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Relationship between the Microstructure and Impact Toughness of the Coarse-Grained Heat-Affected Zone for Offshore Engineering Steels with Different Mg Contents
Steel Research International ( IF 2.2 ) Pub Date : 2021-04-01 , DOI: 10.1002/srin.202100099
Xiaoqian Pan 1 , Jianjun Zhi 2 , Zhengjie Fan 2 , Yinhui Zhang 1 , Jian Yang 1
Affiliation  

The relationship between the microstructure and impact toughness of coarse-grained heat affected zone for offshore engineering steels with 0.0002 and 0.0042 wt% Mg, termed as 2 and 42Mg, respectively, is clarified. With increasing the Mg content from 0.0002 to 0.0042 wt%, the average impact energy at −40 °C decreases from 201 to 59 J. The prior austenite grain size (PAGS) increases from ≈92 to ≈163 μm, the average thickness of lath bainites increases from ≈234 to ≈361 nm. The addition of Mg makes the particle increase in number and refine in size, but the amount of the effective pinning particles at the temperature close to 1350 °C in 42Mg is smaller than that in 2Mg, which leads to the larger austenite grain growth rate and larger PAGS in 42Mg. The larger PAGS with the higher bainite transformation temperature and smaller PAG boundary density in 42Mg makes the bainite coarser. So, in 2Mg, the effective bainitic grain size with misorientation above 45° is smaller and the density of high-angle grain boundaries (HAGBs) is larger, resulting in its higher toughness. Besides, the coalesced bainite containing cementite colonies in 42Mg makes the bimodal bainitic lath thicknesses and heterogeneous microhardness distribution, reducing the toughness.

中文翻译:

不同镁含量海洋工程钢粗晶热影响区组织与冲击韧性的关系

阐明了含 0.0002 和 0.0042 wt% Mg(分别称为 2 和 42Mg)的海洋工程钢粗晶热影响区的显微组织和冲击韧性之间的关系。随着 Mg 含量从 0.0002 增加到 0.0042 wt%,-40 °C 下的平均冲击功从 201 到 59 J。原始奥氏体晶粒尺寸 (PAGS) 从 ≈92 增加到 ≈163 μm,板条的平均厚度贝氏体从≈234 增加到≈361 nm。Mg的加入使颗粒增多、尺寸细化,但42Mg在接近1350℃的温度下有效钉扎颗粒的数量比2Mg小,导致奥氏体晶粒长大速率和尺寸增大。 42Mg 中更大的 PAGS。42Mg 中具有较高贝氏体转变温度和较小 PAG 边界密度的较大 PAGS 使贝氏体更粗。因此,在2Mg中,取向错误大于45°的有效贝氏体晶粒更小,高角晶界(HAGBs)的密度更大,导致其具有更高的韧性。此外,42Mg中含有渗碳体团的聚结贝氏体使双峰贝氏体板条厚度和不均匀的显微硬度分布,降低了韧性。
更新日期:2021-04-01
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