Development of Process Technology for Control of Thick Sulphide Inclusions in Sulphur Bearing Steel

摘要

Thick sulphide inclusions specially manganese sulphide (MnS) in Crank Shaft Quality (CSQ) grades of steel creates lot of processing problem and adversely affects the yield and end properties requirement. The MnS precipitates preferentially in the interdendritic region on oxide inclusions during steel solidification in the temperature range of 1440-1480°C (1). The crystallisation and precipitation temperature of MnS depends upon the type of de-oxidation practice adopted for steel making and oxide inclusions present. Alloy Steels Plant (ASP) Durgapur, pioneer in special and alloy steels production in India, produces many variety of sulphur bearing steels like 40Cr_4Ty-C (IS: 5517/78), 42CrMo_4, 42Cr_4Mo_2 (DIN 17200/1982) etc for automobiles and machine tools industries. The plant was facing quality problem of thick sulphide inclusions, so the present work was carried out keeping in view the prime objective to minimize thickness of sulphide inclusion in end product. Modification of de-oxidation practice and changing the stage of iron pyrite addition helped to control sulphide thickness in desirable limit of 1.0 max for thick series and 2.0 max. for thin series. The paper deals the methodology adopted to solve the quality problem without affecting the mechanical properties.