| Abstract: | Differential thermal analysis was used to determine the effects of variable Si, W and C contents on the behaviour of W-V-Si highspeed steels during melting and crystallization and to develop certain fragments of pseudobinary phase diagrams corresponding to melting and crystallization of these materials. Melting of S 9-0-2 steel involves the following sequence of transformations: reverse three-phase eutectic reaction, direct melting of austenite grains, reverse three-phase and then four-phase peritectic reactions, and melting of high-temperature ferrite. In steels containing more than 2% Si reverse four-phase peritectic reaction occurs immediately after partial completion of reverse eutectic reaction and in steels with more than 4% Si there is also direct melting of carbides. A decrease in tungsten content from 9.5 to 7 % in steels containing 2 % Si and 1.05 or 0.9 % C enhances direct melting of austenite grains; an increase in tungsten content to 12% inhibits this reaction completely. A decrease in carbon content from 1.05 to 0.9 % in steels containing W 7-12, V 2.5 and Si 2 % does not change the nature of transformations on melting. Crystallization of conventional S 9-0-2 steel involves the following sequence of events: formation of high-temperature ferrite crystals from the liquid, three-phase peritectic reaction, direct crystallization of austenite from the liquid, and three-phase eutectic reaction. With silicon contents exceeding 3% direct crystallization of austenite and three-phase eutectic reactions occur simultaneously. This sequence of reactions is not affected by reduction of tungsten content from 9.5 to 7 % in steels containing 2% Si and 1.05 or 0.9% C. An increase in tungsten content to 12% in such materials results in complete inhibition of direct crystallization of austenite from the liquid and in 1.05% C steel there is an additional change involving simultaneous occurrence of three-phase peritectic and eutectic reactions. A decrease in carbon content from 1.05 to 0.9% in steels containing 7–12% W and 2% Si does not change the nature of transformations during cooling but does enhance partially simultaneous occurrence of three-phase peritectic and eutectic reactions. |
