Abstract
The heat treated Nb–Mo steel with 80 kg/mm2 strength level, reported here, is a new type of steel which has been developed to replace the conventional T–1 type steel. The important feature of this steel is that its alloying elements are considerably reduced in number and amount. By such a reduction, the carbon equivalent (Ceq) in welding is considerably reduced and the improvement of weldability is achieved. It is rather surprising that this steel has a sufficiently high strength and toughness as 80 kg/mm2 level high strength steel due to the coexistence of proper amounts of Nb & Mo, in spite of the reduction of alloying elements. In this paper, the effect of Nb and Mo upon the mechanical properties and hardenability of the new steel is investigated.
Tensile tests, Charpy tests and the Jominy tests have been carried out on the base steel, Nb treated steel, Mo steel and Nb–Mo steel. The results are compared with the values calculated according to the known formula with regard to strength and hardenability.
It has been found that the increase in strength by the duplex addition of Nb and Mo is far greater than sum total of strength obtained by the single addition of Nb and Mo, and also that the hardenability of this new steel increases by a combined effect of Nb–Mo–B tripple addition.
