Study on Strength Degradation Mechanism of Material on Inner Bore Surface of Gun Barrel

doi:10.12382/bgxb.2022.0063

Abstract

Abstract:

In the process of gun firing, the inner diameter of the barrel increases by several microns under the action of heat, chemistry and force, which is the main reason for the termination of barrel life. Therefore, it is of great significance to study the change of material properties of the inner bore surface to reveal the barrel life mechanism. The microstructure, thickness and mechanical properties of the inner bore surface materials at different parts of the barrel were obtained by microanalysis of the 155mm barrel that has reached its life end. Through the analysis of barrel temperature gradient and ablation simulation experiment, the degradation mechanism of the bore surface material and its relationship with projectile firing number were revealed. The results showed that: the hardened layer was formed on the surface of the inner bore under the action of gunpowder gas in the early barrel life; the thickness of the hardened layer was related to the temperature and action time of gunpowder gas; barrel ablation and wear occur on the surface of the hardened layer; the strength of the hardened layer was twice as high as that of the barrel at room temperature, and the strength decreased rapidly at high temperatures, resulting in the increase of the inner barrel diameter under rotating band friction and airflow scouring.

Key words: gun barrel bore, hardened layer, material property degradation, phase transformation, ablation and erosion

XU Yaofeng, YANG Diao, LIU Pengke, CHEN Qi, GUO Junhang, WANG Jun. Study on Strength Degradation Mechanism of Material on Inner Bore Surface of Gun Barrel[J]. Acta Armamentarii, 2023, 44(5): 1288-1295.

Figures/Tables 20

Fig.1 Surface microstructure of the inner bore at different axial parts of the barrel

Table 1 Hardened layer thickness

部位	药室部	膛线起始部	高膛压区	身管中部	炮口
厚度/μm	0~140	165	100	55	1~2

Fig.2 Nanoindentation test positions

Table 2 Test results of elastic modulus of barrel material and hardened layer

参数	测点1	测点2	测点3	测点4	平均
硬化层弹性模量/GPa	228.06	219.88	228.86	202.17	219.74
基体弹性模量/GPa	217.08	243.14	220.76	221.47	225.61

Fig.3 Micro Vickers hardness test positions

Fig.4 Variation law of micro Vickers hardness along barrel thickness

Fig.5 Variation curves of hardness of barrel material and hardened layer with temperature

Table 3 Tensile strength of barrel material and hardened layer at different temperatures

基体及硬化层	温度/℃
基体及硬化层	20	200	400	600	700	800
基体	1091	1037	931	498	220	107
硬化层	2340	1495	357	153	-	-

Fig.6 Temperature curves at different positions of inner barrel wall

Fig.7 Variation law of maximum temperature along barrel thickness at different axial positions on barrel

Table 4 Comparison between the thickness with temperature exceeding 830℃ and the measured thickness of hardened layer

参数	膛线起始部	高膛压区	身管中部	炮口
温度超过830℃的厚度/μm	150	131	70	4
硬化层实测厚度/μm	165	100	55	1~2

Fig.8 Inner wall temperature rising and falling process at commencement of rifling

Fig.9 Ablation simulation device with the barrel sample

Fig.10 Part of measured pressure curves

Fig.11 Barrel sample after ablation simulation test

Fig.12 Chromium plating sample after ablation simulation test

Fig.13 Thickness of hardened layer of barrel sample after ablation simulation test

Fig.14 Thickness of hardened layer of chromium plated sample after ablation simulation test

Fig.15 Comparison between hardness of hardened layer after ablation simulation test and that of the barrel

Fig.16 Thickness of hardened layer of barrel sample after ablation simulation test

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