| The cement industry is one of the foundations of modern industries. Crushing andgrinding of the raw materials are important processes in the cement production process.When breaking the ore, extrusion rollers are working under a severely abrasive wear andperiodic compressive stress which will cause the rollers’ surface material consumption, at thesame time cause fatigue failure and eventually lead to being scrapped. The rollers’ surface isoften prepared and repaired by the hardfacing welding method. Improving the bondingstrength between anti-wear layer and base metal of the rollers becomes particularlyimportant.The improved push-off test is used to measure the bonding strength between hardfacingalloys and45steel parent metals. In this paper, Tungsten Inert Gas Welding (TIG) withmanual feeding flux-cored wires was selected to make the hardfacing layers and the weldingmaterials include four kinds of commercially available wires and nine kinds of homemadewires. The commercially available wires include high Cr high Mn-type wire, Nb-type wire,TiC-type wire and high Cr cast iron-type wire.The homemade wires with wear-resistanceinclude three series in which the added amounts of powders of CaB6, B4C or ferroniobiumare changed in the flux cored wires. Each of them has three different kinds of doses. Thebonding properties between hardfacing alloys and parent metal were studied through themicrostructures，EDS and push-off strength after welding，and the fracture analysis ofdifferent welding specimens after the push-off test.Experiments show that the bonding properties of hardfacing alloys made by high Cr andhigh Mn-type wire are good. Their average push-off strength is beyond350MPa, which isthe highest among all the specimens. The microstructures of the hardfacing alloy areaustenite. The alloying elements dissolved in the grains, so the hardfacing alloy has goodductility and toughness. Most of the fractures occurred in the HAZ, which showed thatductile fracture happened during the push-test. Microstructures of the hardfacing alloy madeby TiC-type wire are TiC and martensite plus retained austenite matrix. Comparatively, thebonding properties are lower. Part of the fracture is in the HAZ and another part is in thehardfacing alloys. The fracture of the material was a mixed ductile-brittle fracture.Microstructures of the hardfacing alloy made by Nb-type wire are NbC and carbides with Crin the hypoeutectic matrix. Compared with the bonding properties of TiC-type specimens,those of the Nb-type are lower. The high chromium cast iron surfacing layers contains lots ofhypereutectic structures which result in the lowest push-off strength among hardfacing alloysmade by commercially available wires. Their fractures are mostly in the hardfacing alloyswith typical brittle fractographes.All of the specimens made by homemade flux-cored wires belong to high chromium cast iron type hardfacing alloys. Their bonding strengthes are wholly below200MPa. In thehardfacing alloys changing the CaB6addition, the more contents of CaB6, the more amountsof hypoeutectic matrix and finer the C-B compounds would be. Bonding strengthes of thespecimens have a trend of increasing firstly and then decreasing. In the hardfacing alloyschanging the B4C and ferroniobium addition, more amounts of hypoeutectic matrix occurwhen adding the powders, and the bonding strength is getting worse and worse. Microsegregation exists at grain boundary in the hardfacing alloys which makes the toughness ofsegregation structures worse than grains. Fracture happens easily on the boundary. Lowplastic brittle cracks are easily formed in high chromium cast iron type hardfacing alloys. |
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