The Influence Of Chemical Composition On Pipeline Steel Pipe
The Influence of Chemical Composition on Pipeline Steel Pipe
FATT is the important indicators of pipeline steel brittle transition, determines the function of the low temperature of pipeline steel, directly affects the use scope of pipeline steel. Material chemical composition has a great influence on the indicators, influence in detail as follows:
1. C content
Carbon content of steel has a great influence on the ductile and brittle transition temperature, with the increase of carbon content in steel, plastic material resistance increases, the ductile and brittle transition temperature is remarkably improved, and the transformation temperature range is widened, and it is because that the carbon content makes the pearlite increase so that increase the brittleness of the steel.
2. Mn content
Manganese can be possessed of ferrite and pearlite transformation, and promote the formation of bainite, so that improve the pipeline steel toughness, following the increase of Mn content, ductile to brittle transition temperature decreased.
3. Mo content
Molybdenum can refine grain and second phase particle formation, so that to improve the toughness of the steel, and affect the ductile and brittle transition temperature.
4. S, P content
Impurities such as sulfur and phosphorus is easy to gather in the grain boundary, and this will reduce the grain boundary surface and produce the intergranular fracture, at the same time, it will reduce the brittle fracture stress, affect the ductile and brittle transition temperature.
5. Si content
Silicon has a bad effect on toughness, the control of Si content plays a role in the decrease of ductile and brittle transition temperature.
6. Nb content
Niobium in hot rolling process has the effect of precipitation strengthening, increased the strength of the pipeline steel and reduced the toughness, however, at the same time, the Nb can refine grain and improve strength and toughness of steel.
7. Ti content
Titanium because of its strong affinity with nitrogen, and then easily formed TiN, can fix nitrogen in steel, TiN in steel distributes with fine dispersion particle, and can reduce the slab heating austenitizing temperature, control the austenitic grain growth, so as to achieve the purpose of fine grains, effectively improve the material toughness.
8. V, AI content
Aluminum and vanadium in steel has the ability of precipitation strengthening, fine-grain strengthening and grain boundary strengthening effect, thus to lower ductile brittle transition temperature.
In conclusion, for pipeline steel FATT, the content of S and P should be strictly controlled, and the use of Nb, V, Al microalloying, can refine grain, is beneficial to improve the brittle ductile transition, in addition, Ti can modify the impurity material, improve the toughness, at the same time, reasonable adjust the C, Mn, Mo content.