Sensitivity to Mn content mechanical properties of phase composition of ADI

The effect of manganese content on the phase composition and mechanical properties was studied on ADI materials that are isothermally quenchеd at different temperatures. ADI samples with Mn content of 0.78% and 0.24% were analyzed. The final structure of the cast iron was created by austenitizing heating at 900 ° C for 30 minutes. and subsequent isothermal quenching in liquid tin at temperatures of 310, 330, 350, 380 ° C for samples with high manganese content and at 350, 370 ° C for samples with low content. It is shown that increasing the manganese content increases the amount of residual austenite under the same quenching conditions. This enhances the positive role of the TRIP effect on the hardening processes. In particular, ADI with a high content of Mn show a higher rate of strengthening at the initial region of loading diagram, higher hardness and increased damping capacity. Instead, due to the embrittlement action of manganese, such materials have lower mechanical characteristics, which determined fracture moment. It was found that for the same quenching conditions, deformation to fracture and toughness are reduced by half on samples with higher manganese content. The negative effect of manganese on the fatigue is less significant, because the embrittlement action is compensated by phase transformations in the crack head, which inhibits its spread under cyclic loading. Due to the fact that manganese enhances the positive role of the TRIP effect but decrease fracture résistance, it is proposed to use ADI materials with high Mn content in products that operate in conditions of wear but are not subject to extreme stress. Keywords: ADI materials, manganese alloying, isothermal hardening, TRIP effect, retained austenite, strengthening, hardness. damping capacity.

Enhancement of Uniform Elongation by Temperature Change during Tensile Deformation in a 0.2C TRIP Steel

It is important to control the deformation-induced martensitic transformation (DIMT) up to the latter part of the deformation to improve the uniform elongation (U.El) through the TRIP effect. In the present study, tensile tests with decreasing deformation temperatures were conducted to achieve continuous DIMT up to the latter part of the deformation. As a result, the U.El was improved by approximately 1.5 times compared with that in the tensile test conducted at 296 K. The enhancement of the U.El in the temperature change test was discussed with the use of neutron diffraction experiments. In the continuous DIMT behavior, a maximum transformation rate of about 0.4 was obtained at a true strain (ε) of 0.2, which was larger than that in the tensile test at 296 K. The tensile deformation behavior of ferrite (α), austenite (γ), and deformation-induced martensite (α′) phases were investigated from the viewpoint of the fraction weighted phase stress. The tensile test with a decreasing deformation temperature caused the increase of the fraction weighted phase stress of α and that of α′, which was affected by the DIMT behavior, resulting in the increase in the work hardening, and also controlled the ductility of α and α′, resulting in the enhancement of the U.El. Especially, the α phase contributed to maintaining high strength instead of α′ at a larger ε. Therefore, not only the DIMT behavior but also the deformation behavior of γ, α, and α′ are important in order to improve U.El due to the TRIP effect.

Austenite Stability and Deformation Behavior in Medium Mn Steel Processed by Cyclic Quenching ART Heat Treatment

This study investigated the austenite stability and deformation behavior of cyclic quenching-austenite reverse transformation processed Fe-0.25C-3.98Mn-1.22Al-0.20Si-0.19Mo-0.03Nb medium Mn steel. A number of findings were obtained. Most importantly, the extent of the TRIP effect was mainly determined by an appropriately retained austenite stability rather than its content. Simultaneously, chemical elements were the key factors affecting austenite stability, of which Mn had the greatest impact, while the difference of retained austenite grain size and Mn content resulted in different degrees of retained austenite stability. Additionally, there were still large amounts of strip and granular-retained austenite shown in the microstructure of the CQ3-ART sample after tensile fracture, revealing that the excessively stable, retained austenite inhibited the generation of an extensive TRIP effect.