Coarse Columnar Structure of Transformation-Grown Ferrite in Pure Iron —On Wrought Iron and Sintered Iron—

Abstract

When a nucleus of ferrite crystal is formed in cast-and-rolled or sintered iron, either of which contains less than approximately 50 ppm interstitial elements, namely, carbon and nitrogen, the ferrite crystal may grow into a coarse crystal joining many austenite crystals. Furthermore, such coarse ferrite crystals may compose a columnar macrostructure by unidirectional phase transformation under the condition accompanying a gradient of temperature. The formation of the macrostructure gives a maximum linear expansion of the sample that is numerically equal to the volume expansion at the same time. Even a small amount of carbon in pure iron can cause the condensation of carbon atoms or the formation of a fairly large number of minute cementite precipitates at ferrite/austenite phase boundaries. Both the condensation of carbon and the precipitation of cementite may cause the nucleation of new ferrite crystals, leading to the development of a fine-grained macrostructure.

Coarse Columnar Structure of Transformation-grown Ferrite and Very Low Carbon Content in Pure Iron of Armco Type

“…7 ena. The triplet mechanism in Ar3 transformation [5] gives a clear explanation of the experimental result reported by Lehl [2]. He found a triplet phenomenon simular to the present one, in which the purification of Armco iron by hydrogen resulted in the growth of the iron sample and the growth of ferrite crystals.…”

Embrittling Components in Sintered Steels: Comparison of Phosphorus and Boron

“…Such very coarse-grained specimens are sensitive to intergranular fracture with very low impact energy [38][39][40]. This is also clearly evident from the fracture surfaces shown in Fig.12: Figure 12a depicts the plain iron specimen which shows intergranular decohesion of the very large grains.…”

Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity

“…In the case of plain Fe, coarsening is further enhanced by the transformation effect described e.g. in [24,25]. Furthermore, the fraction of ferrite is rather high considering the carbon content, which is particularly noticeable with Fe-0.8%C; also this can be attributed to the slow cooling which enhances formation of ferrite.…”