Research And Development Of High-performance Steel Bar With Low Cost

With the acceleration of our country's urbanization process,the amount of steel bar's production and consumption will increase greatly in the future.Thus,it's very important to research and develop high-performance steel bar with low cost.In this article,a production technology of high-performance steel bar with low cost was developed based on the results of experimental and industrial investigation. Industrial trials were carried out in field conditions.The main works are shown as following:(1)New steel's microstructure in different cooling rate and temperature range of austenite in non recrystallization zone were determined through thermal-mechanical simulation. The experimental results indicate that experimental steel bar's microstructure is consisted of ferrite and pearlite using forced air cooling after rolling and its temperature range in non recrystallization zone is 770～950℃in field conditions.The experimental steel's model of resistance of deformation and dynamic behavior during high-temperature deformation were investigated using single hit compression test.The research indicates that the dynamical recrystallization of austenite doesn't occur at present industrial conditions.The experimental steel's softening fraction under different thermal deformation conditions was determined through double-hit compression tests.The research indicates that the static recrystallization of austenite doesn't occur in finishing area at present industrial conditions.(2)Through industrial field tests,the influence of different controlled temperature rolling means on the properties of hot rolled ribbed wire rods was determined and the best controlled temperature rolling technology was established. Utilizing controlled temperature rolling and spray cooling combined with adjusting billet's chemical composition,400MPa high-performance hot rolled ribbed wire rods with low cost using plain carbon steel was produced successfully. (3)During rolling 025mm high-performance bar with low cost in Pingxiang Iron and Steel Corporation, the stock's temperature in intermediate and finishing mill group was calculated using plane deformation method.The calculation results show that the stock's temperature increases in intermediate mill.When the stock's temperature in the entry of intermediate mill unit is controlled in 950℃and finishing rolling speed is controlled in 11m/s,the stock's theoretical temperature rise in intermediate and finishing mill unit is 44.7℃and 65℃respectively.(4)A new technology of producing high-performance steel bar with low cost was proposed according to the technology of producing high-performance hot rolled ribbed wire rods.The mechanism of new technology is cooling the fine and strongly hardened austenitic grain which is formed in the rolling process of austenite recrystallization zone and consisted of lots of lattice defects to phase transition temperature with optimized controlled cooling technology. Thus the austenite grain's growth trend is restrained and changes to ferrite with proper grain size and pearlite in the following air cooling process.There is no tempered microstructure in the steel bar's surface.The steel bar's strength increases and the ratio of tensile strength to yield strength doesn't decrease.(5) 025mm steel bar's temperature fields with different water cooling conditions after rolling was simulated by finite element method.The experimental results show that close-loop tempered microstructure will occur in the steel bar's surface and influence its performance when three segment water cooling is adopted after rolling and steel bar's temper temperature in the surface is about 660℃.In order to improve steel bar's performance under the condition of no close-loop tempered microstructure occurring in steel bar's surface as possible, two segment water cooling should be adopted and steel bar's temper temperature should be about 800℃.(6) Welding performance of the steel bar produced by new technology was tested by flash butt welding technique.The experimental results show that the welding performance of high-performance steel bar with low cost produced by new technology is well.Φ12mm steel bar's test results of mechanical properties after aging twenty days show that there is no aging problem in the steel bar produced by new technology.