金刚石与磨料磨具工程2026，Vol.46Issue(4)：489-495,7.DOI:10.13394/j.cnki.jgszz.2025.0080
球形420不锈钢基磁性磨料的制备及研磨性能
Fabrication and grinding performance of spherical 420 stainless steel-based magnetic abrasives
摘要
Abstract
Objectives:Zirconium alloy has become an indispensable key structural material for modern nuclear reactors due to its unique nuclear and mechanical properties,and is widely used in core components such as fuel cladding tubes,pressure tubes,and guide tubes in pressurized water reactors and boiling water reactors.However,the surface roughness of zirconium alloy has a significant impact on corrosion resistance.Currently,the traditional polishing techniques have many drawbacks,especially for the polishing of slender zirconium tubes.Magnetic grinding technology,as a new type of grinding technology,shows great advantages in the grinding of workpieces with complex shapes.Meanwhile,the traditional iron-based magnetic abrasives are prone to rust and oxidation during processing,usage and storage,and have problems such as poor stability.There is an urgent need for the development of new types of corrosion-resistant magnetic abrasives.Methods:A new type of 420 stainless steel-based magnetic abrasive with core-shell structure is synthesized by in-situ gas nitriding method,and its grinding performances,microstructure,and micro-mechanical properties are further studied.The gas-atomized spherical 420 stainless steel metal powder with a diameter of 100 to 150 μm and excellent magnetic permeability is selected.It is subjected to gas nitriding in a ZHK-B06126K tubular furnace at 530℃.During nitriding,the furnace pressure is controlled at 550 Pa,the ammonia gas flow rate is controlled at 20 mL/min,and the holding time is 10 h.The metal powder after nitriding is the 420 stainless steel-based magnetic abrasive 420-N.The metal powder after nitriding has a slight hardening phenomenon and need to be slightly ground and crushed.The phase compositions of 420-N magnetic abrasives is determined by the D/MAX-2500/PC X-ray diffractometer.The longitudinal cross-section microstructures of 420-N powder is observed by using the Hitachi S-3400 scanning electron microscope.The magnetic properties of 420-N are tested using the PPMS-9 vibrating sample magnetometer.The microhardness of the longitudinal section of 420-N is tested using the FM-700/SVDM4R Vickers hardness tester under a load of 25 g for 15 s.The nanoindentation test of 420-N is conducted using the Agilent Nano-Indenter G200 nanoindentation tester under a maximum load of 0.5 g(approximately 4.9 mN).During the test,the loading rate is 0.5 mN/s and the holding time is 10 s.The finishing performance of 420-N stainless steel-based magnetic abrasives is evaluated using a self-developed magnetic grinding system.Tests involved grinding a 9.5 mm Zr-4 zirconium tube at 1 000 r/min with an 8 mm/min feed rate and 2 mm working clearance.The surface roughnesses of the zirconium tube before and after grinding are measured by the TR 2000 roughness tester.Ten points are randomly tested after each grinding,and the average value is taken as the final result of the surface roughness.Results:The longitudinal section of the 420-N powder after nitriding shows a core-shell structure,and it exhibits a dendrite structure in the nitride shell layer.The saturation hysteresis loop test reveals that the original 420 powder has slightly higher saturation magnetization than the 420-N magnetic abrasive,likely due to the presence of(Fe,Cr)4N and CrN phases in the nitride.In view of the CrN phase is an antiferromagnetic phase and the Fe4N type phase exhibits ferromagnetic behavior,and there is a small amount of CrN phase in the dendrite intergranular region of the magnetic abrasive after nitriding,this may slightly reduce its magnetization intensity.However,both of these two powders maintain relatively high magnetic intensification before and after nitriding,and the difference in magnetic properties is very small,indicating that the nitrided magnetic abrasive still maintains excellent soft magnetic properties.The surface of the slender zirconium tube is ground using 420-N magnetic abrasive.The surface roughness of the zirconium tube decreases from 0.291 μm before grinding to 0.129 μm after grinding,and the magnetic abrasive demonstrates excellent grinding performances.At the same time,the Vickers hardness tests reveal that the 420-N magnetic abrasive exhibits a non-uniform Vickers hardness distribution,with lower values in the central region and higher values at the edges of the longitudinal section.The highest Vickers hardness in the edge nitride layer area is about HV 770,while the Vickers hardness in the central area is about HV 540.This indicates that the formation of the nitride layer leads to a higher Vickers hardness in the shell area than in the core area.Moreover,the nanoindentation test results indicate the interdendritic regions within the nitride layer exhibit higher values of Hn,Hn/Er,and Hn3/Er2,which are two key parameters characterizing material wear resistance.Higher values of Hn/Er and Hn3/Er2 indicate excellent wear resistance.Therefore,the formation of nitrides in the interdendritic region can improve the hardness and the wear resistance of 420-N magnetic abrasives.Conclusions:A new type of 420 stainless steel-based core-shell structured spherical magnetic abrasive is successfully synthesized by in-situ gas nitriding,and its nitriding layer is a dendritic structure containing(Fe,Cr)4N and CrN phases.The nitrided 420-N magnetic abrasive still maintains a high saturation magnetization intensity of 146.15 emu/g,which is only 1.9%lower than that of the original 420 metal powder.During the surface grinding process of zirconium tubes,the nitriding 420-N magnetic abrasive can reduce the surface roughness value from 0.291 μm to 0.129 μm through four magnetic grinding processes.In addition,the nitriding layer has high Vickers hardness and nanohardness,which can ensure good wear resistance of the magnetic abrasive.This is the main reason why 420-N magnetic abrasive has good precision machining performance.关键词
气体渗氮/磁力研磨/表面粗糙度/纳米压痕Key words
gas nitriding/magnetic abrasive finishing(MAF)/surface roughness/nanoindentation分类
矿业与冶金引用本文复制引用
徐科,胡明磊,刘君,邓志新,党莹..球形420不锈钢基磁性磨料的制备及研磨性能[J].金刚石与磨料磨具工程,2026,46(4):489-495,7.基金项目
核电厂材料规范及应用导则开发研究项目(QS4FY-22006982-000). （QS4FY-22006982-000）
