3
Results and Conclusions
Table 2 lists the dy- namic toughness of the re- spective steels as a function
of deoxidation practice and inclusion density. Of the steels heat treated to similar hardness values of 36-38 HRC, the HY130 heat B obtained the high- est average toughness of 165 kJ/m2
.
T e 4325 and the Fe-Mn-Al-C steel (aged for 60 hours at 986F [530C]) had similar toughness values of 153 kJ/ m2
a much higher toughness of 376 kJ/ m2
of 32 HRC (13 hours at 986F (530C). Titanium-treated steels showed a reduction in tough- ness when compared to steels deoxidized using aluminum and calcium, as shown in Fig. 1. T e HY130 heat E steel, which was titanium-treated and contained eutectic Type II sulfi des, had the lowest toughness of 59 kJ/m2
.
Adding misch metal to a titani- um-treated HY130 eliminated Type II sulfi des and recovered toughness to 95 kJ/m2
toughness of titanium-treated steels when compared to alu- minum and calcium deoxidized steels was attributed to coarse TiN particles, which fractured
. T e poor
Figure 1. Dynamic fracture toughness (DFT) is shown to have an inverse relationship with inclusion density. Tita- nium treatment sharply decreases DFT when compared with aluminum and calcium deoxidized steels.
Table 2. Dynamic Fracture Toughness as a Function of Deoxidation Practice Steel/Heat
Deoxidation Practice
HY130 - A HY130 - B HY130 - C
HY130 - C, HIP HY130 - D HY130 - E 4325 4130
Fe-Mn-Al-C aged 13 hours @ 986F (530C)
Fe-Mn-Al-C aged 60 hours @ 986F (530C)
Al and Ca Al and Ca Al and Ca Al and Ca
Al, Ti and misch metal Ti
Al only Al, Ca and Ti Al Al Hardness (HRC)
37.7 ± .9 36.9 ± 1 36.2 ± .2 36.1
37.7 ± .8 37.4 ± 1 37 ± 2 38 ± 1
32 ± 1 38 ± 2
This article was adapted from a paper (12-054) included in the Proceedings of the 2012 American Foundry Society Metalcasting Congress.
. T e Fe-Mn-Al-C steel achieved when aged to a hardness
during dynamic loading and exhibited intergranular fracture facilitated by eu- tectic type II MnS inclusions in heats without misch metal additions. In contrast, the calcium and aluminum heats contained mostly globular calcium aluminate and MnS inclusions that facilitated void rupture at the particle interface, a condition less detrimental to toughness than particle fracture. T e uncharacteristi- cally low toughness of HY130 heat C, which was vacuum induction melted, was due to the presence of a high volume fraction 1.8×10-4
, of porosity.
@
ONLINE RESOURCE
Visit
www.moderncasting.com for a copy of the full paper.
Hot isostatic pressing was eff ective at reducing the volume fraction of poros- ity from 1.8×10-4
to 1×10-5 and the
average pore/void size from 2.7 to 1.4 µm which resulted in a restoration of fracture toughness to 162 kJ/m2
, sta-
tistically equivalent to the toughness value of 165 kJ/m2
that was observed
from HY130 heat B. T e benefi t of additional nickel content was not apparent for the steels treated with titanium. T erefore, the use of titanium in chromium and molybdenum steels is strongly discouraged if high toughness is required. Casting suppliers should melt under protective atmosphere utilizing aluminum and calcium for deoxidation. However, if titanium is required for control of nitrogen, it should be accompa- nied by additions of misch metal to prevent type II sulfi des.
Avg. JId (kJ/m2
122 ± 5.7 165 ± 2 114 ± 8 162
88 ± 9 59 ± 4 153 94
376 ± 69 153 ± 25
) Inclusion Density, #/mm2
267 115 76 76 78
247 46 121
77 77 Jul/Aug 2012 | METAL CASTING DESIGN & PURCHASING | 47
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60