High Strain Rate Conditions Research Articles

Research on Compression Failure Characteristics and Damage Constitutive Model of Steel Fiber-Reinforced Concrete with 2% Copper-Coated Fibers Under Impact Load.

This study systematically investigates the mechanical properties of plain concrete (PC) and 2% steel fiber reinforced concrete (SFRC) under both static and dynamic loading conditions, utilizing advanced mechanical testing equipment and dynamic impact testing methods. The strain rate range studied spans from 10-4 s-1 to 483.12 s-1. Under static loading conditions, the maximum bearing capacity and energy absorption capacity of 2% SFRC are 2.16 times and 3.83 times greater than those of PC, respectively, indicating a significant enhancement in toughness and resistance to failure. Under dynamic loading conditions, the energy absorption capacity of SFRC increases to 6.36 times that of PC. The impact failure behavior of SFRC was analyzed using the split-Hopkinson pressure bar-digital image correlation (SHPB-DIC) method, revealing that the failure was primarily driven by splitting tension. The failure process was subsequently categorized into four distinct stages. At high strain rates, the dynamic enhancement factor, peak stress, and peak strain of SFRC exhibit a linear increase with strain rate, whereas the energy absorption capacity increases in a nonlinear manner. This study presents a simplified viscoelastic constitutive model with four parameters and develops a damage-based viscoelastic constitutive model with seven parameters, demonstrating its broad applicability. The findings offer both theoretical insights and experimental evidence to support the use of SFRC under high strain rate conditions.

Dynamic tensile behaviors and crack propagation in fiber-reinforced cementitious composites: Experimental investigation and peridynamic simulation

Fiber-Reinforced Cementitious Composites (FRCC) have gained significant attention in engineering applications due to their superior mechanical properties and toughness, particularly under high strain rate conditions. This study performed dynamic tensile tests on FRCC at high strain rates (35–110 s⁻¹) using a Split Hopkinson Tensile Bar (SHTB) apparatus. Additionally, a novel Peridynamic (PD) model was developed for the SHTB and FRCC system, leveraging the advanced capabilities of the emerging PD theory. The study compared and analyzed dynamic tensile strength, ultimate tensile strain, strain rate effects, failure modes, and crack development in FRCC with different fiber ratios at various high strain rates, using both experimental data and PD simulations. The results show that the PD-SHTB-FRCC dynamic model developed in this study exhibits high consistency between numerical simulations and experimental findings, effectively capturing the processes of crack initiation, propagation, and complete failure in FRCC specimens. The dynamic tensile properties of FRCC improve significantly with increased strain rates, with polyethylene (PE) fibers providing superior reinforcement compared to steel fibers. Notably, the dynamic tensile strength, peak tensile stress, and ultimate tensile strain of FRCC increase significantly with rising strain rates, with specimens containing higher PE fiber content showing a more pronounced enhancement effect. For strain rates between 42.6 s⁻¹ and 76.1 s⁻¹, considering dynamic tensile strength, ultimate tensile strain, and peak tensile stress, the optimal combination for resisting dynamic tensile loads was 1.5 % PE fibers and 0.5 % steel fibers. At a strain rate of 99.8 s⁻¹, a 2 % PE fiber ratio alone provided the best performance.

Parametric Analysis and Improvement of the Johnson-Cook Model for a TC4 Titanium Alloy

Titanium alloys are widely used in the manufacture of gas turbines’ compressor blades. Elucidating their mechanical behavior and strength under damaged conditions is the key to evaluating the equipment’s reliability. However, the conventional Johnson-Cook (J-C) constitutive model has limitations in describing the dynamic response of titanium alloy materials under the impact of a high strain rate. In order to solve this problem, the mechanical behavior of a TC4 titanium alloy under high strain rate and different temperature conditions was analyzed by combining experiments and numerical simulations. In this study, the parameters of the J-C model were analyzed in detail, and an improved J-C constitutive model is proposed, based on the new mechanism of the strain rate strengthening effect and the temperature softening effect, which improves the accuracy of the description of strain sensitivity and temperature dependence. Finally, the VUMAT subroutine of ABAQUS software was used for numerical simulation, and the predictive ability of the improved model was verified. The simulation results showed that the maximum prediction error of the traditional J-C model was 23.6%, while the maximum error of the improved model was reduced to 5.6%. This indicates that the improved J-C constitutive model can more accurately predict the mechanical response of a titanium alloy under an impact load and provides a theoretical basis for the study of the mechanical properties of titanium alloy blades under subsequent conditions of foreign object damage.

High strain-rate fracture behavior of a hollow projectile

In this paper, a hollow projectile made of AISI4340 steel was fabricated based on an arbitrary warhead shape, and high-speed impact tests were performed according to various target encounter conditions including velocity and angle. In order to characterize the dynamic fracture behavior, tensile tests were performed on various notch specimens under three strain rates (10–3 s-1, 100 s-1, 103 s-1), and the stress state histories of the specimens were calibrated through a hybrid experimental-numerical analysis. In particular, for the intermediate (100 s-1) and high (103 s-1) strain rate conditions, the local temperature rose due to adiabatic heating until fracture was experimentally measured, and the thermal softening behavior determined from the inverse optimization technique was considered for the dynamic constitutive model. For the comparison with the high-speed impact test results, a rate-dependent ductile fracture model was utilized for numerical simulation. Considering that the model parameters were calibrated with the thermal softening effect, the proposed fracture model implicitly takes temperature into account. The deformation and fracture modes of the projectile from experimental and numerical study showed very good agreement under all impact conditions. It was confirmed that the softening of a material by adiabatic heating should be considered along with strain rate hardening in dynamic fracture simulation.

Strain rate sensitivity of rotating-square auxetic metamaterials

This study provides an in-depth analysis of the mechanical behavior of rotating-square auxetic structures under various strain rates. The structures are fabricated using stereolithography additive manufacturing with a flexible resin. Mechanical tests performed on structures include quasi-static, intermediate, and high strain rate compression tests, supplemented by high-speed optical imaging and two-dimensional digital image correlation analyses. In quasi-static conditions (5 × 10–3 s-1), multiscale measurements reveal the correlation between local and global strains. It is shown that cell hinges play a significant role in structural deformation and load-bearing capacity. In drop tower impact conditions (intermediate strain rate of ca. 200 s-1), the auxetic structures display significant strain rate hardening compared to loading at quasi-static rates. The thin-hinge structures maintain a Poisson's ratio of approximately -0.8, showing higher auxeticity than slow-rate compression tests. High strain rate conditions (ca. 2000s-1) activate additional deformation mechanisms, including a delayed state of equilibrium exemplified by a heterogeneous distribution of lateral strains, possibly due to stress wave interactions and inertial stresses. The study further reveals nonlinear correlations between Poisson's ratio, strain, and strain rate, indicating reduced auxeticity at higher strain rates. These observations are discussed in terms of complex wave interactions and the strain rate hardening characteristics of the base polymer.

Spall response and microstructure evolution of additively manufactured AlSi10Mg alloy with different states

The spall response and microstructure evolution of additively manufactured AlSi10Mg alloy with different states were investigated systematically through plate impact experiments, microstructure and texture characterization and quasi-static tensile tests. The results show that the microstructure, texture and spall response are related to the impact velocity and material state. Before deformation and fracture failure occur, the as-built and annealed specimens possess the same <001> texture along the building direction; the former consists of numerous networks, columnar grains and fine equiaxed grains, and the latter is comprised of coarser grain structure and coarse particles. For both the as-built and annealed specimens, as the impact velocity increases, the Hugoniot elastic limit (HEL) stress and spall strength are slightly affected by the impact velocity; however, the peak shock stress tends to increase. Under the same impact velocity conditions, compared with the as-built specimen, the annealed specimen corresponds to a similar peak shock stress but a lower Hugoniot elastic limit stress and spall strength. Independent of the material state, as the impact velocity increases, the damage gradually increases, namely, from incipient spall to complete spall; the grain structure, including size and shape changes; and the texture remains almost unchanged. Under the same impact velocity conditions, compared with the as-built specimen, the annealed specimen has a coarser grain structure and a similar texture. Voids tend to nucleate at grain boundaries (at the bottom of the melt pool) and large particles. Compared with the as-built specimen, the annealed specimen has greater strain rate sensitivity. The effect of the material state on the tensile strength is dependent on the strain rate, and the annealing treatment may significantly decrease the tensile strength under low strain rate conditions; and weakly decrease it under high strain rate conditions. Finally, the spall strength dependence on the material state and the effect of the strain rate on the spall behavior were discussed.

Dynamic mechanical properties and uni-axial constitutive model of S30408 stainless steel

This paper investigates its mechanical properties at different strain rates and the uni-axial constitutive model of S30408 (S30408 known as 1.4301 in EN10088:1, 304 in ASTM standard) stainless steel. Firstly, the tensile and compressive mechanical properties of S30408 stainless steel were tested at four strain rates (0.001 s−1, 1000 s−1, 3000 s−1, 5000 s−1) by performing quasi-static tests as well as split Hopkinson tension bar (SHTB) and split Hopkinson pressure bar (SHPB) tests. Based on the tests, the stress-strain curves of S30408 stainless steel under tensile and compressive conditions at different strain rates were obtained. The results show that S30408 stainless steel revealed a significant strain rate strengthening effect, and there were some differences in the mechanical properties of S30408 stainless steel in tension and compression under different strain rates. Then based on these test results, a modified Johnson–Cook model was established under tensile and compression conditions. The accuracy of the proposed modified Johnson-Cook model was verified by the finite element software LS-DYNA. The modified model can provide a reference for the study of mechanical properties and computational simulation of S30408 stainless steel under high strain rate conditions such as impact and blast load.

Transitioning of deformation mode in bicrystalline Al-Mg alloy with Σ3 [1 1 1] 60° {11 8 5} faceted grain boundary

In this letter, the authors have elucidated the effect of alloying biocompatible and lighter magnesium (Mg) solute atoms in a bicrystalline aluminium (Al) solvent incorporated with a faceted coherent-incoherent grain boundary (GB) to analyze the tensile deformation mechanisms. Cryogenic temperature and high strain rate conditions were imposed through molecular dynamics simulations to report the detrimental effect of Mg addition on the tensile strength of Al-Mg alloys. Evidence of transitioning in deformation modes for pure Al and Al-Mg alloys was seen. On elaborating, for pure Al, GBs acted as the dislocation nucleation site; whereas for Al-Mg alloy, it was both the GBs and grains. It was observed that stacking faults (SFs) originated from GBs and propagated toward grains in Al. In contrast, in Al-Mg alloys, SFs were generated simultaneously from both GBs and grains. This simultaneous nucleation of dislocations and SFs from both GBs and grains renders bicrystalline alloys lower the elastic limit than pure metal. Conversely, beyond this elastic limit, the alloys exhibit higher flow stress than the pure metal due to the Mg-dislocation interactions. These findings offer valuable insights for tailoring the mechanical properties of Al-Mg alloys to meet aerospace, automotive and marine engineering-related application requirements.

Effect of interface type on deformation mechanisms of γ-TiAl alloy under different temperatures and strain rates by molecular dynamics simulation

Crystalline interface plays a significant role in strengthening lamellar γ-TiAl alloys through reconciling the strength and ductility. Herein, the effects of temperature and strain rate on the tensile deformation of three lamellar γ-TiAl interface models are investigated by molecular dynamics simulations. The three interfaces, pseudo twin (PT), rotational boundary (RB), and true twin (TT), exhibit different tensile responses due to the different interface effects: TT interface only acts as a barrier of dislocation traversing to facilitate crack extension; PT interface acts as both dislocation barrier and emission source and has a stronger release of strain energy than TT interface, retarding the crack extension; RB interface can retard and resist crack extension due to the blunting and deflection of the crack tip and the best interface geometry compatibility. The defect evolution indicates that the elevated temperature suppresses dislocation propagation at low strain rate, while the high strain rate causes small lamellar stacking faults and slit-shaped holes along tensile direction at low temperature. In addition, the dual conditions of high strain rate and low temperature induce the phase transition from FCC to BCC and then BCC to HCP. These findings provide a specific insight to understand the atomistic mechanism of interface-mediated deformation.

Investigation of constitutive models and microstructure evolution during hot deformation and solution treatment of Al–Zn–Mg–Cu alloy

In this paper, isothermal thermal compression tests were carried out on Al–Zn–Mg–Cu alloys at varying deformation temperatures (360°C∼440°C) and strain rates (0.001s−1∼10s−1) using a Gleeble-3500C thermal simulation tester. Based on the true strain stress data obtained from the tests, the flow behavior of Al–Zn–Mg–Cu alloys during thermal deformation was investigated. Through a comprehensive consideration of deformation temperature, strain rate, and strain compensation, a high-precision constitutive model was established. Additionally, the specimens subjected to hot compression were further treated with solution annealing for different durations (0 h–2 h) to investigate the static recrystallization (SRX) behavior and the associated microstructural evolution of the alloy during the solution treatment process. Electron Backscatter Diffraction (EBSD) was employed to characterize the microstructure evolution of Al–Zn–Mg–Cu alloy under various deformation and solution treatment conditions. The EBSD data were further processed and analyzed using the MTEX toolbox. The results revealed that dynamic recovery (DRV) is the predominant softening mechanism during the deformation process, accompanied by a small amount of dynamic recrystallization (DRX). The dynamically recrystallized grains exhibit a random crystallographic orientation. Further investigation showed that low temperature and high strain rate conditions are unfavorable for the occurrence of dynamic recovery and dynamic recrystallization during the thermomechanical processing. However, dislocations accumulated during deformation provided sufficient stored energy for the growth of static recrystallized grains during subsequent solution treatment, with static recrystallized grains predominantly forming at grain boundaries.

Inhomogeneous deformation behavior and recrystallization mechanism of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar LPSO phase

Inhomogeneous plastic deformation and recrystallization behavior of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar long-period stacking ordered (LPSO) phase were investigated by isothermal compression experiments at the temperatures of 350–450 °C, and the strain rates of 0.001 ∼ 10 s−1. Results showed that Mg-Gd-Y-Zn-Zr alloys with varying degrees of bimodal structures were obtained after compression. The lamellar LPSO phase directions in residual coarse grains were aligned in the radial direction (RD). Dynamic recrystallization (DRX) grains induced at grain boundaries, kinked bands, and lamellar shearing regions during compression synergistically promoted coarse grain refinement. Moreover, the condition of high temperature and medium strain rate (450 °C-0.1 s−1) contributed to the uniform extension of "mantle layers" of fine DRX grains. In contrast, the condition of medium temperature and high strain rate (400 °C-10 s−1) could accelerate the deflection of CD-directed (compression direction) LPSO lamellae and the formation of local high-energy regions, facilitating the generation of recrystallization band. In addition, a high strain rate (400 °C-10 s−1) is more conducive to the formation of a heavily bimodal structure than a high temperature (450 °C-0.1 s−1). Only a larger spacing of LPSO lamellae (∼1.4 μm) could meet the spatial requirements of recrystallization. Further analysis revealed that the continuous dynamic recrystallization (CDRX) mechanism characterized by the expansion of "mantle layers" and nucleation along kinked boundaries and lamellar shearing regions was the primary grain refinement mechanism. The discontinuous dynamic recrystallization (DDRX) mechanism only exhibited a limited role due to the inhibition of the highly dense lamellar LPSO phase on grain boundaries bulging. After compression, the orientation of residual coarse grains gradually deviated toward the CD. While the recrystallization with limited proportion and random orientation cannot significantly weaken the basal texture.

High-Strain-Rate Deformation Behavior of Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 Eutectic High-Entropy Alloy at Room and Cryogenic Temperatures.

The deformation behaviors of Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 eutectic high-entropy alloy (EHEA) under high strain rates have been investigated at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). The current Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 EHEA exhibits a high yield strength of 740 MPa along with a high fracture strain of 35% under quasi-static loading. A remarkable positive strain rate effect can be observed, and its yield strength increased to 1060 MPa when the strain rate increased to 3000/s. Decreasing temperature will further enhance the yield strength significantly. The yield strength of this alloy at a strain rate of 3000/s increases to 1240 MPa under the LNT condition. Moreover, the current EHEA exhibits a notable increased strain-hardening ability with either an increasing strain rate or a decreasing temperature. Transmission electron microscopy (TEM) characterization uncovered that the dynamic plastic deformation of this EHEA at RT is dominated by dislocation slip. However, under severe conditions of high strain rate in conjunction with LNT, dislocation dissociation is promoted, resulting in a higher density of nanoscale deformation twins, stacking faults (SFs) as well as immobile Lomer-Cottrell (L-C) dislocation locks. These deformation twins, SFs and immobile dislocation locks function effectively as dislocation barriers, contributing notably to the elevated strain-hardening rate observed during dynamic deformation at LNT.

Mechanical behavior and fiber reinforcing mechanism of high-toughness recycled aggregate concrete under high strain-rate impact loads

Fiber-reinforced recycled aggregate concrete (FRRAC) is renowned for its excellent mechanical properties and environmental benefits, making it a popular choice in construction engineering. However, the impact damage mechanisms of FRRAC remain unclear. This study leverages advanced in-situ 4D CT technology to investigate the fiber-reinforcing mechanisms of High-Toughness Recycled Aggregate Concrete (HTRAC) using construction waste as a sustainable building material. Under high strain-rate conditions, the dynamic mechanical behaviors of both plain recycled aggregate concrete (PRAC) and HTRAC were examined using the Split Hopkinson Pressure Bar (SHPB) method. The experiments revealed significant strain rate sensitivities in both materials, with HTRAC showing superior fiber reinforcement that markedly enhances its toughness. Quantitative models for dynamic increasing factors of key mechanical parameters, including peak stress, peak strain, initial elastic modulus, ultimate strain, and toughness index, were developed. These findings offer critical design insights for using HTRAC in impact load conditions and other extreme environments, promoting its wider adoption in the construction industry.

Five-fold twin formation in face-centered cubic metals under impact loading

Five-fold twins (FFTs) are unique microstructural features in face-centered cubic (FCC) metals that significantly influence their mechanical strength. This study examines FFT formation in Cu, Au, and Ni under high-strain rate conditions induced by cold spray and compression shock impact loading, using atomistic simulations. We reveal a sequential twinning mechanism for FFT formation under impact loading, where the specific growth path varies, leading to inherently unstable FFTs that decompose post-formation. Interestingly, impact velocity had minimal influence, while elevated temperatures suppressed FFT formation, suggesting a dependency on the twinning mechanism. The stacking fault energy of the FCC metal greatly affected FFT propensity; metals with lower stacking fault energy (e.g., Au) readily formed FFTs, while those with higher stacking fault energy (e.g., Ni) encountered greater difficulty. These findings provide new insights into the behavior of FFTs under dynamic loading conditions, with implications for the design of high-strength nanocrystalline materials.

Research on damage behavior of silicone rubber under dynamic impact

Viscoelastic rubber materials are widely used in various vibration reduction structures of military and construction machinery. The complex driving and working conditions make the mechanical structure suffer severe impact, which leading to the damage or lose efficacy of the important viscoelastic elements. In order to reveal the dynamic mechanical properties of silicone rubber after impact, the Uniaxial compression tests of silicone rubber under different high strain rates were carried out with the separated Hopkinson pressure bar (SHPB) dynamic impact experiment, and the original Zhu-Wang-Tang (ZWT) constitutive model was modified by combining logarithmic law and power function law. The dynamic impact simulation model of silicone rubber was established using the modified ZWT-rate-dependent constitutive model, and the dynamic impact damage behavior of silicone rubber was studied under the condition of high strain rate, and the microscopic damage analysis was carried out on the experimental silicone rubber samples by scanning electron microscopy (SEM). The results show that the silicone rubber has obvious strain rate effect and strong deformation resistance at high strain rate. The modified ZWT-rate-dependent constitutive model can be used to obtain the constitutive expression of unified parameters, which can better describe the dynamic mechanical properties of silicone rubber at high strain rates. After dynamic impact compression, a damage line zone appears in the silicone rubber sample. There is a certain rule between the position of the line zone and the loading strain rate and the friction coefficient of the end face, and the silicone rubber is significantly affected by the friction effect of the end face.

Enhancing steel properties with surface mechanical treatments

This research presents the modification of the microstructure on the surface of a dual phase steel (DP) using three different treatments: surface mechanical attrition treatment (SMAT), surface mechanical carburizing treatment (SMCT), and surface mechanical composite coating treatment (SMCCT). We used SMAT to refine the grain size under high strain and strain rate conditions and successfully induced a phase transformation to martensite. The introduction of carbon during SMAT resulted in surface mechano-chemical carburizing, which enhanced the martensite transformation. Furthermore, the addition of silicon during the process led to the formation of SiC and Fe3C particles dispersed within the ferrite and martensite matrix, creating a surface nano-composite. Analysis using SEM and XRD revealed that the carbon and silicon-treated steel exhibited 41.4% martensite, 4.4% bainite, and 54.1% ferrite, indicating increased transformation by these elements. As a result, the alterations in the surface microstructure led to changes in the mechanical properties of the DP steel. Initially, the DP steel had Y.S. of 250 MPa and U.T.S. of 350 MPa. After SMAT treatment, its Y.S. and U.T.S. increased to 280 MPa and 380 MPa, respectively. The addition of carbon and silicon further enhanced the Y.S. and U.T.S. to 350 MPa and 450 MPa. A significant change in microhardness is achieved from 150HV0.05 to 255HV0.05 while after SMCT and SMCCT is 275HV0.05. Despite an increase in surface roughness contributing to heighten friction, there was a significant reduction in wear. This phenomenon could be attributed to grain refinement, dislocation structures, and martensite phase transformations associated with surface hardening.

Research on microplastic deformation of Inconel718 under the conditions of high temperature and high strain rate

The compression experiments of the nickel-based superalloy Inconel718 were carried out with the help of split Hopkinson pressure bar device, and the microstructure evolution law in the compression deformation of the alloy was studied by means of optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dislocation theory, a three-dimensional discrete dislocation dynamics model is established. By simulating the dynamic evolution of the discrete dislocation, the interaction of the dislocation itself and the formation of the dislocation microstructure were captured, and further explore the microplastic deformation process of Inconel718. The results show that deformation conditions significantly affect the rheological behavior and dynamic recrystallization behaviour. The cross slip of dislocations is closely related to temperature and strain rate, which in turn affect the dislocation configuration. The deformation mechanism of Inconel718 under the conditions of high temperature and high strain rate is jointly dominated by dislocation slip and twin deformation. As the temperature increases, the average Schmidt factor increases, and more dislocation slip systems are activated. As the strain rate increases, the number of deformation twins increases, while the thickness of deformation twins decreases.

Enhanced mobility of dislocation network nodes and its effect on dislocation multiplication and strain hardening

Understanding plastic deformation of crystals in terms of the fundamental physics of dislocations has remained a grand challenge in materials science for decades. To overcome this, the Discrete Dislocation Dynamics (DDD) method has been developed, but its lack of atomistic resolution leaves open the possibility that certain key mechanisms may be overlooked. By comparing large-scale Molecular Dynamics (MD) with DDD simulations performed under identical conditions we uncover significant discrepancies in the predicted strength and microstructure evolution in BCC crystals under high-strain rate conditions. These are traced to unexpected behaviors of dislocation network nodes forming at dislocation intersections, that can move in ways not previously anticipated as revealed by MD. Once these newfound freedoms of nodal motion are incorporated, DDD simulations begin to closely match plastic evolution observed in MD. This additional mechanism of motion whereby non-screw dislocations can change their glide plane profoundly affects fundamental processes of dislocation multiplication, recovery and storage that define strength of metals.

Dynamic Constitutive Model and Numerical Simulation of S32760 Duplex Stainless Steel Based on Dislocation Theory

Background: To describe the complex mechanical behavior of S32760 duplex stain-less steel under high strain rate and high-temperature loading conditions. Objective: The constitutive model of S32760 duplex stainless steel suitable for high strain rate was constructed from the micro-scale. Methods: Based on the theory of dislocation dynamics, the effects of different strain rates and strains on the plastic deformation of ferrite and austenite were analyzed, and the thermal stress term and non-thermal stress term of ferrite and austenite phases were coupled. Results: The simulation results of the model show that the S32760 dual-phase constitutive model has a high degree of fit with the experimental data at high strain rates. Conclusion: Compared with the classical J-C model, the results show that the constitutive model of this patent has more accurate predictability than the J-C model in describing the mechanical behavior of duplex stainless steel in the high strain range of 5000s-1 to 10000s-1.

Dynamic recrystallization behaviors and cracking mechanism for the hot deformation of new-generation high nitrogen bearing steel

In this work, the hot deformation behaviors of the high-nitrogen steel X30CrMoN15-1 from 900 °C to 1200 °C have been investigated. The microstructure observation indicates that the maximum DRXed grain size reaches 59.05 μm under the deformation temperature of 1200 °C with strain rate of 0.005 s−1, while the minimum grain size is 2.12 μm under the condition of 900 °C with strain rate of 1 s−1. The fully dynamic recrystallization (DRX) occurs at the conditions of high temperature and high strain rate (1000 °C − 1200 °C, 1 s−1 –5 s−1). There are two main mechanisms of crack formation. Under lower temperatures (900 °C-1000 °C), the significant stress concentration produced by M2(C, N) should be responsible for crack propagation along the DRXed grain boundaries. As the temperature increases to 1100 °C, the formation of cracks is mainly attributed to the uncoordinated deformation and huge pinning of dislocations by Lomer-Cottrell (L-C) locks. A new hot processing map has been established to reveals that the optimal processing domains are located at 1020 °C − 1090 °C with strain rate of 0.37 s−1 –4 s−1 and 1140 °C − 1200 °C with strain rate of 2 s−1 –5 s−1.