Study On The Microstructure And Properties Of Cu-bearing 5Cr15MoV Martensitic Stainless Steel

Martensitic stainless steel with its excellent strength,hardness and wear resistance and other comprehensive properties,gradually developed into one of the irreplaceable raw materials in the tool industry.After adding proper amount of copper(Cu)into the traditional martensitic stainless steel and undergoing proper antibacterial heat treatment,excellent antibacterial properties can be obtained.However,the heat treatment not only affects its antibacterial property,but also has important effects on its mechanical property and corrosion resistance.Therefore,selecting the appropriate heat treatment is focus to ensure the excellent properties combination including the mechanical property,corrosion resistance and antibacterial property for the research of Cu-bearing antibacterial martensitic stainless steel.In this paper,we systematically studied the effects of Cu content and heat treatment temperatures including quenching and tempering on the microstructure,hardness,corrosion resistance and antibacterial properties of 5Cr15MoV martensitic stainless steel and further explored the relationship between the microstructure and various properties of the materials.The results show that the addition of Cu has no effect on the type and morphology of the undissolved carbides after quenching and the secondary carbides precipitated after tempering.However,the addition of Cu will increase the volume fraction of retained austenite in quenched materials,which further leads to the decrease of hardness.Meanwhile,the corrosion resistance of Cu-bearing 5Cr15MoV martensitic stainless steel is also slightly lower than that of 5Cr15MoV martensitic stainless steel,but the addition of Cu endows the stainless steel good antibacterial ability.For the Cu-bearing 5Cr15MoV martensitic stainless steel,a large number of nanometer Cu-rich phases are precipitated out from the matrix after tempering at 500? and 600?.The dispersion precipitation of Cu-rich phases decreases the corrosion resistance of the material,but greatly improve the antibacterial property,and also have a certain hardening effect.The undissolved carbides of 5Cr15MoV martensitic stainless steel with different Cu content after quenching are mainly the chromium(Cr)rich M23C6 carbides with the FCC structure.With the quenching temperature rising from 1000? to 1100?,the amount of undissolved carbides decreases gradually and the corrosion resistance increases.The content of retained austenite also increases with the increase of quenching temperature.The combined action of carbides and retained austenite results in a parabolic hardness curve after quenching and reaches the maximum hardness value after quenching at 1050?.The matrix microstructure of 5Cr15MoV martensitic stainless steel with different Cu content is tempered martensite after tempering at 200?-500?,and changes into ferrite at 600?.Due to the occurrence of reversed austenite during the tempering treatment,the austenite content of the three steels demonstrate a parabolic change.After tempering at 200?-600?,the hardness curves of three steels all show saddle shape,and the secondary hardening appeared at 500?.This hardness value is close to that of the quenching state,which is mainly due to the precipitation of a large number of fine and dispersed secondary carbides at 500 ?.However,the corrosion resistance is reduced in the tempered state compared with the quenched state.The secondary carbides precipitated in the tempering process are also Cr-rich M23C6 carbides with FCC structure.With the raise of tempering temperature,the content of carbides gradually increases.Consequently,the corrosion resistance decreases owing to losed passivation ability of material after tempering over 500 ?.Especially at 500?,the overall corrosion resistance of the material is poor,but increase at 600?,which is mainly related to the "Cr-depleted zone" around the secondary carbides.In contrast to the corrosion resistance,the antibacterial property of tempering state is better than that of quenching state.After tempering at 500? and 600?,the antibacterial rate of 5Cr15MoV-4.13Cu reaches 99.9%due to the formation of Cu-rich phases.