Which elements determine the high-temperature resistance of stainless steel pipes

The elements that determine the high-temperature resistance of stainless steel tubes mainly include chromium, nickel, molybdenum, titanium, niobium, aluminum, silicon, etc. Here is the detailed analysis:

Chromium (Cr) forms a stable oxide film: Chromium is one of the key elements for enhancing the high-temperature resistance of stainless steel. At high temperatures, chromium can react rapidly with oxygen, forming a dense and stable chromium oxide (Cr₂O₃) protective film on the surface of the stainless steel. This oxide film can prevent oxygen from further penetrating inward, thereby slowing down the oxidation corrosion rate of the metal and enabling the stainless steel to maintain good stability in high-temperature environments. Generally, the higher the chromium content in stainless steel, the better its high-temperature oxidation resistance.

Stabilizing the austenitic phase: Nickel is an important element for forming and stabilizing the austenitic phase. At high temperatures, the austenitic phase has good thermal stability and high-temperature strength, maintaining a good microstructure and not undergoing phase changes or grain growth, thus enabling the stainless steel tube to maintain good mechanical properties and dimensional stability in high-temperature environments.

Improving thermal processing performance: Nickel can reduce the temperature range for hot processing of stainless steel, improving its plasticity, making the stainless steel easier to be formed during high-temperature processing, and reducing the occurrence of thermal cracks and other defects, indirectly improving the performance of stainless steel in high-temperature environments.

Increasing high-temperature strength: Molybdenum can be solid-solved into the crystal lattice of stainless steel, through solid solution strengthening, to increase the high-temperature strength and hardness of stainless steel, enhancing its ability to resist deformation and fracture at high temperatures. In high-temperature and high-pressure working environments, stainless steel tubes containing molybdenum can withstand greater stress and maintain good structural integrity.

Enhancing the stability of the oxide film: Molybdenum can work synergistically with elements such as chromium to further improve the stability and density of the oxide film, preventing the invasion of oxygen and other harmful elements at high temperatures, thereby enhancing the high-temperature corrosion resistance of stainless steel, especially in some high-temperature environments with corrosive media, the effect of molybdenum is more significant.

Titanium (Ti) and niobium (Nb) prevent intergranular corrosion: Titanium and niobium have a stronger affinity for carbon than chromium. At high temperatures, they can preferentially combine with carbon to form stable carbides, such as TiC and NbC, thereby avoiding the precipitation of chromium carbides at grain boundaries and preventing intergranular corrosion, ensuring the corrosion resistance and mechanical properties of stainless steel in high-temperature environments.

Refining grains: Titanium and niobium can also act as nuclei during the solidification and heat treatment of stainless steel, promoting grain refinement. The refined grains can increase the strength and toughness of stainless steel, improve its high-temperature performance, and enable the stainless steel tube to have better fatigue and creep resistance in high-temperature environments.

Aluminum (Al) forms high-melting-point oxides: Aluminum can react with oxygen at high temperatures to form high-melting-point aluminum oxide (Al₂O₃), which has good high-temperature performance and chemical stability, forming an additional protective film on the surface of the stainless steel, working together with the chromium oxide film to further enhance the high-temperature oxidation and corrosion resistance of stainless steel.

Improving steel's oxidation resistance: Aluminum can reduce the oxygen content in steel, reducing the formation of oxide inclusions, and at the same time, it can improve the oxidation resistance of steel, making stainless steel less prone to oxidation in high-temperature environments.

Silicon (Si) enhances the performance of the oxide film: Silicon can improve the density and stability of the oxide film in stainless steel at high temperatures. At high temperatures, silicon can promote the formation of a more continuous and protective oxide film, preventing oxygen and other corrosive media from contacting the metal matrix, thereby enhancing the high-temperature performance of stainless steel. Enhance high-temperature strength: Silicon in stainless steel has a certain solid solution strengthening effect, which can increase the high-temperature strength and hardness of stainless steel. This helps stainless steel pipes maintain the stability of their shape and size in high-temperature environments, and resist deformation and damage under high temperatures.