Continuous hot galvanizing method for 1180 MPa-grade Q&P steel

Abstract

The invention discloses a continuous hot galvanizing method for 1180 MPa-grade Q&P steel. Continuous hot galvanizing is carried out on chilled rolls of the Q&P steel and comprises the heating stage, the soaking stage, the quenching stage, the reheating stage, the partitioning stage, the hot galvanizing stage and the cooling stage; in the heating stage, the chilled rolls are pre-oxidized, the pre-oxidization temperature ranges from 610 DEG C to 750 DEG C, the pre-oxidization time ranges from 10 seconds to 60 seconds, the pre-oxidization atmosphere is the mixed atmosphere of nitrogen gas and air, and the final oxygen content ranges from 300 ppm to 20000 ppm; in the soaking stage, the soaking temperature ranges from 800 DEG C to 950 DEG C, the soaking time ranges from 30 seconds to 150 seconds, the hydrogen content in the furnace atmosphere ranges from 4% to 5%, and the dew point ranges from minus 35 DEG C to 50 DEG C; in the quenching stage, high hydrogen or water is adopted for quenching, and the steel is cooled to 280-350 DEG C; in the reheating stage and the partitioning stage, the partitioning temperature is heated to 380-450 DEG C at the rate of 8-20 DEG C/s, and the partitioning time ranges from 60 seconds to 300 seconds; in the hot galvanizing stage, the hot galvanizing temperature is 460 DEG C, and the hot galvanizing time ranges from 3 seconds to 10 seconds; in the cooling stage, the air or the nitrogen gas is adopted for cooling, the cooling rate is 15 DEG C/s, and the steel is cooled to 150 DEG C. The hot galvanizing adhesion performance of the Q&P steel is improved through the method.

Description

technical field [0001] The invention relates to a hot-dip galvanizing method for steel plates, in particular to a continuous hot-dip galvanizing method for 1180MPa grade Q&P steel. Background technique [0002] Q&P steel has excellent tensile strength and elongation. The tensile strength reaches 1200MPa while the elongation reaches more than 14%. It is widely used in automotive anti-collision bars, structural parts, chassis and other parts. Q&P is reinforced with 80-90% martensite, so its strength is very high; at the same time, it uses "carbon distribution" to improve plasticity. "Carbon distribution" process and principle: Heating the steel to the austenite zone, then rapidly cooling to the quenching temperature and a slightly higher partition temperature for heat preservation, to diffuse the supersaturated carbon in the martensite to the austenite without Form or form very few carbides, so that the stable retained austenite with a volume fraction of 5-20% remains at room...

AI Technical Summary

Problems solved by technology

[0003] Generally, more than 1.0% by mass of Si, Mn, Al and other elements are added to Q&P steel to inhibit the precipitation of cementite and improve the stability of austenite in the steel, thereby improving the mechanical properties of Q&P steel, but adding Si, Mn, When the Al element content is too high, during the hot-dip galvanizing process using conventional methods, Si, Mn and other elements on the surface of Q&P steel are prone to external oxidation during the heating and soaking process. Dezincification

Images