To reduce the precipitation of σ phases and to improve the hot workability of S31254 steels, boron has been added into the composition of S31254 to a concentration of 40 ppm. The precipitation behavior was investigated before and after the addition of boron in different S31254 alloys during the compression deformation, and the nose temperature at 950 °C and the phase dissolution temperature at 1074 °C were selected as the measurement temperature. The result showed that more σ phases were precipitated at the grain boundary of S31254 alloys, compared to the boron-added alloy. Meanwhile, the addition of 40 ppm boron into the alloys has obviously prevented the σ phases from the austenitic matrix, and it takes longer time for the precipitation of σ phase at 950 °C. The specific influence factors of boron on the precipitation of σ phases were also further discussed.