The FactSage FSstel steel alloy database

 

 

General

 

The elements included in the FactSage FSstel steel database are:

 

Al,  B,  Bi,  C,  Ca,  Ce,  Co,  Cr,  Cu,  Fe,  Hf, La,  Mg,  Mn,  Mo,  N,  O,  Nb,  Ni,  P,  Pb,  S,  Sb,  Si,  Sn,  Ta, Ti,  V,  W,  Zn, Zr

 

The FactSage FSstel steel database is based on relevant steel sub-systems from the old SGTE Solution database, but now incorporates updates of those systems as well as new published assessments. “Tramp elements” have also been included to allow calculations relating to recycling and removal of unwanted impurities to be performed.

 

The database contains more than 205 completely assessed binary alloy systems, together with approximately 100 ternary and 20 quaternary systems for which assessed parameters are available for phases of practical relevance. It contains 133 solution phases and 447 stoichiometric compounds.

 

In FactSage 7.3, the liquid phase is described by the Modified Quasichemical Model (MQM). With this model, many previous optimizations with the random mixing model and new optimizations with the MQM can be combined to give a more accurate description of the liquid solution in binary, ternary and higher-order systems. The deoxidation and desulfurization behaviour of liquid steel are well described by this model.

 

For the accurate description of the deoxidation of Fe-Ca and Fe-Mg liquid solutions, CaO and MgO associate species as proposed by Jung, Degterov and Pelton [1], have been incorporated in the liquid phase.

 

Updates in FactSage 7.3 version

 

In this update, the following systems have been completely re-assessed to reproduce recent experimental data for high alloyed steels and other steel systems:

 

(1) Al-C-Fe-Mn-Si (entire binary, ternary and quaternary systems) For high Mn, Si, Al alloyed steel

(2) Al-C-Fe-Mn-Si-N (all binary and ternary systems and several quaternary systems containing N) For high N-containing systems

(3) Al-C-Cr-Fe-Mn-Ni-Si-P (all binary and ternary systems and several quaternary systems containing P) For high P-containing systems

(4) Fe-Ni-Cr-Co-Cu-S (entire range of sulfur containing systems) For high S-containing systems

(5) Al-Co-Cr-Fe-Ni-Ti (all binary systems containing FCC and BCC order/disorder transitions and several key ternary systems including the Fe-Al-Ni system)  For BCC-B2 containing high strength steel

(6) Al-Fe-Zn-Mg-Si (all binary systems and key ternary systems)  For Zn galvanizing and new galvanizing alloy systems

(7) Al-Cr-Cu-Fe-Mg-Mn-Si (entire binary, ternary and higher-order systems)

 

As such, the database is intended to provide a sound basis for calculations covering a wide range of steelmaking processes, e.g.

 

-          reduction of oxygen and sulphur concentration levels through deoxidation and desulphurization of the melt

-          constitution of a wide range of steels, including austenitic, ferritic and duplex stainless steels and including carbide and nitride formation

-          conditions for heat treatment operations to produce a desired constitution

-          conditions for scrap remelting to maintain as low concentrations as possible of undesirable “tramp elements”

-          melt-crucible interactions

-          etc. 

 

As its name implies, the database is intended to allow calculations primarily for Fe-rich composition ranges, but since many of the assessed parameters, particularly for the binary sub-systems, provide reliable descriptions over all ranges of composition, calculations may sometimes be extended to higher concentrations of alloying components in Fe.  

Information on the possibility of calculating phase equilibria or thermodynamic properties for other composition ranges of multi-component alloys may be obtained by referring to the list of systems and phases for which assessed parameters are available (click on List FSSTEL). This will allow the user to determine whether proposed calculations for a particular higher-order system will be based on a complete set of assessed binary and ternary parameters (at best) or a summation of binary parameters only (at worst). Clearly the latter case, or use of incompletely assessed data sets, can lead to incorrect or unreliable results. 

 

In a binary system, if no assessed mixing parameters are available for a particular phase, the phase will be treated as ideal. Correspondingly, the properties of a ternary or higher-order phase will be calculated applying the appropriate models used in the database. This procedure may give useable results if the alloy compositions in question are close to a pure component or to a binary edge for which assessed data are available. However, results of calculations for other composition ranges should be treated with extreme caution. 

 

Specific information on each alloy system can be obtained from the list of references supplied with the List FSstel system and phase listing.

 

 

Composition and Temperature Ranges

 

As mentioned above, the database is intended to allow calculations primarily for Fe-rich composition ranges, although the assessed data are also reliable for higher concentrations of alloying components in a number of cases.

 

The database is generally valid for the temperature range of approximately 400oC to 1800oC, although for some steels containing high melting point metals, calculations are reliable to still higher temperatures.

 

Modeling

 

In the assessments, the liquid phase has been described using the Modified Quasichemical Model (MQM) with various interpolation technique for ternary and high order systems. Some assessments based on a simple substitutional liquid solution model with the Redlich-Kister-Muggianu polynomial expression are also integrated with the MQM. All solid solutions are described using a sub-lattice model. In particular, the FCC(austenite), BCC(ferrite) and HCP phases contain carbon, nitrogen, boron and vacancies on interstitial sites.

 

Use of the Database

 

The phase diagrams of all the binary, many ternary and a good number of multi-component sub-systems have been checked using FactSage.

 

To provide correct or more accurate calculations, the I or J option is automatically selected for several phases including LIQUID, FCC, BCC, B2_BCC and L12_FCC.  Disabling  the I or J option for these phases may result in incorrect results. As well, if necessary, the user must select the I or J option for other solution phases which potentially have miscibility gaps.

 

Reference

 

1.      I.-H. Jung, S.A. Decterov and A.D. Pelton, "A Thermodynamic Model for Deoxidation Equilibria in Steel", Met. & Mat. Trans., 35B, 493-508 (2004).


Text Box: Summary of Binary Systems stored in FSstel 73 version