Research On Friction And Wear Characteristics Of Engine Valve Heat Resistant Steels

Valves are one of the key components that affect the reliability,safety and service life of engines.They are mainly used to open and close the intake and exhaust passages during the operation of the engine to control the entry of fuel mixture or air and the discharge of exhaust gas.Valve working environment is very harsh,not only withstand the corrosion of high temperature gas,but also to withstand the impact of explosion pressure in the cylinder.The main failure modes of valve materials are wear and fracture,and wear will lead to rapid valve failure.Therefore,it is very important to study the friction and wear characteristics of valve materials.23-8N,21-4N and 4Cr9Si2 heat-resistant steels were selected as target materials,which are commonly used for valves.Their mechanical properties,friction and wear properties and contact fatigue properties at different temperatures were studied systematically.The main research contents are as follows:(1)The tensile properties of 23-8N,21-4N and 4Cr9Si2 heat-resistant steel materials at 25,400 and 650 oC temperatures were studied.Through statistical analysis of the tensile data of the materials at each temperature,it was found that the three heat-resistant steels all have good room-temperature mechanical properties.But compared with the better high temperature strength of 23-8N and 21-4N heat-resistant steels,the high-temperature mechanical properties of 4Cr9Si2 heat-resistant steels are significantly reduced.In addition,the fracture morphology of 23-8N heat-resistant steels is clad-like,the fracture morphology of 21-4N heat-resistant steel is dimples and holes,and the main fracture morphology of 4Cr9Si2 heat-resistant steel is fatigue zone.(2)The friction and wear properties of 23-8N and 21-4N heat-resistant steels at 25,400,500,600,650 oC were investigated,and the sliding wear properties of 4Cr9Si2 heat-resistant steel at 25,200,300,400,500,600 and 650 oC were studied.The test results show that the friction coefficient of the three kinds of specimens first decreases and then increases.At room temperature,the wear of the 23-8N heat-resistant steel is the smallest,the wear of the 21-4N heat-resistant steel is the largest,and the wear mechanism is dominated by abrasive wear.At high temperatures,the wear resistance of 4Cr9Si2 is poor,the wear resistance of 23-8N heat-resistant steel is the best,the wear volume of 21-4N heat-resistant steel is slightly higher than that of 23-8N heat-resistant steel.The main wear mechanisms are oxidation wear,abrasive wear,and adhesive wear.(3)The contact fatigue properties of 23-8N,21-4N and 4Cr9Si2 heat-resistant steels materials under oil lubrication were investigated.The study found that: 23-8N heat-resistant steel has the best contact fatigue performance,21-4N heat-resistant steel is slightly lower than the fatigue life of 23-8N heat-resistant steel,4Cr9Si2 heat-resistant steel has the smallest fatigue life.With the surface morphology and BMT analysis of the three sample materials,the fatigue failure of 23-8N heat-resistant steel is mainly manifested as fatigue spalling,the pitting corrosion and delamination are the main failure modes of 21-4N heat-resistant steel.And the mainl fatigue failure mechanisms of 4Cr9Si2 heat-resistant steel are fatigue peeling and pitting corrosion.