Study on properties and failure modes for piercing plug of high alloy steel

Plug is the key tool for cross-piercing, its lifespan has a significant impact on the quality and cost of the hollow bloom. The methods of etallographic microscope, scanning electron microscope, Gleeble thermal simulation, and friction and wear tester were used to study the microstructure, hardness, deformation resistance, and friction and wear performance, and the typical failure modes of piercing plugs of high alloy tube were summarized. Research results show that the micro-structure of the plug is sorbite, the Vickers hardness (HV) is approximate 258, the friction and friction factor is approximate 0.45. Within the range of 900~1250 ℃, as the temperature increases, the deformation resistance of the plug decreases from 290 to 77 MPa. The typical failure modes of plugs used for high alloy tube piercing include nose collapse, wearing a hat, loss of flesh, sticking, and longitudinal cracks. The causes of failure mode are that the plug is subjected to great axial force, compressive stress and shear stress in the environment of quenching and hot rolling.