FR2777995A1 - THERMAL ANALYSIS METHOD OF SPHEROIDAL GRAPHITE CAST IRON - Google Patents

Abstract

A thermal analysis method of spheroidal graphite cast iron is described, in which a small amount of an element selected from the group consisting of rare earth elements is added to a sample of molten spheroidal graphite cast iron.

Description

Thermal analysis process for spheroidal graphite cast iron. This

  The invention relates to a method of thermal analysis of a spheroidal graphite cast iron, and more particularly to an improved method for determining the properties of a spheroidal graphite cast iron by means of

  a thermal analysis of the molten metal thereof.

  During the research of the properties of a spheroidal graphite cast iron using the cooling curve of the molten metal thereof before molding, part of the molten metal is poured into a sampling container fitted with a thermocouple and containing a small amount of sulfur (S) and tellurium (Te) so as to transform the mass into

smelting in white rough cast iron.

  When sulfur and tellurium are used as an additive, elements in molten spheroidal graphite pig iron react with sulfur before tellurium, and the sulfur changes to magnesium sulfide (MgS). Consequently, the tellurium added to the molten mass will not be consumed, and the formation of white pig iron will be favored. Tellurium is placed in the sampling container, and then the molten molten graphite, at a high temperature, is poured into the container, the tellurium reacts with oxygen, and forms tellurium oxide (Te) which is poisonous to humans, and is released into the air. Because tellurium oxide emits white smoke, it attacks the eyes of the operator in the vicinity of an oven operated at a high temperature of around

15000C.

  In light of the above, it is a main object of the present invention to provide a thermal analysis method of spheroidal graphite cast iron without effect on the

environmental pollution.

2 2777995

  It is another object of the invention to provide a method of thermal analysis of a spheroidal graphite cast iron using the sampling container not containing tellurium. According to the invention, in order to achieve the above aims, rare earth elements such as cerium (Ce) or lanthanum (La), as well as rare earth elements in mixture such as mischmetal are used as

additives in place of tellurium.

  Preferably, in order to achieve the above goals, the proportion of said rare earth element or said rare earth elements among the group of rare earth elements in

  mixture is at least 0.4% by weight.

  FIG. 1 is a diagram representing a relation between the modification of the eutectic temperature of a spheroidal graphite cast iron containing 1.4, 2.0 and 3.0% (by weight) of

  silicon and mischmetal added to it.

  FIG. 2 is a photomicrograph representing the microstructure of a spheroidal graphite cast iron not containing

no mischmetal.

  FIG. 3 is a photomicrograph representing the microstructure of a spheroidal graphite cast iron containing

0.2% (by weight) of mischmetal.

  FIG. 4 is a photomicrograph representing the microstructure of a spheroidal graphite cast iron containing

0.4% (by weight) of mischmetal.

  FIG. 5 is a photomicrograph representing the microstructure of a spheroidal graphite cast iron containing

0.6% (by weight) of mischmetal.

  The molten cast iron is poured into a sampling container containing a small amount of the additives mentioned above in order to measure a curve of

cooling of the molten metal.

  From the cooling curve obtained, it is possible to measure a fundamental crystallization temperature showing first and second eutectic temperatures of the molten metal in the same way as in the case where the carbon equivalent, the carbon content and

3 2777995

  the silicon content in the molten metal are examined using the sample container in which

placed tellurium.

  Depending on whether the tellurium reacts with the molten metal, the spheroidal graphite cast iron can be converted into white pig iron, which can be seen by the decrease in

  the eutectic temperature of the molten metal.

  Namely, the conversion of molten spheroidal graphite cast iron to white crude iron can be estimated by lowering the eutectic temperature of molten spheroidal graphite cast iron to the eutectic temperature of white crude iron (or "eutectic temperature of the cementite "). If cementite (FeC) is formed in molten spheroidal graphite cast iron, it is possible to observe the

  structure of white pig iron using a microscope.

  Usually, the silicon content of a spheroidal graphite cast iron is about 1.4 to 3.0% (by weight), and an increase in the silicon content decreases the

  eutectic temperature of white pig iron.

  0.2, 0.4 and 0.6% (by weight) of mischmetal are added to the samples of molten spheroidal graphite pig iron containing 1.4, 2.0 and 3.0% (by weight) of silicon, and changing the eutectic temperature of each

sample is observed.

  We already know that when a molten spheroidal graphite iron contains 1.4% of silicon, the eutectic temperature of this is 1114 C, and when it contains 3.0% of

  silicon, the eutectic temperature is 1101 C.

  Therefore, the above results can be presented in Figure 1, in which the eutectic temperature of the molten metal is plotted according to the ordinates and

  the mischmetal content is shown on the abscissa.

  As shown in Figure 1, if 0.4% of mischmetal is added to the molten spheroidal graphite iron containing 2.0% silicon, the figure shows the eutectic temperature of the white pig iron whatever the

silicon content.

  Next, mischmetal is added to the molten spheroidal graphite iron containing 2.0% silicon, and the microstructure thereof is observed. In Figure 2 showing the structure of a cast iron to which no mischmetal has been added, graphite cast iron

  spheroid can be easily recognized.

  When 0.2% of mischmetal is added to the molten iron, the structure of the iron turns into CV type spheroidal graphite iron, as shown in Figure 3. In the cases where 0, 4% and 0.6% of molten iron mischmetal, as shown in Figures 4 and 5, the two structures are devoid of

  graphite and we recognize the existence of cementite.

  As established in the above, the characteristic feature of the present invention consists in adding more than 0.4% of rare earth elements to the sampling container to be used to analyze the cast iron.

with molten spheroidal graphite.

  When a small proportion of rare earth elements is added to molten iron, in the same way as the addition of tellurium, one can easily measure the eutectic temperature of a cooling curve, and the rare earth elements are combine with oxygen which is mixed with the molten metal, and form cerium oxide or lanthanum oxide. These oxides do not diffuse in the air like tellurium oxide, float on water, and are

  then solidify after a few minutes.

  Therefore, operators in the vicinity of an oven will not be endangered by the above oxide

as in the case of tellurium.

2777995

Claims (8)

  1. A method of thermal analysis of spheroidal graphite cast iron comprising the addition of a small quantity of an element selected from the group consisting of rare earth elements which are added to a sample of cast iron with molten spheroidal graphite.   2. The method of claim 1, wherein said   element of rare earth is cerium.   3. The method of claim 1, wherein said   rare earth element is lanthanum.   4. The method of claim 1, wherein said rare earth elements are selected from   rare earth elements of the cerium group.   5. A method of thermal analysis of spheroidal graphite cast iron comprising the addition of a small quantity of mixtures of rare earth elements which are added to a   sample of molten spheroidal graphite cast iron.   6. The method of claim 5, wherein said mixture is mischmetal.   7. Method according to claims 1 to 4, wherein   the quantity of the element to be added to said sample   is at least about 0.4% by weight.   8. Method according to claims 5 and 6, wherein   the amount of said mixture is at least about 0.4% by weight.