Steel is very strong, and in its unaltered state, can withstand significant natural and man-made abuse. Properly installed and maintained hollow metal doors often last 30 years or longer. When repairs are necessary, they typically occur in the field at relatively low cost.
Steel doors have a low total cost of ownership compared to other door materials. You may hear these doors and frames referred to as “steel” or “hollow metal”. Generally, architects refer to them as “steel” and distributors and manufacturers say “hollow metal”. Please note that they are referencing the same product and the terminology may be used interchangeably