Why can’t regular stainless steel replace high-temperature alloys?

Standard stainless steel loses tensile strength rapidly above 550°C and suffers severe creep under constant load. Its surface oxide film peels off easily above 600°C, causing rapid material thinning and failure. High-temperature alloys form dense, stable protective oxide layers and contain reinforcing phases that resist grain flow under heat. Even above 900°C, they keep bearing capacity that stainless steel completely fails to match.