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Enhanced wear resistance of precipitation hardening steels by laser solution annealing and subsequent aging treatment

Verbesserter Verschleißwiderstand von ausscheidungshärtenden Stählen durch Laserlösungsglühen und anschließendes Aushärten
: Kaspar, Joerg; Brenner, Berndt; Luft, A.; Tietz, F.; Bretschneider, Jörg


Fischer, A. ; Deutsche Gesellschaft für Materialkunde e.V. -DGM-, Oberursel:
Friction, wear and wear protection : International Symposium on Friction, Wear and Wear Protection 2008 Aachen, Germany, from April 9th to 11th, 2008
Weinheim: Wiley-VCH, 2009
ISBN: 978-3-527-32366-1
International Symposium on Friction, Wear and Wear Protection <2008, Aachen>
Fraunhofer IWS ()
Aushärten; ausscheidungshärtender Stahl; chemische Zusammensetzung; Kavitationserosion; Laserstrahlerwärmung; Lösungsglühen; Mikrogefüge; Oberflächenhärte; Randschicht

The experiments were carried out on the precipitation hardening martensitic stainless steel 16-4 PH ofthe following chemical composition (wt%): Cr: 15.65, Ni: 4.30, Cu: 3.05, Mn: 0.45, Nb: 0.30, Si: 0.27, C: 0.038, P: 0.018, S: 0.001, Fe: balance. This steel is strengthened by the precipitation of small Cu particles within lath martensite structure. The as delivered condition of this steel is characterized by the conventional solution annealing and aging treatment specified. In order to increase surface hardness and wear resistance the as delivered samples were subjected to an additional heat treatment cycle which is called 'Surface age hardening' and consists of a short time solution annealing of the surface by laser treatment followed by rapid selfquenching and a subsequent aging treatment of the whole sample at temperatures below 560 deg C. The laser solution annealing was performed with a 6 kW CO2-laser and a 4 kW diode laser, respectively. In order to ensure a fast and exact local temperature control a fast pyrometer or a camera based temperature measuring system E-MAqS and the laser power control unit LompocPro were integrated in the laser surface annealing process. A beam shape device based on approved galvanometer scanner technology and developed for the conventional laser hardening has been applied to generate variable tracks up to 40mm in width. The laser surface annealing was conducted at a constant surface temperature of about 1350 deg C and at different dwell times (0.75 s to 10 s) by varying laser power and transverse speed. The aging of the laser solution annealed samples was done at temperatures between 480 deg C and 550 deg C, i.e. below the conventional aging temperature of 560 deg C, to modify the precipitation structure within the laser annealed surface region but leave the structure in the bulk of the material unchanged. In the present work the innovative Surface age hardening technique which is based on laser solution annealing and subsequent aging treatment was introduced and successfully applied to improve the surface hardness and cavitation erosion resistance of the precipitation hardening steel 16-4 PH. In order to evaluate the capability of this technique the hardness, microstructure and wear resistance ofthe as delivered state and of surface aged hardened samples were comparatively investigated. Based on the results the following conclusions are drawn: 1. By applying the Surface age hardening technique the hardness of the steel 16-4 PH can be increased by about 50 % and the resistance to cavitation erosion by about 300 %. 2. By altering the parameters of the laser and aging treatments the required hardness and depth of the surface age hardened zone can be easily adjusted. 3. In the surface age hardened region a more homogenous and finer arrangement of small Cu rich precipitates is formed than in the conventionally heat treated samples of the as delivered state.