Surface behavior of AISI 4140 modified with the pulsed-plasma technique

Abstract

In this study, the microstructure and surface properties of a low-alloy steel (AISI 4140) treated with pulsed plasma were investigated. Three different plasma-gun nozzle distances of (60, 70 and 80) mm and one battery capacity were chosen for a surface modification. The modified surface layers were examined using a light microscope and X-ray analyses were carried out for all the samples. The X-ray diffraction confirmed a development of new phases after the surface treatment. The samples were subjected to micro-hardness measurements and it was found that the hardness values of the modified surfaces were four times higher than those of the untreated samples. The samples were immersed into liquid nitrogen and then broken in a Charpy machine. The fractured surfaces were exposed to SEM and EDS analyses. At the end of the study, thin grains originating from the consumable electrode were detected. After the pulsed-plasma treatment, new structures were obtained. Keywords: pulsed plasma, fracture, consumable electrode, modification V tej {tudiji so bile preiskovane mikrostruktura in lastnosti povr{ine malolegiranega jekla (AISI 4140) po obdelavi s pulzirajo~o plazmo. Za spremembo povr{ine so bile izbrane tri razli~ne razdalje plazemske {obe od povr{ine: 60 mm, 70 mm in 80 mm, in kapaciteta ene baterije. Spremenjene povr{inske plasti so bile preiskovane s svetlobnim mikroskopom in izvr{ene so bile rentgenske analize. Rentgenska difrakcija je potrdila nastanek novih faz po obdelavi povr{ine. Na vzorcih so bile izvr{ene meritve mikrotrdote in ugotovljeno je bilo, da je trdota spremenjene povr{ine {tirikrat ve~ja od tiste pri neobdelanih vzorcih. Le-ti so bili potopljeni v teko~i du{ik in nato prelomljeni na napravi Charpy. Povr{ina preloma je bila analizirana s SEM in EDS. Odkrita so bila drobna zrna, ki izvirajo iz elektrode. Po obdelavi s pulzirajo~o plazmo je nastala nova mikrostruktura.

Effect of Heat Treatment and Pulse Plasma Process on Surface Properties of Steels

“…The phases and amount of these phases were very important to mechanical properties of surface. Because of this, these phases were very hard and increased hardness values of samples [8][9][10][11]. The variation of the parameters of heat treatment process and pulse plasma process resulted in different nitride layer characteristics; phase type, depth, hardness, hardness profile [10,11].…”

“…The structural defects, or disorder trappings, were easily formed at the high solidification rate induced by pulsed plasma. Another reason for the increase in the hardness values of the samples was the decreased grain size due to the increased cooling rate [11].…”