Grey cast iron

One production line of a paper mill consists according the size and the quality of the produced paper sometimes from more than 50 steam drums to dry and flatten the produced paper. These drums (cylinders with flat bottoms, see figure 1) will be used with a steam pressure up to 500 kPa (5 bar) and additionally with a rotation speed up 1200 m.min the material is mainly grey cast iron (with lamellar graphite). The diameters can reach up to 2.2 m and the cylindrical lengths up to 10 m. For the specific flattening drums the cyhndrical diameters can be up to 5 m and more. 

Based on our practical experiences in the applieation of AE on pressure equipments since 1979, we started in the year 1994 to apply AE on steam drums in combination with pneumatic tests. Before we are able to do this, we have to perform extensive lab tests with the specific material (grey cast iron and cast steel) from which these drums are produced. 

Fig.5 Weibull two-parameters dividing. Exemple of results for grey cast iron with heat treated surfaces [5],...

Fig.8 Total number of AE signal counts dependence on time for grey cast iron(GCI) (a) and GCl with nitrided surface (b) (2500 MPa)...

MAZAL,P.-DVOftACEK,J.- KOLAft,D. AET Utilisation for Pitting Observation of Grey Cast Iron with Heat Treated Sur ce. Surface Modif. Technologies XI, will be published 1998. 

The second example shows results obtained with an angle beam probe for transverse waves in coarse grained grey cast iron. Two commercially available probes are compared the composite design SWK 60-2 and the standard design SWB 60-2. The reflector in this example is a side-drilled hole of 5 mm diameter. The A-scans displayed below in Fig. 5 and 6 show that the composite probe has a higher sensitivity by 12 dB and that the signal to noise ratio is improved by more than 6 dB. 

In principle the selective dissolution of the less noble component of a singlephase alloy would perhaps be expected and is in fact observed (dezincification of an a-brass, etc.) even though the details of the mechanism by which it occurs is not yet fully understood. In contrast, the preferential attack of the less noble phase of a two-phase alloy is not only expected and observed —the mechanism by which it occurs in practice is also quite clear. Selective dissolution of the more active phase of a two-phase alloy is best exemplified by the graphitic corrosion (or graphitisation) of grey cast iron. 

Fig. l.II Light micrograph of the microstnicture of a pearlitic grey cast iron x 720... 

The addition of about 20% nickel to cast iron produces materials with a stable austenitic structure these materials are sometimes known as austenitic cast irons but are more often referred to commercially as Ni-Resist cast irons. The austenitic matrix of these irons gives rise to very different mechanical and physical properties to those obtained with the nickel-free grey cast irons. The austenitic matrix is more noble than the matrix of unalloyed grey irons and it was shown in the early work of Vanick and Merica that the corrosion resistance of cast iron increases with increasing nickel content up to about 20% (Fig. 3.42). 

Graphitic Corrosion corrosion of grey cast iron in which the metallic constituents are removed as corrosion products, leaving the graphite. 

Figure IU3. Predicted elemental partitioning to the liquid during Scheil solidification of a lamellar grey cast iron (Harding and Saunders 1997, Saundeis...

Fig. 18.6 a) Stages in the development of scale on grey cast iron in water at 50 °C with 0,44 mg O2 b) Stages in the development of scale on grey cast iron in water at 50 °C with 3 mg L O2 (Mt magnetite, GR green rust) (Smith and McEaney, 1979 with permission). 

Fig. 18.7 Changes with time in the levels of the three iron oxide components of scale on grey cast iron (Smith and McEaney,...

Grey cast iron is brittle at all usable temperatures... 

The most important of all materials which enter into the construction of chemical apparatus is iron. It is usual to distinguish three kinds which are used in the arts and manufactures, viz., cast-iron, wrought-iron, and steel. But in order to obtain the best technical effects from them it is necessary to make further distinctions, and to consider their properties more in detail, particularly when they have to be used for special purposes. Ordinary grey cast-iron, as it comes from the blast furnace, contains from 2 to 4white cast-iron the carbon is chemically combined with the iron. It may contain manganese in varying quantities, from 1 to over 20 per cent. In steel, the quantity of carbon is more than per cent. in wrought-iron, less. 

Cast iron is obtained in the process for extracting iron from its ores. It occurs in two forms, white and grey. Both fuse far more readily than pure iron. White cast-iron is very hard and brittle it contains about 5 per cent, of carbon. Grey cast-iron is softer and tougher it contains between 3 and 4 per cent, of carbon, in part uncombined. 

G.A. Stone, and G. Grant, Friction Stir Processing of Class 40 Grey Cast Iron, Friction Stir Welding and Processing III,... 

An example of selective attack in a different group of material is the graphitization of grey cast iron, where the iron is eorroded away and graphite is left on the surfaee. 

---