Study On Optimization Of The Heating Parameters Of Austenization And Mechanical Property Heterogeneity For Hot Forming Steel

With the development of the new generation steel,people are putting forward a higher demand for properties on the structural steel materials.Hot forming is a new manufacture technology for high strength steel.It can not only enhance crash safety,but also reduce the auto body weight.The high-strength steel with hot stamping technology can overcome a series of problems that the traditional process may bring,such as serious rebound,forming difficulties and easy to crack.In this paper,the microstructure and properties,phase transformation behavior of 22MnB5 hot forming steel were studied.Using a dilatometer determined the Ac1 and Ac3,We designed different austenization heating parameters and studied the influence of different heating parameters on microstructure and properties of hot forming steel.The Mechanical properties heterogeneity of hot-rolled pickling sheet produced by 1580 line along the wide side was studied.The main research results were shown as follows:(1)The microstructure and phase transformation behavior of hot forming steel were studied after heating in 860? holding 5min.The microstructure of B type hot forming steel was uniform martensite;and both A type and C type hot forming steel were martensite+ferrite.Using a dilatometer determined the Ac1 and Ac3 of the tested steel,which provided the basis for optimizing the heating temperature and holding time of three types of hot forming steel.(2)The appropriate austenization heating parameters were choosen for three types of hot forming steel.The microstructure of the hot forming steel were uniform martensite,The test results show that the best parameters of austenization was heating in 860? and holding 7min for three types of hot forming steel.The grain size of the hot forming steel were growing with the increase of the heating temperature and holding time.(3)Distribution of macro vickers hardness of hot-rolled pickling sheet produced by 1580 line was in the same level.the microstructure of hot-rolled pickling sheet in different position were ferrite+pearlite.(4)The edge of the hot-rolled pickling sheet have the similar microstructure and properties with the middle of the hot-rolled pickling sheet.the tensile strength was about 700MPa with its elongation near 17%.Using a dilatometer determined the critical transformation temperatures of the tested steel.The properties both the edge and the middle of the hot-rolled pickling sheet after heating in 880? and holding 5min were in the same level,the tensile strength is about 1650MPa with its elongation near 8.5%.