钛锆复合脱氧对高强度低合金钢机械性能影响

1、The Effect of Ti-Zr Deoxidation on the Mechanical Properties of High Strength Low Alloy Steels Outline Introduction Purpose Experimental Results and discussion ConclusionIntroductionAlthough carbides and nitrides play an important role in precipitation strengthening and particle pinning, oxides have

2、 other advantages because they tend to be more stable than carbides and nitrides in steels. This is particularly true when steels undergo high heat input welding. Many studies have been reported on the application of Zr in steels, such as the effects on austenite grain growth control, sulphide shape

3、 control, and improving both transverse toughness and weldability. However, very few works have investigated the effects of combined oxidation on the mechanical properties. PurposeThe stability of the mechanical properties, especially elongation and impact toughness, were compared between steel A, w

4、hich was deoxidized with Ti-Zr, and steel B, which was deoxidized with Al. This aims to study the effects of combined oxidation of titanium and zirconium on the mechanical properties of high strength low alloy steels.ExperimentalTable 1 The chemical composition of the investigated plates (wt.%)Resul

5、ts and DiscussionabFig. 1 Optical microstructures of Steels A (a) and B (b)Microstructures Fig. 2 TEM-EDS image of the typical oxide in Steel AThe type and size of oxides 0.00.51.01.52.02.53.03.54.00510152025303540Frequency distribution / %Size / m 0.00.51.01.52.02.53.03.54.00510152025303540Frequenc

6、y distrubution/ %Size / m Fig. 3 The size distribution of inclusions in Steel A and Steel B cbaOxidesefdM/AMembranous M/AFig. 4 The sub-micron and nano-sized inclusions in Steel A(a) oxided on interface (b) and (c) oxides in the matrix Fig. 5 The fracture surface with inclusions in the dimples, and

7、the EDS spectrumDispersed distribution of MnS abFig. 6 Optical micrographs of inclusions in (a) Steel A and (b) Steel B 012345678910 11 12 13 14 15 16 17 18 19 20650675700725750775800825850875900Strength/ MPaNumber Rel/A Rm/A Rel/B Rm/B (a)024681012141618202022242628303234363840204060801001201401601

8、80200220 Elongation/A Elongation/BImpact toughness/ JElongation/ %Number Toughness/A Toughness/B (b)Fig. 7 Distribution of mechanical properties of Steel A and B(a) Yield strength and tensile strength of Steel A and B(b) Elongation and impact toughness of Steel A and BMechanical properties Thermodyn

9、amic analysis of Ti-Zr combined deoxidationThermodynamic analysis of Ti-Zr combined deoxidation Ti-Zr combined deoxidation not only results in deoxidation, but also forms complex oxides such as (Ti, Zr)x Oy in the solidification process. These complex oxides are stable at higher temperatures. Total

10、oxygen in the melt can be presented by the following equation: 3.These complex oxides function as fine-grained strengthening particles which are beneficial for the uniform strength, elongation and toughness of steels.inclusionsDissolvedTotalOOOSpheroidization and dispersion of MnS Clusters of and la

11、rge-sized MnS inclusions reduce the toughness, ductility and fatigue strength of steels. However, when MnS inclusions are small spheres, and are uniformly dispersed in the matrix, they can improve the mechanical properties of steels, especially the transverse impact toughness and fracture resistance

12、. The MnS precipitations on oxide inclusions are affected by the chemical composition of both the inclusions and the matrix. Oxides, such as the Ti-Zr complex oxides, with high sulfide capacities and low melting temperatures can act as sites for MnS precipitation. Conclusion (1) The dispersed oxides

13、 in the matrix were identified as titanium and zirconium complex oxides. Most of these oxides are sub-micron and nano-meter in size. These oxides provided nucleation sites for the precipitation of MnS during solidification. (2) The steel deoxidized with Ti-Zr had more stable mechanical properties than that deoxidized with Al. Elongation and impact toughness at low temperatures were enhanced, and the variabili