Role of Mn and Si in temper embrittlement of low alloy steels
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c
4 D od o
D2d
or In (D Z d/Dód o) = 2 In (D/D o) + in (d/d o) = 0 U
100
ZUU
JUU
4UU
500
Thus, the strain and the strain rate of the disk, e and are obtained as follows,
600
TIME (min)
e = In (d/d o) _ —2 In (D/D o)
Fig. 3—Variation of the strain rate at the bottom of neck.
E
^N = — dt
In DN/DN,o)
[2]
where DN o is an initial diameter of neck. (see Appendix). It can be seen clearly from the above mentioned results that localized deformation is quite effectively re-
dt = —2 dt
I In (D/D o)
The strain rate at the bottom of the neck, É N is obtained finally
t j In (DN/DN,o) éN = — 2d
stricted when m is high. Large necking resistance and
1. W. A. Backofen, I. R. Turner, and D. H. Avery: Trans. ASM, 1964, vol. 57, pp; 980-90. 2. D. H. Avery and W. A. Backofen: ibid., 1965, vol. 58, pp. 551-62. 3. D. Lee and W. A. Backofen: Trans. TMS-AIMS, 1967, vol. 239, pp. 1034-40. 4. W. B. Morrison: ibid., 1968, vol. 242, pp. 2221-27. 5. E. W. Hart: Acta Met., 1967, vol. 15, pp. 351-55.
Role of Mn and Si in Temper Embrittlement of Low Alloy Steels
tion of Cr and Ni to prior austenite boundaries. The purpose of this communication is to demonstrate that segregation of Mn, Si as well as small amounts of P, S and Sn occurs at grain boundaries of these steels. The present experiments were carried out using a high sensitivity, high resolution electron spectrometer consisting of a retarding stage and two cylindrical mirror analyzers in tandem. The technique of fracture surface analysis in AES systems to obtain grain boundary composition has been adequately described earlier.' The specimen examined is identical to that used for the earlier study:' the composition is C-0.43 pet, Ni -3.45 pet, Cr-1.71 pet, Mn -0.90 pct, Si-0.27 pct and Be-0.06 pet by weight. The ABS analysis of the specimen is made in the embrittled' (stepcooled) state. Since the fracture obtained is primarily intergranular, the spectrum (Fig. 1) obtained represents average grain boundary composition. Segregation of P, S, Sn, C and Mn at the surface is noticed. No Be is detected. Reduction in the peak-to-peak height of the —85 eV peak due to sputtering indicates that small but detectable amounts of Si is segregated at the grain boundaries. Ion sputtering caused all the peaks of P, S, Sn and Mn to decrease rapidly; Fig. 2 shows a portion of the high resolution spectra before and after sputtering approximately 75A. The concentrations of Cr and Ni also decrease due to sputtering. From the peak height measurements, the amount of Mn at grain boundaries in the embrittled condition may be estimated to be about 4 wt pct, representing
high ductility without localized deformation are, therefore, expected for the materials with high m. Appendix: The derivation of the Equation [2]. When a specimen deforms inhomogenéously, strain distribution
A. JOSHI, P. W. PALMBERG, AND D. F. STEIN The technique of Auger Electron Spectroscopy (AES) has greatly contributed to the understanding of grain boundary segregation' and the related phenomenon of temper embrittlement in
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