“…On contrary to TBF770 and TBF800 steels, the partial austenitisation at 730°C leads to the degradation of mechanical properties by interrelated factors such as the lack of retained austenite and the presence of carbides at a lower intercritical temperature. Figure 15 Total elongation and tensile strength of recently developed TBF and TAM steels from literature in comparison to partially austenitised TBF steels in this work [7,8,12,18,19,32-35]. …”
Section: Resultsmentioning
confidence: 97%
“…Total elongation and tensile strength of recently developed TBF and TAM steels from literature in comparison to partially austenitised TBF steels in this work [7,8,12,18,19,32-35]. …”
Section: Resultsmentioning
confidence: 99%
“…TBF steels were first proposed by Sugimoto et al as a third-generation AHSS grade [6]. Today, commercial TBF steel grades with tensile strength levels above 980 MPa are used as automobile structural components [7,8]. Conventionally, TBF steels are mainly produced by two-step heat treatment including a full austenitisation and an austempering after the cold rolling [6].…”
A TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe–0.19C–1.7Mn–1.09Si–0.51Al–0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350°C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770°C showed a good combination of ultimate tensile strength and total elongation.
“…On contrary to TBF770 and TBF800 steels, the partial austenitisation at 730°C leads to the degradation of mechanical properties by interrelated factors such as the lack of retained austenite and the presence of carbides at a lower intercritical temperature. Figure 15 Total elongation and tensile strength of recently developed TBF and TAM steels from literature in comparison to partially austenitised TBF steels in this work [7,8,12,18,19,32-35]. …”
Section: Resultsmentioning
confidence: 97%
“…Total elongation and tensile strength of recently developed TBF and TAM steels from literature in comparison to partially austenitised TBF steels in this work [7,8,12,18,19,32-35]. …”
Section: Resultsmentioning
confidence: 99%
“…TBF steels were first proposed by Sugimoto et al as a third-generation AHSS grade [6]. Today, commercial TBF steel grades with tensile strength levels above 980 MPa are used as automobile structural components [7,8]. Conventionally, TBF steels are mainly produced by two-step heat treatment including a full austenitisation and an austempering after the cold rolling [6].…”
A TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe–0.19C–1.7Mn–1.09Si–0.51Al–0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350°C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770°C showed a good combination of ultimate tensile strength and total elongation.
“…It is well-known that metastable retained austenite can absorb a large amount of solute hydrogen in TBF, Q&P, CFB, and D-MMn steels [57,[106][107][108][109][110]. This results in a high delayed fracture strength in these steels because hydrogen concentration on the prior austenitic grain boundary is lowered.…”
This article introduces the microstructural and mechanical properties of low and medium-carbon advanced martensitic steels (AMSs) subjected to heat-treatment, hot- and warm- working, and/or case-hardening processes. The AMSs developed for sheet and wire rod products have a tensile strength higher than 1.5 GPa, good cold-formability, superior toughness and fatigue strength, and delayed fracture strength due to a mixture of martensite and retained austenite, compared with the conventional martensitic steels. In addition, the hot- and warm-stamping and forging contribute to enhance the mechanical properties of the AMSs due to grain refining and the improvement of retained austenite characteristics. The case-hardening process (fine particle peening and vacuum carburization) is effective to further increase the fatigue strength.
“…Sojka et al [22] and Laureys et al [23] reported that conventional TRIP-aided steels with a tensile strength of 780 MPa were sensitive to hydrogen embrittlement, and fracture morphologies were characterized. The authors [24,25] revealed the following three facts in hydrogen-charged TBF steels. First, the hydrogen embrittlement susceptibility increased with a decreasing strain rate.…”
The effects of thermomechanical processing on the microstructure and hydrogen embrittlement properties of ultrahigh-strength, low-alloy, transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steels were investigated to apply to automobile forging parts such as engine and drivetrain parts. The hydrogen embrittlement properties were evaluated by conducting conventional tensile tests after hydrogen charging and constant load four-point bending tests with hydrogen charging. The 0.4 mass%C-TBF steel achieved refinement of the microstructure, improved retained austenite characteristics, and strengthening, owing to thermomechanical processing. This might be attributed to dynamic and static recrystallizations during thermomechanical processing in TBF steels. Moreover, the hydrogen embrittlement resistances were improved by the thermomechanical processing in TBF steels. This might be caused by the refinement of the microstructure, an increase in the stability of the retained austenite, and low hydrogen absorption of the thermomechanically processed TBF steels.
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