Microstructure Evolution of Undercooled Austenite during Deformation for Medium-Carbon Si-Mn Steel

2011 ◽  
Vol 704-705 ◽  
pp. 903-906
Author(s):  
Yun Li Feng ◽  
Shao Qiang Yuan ◽  
Meng Song
Keyword(s):  
Microstructure Evolution ◽  
Ferrite Matrix ◽  
Eutectoid Reaction ◽  
Deformation Bands ◽  
Degree Of Deformation ◽  
Medium Carbon ◽  
Transmission Electron ◽  
Mn Steel ◽  
Carbide Particles ◽  
Undercooled Austenite

The microstructure evolution of a medium-carbon Si-Mn steel during deformation of undercooled austenite at different degree of deformation, temperatures and strain rates has been investigated by means of a hot compression simulation test, metallographic microscope, scanning electron microscope and transmission electron microscopy. Also, the mechanism of carbide spheroidized during deformed process has been discussed. The experiment results demonstrate that the process of evolution experienced three stages: that is, strain-induced transformation, austenite eutectoid decomposed to carbides and ferrite matrix, and spheroidization of pearlite at the range of A3-Ar3. The austenitic grains would be refined for the extra-product of ferrite above the Ar3. The eutectoid reaction was induced on the grain boundaries of ferrite and non-transformed austenite and deformation bands with the increasing volume of deformation. An optimum combination of deformation temperature and strain rate is important to obtian the dulplex microstructure consisting of ultrafine ferrites and dispersed carbide particles. The fine spheroidized microstructures are obtained while the deformed temperature reaches 650°C with ≥1.0, meanwhile, The carbides precipate in globular and shot-rod shapes. Keywords: Medium-carbon Si-Mn steel, Undercooled austentite, Microstructure evolution, Deformation induced transformation, Carbide spheroidization

Ultra-Fine Grained Fe-32%Ni Alloy Processed by Multi-Axial Forging

2010 ◽  
Vol 97-101 ◽  
pp. 187-190 ◽  
Author(s):  
Bao Jun Han
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Microstructure Evolution ◽  
Strain Path ◽  
Internal Stresses ◽  
Deformation Bands ◽  
Fine Grained ◽  
Transmission Electron ◽  
Ni Alloy ◽  
Equiaxed Grains

The Fe-32%Ni alloy was multi-axially forged at the temperature of 873K and strain rate of 10-2s-1, then the microstructure evolution in Fe-32%Ni alloy during deformation was investigated by the transmission electron microscopy (TEM). The results show that the grain size decreases with strain. The severe plastic deformed microstructure is characterized by the ultra-fine equiaxed grains and high internal stresses. The microstructure evolution mechanism is presented as the following: firstly, the dislocations accumulate as deformation bands in some directions with the progress of deformation; then the cellular structured subgrains are formed by continuous intersecting of deformation bands for the changing of strain path; eventually, the ultra-fine structured grains are formed by the subgrains rotation and the dislocations rearrangement.

Grain Refinement of Fe-32%Ni Alloy by Multi-Axial Forging

2011 ◽  
Vol 80-81 ◽  
pp. 18-21
Author(s):  
Xiao Juan Wang ◽  
Bao Jun Han
Keyword(s):  
Electron Microscopy ◽  
Microstructure Evolution ◽  
Large Angle ◽  
Optical Microscope ◽  
Electron Back Scatter Diffraction ◽  
Deformation Bands ◽  
Transmission Electron ◽  
Ni Alloy ◽  
Cumulative Strain ◽  
Austenite Grains

The effect of strain on the microstructure evolution of Fe-32%Ni alloy during multi-axial forging at the temperature of 500°C and a strain rate of 210-2 s-1 was investigated by optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD) observations. The results show that the austenite grains were greatly refined with increasing cumulative strain, and the microstructure evolution during multi-axial forging can be summarized as such a process that deformation bands crossing each other subdivide the original austenite grain into several sub-grains and then these sub-grains are subdivided into more small ones and gradually angled to new independent grains with their boundaries transformed into large angle boundaries in subsequent compression.

High-resolution x-ray imaging of small copper-rich precipitates in steels

1988 ◽  
Vol 46 ◽  
pp. 528-529
Author(s):  
J. R. Michael ◽  
K. A. Taylor
Keyword(s):  
Electron Microscopy ◽  
Thermomechanical Processing ◽  
Atom Probe ◽  
Ferrite Matrix ◽  
Scanning Transmission Electron Microscope ◽  
Probe Field ◽  
X Ray ◽  
Subsequent Transformation ◽  
Transmission Electron ◽  
Scanning Transmission

Although copper is considered an incidental or trace element in many commercial steels, some grades contain up to 1-2 wt.% Cu for precipitation strengthening. Previous electron microscopy and atom-probe/field-ion microscopy (AP/FIM) studies indicate that the precipitation of copper from ferrite proceeds with the formation of Cu-rich bcc zones and the subsequent transformation of these zones to fcc copper particles. However, the similarity between the atomic scattering amplitudes for iron and copper and the small misfit between between Cu-rich particles and the ferrite matrix preclude the detection of small (<5 nm) Cu-rich particles by conventional transmission electron microscopy; such particles have been imaged directly only by FIM. Here results are presented whereby the Cu Kα x-ray signal was used in a dedicated scanning transmission electron microscope (STEM) to image small Cu-rich particles in a steel. The capability to detect these small particles is expected to be helpful in understanding the behavior of copper in steels during thermomechanical processing and heat treatment.

Mechanical Properties of Hypereutectoid Steel with Microduplex (α+θ) Structure Formed by Hot Deformation of Undercooled Austenite

2010 ◽  
Vol 654-656 ◽  
pp. 246-249
Author(s):  
Long Fei Li ◽  
Wei Chen ◽  
Wang Yue Yang ◽  
Zu Qing Sun
Keyword(s):  
Mechanical Properties ◽  
Hot Deformation ◽  
Ferrite Matrix ◽  
Subsequent Annealing ◽  
Test Machine ◽  
Compression Tests ◽  
Simulation Test ◽  
Hypereutectoid Steel ◽  
Lamellar Pearlite ◽  
Undercooled Austenite

Microstructure evolution and mechanical properties of hypereutectoid steel with the microduplex (α+θ) structures formed by hot deformation of undercooled austenite were investigated by hot uniaxial compression tests in a Gleeble-1500 simulation test machine, and the effects of subsequent annealing and the addition of Al were analyzed. The results indicated that at the beginning of hot deformation of undercooled austenite the formation of proeutectoid cementite was retrained and only lamellar pearlite was produced. With further strain, dynamic spheroidization of pearlite took place, leading to the formation of microduplex (α+θ) structure consisting of ultrafine ferrite matrix and dispersed cementite particles. In comparison with the normal microstructure consisting of lamellar pearlite and proeutectoid cementite, the microduplex (α+θ) structure presented higher strengths with similar ductility. Subsequent annealing could make the microduplex (α+θ) structure more uniform, which demonstrated better balance between strength and ductility. The addition of Al is disadvantageous to the formation of microduplex (α+θ) structure, but can result in the further refinement. With the addition of Al, the strength of microduplex (α+θ) structure was improved and the ductility was not deteriorated markedly.

Warm-Forging Characteristics and Microstructural Response of Medium-Carbon High-Strength Steels for High-Duty Components

2014 ◽  
Vol 611-612 ◽  
pp. 167-172 ◽  
Author(s):  
Piotr Skubisz ◽  
Łukasz Lisiecki
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Microstructure Evolution ◽  
High Strain ◽  
Deformation Behaviour ◽  
Metal Flow ◽  
High Strength Steels ◽  
High Strength ◽  
Medium Carbon ◽  
Warm Forging

Paper presents deformation behaviour and microstructural response of selected medium-carbon high-strength steels commonly used for high-duty components deformed under high-strain-rate and warm work temperature range. The investigation of material behaviour is oriented at analysis of hot and warm workability of material and microstructure evolution resultant from deformation mechanisms, strain induced recrystallization and hardening at temperatures of lower forging regime and high strain rate deformation. The effect of these factors on microstructure after forging and subsequent direct-cooling was studied. Metallographic work aided with numerical methods of simulation of the metal flow and microstructure evolution during forging were used to correlate thermo-mechanical parameters observed with microstructure and mechanical properties after forging and cooling.

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