The phase diagram of a new aluminum-bearing Fe-Cr alloy (/%: 1. 60C

26. OOCr

5. 50Al

0. 50Ni0. 12Y) is calculated by using thermodynamics software Thermal calc and combined with X-ray diffraction analysis the phase composition of the new alloy is defined. On this basis

the valence electron structure

covalent bond energy and lattice electrons of conventional high chromium cast iron and aluminum-bearing Fe-Cr alloys are analyzed by using solid and molecule empirical electron theory (EET) to reveal the mechanism for impact toughness decreasing of aluminum-bearing Fe-Cr alloy at electronic level. Results show that with adding 5. 50% Al

the aluminum-bearing structure units occur in Fe- Cr alloy

the strongest bond covalent electron pairs in the units decrease from 0. 486 40 to 0. 450 31

second strong bond covalent electron pairs also decrease from 0. 199 83 to 0. 118 88

while the number of lattice electrons decreases led to the impact toughness lowing. The EET predicting results for impact toughness of Fe-Cr alloy containing 5. 50% Al nicely coincide with the test measured results.