Joo Ishihara

Microstructures and mechanical properties of melt-quenched ferritic stainless steels

Using the twin-roller type melt-quenching technique, the effects of rapid solidification on the microstructures and mechanical properties of ferrite have been examined in 17 pct Cr and 17 pct Cr-M steels where M = Ti, Nb, Si, or Al. The melt-quenched 17 pct Cr steels have the columnar and equiaxed grains which become finer with decreasing of specimen thickness. But the yield strength of these steels, which is about 0.48 GPa, remains almost unchanged with grain size refinement, contrary to predictions based on Hall-Petch’s relationship. The columnar structure of the melt-quenched 17 pct Cr-M steels is very fine on alloying with Ti and Si, while it is slightly coarse on alloying with Nb and Al. The hardness, yield strength, and fracture strength of these 17 pct Cr-M steels increase with increased amount of alloying element, these maximum values being about 460 DPN, 1.0 GPa, and 1.35 GPa, respectively, for 17 pct Cr- 6 pct Si steel, in the ductile compositional range. These are suitable values for a fine-gauge material having high hardness and strength as well as good ductility.