The most common and most likely answer to this crossword clue is the 8 letter word IRONWORK
I've seen this crossword clue in Financial Times
I
R
O
N
W
O
R
K
More clues leading to the result IRONWORK
Buddy explains!

The straight part
We know that "heavy metal piece" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heavy metal piece = ironwork.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IRONWORK mean?
IRONWORK noun- Anything made wholly or largely of iron, especially when used for decoration.
- An ironworks.