| The barrel is the core component of automatic weapons,and its importance is like the engines of aircraft.The development of new high-strength steel is conducive to improving the performance of the barrel.However,to take advantage of the heat resistance of new high-strength steel,the guarantee of cold radial forging technology is also required.The microstructure and residual stress are the main factors that affect the strength and dimensional accuracy of the forged barrel.If the residual stress is too high or unevenly distributed during forging,it is easy to cause straightening difficulties or cracking after forging,which is directly related to the safety of production and use.At present,there are difficulties in characterizing the internal residual stress of the barrel.The optimization control process of residual stress and microstructure in the forging process is unclear,and the adverse effect of stress relief treatment on the strength of the barrel is difficult to control.Given the above problems,this paper systematically studied the microstructure and residual stress of cold radial forged high-strength steel barrels.First,a method for measuring the three-dimensional residual stress distribution of the whole section of the barrel was studied.Secondly,the effect of the forging process on the microstructure and residual stress was analyzed.Thirdly,a mathematical model was established to infer the overall distribution of internal stress based on surface residual stress.Finally,a stress relief process that effectively reduced residual stress and maintained the performance of the barrel to the greatest extent was explored.This study can guide the precise and efficient fabrication of new high-strength steel barrels.The main contents and results of the research are as follows:(1)The residual stress gradient of the barrel is high,which is not conducive to the accurate test of the traditional stripping method,and the residual stress near the inner surface is difficult to measure.Aimed at this problem,a new method of residual stress correction was proposed,and an analytical method for analyzing the residual stress near the inner surface was presented.The results calculated by the new correction method and analytical method are highly consistent with the measured values of neutron diffraction and short-wavelength characteristic X-ray diffraction.This work realizes the characterization of the three-dimensional residual stress in the full section of the small-diameter thick-walled barrel.(2)Based on the quantitative analysis of the residual stress,grain size,grain boundary distribution,and dislocation density,the effects of forging ratio,hammer angle,and mandrel structure on the through-thickness microstructure and strength unevenness of the barrel were investigated.The optimized process of cold radial forging was given.A large forging ratio,a threaded mandrel,and a hammer with a large exit angle are beneficial to increase the dislocation density and the proportion of low-angle grain boundaries of the outer surface of the barrel,which can improve the overall strength of the barrel without affecting the performance of the inner surface.(3)Based on the dimensional analysis method,the mathematical model of the residual stress distribution of the barrel was established,and the correlation parameters between the forging process and the residual stress were obtained.The effective method to infer the overall distribution of the internal residual stress according to the limited data of the surface residual stress was given.This method enables the batch,rapid,non-destructive,and simple determination of the internal residual stress of the barrel.(4)The microstructure evolution behavior of thermal,single vibration,and thermal-vibration stress relief were investigated,and the residual stress relaxation mechanism was analyzed.A multi-objective optimal control process for the mechanical properties,microstructure,and residual stress of the barrel was obtained.The optimal process achieves a reduction in hardness within 4%while the residual tensile stress is controlled below 50 MPa.The performance of the barrel is maintained to the greatest extent possible while substantially eliminating the negative effects of tensile residual stress. |
