Effect of alloying additions on fracture behavior of Mo-Containing secondary hardening steels
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Table I. Chemical Compositions of Alloys (Weight Percent) Alloy Designation Mo Mo-Cr Mo-Cr-Co Mo-Cr-Co-Ni
C
Mo
Cr
Co
Ni
0.31 0.22 0.27 0.24
4.22 2.10 1.95 1.55
-2.41
--14.75 14.25
---10.80
2.66
2.90
,,-,55 r
45
REFERENCES
~
Y. Bergstrom: Mater. ScL Eng, 1970, vol. 5, pp. 193-200. Kanji Ono: Metall. Trans., 1972, vol. 3, pp. 749-51 W.B. Morrison: MetalL Trans., 1971, vol. 2, pp. 2947-48. H.J. Kleemola and M.A. Nieminen: MetalL Trans., 1974, vol. 5, pp. 1863-66. 5. J.R. Cahoon: Metall. Trans., 1972, vol. 3, pp. 3040-41
1. 2. 3. 4.
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a~ 35
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Effect of Alloying Additions on Fracture Behavior of Mo-Containing Secondary Hardening Steels
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H. KWON, C.M. KIM, K.B. LEE, H.R. YANG, and J.H. LEE
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0.(5.
METALLURGICAL AND MATERIALSTRANSACTIONS A
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i 400
.
.
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.
.
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0
.
.
i 450
i 500
I 550
i 600
Aging T e m p .
(*C)
i 650
700
Fig. 1--Absolute hardness values and relative values with respect to the as-quenched hardness as a function of aging temperature in Mo, Mo-Cr, Mo-Cr-Co, and Mo-Cr-Co-Ni steels. 150
Test Temp. .....
25"C 200"C
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H. KWON, Professor, is with the Department of Metallurgy and Materials Engineering, Kookmin Unlverstty, Seoul 136-702, Korea and jointly appointed at the Center for Advanced Aerospace Materials. J.H. LEE, Professor, and K.B. LEE, Graduate Student, are with the Department of Metallurgy and Materials Engineering, Kookmin University, Seoul 136702, Korea. C.M. KIM, formerly Graduate Student, Department of Metallurgy and Materials Engineering, Kookmin University, is with the Korea Gas Corporation, Kyunggi-Do 425-150, Korea. H.R. YANG, Professor, is with the Department of Mechanical Engineering, lnchun Junior College, Inchun 402-750, Korea. Manuscript submitted September 22, 1995.
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350
The effect of Cr, Co, and Ni additions on the secondary hardening behavior in Fe-C-Mo steels was systematically analyzed in terms of their effect on M2C carbide formation and reported elsewhere in this journal.t1] In this study, the fracture behavior has been analyzed for the same alloy systems. The chemical compositions of the alloys used in this study are presented in Table I. After austenitizing at 1200 ~ for 1 hour, standard Charpy V-Notch impact specimens were aged in the range of 400 ~ to 650 ~ for 1 hour. The variations in the absolute hardness values and relative values with respect to the hardness in as-quenched condition for 4Mo, 2Mo-2.5Cr, 2Mo-2.5Cr-14Co, and 1.5Mo3Cr-14Co-10Ni steels are shown in Figure 1. The effect of alloying additions on secondary hardening is summarized in the following paragraph.['l The strong secondary hardening peak in the 4Mo steel at 600 ~ is due to the formation of fine M2C carbides following the dissolution of M3C cementite. The Cr addi-
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1
.4.q
I
400
Aging
I
I
500
Temp.
600
?00
(*C)
Fig. 2--Variation in impact toughness with aging temperature of the MoCr steel tested at room temperature and 200 ~
tions eliminated the secondary hardening behavior due
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