Microstructure and Properties of 28MnB5 Fe-Based Alloys for High-Speed Plough with Quenching-Tempering Process
28MnB5 Fe-based alloys,as a new wear-resistant material,are widely applied in the agricultural equipment industry,es-pecially in the application of high-speed plow entry components.With the rapid development of the application of high-speed ploughing parts,the demand for wear resistance of 28MnB5 Fe-based alloys is more advanced.To further enhance the service life of 28MnB5 Fe-based alloys,a quenching-tempering(QT)treatment was employed in this study to improve the strength and hardness of this alloy.The microstructure and mechanical properties of 28MnB5 Fe-based alloy were investigated.The thermal simulation experiment of 28MnB5 iron-based alloy was carried out by the Gleeble-3500 thermal simulation tester.The microstructure of QT-state 28MnB5 Fe-based alloy was analyzed using optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction instrument(XRD)and electron backscatter diffraction(EBSD).The misorientation of the grains was analyzed by using the Channel 5 software.It was found that the flow curve of 28MnB5 Fe-based alloy could be mainly divided into the following two categories:one category was dynam-ic recovery and the other category was dynamic recrystallization.As the increases of hot working temperature of 28MnB5 Fe-based al-loy,its work-hardening effect was weakened or even vanished.The alloy's deformation resistance was reduced and good thermoform-ing properties were displayed.Thus,the alloy's deformation resistance was reduced and good thermoforming properties were dis-played.The microstructure test results showed that the hot-rolled 28MnB5 Fe-based alloy was mainly composed of the banded structure formed by alternating distribution of ferrite and pearlite due to composition segregation during hot rolling solidification,which led to its poor strength and obvious anisotropy.Compared to hot-rolled 28MnB5 Fe-based alloy,QT-state 28MnB5 Fe-based alloy consisted pri-marily of tiny and uniformly distributed lath martensite,the majority of which lied in the size range of 0～5 μm2,the rate of them as high as 81.3％.Reducing the grain size could increase the number of grain boundaries per unit volume,and could be described by the classical Hell-Petch relationship.So,the movement of dislocations had gotten more difficult,thus improving the strength of metal ma-terials.According to the analysis of the classical Hell-Petch relationship,it clearly showed that reducing the grain size could increase the number of grain boundaries per unit volume,thereby hindering the movement of dislocations and improving the strength.Further-more,the refinement of the martensitic laths could lead to the increase of grain boundary area,which further hindered the movement of dislocations,resulting in increases in the strength and hardness of the material of metal materials.By analyzing EBSD results,it could be found that the distribution of lath-martensite misorientations(θ)in the QT-state 28MnB5 Fe-based alloy was mainly concen-trated in the range of θ＜2°(sub-grain boundaries),2°＜θ＜10°(low angle grain boundary)and 50°＜θ＜60°(high angle grain bound-ary).Due to the cooperative deformation of martensite and matrix during the formation of martensite,the low angle grain boundaries were mainly scattered in the interior of the lath martensite,while the high angle grain boundaries were mainly distributed at the bound-ary of the martensite lath.The presence of small-angle grain boundaries indicated the large number of dislocations that might appear in-side the martensitic lath,which could suppress the slip of grain boundaries,so that the strength of the metal material was improved.The tempering of 28MnB5 Fe-based alloy at 180 ℃ could reduce and eliminate the quenching stresses generated during quenching and reduce the brittleness of the material,making the QT-state 28MnB5 Fe-based alloy with more stable mechanical properties,and the QT-state 28MnB5 Fe-based alloy had more stable mechanical properties.The stress-strain curves and related mechanical properties of the hot-rolled and the QT-state 28MnB5 Fe-based alloy were analyzed,and it was found that the hot rolled and the QT-state 28MnB5 Fe-based alloy exhibited continuous yielding characteristics during the tensile process.Additionally,the QT-state 28MnB5 Fe-based alloy consisted of a nearly full martensitic phase due to the addition of B elements that could greatly improve the hardenability of the Fe-based alloy.Therefore,the yield strength,tensile strength and hardness of the QT-state 28MnB5 Fe-based alloy were 1451 MPa,1843 MPa and HRC 51.3,respectively,which was significantly higher than those of hot rolled 28MnB5 Fe-based alloy(yield strength of 561 MPa,tensile strength of 744 MPa and hardness of HRC 18.8).The above study illustrated the internal correlation mechanism between microstructure and excellent properties of 28MnB5 Fe-based alloy after the quenching-tempering process,and confirmed that 28MnB5 Fe-based alloy had excellent hot forming properties and good strength and hardness,which provided a reference for the devel-opment of new agricultural machinery materials and heat treatment process improvement.This was hopeful to provide a promising tech-nical proposal for manufacturing soil-engaging components with high stiffness and high strength properties,and to achieve efficient farming operations and promote the transformation and upgrading of agricultural mechanization.
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