Study On Effects Of Heat-treatment Processes On Microstructures And Properties Of Wear-resistant Steel For High-pressure Grinding Roller

Because of their excellent mechanical properties and wear resistance,high vanadium high speed steel and ductile iron are often used in high-pressure roller mill grinding rolls.Nevertheless,high vanadium high speed steel and ductile iron both have poor performance in the as-cast condition and can't be directly applied to actual production,so they're supposed to be heat treated to improve their stability.The effects of heat treatment processes on microstructure,mechanical properties and wear resistance of high vanadium high speed steel and ductile iron for high-pressure grinding roller were studied,and the optimal heat treatment processes for abrasive wear were acquired for both.High vanadium high speed steel specimens were treated by means of quenching at 1050? for 10min,20min,40min,120min and tempering at 540? for 30min,60min,90min.The effects of different heat treatment processes on microstructure and properties of high vanadium high speed steel were studied with metallurgical microscope,SEM,X-ray diffraction and measurement of Rockwell hardness,compressive strength and wear resistance.The results showed that the heat treatment process had little effect on morphology and distribution of carbide vanadium,but had remarkable effect on the relative content of retained austenite and martensite in the matrix.As the quench holding time was longer,the edges of M7C3 type carbides are slightly dissolved and granular carbides are generated and evenly distributed in the matrix after treatment.The hardness of high vanadium high speed steel increased gradually with the extension of tempering heat preservation time.Otherwise,the hardness increased at first and then declined with the extension of quenching heat preservation time.The compressive strength of high vanadium high speed steel declined at first and then increased with the extension of tempering heat preservation time.The optimal heat treatment process of the steel for comprehensive performance is quenching at 1050?for 120 minutes and then tempering at 540? for 90 minutes.Compression test showed that the fracture of high vanadium high speed steel belonged to the ductile fracture,"groove" of the specimen with high compressive strength was shallow and uniform.However,"groove" of the specimen with low compressive strength had different depth.Ductile iron specimens were treated by seven different heat treatment processes.The results showed that ductile iron was composed of bainite,tempered sorbite,M3C type eutectic carbides,tempered martensite,secondary carbides,graphite and a small amount of residual austenite after heat treatment;The heat treatment process had remarkable effect on microstructure,morphology of eutectic carbides and distribution of secondary carbides.The hardness of NO.6 sample reached the highest value(58.2HRC).The results of impact test showed that impact toughness value fluctuates significantly,fluctuation range was(3.88-7.99 J/cm2);The impact toughness of NO.6 sample reached the highest value(7.99 J/cm2).The optimal heat treatment processes of the steel for comprehensive performance are NO.2 sample and NO.6 sample.According to the analysis of the fracture of the impact specimen,torn edges were found around toughness nest of the fracture of ductile iron with good impact toughness.And the edges were generated due to the plastic deformation and continuous.Hoewever,the fracture of ductile iron with poor impact toughness had certain river pattern and obvious cleavage stage.Combined with the actual service conditions of wear-resistant materials,loose abrasive wear experiment was carried out by putting high vanadium high speed steel and ductile iron standard samples on dynamic load abrasive wear testing machine.Test abrasion resistance of steel and respectively compared to the wearability of the sample under different heat treatment conditions.The results showed that the heat treatment of high vanadium high speed steel samples with the best wear resistance was quenching heat for 120 min and tempering heat for 90 min.The relative wearability was 1.6 times of the sample with poor wearability.The NO.2 sample presented the best relative wear resistance among ductile iron samples.The relative wearability was 1.6 times of the sample with poor wearability.Combined with the actual conditions of service of wear-resistant materials,compared to the wear properties of high vanadium high speed steel and ductile iron,the comprehensive performance and abrasion resistance of high vanadium high speed steel was better than that of ductile iron.High vanadium high speed steel is more suitable for actual production.