A new method for dating ancient steel samples using Vickers microhardness Jose ´ Manuel Jime ´nez, Esther Bravo, Antonio Javier Criado, Raquel Are ´valo, Christian Dietz, Juan Antonio Martı ´nez * , Antonio Jose ´ Criado Department of Material Science and Metallurgical Engineering, Faculty of Chemistry, Complutense, University of Madrid, E-28040 Madrid, Spain Received 20 February 2004; received in revised form 28 April 2004; accepted 28 April 2004 Abstract A simple, fast and economic method for age determination of steel samples is presented, based on the change of mechanical properties over time. The mechanical strength was determined by Vickers microhardness testing, finding a linear relationship in between this parameter and the age of the sample. For calibration, four different archaeological samples of different ages were used, all of them hypoeutectoid steels. They were taken from excavation sites spread all over the Iberian Peninsula. The samples’ age ranged from 1st century B.C. up to 18th century A.C. Microhardness was measured on either ferritic or pearlitic zones, obtaining a slightly better regression coefficient for the pearlitic zones, which was attributed to particular characteristics of the samples used. The proposed method should have the potential to be extended to hypereutectoid steels. D 2004 Elsevier Inc. All rights reserved. Keywords: Dating; Ancient steels; Archaeological steels; Mechanical properties 1. Introduction An ageing process, altering the microstructure of iron and steel [1,2], occurs when these materials are exposed to the passing-by of large periods of time. This can be proved by the observation of a large amount of archaeological samples taken from differ- ent historical periods, where a series of complex microstructures can be distinguished and classified. These structures, having changed over time, are cer- tainly different from those characterising the material at the moment of its production. These changes can be clearly seen in structures such as ferrite, pearlite, martensite and bainite. This time-dependent structural evolution also implies changes of the physical and mechanical properties of iron or steel [3,4], a process that has potential to be used to determine the age of these samples. The samples under study were taken from different archaeological sites in Spain, as shown in Fig. 1. In Fig. 2A–D, pictures of the chosen artefacts are shown. Further details of the findings, whose chro- nologies range from an age of 2000 to 200 years, are summarised in Table 1. The ages of these sites are very well defined by relevant archaeological studies 1044-5803/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2004.04.005 * Corresponding author. Tel.: +34-91-3944288; fax: +34-91- 3944357. E-mail address: jamartinez@quim.ucm.es (J.A. Martı ´nez). Materials Characterization 52 (2004) 145 – 151