Control and low-temperature characteristics of seamless steel pipe
(1) decreased P, S content. By using high-quality components suitable scrap and slag refining to meet the needs off S, made by electric furnace slag and high alkalinity strict control of the steel slag to reduce the P content in steel.
(2) control C content. EAF and refining phase matching is an effective means of achieving precise control of the C content, and strictly control the C content of the end of the furnace smelting, refining and using argon gas flow rate is increased in diameter and snorkel blowing ways on VD or RH vacuum furnace de-C, in order to ensure accurate C content pipeline requirements;
(3) ensure that the seamless steel pipe content of Ca and weak mixing time, strengthen the interface between the management casting heats up and down, as well as the protection of casting, can effectively reduce non-metallic inclusions in steel.
Heat treatment process control: seamless steel pipe heat treatment is established within a reasonable temperature range, the temperature range is determined by the CCT curve of steel. The design of steel were 840 ℃ austenitizing insulation 3min test CCT curve, the cooling rate observed organizational relationship with microstructure, heat treatment process to determine the time of production.
Rolling Process Control: low-temperature seamless steel pipe specifications for Φ60 ~ 720mm × 4 ~ 10mm, for a geometry precision thin wall thickness will directly affect the customer’s product quality and efficiency of construction welding in the construction site, so the use of PQF pipe Mill rolling, tube and adjust the heating temperature and time, reducing the eccentric piercing process and reduce uneven thickness.
Through the above process measures to develop a low-temperature seamless steel pipe has the following characteristics:
(1) a wide range of sizes, diameter from 60mm to 720mm;
(2) has an excellent low-temperature toughness and corrosion resistance, through a rigorous anti-corrosion evaluation test;
(3) heat treatment after elbow bend, bend the performance has been improved.
In summary, the low-temperature heat treatment need to be considered seamless heating rate and holding time, avoid burnout and oxide scale steel pipe production, while controlling the austenite grain size to improve the strength and toughness of steel and corrosion resistance.