The Effect of Intercritical Annealing on the Microstructure and Mechanical Properties of Ferritic–Martensitic Two‐Phase Steels

Abstract

Modified press‐hardening processes are very attractive for manufacturing safety‐relevant vehicle body parts from steels with martensitic–ferritic microstructures. In the process developed, the formation of the two‐phase microstructure and the hot sheet forming simultaneously occur subsequently to an intercritical annealing. By contrast, previously used process chains do not integrate setting of a multi‐phase microstructure within the forming step. In order to successfully combine the intercritical annealing with the actual forming, comprehensive knowledge of the microstructural evolution and the resulting mechanical properties is needed. Specifically, different heat‐treating routes are used to obtain different microstructures of ferritic–martensitic dual‐phase steels and partial martensitic steels. As a result of intercritical annealing in the temperature range of Ac1–Ac3, it is possible to vary the martensite volume fractions from 7 to 96 vol%. The data obtained can be employed for numerically describing the microstructural transformation and for designing the heat treatment process. It is demonstrated that this combined process allows for designing steels that feature properties that are similar to complex‐phase steels.

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

“…In fact, the volume change during quenching from the intercritical annealing range induces plastic deformation of adjacent ferrite grains, and therefore, creates a high density of unpinned dislocations in the vicinity of martensite. These martensite‐induced dislocations move at low stresses, creating low yield strengths, and interact to produce high rates of strain hardening . Among DP steels, DP3 shows higher initial n ‐values compared with DP1 while DP3* is even better than DP3.…”

Effect of Intercritical Annealing on Mechanical Properties and Work‐Hardening Response of High Formability Dual Phase Steel

“…Several studies have systematically studied the effect of volume fraction of martensite on mechanical properties of DP steels . It has been also revealed that the strength increases and total elongation decreases by increasing the amount of martensite in steels with carbon contents between 0.05 and 0.4 wt% . However, the main focus has been on achieving DP steels with high strength and acceptable formability and there are few reports on the low carbon side.…”

Pengaruh Kecepatan Pendinginan Baja Fasa Ganda Fe-Ni hasil Tempa Panas terhadap Struktur Mikro dan Nilai Kekerasan

“…Seiring berjalannya waktu, teknologi modifikasi struktur mikro makin berkembang melalui berbagai rute proses untuk memenuhi kebutuhan sifat mekanik yang beraneka ragam. Salah satu proses yang saat ini banyak digunakan yaitu pemanasan fasa-ganda [2][3][4][5][6][7][8][9][10][11][12] .…”