Please wait a minute...
Acta Metall Sin  2019, Vol. 55 Issue (6): 783-791    DOI: 10.11900/0412.1961.2018.00485
Current Issue | Archive | Adv Search |
The Strengthening Mechanism of Cu Bearing High Strength Steel As-Quenched and Tempered and Cu Precipitation Behavior in Steel
Zhengyan ZHANG(),Feng CHAI,Xiaobing LUO,Gang CHEN,Caifu YANG,Hang SU
Department of Structural Steels, Central Iron and Steel Research Institure, Beijing 100081, China
Download:  HTML  PDF(18289KB) 
Export:  BibTeX | EndNote (RIS)      
Abstract  

High strength low alloy (HSLA) steels are widely used in the construction of ship structures, oil pipelines, offshore platforms and so on because of their good strength, toughness and weldability. HSLA steel is generally designed with low carbon and Cu alloying. Tempered lath bainite or martensite and nano-precipitate phase of Cu can be obtained by quenching and ageing process after rolling to ensure the excellent matching of strength, low temperature toughness and weldability of HSLA steel. At present, increasing attention has been focused on the precipitation behavior and strengthening mechanism of Cu particles in HSLA steel which was aged at the peak hardness of ageing curve. However, in practical engineering applications, overageing heat treatment is generally used to make HSLA steel achieve a good match of strength and toughness. In this work, the microstructure and nano-sized Cu precipitates of an industrial production HSLA steel plate with thickness of 35 mm were characterized by SEM, EBSD, HRTEM and APT. Meanwhile, the strengthening mechanism of the tested steel was investigated. The results show that Cu precipitates in the tested steel processed by overageing are mainly in the range of 6~50 nm, Cu particles exhibiting short rod or spherical shape within 30 nm are 9R structure, and other particles size larger than 30 nm exhibiting long rod or spherical shape are fcc structure. The segregation of trace Mn and Ni in rod particles on the interface between Cu particles and matrix is more obvious. After ageing at a higher temperature range, the yield strength of the tested steel decreases linearly with the increase of tempering temperature. The main strengthening mechanism of the HSLA steel is fine grain strengthening, followed by dislocation strengthening and precipitation strengthening. The calculated results show that every 1%Cu added in the tested steel can produce about 90 MPa precipitation strengthening increment under the condition of overageing heat treatment. The strength difference between the surface and the center of the tested steel plate is about 40 MPa, which is mainly due to the difference of grain size and dislocation density of steel.

Key words:  Cu alloyed      strength mechanism      Cu precipitate      strength difference of thick plate     
Received:  25 October 2018     
ZTFLH:  TG142  
Fund: National Key Research and Development Program of China(No.2017YFB0304501)
Corresponding Authors:  Zhengyan ZHANG     E-mail:  zhangzhengyan@cisri.com.cn

Cite this article: 

Zhengyan ZHANG,Feng CHAI,Xiaobing LUO,Gang CHEN,Caifu YANG,Hang SU. The Strengthening Mechanism of Cu Bearing High Strength Steel As-Quenched and Tempered and Cu Precipitation Behavior in Steel. Acta Metall Sin, 2019, 55(6): 783-791.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00485     OR     https://www.ams.org.cn/EN/Y2019/V55/I6/783

Fig.1  The relationship of yield strength of tested steel and tempering temperature (a) and the hardness of thickness section of tempered steel plate at 660 ℃ (b)
Fig.2  SEM images of Cu bearing steel with different positions including surface (a), quarter (b) and center (c) along thickness direction
Fig.3  The EBSD interface distribution maps of surface (a) and center (b) of tested steel (Where black and red lines represent the high angle grain boundaries (≥15°) and low angle grain boundaries (2°~15°), respectively), and the total grain boundary density (GBD) of surface and center of steel vs the misorientation of ferrite grain ranged 0°~60° (c)
Fig.4  TEM images of particles precipitated during ageing process in surface (a) and center (b) of steel, and its EDS (c)
Fig.5  HRTEM images of Cu particles with the size of ≤10 nm (a), 10~20 nm (b), 20~30 nm (c), 30~40 nm (d), >40 nm (e) precipitated in the tested steel, and the fast Fourier transformed (FFT) result of a lager particle along the [1ˉ11]Cu zone axis (f)
Fig.6  APT image of Cu precipitates in the test steel aged at 660 ℃, where "a" expresses a spherioidal particle and "b" expresses a rod-like particle
Fig.7  APT images (a, c) of Cu particles and their composition profiles (b, d) with the spherality (a, b) and shot rod-like (c, d)
Fig.8  The amount of Cu precipitated in steel during ageing process calculated by Thermo-Calc software
Fig.9  Analysis and comparison of strengthening mechanism for the surface and center of tested steel (σp—precipitation hardening, σd—dislocation hardening, σg—grain refinement hardening, σs—solid solution hardening, σ0—lattice friction stress)
[1] Yang C F. Zhang Y Q. Cu Precipitation in Cu age-hardening steel [J]. Iron Steel, 2005, 40(4): 62
[1] (杨才福, 张永权. Cu时效硬化钢中Cu的析出 [J]. 钢铁, 2005, 40(4): 62)
[2] Yang J B, Yamashita T, Sano N, et al. Simulation of competitive Cu precipitation in steel during non-isothermal aging [J]. Mater. Sci. Eng., 2008, A487: 128
[3] Ghosh S K, Haldar A, Chattopadhyay P P. Effect of pre-strain on the ageing behavior of directly quenched copper containing micro-alloyed steel [J]. Mater. Charact., 2008, 59: 1227
[4] Shi X B, Yan W, Wang W, et al. Novel Cu-bearing high-strength pipeline steels with excellent resistance to hydrogen-induced cracking [J]. Mater. Des., 2016, 92: 300
[5] Liu D S, Cheng B G, Chen Y Y. Fine Microstructure and toughness of low carbon copper containing ultra high strength NV-F690 heavy steel plate [J]. Acta Metall. Sin., 2012, 48: 334
[5] (刘东升, 程丙贵, 陈圆圆. 低C含Cu NV-F690特厚钢板的精细组织和强韧性 [J]. 金属学报, 2012, 48: 334)
[6] Yu X M, Zhao S J. Study on Cu precipitate of the low C high strength steel containing Cu and Ni during isochronal tempering [J]. Acta Metall. Sin., 2013, 49: 569
[6] 余锡模, 赵世金. 含Cu和Ni低碳高强度钢等时回火析出富Cu相的研究 [J]. 金属学报, 2013, 49: 569
[7] Wen Y R, Hirata A, Zhang Z W, et al. Microstructure characterization of Cu-rich nanoprecipitates in a Fe-2.5Cu-1.5Mn-4.0Ni-1.0Al multicomponent ferritic alloy [J]. Acta Mater., 2013, 61: 2133
[8] Isheim D, Kolli R P, Fine M E, et al. An atom-probe tomographic study of the temporal evolution of the nanostructure of Fe-Cu based high-strength low-carbon steels [J]. Scr. Mater., 2006, 55: 35
[9] Sun M X, Zhang W N, Liu Z Y, et al. Direct observations on the crystal structure evolution of nano Cu-precipitates in an extremely low carbon steel [J]. Mater. Lett., 2017, 187: 49
[10] Chi C Y, Yu H Y, Dong J X, et al. The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe-Cr-Ni type austenitic heat resistant steel for USC power plant application [J]. Prog. Nat. Sci. Mater. Int., 2012, 22: 175
[11] Liu Q D, Gu J F, Liu W Q. On the role of Ni in Cu precipitation in multicomponent steels [J]. Metall. Mater. Trans., 2013, 44A: 4434
[12] Kapoor M, Isheim D, Ghosh G, et al. Aging characteristics and mechanical properties of 1600 MPa body-centered cubic Cu and B2-NiAl precipitation-strengthened ferritic steel [J]. Acta Mater., 2014, 73: 56
[13] Zhou B X, Wang J A, Liu Q D, et al. Effect of nickel alloying element on the precipitation of Cu-rich clusters in RPV model steel [J]. Mater. China, 2011, 30(5): 1
[13] (周邦新, 王均安, 刘庆东等. Ni对RPV模拟钢中富Cu原子团簇析出的影响 [J]. 中国材料进展, 2011, 30(5): 1)
[14] Mulholland M D, Seidman D N. Nanoscale co-precipitation and mechanical properties of a high-strength low-carbon steel [J]. Acta Mater., 2011, 59: 1881
[15] Zhang C, Enomoto M. Study of the influence of alloying elements on Cu precipitation in steel by non-classical nucleation theory [J]. Acta Mater., 2006, 54: 4183
[16] Kapoor M, Isheim D, Vaynman S, et al. Effects of increased alloying element content on NiAl-type precipitate formation, loading rate sensitivity, and ductility of Cu- and NiAl-precipitation-strengthened ferritic steels [J]. Acta Mater., 2016, 104: 166
[17] Jiao Z B, Luan J H, Zhang Z W, et al. Synergistic effects of Cu and Ni on nanoscale precipitation and mechanical properties of high-strength steels [J]. Acta Mater., 2013, 61: 5996
[18] Isheim D, Gagliano M S, Fine M E, et al. Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale [J]. Acta Mater., 2006, 54: 841
[19] Jiao Z B, Luan J H, Miller M K, et al. Precipitation mechanism and mechanical properties of an ultra-high strength steel hardened by nanoscale NiAl and Cu particles [J]. Acta Mater., 2015, 97: 58
[20] Pan J S, Tong J M, Tian M B. Fundamentals of Material Science [M]. Beijing: Tsinghua University Press, 2011: 660
[20] (潘金生, 仝健民, 田民波. 材料科学基础 [M]. 北京: 清华大学出版社, 2011: 660)
[21] Zhang Z Y, Sun X J, Li Z D, et al. Effect of nanometer-sized carbides and grain boundary density on performance of Fe-C-Mo-M (M=Nb, V, or Ti) fire resistant steels [J]. Chin. J. Mater. Res., 2015, 29: 269
[21] (张正延, 孙新军, 李昭东等. 纳米级碳化物及小角界面密度对Fe-C-Mo-M (M=Nb、V或Ti)系钢耐火性的影响 [J]. 材料研究学报, 2015, 29: 269)
[22] Zhang Z Y, Chai F, Luo X B, et al. Method for measuring dislocation density of steel through electron back-scattered diffraction (EBSD) [P]. Chin Pat, CN201810254056, 2018
[22] (张正延, 柴 锋, 罗小兵等. 一种利用EBSD测量钢中位错密度的方法 [P]. 中国专利, CN201810254056, 2018)
[23] Wang W. Precipitation and structural evolution of copper-rich Nano phases in reactor pressure vessel model steels [D]. Shanghai: Shanghai University, 2011
[23] (王 伟. 反应堆压力容器模拟钢中富Cu相的析出及晶体结构演化研究 [D]. 上海: 上海大学, 2011)
[24] Xu G, Chu D F, Cai L L, et al. Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel [J]. Acta Metall. Sin., 2011, 47: 905
[24] (徐 刚, 楚大锋, 蔡琳玲等. RPV模拟钢中纳米富Cu相的析出和结构演化研究 [J]. 金属学报, 2011, 47: 905)
[25] Zhang Z Y, Li Z D, Yong Q L, et al. Precipitation behavior of carbide during heating process in Nb and Nb-Mo micro-alloyed steels [J]. Acta Metall. Sin., 2015, 51: 315
[25] (张正延, 李昭东, 雍岐龙等. 升温过程中Nb和Nb-Mo微合金化钢中碳化物的析出行为研究 [J]. 金属学报, 2015, 51: 315)
[26] Yong Q L, Ma M T, Wu B R(. Micraoalloyed Steel——Physical and Mechanical Metallurgy [M]. Beijing: China Machine Press, 1989: 22
[26] 雍岐龙, 马鸣图, 吴宝榕. 微合金钢——物理和力学冶金 [M]. 北京: 机械工业出版社, 1989: 22)
[27] Yong Q L. Secondary Phase in Steels [M]. Beijing: Metallurgical Industry Press, 2006: 361
[27] (雍岐龙. 钢铁材料中的第二相 [M]. 北京: 冶金工业出版社, 2006: 361)
[28] Zhang Z Y, Sun X J, Yong Q L, et al. Precipitation behavior of nanometer-sized carbides in Nb-Mo microalloyed high strengh steel and its strengthening mechanism [J]. Acta Metall. Sin., 2016, 52: 410
[28] (张正延, 孙新军, 雍岐龙等. Nb-Mo微合金高强钢强化机理及其纳米级碳化物析出行为 [J]. 金属学报, 2016, 52: 410)
[1] Zhengyan ZHANG,Xinjun SUN,Qilong YONG,Zhaodong LI,Zhenqiang WANG,Guodong WANG. PRECIPITATION BEHAVIOR OF NANOMETER-SIZED CARBIDES IN Nb-Mo MICROALLOYED HIGH STRENGH STEEL AND ITS STRENGTHENING MECHANISM[J]. 金属学报, 2016, 52(4): 410-418.
[2] YU Ximo, ZHAO Shijin. STUDY ON Cu PRECIPITATE OF THE LOW C HIGH STRENGTH STEEL CONTAINING Cu AND Ni DURING ISOCHRONAL TEMPERING[J]. 金属学报, 2013, 49(5): 569-575.
No Suggested Reading articles found!