Research On Precipitation And Solid Solution Behavior Of Ti Inclusions In Hypereutectoid Tire Cord Steel

Tire cord steel, commonly known as steel cord, is a high-tech product. The brittleinclusions such as Ti inclusions are the main reason for the cord steel ruptures duringthe wire drawing process.In this paper, tire cord steel82A from a certain steel plant is taken as researchobjects. Through the theoretical calculation of thermodynamic conditions of theprecipitation and solid solution and the dynamics of growth process of Ti inclusions intire cord steel, the properties, genetic and law of precipitation of Ti inclusions indifferent strength levels of tire cord steel were studied. The solid solution behavior of Tiinclusions during high temperature heating process was studied. The samples of82Awith higher Ti and N contents was smelted by a medium frequency induction furnace.Size changes after solid solution (decomposition, diffusion) of Ti inclusions at differentheat treatment conditions were studied under laboratory condition. Ti inclusions areisolated and extracted from82A with electrolytic extraction method, the morphologychanges of Ti inclusions can be detected with a scanning electron microscope. Theabove study lays a foundation for knowing the source of Ti inclusions, morphology,properties, law of precipitation and solid solution behavior, and provides a guide for theestablishment of process measures of reducing Ti inclusions in steel in production.The results showed that:(1) The N content of tire cord steel82A has greater impacton the ultimate particle sizes of TiN inclusion than the Ti content.(2) Both TiNinclusions and Ti(C,N) inclusions are present in tire cord steel82A; When the solidfraction (g) reaches30%, Ti(C0.118,N0.882) will be first precipitated; When the solidfraction (g) reaches91.9%, the thermodynamic conditions of TiN precipitation havebeen met; Ti(C,N) could start to be precipitated before TiN. It is reasoned that TiNinclusions could be precipitated separately, and they could also be precipitated andgrown up on the outside of the core of Ti(C,N) which had been precipitated duringsolidification.(3) If foreign Ti inclusions are present in casting slabs of82A, whichcould only come from mold powder, but could not come from the smelting processearlier than the converter.(4) Through raising the casting slab heating temperature, thethermodynamic conditions of Ti inclusions dissolve or solid solution can be reached.