Effects Of Heat Treatment On Microstructures And Properties Of Ultra-high Chromium High Carbon Steel

Duplex stainless steel has been used in many fields such as chemical industry,power station,marine and environmental engineering due to its excellent mechanical properties and corrosion resistance.However,in the medium environment where corrosion and wear coexist,the traditional duplex stainless steel is difficult to meet the requirements of use.Some experts and scholars have developed an ultra-high chromium high carbon steel with excellent performance on the basis of duplex stainless steel.Based on the identification and characterization of the as-cast microstructure of ultra-high chromium high carbon steel,this paper conducts an experimental study on the heat treatment parameters of ultra-high chromium high carbon steel.The microstructure and properties of ultra-high chromium high carbon steel under various heat treatment parameters were investigated.The evolution of microstructure and properties of ultra-high chromium high carbon steel under various heat treatment parameters was explored.It is expected to obtain alloy structures with appropriate ratios,reasonable shape of distribution,excellent wear-resistance and corrosion-resistance,and provide a reliable experimental basis for the development of a reasonable heat treatment process for the steel.The specific research results are as follows:?1?At the beginning of solidification of ultra-high chromium high carbon steel,?ferrite is firstly precipitated from the liquid phase,and a eutectic reaction occurs as the reaction proceeds to form a small amount eutectic structure(?+M₂₃C₆).As the temperature decreases,the remaining liquid phase undergoes a peritectic reaction with the?ferrite,and a peritectic austenite is formed on the periphery of the?ferrite.Finally,the remaining liquid phase undergoes a eutectic reaction to form a large amount of eutectic structure(?+M₂₃C₆)with a dense network structure until the end of solidification.The as-cast microstructure is:?ferrite,eutectic structure(?+M₂₃C₆),eutectic structure(?+M₂₃C₆),and peritectic austenite.?2?The solution temperature will have a great influence on the microstructure of ultra-high chromium high carbon steel.Compared with the as-cast microstructure,after solution treatment,the peritectic austenite is significantly increased and granular carbides are precipitated around it.As the solution temperature increases,the amount of ferrite transformed into austenite increases,and the precipitated carbide particles also increase.The eutectic structure(?+M₂₃C₆)can maintain a dense network structure at 1060°C.When the solution temperature rises to 1160°C,the eutectic structure(?+M₂₃C₆)gradually dissolves,changing from mesh to broken mesh-shape,When the solid solution temperature is further increased to 1210°C,the carbides in the eutectic structure are agglomerated and grown.The performance test shows that the Rockwell hardness decreases with the increase of solid solution temperature.When it is solid solution at 1210°C,the hardness is the lowest,but the wear resistance is the best.The solution temperature has little effect on the corrosion resistance.When solid solution at 1160°C,the corrosion resistance is slightly better.?3?When it is kept at 1060°C for 2 hours,it is slowly cooled to 980°C,960°C,940°C,900°C,and air-cooled.The temperatures of the furnace has little effect on the microstructures.As the temperature of the furnace is lowered,the peritectic austenite becomes more and more.When it is slowly cooled to 980?,the tip-like carbide starts to precipitate in the vicinity of the peritectic austenite and grows toward to the center of the?ferrite.As the furnace temperature is gradually lowered,more and more particulate carbides are precipitated near the austenite.Despite slowly cooling to 900°C,there is still no precipitation of harmful phases such as?,?and Cr₂N.Performance tests show that ultra-high chromium high carbon steel has the lowest hardness at 960°C,but it also has the best wear resistance.Different furnace temperatures have little effect on corrosion resistance.?4?When it is kept at 1060°C for 2 hours,when it is cooled by water cooling,oil cooling and air cooling,the cooling methods have little change to the microstructure of ultra-high chromium high carbon steel,and no new phase is produced.Since there is no slow cooling after solid solution heat retention,no particulate carbide precipitates in the vicinity of the peritectic austenite.Performance tests show that cooling with different cooling methods has little effect on hardness,and is around 46 HRC.The surface integrity of the air-cooled wear scar is significantly better than that of water-cooled and oil-cooled,and the wear resistance is better.Although the corrosion resistance using water cooling and oil cooling is slightly better than air cooling,the overall difference is not large.From the economic point of view,air cooling should be used for cooling.