THE NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

By means of high resolution particle-tracking autoradiography the regularity of boron segregation to austenite grain boundaries has been studied, and the boron concentration profiles across segregated grain boundaries and characteristic parameters for non-equilibrium grain boundary segregation (width of boron-depleted zone, degree and width of boron-segregated band) have been measured. It has been shown that this kind of grain boundary segregation has following features:There exists boron-depleted zone adjacent to segregated grain boundary, which is responsible for supplying of boron to grain boundary during cooling. This kind ofl segregation during cooling is very sensitive to cooling rate. Rapid cooling can inhibit it, and the segregation state would progressively develop from continuous band to discontinuous aggregation and even apparent precipitation as cooling rate decreases. The width of boron-depleted zone is inversely proportional to the square root of cooling rate. The temperature relationship of segregation opposites to the expectation of equilibrium grain boundary segregation. The higher the quenching temperature, the more incremental are the segregated degree and the width of boron depleted zone.The test has been demonstrated that the boron segregation at austenite grain boundaries in quenched steel is a non-equilibrium grain boundary segregation phenomena occurred during cooling.