Microstructure And Performance Of Nitriding Layer Of Medium Mn Steel 10Mn4CrNiMoVCu

Fracturing pumps,one of the most important components applied in the field of exploring and drilling for oil and gas,are currently being investigated and developed in the direction of large displacement,high power and high pressure.Due to its harsh service conditions,longterm wearability and alternating stress,corrosion fatigue failure are prone to occur,resulting in frequent replacements of fracturing pumps in production,reducing work efficiency.The representative material used in the current fracturing pump is the traditional AISI4330 steel.However,there still exists problems of low hardness,poor wear resistance and insufficient corrosion fatigue strength.The 10Mn4CrNiMoVCu steel studied in this paper is a new alloy steel material developed by Central Iron&Steel Research Institute.This paper compared the nitriding layer microstructure and properties of 10Mn4CrNiMoVCu steel and conventional AISI4330 steel,used optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),nanoindenter,microhardness tester,transmission electron microscope(TEM),electrochemical workstation and other testing and analysis methods.The differences in microstructure,phase constitution,hardness distribution,nitriding depth and corrosion resistance of their nitriding layers were discussed to investigate the reasons for the high corrosion fatigue performance of the new steel grades after nitriding.The results showed that both 10Mn4CrNiMoVCu and AISI4330 formed compound layers after nitriding.The thickness of the 10Mn4CrNiMoVCu compound layer was about 5 μm,and the AISI4330 was about 6 μm.Compared with AISI4330 steel,the 10Mn4CrNiMoVCu steel compound layer was more uniform and compact.The grade of vein nitride was 1 and the grade of AISI4330 steel was 1-2.With the time increasing,the thickness and compactness of the 10Mn4CrNiMoVCu steel compound layer increased.y’ and ￡ phases existed in the compound layer of both two steel after nitriding.However,the y’ phase ratio in 10Mn4CrNiMoVCu steel was higher than AISI4330 steel,what’s more,the surface also contained ε phase which offered a good corrosion resistance.The proportion of ε phase was increased with time.When nitriding time come to 16 h,the proportion of its γ’ phase was higher.Nanoindentation,microhardness,and electron microprobe analysis showed that in the nitriding process,the diffusion of N in 10Mn4CrNiMoVCu steel was more sufficient than AISI4330 steel,which increased the overall diffusion depth.The overall change in hardness and elastic modulus was also lower than AISI4330.The surface hardness of 10Mn4CrNiMoVCu up to 740 HV0.2,which was about 2-3 times of the matrix.The electrochemical test showed that the corrosion rate of 10Mn4CrNiMoVCu steel was less than AISI4330 steel.Its corrosion current was 6.411 × 10-6 A/cm2,and corrosion potential was-0.665 V.AISI4330 steel had a higher corrosion tendency in NaCl solution.Its corrosion current was 1.466×10-5 A/cm2 and the corrosion potential was-0.776 V.With the nitriding time increasing,the corrosion resistance became better.The alloying and microstructure design of the new steel grades make the phase composition,microstructure,N-element distribution,and hardness distribution of the nitriding layer favorable for its corrosion fatigue resistance.