Influence of marganese content on the amount of residual austenite and mechanical properties of ADI after different modes of isothermal hardening

The influence of manganese content on the phase composition and mechanical properties of ADI materials after isothermal quenching at temperatures of 310 -380 оС is investigated. The results of X-ray diffraction studies have shown that under these quenching conditions, the content of the martensitic phase increases with an increase in the quenching temperature. It was found that increasing the manganese content increases the amount of residual austenite under the same quenching conditions. This enhances the effect of TRIP on the strengthening process. The consequence is increased level of strengthening in materials with a higher manganese content. It is shown that under the same quenching conditions, ADI with a low Mn content has the highest yield strength, while the hardness is higher for samples with a high content. The different sensitivity of these hardening characteristics to the Mn content is explained by the increased influence of the TRIP effect on the hardening rate at the initial interval of loading curves in materials with higher manganese content. Instead, such materials exhibit lower mechanical properties, which are determined at failure. Deformation and impact strength  are reduced by half due to the embrittlement action of this element. The effect of manganese on the fatigue is less significant, because the tendency to embrittlement is compensated by phase transformations in the crack tip, which create compressive stresses at the crack tip and inhibits its spread during fatigue. Due to the fact that manganese enhances the TRIP effect but impairs the resistance to fracture, it is proposed to use ADI with high Mn content in tillage products that operate in conditions of wear but are not exposed to extreme loads.