JOINT INFLUENCE OF Cr AND Si ON THE MECHANICAL PROPERTIES OF GRAY IRON

Abstract

The processes of ladle treatment of gray cast iron with masters-alloy containing chromium and silicon are considered. It is shown that the use of chromium for the treatment of gray cast iron without compensating for its bleaching effect by means of appropriate additives leads to a significant increase in hardness in samples of different diameters (from 20 to 120 mm), with samples of smaller diameter being more sensitive to the action of chromium. Comparative studies of the effectiveness of simultaneous use to improve the mechanical properties of gray cast iron of chromium and silicon, which were introduced into the melt in the form of a complex master-alloy melted from silicate calcium and ferrochrome, as well as a mixture of these ferroalloys, were conducted. The advantages of using such an master-alloy are shown. The use of an master-alloy allows to significantly improve the mechanical properties of gray cast iron. The tensile strength increases sharply with an increase in the amount of introduced ligature, reaching a value of 300 MPa when adding 1.0 % of the mass of liquid metal (the strength of raw cast iron was 150 MPa). With a further increase in the amount of introduced ligature, the increase in tensile strength slows down. The bending strength changes similarly. With the introduction of 1.0 % of ligature, the bending strength increases from 340 to 490 MPa, and a further increase in the amount of introduced ligature does not lead to its significant increase. The increase in the strength of cast iron is accompanied by an increase in hardness, but much less than when treated with chromium without silicon. The effectiveness of the proposed master-alloy has been confirmed by experimental and industrial testing. The ligature can be recommended for increasing the mechanical properties of cast iron in production conditions. At the same time, the phased introduction of the alloy will master-alloy to obtain cast irons of different grades from one melt. The use of a mixture of ferroalloys (silicocalcium and ferrochrome) for the treatment of gray cast iron turned out to be not so effective. Similar additives in quantity lead to a much smaller increase in mechanical properties compared to the use of a complex master-alloy. Additives introduced in the form of a mechanical mixture are poorly absorbed, which does not allow to achieve the desired result.