Effect of Nb Microalloying and Hot Rolling on Microstructure and Properties of Ultrathin Cast Strip Steels Produced by the CASTRIP® Process

Abstract

The microstructure and corresponding tensile properties of both plain and Nb-microalloyed grades of ultrathin cast strip (UCS) low alloy steel produced using the CASTRIP Ò process were studied. Both as-cast and hot-rolled strip cast steels with various levels of Nb microalloying were manufactured and investigated in this study. Hot rolling had little effect on the yield strength of Nb microalloyed UCS specimens for a given chemical composition, but resulted in a slightly finer microstructure. The effect of Nb microalloying was significant, and this is attributable to the promotion of finer, tougher austenite transformation products such as bainite and acicular ferrite at the expense of large polygonal ferrite grains. A fine dispersion of Nb solute clusters was observed in all Nb-containing steels following hot rolling, and it is suggested that this also contributes to the observed strengthening.

Progress in Strip Casting Technologies for Steel; Technical Developments

“…It was found that in low carbon steel (~0.03% C, ~0.85% Mn and 0.2% Si), a 0.084% Nb addition would increase the yield strength of hot-rolled strips by 20-30%. 17,25) This strengthening is attributed to niobium's effect in promoting bainite and acicular ferrite formation during austenitic transformation, as well as the formation of Nb-N clusters. 17,25) …”

“…17,25) This strengthening is attributed to niobium's effect in promoting bainite and acicular ferrite formation during austenitic transformation, as well as the formation of Nb-N clusters. 17,25) …”

Castability and Microstructural Development of Iron-based Alloys under Conditions Pertinent to Strip Casting – Specialty Fe–Cr–Al Alloys

“…Cooling rates of 10 2 to 10 4 °C/s are typically encountered during strip casting and the information on castability of different alloys under rapid solidification conditions have been largely gathered either by characterization of industrial scale strip cast products [3][4][5][6][7][8][9][10] or by carrying out targeted experiments with techniques such as levitation droplet melting and solidification, [11][12][13][14] and/or immersion solidification testing using a specially designed dip tester. [15][16][17][18][19][20] The dip tester 15) is based on the principle of rapidly submerging a copper substrate into a bath of molten metal, with a liquid-solid contact time of around 0.2 s. Thermocouples embedded below the substrate surface measure the temperature response of the substrate with millisecond resolution, and these measurements are used to calculate instantaneous heat flux during solidification.…”

Atom Probe Tomography Study of Multi-microalloyed Carbide and Carbo-Nitride Precipitates and the Precipitation Sequence in Nb-Ti HSLA Steels

“…[15] To add to the complexity, similar systems with small variations in composition can result in steels with different microstructures and/or mechanical properties. [17] For instance, addition of only 0.08 wt pct Nb altered the austenite-ferrite transformation temperature, thereby the microstructure resulting iñ 30 pct increase in yield strength. [17,18] This brief overview illustrates how the type and amount of alloying elements control the mechanical properties in multi-microalloy steel through microstructure control and precipitation.…”