Grain growth in steels during carburizing or carbonitriding is often accompanied by the occurrence of a varied grain size. Authors explain this phenomenon by the presence of impurities and excess phases along grain boundaries which restrain their growth. If for a given metal and amount of excess phase particles is taken to be constant and equal to N, then the density of their distribution long grain boundaries should depend on grain size. The steels with a coarse grain size the specific distribution density for particles N/S is higher than in fine grained material. In view of this in coarse-grained steels the retarding force prevails over the moving force of grain growth, which makes it impossible for both massive selective grain growth. With a certain {open_quotes}optimum{close_quotes} grain size the regrains is retarded, but individual grains may start to coarsen which leads to a difference in grain size. In steel with a grain size less than the optimum there is intense grain growth, and their tendency towards selective growth decreases. Release of dislocations from fixing by impurities and dissolution of excess phases lead to spreading of boundaries and grain growth by merging of them. 5 refs., 4 figs.