Inclusions and Microstructure of Q355 Steel with Lanthanum Treatment AITranslate
Abstract AITranslate
Q355 is a high strength low alloy steel，which has high strength，high toughness，fatigue resistance，impact resistance，wear resistance，corrosion resistance and other comprehensive quality performance，so often used in atmospheric construction equipment. Because the steel is mainly used in atmospheric corrosion environment，it puts forward higher requirements for pitting corrosion and matrix stability. Studies have fully confirmed that rare earth has a good role in improving the corrosion resistance of low alloy. Rare earth elements due to the gradual maturity of the extraction process，its use cost is getting lower and lower，the high abundance of La element also makes it more widely used in steel. The activity of rare earth La element is between Mg and Ca. Due to its special physical and chemical properties，La treatment can transform MnS and Al2O3 inclusions into rare earth oxides，sulfur oxides and sulfides，thus improving the comprehensive properties of steel. Aiming at the problem that the influence mechanism of the coupling effect of elements and La elements in steel on the formation of inclusions is not clear，the effects of temperature，La content，Al content，O content and S content on the formation of inclusions were studied by thermodynamic calculation and high temperature thermal simulation experiment，and the change rule of microstructure of steel was summarized. The metal material used in this experiment was Q355 steel produced by a steel plant. The experimental device was a 50 kg vacuum induction furnace，and the alloying raw material was 30% lanthanum-iron alloy. End point sample was rolled into 7 mm steel plate on small mill by induction furnace smelting. The mass fraction of O and N in the end point sample was detected by ONH-5500 oxygen and nitrogen analyzer，and the mass fraction of each element in the end point sample was determined by M4 TORNADO fluorescence spectrometer. The morphology and composition of inclusions in Q355 high strength steel were observed and analyzed by JEOL JSM 7200F scanning electron microscope （SEM）and energy dispersive spectrometer （EDS）. The composition，size and position coordinates of inclusions in steel were statistically analyzed by Aspex software. Q355 steel was corroded by 4% nitric acid alcohol for 10~20 s，and then the microstructure and grain size were observed by metallographic microscope. It was found that the color of inclusions in steel without rare earth was dark，and the size was about 2~3 μm. The inclusions were mainly CaxAlyOz，MgAl2O4 and CaS，and some MnS adhere to the surface. When the La content was 19×10−6，the inclusions were mainly La2O2S，a large number of CaS and calcium aluminate were attached to the surface，and the color of the inclusions was dark. When the content of La increases to 23×10−6，the inclusions change into La2O2S，calcium aluminate disappeared，a small amount of black CaS adheres to the surface，and the color was white. Rare earth content continued to increase inclusions to La2O2S-LaxSy-CaS eutectic compounds，the composition was more uniform，the color was bright white，there was no black CaS inclusions. The transformation process of inclusions was MgAl2O4 （CaxAlyOz）→ La2O2S+CaxAlyOz →La2O2S→ LaxSy. Through the distribution of inclusions could be seen that non-rare earth inclusions （black）exhibit aggregation，that was easy to collide and grow，and the size were larger；rare earth inclusions （white）were more inclined to disperse distribution，that meant there was no tendency to aggregate，and with the increase of rare earth content，the size of rare earth inclusions tends to decrease. The analysis of its distribution density showed that with the increase of rare earth content，the density between inclusions tended to decrease，indicating that the spacing between inclusions gradually became larger，reducing the possibility of defects caused by inclusion aggregation. With the increase of rare earth content，the grain size of the matrix gradually became smaller. The grain size of the blank sample was grade 9，and the average size was 17.64 μm. After adding rare earth，the grain size decreased to varying degrees. When the addition amount of La was 47×10−6，the minimum grain size was 9.4，and the average size was 13.53 μm，indicating that the addition of rare earth achieves the effect of grain refinement. The proportion of pearlite structure decreased with the increase of rare earth content. The proportion of pearlite in the test steel without rare earth was 45%. When the addition of La was 47×10−6，the proportion of pearlite decreased to 38%，indicating that rare earth inhibits the formation of pearlite. At the same time，the misfit of inclusions with α-Fe，γ-Fe and δ-Fe was calculated. It was concluded that the coherent structure of rare earth inclusions with ferrite and austenite was the main reason for the decrease of grain size.
KeyWords AITranslate
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Basic Information:
DOI：10.13373/j.cnki.cjrm.XY22110024
Chinese Library Classification Number:TF769
Citation Information:
Q355 is a high strength low alloy steel，which has high strength，high toughness，fatigue resistance，impact resistance，wear resistance，corrosion resistance and other comprehensive quality performance，so often used in atmospheric construction equipment. Because the steel is mainly used in atmospheric corrosion environment，it puts forward higher requirements for pitting corrosion and matrix stability. Studies have fully confirmed that rare earth has a good role in improving the corrosion resistance of low alloy. Rare earth elements due to the gradual maturity of the extraction process，its use cost is getting lower and lower，the high abundance of La element also makes it more widely used in steel. The activity of rare earth La element is between Mg and Ca. Due to its special physical and chemical properties，La treatment can transform MnS and Al2O3 inclusions into rare earth oxides，sulfur oxides and sulfides，thus improving the comprehensive properties of steel. Aiming at the problem that the influence mechanism of the coupling effect of elements and La elements in steel on the formation of inclusions is not clear，the effects of temperature，La content，Al content，O content and S content on the formation of inclusions were studied by thermodynamic calculation and high temperature thermal simulation experiment，and the change rule of microstructure of steel was summarized. The metal material used in this experiment was Q355 steel produced by a steel plant. The experimental device was a 50 kg vacuum induction furnace，and the alloying raw material was 30% lanthanum-iron alloy. End point sample was rolled into 7 mm steel plate on small mill by induction furnace smelting. The mass fraction of O and N in the end point sample was detected by ONH-5500 oxygen and nitrogen analyzer，and the mass fraction of each element in the end point sample was determined by M4 TORNADO fluorescence spectrometer. The morphology and composition of inclusions in Q355 high strength steel were observed and analyzed by JEOL JSM 7200F scanning electron microscope （SEM）and energy dispersive spectrometer （EDS）. The composition，size and position coordinates of inclusions in steel were statistically analyzed by Aspex software. Q355 steel was corroded by 4% nitric acid alcohol for 10~20 s，and then the microstructure and grain size were observed by metallographic microscope. It was found that the color of inclusions in steel without rare earth was dark，and the size was about 2~3 μm. The inclusions were mainly CaxAlyOz，MgAl2O4 and CaS，and some MnS adhere to the surface. When the La content was 19×10−6，the inclusions were mainly La2O2S，a large number of CaS and calcium aluminate were attached to the surface，and the color of the inclusions was dark. When the content of La increases to 23×10−6，the inclusions change into La2O2S，calcium aluminate disappeared，a small amount of black CaS adheres to the surface，and the color was white. Rare earth content continued to increase inclusions to La2O2S-LaxSy-CaS eutectic compounds，the composition was more uniform，the color was bright white，there was no black CaS inclusions. The transformation process of inclusions was MgAl2O4 （CaxAlyOz）→ La2O2S+CaxAlyOz →La2O2S→ LaxSy. Through the distribution of inclusions could be seen that non-rare earth inclusions （black）exhibit aggregation，that was easy to collide and grow，and the size were larger；rare earth inclusions （white）were more inclined to disperse distribution，that meant there was no tendency to aggregate，and with the increase of rare earth content，the size of rare earth inclusions tends to decrease. The analysis of its distribution density showed that with the increase of rare earth content，the density between inclusions tended to decrease，indicating that the spacing between inclusions gradually became larger，reducing the possibility of defects caused by inclusion aggregation. With the increase of rare earth content，the grain size of the matrix gradually became smaller. The grain size of the blank sample was grade 9，and the average size was 17.64 μm. After adding rare earth，the grain size decreased to varying degrees. When the addition amount of La was 47×10−6，the minimum grain size was 9.4，and the average size was 13.53 μm，indicating that the addition of rare earth achieves the effect of grain refinement. The proportion of pearlite structure decreased with the increase of rare earth content. The proportion of pearlite in the test steel without rare earth was 45%. When the addition of La was 47×10−6，the proportion of pearlite decreased to 38%，indicating that rare earth inhibits the formation of pearlite. At the same time，the misfit of inclusions with α-Fe，γ-Fe and δ-Fe was calculated. It was concluded that the coherent structure of rare earth inclusions with ferrite and austenite was the main reason for the decrease of grain size.
quote
| GB/T 7714-2015 | [1] Bo Zhao, Wei Wu, Feng Yang, et al. Inclusions and Microstructure of Q355 Steel with Lanthanum Treatment[J]. Chinese Journal of Rare Metals, 2025, 49(5): 657-668. DOI:10.13373/j.cnki.cjrm.XY22110024. |
| MLA | [1] Bo Zhao, et al., "Inclusions and Microstructure of Q355 Steel with Lanthanum Treatment." Chinese Journal of Rare Metals, vol. 49, no. 5, 2025, pp. 657-668, https://doi.org/10.13373/j.cnki.cjrm.XY22110024. |
| APA | [1] Bo Zhao, Wei Wu, Feng Yang, Jiaqing Zeng, Jianzhong He, & Zhigang Liang. (2025). Inclusions and Microstructure of Q355 Steel with Lanthanum Treatment. Chinese Journal of Rare Metals, 49(5), 657-668. https://doi.org/10.13373/j.cnki.cjrm.XY22110024 |
| IEEE | [1] Bo Zhao, Wei Wu, Feng Yang, Jiaqing Zeng, Jianzhong He, and Zhigang Liang, "Inclusions and Microstructure of Q355 Steel with Lanthanum Treatment," Chinese Journal of Rare Metals, vol. 49, no. 5, pp. 657-668, 2025, doi: 10.13373/j.cnki.cjrm.XY22110024. keywords: {Q355 corrosion resistant steel;La treatment;inclusion evolution;microstructure;misfit} |