The work determined the influence of aluminium in the amount from about 1% to about 7% on the graphite precipitates in cast iron with

relatively high silicon content (3.4% to 3.90%) and low manganese content (about 0.1%). The cast iron was spheroidized with cerium

mixture and graphitized with ferrosilicon. The performed treatment resulted in occurring of compact graphite precipitates, mainly nodular

and vermicular, of various size. The following parameters were determined: the area percentage occupied by graphite, perimeters of

graphite precipitates per unit area, and the number of graphite precipitates per unit area. The examinations were performed by means of

computer image analyser, taking into account four classes of shape factor. It was found that as the aluminium content in cast iron increases

from about 1.1% to about 3.4%, the number of graphite precipitates rises from about 700 to about 1000 per square mm. For higher

Al content (4.2% to 6.8%) this number falls within the range of 1300 – 1500 precipitates/mm2

. The degree of cast iron spheroidization

increases with an increase in aluminium content within the examined range, though when Al content exceeds about 2.8%, the area

occupied by graphite decreases. The average size of graphite precipitates is equal to 11-15 μm in cast iron containing aluminium in the

quantity from about 1.1% to about 3.4%, and for higher Al content it decreases to about 6 μm.

The influence of aluminium (added in quantity from about 0.6% to about 2.8%) on both the alloy matrix and the shape of graphite precipitates in cast iron treated with a fixed amounts of cerium mischmetal (0.11%) and ferrosilicon (1.29%) is discussed in the paper. The metallographic examinations were carried out for specimens cut out of the separately cast rods of 20 mm diameter. It was found that the addition of aluminium in the amounts from about 0.6% to about 1.1% to the cast iron containing about 3% of carbon, about 3.7% of silicon (after graphitizing modification), and 0.1% of manganese leads to the occurrence of the ferrite-pearlite matrix containing cementite precipitates in the case of the treatment of the alloy with cerium mischmetal . The increase in the quantity of aluminium up to about 1.9% or up to about 2.8% results either in purely ferrite matrix in this first case or in ferrite matrix containing small amounts of pearlite in the latter one. Nodular graphite precipitates occurred only in cast iron containing 1.9% or 2.8% of aluminium, and the greater aluminium content resulted in the higher degree of graphite spheroidization. The noticeable amount of vermicular graphite precipitates accompanied the nodular graphite.

The influence of aluminium added in amounts of about 1.6%, 2.1%, or 2.8% on the effectiveness of cast iron spheroidization

with magnesium was determined. The cast iron was melted and treated with FeSiMg7 master alloy under industrial conditions.

The metallographic examinations were performed for the separately cast rods of 20 mm diameter. They included the assessment of the

shape of graphite precipitates and of the matrix structure. The results allowed to state that the despheroidizing influence of aluminium

(introduced in the above mentioned quantities) is the stronger, the higher is the aluminium content in the alloy. The results of examinations

carried out by means of a computer image analyser enabled the quantitative assessment of the considered aluminium addition influence.

It was found that the despheroidizing influence of aluminium (up to about 2.8%) yields the crystallization of either the deformed nodular

graphite precipitates or vermicular graphite precipitates. None of the examined specimens, however, contained the flake graphite

precipitates. The results of examinations confirmed the already known opinion that aluminium widens the range of ferrite crystallization.

The work presents results of investigations concerning the production of cast iron containing about 5-6% aluminium, with the ferritic

matrix in the as-cast state and nodular or vermicular graphite precipitates. The examined cast iron came from six melts produced under the

laboratory conditions. It contained aluminium in the amount of 5.15% to 6.02% (carbon in the amount of 2.41% to 2.87%, silicon in the

amount of 4.50% to 5.30%, and manganese in the amount of 0.12% to 0.14%). After its treatment with cerium mixture and graphitization

with ferrosilicon (75% Si), only nodular and vermicular graphite precipitates were achieved in the examined cast iron. Moreover, it is

possible to achieve the alloy of pure ferritic matrix, even after the spheroidizing treatment, when both the aluminium and the silicon occur

in cast iron in amounts of about 5.2÷5.3%.

The paper presents results of a study on the effect of passage of time on magnesium content in iron alloys and the effect of magnesium content on the number of vermicular graphite precipitations per unit surface area and value of the longitudinal ultrasonic wave velocity for two different vermicularization methods. The study was carried out with the use of inspection bar castings. For specific production conditions, it has been found that in case of application of both the cored wire injection method and the method of pouring liquid metal over magnesium master alloy on ladle bottom, the satisfactory level of magnesium content in the bottom-pour ladle, for which it was still possible to obtain castings with vermicular graphite, was 0.018% Mg. In case of the cored wire injection method, the “time window” available to a pouring station at which castings of vermicular cast iron are expected to be obtained, was about 5 minutes. This corresponds to the longitudinal ultrasonic wave velocity values exceeding 5500 m/s and the number of graphite precipitations per unit surface area above 320 mm–2. In case of the master alloy method, the respective “time window” allowing to obtain castings of vermicular cast iron was only about 3 minutes long. This corresponds to the longitudinal ultrasonic wave velocity value above 5400 m/s and the number of graphite precipitations per unit surface area above 380 mm–2.