Study on the resistance spot welding technology of 22MnMoB hot stamping quenched steel

In this paper, the spot welding technology of a new kind of 22MnMoB hot stamping quenched steel sheet was systematically studied by power frequency spot welder. Through a series of technology and test experiments, we have obtained the optimal spot welding technological parameter condition. According to the results, the relations among spot welding technological parameter, welding nugget, mechanical property and fracture mode were discussed. The effects of all the welding parameters such as welding current, welding time and electrode force on the quality of joint can be boiled down to one thing--the diameter of welding nugget. The experimental results showed that welding nugget diameter determines the mechanical property of spot welding joint and the relation between welding nugget diameter and the mechanical property of joint presents a kind of linear mathematic representation. There are two typical fracture models of 22MnMoB hot stamping quenched steel sheet, i.e., interracial fracture and nugget pullout. Other than mild steel or normal high strength steel, in the shearing tensile test, hot stamping quenched steel has a great tendency to fail in interfacial mode due to the effects of high strength matrix structure, welding soft zone and the porosity level of fusion zone.

The influence of adding niobium and vanadium on hydrogen diffusion in 22MnB5 hot stamping steel

Adding alloying elements is always considered as an effective method to enhance the resistance against hydrogen embrittlement in steels.Nb and V were added into 22MnB5 hot stamping steel,and then their influences on hydrogen permeation of 22MnB5 steel suffering from corrosion in 3.5%NaCl aqueous solution were investigated.The results showed that the addition of Nb/V could reduce the hydrogen permeation content due to solution corrosion.Electrochemical techniques including electrochemical impedance spectroscopy and overpotential stepping hydrogen permeation test con-firmed that compared to the original 22MnB5 steel,22MnB5-NbN steel owned a higher corrosion resistance and a higher hydrogen diffusion resistance.Furthermore,it was confirmed that Nb-V-alloyed 22MnB5 steel showed higher resistance against hydrogen embrittlement than the Nb-V-free counterpart,which should be related to the presentence of nanoscaled Nb/V-containing precipitates as the irreversible trapping sites for hydrogen detected by thermal desorption spectroscopy.Finally,the lattice diffusion coefficient of hydrogen DL was determined in steels with and without Nb and V.

Intermetallic Evolution of Al–Si-Coated Hot Stamping Steel During Modified Electrically Assisted Rapid Heating

Modified electrically assisted(EA) rapid heating of Al–Si-coated hot stamping steel is suggested, and the intermetallic evolution in the coating during heating is experimentally investigated. In the modified EA rapid heating, a continuous electric current for a suitable duration is applied to a specimen to heat it to a temperature slightly below the melting temperature of the coating. The temperature of the specimen is then kept constant for a specified dwell time. The result of the microstructural analysis shows that the modified EA rapid heating could effectively increase the thickness of the intermetallic layer between the coating and steel substrate much faster than conventional furnace heating and induction heating. The effectiveness of EA rapid heating may be due to the athermal effect of the electric current on the mobility of atoms, in addition to the well-known resistance heating effect. EA rapid heating also provides a technical advantage in that partial austenization can be easily achieved by properly placing the electrodes, as demonstrated in the present study.

Tailoring of Mechanical Properties of Indirect Hot Stamping Steel Tubes by Laser Assisted Local Rapid Heating

The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was in vestigated. A heated region with a spiral shape was generated on the surface of the tube by combining the linear movement of the laser and the rotation of the tube. The results of axial crush tests show that the laser assisted local heating can be effectively used to modify the mechanical performance of the tube. A microstructural analysis confirms that the laser locally induces a martensitic phase transformation in the heated region and results in inhomogeneous microstructures alon- the length of the tube.

Research on Mechanical Properties of 22MnB5 Steel Quenched in a Steel Die

22MnB5 is one of the most typical hot stamping boron steels.In order to study the effect of austenitizing temperature and holding time on the mechanical properties of hot stamping boron steel 22MnB5,a series of quenching process are done.The tensile strength and hardness of 22MnB5 samples are measured.The results show that 22MnB5 has a good quenching performance,and the tensile strength and hardness of samples quenched in a water-cooled steel die are similar to those of water quenching.The higher tensile strength and HRC hardness are achieved when austenitizing at temperatures of 880-910.Holding at 910 for 5 min and then quenching gives rise to a better combination of tensile strength,hardness and ductility.