Phase transformations during heat treatment of WMoV 11-2-2 type high-speed steels with increased contents of Si and Nb or Ti

Fabrication, Structure, Properties and Application of Gradient Sintered Carbide-Steels with HS6-5-2 Matrix

“…High-speed sintered steels are annealed twice or thrice, in the temperature range ensuring the maximum secondary hardness (550-560°C). The secondary hardness effect attained is caused by the precipitation of coherent M 4 C 3 carbides in a martensitic matrix and by the transformation of retained austenite into martensite during cooling from the tempering temperature [4,[14][15][16][17][18][19]. The secondary hardness range in sintered steels is shifted to a slightly lower temperature than in convention steels with a similar chemical composition.…”

“…The secondary hardness range in sintered steels is shifted to a slightly lower temperature than in convention steels with a similar chemical composition. The maximum hardness achieved depends on the applied austenitisation temperature [2,4,[14][15][16][17][18][19]. The fabrication costs of sintered high-speed steels are higher than manufacturing costs of conventional steels, but the tools made of sintered steels are much more durable than those made of conventional steels.…”

“…Cutting tools made of sintered highspeed steels are heat treated to achieve an optimum structure consisting of fine matrix grains with identical size and carbides uniformly distributed in it. In the softened condition, the structure of sintered high-speed steels contains alloy ferrite with uniformly arranged MC, M 6 C and M 23 C 6 carbides and also contains M 2 C carbides in steels with a high concentration of molybdenum and M 7 C 3 -type carbides in steels with a high concentration of silicon, and in steels containing M 23 C 6 -type carbides with a higher concentration of carbon [2,4,[14][15][16][17].…”

The secondary precipitates of niobium-alloyed M3:2 high speed steel prepared by spray deposition

“…As a substitutional element, Niobium (Nb) has a higher affinity with carbon compared to V, and can be used as a carbide-forming element to form very stable carbides [13][14][15]. At Nb content at and above 3%, Nb-rich MC-carbides can be precipitated straightly from the melts and grow up to very large sizes [16].…”

“…Besides the primary carbides, considerable nano-sized secondary carbides can be precipitated from the oversaturated martensite during tempering so as to provide secondary hardening for HSSs. To date, the influences of Nb on the microstructures and properties of HSSs prepared by IM and PM have been extensively carried out [13,[15][16][17][18][19][20], however, the metallographic investigation of the Nb-containing HSSs produced by spray forming has barely been reported. Because of ultra-fine (several in nano size) secondary carbides and poor quality of the thin foil for TEM observation, these carbides with a coherent transition to the matrix cannot be imaged well after conventional tempering, so the evaluation of the secondary carbides compared to that of the primary carbides in HSSs is insufficient.…”