Study On Erosion Resistance Of High Chromium Cast Iron To Low Flow Rate Solid/Liquid Two-Phase Flow

In industrial production,wear,corrosion,and fracture of workpieces are the three standard failure modes.The annual loss due to friction and wear accounts for about 5%of the gross domestic product（GDP）,of which erosion accounts for 8%of the total wear and tear..In the fields of marine engineering,mining,chemical industry,etc.,as the critical pipeline hydraulic conveying technology equipment,the demand for pumps is increasing.China’s pump output has proliferated from 29 million units in 2004 to 183 million units in 2020.In the production process of the phosphorus chemical industry,the slurry needs to be transported by a slurry pump,which is seriously corrosive,and the hard particles contained in the slurry also cause serious erosion damage to the flow-through parts of the slurry pump and the service conditions are poor.High chromium cast iron has good wear and corrosion resistance and is a common material for slurry pump flow parts.This project aims to develop a high-chromium cast iron material for slurry pump overflow parts resistant to erosion damage by the solid-liquid two-phase flow.In this project,high Cr/C ratio is selected to design high-chromium cast iron materials.At the same time,V and Mo are added to promote the spheroidization of carbides.The phases are prepared by alloy melting and sand casting methods:high chromium cast iron specimens with（Cr,Fe）₇C₃ type+a small amount of（Cr,Fe）₂₃C₆ type carbide and ferrite+austenite matrix.Moreover,the erosion test was carried out on the specimen.The results showed that the matrix in the as-cast specimen was seriously worn and corroded,indicating that the matrix was the weak link in the erosion damage process.Three heat treatment processes were designed to improve the damage resistance of the substrate.（1）The as-cast specimen（A）was heated to 700°C for 24 h,and air-cooled to room temperature to obtain the B specimen with ferrite and austenite+secondary carbide matrix;（2）The as-cast specimen was heated to 1050°C for 16 h,water-cooled to obtain supercooled austenite,and then tempered at low temperature to obtain C specimen;（3）The as-cast specimen was heated to 1050°C for 16 h,cooled to 500°C for 6 h,and then air-cooled to obtain D specimen with austenite+secondary carbide matrix.Through the metallographic microscope,X-ray diffractometer,hardness tester,electrochemical workstation and other testing equipment,the four specimens were obtained from high to low hardness was:D>C>B>A,and from high to low corrosion resistance was:C>D>A>B.The subject uses the erosion test machine to study the damage behavior of the as-cast specimen and the different heat treatment specimens in the phosphorus chemical beneficiation environment.The research contents include:（1）The erosion rates of the four specimens at four erosion angles of 20°,45°,70°,and 90°were tested.The results show the erosion angle from 20°to 45°is low damage zone.The erosion resistance of the specimen is:C>D>A>B,which is in the same order as the corrosion resistance of the specimen,and the corrosion effect is the main factor at this time;The erosion angle from 45°to 70°is middle damage zone,and the erosion rate is affected by corrosion and wear together;The erosion angle from 70°to 90°is high damage zone.The erosion resistance of the specimen is D>C>B>A,which is the same as the hardness of the specimen.At this time,the wear effect is the main influencing factor.（2）The erosion rates of the four specimens were tested at three speeds of 300 rpm,350 rpm,and 400 rpm.The results show that the erosion rate increases rapidly with the increase in rotational speed,and the as-cast specimen increases significantly.At low speed（300 rpm）,the corrosion effect is the main influencing factor,and the erosion resistance of the specimen is:C=D>A>B;at 350 rpm,the corrosion effect and the wear effect jointly affect the erosion rate,and the erosion resistance of the specimen is The corrosion resistance is:C=D>A=B;the wear effect is the main factor at high speed（400 rpm）,and the erosion resistance of the specimen is:D>C>B>A,which is the same as the hardness of the specimen.（3）The erosion rates of four specimens were tested at p H=7,p H=4,p H=1.The results showed that the erosion rate increased continuously with the decrease of p H value.When the p H of the slurry is 7,the matrix is mainly damaged by wear,and the erosion resistance is:D>C>B>A,which is the same as the hardness of the sample;in the acidic slurry of p H=4,the resistance of the sample is The erosion performance is in the same order as the hardness of the samples.At this time,the wear effect is the main influencing factor.The erosion resistance of the D sample with the highest hardness is the highest;when p H=1,the corrosion effect is the main influencing factor,and the erosion resistance of the sample is:C>D>A>B,the same order as the corrosion resistance.In this subject,Three kinds of high-chromium cast iron specimens with different structures and properties were obtained through different heat treatment systems.By analyzing its damage behavior and erosion resistance under different erosion angles,different rotational speeds,and different slurry p H values,the damage laws of slurry pump flow-through parts in different service environments were obtained.It can be judged which tissue has stronger erosion resistance under different service environments.This can provide a reference for the design of slurry pumps and guide the development of flow parts（structure optimization of flow parts,composition design,heat treatment process formulation,etc.）.