Heat Treatment Equipment with Controllable Cooling Rate and the Application on the Quenching of Hot Work Tool Steel
Date Issued
2010
Date
2010
Author(s)
Tzou, Yi-Kang
Abstract
To quench at a constant rate, in this research, a quenching equipment was designed by controlling the position of specimen in the furnace tube with a PID temperature controller. Standard and modified hot work tool steels were quenched with a constant cooling rate, then tempered to the same hardness to compare their toughness. After observing the microstructure and comparing the composition of each steel, the effect of alloying elements on the toughness in the constant rate quenching was varified.
The result indicates that the cooling curves were well-controlled to be a smooth straight line by the designed equipment, and the toughness decreased with the reducing of cooling rate for each steel. Between different steels, the modified ones with higher alloy elements are with higher hardness after quenching because of their higher hardenability; however, their toughness performance are inferior to the standard ones.
According to the effect of the constant-rate- quenching and composition on the CCT diagram of each steel, the reasons why the modified steels are inferior to the standard ones on toughness are presumed below:
1.The initial(above 750℃) cooling rate of constant-rate-quenching is far slower than the conventional quenching for the same average cooling rate, that is, the chance to form prior grain boundary carbide is higher than the conventional.
2.Because of the higher molybdenum, the modified steels are with higher tendency to form prior grain boundary carbide than the standard ones. This prior grain boundary carbide could severely cause the deterioration of toughness.
3.Compared with standard steels, the modified ones contain higher manganese and lower vanadium, causing lower austenizing temperature and fewer vanadium carbide to suppress coarsing of grains. Modified steels, quenching from the same temperature as standard ones, maybe overheated to form coarse grains, therefore, worse toughness performance is expectable.
Subjects
PID controller
quenching
hot work tool steel
toughness
Type
thesis
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