| As the most widely used steel in construction,hot-rolled ribbed steel rebars have a huge annual production.In order to narrow the gap with other countries,China promulgated new benchmarks《GB/T 1499.2-2018 Steel for the reinforcement of concrete-Part 2:Hot rolled ribbed bars》.The new benchmarks formulated more stringent specifications for hot-rolled ribbed steel rebars.After the promulgation of new benchmarks,the residual heat treatment method was replaced by the vanadium microalloying due to its poor performance stability.Although vanadium microalloying has become a common production method,its current production capacity would not meet the growing demand for rebar output because of the massively used vanadium alloy.Aiming at alleviating the huge economic pressure caused by the consumption of precious metals,hot-rolled ribbed steel rebars with low-alloy and highperformance are of urgent need.Lacked the refining treatment,reinforcing steel contains a lot of inclusions that have not yet been fully used.At present,oxide metallurgy technology is one of the effective means to strengthen the steel based on its deoxidation products.This paper therefore explores the innovative application of oxide metallurgy technology in producing hotrolled ribbed steel rebars with low-alloy and high-strength.Main contents are as follows.To clarify inclusion precipitation rules with oxide metallurgy technology,thus providing guidance for experimental and industrial research,this paper analyzed the deoxidization thermodynamics of oxide metallurgy.Calculation results showed that Ti2O3 is the most stable one among different Ti oxide types in common microalloying steel.In order to avoid the precipitation of Al2O3,the content of Al should be controlled below 0.009%when Ti content is 0.025%.The element segregation during the precipitation process further resulted in the competition of TiN with TiO3 under different oxygen and nitrogen contents,since TiN would precipitate at 1468℃.The transformation rule of coarse-grained austenite microstructure and the mechanism of inclusion refinement of ferrite grains were analyzed by performing austenite continuous cooling and isothermal transformation experiments.In the continuous cooling transformation of coarsegrained austenite of Ti deoxidized steel,polygonal ferrite and pearlite structures were formed at low cooling rates,while mixed structures of polygonal ferrite,bainite and martensite structures were obtained at high cooling rates.With the increase of isothermal temperature,the martensite structure is obtained during the subsequent rapid cooling process when part of austenite had not been transformed completely.At a lower isometric temperature,the blockshaped transformation was finally obtained due to the coarseness of the original leachate of austenite and the inhibited formation of the first co-analysis ferrite body.The research also examines the influence of the rolling process parameters on the properties of oxide metallurgical hot-rolled steel rebars based on experimental results.Compared with cooling rates,the austenitizing and rolling temperature has little effect on the performance of rebars.Meanwhile,when the austenite was cooled to 650℃ after deformation at a relatively rapid rate,the experiments indicate that it is beneficial to improve the performance of rebars and ensure that the microstructure of the steel bar meets the requirements of the new national benchmarks.For the enhancement of the performance of rebars,a new process route of "Oxide Metallurgy+Pre-piercing" was proposed and tested in experiments.The techniques of multistage rolling and the rapid cooling within an appropriate temperature range are able to refine the grains and improve the performance of the rebars,on the basis of ensuring the microstructure of the steel bar to meet the requirements.Its application would significantly reduce the consumption of alloy and have stable performance when compared with the microalloying process that uses a large amount of vanadium and residual heat treatment. |
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