Microstructure of Pearlite Independently Nucleating on Grain Boundary Proeutectoid Phase in 100Mn13 Steel

Abstract

After 798 K aging treatment, lamellar pearlite connecting with grain boundary proeutectoid phase occurs in 100Mn13 steel. The proeutectoid phase is M23C6 carbide, which is different from pearlitic carbide, cementite. However, the lamellar pearlite has an orientation relationship (OR) with proeutectoid M23C6. Simultaneously, the pearlite also keeps a new OR with austenite where it occurs, (10)α//( 1)M3C//(1 )γ, [111]α//[113]M3C//[211]γ, indicating nucleation and growth of pearlite both are carried out in coherent austenite. Therefore, it is considered that pearlite does not develop from proeutectoid M23C6 but nucleates on proeutectoid M23C6 independently. The pearlite nucleation is probably affected by elastic deformation caused by M23C6 carbide, and pearlite growth mainly relies on new OR between pearlite and austenite. Under new OR, both ferrite and cementite can form by simple atomic movement based on the austenite lattice.

3D Growth of Intragranular Pearlite in an Aged 100Mn13 Steel

“…[ 23–25 ] However, second‐phase particles precipitated at austenite grain boundaries were activated as intragranular nucleation sites of pearlite when some certain alloying element was added, and the intragranular pearlite had a specific OR with the particles, but had no OR with the austenite grain from which it formed. [ 26–28 ] Although pearlite formed on the proeutectoid M 23 C 6 was observed in 100Mn13 high‐carbon, high‐manganese steel, [ 29 ] it could directly nucleate in austenite grain, and the sites provided by the second‐phase particles has not been found in the steel. Furthermore, Mehl proposed the model for pearlite transformation as “sidewise nucleation and edgewise growth,” [ 30 ] but it is important to note that the sidewise nucleation model is not accepted today as pearlitic structure has been reported to be controlled by lamellar branching.…”