A method to control the ausferritic as-cast microstructure in a process for obtaining iron parts with sections of different thickness, which comprises: a) Calculate a maximum thermal modulus, which corresponds to the section of the part with the greatest thickness, and a minimum thermal modulus, which corresponds to the section of the part with the lowest thickness, of the part; b) Obtain the cooling rate (oC/s) for the maximum and minimum thermal moduli considering air cooling, said cooling rates being extracted from a cooling curve experimentally obtained from several samples having different thermal moduli; c) Calculate the minimum cooling rate (CR min) needed to avoid the pearlitic nose, as a function of different contents of Ni, Cu and Mo (wt.%) comprised in a chemical composition of the iron part, in which said contents of Ni, Cu and Mo vary as follows: Ni: 3.0 - 5.0 % in wt, Mo: 0.0 - 0.2 % in wt, Cu: 0.0 - 1.0 % in wt wherein the minimum cooling rate (CR min) is calculated using the following formula: d) Select one of said compositions with a minimum cooling rate (CR min) lower than the cooling rate for the maximum thermal modulus; e) Calculate the eutectoid temperature (T eutectoid, oC) as a function of the thermal modulus for the composition selected, for all the different thermal moduli of the part; f) Calculate the shakeout temperature (T shakeout, oC) for each thermal modulus of the part; g) Identify if the shakeout temperature T shakeout for the minimum thermal modulus is over the eutectoid temperature (T eutectoid) calculated in e) and if the shakeout temperature T shakeout for the maximum thermal modulus is below the solidus temperature (T solidus, oC); h) Select among the T shakeout, the lowest temperature, i) Calculate the isothermal transformation temperature T isothermal_transformation for each thermal modulus of the part. j) Identify if the isothermal transformation temperature T isothermal_transformation for the minimum and maximum thermal moduli are between 450oC and 170 oC. k) Select among the isothermal transformation temperatures T isothermal transformation, the one that better fits the targeted mechanical properties. a) Calculate a maximum thermal modulus, which corresponds to the section of the part with the greatest thickness, and a minimum thermal modulus, which corresponds to the section of the part with the lowest thickness, of the part; b) Obtain the cooling rate (oC/s) for the maximum and minimum thermal moduli considering air cooling, said cooling rates being extracted from a cooling curve experimentally obtained from several samples having different thermal moduli; c) Calculate the minimum cooling rate (CR min) needed to avoid the pearlitic nose, as a function of different contents of Ni, Cu and Mo (wt.%) comprised in a chemical composition of the iron part, in which said contents of Ni, Cu and Mo vary as follows: Ni: 3.0 - 5.0 % in wt, Mo: 0.0 - 0.2 % in wt, Cu: 0.0 - 1.0 % in wt wherein the minimum cooling rate (CR min) is calculated using the following formula: Ni: 3.0 - 5.0 % in wt, Mo: 0.0 - 0.2 % in wt, Cu: 0.0 - 1.0 % in wt wherein the minimum cooling rate (CR min) is calculated using the following formula: d) Select one of said compositions with a minimum cooling rate (CR min) lower than the cooling rate for the maximum thermal modulus; e) Calculate the eutectoid temperature (T eutectoid, oC) as a function of the thermal modulus for the composition selected, for all the different thermal moduli of the part; f) Calculate the shakeout temperature (T shakeout, oC) for each thermal modulus of the part; g) Identify if the shakeout temperature T shakeout for the minimum thermal modulus is over the eutectoid temperature (T eutectoid) calculated in e) and if the shakeout temperature T shakeout for the maximum thermal modulus is below the solidus temperature (T solidus, oC); h) Select among the T shakeout, the lowest temperature, i) Calculate the isothermal transformation temperature T isothermal_transformation for each thermal modulus of the part. j) Identify if the isothermal transformation temperature T isothermal_transformation for the minimum and maximum thermal moduli are between 450oC and 170 oC. k) Select among the isothermal transformation temperatures T isothermal transformation, the one that better fits the targeted mechanical properties.