Opportunities and dangers of using residual elements ... - Jernkontoret

5.2.3 End-propertiesTensile properties, strengthIn reference [6], which reviews the influence of residual elements on mechanical propertiesof low-carbon steels, it is observed that all residual elements increase strength and decreaseductility and drawing properties. These effects are more pronounced for low carbon cleansteels (low-carbon, extra low carbon and ULC-IF steel grades) than for medium and highcarbon steel grades.For cold rolled and annealed sheet, the major part of the product mix is low carbon or ULCsteel. These steel grades are very sensitive to the content of residual elements. Sn, Cu, Niand Cr increases the tensile strength of ULC-Ti steel grades and decrease their ductility(elongation). Sn, As, Cu, Ni and Mo decrease ductility of ULC-IF and ELC.Thereafter are presented results of studies about mechanical properties on specific types ofLC steels.The effects of some residual elements on the properties of low carbon steel sheetscontaining titanium are reported in reference [45]. Copper specifically lowers theelongation of the material and increases the yield strength (Figure 24 A) while contributingto a refinement of the microstructure Tin increases the tensile strength of and lowerselongation and r-value (Figure 24 B). A refinement of the grain size was observed withincreasing tin content. The change in tensile strength was reported to be approximately 45MPa / 0.1 w% tin. Tin has a larger difference in atomic radius versus iron compared tocopper, nickel and chromium. This causes tin to have a larger effect in both solid solutionand as a precipitate.The influence of nickel is at about the same magnitude as copper with respect to tensilestrength increase. Only minor influences on elongation and r-value were observed atvarying nickel content and at different heating temperatures, though the small changes islikely closer related to the low carbon content in combination with the presence oftitanium. In total the influence of nickel contents up to 0.12 w% have little effects on themechanical properties of low-carbon titanium containing steel sheet.The effect of residuals on tensile properties and microstructure of low-carbon (0.04%) andmedium carbon (0.2%) steel grades was studied in [46]. An increase in tensile strength anda slight decrease in ductility (combination of solid solution hardening and grainrefinement) was observed for both types of steel The high tensile strength of steelcontaining more Mn and Si is thought to be mainly associated with increased pearlitecontent. For low carbon steels, the ferrite grain-size decreases from 24 to 18,5 µm for0.04%Sn. But further addition (0.08%Sn and 0.05%P) and addition of 1.2%Mn and 0.3%Si only slightly decrease ferrite grain-size. For medium C steels (with 1.2%Mn and 0.3%Si), the ferrite grain-size decreases from 14 to 10µm for residuals increasing (0.08%Sn,0.4%Cu, 0.4%Ni).39