Experimental Investigation of Phase Transitions in Die Steels by the Acoustic Method

In this study, an ultrasonic pulse method was used in an updated IMASH-ALA-TOO-75 facility by an original procedure [1] to investigate specimens of 3Kh2V8F and 4Kh4VMFS die steels. The specimens were preliminarily drawn out from a rod 20 mm in diameter to 2 mm in diameter and then fully annealed. The annealing consisted in heating the specimens to a temperature somewhat above point A ae 3 (900ie) , holding them at this temperature for 1 h, and then cooling slowly in a furnace. Figures 1 and 2 give the temperature dependences of the sound velocity ae ( t ) for steels of both grades. A wide range of variation in the sound velocity ae in the 3Kh2V8F steel is probably due to alloying this steel with tungsten, which imparts a high plasticity to the alloy. For 4Kh4VMFS steel, in the temperature region of 620ie , an inflection of the curve and an abrupt lowering of ae are observed during heating. This may be explained by passing through temperatures corresponding to magnetic transformation in the steel and phase transformation in the vicinity of point A ae 1 , 830ie . The alloying of 4Kh4VMFS steel with nickel must contribute to decreasing the temperature of magnetic transformation [2]. A variation of the slope of the curve in the region of 850ie points to the beginning of phase transformation in the vicinity of A ae 3 , i.e., the transformation of ferrite into austenite. On cooling, the curve passes the same phase transitions at temperatures of 750 and 570ie , respectively.