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On the Strengthening Effects Affecting Tensile and Low Cycle Fatigue Properties of Low-Alloyed Seismic/Fire-Resistant Structural Steels
Metals and Materials International ( IF 3.5 ) Pub Date : 2020-09-09 , DOI: 10.1007/s12540-020-00870-y
Jung-Ho Sim , Tae-Yeong Kim , Jun-Yeon Kim , Chi-Won Kim , Jun-Ho Chung , Joonoh Moon , Chang-Hoon Lee , Hyun-Uk Hong

Abstract

In the present study, low carbon ferritic and bainitic steels with different contents of Mo, Ti, and Nb were designed for both seismic and fire-resistant applications. The microstructure of steels containing 0.3 wt% Mo–0.02 wt% Nb (‘A’ hereinafter) was mainly composed of bainite. By contrast, the microstructure of steels with 0.2 wt% Mo–0.13 wt% Ti (‘B’ hereinafter) consisted of ferrite with a high density of nano-sized (Ti,Mo)-rich MX precipitates. The results showed that the bainitic microstructure (‘A’ steel) was quite favorable to high-temperature strength and thermal stability. The yield strength of ‘A’ steel at both room and 600 °C temperatures increased consistently with increasing thermal exposure time (600 °C/200–1000 h), since the precipitation of NbC particles occurred while maintaining bainitic ferrite platelets with a high density of dislocations during exposure. In the ‘B’ steel, the formation of nano-sized (Ti,Mo)-rich MX particles was effective to impede dislocation movement, leading to excellent plasticity (lower yield ratio) at room temperature. However, their contribution to precipitation hardening was not so much at 600 °C, as compared to the bainitic strengthening. During low cycle fatigue tests at room temperature, the main different feature between the two steels is that the ‘A’ steel showed cyclic softening while cyclic hardening was evident in the ‘B’ steel. The bainitic microstructure showed a better fatigue life due to increased ductility manifested by cyclic softening, by which dislocation cell was developed.

Graphic Abstract



中文翻译:

低合金抗震/耐火结构钢的拉伸和低周疲劳性能的强化效应研究

摘要

在本研究中,设计了具有不同Mo,Ti和Nb含量的低碳铁素体和贝氏体钢,用于抗震和耐火应用。含有0.3 wt%Mo–0.02 wt%Nb(以下简称“ A”)的钢的显微组织主要由贝氏体组成。相比之下,具有0.2 wt%Mo–0.13 wt%Ti(以下称为“ B”)的钢的显微组织由具有高密度的富含纳米(Ti,Mo)的MX析出物的铁素体组成。结果表明,贝氏体组织('A'钢)对高温强度和热稳定性非常有利。“ A”型钢在室温和600°C温度下的屈服强度都随着暴露时间的延长(600°C / 200–1000 h)的增加而一致地增加,因为在暴露过程中NbC颗粒发生了沉淀,同时保持了高位错密度的贝氏体铁素体血小板。在“ B”钢中,富含纳米(Ti,Mo)的MX颗粒的形成可有效阻止位错运动,从而在室温下具有出色的可塑性(较低的屈服比)。但是,与贝氏体强化相比,它们在600°C下对沉淀硬化的贡献不大。在室温下的低循环疲劳试验中,两种钢之间的主要区别在于'A'钢表现出循环软化,而'B'钢表现出明显的循环硬化。贝氏体的显微组织由于循环软化表现出的延展性增加而表现出更好的疲劳寿命,由此形成了位错单元。在“ B”钢中,富含纳米(Ti,Mo)的MX颗粒的形成可有效阻止位错运动,从而在室温下具有出色的可塑性(较低的屈服比)。但是,与贝氏体强化相比,它们在600°C下对沉淀硬化的贡献不大。在室温下的低循环疲劳试验中,两种钢之间的主要区别在于'A'钢表现出循环软化,而'B'钢表现出明显的循环硬化。贝氏体的显微组织由于循环软化表现出的延展性增加而表现出更好的疲劳寿命,由此形成了位错单元。在“ B”钢中,富含纳米(Ti,Mo)的MX颗粒的形成可有效阻止位错运动,从而在室温下具有出色的可塑性(较低的屈服比)。但是,与贝氏体强化相比,它们在600°C下对沉淀硬化的贡献不大。在室温下的低循环疲劳试验中,两种钢之间的主要区别在于'A'钢表现出循环软化,而'B'钢表现出明显的循环硬化。贝氏体的显微组织由于循环软化表现出的延展性增加而表现出更好的疲劳寿命,由此形成了位错单元。但是,与贝氏体强化相比,它们在600°C下对沉淀硬化的贡献不大。在室温下的低循环疲劳试验中,两种钢之间的主要区别在于'A'钢表现出循环软化,而'B'钢表现出明显的循环硬化。贝氏体的显微组织由于循环软化表现出的延展性增加而表现出更好的疲劳寿命,由此形成了位错单元。但是,与贝氏体强化相比,它们在600°C下对沉淀硬化的贡献不大。在室温下的低循环疲劳试验中,两种钢之间的主要区别在于'A'钢表现出循环软化,而'B'钢表现出明显的循环硬化。贝氏体的显微组织由于循环软化表现出的延展性增加而表现出更好的疲劳寿命,由此形成了位错单元。

图形摘要

更新日期:2020-09-10
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