This work focused on the stress response of anisotropic 30SiMn2MoVA steel gun barrel under coupled thermo-mechanical loads, namely, the contact pressure and friction of projectile, thermal load and pressure of propellant gas. The effect of temperature on the mechanical properties of gun barrel was considered. Two thermal-displacement coupled finite element models (FEM) were built by ABAQUS software. The first was the interaction model of projectile and barrel which was to calculate the stress of barrel engraved by copper jacket and steel jacket projectile. The results of barrel in the interaction model, as an initial condition, were imported to the second FEM which was applied with thermal load and pressure of propellant gas. The results show that the rifling at chamber throat has the largest stress and circumferential stress under coupled loads. It gives a request that the gun barrel should have the better circumferential mechanical properties. The plastic deformation of the rifling at the chamber throat is observed which indicates that 30SiMn2MoVA gun barrel has a low service life due to the poor mechanical properties. Keywords 30SiMn2MoVA steel; anisotropic gun barrel; stress response; coupled thermo-mechanical loads; copper jacket and steel jacket projectile; thermal load and pressure of propellant gas

This work focused on the mechanical properties of 30SiMn2MoVA high strength steel gun barrel processed by cold radial forging. Three states of the tube made of this material (the state without forging, the as-forged state without annealing, the as-forged state with annealing) were chosen to compare the axial and circumferential mechanical properties. As a result, anisotropy was found at as-forged state. The circumferential mechanical properties were inferior to the axial. The circumferential yield and tensile strength were about 150MPa lower than the axial after forging. And the axial elongation was 155% higher than the circumferential. Even after annealing, the circumferential elongation cannot be restored to the same level as the state without forging. The reasons for anisotropy were investigated by the microstructure. The banded structure along the axial direction was observed in the forged barrel. Meanwhile, the crystalline grains of the forged gun barrel had the highest intensity of {111}<110> texture which meant the grains had obvious preferential orientation. The relationship between crystallographic texture and yield strength was analyzed based on the Schmid factor. Additionally, the elastic limit internal pressure of anisotropic gun barrel was calculated and it was lower than that under isotropic condition.

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Mechanical properties of 30SiMn2MoVA steel gun barrel processed by cold radial forging with stepped mandrel under the different forging ratios were investigated in the present work. This work mainly reported the axial and circumferential mechanical properties of forged gun barrel before and after annealing. The axial and circumferential mechanical properties were measured by tensile test and bulging test, respectively. The results suggested that the strength was enhanced and elongation was decreased by forging which was caused by cold work hardening. After annealing, the anisotropy of elongation was observed. The circumferential elongation was weaker than the axial. With the increasing of forging ratios, strength anisotropy was exacerbated gradually. The circumferential strength was inferior to the axial. Besides, there were axial penetrating cracks in the failure state of circumferential bulging test specimens. Through the electron microscopic examination, the axial micro cracks and wrinkles in the inner wall of the forged tubes were observed. It showed that the cold radial forging with stepped mandrel may result in the defect in the inner surface of the gun barrel which should be paid attention.

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There is anisotropy in 30SiMn2MoVA steel gun barrel processed by radial forging which results in the low service life of the gun barrel. While the texture is the main reason for the anisotropy. The crystal plasticity finite element (CPFE) method is usually used to simulate the microstructure and the texture of the metal. In the present work, a two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline 30SiMn2MoVA steel. The displacement of nodes in the macro radial forging process finite element model is used as the cross-scale boundary condition in the CPFE model which realizes cross-scale simulation. The texture evolution and inhomogeneous deformation of 30SiMn2MoVA steel in the radial forging processing under three different forging ratios were simulated. The simulated texture results are consistent with the experimental results. The inhomogeneous deformation of grains is obvious and will intensify with the increase of the forging ratio. The distributions of stress and equivalent plastic strain in polycrystals are statistically Gaussian. With the increase of deformation, the further refinement of grains is due to the large shear strain in large grains.