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2 Archives of Foundry Engineering

2 2009

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The influence of carbon and copper on the solidification process of the ferritic-austenitic cast steel

Stradomska J.

Archives of Foundry Engineering

2009

Vol. 9, iss. 3

177-180

Technological problems which occur during the production of castings made of ferritic-austenitic (duplex) cast steel have caused that this most modern material among corrosion-resistant cast steels is seldom produced in Poland. The main reason of arising problems is the necessity of achieving a very low carbon content (Cmax = 0.03%, according to PN-EN 10283:2004) and the occurring of hot cracking. It is impossible for our domestic foundries to achieve such a low carbon content, because it demands for out-of-furnace treatment. It should be mentioned that the standards developed by international cast steel producers admit also cast steel grades with higher carbon content than the PN-EN 10283:2004 Standard. The so far produced in Poland massive castings have exhibited higher (0,05 - 0,12) carbon content, but also the significant hot cracking susceptibility. Is the increased carbon content along with about 3% copper addition, which lowers the temperature of the end of solidification process, the reason of hot cracking of produced castings? The paper presents the results of investigation performed by DDTA and ThermoCalc analyses, as well as by microstructural examination for duplex cast iron with varying carbon content.

The analysis of solidification process of ferritic-austenitic cast steel

Stradomska J., Stradomski Z., Soiński M. S.

Archives of Foundry Engineering

2009

Vol. 9, iss. 1

83-86

One of the most common defects leading to the rejection of faulty castings made of duplex cast steel is hot cracking. Hot cracking - differently from cold cracking which occur on cooling, when the material exhibits already distinct elastic properties - proceeds in the semi-solid state, particularly when the temperature of solidifying casting is close to the equilibrium solidus point. There exist a range of temperatures in the vicinity of the solidus point within which the solidifying metal shows very small deformation ability and small strength. Therefore even little stresses occurring at the solidification stage and caused by density difference between ferrite and austenite, or restricted shrinkage, or various temperature gradients, can be the reason of hot cracking. Copper addition, as it is used in cast steel grades implemented in Polish power industry applications, decreases the temperature of the end of solidification, thus affecting beneficially the surface reproduction quality, but on the other hand it can promote, along with several other elements contained in duplex cast steel, the peritectic transformation during the last stage of solidification. The presence of peritectic solidification, i.e. strictly speaking the structural stresses accompanying that process, is the well-known and significant reason of the increased steel defectiveness in the continuous steel casting (CSC) technology if the steel with carbon content promoting the peritectic transformation is processed. The authors have presented the examination results of the solidification phenomenon for two duplex cast steel grades - one without copper addition, and the other with addition of about 3.0% Cu.