| الملخص: | By using JMatPro software and according to the 0. 70C steel coil (/%：0. 67C, 0. 17Si, 0. 50Mn, 0. 010P, 0. 010S, 0. 10Cr) produced at steel works, the effect of C (0. 65% ~ 1. 00% ), Si (0. 20% ~ 0. 55% ), Mn(0. 50% ~ 1. 45% , Cr (0. 10% ~0. 75% ), S (0. 010%~0. 070% ) , P (0. 010%~0. 060% ) and austenite grain ratting (5. 0 ~ 8. 0) in high carbon steel rod coil on martensite formation critical cooling rate (CCR<sub>Mf</sub>) has been simulate to get the predict high carbon steel CCR<sub>Mf</sub>expression: CCR<sub>Mf</sub>/(℃·s<sup>-1</sup>) =4. 088 -9. 98 x [C]/% -3.58 x [Si]/% -5.12[Mn]/% - 0. 001 [P]/% +23. 45 x [S]/% -7.42 X [Cr]/% +2 x G<sub>m</sub>G<sub>m</sub>-austenite grain size rating. Results show that with increasing the C, Mn, Si and Cr content in steel the CCR<sub>Mf</sub>decreases, with increasing the S content in steel and original austenite grain size rating the CCR<sub>Mf</sub>increases and the effect of P on CCR<sub>Mf</sub>is minor； the effect of C and Mn on CCR<sub>Mf</sub>is largest； and the measure value of martensite formation critical cooling rate ( CCR<sub>Mf</sub>) of the 70C steel is 8. 51 ℃/s, and its calculated value is 8. 79℃/s with error 0. 28 ℃/s. It is suggested that during high carbon steel casting process the key point is to control C and Mn segregation and to fine austenite grain size during rolling process for decrease of formation of martensite structure.
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