The Influence of Retained Austenite on Residual Stresses in Laser Remelted Cast Iron

Abstract

The presence and amount of residual stresses is very important in dynamically loaded automotive machine parts. In this investigation, the residual stresses after laser surface remelting were measured as a function of the modified layer depth on flat specimens from nodular cast iron. The results of the measured residual stresses confirm that the stresses strongly depend on the presence and quantity of the microstructure constituents in the surface remelted layer. Residual stresses have a characteristic profile in the modified surface layer. In the surface remelted layer, tensile residual stresses were found in a range between +70 and +200 MPa. The change from tensile into compressive residual stresses takes place in the lower part of the remelted layer. Maximum compressive residual stress values were found in the middle of the hardened layer in a range between 225 and 280 MPa.

Laser Surface Hardening of Ni-hard White Cast Iron

“…After laser surface-hardening, mostly mild and low wear rates have occurred for the samples, the wear rate was reduced by almost three times than the value of the untreated samples (for example, 2.8 mg/min versus 8 mg/min, for S1 alloy) as shown in Figure 17. This is due to the homogeneous martensitic transformation of the austenite dendrites in the microstructure that causes local increase of the microstructure volume and contributes to compressive residual stresses which resulted in the increase of the resistance to subsurface crack formation [31,35]. as-cast matrix as was pointed earlier [25].…”

“…A similar microstructure was obtained in all specimens treated at various laser processing parameters. transforms into martensite with some retained austenite [31]. Consequently, the HZ contains ultrafine martensite, retained austenite and eutectic M3C carbides.…”

“…According to Strum's work [31] the residual stress variation in the hardened layer can be described with the concentration of retained austenite, martensite and carbides in vol%. In the hardened layer martensite transformation causes local increase of the microstructure volume and contributes to compressive residual stresses.…”

“…During laser heating, the matrix transforms into a carbon-rich austenite, into which additional carbon diffuses from eutectic carbides. During rapid self-quenching, the carbon-rich austenite transforms into martensite with some retained austenite [31]. Consequently, the HZ contains ultrafine martensite, retained austenite and eutectic M 3 C carbides.…”

Fine-structured Morphology of a Silicon Steel Sheet after Laser Surface Alloying of Sb Powder

“…On the other hand, various laser melting procedures can be effectively used during the creation of functional parts [10] to [13]. In recent years a laser beam has been used for a wide range of applications in order to modify the microstructure and the properties of the steel.…”