Wj. Nam et al., Effects of alloy additions and tempering temperature on the sag resistanceof Si-Cr spring steels, MAT SCI E A, 289(1-2), 2000, pp. 8-17
The effects of Mo, W, and V additions and tempering temperatures on the sag
resistance in relation to the microstructural evolution during tempering o
f Si-Cr spring steels were investigated by performing TEM examination, tors
ional Bauschinger tests, hardness tests and tensile tests. The hysteresis l
oop area measured in torsional Bauschinger tests, which is closely related
with the sag resistance, is directly influenced by the distribution of prec
ipitates. It increases and then decreases with tempering temperature, after
reaching its maximum value at 350 degrees C. The additions of Mo and/or W
result in a finer distribution of tempered carbide particles due to the dec
rease in the rate of the spheroidization and of the coarsening of carbide p
articles above 400 degrees C. However, they do not affect the behavior of t
empered carbides at low tempering temperatures. Accordingly, the additions
of Mo and/or W increase the hysteresis loop area at tempering temperature a
bove 400 degrees C. The V addition increases the hysteresis loop area as we
ll as hardness due to the precipitation of vanadium carbonitrides, regardle
ss of tempering temperature. In considering industrial application of sprin
g steels. a new parameter, the ratio of the hysteresis loop area in the tor
sional Bauschinger test to hardness, is suggested. (C) 2000 Elsevier Scienc
e S.A. All rights reserved.