Characterization of a Historical Cannonball from the Fortress of San Juan De Ulúa Exposed to a Marine Environment

Abstract

Metallurgical analyses and chemical characterizations were carried out on historical cannonballs from the Fortress of San Juan de Ulúa, Veracruz, México. Cannonballs dating from the 18th and 19th centuries share metallurgical characteristics similar to those of material coming from a shipment of ammunition found in the wreck of a sunken French ship from the battle of Trafalgar. The analyses show that the base material is grey cast iron with a carbon equivalent of 4.94 and a ferritic–perlitic matrix, in which the high phosphorus content has led to the formation of iron phosphide compounds in conjunction with a homogeneous distribution of carbon graphite flakes of Type C. In addition, corrosion products from samples revealed the presence of various crystalline iron compounds (X‐ray diffraction), mostly highly chlorinated iron compounds identified as akaganeite. X‐ray fluorescence identified various characteristics of the corrosion products as a function of the sampling depth. FT–IR spectroscopy revealed that the main difference between the corrosion products (internal and external) is determined by the number of organic species. Differential scanning calorimetry corroborated that these corrosion products are thermally stable compounds at elevated temperatures.

Characterization of two iron bullets from the royal ammunition factory of Eugi (Spain)

“…The steadite is a ternary eutectic composed of austenite, cementite and iron phosphide (Fe 3 P) with at least 10 wt% of phosphorous. Eutectic grains surrounded by a cellular phosphide network have been observed in previous works [12,[20][21].of different phases in the sinters. That means that only the proportion of the phases in the samples changed.…”

“…The obtained values are in strong concordance with the resultant microstructure since the E1 bullet had a higher hardness value of around 500 HV. In the literature, it can be observed that the average hardness of this phosphide eutectic was around 482 HV and the pearlite 252 HV [12]. Therefore, the E1 bullet hardness values can be associated with a cast iron with high steadite content.…”

“…The most significant differences between both bullets were related to the silicon and phosphorus contents. In literature, most works showed that projectiles presented a phosphorus content in the range of 0.07 -0.7 wt% P, and silicon content from 0.53 wt% to 1.6 wt% Si [9][10][15][16][17], except the cannonball analyzed by M. Hernández et al [12] which showed a higher amount of phosphorus (1.4 wt%). In this work, for E1 bullet the content in phosphorus and silicon was 0.113 wt% and 1.63 wt%, respectively.…”

“…In spite of the huge advances that archaeometallurgy has experienced in recent years, there are few reports related to antique projectiles [7][8][9][10][11][12][13][14][15]. The majority of the analyzed projectiles belong to the 18 th and 19 th centuries.…”

“…The use of such manganese concentration in cast iron to avoid gas holes and porosity, indicated a post-1839 manufacturing date. Hernández et al characterized cannonballs found in the Fortress from San Juan de Ulúa, México [12]. The analyzed specimens were composed of grey cast iron with steadite.…”