Q1: What are the key steps in the production process of 12Cr1MoVG steel pipes?
Steelmaking utilizes an electric arc furnace combined with LF/VD refining, with strictly controlled sulfur and phosphorus contents (S ≤ 0.010%, P ≤ 0.025%). Electromagnetic stirring is used during continuous casting to reduce segregation, and the ingots require slow cooling to prevent cracking. Hot rolling utilizes a piercing and rolling process, with the final rolling temperature controlled between 850 and 880°C. Heat treatment must include normalizing and tempering to ensure a uniform tempered bainite structure. Finally, UT/ET nondestructive testing and mechanical property testing are performed.
Q2: Why is normalizing and tempering necessary for 12Cr1MoVG?
Normalizing (930-960°C) homogenizes the austenite and eliminates rolled banding. Tempering (680-730°C) promotes carbide precipitation, improving toughness and stability. This process achieves the best combined mechanical properties (strength + ductility + toughness). High-temperature creep properties of unheat-treated steel pipes are significantly reduced. GB 5310 explicitly requires normalizing and tempering as mandatory delivery conditions.
Q3: What are the difficulties in producing 12Cr1MoVG welded steel pipe?
The welding consumables must match the base metal composition (e.g., R317 welding rod, Cr-Mo-V series). Preheat to 200-250°C before welding, and control the interpass temperature between 200-300°C. Immediately after welding, stress relief heat treatment at 720-750°C is required. Circumferential welds require 100% RT+UT testing to ensure the absence of incomplete fusion/cracks. For thick-walled pipes, welding should be performed in sections with controlled heat input (15-25 kJ/cm).
Q4: How can the core properties of thick-walled 12Cr1MoVG steel pipes (>50 mm) be guaranteed?
The steel ingots must be forged with center compaction, with a compression ratio ≥3:1. During rolling, a high reduction ratio (>60%) is used to eliminate core defects. The normalizing holding time is calculated as 2.5 min/mm (e.g., 4 hours for a 100mm wall thickness). Core samples are taken to verify impact energy (≥27J) and metallographic structure. Ultrasonic testing is performed to focus on core defects (flat-bottom holes Φ ≥3mm are rejected).
Q5: What are the main production standards for 12Cr1MoVG steel pipes?
National standards: GB 5310 (high-pressure boiler tubes) and GB 9948 (petroleum cracking tubes). International standards: ASTM A335 P11 (American standard) and EN 10216-2 (European standard). Special requirements: ASME SA335 (for nuclear power applications) and JIS G3463 (Japanese standard). CE/PED certification and a high-temperature performance report are required for export.
