J and KIC fracture toughness values of 235 MPa.m1/2 and 170 MPa.m1/2, respectively. This significant difference in fracture toughness is attributed to the fact that titanium carbosulfide particles are more resistant to void nucleation than the chromium sulfide particles, which appear to nucleate voids at the onset of plastic strain. In addition to altering the sulfide particle type, the titanium addition also results in the presence of undissolved MC carbides in the titanium-modified steel in addition to the M2C carbides found in heat 91. These carbides act as grain growth inhibitors, resulting in a finer prior austenite grain size and martensite packet size in heat 811.

Lanthanum additions and the toughness of ultra-high strength steels and the determination of appropriate lanthanum additions

Studies of commercial heats of AF1410 steel suggest that under appropriate conditions additions of rare-earth elements can significantly enhance fracture toughness. This improvement in toughness is not due to an extremely low inclusion volume fraction but is apparently due to the formation of larger and more widely spaced inclusions. The purpose of this work is to discuss our experience in using rare-earth additions to laboratory scale vacuum induction melted and subsequently vacuum arc remelted heats of ultra-high strength steels to achieve inclusion distributions similar to those observed in commercial heats modified with lanthanum additions. The results indicate that lanthanum additions of 0.015 wt.% to low sulfur steels which have been well deoxidized using carbon-vacuum deoxidation can result in lanthanum rich inclusions which are similar in size, volume fraction and spacing to those obtained in commercially produced heats of ultra-high strength steel to which lanthanum has been added. The heat of steel to which lanthanum additions of 0.015 wt.% were made had significantly higher toughness than did the heat of the same steel in which the sulfur had been gettered as small and closely spaced particles of MnS and which had an inclusion volume fraction similar to that of the heat modified by the addition of 0.015 wt.% lanthanum. This improvement in toughness was attributed to an increase in inclusion spacing. An addition of 0.06 wt.% lanthanum was excessive. Such an addition of lanthanum resulted in a huge volume fraction of large cuboidal inclusions which primarily contain lanthanum and oxygen and which are extremely detrimental to toughness.