强流脉冲电子束M2高速钢表面改性组织和耐磨性能

Microstructure and Wear Resistance of M2 High Speed Steel after High Current Pulsed Electron Beam Surface Modification

目的 改善M2高速钢表面组织,提高其耐磨性和红硬性。方法 利用强流脉冲电子束(HCPEB)进行M2高速钢表面辐照改性处理,工作参数包括加速电压25 kV,脉冲宽度2.5μs,能量密度4 J/cm^(2),脉冲次数3、8和15次。采用MEF-4型光学显微镜和Zygo 9000型3D表面光学轮廓仪观察辐照前后样品表面形貌。采用XRD-6000型X射线衍射仪分析改性层组成。采用DMH-2LS型努氏显微硬度计测量样品表面和截面硬度。采用CFT-I型摩擦磨损试验机测量表面耐磨性能。在600℃下保温1 h后空冷,测量样品表面硬度变化用以比较红硬性。结果 HCPEB改性M2高速钢样品表面重熔并出现熔坑,随脉冲次数增加,熔坑数量减少且尺寸增加,表面粗糙度下降,15次脉冲处理样品表面形成大量孪晶,熔坑内部出现熔孔和微裂纹。重熔层组织细化致密,碳化物类型改变,碳化物颗粒尺寸减小,残余奥氏体数量增加。相对于未改性样品,15次脉冲处理样品表面硬度提高53.5%,磨损体积减小16.5%,红硬性提高19.2%。结论 HCPEB可有效改善M2高速钢表面组织,使表面显微硬度、耐磨性和红硬性指标均有明显提高。

As a new type of high energetic beam technique,high current pulsed electron beam(HCPEB)has been rapidly developed in recent years.Under HPCEB irradiation,the beam energy can be deposited with the featured characteristics including high density,fast heating speed,large depth and spot area.As a result,the material modification process is realized instantaneously with the following advantages,high working efficiency,small workpiece deformation and precise controlling of modified zone.The as-treated material endures the severe thermal-mechanical coupling effect and exhibits significant improvement in the surface properties.M2 high-speed steel(W6Mo5Cr4V2)has been widely applied for cutting tools in the machinery industries,With the desire of more strict working conditions,the comprehensive performance of M2 steel tools needs to be enhanced further.In this article,self-developed HCPEB equipment was adopted to treat M2 steel samples.The modification effects of HCPEB irradiation were studied basing on the characterizations of surface microstructure,phase composition,wear resistance and red hardness.The M2 steel samples with size of 10 mm×10 mm×10 mm was quenched at 1220℃ and tempered at 560℃ for 3 times.The sample surface was smoothed by sandpaper 200#-1500#and polished,then cleaned by alcohol and acetone in an ultrasonic bathing pot.The HCPEB treatment was carried out with working parameters of accelerating voltage 25 kV,pulse width 2.5ms,energy density 4 J/cm^(2),pulse number 3,8 and 15 respectively.The surface morphology was studied by MEF-4 optical microscopy(OM)and Zygo 90003D optical profilometer.The phase composition was analyzed by XRD-6000 X-ray diffractometry where the copper target,scanning scope 20°-100°and step 0.02°were used.The surface and cross-sectional hardness were detected by DMH-2LS Knoop microhardness tester with pressing load 5 g and sampling time 15 s.The wear resistance was measured by CFT-I type friction and wear tester,where the counterpart is Si_(3)N_(4) ball of diameter 4 mm with pressing load 20 N and testing time 30 min.The red hardness was compared by recording the Rockwell hardness after heating at 600℃ for 1 hour and cooling in the air.According to the analysis results,the surface layer of M2 steel sample was remelted with the formation of scattered craters.With the increasing pulse number,the quantity of craters increased and became larger,at the time,the surface toughness decreased.For the sample treated with 15 HCPEB pulses,the twins microstructure was observed universally with some melting holes and microcrack morphologies emerged in the craters.On the whole,the microstructure of remelted layer was refined and densified.The quantity of carbide particles decreased while the residual austenite showed the opposite trend.The microhardness of HCPEB modified M2 steel increased 53.5%,the wear volume decreased 16.5%with an abrasive wear mechanism and the red hardness showed an improvement 19.2%.In conclusion,the surface microstructure of M2 steel can be modified effectively by HCPEB treatment,and the surface microhardness,wear resistance and red hardness show an obvious improvement consistently.