Effect of Thermo-Mechanical Variables on the Dynamic Ferrite Transformation Induced by Hot Deformation in 0.22C-Mn Steel

Hot torsion of a C (0.22 wt%)-Mn steel was used to investigate the influence of thermomechanical arameters on the strain induced dynamic transformation (SIDT) of ferrite. The pecimens were strained as a function of strain rate (0.05/sec - 5/sec) and strain (- 5.0) at right bove Ar3 temperature. The critical strain to initiate dynamically transformed ferrite nuclei during deformation increased as increasing the strain rate. On the other hand the completion of SIDT was hifted to larger strain by decreasing strain rate. This is due to the fact that the dynamic ransformation of ferrite was processed in the interior of austenite grain as well as at grain boundary y large stored energy and many nucleation sites for high strain rate. The dynamic transformed micro-structure of ferrite was developed to higher angle and the grain size could be refined to ~3 ㎛ at strain of 3.0 and 5/sec.

Download Full-text

Formation of Ultra Fine Ferrite and Determination of Critical Strain in the Strain Induced Dynamic Transformation for 0.22C-Mn Steel

Materials Science Forum - Eco-Materials Processing & Design VII ◽

10.4028/0-87849-995-4.514 ◽

2006 ◽

pp. 514-517

Author(s):

Sang Min Lee ◽

Young Jae Kwon ◽

Duk Lak Lee ◽

Sang Hyun Cho ◽

Sun Keun Hwang ◽

...

Keyword(s):

Critical Strain ◽

Dynamic Transformation ◽

Mn Steel

Download Full-text

Development of an Ultrafine Grained Ferrite in a Low C-Mn Steel Intensely Deformed under Hot Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.467-470.1271 ◽

2004 ◽

Vol 467-470 ◽

pp. 1271-1276

Author(s):

G. Azevedo ◽

Ronaldo Barbosa ◽

Dagoberto Brandão Santos

Keyword(s):

Mechanical Properties ◽

Grain Sizes ◽

Dynamic Transformation ◽

Ultrafine Grained ◽

Size And Morphology ◽

Hot Torsion ◽

Hot Rolled ◽

Mn Steel ◽

Ferrite Grain Size ◽

Torsion Deformation

In the last years, several studies concerning ultra refinement of ferrite grains have been conducted using different experimental techniques (ECAP, ARB, HPT). The aim of all investigations was to provide an optmized relationship between mechanical properties and microstructure of steels. The present work, likewise, deals with strain induced dynamic transformation of ferrite. Samples of low C-Mn steel were intensely deformed in hot torsion aiming at the production of ultrafine grains of ferrite thereby enhancing the mechanical properties when compared to hot rolled products. After soaking during 5min at 900°C, the samples were quenched and then reheated and submitted to hot torsion deformation at temperatures of 700 and 740°C. The torsion schedule consisted of 7 isothermal passes leading to a total strain of ≈1, generating an ultrafine microstructure with grain sizes of the order of 1µm. The shape of stress-strain curves so obtained suggested that ferrite refinement occurred by dynamic recrystallization. The various constituents present in the microstructure as well as ferrite grain size and morphology were examined by optical and scanning electron microscopy. Microhardness tests were performed to evaluate mechanical properties.

Download Full-text