Research On The High-speed Wire Rod Rolling Force Models Of GCr15and Its Controlled Cooling Technology

Wire rods have been always widely uesd in infrastructure and manufacturing,according to the increasingly standard of materials, high speed wird rod TMCP(Thermo-Mechanical Control Processing) technology plays a more and more importantrole in size reducing rolling process. As the performance and dimensional accuracy ofproducts were dominated by the last four RSB (reducing and sizing mill), when settedwith reasonable rolling parameters and controlled cooling, high-quality and highdimensional accuracy of the products can be got.This paper studies on GCr15, the experiments of size reducing simulation for thesetwo steels were carried out on the Gleeble-3500thermo-mechanical simulators, bysetting different deformation parameters (deformation temperature, strain and strainrate), mechanical models of resistance and rolling force to deformation at hightemperature were built respectively based on the rolling characteristics. According tothe dynamic CCT curves plotted of GCr15, microstructures under different coolingconditons were characterized, including the composition, microstructure, morphologicalcharacteristics and hardness, through which can provide some technical guidance for thedesign and optimization of the production processes.Results showed that:(1) according to the characteristics of deformation resistancefactors of GCr15, when strain rate was less than20s-1, Zhou J.H. deformation resistancemodel had a high precision, while under high strain rate, the new modle based onMoshitami was better, and the average values of fitting precision of the modles were allabove90%.(2) When calculating rolling force of the two steels, the mean unit forcemodle P=pF was used, and the fitted rolling forces were slightly greater than theactual ones which can play a protective role in the actual production process by settingthis rolling parameters.(3) According to the dynamic CCT curves plotted, pearlitetransformation temperature of GCr15was about550-700oC.(4) Strain rate showed littleimpact on microstructure in this paper, however, the greater the degree of deformation,the smaller grain size.(5) After GCr15was hot compressed at830oC, when cooling ratewas controlled at8~10oC/s to600oC and then0.5oC/s to room temperature, organizationwould get fine pearlite, of which the hardness was about550-620. Meanwhile, theprecipitate of cementite was restrained and the content of martensite was also controlled.When cooled at4oC/s, a big amount of troostite was precipitated on grain boundaries.As the cooling velocity increased, cementite and ferrite as well as their interval distance became thinner and Sorbite with obviously refined grains was formed, moreover,carbide was also eliminated.(6) For the sake of performance optimization of the GCr15in this paper, the cooling rate of8-10oC/s is selected in order to obtain the desirablemicrostructure, which consisting of about94%of fine pearlite with little networkcarbide on the grain boundary and3%of matensite.