700 MPa級別熱軋高強鋼氧化鐵皮結構轉變規律

曹光明; 劉怡私; 高欣宇; 李光輝; 王皓; 劉振宇

doi:10.13374/j.issn2095-9389.2019.04.24.001

700 MPa級別熱軋高強鋼氧化鐵皮結構轉變規律

doi: 10.13374/j.issn2095-9389.2019.04.24.001

1.
東北大學軋制技術及連軋自動化國家重點實驗室，沈陽 110819
2.
華菱漣源鋼鐵有限公司，婁底 417000

基金項目: 國家重點研發計劃資助項目(2017YFB0305002)；國家自然科學基金聯合基金資助項目(U1660117)；中央高校基本科研業務費資助項目(N180704008)

詳細信息

通訊作者:
E-mail：caogm@ral.neu.edu.cn

中圖分類號: TG335.1
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出版歷程
- 收稿日期: 2019-04-24
- 刊出日期: 2019-12-01

Structural transformation of oxide scale of 700-MPa grade hot rolled high strength steel

1.
The State Key Laboratory of Rolling and Automation,Northeastern University, Shenyang 110819, China
2.
VALIN LYsteel Co., Ltd, Loudi 417000, China

More Information

Corresponding author: E-mail: caogm@ral.neu.edu.cn

摘要

摘要: 選取700 L作為試驗用典型鋼種，利用高溫同步熱分析儀（TGA）研究了熱軋過程中不同卷取溫度和冷卻速率條件對氧化鐵皮結構轉變的影響規律。實驗結果表明，450～500 ℃為700 L共析轉變的“鼻溫”區間，此時共析轉變的孕育期最短，容易發生共析轉變，生成大量的共析組織（Fe+Fe₃O₄）。相較于其他成分鋼種的氧化鐵皮共析組織轉變規律，700 L中添加的Mn、Nb、Ti元素會使晶粒細化，進而使參與反應的離子的擴散通道增加，并最終使共析轉變速率發生一定的延遲，共析“C”曲線整體出現向左偏移。
- 高強鋼 /
- 氧化鐵皮 /
- 結構轉變 /
- 共析“C”曲線 /
- Mn元素
Abstract: Due to exposure to air during rolling processes, a layer of oxide scale always coats the surface of the hot-rolled steel plates. During the subsequent cooling processes, the FeO in the oxide scale undergoes a eutectic reaction. The formation of a lamellar structure (Fe+Fe₃O₄) during this reaction is influenced by different cooling methods. The addition of alloying elements, however, also affects the eutectic reaction. The final oxide scale, hence, varieswith different compositions. For 700-MPa grade high strength steels, poor control of iron oxide scale is detrimental to the surface quality; such surface defects as iron oxide scale shedding, surface red rust, pit, are incurred. These defects, however, affect the overall performance of the steel. Consequently, the improvement of the surface quality of hot-rolled steel by controlling the iron oxide scale, without compromising the mechanical properties, has attracted the interest of many researchers. In this paper, the effect of cooling temperature and cooling rate on the structural transformation of tertiary oxide scale during hot-rolling was studied. A sample of 700 L steel grade was used. The study was carried out by the thermogravimetric analysis (TGA). The results show a "nose temperature" range of 450?500 ℃ for the 700 L eutectoid transformation. The FeO shows the shortest incubation period of eutectoid transformation, hence, is prone to eutectoid transformation, forminga large number of eutectoid phase (Fe+Fe₃O₄). Addition of alloying elements such as manganese (Mg), niobium (Nb), and titanium (Ti) to the 700 L steel lead to grain refinement in the steel. It also increases the amount of diffusion channel of ions that participate in the eutectoid phase transformation. Consequently, the eutectoid transformation is delayed, and the eutectoid " C” curve shifts to the left. This is comparableto the eutectoid transformation rule of oxide scale on the surface of other steel grades.
- high strength steel /
- oxide scale /
- structural transformation /
- eutectoid "C" curve /
- Mn element

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圖 1 試驗用鋼的氧化鐵皮結構

Figure 1. Oxide scale structure of the tested steel

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圖 2 0.5 ℃·min^?1冷速條件下不同卷取溫度得到的氧化鐵皮結構. (a) 650 ℃；(b) 600 ℃；(c) 550 ℃；(d) 500 ℃；(e) 450 ℃；(f) 400 ℃

Figure 2. Structure of oxide scale at different coiling temperatures at a cooling rate of 0.5 ℃·min^?1: (a) 650 ℃; (b) 600 ℃; (c) 550 ℃; (d) 500 ℃; (e) 450 ℃; (f) 400 ℃

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圖 5 20 ℃·min^?1冷速條件下不同卷取溫度得到的氧化鐵皮結構. (a) 650 ℃；(b) 600 ℃；(c) 550 ℃；(d) 500 ℃；(e) 450 ℃；(f) 400 ℃

Figure 5. Structure of oxide scale at different coiling temperatures at a cooling rate of 20 ℃·min^?1: (a) 650 ℃; (b) 600 ℃; (c) 550 ℃; (d) 500 ℃; (e) 450 ℃; (f) 400 ℃

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圖 3 1 ℃·min^?1冷速條件下不同卷取溫度得到的氧化鐵皮結構. (a) 650 ℃；(b) 600 ℃；(c) 550 ℃；(d) 500 ℃；(e) 450 ℃；(f) 400 ℃

Figure 3. Structure of oxide scale at different coiling temperatures at a cooling rate of 1 ℃·min^?1: (a) 650 ℃; (b) 600 ℃; (c) 550 ℃; (d) 500 ℃; (e) 450 ℃; (f) 400 ℃

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圖 4 5 ℃·min^?1冷速條件下不同卷取溫度得到的氧化鐵皮結構. (a) 650 ℃；(b) 600 ℃；(c) 550 ℃；(d) 500 ℃；(e) 450 ℃；(f)400 ℃

Figure 4. Structure of oxide scale at different coiling temperatures at a cooling rate of 5 ℃·min^?1: (a) 650 ℃; (b) 600 ℃; (c) 550 ℃; (d) 500 ℃; (e) 450 ℃; (f) 400 ℃

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圖 6 氧化鐵皮組織結構轉變曲線

Figure 6. Structural transformation curve of oxide scale

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圖 7 Fe?O相圖

Figure 7. Fe?O phase diagram

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圖 8 Fe_1?xO層組織結構轉變機制示意圖. (a) 鋼氧化后氧化鐵皮的結構；(b)先共析Fe₃O₄的生成；(c)共析組織的生成

Figure 8. Schematic diagram of transformation mechanism of Fe_1?xO layer: (a) structure of oxide scale after oxidation of steel; (b) generation of pre-eutectoid Fe₃O₄; (c) generation of eutectoid structure

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圖 9 氧化鐵皮組織結構轉變曲線

Figure 9. Structural transformation curves of oxide scale

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圖 10 FeO?MnO相圖

Figure 10. FeO?MnO phase diagram

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圖 11 加入Nb、Ti前后的晶粒狀態. (a) 加入前；(b)加入后

Figure 11. Grain states before and after addition of Nb and Ti: (a) before addition; (b) after addition

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圖 12 晶粒細化后的共析反應過程

Figure 12. Eutectoid reaction process after grain refinement

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表 1 實驗鋼種的化學成分(質量分數)

Table 1. Chemical composition of the tested steel %

C Si Mn P Nb Ti Cr Al Fe

0.08 0.13 1.61 0.01 0.06 0.10 0.04 0.03 余量

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表 2 對比鋼種的化學成分（質量分數）

Table 2. Chemical composition of comparative steel %

試樣 C Si Mn P S Nb Ti

SPHC 0.07 0.05 0.30 0.02 0.02 — —
700 L 0.08 0.13 1.61 0.01 — 0.06 0.10

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