Review on regulation of MnS in non-qquenched and tempered steel

An overview of the current research status and control methods of MnS in non-quenched and tempered steel was provided.As a low-melting plastic inclusion,the morphology and distribution of MnS were influenced by various production processes.Therefore,control of MnS is a systematic problem that must be integrated into the entire production process.Based on the production process,the factors affecting the morphology and distribution of MnS in steel were introduced.The effects of oxygen activity,manganese,sulfur,and some alloys on MnS inclusion precipitation were summarized,mainly including MnS modification treatment and oxygen-sulfide composite precipitation control.It is believed that MnS precipitates during the solidification process of steel,and controlling the solidification cooling rate could effectively regulate the size and morphology of MnS,avoiding the precipitation of II-MnS.Additionally,by changing the deformation rate,deformation amount,deformation temperature during the hot deformation process,and heating time and temperature during heat treatment,the distribution and morphology of MnS could be improved.Through the fine control of the above process parameters,the number of II-MnS in steel could be effectively reduced,and their morphology could be improved,thereby enhancing the performance of non-quenched and tempered steel and promoting its wider application.Furthermore,applying laboratory research results to industrial production is an important direction for future research efforts in this field.

Evolution of inclusion and microstructure in Ti-Zr deoxidized steel during hot compression

The effects of different hot deformation amounts on the evolution of inclusion and microstructure in Ti-Zr deoxidized steel were studied by utilizing the Thermecmaster-Z hot simulation test machine,automatic scanning electron microscope equipped with energy-dispersive spectrometer,and electron backscattered diffraction.The results indicated that hot deformation amount has no significant effect on the number density of oxide,but the MnS that precipitated on the Ti-Zr oxide surface undergoes extension and breakage,resulting in the changes in oxide aspect ratio.Moreover,the fracture of nitride mainly occurs in the sample with the second pass deformation amount of 42.9%and 71.4%,and the degree of fragmentation of nitride is more serious with the deformation amount increasing.During the hot compression,sulfide undergoes breakage and extension,and with the second pass deformation amount increasing,the breakage and extension of sulfide present a periodic change.Finally,with the increase in hot compression amount,the ferrite types in microstructure change from acicular ferrite and bainitic ferrite to polygonal ferrite,and the ferrite grain size is refined.When the total deformation amount increases from 30%to 80%,the ferrite grain sizes of grain boundary with the misorientation of 4°and 15°decrease from 4.14 and 5.67μm to 3.47 and 4.40μm,respectively.However,when the total deformation amount increases to 80%,the harmful ferrite/pearlite banded structure appears in the micro structure.Refining ferrite grain size and avoiding harmful microstructure are the key for the optimization of hot compression process.

A review of research on central crack in continuous casting strand

Central crack is a common quality defect in continuous casting strand,which is difficult to fully weld in the rolling and forging processes,and has become a key technical problem that restricts the stable production of high-end alloy rod/forging/pipe.In recent years,the central crack control has been one of the main focuses in high quality steel research.In order to fully understand the central crack,the research status of central crack characteristics,formation mechanism,influencing factors,and control methods in the world was reviewed.The deficiencies in the research of the central crack and the key research directions in the future were pointed out,which will provide references for other scholars in this field of research.It is found that alloying elements segregation during solidification and inclusions precipitated at grain boundaries are the main reasons for the central crack formation,while the unreasonable application of production processes can also induce the initiation of central crack.The optimization of alloying element composition and production process is helpful to reduce the initiation of central cracks.In addition,the quantitative characterization mechanism based on steel grades,temperature,stress,and other factors induced central crack should be established in the further study,forming a systematic quantitative determination criterion and control strategy for coupling the composition,process and thermal/mechanical characteristic.

Banded structure control of low carbon microalloyed steel based on oxide metallurgy

Banded structure is a common harmful microstructure for low carbon microalloyed steel,which seriously shortens the service life of processed parts.In order to study the effect of oxide metallurgy on improving banded structure,the Ti-Zr deoxidized low carbon microalloyed steel that can play the oxide metallurgical role of inclusion was chosen as the research object,and the inclusion characteristics,microstructure and transverse and longitudinal mechanical properties after hot rolling were analyzed.The results showed the inclusion number density increased in all experimental steels after hot rolling,and a large number of long strip inclusions with aspect ratio greater than 3 appeared along the rolling direction.In addition,after hot rolling,there were element segregation bands in the experimental steels,and granular bainite bands were formed in the element enrichment zone.However,the intragranular ferrite generated in the cooling process destroyed the continuity of granular bainite bands,so that the microstructure anisotropy indexes of experimental steels were small.The mechanical properties analysis showed that the anisotropy of performance was mainly reflected in plasticity and toughness in the experimental steels.Among them,the difference ratio of elongation,section shrinkage and impact energy of No.2 steel was 1.69%,3.87% and 1.69%,respectively,which were less than those of No.1 steel and No.3 steel.The anisotropy of microstructure and mechanical properties of No.2 steel that full played the role of oxide metallurgy were improved,and the banded structure control of low carbon microalloyed steel can be realized by oxide metallurgy technology.

Computer Navigation-aided Resection of Sacral Chordomas

Background： Resection of sacral chordomas is challenging. The anatomy is complex, and there are often no bony landmarks to guide the resection. Achieving adequate surgical margins is, therefore, difficult, and the recurrence rate is high. Use of computer navigation may allow optimal preoperative planning and improve precision in tumor resection. The purpose of this study was to evaluate the safety and feasibility of computer navigation-aided resection of sacral chordomas. Methods： Between 2007 and 2013, a total of 26 patients with sacral chordoma underwent computer navigation-aided surgery were included and followed for a minimum of 18 months. There were 21 primary cases and 5 recurrent cases, with a mean age of 55.8 years old （range： 35 84 years old）. Tumors were located above the level of the $3 neural foramen in 23 patients and below the level of the $3 neural foramen in 3 patients. Three-dimensional images were reconstructed with a computed tomography-based navigation system combined with the magnetic resonance images using the navigation software. Tumors were resected via a posterior approach assisted by the computer navigation. Mean follow-up was 38.6 months （range： 18-84 months）. Results： Mean operative time was 307 min. Mean intraoperative blood loss was 3065 ml. For computer navigation, the mean registration deviation during surgery was 1.7 ram. There were 18 wide resections, 4 marginal resections, and 4 intralesional resections. All patients were alive at the final follow-up, with 2 （7.7%） exhibiting tumor recurrence. The other 24 patients were tumor-free. The mean Musculoskeletal Tumor Society Score was 27.3 （range： 19-30）. Conclusions： Computer-assisted navigation can be safely applied to the resection of the sacral chordomas, allowing execution of preoperative plans, and achieving good oncological outcomes. Nevertheless, this needs to be accomplished by surgeons with adequate experience and skill.