Study On The Optimization Of Microstructure And Properties Of Wear Resistant Steel By Rare-earth Compound Modifier

With the rapid development of modern industry,low-cost,high-performance low-alloy wear-resistant steel is increasingly used in harsh conditions.How to further improve the wear resistance of wear-resistant steel has been a subject of great concern to researchers.This article took NM500 low-alloy wear-resistant steel as the research object,adopts low-alloyed wear-resistant steel components and rare earth-based compound modifiers.Four groups of compound modifiers of 15%boron+rare earth silicon ferrosilicon+nano TiC particles were prepared,and a wear resistant steel treated with a five-furnace compound modifier was smelted.And the appropriate heat treatment process was used to study the effect of different modificator composition on the microstructure and properties of wear-resistant steel.The characteristics of inclusions and precipitates in the steel were characterized by scanning electron microscopy and transmission electron microscopy.The effects of complex modificators on inclusions and microstructure in the steel were investigated,and the properties of the 5 furnace steel were examined and analyzed.Its main conclusions were as follows:?1?Computation of misfits of components and iron crystals in composite modificators,the results showed that the misfits of TiC and TiN with iron matrix were less than 12%,which could be used as an effective nucleation core.The nucleation of CeO₂ and Ce₂O₂S in Ce oxides formed by Ce was effective to a certain extent,while the nucleation of CeS and Ce₂S₃ was effective and could not be used as a heterogeneous nucleation core.?2?Compared to the 1^#control group,the number of inclusions in the 2^#5#experimental group decreased,the number of particles smaller than 0.5?m increased,the number of large-sized inclusions decreased,and the steel cleanliness increased.At the same time,increasing the number of particles required for nucleation increased the nucleation rate and helped refine the microstructure of the steel.?3?Thermodynamic calculation showed that,at the end of solidification?f_s about0.95?,the MnS began to form in 5 groups of experimental steel,which was added 2^#5#composite modifier.Ce would combine with sulfur in liquid steel to produce Ce_xS_y,at the end of solidification and segregation of Mn enrichment,CeS could promote the nucleation of precipitates MnS,rare earth manganese sulfur inclusioned formation,realized the degeneration of manganese sulfide.?4?Scanning and transmission electron microscopy characterizations showed that rare earth modified inclusions could help reduce the damage of the network carbides and refine the microstructure.In the 1^#steel without modificator,the secondary cementite appeared in a continuous network,and 2^#5#steels with modificators were added.The network carbides had different degrees of network breakage and reduction,and the 5^#steel had the best modification degree.TEM observations showed that rare earth oxysulfides cut off the continued growth of cementite,and that rare earth-based modifiers could reduce the hazards of good network carbides on steel substrates.At the same time,it was found that the spherical Ce-Mn-S composite inclusions and nano-TiC precipitated on the martensite boundary,resulting in pinning effect at grain boundaries.The grain sizes of the five steel samples were 12?m,10?m,7?m,9?m,and 6?m,respectively,and the addition of the modifier significantly refined the grain,and the grain size of 5^#steel was the smallest.?5?Hardness and wear resistance tests showed that the hardness increased by8.36%,13.4%,6.22%,and 15.6%,respectively,in steel 2^#to 5^#with addition of a modificator,compared to 1#steel.The wear resistance increased by 14%,39%,21%,and 63%,respectively,the 4^#modifier had the best metamorphic effect.