ON THE INFLUENCE OF SMALL AMOUNTS OF IMPURITIES ON RECRYSTALLIZATION AND GRAIN GROWTH OF HIGH PURITY IRON. NOTE III. EFFECT OF BORON ON RECRYSTALLIZATION AND EFFECT OF IMPURITIES ON NORMAL AND ANOMALOUS GRAIN GROWTH.
Final technical rept. for 1 Oct 62-29 Feb 64,
TURIN UNIV (ITALY)
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In Part I the results obtained led to conclude that boron is insoluble in very pure alpha iron. Research on the problem of the conditions of boron in pure iron both by making a theoretical verification based on thermodynamic considerations and by internal friction methods was extended. The first results confirm a nearly complete interstitial insolubility of boron in very pure iron. In a series of iron specimens silicon contaminations were observed, caused by the impurities of silica still present in the purest commercial sintered alumina refractories used. It was found that a 0.16 wt. content of silicon delays the 50 recovery and recrystallization temperature by 110C and 40C respectively. The Part II of this report concerns the effect of precipitated impurities and of medium and low amounts of strain on grain growth. Specimens of high-purity iron, with or without precipitated oxides, and of normal and deoxidized Armco iron were used. It was confirmed that the presence of precipitates stops grain growth up to a higher temperature, above which grain size increases suddenly. Medium amounts of strain 25-40 produce an additional driving force that enhances grain growth. In the case of specimens cold-worked by low amounts 3-6 grain growth temperature is raised.