Effect of Zr content on strain-induced precipitation behavior of Ti–Zr microalloyed low-carbon steel

Abstract With two different Zr content Ti–Zr microalloyed low-carbon steels, isothermal relaxation tests at 875–950 °C were conducted using a Gleeble-3500 thermal simulation testing machine. Based on the Avrami equation, the thermodynamic and kinetic model for the precipitation of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msub> <m:mtext>Ti</m:mtext> <m:mrow> <m:mo>(</m:mo> <m:mrow> <m:msub> <m:mi>k</m:mi> <m:mn>1</m:mn> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mi>m</m:mi> <m:mn>1</m:mn> </m:msub> </m:mrow> <m:mo>)</m:mo> </m:mrow> </m:msub> <m:msub> <m:mtext>Zr</m:mtext> <m:mrow> <m:mo>(</m:mo> <m:mrow> <m:msub> <m:mi>k</m:mi> <m:mn>2</m:mn> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mi>m</m:mi> <m:mn>2</m:mn> </m:msub> </m:mrow> <m:mo>)</m:mo> </m:mrow> </m:msub> <m:msub> <m:mi mathvariant="normal">C</m:mi> <m:mrow> <m:mo>(</m:mo> <m:mrow> <m:msub> <m:mi>k</m:mi> <m:mn>1</m:mn> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mi>k</m:mi> <m:mn>2</m:mn> </m:msub> </m:mrow> <m:mo>)</m:mo> </m:mrow> </m:msub> <m:msub> <m:mi mathvariant="normal">N</m:mi> <m:mrow> <m:mo>(</m:mo> <m:mrow> <m:msub> <m:mi>m</m:mi> <m:mn>1</m:mn> </m:msub> <m:mo>+</m:mo> <m:msub> <m:mi>m</m:mi> <m:mn>2</m:mn> </m:msub> </m:mrow> <m:mo>)</m:mo> </m:mrow> </m:msub> </m:mrow> </m:math> ${\text{Ti}}_{\left({k}_{1}+{m}_{1}\right)}{\text{Zr}}_{\left({k}_{2}+{m}_{2}\right)}{\mathrm{C}}_{\left({k}_{1}+{k}_{2}\right)}{\mathrm{N}}_{\left({m}_{1}+{m}_{2}\right)}$ in austenite was established. The results indicate that the microalloyed elements in Ti–Zr microalloyed low-carbon steel will form composite precipitates through replacement and heterogeneous mechanisms, and nucleate and precipitate at grain boundaries and dislocations in the form of (Ti, Zr) (C, N). For the nucleation and precipitation of carbonitrides at dislocations in 0.035Zr steel and 0.091Zr steel, their nucleation rate–temperature curves (NrT) and Precipitation–time–temperature (PTT) curves intersect at a certain point. The increase in Zr content suppresses the precipitation of carbonitrides from austenite, reducing the strain-induced precipitation in Ti–Zr microalloyed low-carbon steel during rolling process.