Superplastic boronizing of a low alloy steel — microstructural aspects

The formation and mechanisms of the texture growth of boride phases during superplastic boronizing were studied in comparison with conventional boronizing. The texture degree was quantitatively determined by using X-ray diffraction with Lotgering method. The microstructures and distributions of the alloy elements were studied by using SEM and electron probe microanalysis. Microhardness tests across the boride layers were also performed. The results indicated that the superplastic boronizing retarded the formation of the high boron containing boride phases and reduced the growth texture of the borides. Compared with the conventional boronizing, the FeB growth texture was eliminated and Fe2B growth texture was reduced significantly with the superplastic boronizing. The superplastic boronizing processes also suppressed the formation of the Si-rich zones which otherwise would form between the boride grains. The microhardness of the boride layer processed by the superplastic boronizing was more uniform than that produced by the conventional boronizing.