20 May 2022, Volume 34 Issue 5

    

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   Progress and challenge of liquid metal embrittlement in galvanized advanced high strength steel 

   

  DING Kai1,2， DONG Wufeng1,2， WANG Li3,4， PAN Hua3,4， LEI Ming3,4， GAO Yulai1,2

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 399-410. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210209

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   Attributing to its great application potential in automobile lightweight, advanced high strength steel (AHSS) is extensively used in car white body, which can meet the demands of saving fuel and reducing exhaust emission by reducing the car weight while ensuring its safety. To increase the service life of vehicle structure, it is required to protect AHSS from corrosion, mostly by zinc (Zn)based coating. However, advanced high strength steel with Zn coating is prone to liquid metal embrittlement (LME) during welding, resulting in the reduction of loadcarrying property of the involved welded joints. Liquid metal embrittlement also occurs in galvanized hot stamping steel during hotpress forming process, which can deteriorate its mechanical property and resultantly limit its application. The LME occurred in galvanized AHSS sheets and its forming mechanism were reviewed, and the factors to cause LME were also emphatically analyzed. Combined with the recent investigations of LME in Zncoated AHSS, the challenges were discussed and correspondingly the feasible research approaches were put forward.  
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  Numerical simulation research on tuyere air supply characteristics of large blast furnace 

  NI Ao1， LI Chengzhi1， ZHANG Wei2， YIN Teng3， LU Zhengdong3， XUE Zhengliang2

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 411-420. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210138

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   1.Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology， Wuhan 430081, Hubei, China；2.Hubei Provincial Key Laboratory for New Processes of Ironmaking and Steelmaking, Wuhan University of Science and 

  Technology， Wuhan 430081, Hubei, China；3.China Baowu Group Wuhan Iron and Steel Co., 

  Ltd.， Wuhan 430080, Hubei, China
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   Effect of w(MgO) on strength of pellets made of local 

  high silicon iron powder 

  BAI Jiapei1， LIU Wenqiang1， YANG Aimin1， LI Jie1， LI Daliang2， LI Fei2

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 421-428. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210156

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   The basic characteristics of local high silicon iron concentrate M, Y and low silicon iron concentrate were tested by using the basic characteristics measurement system of iron ore powder. And the effect of w(MgO) on the  strength of pellets was studied by mineral phase analysis using polarizing microscope. The experimental results show that M powder has high assimilation temperature and high crystalline strength, which is suitable to be used as the main raw material for pelletizing. And the reasonable ratio of the mixture is M∶Y∶low silicon iron concentrate =5∶3∶2, under the w(SiO2) was about 55%-56%. Then the roasting briquette experiment was carried out. The results show that with the increase of w(MgO), the compressive strength of the briquette increases first and then decreases, reaching the highest value of 3531N/pcs when w(MgO)=18%. When w(MgO)=18%, the ore phase is mainly hematite phase, hematite is crystallized and connected into pieces, and calcium silicate phase is less, bonding phase and calcium ferrite phase stabilize the overall structure to a certain extent, and the strength reaches the highest. However, as w(MgO) continues to increase, the increase of magnesium ferrite phase inhibits the crystallization of hematite, the connection crystal growth is poor, the grain is fine and dispersed, and the strength decreases.  
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   Effect of SO2 and H2O(g) in flue gas of pellet on SCR catalytic denitrification 

  FAN Xiaohui， ZHU Yuan， GAN Min， JI Zhiyun， SUN Zengqing， WU Yufeng

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 429-437. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210157

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    Selective catalytic reduction (SCR) has the advantages of high efficiency and mature technology, but the flue gas of the pellets needs to be heated to reach the reaction temperature of SCR denitrification, resulting in high energy consumption and operating costs. The flue gas temperature of oxidized pellet preheating section II (PH section) is above 300℃, which meets the temperature required for the SCR reaction, but the SO2 and H2O (g) contained in the flue gas will affect the denitrification performance of the catalyst. The effect of SO2 and H2O(g) in the flue gas in the PH section on the denitrification performance of the V/Ti catalyst and its mechanism were studied. The results show that both SO2 and H2O(g) will reduce the denitrification performance of the catalyst to a certain extent. The effect of denitrification is smaller and reversible than that of SO2. The presence of SO2 and H2O(g) has the worst impact on the denitrification performance of the catalyst and is irreversible. The denitrification rate of the catalyst decreases from 96.1% to 77.2% after reacting for 5 hours at a concentration of 10%H2O(g)+1100mg/m3SO2. The ammonium sulfate formed by the reaction of SO2 and H2O(g) in the flue gas with NH3 is deposited and adsorbed on the surface of the catalyst, which reduces the specific surface area and dispersion of the reacted catalyst, which is not conducive to the adsorption of NO and NH3, thereby reducing the denitrification performance of the catalyst. Therefore, the control of the content of SO2 and H2O(g) in the flue gas and the optimization of the denitrification conditions are very important for the SCR denitrification in the PH section.  

   
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   Numerical study on strandblocking operation of a sixstrand square billet tundish 

  ZHAO Peng1,2，ZHANG Hua1,2，FANG Qing1,2，WANG Jiahui1,2， WU Guoliang1,2，NI Hongwei1,2

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 438-450. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210123

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    During the continuous casting production, the strandblocking operation is often carried out due to the insufficient supply of molten steel or equipment failure to adjust the production rhythm. The flow, temperature field and inclusion removal rate in a sixstrand bloom casting tundish under the conditions of blocking one strand and two strands were numerically investigated to determine the optimum strandblocking operation, which can provide theoretical guidance for industrial production. The results show that in the case of blocking one strand and two strands, with the blocked strands move from the edge of the tundish to the impact zone, the average residence time of the tundish increases by 433s and 1093s, the volume fraction of the plug zone increases by 13% and 123%, while the volume fraction of the dead zone decreases by 04% and 41%, respectively. The flow consistency among the strands is apparently enhanced, and the temperature of liquid steel in the tundish is more uniformly distributed. Furthermore, the removal rates of nonmetallic inclusions with the diameters of 5, 10, 20 and 40μm increase, while the removal rates of inclusions with diameters of 80 and 100μm decrease. When blocking only one strand, the third strand or the fourth strand is the optimum choice. When blocking two strands, it is best to choose both the third and the fourth strands.  

   
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   Numerical simulation of influence of impellers′ shape on mixing behavior by KR method desulfurization 

  JI Junhong，JIANG Yu，DU Hongxian，WANG Shuoshuo

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 451-460. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210135

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    Three new types of impellers were developed to strengthen the mixing effect of molten iron and desulfurizer, in order to improve the serious waste of desulfurizer in KR stirring process. CFD technology was used to describe the entrapping ability of the liquid surface and internal mixing ability with the velocity field, the turbulent dissipation rate and mixing time, respectively. The influence rules between structural parameters and operating parameters were analyzed by comparing the flow structures of molten iron with three new types of impellers and traditional impeller type (A impeller). The results show that the square impeller (B impeller) is better than the other three types impellers in its ability of desulfurizer and improving mixing effect, the volume of the columnar turning zone decreases by 60%, the volume of the dead zone decreases by 67%, and the mixing time decreases by 52%, respectively, with the rotation speed increasing from 60r/min to 80r/min of the B impeller. The downward dip angle and radial beveling edge of the impeller D improves the mixing effect of dead zone under the impeller, the dead zone volume decreases by 51% and the mixing time decreases by 48%, with the speed increasing from 60r/min to 80r/min. The entrapment ability and mixing ability of the C impeller are between those of the D impeller and the B impeller. And the effect of A impeller is the worst.  

   
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   Transient movement and capture behavior of dispersed argon bubbles in continuous casting mold 

  GONG Jiarui，LIU Zhongqiu，WU Yingdong，YAO Yuchao，JIANG Jiuhua，LI Baokuan

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 461-469. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210132

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   In order to study the transient movement of the dispersed argon bubbles in the continuous casting mold, a large eddy simulation model coupled with flowheat transfer and solidificationbubble movement was developed. The unsteady turbulent flow field of molten steel in the solidified shell and the transient motion characteristics of argon bubbles in the mold were studied. The results show that the solidified shell has a great influence on the flow field of molten steel in the mold. Asymmetric flow of molten steel in the liquid phase leads to uneven distribution of bubble movement and capture positions. And smallsized bubbles are more likely to move to the deeper areas of the liquid core, and the penetration depth of the bubble increases with the increase of the casting speed.  The critical bubble diameter is defined as the bubble diameters that make the escape rate and retention rate reach the extreme.  the critical bubble diameter is between 05 and 1mm. When the bubble diameter is larger than the critical bubble diameter, the upper surface escape rate and the shell capture rate and retention rate are relatively low at a given casting speed; while when the bubble diameter is smaller than the critical bubble diameter, the shell capture rate and the retention rate increases with increasing casting speed and decreasing bubble diameter. 

   
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   Study on high temperature mechanical properties of 09MnNiDR cryogenic vessel steel 

  DING Hang1， WEI Kangji1， YANG Yong2， ZENG Fanzheng2， WANG Lijun1， CHOU Kuochih1

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 470-477. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210059

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   igh temperature mechanical properties of 09MnNiDR steel were investigated on Gleeble1500 thermal simulation testing machine. The percentage of section shrinkage, tensile strength and stressstrain curves were obtained within the temperature range of 600-1350℃, and the fracture morphology was analyzed with the help of scanning electron microscope (SEM). Solidification phase transition was calculated by FactSage software. The results show that the high temperature interval of brittleness (Ⅰ) starts from liquidus temperature(tL) to 1350℃, afterwards following with the high temperature interval of plasticity from 1350 to 950℃, and the third area from 950 to 600℃ is the low temperature interval of brittleness(Ⅲ). The high temperature interval of plasticity is related to the austenite phase with great plasticity, while the high temperature tensile strength is low; the reason for the decrease of plasticity in the low temperature interval of brittleness(Ⅲ) is attributed to the γ→α phase transition when temperature lower than 950℃. The observation of fracture morphology showed the high temperature interval of plasticity is transcrystalline rupture and the low temperature interval of brittleness(Ⅲ) is intergranular fracture. Meanwhile the liquid inclusion MnOSiO2Al2O3 was observed on the fracture morphology of the high temperature interval of plasticity. Based on ternary phase diagram calculation, the melting point of inclusion is less than 1300℃. In order to control the inclusion with low melting, the ration of MnO/SiO2 should be controlled between 1 and 15, while the content of Al2O3 is from 10 mass% to 17 mass%, so as to reduce the risk of internal cracks during continuous casting.  

   
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   Effect of impact load on wear resistance of 10Mn steel and analysis of wear resistance mechanism 

  WANG Tao1,2， HU Feng1,2,3， ZHOU Wen1,2,3， YIN Chaochao1,2， KE Rui1,2， WU Kaiming1,2,3

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 478-488. https://doi.org/10.13228/j.boyuan.issn1001-0963.20200319

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   The wear resistance of 10Mn steel under 2 and 5J impact load was studied by water toughening treatment and 450℃ aging heat treatment. The results show that the weight loss of 10Mn steel under 5J impact load is less, the work hardening rate is faster, and the weight loss of 10Mn steel changes periodically under different impact loads. SEM results show that there are ploughing wear, chiseling wear and cracks on the worn surface. The volume fraction of austenite and martensite on the subsurface was quantitatively calculated by XRD data. With the increase of impact energy, the content of austenite decreases and the content of martensite increases. TEM analysis shows that there are high density dislocations, stacking faults and deformation twins in the worn layer, and the dislocations accumulated in the carbides. EBSD results of subsurface layer show that deformation martensite and crack are formed during wear process. Martensite nucleates and grows in high dislocation density region, while crack propagates along austenite grain boundary. Finally, it is blocked in high dislocation density region and deformation martensite and stops propagation. The wear resistance mechanism consists of dislocation strengthening, deformation induced transformation strengthening and deformation twin strengthening.  

   
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   Toughening mechanism of medium carbon 25Mn cryogenic steel

  YANG Yuehui， LI Jing， YUAN Shaoqiang， LIANG Guoli， ZHANG Xiaojuan

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 489-495. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210055

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    In order to study the lowtemperature toughening mechanism of medium carbon 25Mn steel, the impact energy of this steel at different temperatures was measured, and the deformation mechanism and its effects on toughness of tested steel was discussed by the observing of microstructure, analyzing the composition of phases and grain boundaries in the microstructure near fracture. The results show that at room temperature, the crack tip region is toughened mainly by TWIP mechanism. With the decreasing of temperature, TRIP mechanism is enhanced. Although the stress concentration at crack tip can be alleviated, the martensite obtained promotes the crack growth. Moreover, the deformation mechanism near the fracture includes both twinning and slipping, and the slipping of dislocation is easy to induce the "slipping off" mechanism, which also makes the toughness of the steel deteriorate. Totally, the low temperature toughness of the tested steel mainly depends on the deformation mechanism within a small range of the crack tip, and the toughening effect of TRIP mechanism is lower than that of TWIP mechanism.  

   
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  Hot deformation behavior of C-HRA-5 new austenitic heat resistant stainless steel  

  WANG Weicong， DU Huayun， HOU Lifeng， WEI Huan， LIU Xiaoda， WEI Yinghui

  JOURNAL OF IRON AND STEEL RESEARCH　. 2022, 34(5): 496-503. https://doi.org/10.13228/j.boyuan.issn1001-0963.20210071

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   To obtain the optimum process parameters for rolling production of CHRA5 steel, a series of doublehit hot compression experiments were conducted on the CHRA5 steel by a Gleeble3800 thermal simulation tester. The true stressstrain curves of CHRA5 steel were obtained under the conditions that the deformation temperature range is 900-1100℃, the strain rate range is 001-1s-1, and the interval time is 1, 5, 15, and 30s, respectively. The 02% offset method was used to calculate softening fraction, and the softening fraction increases with the increase of deformation temperature and strain rate. The kinetic equations of MDRX were obtained by linear regression analysis. The established hot processing maps of C-HRA-5 steel show that the deformation of the material in the range of 1000-1100℃ is stable. In addition, the C-HRA-5 steel will be no instability during the second channel compression at a lower temperature when the interval time is 5s.