Abstract
Herein, we correlate the prior austenite grain (PAG) microstructure to deformation and fracture mechanisms of an ultra-high strength martensitic steel. To this end, a low-carbon martensitic steel is subjected to five heat-treatments and the PAG microstructure in the material is reconstructed from the EBSD inverse pole figure maps of the martensitic microstructure. The deformation and fracture response of all heat-treated materials are characterized by in situ tension tests of dog-bone and single-edge notch specimens that allow us to capture both the macroscopic mechanical response and the evolution of microscopic strains via microscale digital image correlation. The experimental results, together with microstructure-based finite element analysis, are then used to elucidate the effect of the PAG microstructure on the mechanical response of the material. Our results show that the interaction between the heterogeneous deformation fields induced by the notch and the bimodal PAG size distribution leads to an increase in the propensity of shear deformation and degradation in the fracture response of the material with increasing heat-treatment temperature and time. Our results also suggest that achieving a unform distribution of fine grains is an effective way to enhance both the strength and fracture properties of this class of materials.
Highlights
Our results show that both the average size and bimodality of the prior austenite grain (PAG) in the low-carbon martensitic steel increase significantly with large grains) of the PAGs in the low-carbon martensitic steel increase significantly with increasing heat-treatment temperature and time, for the range of temperature and time increasing heat-treatment temperature and time, for the range of temperature and time
We have quantified the effects of small variations in the heat-treatment parameters on the microstructure, and the deformation and fracture response of an ultra-high strength low-carbon martensitic steel
The material of interest was subjected to five heat-treatments and the prior austenite grain (PAG) microstructure in the resultant microstructures was characterized by reconstructing PAGs from the electron backscatter diffraction (EBSD) IPF maps of the martensitic microstructure
Summary
The strength–ductility (toughness) trade-off limits the strength level of AHSS that can be used in the manufacturing of complex shapes. On the contrary, during a side-impact collision, there is very limited space for the structure to deform. Vehicle parts such as the A-pillar that supports the windshield, the B-pillar between the front and the rear doors, and the beams in the vehicle doors call for materials with ultra-high strength. Advanced low-carbon martensitic steels with a strength level more than 1.2 GPa are the most widely sought-after structural materials for these parts, to enhance the overall crashworthiness of a vehicle [5,6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
