Can valves made of 15CrMo be replaced with 1Cr5Mo?

It should be possible; the material used later has a higher operating temperature.

No. At around 450°C, a high Cr content can effectively prevent carbon graphitization and the formation of nodules; it is therefore recommended not to replace it.

Absolutely. In terms of composition, both 15CrMo and 1Cr5Mo belong to low-alloy chromium-molybdenum steels. The Cr content in 15CrMo ranges from 0.8% to 1.1%, while the Mo content ranges from 0.4% to 0.55%. The Cr content in 1Cr5Mo is between 4% and 6%, while the Mo content is between 0.45% and 0.6%. Organically speaking, both 15CrMo and 1Cr5Mo belong to pearlitic heat-resistant steels; the maximum operating temperature for 15CrMo is 550°C, while that for 1Cr5Mo is 600°C. In terms of application, chromium-molybdenum steel is widely used in the petrochemical industry for high-temperature oils and gases, steam, and hydrogen-containing media. Therefore, under the operating conditions specified by the poster (medium-pressure steam, temperature of about 450°C, pressure of about 4.0 MPa), it is fully suitable.

Your view is debatable: 1. Graphitization is a phenomenon in which changes occur in the microstructure of steel (primarily due to the decomposition of carbides), resulting in the formation of graphite in aggregates, which leads to a decrease in strength, ductility, and creep resistance. 2. The chemical composition of the material is one of the important factors affecting graphitization. Materials that are significantly affected by graphitization include carbon steel, carbon-manganese steel, carbon-molybdenum steel, etc., while other materials are only minimally affected. 3. Furthermore, graphitization is highly dependent on temperature and also related to exposure time. Because the decomposition of carbides requires temperature, and diffusion and aggregation into graphite also require temperature. Generally, graphitization occurs only when carbon steel and carbon-manganese steel are used for extended periods at temperatures above 425°C, and carbon-molybdenum steel at temperatures above 468°C. 4. According to API571, graphitization has occurred in carbon-molybdenum steels with a Mo content below 1%, but adding more than 0.7% Cr to the steel can eliminate graphitization. In summary, buddy’s view is debatable.

The main consideration is the ballitization of the material; it is described in API571, so please take that into account.

Bro, you didn’t read carefully: 1. The mechanisms of spheroidization and graphitization are similar, as both involve changes in the internal structure; the difference is that graphitization results in the formation of graphite, while spheroidization involves the aggregation of carbides into spheres. 2. Spheroidization and graphitization are competitive within the overlapping temperature range. At temperatures above 552°C, graphitization occurs after spheroidization, whereas at temperatures below 552°C, it occurs before the steel is fully spheroidized. 3. The spheroidization rate depends on temperature and the initial microstructure; it can occur within a few hours when exposed to temperatures above 552°C, whereas it may take several years at temperatures above 454°C. 4. Organically, annealed steel is more resistant to spheroidization than normalized steel; coarse-grained steel is more resistant to spheroidization than fine-grained steel; and fine-grained silicon-killed steel is more resistant to spheroidization than aluminum-killed steel. Generally, 15CrMo is treated by normalizing followed by tempering, while 1Cr5Mo is subjected to full annealing or isothermal annealing (the microstructure of 5Cr steel in the annealed state is more stable than that in the normalized state, as the annealed state corresponds to the most stable microstructure). Therefore, from an organizational perspective as well, 1Cr5Mo is more resistant to spheroidization. 5. Also, you said “No.” At around 450°C, a high Cr content can effectively prevent carbon graphitization and the formation of nodules; it is therefore recommended not to replace it. “The original poster used 1Cr5Mo in place of 15CrMo – isn’t that contradictory?