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Evolution of nonmetallic inclusions in pipeline steel during LF and VD refining process

  • Hangyu Zhu EMAIL logo , Jixuan Zhao , Jianli Li EMAIL logo , Qian Hu and Chenxi Peng
Published/Copyright: September 10, 2020
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High Temperature Materials and Processes
From the journal High Temperature Materials and Processes Volume 39 Issue 1

Abstract

The formation and evolution of nonmetallic inclusions in pipeline steel were investigated by SEM, EDS and INCA Feature Analysis System, with the industrial process of electric arc furnace → ladle furnace (LF) refining → vacuum degassing → continuous casting. The composition, size and amount of inclusions during refining process were discussed systematically. The results show that inclusions at each refining step are mainly small-particle inclusions (below 5 µm), and the total number of inclusions has been reduced significantly due to the refining effect of slag during LF refining. The calcium (Ca) treatment increases the amount of small inclusions. The types of inclusion are mainly Al2O3 and MnO–SiO2–Al2O3 before LF, and they are transformed into CaO–Al2O3, MgO–Al2O3 and CaO–MgO–Al2O3 during LF process. After Ca treatment, inclusions are changed to CaO–Al2O3–(CaS) and CaO–MgO–Al2O3–(CaS). Typical inclusions are still mainly CaO–Al2O3 and CaO–MgO–Al2O3 in tundish, but the composition of those inclusions has been changed and located to the low melting point region in ternary phase diagram. Such inclusions will further be removed as continuous casting approaches.

Keywords: nonmetallic inclusion; pipeline steel; refining process; calcium treatment

1 Introduction

Pipeline steels are usually used for the transportation of oil and natural gas over long distances under high pressure and require high strength, toughness, fatigue resistance and corrosion resistance. Nonmetallic inclusions directly affect the quality of pipeline steel [1,2,3]. Most of the researchers believe that noncoherent inclusions are considered as hydrogen-induced cracking (HIC)- initiation sites, and there is a strong correlation between HIC susceptibility, sulfur content, MnS and CaO–Al2O3 inclusions [4,5,6]. In our previous study, we have discussed the relationship between CaO–Al2O3, MgO–Al2O3 inclusions and inner fold and bulge defects; those brittle nonmetallic inclusions are the main causes of bulge and inner fold defects [7,8]. Moreover, nonmetallic inclusions will cause nozzle clogging and affect continuous casting (CC) process [9,10]. Therefore, the effective control of nonmetallic inclusions is very important for the production of pipeline steel.

The addition of Ca during refining process is a commonly used technique for the modification of MnS and Al2O3 inclusions and improvement of the steel cleanliness. Sidorova et al. [11] reported that MgO–Al2O3 and SiO2–Al2O3 inclusions were modified to CaO–MgO–Al2O3 inclusions after Ca treatment, and the hot rolling process can change the number and composition of the corrosion-active nonmetallic inclusions. Hao et al. [12] and Li et al. [13] reported that the inclusions could be turned into CaO–Al2O3–CaS inclusions after Ca treatment, by changing the refining slag composition and Si–Ca wires during the LF process. Xu et al. [14] summarized two kinds of precipitation forms of CaS inclusion: one by the direct reaction of Ca and S and the other by the reaction of CaO in CaO–Al2O3 with dissolved Al and S in liquid steel. They also reported that the modification degree of Al2O3 inclusions had a great effect on the generation of CaS [15].

In the current study, the variation in the composition, size and amount of inclusions in pipeline steels produced by a 90 ton electric arc furnace (EAF) → ladle furnace (LF) refining → vacuum degassing (VD) → CC process was systematically investigated.

2 Materials and methods

2.1 Industrial process and sampling

The pipeline steel in the current study was produced by the process of 90 ton EAF → LF → VD → CC, and the steel samples were taken at each production step, as shown in Figure 1. About 40 ton scrap and 50 ton molten iron were smelted at EAF, and then the molten steel was tapped from the EAF into the ladle. The smelting time of EAF was 50–60 min, and the tapping temperature was about 1,625°C. During the tapping process, silicon manganese, silicon ferrosilicon and aluminum were added to the ladle for predeoxidization, then low-carbon ferrochromium, ferromolybdenum and ferroniobium were added for element alloying. At the same station, slag formers were added to form a synthetic slag. The ladle was then transferred to LF station, and deoxidization, desulfurization and adjusting composition of the molten steel were processed depending on the specification of the steel grade at this stage. After the target steel composition had been reached, the ladle was transferred to the VD station. During VD, the molten steel was stirred by argon gas to remove nitrogen, hydrogen and inclusion. The vacuum degree was 10 Pa, and the degassing time was about 15 min. After VD, Ca treatment was performed to modify inclusion. Then, the molten steel was transported to the CC platform for casting.

Figure 1 Steel-making process and sampling location in the current study.
Figure 1

Steel-making process and sampling location in the current study.

2.2 Analysis of samples

The steel samples (Φ 30 mm × 10 mm) were cleaned by machining the surface, and the chemical composition of pipeline steel in the current study is shown in Table 1. The contents of carbon and sulfur in steel samples were analyzed with a JF infrared absorption C/S instrument (CS-996), and the contents of nitrogen and oxygen in the steel samples were measured with a LECO Analyzer (TC-500).

Table 1

Chemical composition of pipeline steel in the current study (wt%)

CSiMnCrMoNbTiPS
0.090.311.50.230.190.020.0180.0130.003

The 15 mm × 15 mm × 10 mm samples for the scanning electron microscopy (SEM, ZEISS ASIN EVO10, Carl Zeiss Microscopy Ltd, Germany) were made by cutting, grinding and polishing. The composition of nonmetallic inclusions of the steel specimens was detected by the energy-dispersive spectrometer (EDS, X-Max 80, Oxford Instruments, High Wycombe, UK). Inclusions in the current steel samples were analyzed using INCA Feature Analysis System for their two-dimensional morphology, size and composition. In the current study, only inclusions larger than 1 µm are considered.

3 Results and discussion

3.1 Changes of oxygen and nitrogen contents

The O and N contents of the steel samples from different refining steps in this study are shown in Figure 2. During LF refining, the O content decreases from 42.98 to 27.95 ppm, before LF refining is 42.98 ppm, due to the deoxidization reaction with aluminum, silicon manganese and ferrosilicon. After VD, the O content is reduced to 15.72 ppm due to argon blowing and vacuum degassing treatment, which is conducive to the flotation of inclusions and precipitation of dissolved oxygen in the molten steel. The content of oxygen in the steel sample from tundish increases slightly to 17.23 ppm due to secondary oxidation during the transportation of ladle and casting process.

Figure 2 Changes of oxygen and nitrogen contents during refining process.
Figure 2

Changes of oxygen and nitrogen contents during refining process.

The N content in the molten steel is generally on the rise during refining process. As a note, the N content decreases from 44.78 to 42.5 ppm during VD process due to the precipitation of dissolved nitrogen in the molten steel under vacuum. The nitrogen content will continue to decrease with the increase in vacuum holding time. When the liquid steel is transferred to tundish, the N content increases significantly to 45.75 ppm due to liquid steel reacting with air during the ladle transportation and casting process.

3.2 Composition of inclusions in refining process

INCA Feature Software is used to analyze the composition and size distribution of inclusions from different refining steps, and the scanning area is 2 × 3 mm. The elements such as Al, Mg, Ca, Si and Mn in inclusions were normalized and converted into various types of oxidation, and then the inclusion composition was mapped to ternary phase diagram for further analysis, as shown in Figure 3. Red line represents the liquidus of 1,600°C by considering ternary phase diagram and the blue line represents the liquidus of 1,500°C.

Figure 3 Composition distributions of inclusions in steel samples at different refining stages: (a) before LF, (b) after LF, (c) after VD and (d) tundish.
Figure 3

Composition distributions of inclusions in steel samples at different refining stages: (a) before LF, (b) after LF, (c) after VD and (d) tundish.

The inclusions before the LF treatment mainly consist of Al2O3, MnO and SiO2. A small amount of large CaO inclusions are detected, and no MgO inclusions are detected. As shown in Figure 3(a), it can be seen from the CaO–Al2O3–SiO2 phase diagram that there are many aluminosilicate inclusions, which are not located to the low melting point region. Moreover, for the Al2O3–SiO2–MnO ternary phase diagram, there are many Al–Si–Mn composite inclusions, and many small-particle composite inclusions are located in the low melting point region, which will be effectively removed during LF refining.

After LF refining, MnO inclusions are significantly reduced, only with few small size MnO inclusions due to the reaction of MnO inclusions and SiO2 from refining slag. On the contrary, the number of CaO–Al2O3, MgO–Al2O3 and CaO–MgO–Al2O3 inclusions increases. It can be seen from Figure 3(b) that CaO–Al2O3 and CaO–MgO–Al2O3 inclusions have larger size, but fortunately, these are located in the low melting point region and those inclusions will be removed by floating to the top slag in the subsequent refining processes. In addition, inclusions containing SiO2 decrease in this stage due to the interfacial reaction between CaO (slag) and SiO2 (inclusion), and the formed calcium silicate inclusions may be captured by the refining slag.

After VD treatment, as shown in Figure 3(c), almost no MnO-containing inclusions are found. Al2O3-Containing inclusions are significantly reduced due to Ca treatment. The main inclusions are still CaO–Al2O3-type inclusions, and the small-particle inclusions increase. A large amount of CaO–MgO–Al2O3 inclusions are still outside the low melting point region, because of the rise in MgO content in inclusions.

For the steel sample from tundish, its quality improves significantly, as shown in Figure 3(d). There are few SiO2 type inclusions, and no MnO-containing inclusions are found. The detected inclusions are CaO–Al2O3 and CaO–MgO–Al2O3, which are located in the low melting point region. Those inclusions will further be removed during the tundish casting process.

3.3 Morphology of inclusions during refining process

The typical Al2O3 and Al–Si–Mn composite inclusions before the LF treatment are shown in Figure 4. A large number of Al2O3 inclusions with small size are observed, generally about 2 µm. In addition, partical Al2O3 inclusions are wrapped up with MnS. The size of typical Al–Si–Mn composite inclusions are up to 20 µm, which consist of Al2O3 and MnO–SiO2. The formation reason of the above-mentioned inclusions is that the molten steel is deoxidized by aluminum and silicon-manganese alloys during tapping process, and the inclusions are mainly endogenous.

Figure 4 Element mapping of typical inclusions in steel samples before LF treatment. (a) MnO–SiO2–Al2O3, (b) Al2O3–MnS and (c) Al2O3.
Figure 4

Element mapping of typical inclusions in steel samples before LF treatment. (a) MnO–SiO2–Al2O3, (b) Al2O3–MnS and (c) Al2O3.

During the LF treatment, high basicity refining slag is used to desulfurize. The refining slag is composed of CaO, Al2O3 and MgO, which will modify the composition of inclusion in the molten steel. Typical inclusions after LF treatment are CaO–Al2O3 and CaO–MgO–Al2O3, with a size of about 5 µm, as shown in Figure 5. The formation mechanism of CaO–Al2O3 and CaO–MgO–Al2O3 is aluminum reacting with MgO and CaO from slag, as shown in equations (1)–(5) [12,13].

(1)2[Al]+3(MgO)slag=3[Mg]+(Al2O3)slag
(2)[Mg]+n/3(Al2O3)inclusion=(MgO⋅(n−1)/3Al2O3)inclusion+2/3[Al]
(3)2[Al]+3(CaO)slag=3[Ca]+(Al2O3)slag
(4)x[Ca]+(yMgO⋅zAl2O3)inclusion=(xCaO⋅(y−x)MgO⋅zAl2O3)inclusion+x[Mg]
(5)x[Ca]+(y+x/3)(Al2O3)inclusion=(xCaO⋅yAl2O3)inclusion+2x/3[Al]
Figure 5 Typical inclusions in steel samples after LF refining: (a) CaO–MgO–Al2O3, (b) CaO–Al2O3 and MgO–Al2O3.
Figure 5

Typical inclusions in steel samples after LF refining: (a) CaO–MgO–Al2O3, (b) CaO–Al2O3 and MgO–Al2O3.

After VD, the Ca-containing inclusions increase significantly due to Ca treatment. It is mainly spherical endogenous inclusion, and there are also a large number of composite inclusions wrapped up with CaS. Figure 6(a) shows the nearly spherical CaO–Al2O3 inclusion, and Figure 6(b) and (c) show the typical CaO–MgO–Al2O3 composite inclusion covered with CaS inclusion. Equations (6)–(9) indicate that calcium reacts with MgO and Al2O3 inclusions in the molten steel, resulting in Ca-containing inclusions increase and MgO and Al2O3 inclusions decrease [12,13]. Moreover, calcium reacts with sulfur in the molten steel to form CaS inclusion.

(6)[Ca]+(MgO)inclusion=[Mg]+(CaO)inclusion
(7)[Ca]+(Al2O3)inclusion=2[Al]+3(CaO)inclusion
(8)[Ca]+[S]=(CaS)inclusion
(9)2[Al]+3[S]+3(CaO)inclusion=3(CaS)inclusion+(Al2O3)inclusion
Figure 6 Typical inclusions in steel samples after vacuum degassing: (a) CaO–Al2O3–CaS, (b) and (c) CaO–MgO–Al2O3–CaS.
Figure 6

Typical inclusions in steel samples after vacuum degassing: (a) CaO–Al2O3–CaS, (b) and (c) CaO–MgO–Al2O3–CaS.

For the steel sample from tundish, the inclusion type is similar to that from VD stage, as shown in Figure 7. The only difference is that the content of CaS decreases, and the number of CaS-containing inclusions is lower. During the transfer of ladle to tundish step, the number of inclusions in the molten steel is significantly reduced, and further reaction of inclusions in the molten steel occurred. Inclusion composition has significantly been changed comparing with the steel sample from the VD step, and they all aggregated into the low melting point regions of CaO–Al2O3–MgO and CaO–Al2O3–SiO2 phase diagrams, as shown in Figure 3(d). Such inclusions can be further reduced as time approaches.

Figure 7 Element mapping of typical inclusions in the tundish: (a) MgO–Al2O3, (b) CaO–MgO–Al2O3 and (c) CaO–Al2O3.
Figure 7

Element mapping of typical inclusions in the tundish: (a) MgO–Al2O3, (b) CaO–MgO–Al2O3 and (c) CaO–Al2O3.

3.4 Size distribution of inclusions

It can be seen that inclusions at each refining station are mainly small-particle inclusions below 2 µm, followed by 2–5 µm inclusions, as shown in Figure 8. Before the LF treatment, the number of inclusions is larger, with size of 1–2 µm and 2–5 µm, which is 302 and 150 separately. After LF refining, the total number of inclusions is reduced due to the refining effect of slag. The Ca treatment after VD increases the number of small-particle inclusions with the composition of CaS. The tundish molten steel has higher cleanliness, and the number of inclusions is significantly reduced. No inclusions larger than 10 µm are detected.

Figure 8 Size distribution of inclusions during refining process: (a) inclusion counts and (b) number percent.
Figure 8

Size distribution of inclusions during refining process: (a) inclusion counts and (b) number percent.

3.5 Inclusion variation during refining process

The inclusion evolution behavior of the current pipeline steel during refining process is shown in Figure 9. Before the LF treatment, the inclusions are mainly Al2O3 and MnO–SiO2–Al2O3. After LF refining, the SiO2 and MnO inclusions are significantly reduced under the action of the refining slag. Al2O3 inclusions in the molten steel are transformed into CaO–Al2O3, MgO–Al2O3 and a small amount of CaO–MgO–Al2O3 composite oxides due to the dissolved aluminum in steel reacting with MgO and CaO from slag. Although the CaO–MgO–Al2O3 composite inclusions are relatively larger in size, they are all located in the low melting region and will float to slag in the subsequent refining process. For inclusions in the steel sample from VD with Ca treatment, they are transformed into CaO–Al2O3–(CaS) and CaO–MgO–Al2O3–(CaS). The reason is that calcium is difficult to diffuse in a short time, and the local calcium content in the molten steel is high, which leads to the formation of CaS inclusions. As the ladle is transferred to turret, the typical inclusions are still mainly CaO–Al2O3 and CaO–MgO–Al2O3; however, composition of inclusions has been changed and is closer to the low melting point region in ternary phase diagram. These inclusions are further removed during the casting process.

Figure 9 Inclusion evolution behavior during refining process.
Figure 9

Inclusion evolution behavior during refining process.

4 Conclusions

In the current study, the characteristics and the evolution behavior of nonmetallic inclusion in pipeline steel during refining process are systematically investigated by microanalysis. Final conclusions from this work are as follows:

  1. The O content generally decreases during refining process, and its content increases slightly from 15.75 ppm to 17.23 ppm, due to secondary oxidation during the transportation of ladle and casting process. VD decreases N content from 44.78 ppm to 42.5 ppm, and its content increases to 45.75 in tundish with a reason of reoxidation.

  2. Inclusions at each refining step are mainly small-particle inclusions below 2 µm, followed by 2–5 µm. The total number of inclusions is reduced significantly due to the refining effect of slag during LF refining. The Ca treatment increases the amount of small-particle inclusion. The molten steel in tundish has higher cleanliness.

  3. Inclusions are mainly Al2O3 and MnO–SiO2–Al2O3 before LF, which will be transformed into CaO–Al2O3, MgO–Al2O3 and CaO–MgO–Al2O3 composite oxides during the LF process. Inclusions are changed to CaO–Al2O3–(CaS) and CaO–MgO–Al2O3–(CaS) due to Ca treatment. Typical inclusions are still mainly CaO–Al2O3 and CaO–MgO–Al2O3 in tundish, but the composition of those inclusions has been changed and is located in the low melting point region in ternary phase diagram. Such inclusions will further be removed as time approaches.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 51604198 and 51974210). The authors would like to thank the engineers at Hengyang Steel Tube for their efforts in helping to perform this research.

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Received: 2020-04-29
Revised: 2020-08-05
Accepted: 2020-08-12
Published Online: 2020-09-10

© 2020 Hangyu Zhu et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/htmp-2020-0088
Keywords for this article
nonmetallic inclusion; pipeline steel; refining process; calcium treatment
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  2. Electrochemical reduction mechanism of several oxides of refractory metals in FClNaKmelts
  3. Study on the Appropriate Production Parameters of a Gas-injection Blast Furnace
  4. Microstructure, phase composition and oxidation behavior of porous Ti-Si-Mo intermetallic compounds fabricated by reactive synthesis
  5. Significant Influence of Welding Heat Input on the Microstructural Characteristics and Mechanical Properties of the Simulated CGHAZ in High Nitrogen V-Alloyed Steel
  6. Preparation of WC-TiC-Ni3Al-CaF2 functionally graded self-lubricating tool material by microwave sintering and its cutting performance
  7. Research on Electromagnetic Sensitivity Properties of Sodium Chloride during Microwave Heating
  8. Effect of deformation temperature on mechanical properties and microstructure of TWIP steel for expansion tube
  9. Effect of Cooling Rate on Crystallization Behavior of CaO-SiO2-MgO-Cr2O3 Based Slag
  10. Effects of metallurgical factors on reticular crack formations in Nb-bearing pipeline steel
  11. Investigation on microstructure and its transformation mechanisms of B2O3-SiO2-Al2O3-CaO brazing flux system
  12. Energy Conservation and CO2 Abatement Potential of a Gas-injection Blast Furnace
  13. Experimental validation of the reaction mechanism models of dechlorination and [Zn] reclaiming in the roasting steelmaking zinc-rich dust process
  14. Effect of substituting fine rutile of the flux with nano TiO2 on the improvement of mass transfer efficiency and the reduction of welding fumes in the stainless steel SMAW electrode
  15. Microstructure evolution and mechanical properties of Hastelloy X alloy produced by Selective Laser Melting
  16. Study on the structure activity relationship of the crystal MOF-5 synthesis, thermal stability and N2 adsorption property
  17. Laser pressure welding of Al-Li alloy 2198: effect of welding parameters on fusion zone characteristics associated with mechanical properties
  18. Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy
  19. Effects of different deoxidization methods on high-temperature physical properties of high-strength low-alloy steels
  20. Solidification pathways and phase equilibria in the Mo–Ti–C ternary system
  21. Influence of normalizing and tempering temperatures on the creep properties of P92 steel
  22. Effect of temperature on matrix multicracking evolution of C/SiC fiber-reinforced ceramic-matrix composites
  23. Improving mechanical properties of ZK60 magnesium alloy by cryogenic treatment before hot extrusion
  24. Temperature-dependent proportional limit stress of SiC/SiC fiber-reinforced ceramic-matrix composites
  25. Effect of 2CaO·SiO2 particles addition on dephosphorization behavior
  26. Influence of processing parameters on slab stickers during continuous casting
  27. Influence of Al deoxidation on the formation of acicular ferrite in steel containing La
  28. The effects of β-Si3N4 on the formation and oxidation of β-SiAlON
  29. Sulphur and vanadium-induced high-temperature corrosion behaviour of different regions of SMAW weldment in ASTM SA 210 GrA1 boiler tube steel
  30. Structural evidence of complex formation in liquid Pb–Te alloys
  31. Microstructure evolution of roll core during the preparation of composite roll by electroslag remelting cladding technology
  32. Improvement of toughness and hardness in BR1500HS steel by ultrafine martensite
  33. Influence mechanism of pulse frequency on the corrosion resistance of Cu–Zn binary alloy
  34. An interpretation on the thermodynamic properties of liquid Pb–Te alloys
  35. Dynamic continuous cooling transformation, microstructure and mechanical properties of medium-carbon carbide-free bainitic steel
  36. Influence of electrode tip diameter on metallurgical and mechanical aspects of spot welded duplex stainless steel
  37. Effect of multi-pass deformation on microstructure evolution of spark plasma sintered TC4 titanium alloy
  38. Corrosion behaviors of 316 stainless steel and Inconel 625 alloy in chloride molten salts for solar energy storage
  39. Determination of chromium valence state in the CaO–SiO2–FeO–MgO–CrOx system by X-ray photoelectron spectroscopy
  40. Electric discharge method of synthesis of carbon and metal–carbon nanomaterials
  41. Effect of high-frequency electromagnetic field on microstructure of mold flux
  42. Effect of hydrothermal coupling on energy evolution, damage, and microscopic characteristics of sandstone
  43. Effect of radiative heat loss on thermal diffusivity evaluated using normalized logarithmic method in laser flash technique
  44. Kinetics of iron removal from quartz under ultrasound-assisted leaching
  45. Oxidizability characterization of slag system on the thermodynamic model of superalloy desulfurization
  46. Influence of polyvinyl alcohol–glutaraldehyde on properties of thermal insulation pipe from blast furnace slag fiber
  47. Evolution of nonmetallic inclusions in pipeline steel during LF and VD refining process
  48. Development and experimental research of a low-thermal asphalt material for grouting leakage blocking
  49. A downscaling cold model for solid flow behaviour in a top gas recycling-oxygen blast furnace
  50. Microstructure evolution of TC4 powder by spark plasma sintering after hot deformation
  51. The effect of M (M = Ce, Zr, Ce–Zr) on rolling microstructure and mechanical properties of FH40
  52. Phase evolution and oxidation characteristics of the Nd–Fe–B and Ce–Fe–B magnet scrap powder during the roasting process
  53. Assessment of impact mechanical behaviors of rock-like materials heated at 1,000°C
  54. Effects of solution and aging treatment parameters on the microstructure evolution of Ti–10V–2Fe–3Al alloy
  55. Effect of adding yttrium on precipitation behaviors of inclusions in E690 ultra high strength offshore platform steel
  56. Dephosphorization of hot metal using rare earth oxide-containing slags
  57. Kinetic analysis of CO2 gasification of biochar and anthracite based on integral isoconversional nonlinear method
  58. Optimization of heat treatment of glass-ceramics made from blast furnace slag
  59. Study on microstructure and mechanical properties of P92 steel after high-temperature long-term aging at 650°C
  60. Effects of rotational speed on the Al0.3CoCrCu0.3FeNi high-entropy alloy by friction stir welding
  61. The investigation on the middle period dephosphorization in 70t converter
  62. Effect of cerium on the initiation of pitting corrosion of 444-type heat-resistant ferritic stainless steel
  63. Effects of quenching and partitioning (Q&P) technology on microstructure and mechanical properties of VC particulate reinforced wear-resistant alloy
  64. Study on the erosion of Mo/ZrO2 alloys in glass melting process
  65. Effect of Nb addition on the solidification structure of Fe–Mn–C–Al twin-induced plasticity steel
  66. Damage accumulation and lifetime prediction of fiber-reinforced ceramic-matrix composites under thermomechanical fatigue loading
  67. Morphology evolution and quantitative analysis of β-MoO3 and α-MoO3
  68. Microstructure of metatitanic acid and its transformation to rutile titanium dioxide
  69. Numerical simulation of nickel-based alloys’ welding transient stress using various cooling techniques
  70. The local structure around Ge atoms in Ge-doped magnetite thin films
  71. Friction stir lap welding thin aluminum alloy sheets
  72. Review Article
  73. A review of end-point carbon prediction for BOF steelmaking process
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