Microstructures and Nitrides of Fe-Cr-N Ternary System

The microstructures and the characters of nitrides in various alloys of the Fe-Cr-N system in the range of 0.5 to 40% chromium with up to about 1% nitrogen were studied by optical- and electron-microscope and by X-ray diffraction and chemical analysis of the extracted residue. The results are summarized as follows : (1) The nitrides detected were Fe_4N, CrN and Cr_2N. (2) In the content of about 0.1% N, the changes in microstructure with the lowering of temperature were as follows : 0.5% Cr : γ→α+γ→α+γ+CrN→α+CrN+Fe_4N ; about 0.5～6% Cr : γ→α+γ→α+γ+CrN→α+CrN ; abaut 6～7% Cr : γ→α+γ→α+γ+Cr_2N→α+Cr_2N+CrN ; about 7～13% Cr : γ→α+γ→α+γ+Cr_2N→α+Cr_2N ; about 13～26% Cr : α+γ→α+γ+Cr_2N→α+Cr_2N ; above about 26% Cr : α→α+Cr_2N. (3) In the case of alloys containing chromium above about 13%, the minimum content of nitrogen to obtain a completely austenitic structure increased with the chromium content ; for example, the minimum nitrogen contents in 13, 18 and 16% Cr alloys were about 0.1, 0.4 and 0.8%, respectively. The microstructures of these alloys revealed such a change as γ→γ+Cr_2N→α+γ+Cr_2N→α→Cr_2N. (4) The very fine acicular phase was observed within ferrite in the Fe-Cr-N alloys, which contained chromium above about 15% and were quenched in water from above about 1100℃. It was confirmed that this phase was Cr_2N precipitated during cooling clue to a remarkable decrease of the solubility of nitrogen in ferrite, and that the suppression of this precipitation was very difficult

Atraumatic Femoral Insufficiency Fracture in Postmenopausal Women Taking Bisphosphonate

The patient was 85-year-old woman. Five years and 8 months previously, bisphosphonate was prescribed for osteoporosis at a local clinic. Deformity of the thigh occurred when she tried to stand after sitting. X-ray findings revealed a transverse fracture of the right femoral diaphysis. Intramedullary nailing of the right femur was performed. Bone union was slightly delayed, but it was eventually achieved. Bisphosphonates have been reported to severely suppress bone turnover, resulting in the occurrence of fractures at the diaphysis or metaphysis of the femur. This type of fracture is characteristically induced by minor trauma and usually shows a simple transverse fracture. Bone union is delayed and these patients complain of prodromal symptoms. Because our case met all of the above criteria, it was concluded that the cause of her fracture was severely suppressed bone turnover (SSBT). We treated a patient who had a pathologic fracture associated with bisphosphonate therapy. Careful follow-up will be required, because it has been reported that such fractures can also occur on the contralateral side

Structural Diagrams and Phase Reactions of Fe-Cr-N Ternary System

Isothermal structural diagrams of Fe-Cr-N system in the range of composition from 0 to 40% chromium and up to 1% nitrogen were described at various temperatures below 1300℃. From the considerations on the phase relationship and the phase reaction, the structural diagrams were also obtained with various cross-sections at 0.1, 0.2 and 0.3% nitrogen, and 7, 13, 18 and 26% chromium. In this ternary system, the existence of the following three invariant reactions was presumed : (1) L+α⇄γ+Cr_2N at about 1330℃, (2)γ+Cr_2N⇄α+CrN at about 790℃ and (3)γ+CrN⇄α+Fe_4N at about 760℃