Effect of nitrogen on the microstructure and strengthening mechanism of high performance tinplate

In order to meet the high strength and high formability requirements of the tinplate market, the nitrogen strengthening method was used for the chemical composition of the tinplate, and the action mechanism of nitrogen on the full-process tinplate substrate was explored. The present study designed tinplate with different nitrogen contents (named as 20 N steel and 150 N steel), and conducted phase transformation research and recrystallization temperature tests. SEM, XRD, EBSD, TEM, chemical dissolution analysis and tensile tests were carried out, and the influence of annealing process on the microstructure, mechanical properties and precipitation of annealed sheet was also explained. With the increase of nitrogen content, the phase transformation temperature decreases, the hardness increases and the recrystallization temperature increases. The microstructures of 20 N steel and 150 N steel annealed at different annealing temperatures are composed of ferrite and cementite distributed in chains. At the same annealing temperature, the recrystallization degree of 20 N steel is higher, the {111} texture accounts for a larger proportion, and the grain size is larger. With the increase of annealing temperature, the yield strength and tensile strength show a downward trend, while the elongation shows an upward trend. Compared with 20 N steel, the yield strength and tensile strength of the 150 N annealed sheet are significantly improved, and the elongation is slightly reduced. The calculation results show that the mechanism of nitrogen improving the strength of tinplate is mainly solid solution strengthening, and the improvement effect of fine grain strengthening and precipitation strengthening is weak.