Study On The Preparation And Mechanical Properties Of GPS High Wear-resisting Silicon Nitride Ceramic High Wire Guide Roller

In this paper,highly wear-resistant silicon nitride based ceramic guide rolls were prepared by pneumatic sintering(GPS)by determining the optimum sintering aid composition ratio and the optimum sintering temperature,and finally the wear resistance was evaluated by field experimental tests to verify the feasibility of the preparation process.The research content and results are as follows.(1)The optimum sintering aid ratios and sintering temperature ranges for Al₂O₃-Y₂O₃ and Mg O-Y₂O₃-based Si₃N₄ ceramics were initially obtained by designing orthogonal experiments,and the sintering temperature ranges obtained were gradient refined to investigate the effects of different maximum holding temperatures on the relative density,grain distribution,mechanical properties and?-Si₃N₄ conversion rate of Si₃N₄ ceramic guide roll materials.The results show that the best overall performance of the 3wt.%Y₂O₃-3wt.%Al₂O₃ Si₃N₄ceramic guide roll material was achieved at 1820? with a relative density of 99.58±0.11%,Vickers hardness,fracture toughness and flexural strength of 1562±20 HV,5.51±0.12 MPa-m^1/2and 663±30 MPa,respectively.The best overall performance of the 4wt.%Y₂O₃-3wt.%Mg O Si₃N₄ ceramic was achieved at 1760? with a relative density of 99.45±0.10%,Vickers hardness,fracture toughness and flexural strength of 1525±14 HV,6.58±0.15 MPa-m^1/2 and663±30 MPa,respectively.The microstructure is dominated by?-Si₃N₄ grains,and the?-Si₃N₄phase conversion rate can reach 94.4%.(2)On the basis of the 3wt.%Y₂O₃-3wt.%Al₂O₃ system Si₃N₄ ceramic guide roll material,the effect of La₂O₃ content on the properties of the silicon nitride based ceramic guide roll material at a sintering temperature of 1820? was investigated.The results of the physical phase analysis showed that the sintered samples mainly consisted of?-Si₃N₄ and the second phase La₃Si₈O₄N₁₁,and the most balanced mechanical properties were obtained for the silicon nitride based ceramic guide roll material(SLA91)with 3 wt.%La₂O₃,in which the fracture toughness could reach 5.84±0.13 MPa-m^1/2 and the hardness could reach 1570±17 HV,and the The grain size distribution is relatively uniform.When the addition amount is increased to 4 wt.%,the Si₃N₄ ceramic forms short,coarse?-Si₃N₄ grains,which reduces the overall?-Si₃N₄ grain aspect ratio,resulting in a lower fracture toughness of 5.58 MPa-m^1/2,but a hardness of 1593HV.The hardness and fracture toughness of Vickers hardness are improved.(3)The frictional wear performance of SA94,SM93 and SLA91 ceramic guide roll materials with Si₃N₄ mating pairs was investigated under dry sliding conditions.The results show that the friction coefficients and wear rates of the three silicon nitride based ceramic guide roller materials and Si₃N₄ mating pair are different,under the same load,the friction coefficient of SA94 ceramic guide roller material decreases with the increase of frequency,and the minimum friction coefficient is 0.511,while the friction coefficients of SM93 and SLA91ceramic guide roller materials increase with the increase of frequency,and the minimum friction coefficients are 0.497 and 0.486 respectively.At the same sliding frequency,the coefficient of friction of SA94 and SLA ceramic guide roller materials with Si₃N₄ mating pairs increases and then decreases with increasing load,with a minimum coefficient of friction of 0.488 and 0.482respectively,while the coefficient of friction of SM93 and Si₃N₄ mating pairs increases with increasing load,with a minimum coefficient of friction of 0.510.The wear mechanism of the different silicon nitride based ceramic guide roll materials is different,the wear of the SA94guide roll is mainly in the form of adhesive wear,accompanied by oxidation wear and abrasive wear at high loads.wear.(4)The wear resistance of SA94 ceramic guide rolls,SLA91 ceramic guide rolls and commercially available cemented carbide guide rolls(comparison guide rolls)under actual working conditions was investigated in an online service test on a steel mill's high line production line for 4 hours of continuous operation.The results show that,under the same conditions,the SLA91 guide roll has the longest working life among the three types of guide rolls and shows superior wear resistance in actual operation,much longer than the carbide guide rolls,with the life of the SLA91 guide roll being approximately three times that of the SA94guide roll.Through comparative analysis,it has been demonstrated that both SLA91 and SA94ceramic materials can be used as alternative materials for highly wear resistant high wire mill guide rolls.