Study on the Thermochemical Erosion Mechanism and Fatigue Behavior of Gun Steel Under High‐Temperature and High‐Pressure Gas Environment

ABSTRACT This work focuses on studying the corrosion fatigue characteristics of Cr‐Ni‐Mo‐V gun steel under high‐temperature and high‐pressure propellant gas cyclic loading. Using a pressure vessel–based high‐temperature and high‐pressure erosion experimental device, experimental research was conducted to analyze the thermochemical erosion mechanisms and fatigue behavior of gun steel under cyclic high‐temperature gas loading at 194 and 256 MPa, respectively. The findings reveal that the erosion of gun steel under propellant gas constitutes a transient process. In such environments, the gun steel specimen develops a surface white layer under the combined action of pressure, thermal stress, and gas corrosion. The thickness of this white layer exhibits a positive correlation with both the number of erosion cycles and the gas pressure. Specifically, the white layer thickness ranges from 2.03 to 3.04 μm at 194 MPa and from 3.69 to 4.26 μm at 256 MPa. In the upper portion of the white layer, large‐size cracks are observed, whereas a continuous microcrack layer emerges at the base. The white layer contains C, O, and S as the primary impurity elements, with C exhibiting the highest concentration and an interspersed distribution. The distribution of O and S demonstrates distinct stratification. With an increase in the number of erosion cycles, the large‐size crack distribution area expands, accompanied by a growth in the thickness of the basal microcrack layer. Both the thickness of the S‐rich layer and the O‐rich layer increase.