Influence of Purity and Cooling-Rate on the Microstructure of Hot-Forged Pure Irons

Abstract

The influence of purity and cooling-rate on the microstructure of hot-forged pure irons was investigated by using two kinds of pure irons. One was K-Iron of 99.981 mass% purity and the other was M-Iron of 99.993 mass% purity. After forging at 1263 K, above the α-γ transformation temperature, the specimens were immediately cooled to room temperature at various cooling-rates: by water-quenching, oilquenching, air-cooling, ash-cooling, and furnace-cooling. The microstructure of forged iron was strongly affected by the purity and the cooling-rate. It should be emphasized that in M-Iron columnar grains grew in parallel to the forging direction independent of the coolingrate. On the other hand, equiaxed grains were formed in all specimens of K-Iron forged at 1263 K. On both M-Iron and K-Iron, α-grains became larger with decreasing cooling-rate. The crystal orientation of α-grains on the forged plane of each specimen was measured by electron back-scattering diffraction-pattern method. On the forged plane of M-Iron, {101} of α-grains was predominant in the case of water-quenching and {111} or {221} was predominant in the other cases; on the other hand, the crystal orientation in K-Iron was random at all cooling-rates. Metallurgical factors controlling these characteristic microstructures in M-Iron were discussed in terms of growth of recrystallized of α-and γ -grains, mobility of γ /α interface, nucleation site and cooling-rate.

Influence of cross-rolling on the micro-texture and biodegradation of pure iron as biodegradable material for medical implants

“…In addition, since air quenching is faster than furnace cooling, the growth rate of recrystallized grains is constrained. The faster the cooling rate, the ferrite grain size of pure iron could be smaller [26]. Another reason for this result could also be due to substitutional impurities contained in the as-received material (Cu, Cr, Mn, Ni, Mo, Sn, Si, Al) ( Table 2).…”

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

“…1 clearly show the suppression of the coarse crystals by the presence of carbon in sintered plain iron. 1) For Abiko iron, 3) one of the purest types of iron available in the world today, Figure 2 shows that a decrease in the concentration of interstitial elements leads to the growth of ferrite crystals even at the ultralow concentration in sample (a) listed in Table 1. Another series of ferrite macrostructures, shown in Fig.…”

“…In ultrahigh-purity iron with 5 ppm carbon and 14 ppm nitrogen, lattice defects of deformed austenite also seem to become sites for the formation of ferrite nuclei that lead to the formation of equiaxial crystals. 3) 3. Growth of Samples through Transformation 3.1 Growth of Armco iron samples annealed in wet hydrogen The unidirectional A 3 transformation results in a unique permanent dimensional change of the sample.…”

“…1,2) Cast-and-rolled or wrought iron of ultrahigh purity 3) and wrought steel of the interstitial-free class 4) have been developed. Powder metallurgy, however, is an easier means than wrought metallurgy for producing iron with a very low concentration of interstitial elements because sintering iron powder in vacuum or hydrogen significantly reduces both carbon and nitrogen levels.…”

“…Naturally, researchers upon observing the optical microstructures and macrostructures of such crystals conclude that they have made a discovery. [1][2][3][4] These structures, however, were in fact reported several times [5][6][7][8][9][10] in the latter half of the 20th century, but attracted little attention from researchers since pure iron had negligible importance in the industry at that time.…”