Effect Of Nb Microalloying On Microstructure And Properties Of Quasi-bainite Shovel Steel

The shovel teeth are the main wear parts of the excavator.With the rapid development of China's industry,the working environment of the excavator shovel teeth in production and construction has become more and more severe,the wear and tear consumption is extremely fast,and the economic losses are serious;At the same time,due to the prosperity of China's mining industry,the demand for shovel teeth has increased.At present,the commonly used shovel teeth are still severely worn under high abrasive wear conditions,showing insufficient wear resistance of the material,and the quasi-bainite steel shovel teeth table has good wear resistance,but its cost is expensive and the process is complicated,Still need innovation and active inquiry.Therefore,in this paper,the quasi-bainite is used as the matrix structure of the shovel teeth of the excavator.Nb microalloying is used for fine grain strengthening and precipitation strengthening to improve the strength and toughness of the shovel tooth steel and their cooperation,and obtain a shovel with high wear resistance.The tooth material has extremely important economic value for the production and application of excavator shovel teeth.The results show that:The structure of the test steel is quasi-bainite,and the addition of Nb to the steel promotes the growth of the structure.The experimental steel contains(V,Nb)C,NbC and?-Fe in the austenite transformation interval,which is dragged and pinned through grain boundary solid solution to refine the grains;In the isothermal phase of the bainite transformation zone,the precipitation is mainly(V,Nb)C.The precipitation strengthening function strengthens the steel matrix.With the increase of Nb content,it has little effect on Ac3,Ac1,and Ms of the experimental steel,and the Bs phase transition point shows a gradually decreasing trend,making the phase transition temperature range of bainite narrow,which helps to refine quasi-bainite Body organization.The original austenite grains gradually decreased with the increase of Nb content,which decreased by 27.4%at 0.062%Nb compared to the absence of Nb;The addition of Nb to the steel increases the amount of retained austenite,which is higher at 8.4%at 0.024%Nb.The large-scale inclusions in the experimental steel are mainly silicate-type inclusions.The structure of such inclusions is complex,the size is large,and the damage to the steel matrix is relatively large;Tensile fracture inclusions are of various types,simple structure,relatively small size,and relatively few in number,but such inclusions are generally the source of cracking sources,so they have a certain impact on the material properties of steel;Counting the inclusions in the steel,the number of beneficial inclusions in the steel within2um is about 70%,so the inclusions have little destructiveness on the steel matrix and the cleanliness of the steel is high.After adding Nb,the original austenite grains are refined step by step,and the structure is refined during the post-isothermal transformation.Due to the increase of the residual austenite volume and the combined effect,the hardness of the steel is reduced from HV472.3 to HV420.4,after hardness increased to HV455.1.The morphology of the impact fracture is less dimple+quasi-dissociation surface,which belongs to brittle fracture,Since the addition of Nb promotes the growth of the structure,the structure morphology of 2~#steel is the best,and the amount of retained austenite is higher,the shear section rate and impact energy are the highest.The tensile specimens have little change in macroscopic and microscopic morphology,and generally show the coexistence of plasticity and brittleness,with brittle fracture as the main;as the original austenite grains decrease step by step,the macroscopic tensile strength also gradually increases,the yield strength does not change much,and the section shrinkage rate and toughness maintain a consistent relationship.The addition of Nb promotes the growth of the tissue and increases the residual austenite content,the tensile properties are improved,and the wear rate is lower than that without Nb.At 0.024%Nb,the wear rate is the lowest and the wear resistance is the best.