Influence of Mn Content on the Microstructure and Mechanical Properties of Ultrafine Grained C-Mn Steels

Abstract

The effect of Mn content on the microstructure and mechanical properties of two ultrafine grained 0.2%C-Mn steels has been investigated. The ultrafine grained microstructure was produced by use of large strain warm deformation and subsequent annealing. The final microstructure consists of fine cementite particles within an ultrafine grained ferrite matrix. The increase in the Mn content leads to a decrease in the average ferrite grain size (from 1.3 to 0.8 mm for an increase in the Mn content from 0.74 to 1.52 mass%). This can be attributed to the enrichment of Mn in the cementite particles, which becomes finer in the steel with a higher Mn content. The increase in the Mn content results in an increase in strength at equal ductility and toughness.

Microstructure Control during Fabrication of Ultrafine Grained Dual-phase Steel: Characterization and Effect of Intercritical Annealing Parameters

“…it delays carbon flux through austenite. This is of particular importance in the present case because it was observed that cementite is enriched in Mn during the course 47) For these reasons, phase transformation and austenite growth are sluggish at low temperatures and the resulting martensite fraction is small. At higher temperatures, phase transformation is controlled by carbon diffusion, Mn diffusion playing a minor role.…”

“…Mn is enriched in cementite before intercritical annealing. 47) It was shown in a previous study 27) that the Mn enrichment is inherited by austenite and is clearly visible inside martensite after quenching. From this observation it is clear, that after equilibrium carbon activity is reached throughout the phases at the given intercritical annealing temperature, Mn has to diffuse from austenite to ferrite to reach the final equilibri- Table 1 and text for details.…”

“…This effect is enhanced by the fairly high Mn content (1.63 wt.%) which was shown to refine the cementite particle size. 47) 3) The growing austenite decelerates the grain boundary migration. 29) 4) The grain boundary mobility is further restricted due to Mn in solid solution which exerts a solute drag effect.…”

Ultrafine Grained Ferrite/Martensite Dual Phase Steel Fabricated by Large Strain Warm Deformation and Subsequent Intercritical Annealing

“…It was shown in a previous project 14) that Mn is advantageous for the production of ultrafine grained ferrite/cementite steels using large strain warm deformation. An increase in Mn content from 0.74 to 1.52 mass%, which is very close to the present investigation composition (0.87 and 1.63 mass%), decreases the average ferrite grain size, increases the fraction of HAGB and leads to a lower aspect ratio.…”

Influence of Carbon Content and Deformation Temperature on Ultra-Grain Refinement of Plain Carbon Steels by Means of Torsion Test

“…Despite the high strength and toughness of the UFG steels they tend to show reduced ductility due to their low work hardening rate. [9][10][11] On the other hand, it seems there is a consensus on the practical ways one can increase ductility of UFG metals. This could be doing by obtaining a final microstructure containing either a dispersion of fine second phase particles or by including a novel mechanism such as TRIP effect in the matrix.…”