How is the corrosion resistance of 904L stainless steel at different temperatures

Due to its alloy composition of high chromium (23%-28%), high nickel (19%-23%), high molybdenum (4%-5%), and copper (1.0%-1.5%), 904L stainless steel demonstrates excellent corrosion resistance over a wide temperature range. However, as the temperature rises, its corrosion resistance will be affected to a certain extent, as detailed below: 

At normal temperature (≤60℃): extremely strong corrosion resistance

At normal temperature, 904L demonstrates outstanding resistance to a variety of corrosive media: 

In neutral or weakly acidic environments, such as ultrapure water and dilute organic acids (citric acid, acetic acid), the passivation film is stable and there is almost no corrosion (corrosion rate ≤ 0.01mm/year). 

Chloride ion environment: It can resist pitting and crevice corrosion even in a 3% NaCl solution (critical pitting temperature CPT ≈ 50℃), which is much higher than that of 316L (CPT ≈ 25℃). 

In slightly oxidizing media, such as dilute nitric acid (≤10% concentration), the corrosion resistance is stable with no obvious corrosion. 

2. Medium to high temperatures (60 - 150℃): Corrosion resistance slightly decreases but still outperforms conventional stainless steel. As temperature rises, it accelerates the corrosion reaction. The corrosion resistance of 904L is more significantly affected by the type of medium: 

Neutral / weakly corrosive media: In purified water (80-120℃), the corrosion rate remains low (≤0.05mm/year), making it suitable for semiconductor hot water cleaning pipelines. 

When the chloride ion concentration is relatively high, such as in a 2% NaCl solution at 80℃, the risk of pitting corrosion increases. However, the critical pitting temperature is still higher than that of 316L (904L ≈ 40℃ vs 316L ≈ 10℃), and it can still be tolerated for a short period. 

Oxidizing medium: In 50% nitric acid (80°C), its corrosion resistance is superior to that of 316L, but uniform corrosion may occur over long-term use (rate ≈ 0.1 - 0.3 mm/year). 

3. High temperature (＞150℃): Corrosion resistance significantly decreases, use with caution.

Strong corrosive media: In highly corrosive environments such as high-temperature (180℃) concentrated hydrochloric acid and sulfuric acid, the passive film of 904L is prone to damage, and the corrosion rate increases significantly (＞0.5mm/year). It is not recommended for use. 

Steam / Hot water: In saturated steam (100 - 121℃) or high-pressure hot water, if the water quality is pure (low chloride ions), short-term operation is still possible, but the formation of oxide scale should be regularly inspected. 

Summary

The corrosion resistance of 904L is best in low-chloride and weakly corrosive environments at normal to medium temperatures (≤120℃), making it suitable for applications such as semiconductor ultra-pure water and the transportation of weak acids in the chemical industry. However, at high temperatures (>150℃) or in strongly corrosive media, its advantages diminish. In such cases, a specific assessment of the working conditions is necessary, and in some cases, it may be advisable to apply anti-corrosion coatings or choose more heat-resistant nickel-based alloys. Compared with 316L, 904L has superior corrosion resistance across the entire temperature range, especially in medium-temperature environments with chloride ions.