AboutJavad Mola Expertise I welcome questions related to physical metallurgy of steels preferably stainless steels.
Experience I have been lecturer in an institution of higher education from 2004. The courses taught include 'Casting principles', 'Casting of Ferrous and Non-Ferrous Alloys', 'Physical Metallurgy', 'Extractive Metallurgy', 'Technical English of Metallurgy' and 'Materials Science". My MS thesis dealt with processing of A356 and ZA27 alloys in the semisolid state. I have additionally worked on optimization of melt spinning parameters in order to obtain high quality amorphous ribbons made of CoFeSiB alloys.
Organizations Materials Research Center of Technology Development Institute affiliated to Sharif University of Technology
Publications Solid State Phenomena, Materials Science and Technology
Education/Credentials BS degree in Materials Engineering earned from Isfahan University of Technology, Isfahan, Iran. MS degree in Materials Science and Engineering earned from Sharif University of Technology, Tehran, Iran. Currently PhD candidate at Graduate Institute of Ferrous Technology (GIFT), Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
Question Hello Sir, and Thank You in advance for any help you may be able to impart.
I found this site Googling for a formula to obtain ferrite numbers. Back in 2004, someone had questioned them. The answer was that the formulas are not valid as physical testing would be, but I do not have that capability.
I need to find something that will get me fairly close, but I have had no success in finding any formulas whatsoever. Can you be of assistance?
Best Regards,
Stephanie Russell
Answer For sure, performing actual tests on your desirable stainless steel and under your processing conditions gives the most precise answer. So, one may resort to choose one of the followings only when actual tests cannot be done.
If you cannot conduct tests, I believe the best way of finding ferrite content after high temperature exposure of austenitic or duplex stainless steels, e.g. after welding, is to use one of the several commercial modeling packages such as ThermoCalc, FactSage, etc. These software can produce the phase diagram of your desirable steel composition. For instance, they can plot an equilibrium phase diagram of Fe-C while you have fixed the other elements' content. For instance, if you have a steel with the composition Fe-0.04C-18Cr-8Ni-2Mo-0.5Mn-0.25Si, you can plot Fe-C phase diagram (vertical and horizontal axes temperature and weight percent of C respectively) at 18wt%Cr, 8wt%Ni, 2wt%Mo, 0.5wt%Mn, and 0.25wt%Si. Then you look at the produced diagram and find the equilibrium phases that exist at any high temperature your stainless steel may experience during processing. These powerful packages which are developed based on the free energy of different phases at different temperature, are quite reliable in the case of steels because of numerous verification and strong databases. They can also give you plots of ferrite content as a function of temperature so you can predict the ferrite content on your desired temperature. If the cooling rate from the processing high temperature is high, we can claim that the high temperature ferrite is frozen due to rapid cooling and thus, room temperature ferrite content is the same as the ferrite present in the quenching temperature.
If you do not have access to such packages, then I might be able to do this calculation for you if you give me your composition; perhaps it is not be the best solution to buy such packages for only one calculation.
Another method to calculate ferrite number is to refer to one of the available Schaeffler diagrams. These diagrams show the stability field of different phases (austenite, ferrite, and martensite) as a function of Cr and Ni equivalents. Cr equivalent is a measure of amount of ferrite stabilizing elements whereas Ni equivalent quantifies contributions, to austenite stability, from different austenite stabilizing elements. Different researcher have put forward different formulas to calculate Cr and Ni equivalents, that is the coefficient of elements in different formulas is not the same. Schaeffler diagram helps to tell if the steel is susceptible to delta ferrite (high temperature ferrite) formation after welding. Such diagrams may be found for instance on books related to stainless steels.
