300M Ultra-high Strength Steel Research Articles

Effect of quenching and tempering treatments on microstructure and mechanical properties of 300M ultra-high strength steel fabricated by laser powder bed fusion

To achieve high-performance 300 M steel parts through the Laser Powder Bed Fusion (LPBF) additive manufacturing process, post-heat treatments are indispensable. Herein, the effects of quenching and tempering treatments on the microstructure and mechanical properties of LPBF-fabricated 300M ultra-high strength steel were investigated, and the relevant strengthening and toughening mechanisms were analyzed. The microstructure of quenched samples primarily consisted of quenched martensite with minor amounts of bainite and some grain boundary allotriomorphic ferrite. The quenched samples presented significantly higher strength than the 300M forgings, primarily attributed to the contributions of solid solution strengthening, grain boundary strengthening and dislocation strengthening. After following tempering treatment, the microstructure of LPBF-fabricated samples mainly consisted of tempered martensite with minor amounts of bainite and residual austenite. Compared to the quenched samples, the tempered samples exhibited a decrease in strength while demonstrating a significant increase in ductility. The samples treated with the optimal heat treatment process (900 °C/1 h/Oil Cooling for quenching + two times of 300 °C/2 h/Air Cooling for tempering) demonstrated a remarkable strength–ductility balance, with a yield strength (YS) of 1834 MPa, an ultimate tensile strength (UTS) of 2099 MPa, and an elongation (EL) of 10.2%, which are all beyond or comparable to those of 300M forgings.

Improvement of corrosion and wear resistances of 300M ultra high strength steel by low temperature cathode assisted plasma nitriding

This study intends to systematically study the influence rule and mechanism of low temperature cathode assisted plasma nitriding (LTCPN) on the corrosion and wear properties of 300M steel. The research results were as follows: LTCPN technology effectively improved the nitride efficiency by accelerating the ionization rate of the working medium and the activity of nitrogen ions, so that the 300M steel could obtain the nitrided layer of 4 μm, 10 μm, 60 μm, 170 μm and 210 μm at 250 °C, 300 °C, 350 °C, 400 °C and 450 °C. LTCPN technology effectively improved the corrosion resistance of samples at 250 °C ~ 450 °C. Among them, more excellent corrosion resistance could be produced on the sample surface by LTCPN-treated at 350 °C, which attributed to introducing more ε-Fe3N phases, higher residual compressive stress, and lower surface roughness. In addition, LTCPN technology also reduced the wear damage of 300M steel at different temperatures. LTCPN-treated sample at 300 °C achieved the best wear resistance due to the introduction of the higher hardness and surface compressive residual stress (CRS), deeper nitride layer, and lower surface roughness on the sample surface. The above results showed that LTCPN treatment had a great application prospect in synchronously improving the wear and corrosion behavior of martensitic ultra-high strength steel.

Deformation behavior and microstructure evolution of 300M ultrahigh strength steel subjected to high strain rate: an analytical approach

In this paper, the deformation behavior and microstructure evolution of 300M steel are comprehensively studied by using the split-Hopkinson pressure bar technology, with an emphasis on the analytical estimate of material flow and microstructure distribution subjected to high strain rate. It is found that the grains have been significantly refined due to dynamic recrystallization (DRX) and major continuous DRX supplemented by few discontinuous ones governs the microstructure evolution. The dislocation activities associated with the angle change of grain boundaries and mechanical twinning dominate the deformation mechanism of 300M steel under high strain rate. Besides, nanoparticles in the form of carbide precipitation are uniformly distributed in the deformed zone, which strengthens the material by pinning the dislocations. A thermo-mechanical coupled analytical model considering dynamic recovery and dynamic recrystallization was innovatively developed, based on which the distribution of grain size and microhardness was predicted. The results indicated that the flow behavior described by the models and the calculated grain size as well as microhardness are proven to agree well with the results of experimental analysis.

Development and Improvement of Phenomenological Constitutive Models for Thermo-Mechanical Processing of 300M Ultra-High Strength Steel

Development and Improvement of Phenomenological Constitutive Models for Thermo-Mechanical Processing of 300M Ultra-High Strength Steel

Cutting Force Prediction for Trochoid Milling of 300M Ultra-High Strength Steel

Trochoid milling can improve the quality of machining of difficult materials as well as the efficiency of machining. However, its complex tool trajectory makes it difficult to predict the instantaneous cutting forces during cutting. Therefore, in this paper, the transient cutting thickness model in the cycloidal milling process was established using numerical combined with analytical methods, and the semi-mechanical cutting force model was established. Experiments were designed to compare the differences between the cutting force coefficients extracted from the slot milling experiments and those extracted from the trochoid milling. Finally, experiments were designed to validate the established cutting force model. The results showed that there was an error of 5–23% between the tangential cutting force coefficients extracted from slot milling and the tangential cutting force coefficients extracted from trochoid milling, while there was an error of 21–35% in the radial cutting force coefficients, indicating that the cutting force coefficients extracted from slot milling cannot be used to predict the cutting force in the trochoid milling process. It was verified that the error of the established cutting force model in predicting the cutting force of trochoid milling was 12%, indicating that the established model has a high accuracy, which provides a theoretical basis for the selection of cutting parameters and parameter optimization in the future.

Study on the surface integrity distribution of 300M ultrahigh strength steel subjected to different surface modification treatments

The surface integrity of 300M steel subjected to shot peening (SP), laser shock peening (LSP), ultrasonic surface rolling process (USRP), and hybrid laser shock peening with ultrasonic surface rolling process (LSP + USRP) processes were compared. The results indicate that USRP and LSP + USRP generate a smooth surface with Ra in the range of 0.05 μm ~ 0.10 μm while SP and LSP increase the Ra magnitude regarding grinding by 56.5 % and 18.8 %, respectively. Severe plastic deformation is introduced on the treated specimens, owing to which a gradient microstructure with nanostructured grains at the topmost surface (320 nm ~ 1130 nm in thickness) is observed. The depth of the compressive residual stress layer after SMTs achieves in the range of 200 μm ~ 2000 μm, of which the LSP + USRP generates the maximum value. The magnitude of surface compressive residual stress significantly increases compared with the control sample, which locates in the range of −709 MPa ~ −1167 MPa. An obvious work hardening is characterized after SMTs, of which the SP process presents a 31.2 % increase in the magnitude of surface microhardness and LSP + USRP holds the deepest hardening layer of 600 μm ~ 700 μm. Comparing the single SMT, the hybrid LSP + USRP treatment was found to be the most effective surface modification technique.

Influence of heat treatment (routes) on the microstructure and mechanical properties of 300M ultra high strength steel

Influence of heat treatment (routes) on the microstructure and mechanical properties of 300M ultra high strength steel

On the Deformation Behavior and Microstructure Evolution of 300m Ultrahigh Strength Steel Subjected to High Strain Rate: An Analytical Approach

On the Deformation Behavior and Microstructure Evolution of 300m Ultrahigh Strength Steel Subjected to High Strain Rate: An Analytical Approach

Microstructure and properties characterization of Ti-containing Ni60/Graphite self-lubricating composite coatings applied on 300M ultra-high strength steel by laser cladding

To improve the wear and corrosion resistance of 300M ultra-high strength (300M) steels, the Ni-based alloy (Ni60)/nickel-coated graphite composite coatings with the addition of titanium (Ti) were claded on 300M by laser. The microstructure, micro-hardness, tribological performance, corrosion resistance, thermal property, and dynamic mechanical property of the coatings were characterized. The cladding-layer microstructure of the Ti-containing (6 wt% Ti) coatings showed an equiaxial tendency. The microhardness of the Ti-containing coatings was higher and more homogeneous. The wear rate of the matrix was 29.4 times higher than that of Ti-containing composite coatings and was 2.4 times larger than that of the Ti-free (0 wt% Ti) composite coatings. However, the friction coefficient of the Ti-containing composite coatings was higher than that of the Ti-free composite coatings. The self-corrosion current densities of the Ti-containing, Ti-free composite coating and 300M were 0.25, 3.16 and 232.51 μA/cm2, respectively, indicating that the corrosion resistance of Ti-containing composite coatings was improved. The impact-resistance of the Ti-containing composite coatings was better than that of the Ti-free composite coatings.

Effects of ultrasonic nanocrystal surface modification on the surface integrity, microstructure, and wear resistance of 300M martensitic ultra-high strength steel

Abstract In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment on the surface integrity, microstructures and wear resistance of 300M ultra-high strength steel (300M steel) were investigated. The results showed that surface roughness of 300M steels after UNSM processing was significantly decreased with a lower scanning speed even though the surface roughness values were higher than that of mechanically polished control samples. In addition, the surface hardness of 300M steel was significantly enhanced as the static load increased. It was found that using a static load of 50 N and a scanning speed of 250 mm/min in the UNSM process can significantly improve surface hardness (797 HV) while slightly increasing the surface roughness. With these parameters, the resulting microstructure of UNSM-processed samples have three layers: the layer of severe plastic deformation, the layer with gradual plastic deformation, and the unaffected layer. Due to the plastic deformation, greater and deeper compressive residual stresses were induced in the UNSM-processed samples. In addition, the wear resistance of UNSM-processed samples was significantly improved, which was attributed to the refined martensite laths, work hardening and compressive residual stress.

Microstructural evolution and mechanical properties of 300M steel produced by low and high power selective laser melting

300M ultra-high strength steel has been widely used in critical structural components for aviation and aerospace vehicles, owing to its high strength, excellent transverse plasticity, fracture toughness and fatigue resistance. Herein, low and high power selective laser melting (SLM) of 300M steel and their microstructural evolution and mechanical properties have been reported. The results show that the optimal energy density range with the highest relative density for SLMed 300M steel is between 60 and 160 J/mm3. Furthermore, molten pools for deposition exhibit a conduction mode with semi-elliptical shape at a lower laser power of 300–600 W but a keyhole mode with “U” shape at a higher laser power of 800–1900 W. The heterogeneous microstructure of as-built samples is characterized by a skin-core structure which is that tempered troostite with the coarse non-equiaxed grains in the molten pool is wrapped by tempered sorbite with the fine equiaxed grains in the heat-affected zone. The skin-core structure of SLMed 300M steel has the characteristics of hard inside and soft outside. The average microhardness of samples varies from 385 to 341 HV when laser power increases from 300 to 1900 W. Interestingly, ultimate tensile strength (1156–1193 MPa) and yield tensile strength (1085–1145 MPa) of dense samples fabricated at different laser powers vary marginally. But, the elongation (6.8–9.1%) of SLMed 300M steel is greatly affected by the laser power.

Effect of microstructure on the Charpy impact properties of directed energy deposition 300M steel

Direct manufacturing techniques, such as directed energy deposition (DED), are able to produce complex components efficiently. In this study, microstructure evolution and impact toughness of DED 300M ultra-high strength steel are investigated. The results show that the microstructure of the as-deposited DED 300M ultra-high strength steel is mainly composed of martensite and some blocky bainite. The micro-segregation of elements is observed within the interdendritic area. After heat treatment, the microstructure becomes uniform and consists of martensite and lower bainite. The impact toughness of the as-deposited DED 300M ultra-high strength steel is 9 J/cm2, while it is significantly increased to 25 J/cm2 after heat treatment. Furthermore, it is observed that the fracture mode of the as-deposited sample is quasi-cleavage fracture. During the process of propagation, the main cracks would go across the martensite packet and deflect in the another one, and secondary cracks also deflected in the high-angle grain boundaries. By contrast, the fracture mode of heat-treated DED 300 M steel is ductile fracture.

The effect of ultrasonic nanocrystal surface modification on low temperature nitriding of ultra-high strength steel

In this research, a surface plastic deformation layer was induced on 300M ultra-high strength steel using ultrasonic nanocrystal surface modification (UNSM). The UNSM-treated and control specimens were then nitrided at 450 °C for 6 h. After gas nitriding, the microstructure, corrosion and wear resistance of 300M steel with and without UNSM pre-treatment were investigated. After nitriding, the UNSM-treated specimens generated a dense surface nitride layer that was thicker than that of the control specimens. The high defect density and refined lath martensite induced by UNSM were found to accelerate the nitrogen diffusion and efficiency. X-ray diffraction patterns revealed that α-Fe phase occupied the largest proportion in the nitriding layer of specimens without UNSM pre-treatment. However due to the higher nitriding efficiency, the main phase of UNSM-treated specimens after nitriding was found to be ε-Fe2-3N. Compared with the specimens without pre-treatment, UNSM-treated specimens exhibited higher surface hardness as well as higher corrosion and wear resistance after nitriding.

Hard turning multi-performance optimization for improving the surface integrity of 300M ultra-high strength steel

Hard turning technology was proven effective in enhancing the surface finish and dimensional accuracy of hardened steel. For this reason, it is used for finishing operations in the manufacturing of some critical aircraft landing gear components where bulk material hardness exceeds 45 HRC such as 300M ultra-high-strength steel. Nonetheless, the selection of cutting conditions remains critical to ensure generated surface characteristics meet the performance requirements. In this context, this study focuses on the optimization of hard turning cutting conditions to reduce surface roughness, increase compressive surface residual stresses, and reduce surface white layer thickness of 300M ultra-high-strength steel (55 HRC). To this end, a design of experiments (DoE) is used to investigate the effects of cutting tool (T), cutting speed (V), feed rate (f), and depth of cut (D) during hard turning. The cutting tool materials investigated include physical vapor deposited AlTiN–coated cemented carbide, mixed ceramic, and polycrystalline cubic boron nitride (PCBN), all commonly used in hard turning. Three different optimization approaches are evaluated and compared, namely the single-response Taguchi method, the multi-response grey relational analysis (GRA), and the proportion quality loss reduction (PQLR) methodologies. Because responses were found to be correlated, the selected multi-response optimization approaches were combined with the principal component analysis (PCA) method to transform correlated parameters into uncorrelated ones. The effect of cutting parameters and their interactions on surface roughness (Ra) and white layer thickness (WL) were considered in detail, particularly the effect of cutting tool material. Results demonstrate that the PCA-based GRA approach is a very suitable optimization technique for hard turning of 300M steel. Under those optimized conditions, Ra was decreased by 50%, and WL was decreased by 6% while compressive axial surface residual stress (ASRS) and hoop surface residual stress (HSRS) were increased by 307% and 74%, respectively.

Improving the fretting and corrosion fatigue performance of 300M ultra-high strength steel using the ultrasonic surface rolling process

300M ultra-high strength steels (300M steels) are frequently used in the manufacture of aircraft landing gear due to their high strength and ductility. However, their high sensitivity to surface defects accelerates fatigue failure and hinders their wider application. In this work, ultrasonic surface rolling processing (USRP) was used to process 300M steel. The surface roughness, hardness, microstructure, and residual stresses before and after USRP treatment were compared. The surface roughness for USRP-treated samples (0.062 μm) was found to be lower than that for untreated samples (0.32 μm). In addition, a plastically deformed layer was generated on the surface of USRP-treated samples that resulted in higher hardness. Beneficial compressive residual stresses were introduced as a result of USRP treatment. The better surface finish, higher surface hardness and compressive residual stresses lead to significant improvement in the resistance of the 300M steels to fretting fatigue and corrosion fatigue. The fretting fatigue life increased from 11.9 K cycles to 56.3 K cycles, while the corrosion fatigue life increased from 29.9 K cycles to 702.1 K cycles.

Research on the High Temperature Constitutive Model of 300M Ultrahigh Strength Steel

300M ultrahigh strength steel has good mechanical properties. It has been widely used in the force bearing components of aircraft. In this paper, By using Gleeble1-500D thermal simulator, we studied the change regularity of stress-strain curve of 300M steel using hot compression deformation when temperature is from 800°C to1100°C, strain rate is from 0.001 S-1to 1 S-1 and the strain is 0.7.The experimental results showed that when the strain rate is constant, the flow stress and the peak stress decrease with the increase of deformation temperature. When the deformation temperature is constant, the flow stress and peak stress increase with the increase of strain rate. From the test, we got the true stress-strain curve, calculated the thermal deformation constants such as the deformation activation energy of 300M ultrahigh strength steel. Eventually, we built the thermal deformation constitutive model in hyperbolic sine form of 300M steel.

Mechanism of corrosion fatigue cracking of automotive coil spring steel

The AISI 300M ultra-high strength steel was applied for the automotive suspension coil spring. Recently, some premature failures were reported, which caused by synergistic effect of cyclic mechanical stress and corrosion, namely corrosion fatigue cracking. In this study, the accurate mechanism of corrosion fatigue cracking for coil spring steel was studied for the proper prevention method against the catastrophic failure. Fatigue life was evaluated in 5 wt% NaCl solution under the anodic dissolution and hydrogen embrittlement conditions, which is simulated by applying constant potentials. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis indicated that the corrosion fatigue cracking was initiated at the MnS inclusion of the pit initiation site. The calculation of hydrogen production corresponding to each corrosion fatigue test condition revealed the two operating mechanisms of the cracking process. The corrosion fatigue cracking failure of coil spring steel was mainly caused by the anodic dissolution combined with hydrogen embrittlement.

Milling Force Modeling and Experimental Research of 300M Ultra High Strength Steel

300M ultra high strength steel, a new type of steel with broad prospects for development, has good mechanical properties, and is widely used for manufacture of aircraft landing gear. In order to reveal influence law of cutting parameters on milling force of 300M ultra high strength steel, the influence law of feed rate, milling width, and depth of cut and spindle speed on milling force is firstly studied through the single factor experiments in this paper. Secondly, the influence level of experimental factors is compared by orthogonal experiment. Finally, combined with orthogonal test data and the least square method, the multiple linear regression model of milling force in 300M ultra high strength steel milling is built. The accuracy of the model has been verified well by experimental verification, which has the guiding significance to reveal the milling mechanism and actual production.

Optimization of Parameters of Aircraft Landing Gear with Orthogonal Turn-Milling Based on GRA-PSO Algorithm

In the light of the characteristic of 300M ultra high strength steel and the feature of orthogonal turn-milling machining,an optimization model of orthogonal turn-millng machining parameters is consisted of maximum tool life,minimum surface roughness and maximum productivity. Based on multi-objective optimazation algorithm which is applied in coupling particle swarm optimization algorithm and gray relevancy analysis,it can achieve the purpose which is above mentioned. By introducing the chatter stability lobe diagram of aircraft landing gear with orthogonal turn-milling which is conformed with DMG turn-milling machine tool,it can optimize the parameters of the orthogonal turn-milling machining of the aircraft landing gear with high efficiency and good quality.

Enhancement of mechanical properties and failure mechanism of electron beam welded 300M ultrahigh strength steel joints

In this study, four post-weld heat treatment (PWHT) schedules were selected to enhance the mechanical properties of electron beam welded 300M ultrahigh strength steel joints. The microstructure, mechanical properties and fractography of specimens under the four post-weld heat treatment (PWHT) conditions were investigated and also compared with the base metal (BM) specimens treated by conventional quenching and tempering (QT). Results of macro and microstructures indicate that all of the four PWHT procedures did not eliminate the coarse columnar dendritic grains in weld metal (WM). Whereas, the morphology of the weld centerline and the boundaries of the columnar dendritic grains in WM of weld joint specimens subjected to the PWHT procedure of normalizing at 970°C for 1h followed by conventional quenching and tempering (W-N2QT) are indistinct. The width of martensite lath in WM of W-N2QT is narrower than that of specimens subjected to other PWHT procedures. Experimental results indicate that the ductility and toughness of conventional quenched and tempered joints are very low compared with the BM specimens treated by conventional QT. However, the strength and impact toughness of the W-N2QT specimens are superior to those of the BM specimen treated by conventional QT, and the ductility is only slightly inferior to that of the latter.