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Research on Mechanical Properties and Wear Behavior at Extremely Low Temperature of a 16Cr-6Ni Austenitic Steel

The tensile strength and plastic behavior of the Cr16Ni6 steel were investigated at 298K (298K) and 76K. The yield strength and tensile strength of the alloy increased significantly with lower temperatures, from 990 MPa to 1350 MPa and from 1313 MPa to over 1800 MPa, respectively. Young’s modulus and impact behavior were found when testing temperature decreased. It was revealed from the microstructure observation conducted by scanning electron microscopy (SEM) and x-ray diffraction technique (XRD) analysis that the face-centered-cubic (FCC) structure of the matrix remained stable with a very small amount of tangent phase transformation to martensitie during the tensile tests at 76 K. The matrix grains deformed at 298K were cut apart into many small sub-grains with similar crystallographic orientation in the size of only 60-200 nm wide. Very small amount of dislocation cells or bands observed in the specimens deformed at 76 K, although many sub-grains and areas containing dislocation network were found. The formation of twin-structures along the 1/3(420) planes was found in the deformation areas at 76 K. The improvement of strength was mainly attributed to the fact that it was more difficult for the dislocation slipping along lattice planes at 76 K than at 298K, due to the reduction of the movement and diffusion abilities of atoms. The friction coefficient was found to be a little higher at 93 K than at 298 K due to the bad lubricity of the graphite material at cryogenic temperature.