Effects of roller burnishing on the surface integrity and mechanical properties of duplex and 316L stainless steels

Abstract

Roller burnishing (RB) or deep rolling is a mechanical surface treatment method to enhance the surface integrity of manufactured components which affects component’s performance. Although there are some valuable researches on the effects of RB on different materials, there is no comprehensive investigation about roller burnishing of duplex stainless steel (DSS) and 316L stainless steel, in a comparative manner. The main purpose of the present thesis is to reveal the effect of RB on surface integrity and mechanical properties of duplex and 316L stainless steel. In order to understand the effect of RB parameters on surface integrity, Taguchi L9 (34) experimental design method was utilized. The changes in microstructure, surface microhardness, and surface roughness were measured after the RB process and the optimized parameters for the maximum surface microhardness (condition H) and the minimum surface roughness (condition R) were determined. It was shown that bur nishing created a refined surface layer up to 0.6 mm and 0.8 mm, enhanced surface microhardness to 118%, and 147%, and reduced surface roughness to 52%, and 40% of the initial values, respectively for DSS and 316L. Ambient temperature tensile tests were performed and the results revealed no no table improvement in yield and tensile strengths after the RB process. On the other hand, significant enhancements were observed in the cyclic performance after the bur nishing process. Subsequently, the results of high cycle fatigue (HCF) tests revealed that the cyclic performance of the burnished sample with H condition was signifi cantly higher than those of both unburnished and condition R samples, especially at low-stress amplitudes. Besides, fracture surface analysis exposed the restriction of crack initiation and propagation in the hardened surface layer. Subsequently, the re sults of reciprocating wear tests unveiled a significant increase in wear resistance after the burnishing process. It was detected that the condition H samples have superior wear resistance in hard abrasive cases, while condition R samples are more resistive in soft abrasive conditions.

Makaralı perdahlama i¸slemi, i¸s par¸casının performansını etkileyen y¨uzey b¨ut¨unlu˘g¨un¨u iyile¸stirmek amacı ile uygulanan mekanik bir y¨uzey geli¸stirme y¨ontemidir. Bu konuda yapılmı¸s de˘gerli ¸calı¸smalar olmasına ra˘gmen duplex ve 316L paslanmaz ¸celiklerinin makaralı perdahlanması ile ilgili kapsamlı bir ara¸stırma bulumamaktadır. Bu tez ¸calı¸smasında, makaralı perdahlama i¸sleminin duplex ve 316L paslanmaz ¸celiklerinin y¨uzey b¨utunl¨u˘g¨u ve mekanik ¨ozellikleri ¨uzerine olan etkisini belirlemek ama¸clanmı¸stır. ˙I¸slemin y¨uzey b¨ut¨unl¨u˘g¨u ¨uzerindeki etkisini anlamak amacı ile Taguchi L9(34 ) deneysel tasarım metodu kullanılmı¸stır. Mikroyapı, y¨uzey sertli˘gi ve y¨uzey p¨ur¨uzl¨ul˘g¨undeki de˘gi¸siklikler perdahlama i¸sleminden sonra g¨ozlemlenmi¸s, maksimum y¨uzey mikro sertli˘gi (ko¸sul H) ve minimum y¨uzey p¨ur¨uzl¨ul¨u˘g¨u (ko¸sul R) i¸cin opti mize edilmi¸s parametreler Taguchi y¨ontemi ile bulunmu¸stur.˙I¸slemin sırası ile duplex ve 316L paslanmaz ¸celiklerinde 0.6 mm ve 0.8 mm derinli˘ge kadar rafine olmu¸s bir mikroyapı olu¸sturdu˘gu, 18% ve 47% y¨uzey mikro sertli˘gini arttırdı˘gı ve 52% ve 40% y¨uzey p¨ur¨uzl¨ul¨u˘g¨un¨u azalttı˘gı g¨ozlemlenmi¸stir. Ayrıca, yapılan ¸cekme testlerinde perdahlama i¸slemi yapılmı¸s malzemelerin akma ve azami ¸cekme dayanımlarında de˘gi¸siklik g¨ozlemlenmemi¸stir. Bununla birlikte, per dahlama i¸sleminin, malzemelerin y¨uksek ¸cevrimli yorulma dayanımını ve a¸sınma per formansını kayda de˘ger miktarda arttırdı˘gı g¨ozlemlenmi¸stir.