Effect Of Intercritical Temperature Research Articles

Effect of Intercritical Temperature on the Microstructure and Mechanical Properties of a Ferritic-Martensitic Dual-Phase Low-Alloy Steel with Varying Nickel Content.

Dual-phase low-alloy steels combine a soft ferrite phase with a hard martensite phase to create desirable properties in terms of strength and ductility. Nickel additions to dual-phase low-alloy steels can increase the yield strength further and lower the transformation temperatures, allowing for microstructure refining. Determining the correct intercritical annealing temperature as a function of nickel content is paramount, as it defines the microstructure ratio between ferrite and martensite. Likewise, quantifying the influence of nickel on the intercritical temperature and its synergistic effect with the microstructure ratio on mechanical properties is vital to designing dual-phase steels suitable for corrosive oil and gas services as well as hydrogen transport and storage applications. In this work, we used a microstructural design to develop intercritical annealing heat treatments to obtain dual-phase ferritic-martensitic low-alloy steels. The intercritical annealing and tempering temperatures and times were targeted to achieve three different martensite volume fractions as a function of nickel content, with a nominal content varying between 0, 1, and 3-wt% Ni. Mechanical properties were characterized using tensile testing and microhardness measurements. Additionally, the microstructure was studied using scanning electron microscopy coupled with electron backscatter diffraction analysis. Tensile strength increased with increasing martensite ratio and nickel content, with a further grain refinement effect found in the 3-wt% Ni steel. The optimal heat treatment parameters for oil and gas and hydrogen transport applications are discussed.

Effect of Intercritical Temperature on the Microstructure and Mechanical Properties of 10CrMnMoSi Dual-phase Steel

Effect of Intercritical Temperature on the Microstructure and Mechanical Properties of 10CrMnMoSi Dual-phase Steel

Effect of intercritical temperature on the strain hardening of dual-phase bainite/ferrite steel

Medium-carbon dual-phase bainite/ferrite steels with different bainite and carbide volume fractions were prepared via intercritical annealing and austempering. Bainite dominated the microstructure at high intercritical temperatures, and carbides and ferrite phase dominated at low temperatures. Carbides existed in two types, undissolved alloy–cementite and vanadium carbide. The ferrite grain size was reduced to 1.22 ± 0.7 µm at 790°C. Modified Crussard–Jaoul (MC–J) model was used to analyse the strain hardening process, and the highest strain hardening rate was obtained at 755°C. The high carbide fraction at 755°C increased the ferrite dislocation density and enhanced the ferrite phase strength. The high dislocation density in ferrite and the small strength difference in bainite and ferrite enhanced the strain hardening rate at 755°C.

Effect of Intercritical Temperature on the Structure Property Correlation of Multiphase High-C Spheroidized Steel

The present investigation deals with the development of multiphase steels combining spheroidal carbides and bainite in a ductile ferrite matrix. An attempt is made to get a promising combination of high strength and ductility through changes of microstructure by heat treatment. A high-carbon (0.61 wt.%) and high-silicon (1.71 wt.%) spring steel (EN45) was annealed to obtain an initial ferrite pearlite microstructure. The samples were given 10% cold working followed by holding at a temperature just below Ac1 for 180 min. Then the samples were held at intercritical temperatures of 770 and 800 °C for different durations varying from 10 to 30 min for partial re-austenitization followed by quenching in a salt bath kept at 350 °C and holding there for 10 min for bainite transformation. The samples were finally water quenched. The heat-treated samples were characterized by optical microscopy, x-ray diffraction, and scanning electron microscopy. The effects of intercritical temperature and holding time on the microstructure and mechanical properties were studied. With more bainitic transformation, the strength values went up considerably with a compromised elongation. The best combination of tensile strength (~805 MPa) with high elongation (~28%) was obtained. Finally, structure property correlation was established.

Effect of intercritical temperature on quenching and partitioning steels originated from martensitic pre-microstructure

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