. Transactions. r structure showing small-scale Widmannstattian. 650° C. (first heated to 850° C.) came out of the furnace so hard on thesurface that it had to be ground to finish size. The same heat treatmentwas given a duplicate bar in hydrogen. The bar treated in ammoniacracked on its surface when pulled as though case hardened; the hydrogen H. E. WHEELER 277 bar did not; see Fig. 25. The structure of the NH^ treated bar isshown in Fig. 26. Charpy Bar Test.—The second sample, which contained per and per cent. Ni, was made up into Charpy impact test was heated to 85
. Transactions. r structure showing small-scale Widmannstattian. 650° C. (first heated to 850° C.) came out of the furnace so hard on thesurface that it had to be ground to finish size. The same heat treatmentwas given a duplicate bar in hydrogen. The bar treated in ammoniacracked on its surface when pulled as though case hardened; the hydrogen H. E. WHEELER 277 bar did not; see Fig. 25. The structure of the NH^ treated bar isshown in Fig. 26. Charpy Bar Test.—The second sample, which contained per and per cent. Ni, was made up into Charpy impact test was heated to 850° C, cooled to 650° C, and treated with NHs atthis temperature for 48 hr.; a second was treated the same way in nitrogen,and a third left untreated. They broke as follows: untreated, 180 per sq. in., with dark fracture; in nitrogen, 168 per sq. in., withdark fracture; in ammonia, 32 per sq. in., with bright broken ammonia-treated bar was ground off on the fractured end. Fig. 27.—Charpy bak at fractured end. per cent. C, per Treated above critical change 48 hr. in NH3 at 650° C. Etched 15 4 per cent, nitric acid. X 25. and polished and etched. The entire end is shown in Fig. 27, the hghtarea being the area opposite the slot during treatment. This area isshown in Fig. 28; this grades off into the structure shown in Fig. 29,then Fig. 30, then Fig. 31, which last is characteristic of all the restof the dark area. For brevit^^ from here on these and similar structureswill be referred to as austenitic. Fig. 28, martensitic, Figs. 29 and 30,Widmannstattian, Fig. 31. The martensitic area is rarely encounteredspread out, as here, but usually is a very narrow zone, if it is visible at always etches to a purplish color with nitric acid. A third sample of per cent, carbon and per cent, nickel wasused to make 60 Charpy bars. Of these, 15 were treated 20 hr. in NH3at 700° C, first heating to 850° C.
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
