We generally use the English word "metal" for metal in general and for heavy metal. Some specific subgenres use the Swedish word instead, e.g. death metal = either dödsmetall or the English term. For the most part, you can always use English "metal", and in some cases you can also use the Swedish metall, so it's easier to just default to English.
Either way, metalheads tend to be nice people who wouldn't dream of being insulted by a slight error. :)