Research On Microstructure And Mechanical Of 600MPa Grade High Strength Steel Rebar

The requirements for steel and iron materials' performance are higher because of the rapid development of our country's economy and society; we need materials to have higher strength and longer service life and also to be resources-saving, cost-reducing, energy-saving and environment-protecting.In this paper, four kinds of test steel of different components were designed according to the requirements of the performance of HRB600 high strength steel rebar; the relationship was studied between composition and microstructure properties and hot deformation parameters. The effect of heating temperature and heat preservation time on the test steel's austenite grain growth tendency was studied by using the box type resistance heating furnace. Respectively studied four test steel's austenite continuous cooling transformation and phase transition rules and thermal simulation technology, determined four test steel's CCT curves and investigated the influence of deformation temperature and cooling speed on the microstructure and mechanical properties(hardness) using Gleeble thermal simulation testing machine.Studies on austenite continuous cooling transformation and phase transition rules of four test steel showed that: in the process of cooling, to obtain ideal ferrite and pearlite, cooling speed is less than 5?/s for test steel added V; cooling speed is no more than 5?/s for test steel of low Nb and for high Nb it is less than 3?/s; when cooling speed is about 3?/s, its strength could meet 600 MPa level basically, and hardness from high to low are, in order, test steel of low V, test steel of high V, test steel of Nb.Studies on thermal simulation technology rules of four test steel showed that: when the cooling conditions are the same, the micro-hardness value changes along with deformation temperature, for No.1 to No.4 test steel the maximum fluctuation values are 61 HV, 65 HV, 104 HV and 79 HV, so deformation temperature has a great influence on test steel's mechanical properties; when the deformation temperature is constant, the test steel micro-hardness increases along with the cooling speed increasing; when the cooling speed is less than 10 ? /s, ferrite and island-like martensite increase and bainite reduces along with deformation temperature decreasing.On the basis of the above research, determine the preferred composition design and process system assuring to obtain the composition of ferrite and pearlite and good performance of HRB600 high strength steel bar, put into rolling practice of high strength steel bar of good strength and toughness and shock resistance, and achieve good results.