The asquenched microstructure and tempering behavior of rapidly solidified tungsten steels
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would almost certainly result in a finer microstructure, and this might be expected to alter the isothermal tempering characteristics. The iron-tungsten-carbon alloys ranged from 6.3 wt pct to 23 wt pct tungsten, with a constant tungsten:carbon atomic ratio of 2:1 (see Table I). The Fe-23 wt pct W-0.75 wt pct C alloy was chosen to represent a simplified T1 steel, the carbon content being the same in both alloys, while the vanadium and chromium in T1 is replaced by additional tungsten in the ternary alloy. At the other end of the range of ternary alloys was the Fe-6.3 wt pct W-0.21 wt pct C alloy previously examined in the solid state. 2 The other four alloys were chosen to span the range between the two alloys mentioned above. The effect of RS upon the microstructure and hardness of these ternary alloys as a function of composition was investigated and the relative isothermal tempering behaviors of RS and solid-state quenched Fe.6.3 wt pctW-0.21 wt pct C were compared. A preliminary investigation was also made of the relative isochronal tempering behaviors of RS and solid-state quenched Fe-23 wt pct W-0.75 wt pct C and TI tool steel. EXPERIMENTAL PROCEDURE Commercial grade T l high speed tool steel was obtained in the form of 13 mm diam rod. The other alloys, shown in Table I, were prepared from >_99.99 pct pure iron, tungsten and carbon by induction melting in recrystallized alumina crucibles under a dynamic argon atmosphere. The as-cast alloys were homogenized for 100h at 1130 ~ and specimens were taken from the homogenized alloys for rapid solidification. RS was achieved by means of a two-piston apparatus described previously. 3 Individual specimens of ~ 0 . 7 g mass were levitation melted in an argon atmosphere and then allowed to fall under gravity until quenched between two pistons accelerated magnetically. The RS foils were generally 70 to 120/.tm in thickness and approximately 30 mm in diam. The effective cooling rate has been measured as ~ 10 7Ks- 1 at the melting point, falling to ~105 Ks -1 at 700 ~ 4
ISSN 0360-2133/8110911-1557500.7510 METALLURGICALTRANSACTIONSA 9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME 12A, SEPTEMBER 1981--1557 THE METALLURGICAL SOCIETY OF AIME
Table I. Chemical Compositions of Six Ternary Iron-TungstenCarbon Alloys and Commercial High Speed Tool Steel T1 Weight Pct of Alloying Element (At Pct) Alloy FEWC FEWC FEWC FEWC FEWC FEWC TI
W 1 2 3 4 5 6
C
6.3 (1.99) 9.5 (3.05) 13.0(4.27) 16.5(5.54) 20.0 (6.80) 23.0 (8.06)
0.21 (0.99) 0.32 (1.53) 0.42 (2.14) 0.54 (2.77) 0.65 (3.43) 0.75 (4.03)
18.0
0.75
V
Cr
Fe Balance Balance Balance Balance Balance Balance
1.10 4.0
Balance
In order to compare the structural and mechanical properties of the RS alloys with solution treated and solid-state quenched alloys, specimens of the latter were obtained by cold rolling the homogenized alloys ~ 5 0 pct and then solution treating at 1150 ~ for 50 h, followed by a brine quench. All heat treatments were carried out either in sealed silica capsules which had been evacuated and then flushed
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