The Process Study On The Side Tempering Microstructure Control Of HRB400

With the fast expansion of our national economy,the construction industry has developed rapidly in recent years,and the consumption of steel also grows.As an important material for construction,the product standard of steel bars becomes higher.Hot-rolled Ribbed Bar is the main kind of steel bars utilized in Chinese architecture,which is very popular with its low cost and high mechanical properties.Based on the actual production in this study,The water cooling process after rolling was investigated according to the problem of "tempering circle" emerged during the actual production,and finally the problem of "tempering circle" in the small specifications of HRB400 are eliminated.Through the theoretical analysis in this investigation,the following conclusions can be obtained:According to the determination of the chemical composition and mechanical properties of the Φ10HRB400/Φ12HRB400 produced in the field,the ratio of alloying element content is relatively low,especially for the content of Mn/Si,the production cost of these steel bars can be reduced under the premise of ensuring the mechanical properties of steel bars.The cooling control process of the steel bars adopt water cooling,according to the results of microstructures,the middle of microstructures are composed of ferrite + pearlite + widmanstatten structure;the transition layer of microstructures are composed of ferrite + troostite + bainite;the edge of microstructures are composed of tempering martensite + a small amount of tempering sorbite + ferrite,the outer microstructures form the "tempering circle",and the microstructures of HRB400 do not meet the requirements of the national standard.For the problems in the microstructures of the product,the final temperature of the water cooling process after rolling is adjusted,according to the temperature of HRB400 phase transition point,the different final temperatures of water cooling are designed,Through the finite element simulation of ANSYS,the following results can be obtained: Time of 0.5s;0.88s;1.34 s are respectively required when the surface of the Φ10 rod is water cooled to about 700℃;600℃;500℃.Time of 0.62s;1.08s;1.66 s are respectively required when the surface of the Φ12 rod is water cooled to about 700℃;600℃;500℃.The simulated cooling time offers guidance on experiments.the experimental temperatures of water cooling are basically consistent with the simulation results.Based on the analysis of the simulation results,the best final temperature of water cooling is 600℃.The experiment results: as for Φ10HRB400/Φ12HRB400,when the surface temperature of water cooling reaches about 700℃,the edge of microstructures are composed of ferrite + pearlite + widmanstatten structure;When the surface temperature of water cooling reaches about 600℃,the edge of microstructures are composed of ferrite + pearlite + widmanstatten structure,at this time,the ferrite grains are smaller than when they are finally cooled to about 700℃,moreover,the widmanstatten structure also reduces as well as the massive pearlite,and the pearlite grains are also smaller;When the surface temperature of water cooling reaches about 500℃,the edge of microstructures are composed of bainite + ferrite + pearlite + widmanstatten structure,and bainite has been produced at this time.In summary,when the final temperature of water cooling is above 600℃,the problem of "tempering circle" in the small specifications of HRB400 can be successfully eliminated,and the microstructures of HRB400 meet the requirements of the national standard,the best final temperature of water cooling is 600℃.