鍛造焼入法が炭素鋼の機械的性質におよぼす影響について

抄録

Recently, the “Deform-quenching” method, in which steel is quenched immediately after hot working in the stable phase of austenite, has been high-lighted for its industrial application because of the resulting better mechanical properties and higher heat efficiency.
It is investigated how the “Deform-quenching” method works on the mechanical properties of steel and how its process will be. The materials used as specimens were three plain carbon steels with 0.26, 0.45 and 1.07%C. The specimens were prepared by (i) the “Deform-quenching” method, (ii) quenched and tempered after the treatments of hot working and keeping at the forge-finishing temperature for 15, 30 and 120 minutes, or (iii) normal quenching.
It was found that the steels which were subjected to the “Deform-quenching” method were much superier in hardness and mechanical properties after tempering, and the carbides were more uniformly dispersed than the steels treated by other methods for all the specimens. When the “Deform-quenched” steel was kept longer in the as-forged condition at about 900°C, the hardenability became inferior and almost disappeared in the case of quenching after keeping two hours at that temperature. It seems that the stress in forging promotes the martensite transformation and improves the hardenability of steel. That is the reason why mechanical properties in the tempered steels in the “Deform-quenching” method are improved, although the grain size of austenite grows.
When applied the same method to 99.9%Ni, the effect of work hardening remained for 15∼20 min even at a temperature of about 900°C which is higher than the recrystalization temperature. Namely, it has been found that forging effect can be retained for a fairly long time.