Effect Of Deep Cryogenic Treatment On The Microstructure And Properties Of YG20 Cemented Carbide

Cemented carbides are widely applied as cutting tools and impacting tools,as well as wear and corrosion resistant parts due to the exceptional combination of strength,toughness and wear resistance.Although the cemented carbide tools have excellent comprehensive properties,their main failure causes are still wear and fracture due to the high temperature and stress under extreme working conditions.Many modification processes of cemented carbides,such as refining microstructure,optimizing sintering processes and surface strengthening technology,have entered the mainstream to extend the service life of cemented carbide tools.However,there still exist some defects in these improving measures of cemented carbides,including the high cost of complicate equipment and the difficulty of the preparation of new-type cemented carbides materials,which have restricted the development and application of high-end cemented carbides production.Deep cryogenic treatment(DCT),which is regarded as a new-type process with non-polluting and low energy consumption,has been proved to enhancae the mechanical properties,wear resistance and dimensional stability of materials.With the application of deep cryogenic treatment technology becoming more and more widely,there has been an increase of interest in the research of deep cryogenic treatment on cemented carbides over the past few decades.However,due to the late start,there still exsist many lacks in terms of cryogenic processes and micro-mechanisms.In this paper,the effect of deep cryogenic treatment on the hardness,bending strength,impact toughness,fracture toughness and wear resistance of YG20 cemented carbides,and the influence rules of different process parameters on the properties of YG20 cemented carbide are analyzed.The changes of microstructures in YG20 cemented carbide after deep cryogenic treatment are studied by using different methods,and the strengthening mechanisms of deep cryogenic treatment are revealed.Based on the results,the preliminary exploration of industrial application of deep cryogenic treatment on cemented carbides is conducted.The results show that dee cryogenic treatment can improve the bending strength and fracture toughness of YG20 cemented carbide,but has little effect on hardness and impact toughness(less than 5%).The main reasons for the improvement of fracture toughness after cryogenic treatment are that the strength of cohesive phase Co and WC/Co interface are increased,which induce that more fracture work is consumed during fracture.In addition,deep cryogenic treatment can significantly improve the wear resistance of YG20 cemented carbide,and the degree of improvement on wear resistance is closely related to cryogenic process parameters.The results show that the improvement of wear resistance after deep cryogenic treatment does not increase with treating temperature decreased and holding time prolonged.There is a specific matching relationship between treating temperature and holding time.The enhancement of wear resistance after deep cryogenic treatment can be attributed to the martensitic transformation of bonding phase Co from a-Co to ?-Co,and the precipitation of ?-phase particles on the Co matrix,which makes a tough,compact and stable material,and reduces the risk of WC particles spalling during wear behavior.A professional deep cryogenic treatment service is provided for the cemented carbide die tools produced by a company.Through the trace records of test tools,it is found that the tool life of mandrels of the first batch and the second batch is increased by approximately 17%and 22.5%respectively,and the performance of other die tools is also signicicantly improved.The results not only verify the effectiveness of deep cryogenic treatment in practical production,but also reflect the stability and reliability of the treating effects,which brings great prospects for the industrial promotion of deep cryogenic treatment on cemented carbides.