The effects of alloying elements on strength, hardenability, and interchangeability in dual phase steels

The effects of alloying elements (Nb, V, Mo) on dual phase steels have been studied in relation to ultimate tensile strength (U.T.S.) ductility and hardenability. C-Mn, Nb-Mo, Nb and Nb-V steels were hot rolled from 25mm to 4.5mm finishing at temperatures in the range 780oC – 950oC. They were then air cooled before being cold rolled to ~0.9mm and annealed. Dual phase heat treatment was carried out at 755oC followed by quenching in water. Tensile and hardenability tests were carried out. Results showed that alloying elements in steel increased strength in the dual phase steels by amounts ranging from 150 Mpa for Nb-V steel to 226 MPa for Nb steel. Strain hardening exponent, n, was also increased from ~0.22 for annealed to 0.35 in the dual phase steels. Using the multiplying factor principle, increase in hardenability recorded ranged from 1.1 times for Nb-V to 1.37 times for Nb-Mo steels over alloy free steels. Possible interchangeability between Nb and V alloys was also observed. Key words : Alloying elements, Ultimate tensile strength, Hardenability, Interchangeability. [Global Jnl Engineering Res. Vol.2(1&2) 2003: 41-48