Nitridable steels for cold forming processes
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which the ratio Ti:C was larger than 4, only to a very small extent. This was attributed to the stabilization of interstitials by titanium.4 These early investigations indicate that titanium alloyed low carbon steel is a promising candidate for combining formability and nitridability. Such steels however, due to their 10w carbon content, exhibit low strength. The work to be reported here was concerned with increasing the strength of titanium alloyed low carbon steel by additional alloying elements without impairing formability and nitridability, and to study the formability and nitridability of these new alloys. In the second phase of this work, the results of which are published elsewhere: machinability tests and an experimental manufacture of pivoted types of a high speed impact printer were made of these new alloys. The manufacture of this type involved fine flow blanking, and a severe cold forming process, the "kneading" of characters. This was followed by a number of grinding operations. Finally, the types were nitrided to improve wear resistance. Distortion due to nitriding was evaluated on a sample of 33 types. The mean value of distortions was 0.0/~m with a standard deviation of 1.5/~m.
THE COMPOSITION OF ALLOYS The carbon content was restricted to a maximum of 0.05 pct, because carbon both decreases ductility and inhibits the diffusion of nitrogen in iron. Titanium content was varied between 0.5 to 2.0 pct. Titanium by forming a carbide depletes iron from interstitial carbon and thereby promotes both formability and nitridability. It also is the active nitride former imparting hardness to the nitrided layer. While titanium in solid solution strengthens iron, the strength increase by 1 to 2 pct titanium alone is not sufficient. The increase of strength by solute silicon and manganese is large, nevertheless their quantities were limited to 0.3 and 0.4 pct respectively in order to avoid a decrease in formability, Perhaps the most favorable alloying element of iron for this application is nickel, it strengthens iron considerably while it also increases notch toughness. It is believed that the change in bonding with nickel alloying increases the cross slip of screw dislocations6 which
ISSN 0360-2133/81 / 1111-1951500.75/0 METALLURGICAL TRANSACTIONS A 9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME 12A, NOVEMBER 1981--1951 THE M E T A L L U R G I C A L SOCIETY OF AIME
explains the increase in notch toughness and should be favorable for formability as well. The alloys were prepared in a sequence of several operations including vacuum induction melting and casting, forging, hot rolling, cold rolling to plate, annealing to obtain the desired grain size and machining the plate to strips of the desired dimensions. The alloys were prepared at the Columbus Laboratories of Battelle. Compositions and grain sizes are given in Table I. For all alloys S
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