Enhanced mechanical properties by retained austenite in medium–carbon Si-rich microalloyed steel treated by quenching–tempering, austempering and austempering–tempering processes

Keeping through‐thickness homogeneity of mechanical properties has been a great challenge for producing heavy gauge steel plates. Herein, a superior homogeneity of microstructure and hence strength and toughness achieved in a quenched and tempered (QT) 210 mm‐thickness steel plate produced by advanced electroslag remelting casting and roller quenching (ESR–RQ) technologies are reported. Some comparisons are made with a QT 178 mm steel plate produced by conventional mold casting and immersion quenching in the water tank (MC‐IQ). The martensite of the as‐quenched ESR–RQ steel is distributed homogeneously across the thickness with a fraction of 39% at the 1/2 thickness, remarkable higher 34% than that of MC‐IQ steel. ESR–RQ steel appears excellent comprehensive mechanical properties even for the as‐quenched samples, as well as QT samples. Comparing with the MC‐IQ steel, the Charpy impact energy at −60 °C is 150 J (278%) higher for the samples tempered at 650 °C, and the yield strength is 137 MPa (18%) higher for the samples tempered at 600 °C than those of MC‐IQ steel, respectively. The considerable improvement can be attributed to homogeneous through‐thickness microstructures, including refined prior austenite grains, effective grain size, and carbide precipitates.

Section: Microstructural Characteristicsmentioning

confidence: 99%

Superior Through‐Thickness Homogeneity of Microstructure and Mechanical Properties of Ultraheavy Steel Plate by Advanced Casting and Quenching Technologies

Wang

et al. 2021

“…c) The comparison of the mechanical properties of the experimental steel with other spring steels and high‐strength steels. [ 1, 3–5, 8, 9, 23–35 ]…”

Section: Resultsmentioning

confidence: 99%

“…[ 39 ] The blocky retained austenite could effectively relieve local stress concentration and reduce the probability of micropores formation. [ 9 ] Thus, both ultrahigh strength and good toughness were obtained in the Q‐T400 sample. The orientation relationships between the matrix and retained austenite were identified by the selected area electron diffraction (SAED) pattern in Figure 8c as the Kurdjumov–Saches (K–S) relationship:

()

[

\overset{1}{true}

11] α //[011] γ , (110) α //(111) γ .…”

Section: Discussionmentioning

confidence: 99%

“…For example, in the study by Wang et al, [ 8 ] the primary austenite grain of 65Mn spring steel is refined to 5.6 μm using the warm deformation process; 2220 MPa ultrahigh tensile strength and 8.6% elongation were finally achieved. Chen et al [ 9 ] in their study showed that the retained austenite is introduced through the salt bath isothermal process, so that the medium‐carbon high‐silicon microalloyed steel has both ultrahigh strength of 2200 MPa and elongation of 15%, but the yield strength is only 1624 MPa. It can be seen from the above that although ultrafine grains can be obtained through special processes or soft second phases can be introduced to improve strength and toughness simultaneously, complex processes will significantly increase costs and are not conducive to industrial production.…”

Section: Introductionmentioning

confidence: 99%

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Microstructures and Mechanical Properties of an Ultrahigh‐Strength and Ductile Medium‐Carbon High‐Silicon Spring Steel

Wang

Zhao

et al. 2022

Herein, the microstructure and mechanical properties of medium‐carbon high‐silicon spring steel are studied, which is alloyed and/or microalloyed with Cr, Mo, Ni, Cu, Nb, and V, and subjected to various austenitizing and tempering processes. The steel has a mixed microstructure consisting of fine lath martensite, nanoscale cementite, ε‐carbide, and an amount of retained austenite (10.4 vol%). At room temperature, the steel exhibits ultrahigh tensile strength (2002 MPa) and yield strength (1775 MPa) with total elongation of 11.1%, while a good toughness is obtained characterized by Charpy impact energy as 38 J. The ultrahigh strength of this steel is attributed to the dislocation and precipitation strengthening, while the excellent total elongation is closely associated with the retained austenite. In addition, tempered martensite embrittlement is found in this steel when tempered at 450 °C. This is due to the retained austenite decomposition and cementite coarsening along the prior austenite grain and martensite laths.

“…And film‐like retained austenite precipitates along the boundary of lath bainite, which is helpful to improve toughness. [ 7 ] In recent years, Mn–Si–Cr bainitic steels have been widely used in fields such as railway transportation, ocean engineering, and heavy machinery industry owing to their excellent combination of high strength, high toughness, and satisfactory elongation. [ 8–10 ]…”

Section: Introductionmentioning

confidence: 99%

On the Significance of Thermal Deformation and Dynamic Recrystallization on Flow Behavior of 25Mn2Si2Cr Bainitic Alloy

Tan

Zhang

et al. 2020

Thermal deformation characteristics, dynamic recrystallization behavior, and processing map of 25Mn2Si2Cr high strength bainitic steels are elucidated during wide temperature range (850–1100 °C) and strain rate (0.1–10 s−1) from flow behavior. Thermomechanical analysis by Thermo‐Calc software indicates that microstructure during thermal deformation is austenite, which is conducive to dynamic recrystallization. Phenomenological constitutive equations of thermal deformation, dynamic recrystallization equation, and processing map are established to predict flow behavior. The experimental results indicate that deformation temperature and strain rate have significant effect on thermal deformation process. Flow stress increases with decrease in deformation temperature and increase in strain rate. Increasing deformation temperature and decreasing strain rate promote dynamic recrystallization occurrence. However, the grain size increases with increase in deformation temperature. Thermal simulations predict that optimum thermal deformation parameters are deformation temperature (950–1000 °C), strain rate (0.25–5 s−1) and deformation temperature (850–950 °C), strain rate (1–5 s−1) for processing of Mn–Si–Cr bainitic steels.