On the Morphology of Strain-Induced Martensite and the Transformation-Induced Plasticity in Fe-Ni and Fe-Cr-Ni Alloys

Abstract

Synopsis [n order to study the morphology q[ strain-induced martensite and the plasticity induced by the martensitic transformation, tellsile tests at various temperatures were carried out using Fc-31% N i, Fe-29%N i-O.26% C and Fe-15% Cr-13%N i alloys whose Ms temperatures u:ere below room temjlerature and the microstructures were observed. The results obtained are summarized as fo llows. In Fe-Ni and Fe-Ni-C alloys, a characteristic martensite whose morphology is entirely different fiom that of thermalfv transformed martensite is formed ~y tensile deformation mainly at the temperatures between Md and M s. This characteristic martensile is forme d continuously little by Little with increasing strain and contributes to the transformation-induced jJlasticity. The difference of morphology between thermally transformed martensite and stra in-induced martellsite must be caused by the change of transformation mechanism. In the case of Fe-Cr-N i alloy, however, the morjJ!wlogy of strain-induced martensite is not dijJerent from that of thermally transformed martensite. Transform ation-induced plasticity occurs in Fe-N i alLqys and the Fe-Cr-N i alloy. The elongation has a maximum value at a temperature between M d and M s. I n the test in which the maximum elongation is obtained, the strain-hardening exjJonent increases continuously with increase in strain. The main prerequisite for maximum elongation is that the martensite is constantly .f~m7Cd Little by little du ring deformation up to fracture. The difference between the F c-Ni alloys and the Fe-Cr-N i alloy is that the temperature range showing large elollgation is wider in the Fe-Cr-Ni alloy than in Fe-N i alloys. This is caused by the dijJerence in transformation behavior of martensite.

Deformation-Induced Martensitic Transformation Behavior of Retained Austenite during Rolling Contact in Carburized SAE4320 Steel

“…In addition to the chemical composition of austenite, such as the amount of carbon in solid solution, the M S temperature, stacking fault energy [1][2][3][4][5][6][7] and microstructural factors such as grain size, [7][8][9][10][11] morphology [12][13][14] and crystal orientation 15,16) of austenite, the transformation behavior is also heavily dependent on the stress state 17) and deformation temperature. [18][19][20] The trans-formation mechanism varies but is mainly dependent on the deformation temperature. As the temperature exceeds M S , stress-induced martensitic transformation occurs during the elastic deformation of austenite in a similar manner as found in thermally induced regular martensite.…”

“…Previous studies regarding the microstructural characteristics of deformation-induced martensite focus on single-phase austenitic high alloy TRIP steels. For instance, studies using Fe-Ni alloys 19,20) showed that deformation-induced martensite subjected to tensile deformation above the M S temperature is typical lenticular martensite with a midrib. However, in contrast to the deformation mechanism of athermal martensite, deformation-induced martensite subjected to tensile deformation at higher temperatures has no mid-rib or deformation twins but instead forms notably fine butterfly martensite.…”

“…However, in contrast to the deformation mechanism of athermal martensite, deformation-induced martensite subjected to tensile deformation at higher temperatures has no mid-rib or deformation twins but instead forms notably fine butterfly martensite. Additionally, deforming Fe-Cr-Ni alloys with low stacking fault energy or austenitic stainless steels results first in hcp ε martensite, followed by the generation of bcc α' martensite from the ε phase 19,27,28) or α' martensite from slip bands. 24,25) A study focusing on an Fe-Ni-Co-Ti alloy 29) reports that deformation-induced martensite will grow from thin plate martensite produced in advance by sub-zero processing.…”

FCC to BCC transformation-induced plasticity based on thermodynamic phase stability in novel V10Cr10Fe45CoxNi35−x medium-entropy alloys

“…Tamura et al . 56 interpreted that strain softening was caused by the normal slip deformation and the deformation due to ε-martensite formation. Bhadeshia et al .…”

Observation of Chemical State for Interstitial Solid Solution of Carbon in Low-carbon Steel by Soft X-ray Absorption Spectroscopy

“…The use of steel with a martensitic structure having the highest hardness has also been considered. [4][5][6][7][8] However, although it shows high strength, the steel made by these methods has poor ductility and processability. 9,10) Recently, carbon clusters have attracted attention in the steel industry as an effective material for overcoming this disadvantage.…”