Study On The Fracture Behavior Of The Large Deformation Pipeline Steel

In this paper, the high strength-toughness and excellent deformability of a X100pipeline steel could be acquired by the heat treatment methods of the critical region accelerated cooling. The relationship of technology-micro structure-properties of pipeline steel with excellent deformability was established by material microscopic analysis method, Orthogonal test and mechanical properties test. Using CTOD test, electrochemical, anti hydrogen sulfide stress corrosion test, we also make a comparative study on the fracture behabior of the X100pipeline steel largely deformated and the ordinary X100pipeline steel.Research shows that the reasonable control of the heat treatment process parameters can improve the structure and mechanical properties of tissue X100pipeline steel. When the heating temperature is830℃, water-cooled cooling mode when the test steel available (B+F) duplex structure and large deformation pipeline to meet the mechanical properties.Resistance curve equation is obtained through the CTOD test of dual phase X100pipeline steel and X100pipeline steel were CTOD=0.5827×(2.2128×10-8+△a)0.6223and CTOD=0.7004×(1.8440×10-9+△a)0.8058, and double phase steel apparent initiation values δ0.05=0.090mm,conditions crack initiation values δ0.2=0.214mm and maximum load values δm=0.328mm are all more greater than the ordinary X100pipeline steel,which illustrate toughness and tearing strength of the double phase X100pipeline steel is increased.Corrosion electrochemical testing results showed that the smaller initial cooling temperature was830℃dual phase structure, and different corrosion rate wascold temperatures of dual phase steel was lower than that of the base metal, dual phase steel has good corrosion resistance. The large deformation of X100pipeline steel resistance to sulfide stress corrosion test showed that the better resistance to sulfide stress corrosion ability has obtained the pipeline steel.By observing the tensed and impacted fracture surface of the bainite and ferrite dual phase pipeline steel, we can get that the plastic deformation happens in the ferrite preferentially in the bainite and ferrite dual phase microstructure. With the development of plastic deformation, the dual phase microstructure gradually comes to the orientated distirbution. Crack nucleation usually adopts the inclusion (or second phase particles)nuclcation, phase interface nuclcation and ferirtic or bainite matirx nucleation. And the crackgrowth mainly adopts the ferirte. In the state of high stress, the crack is more extended bybainite. Use of dislocation pile，dislocation reaction theory explains bainite+ferirte phaseorganization crack initiation, expansion, and on this basis to establish a fracture model ferrite+bainite duplex organizations.