Abstract: Compared with traditional hot forming technology, the technology with tailored properties can make different regions of the same part have different strength and plastic toughness, so as to improve the ductility of some regions of the part absorbing the collision kinetic energy, and prevent collision intrusion.A new hot forming process of high strength steel with tailored properties by partial cooling pretreatment was proposed as well designing a customized zone cooling platform with dry compressed air as the medium. The temperature distribution and variation of the plate under partial cooling with the jet pressure of 0.3-0.7 MPa and the influence of return air structure on the cooling capacity and transition zone width of the platform were studied. The results show that when the jet pressure is 0.3 MPa and the air return structure is added, when the air cooling zone temperature is reduced to 410 ℃ (Ms), the hard zone temperature is slowly cooled to 750 ℃ (above Ar₃). After tempering at 800 ℃ and quenching, the soft zone comprises low-strength and high-plasticity ferrite and lamellar pearlite microstructure, and the hard zone comprises high-strength and low-plasticity lath martensite microstructure. These show that the high strength steel plate with tailored properties can be obtained with the new hot forming process and the customized zone cooling platform.

Key words: high strength steel, hot forming, tailored properties, partial cooling, transition zone