Developing laser welding (LW) technology in a hyperbaric environment is significant for manufacturing and maintaining nuclear power facilities, offshore engineering structures, etc. However, the penetration is significantly reduced during LW in a hyperbaric environment, which has not been solved yet. Previous research has shown that compared with the penetration of LW in a hyperbaric argon (Ar) environment, the penetration of 304 stainless steels attained through LW in a hyperbaric environment can be remarkably increased when using helium (He) as the shielding gas on same conditions. Hence, the plasma and molten pool behaviors in the LW process of 304 stainless steels in a hyperbaric He atmosphere were systematically explored. Furthermore, the effect of the growth of ambient pressure on the process of pulsed laser spot welding of 304 stainless steels was analyzed. It was found that when ambient pressure gradually rose from 0.1 to 1.8 MPa, the height and the intensity of characteristic plasmas above the molten pool gradually increased. In the initial stage of welding, the expansion velocity of plasmas under 1.8 MPa was about 1/4 of that under 0.6 MPa; the growth rate of the molten pool depth under 1.8 MPa was about 1/13 of that under normal pressure (0.1 MPa). The increase in ambient pressure led to the great decrease in weld penetration. Under experimental conditions in this paper, the weld penetration at the ambient pressure of 1.8 MPa was only 25% of that at normal pressure (0.1 MPa).

中文翻译：

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高压环境压力对304不锈钢脉冲激光焊接熔深的影响及其影响机制

开发高压环境激光焊接（LW）技术对于制造和维护核电设施、海洋工程结构等具有重要意义。但高压环境激光焊接（LW）过程中熔深显着降低，目前尚未解决。前人研究表明，与高压氩（Ar）环境下LW的渗透率相比，在同等条件下使用氦（He）作为保护气体时，304不锈钢在高压环境下通过LW的渗透率可显着提高. 因此，系统地探索了 304 不锈钢在高压 He 气氛中 LW 工艺中的等离子体和熔池行为。此外，分析了环境压力的增长对304不锈钢脉冲激光点焊过程的影响。发现当环境压力从0.1 MPa逐渐升高到1.8 MPa时，熔池上方特征等离子体的高度和强度逐渐增加。在焊接初期，等离子体在1.8 MPa下的膨胀速度约为0.6 MPa下的1/4；1.8 MPa下熔池深度的增长速度约为常压（0.1 MPa）下的1/13。环境压力的增加导致焊缝熔深大幅下降。在本文的实验条件下，1.8 MPa 环境压力下的焊缝熔深仅为常压（0.1 MPa）下的 25%。熔池上方特征等离子体的高度和强度逐渐增加。在焊接初期，等离子体在1.8 MPa下的膨胀速度约为0.6 MPa下的1/4；1.8 MPa下熔池深度的增长速度约为常压（0.1 MPa）下的1/13。环境压力的增加导致焊缝熔深大幅下降。在本文的实验条件下，1.8 MPa 环境压力下的焊缝熔深仅为常压（0.1 MPa）下的 25%。熔池上方特征等离子体的高度和强度逐渐增加。在焊接初期，等离子体在1.8 MPa下的膨胀速度约为0.6 MPa下的1/4；1.8 MPa下熔池深度的增长速度约为常压（0.1 MPa）下的1/13。环境压力的增加导致焊缝熔深大幅下降。在本文的实验条件下，1.8 MPa 环境压力下的焊缝熔深仅为常压（0.1 MPa）下的 25%。8MPa是常压(0.1MPa)下的约1/13。环境压力的增加导致焊缝熔深大幅下降。在本文的实验条件下，1.8 MPa 环境压力下的焊缝熔深仅为常压（0.1 MPa）下的 25%。8MPa是常压(0.1MPa)下的约1/13。环境压力的增加导致焊缝熔深大幅下降。在本文的实验条件下，1.8 MPa 环境压力下的焊缝熔深仅为常压（0.1 MPa）下的 25%。