The influence of tramp elements in the steel on the castability and deformation behaviour of beam blanks

In February 1995 Stahlwerk Thuringen GmbH started up a new scrap-based elec tric steelmaking shop. The rolling mill produces long products from three d ifferent entry sections. From commissioning of the production plants until 1998, the output of beam blanks increased from 268 000 to 853 000 t/a. In order to be able to objectively adjust the mechanical material propertie s, an investigation was carried out on how these properties are influenced by alloying and tramp elements in the steel: With carbon contents of approx . 0.12% C, there were frequent breakouts and surface defects on the finishe d product. The elements silicon and manganese may only be added in a specif ied ratio. Too high phosphorus and sulphur contents can lead to segregation on the beam blanks. Copper, chromium and nickel contents can only be influ enced by purchasing high-grade sorted scrap. Cu contents of 0.35 % and Cr o r Ni contents of 0.2 % have proved to be unproblematic. The desired mechani cal properties of the final product were also achieved with 0.030 % Zn and 0.040 % Sn. In order to avoid clogging, it is recommended that the aluminiu m content be kept low. This also improves the globularly solidified shell. Niobium and titanium are added up to 0.025 %, depending on the steel grade. Dissolved gases may only be present in the steel in low quantities. The production of long products using high-grade sorted scrap has proved te chnologically and economically successful. As the feared negative effect of the tramp elements did not always materialise or could be securely control led by not exceeding specific boundary values, the transition from trial to standard production could take place very soon. This technical field calls for further research, and in parallel, currently valid standards must be r evised and made up to date.