What is the typical chemical composition of CrMo steel alloy steel pipe?
The main alloying elements of CrMo steel alloy steel pipe are chromium (Cr) and molybdenum (Mo), and typical grades are 15CrMo, 12Cr1MoV, etc. The chemical composition of 15CrMo is usually: carbon (C) 0.12%-0.18%, chromium (Cr) 0.80%-1.20%, molybdenum (Mo) 0.40%-0.55%, and contains a small amount of silicon (Si), manganese (Mn), phosphorus (P), sulfur (S). The addition of chromium improves the oxidation resistance and corrosion resistance of steel, while molybdenum enhances high temperature strength and creep resistance. This combination of ingredients makes CrMo steel suitable for high temperature and high pressure environments, such as power station boilers and petrochemical equipment.
What are the mechanical properties of CrMo steel alloy steel pipe?
CrMo steel alloy steel pipe has excellent mechanical properties. The tensile strength of 15CrMo is usually 440-640MPa, the yield strength is ≥295MPa, and the elongation is ≥19%. 12Cr1MoV has higher high temperature strength due to the presence of vanadium (V), and can still maintain a high creep resistance at 550℃. The hardness of CrMo steel is usually HB170-220, which can be further improved after quenching and tempering. Compared with ordinary carbon steel, CrMo steel has a slower strength drop at high temperatures, so it is widely used in thermal pipelines and pressure vessels.
What is the high temperature resistance of CrMo steel alloy steel pipe?
CrMo steel alloy steel pipe performs well in high temperature environments. 15CrMo can be used for a long time below 500℃, and 12Cr1MoV is suitable for high temperature conditions below 580℃. The dense oxide film (Cr₂O₃) formed by chromium can effectively prevent further oxidation, while molybdenum improves the creep resistance of steel. In power plant boilers, CrMo steel pipes are often used in superheaters and reheaters, and can withstand the erosion of high-temperature and high-pressure steam. Compared with austenitic stainless steel, CrMo steel has a lower cost, but higher-grade alloy steels are still required in extremely high-temperature (>600℃) environments.
What is the welding performance of CrMo steel alloy steel pipes?
CrMo steel alloy steel pipes have good welding performance, but due to their high alloy content, preheating (200-300℃) and post-weld heat treatment (600-650℃ annealing) are required during welding to prevent cold cracks and hydrogen embrittlement. Commonly used welding methods include manual arc welding (using R307 electrodes), submerged arc welding and TIG welding. For thick-walled pipes, the interlayer temperature needs to be controlled and multi-pass welding is used to reduce welding stress. Non-destructive testing (such as UT, RT) must be performed after welding to ensure the quality of the weld.
What are the main heat treatment processes for CrMo steel alloy steel pipes?
The heat treatment processes of CrMo steel alloy steel pipes mainly include normalizing, tempering and quenching and tempering. Normalizing (900-930℃) can refine grains and improve strength and toughness; tempering (600-680℃) is used to eliminate internal stress and improve plasticity; quenching and tempering (quenching + high temperature tempering) can obtain the best comprehensive mechanical properties. For boiler tubes, normalizing + tempering process is usually used to meet high temperature strength requirements. CrMo steel after heat treatment also needs hardness testing and metallographic analysis to ensure uniformity of structure.
