Mechanical and tribological characterization of additivemanufactured Co-free tool steels aimed for cutting tool bodies

Sammanfattning: Additive manufacturing (AM) is an emerging and interesting technology that enables some of theproduct development projects (PDPs) to produce products that have mechanical and tribologicalproperties comparable to products that are conventionally manufactured. Selective laser melting(SLM) is an additive manufacturing technology that is predominantly used for the production of metalbased components (i.e. it could be pure metal, alloys, and metal matrix composites). This workevaluates and ranks two different steel grades produced with SLM technology in tribological andcutting tool applications at AB Sandvik Coromant. The two steel grades used in this work were Cofree maraging steel alloy and Co-free W360 AMPO alloy. Both the grades are Cobalt free, hencedeveloped as a sustainable alternative for the future. The W360 AMPO alloy is a hot-work tool steelwith high temperature wear resistance and heat resistance. The work covers the characterization ofmicrostructure and chemical composition, mechanical properties, and tribological properties toevaluate the performance of the tool steel grades when used as tool bodies in drilling applications.The microstructure and chemical composition of the additive manufactured and heat-treated tool steelswere analyzed using SEM and EDS. The mechanical properties were evaluated using micro-Vickersindentation and scratch testing while the tribological properties were evaluated using pin-on-disctesting where counter material used was quenched and tempered steel. The application test included asimulated chip wear test using chip breakers (CB’s) and an actual drilling test, both performed at ABSandvik Coromant. To study the effect of surface topography on the adhesion tendency, the simulatedchip wear test was performed on both milled and grounded chip breaker (CB) samples. The drillingtest was done with three different test-set ups; function test, 30° inclined exit, and forced tool life test.The cellular microstructure was observed on Co-free maraging steel alloy sample, while themicrostructure was tempered martensite in W360 AMPO alloy. Elemental analysis revealed thechemical composition of the two steel grades. The measured hardness for both the samples Co-freemaraging steel alloy and W360 AMPO was found to be within the specification of demands (50-52HRC), although the hardness of W360 AMPO was a bit higher than Co-free maraging steel alloy. Theresults of the pin-on-disc tests showed that the wear resistance of the W360 AMPO alloy issignificantly higher than that of the Co-free maraging steel alloy, the tribo-system used was similarwhen compared to the actual application. Also, after analyzing the pin made up of quenched andtempered steel 34CrNiMo6 (SS2541) it can be seen that due to the W360 AMPO sample the volumeloss of the pin is almost 4 times when compared to Co-free maraging steel alloy. The result from thesimulated chip wear test showed that W360 AMPO has better wear characteristics. Adhesion ofworkpiece material (SS2541) was observed on both samples. In the simulated chip wear test, thesurface topography effect was studied by performing a test on milled and grounded CBs. GroundedCBs showed less adhesion tendency compared with milled CBs on both samples but the wearcharacteristics were similar irrespective of the surface roughness. The result from the drilling testshowed wear scar was predominant on a drill with Co-free maraging steel alloy and a drill with W360AMPO alloy was intact. Future possible investigations proposed after findings from experimentalresults may lead to future work.