The austenitization behaviors of two high niohium-containing X80 pipeline steels with different titanium contents, including the dissolution of microalloying precipitates and the austenite grain growth, were investiga...The austenitization behaviors of two high niohium-containing X80 pipeline steels with different titanium contents, including the dissolution of microalloying precipitates and the austenite grain growth, were investigated by using physical-chemical phase analysis method and microstructural observation. The results illustrated that most niobium could be dissolved into austenite during soaking at 1 180 ℃, whereas little amount of titanium could be dissolved. It was found that during soaking, the austenite grain growth rate was initially high, and then decreased after soaking for 1 h; moreover, the austenite grains grew up more rapidly at temperatures above 1 180 ℃ than below 1 180 ℃. The results show that the steel with titanium content of 0. 016% has a larger austenite grain size than that with titanium content of 0. 012% under the same soaking conditions, which is explained by considering the particle size distribution.展开更多
In order to ensure the safety of long-distance oil and natural gas transmission pipeline installed in seismic and/or permafrost region, high strength pipeline steel with excellent deformability has been developed. The...In order to ensure the safety of long-distance oil and natural gas transmission pipeline installed in seismic and/or permafrost region, high strength pipeline steel with excellent deformability has been developed. The ferrite and bainite dual phase pipeline steel is a very important kind of high deformability pipeline steel. Polygonal ferrite is a key microstructure in ferrite and bainite dual phase deformability pipeline steel. Ferrite evolution during isothermal process at 700 ℃ after 50% deformation at 800 ℃ was conducted by using a Gleeble-3800 thermal simulator, and microstructure was characterized by using an optical microscope, a scanning electron microscope and a transmission electron microscope. There are two types of ferrite, ferrite with high density dislocation and ferrite with a little dis location. There is about 7% （volume percent） deformation induced ferrite （DIF） for compression of 50% at 800 ℃ and strain rate of 1 s-1. During the isothermal process at 700 ℃, with the holding time increasing, ferrite volume percent, ferrite grain number and average ferrite grain size increase. As the holding time is prolonged, dislocation re-covery occurs in DIF. There are secondary phases in ferrite when the holding time is too long, and secondary phases and dislocation formation in dislocation pinning.展开更多
The influence of alloying design,controlled rolling technology and cooling system of X100 hot-rolled strips on microstructure and micro-hardness has been discussed in detail in this paper.The results show that optimal...The influence of alloying design,controlled rolling technology and cooling system of X100 hot-rolled strips on microstructure and micro-hardness has been discussed in detail in this paper.The results show that optimal chemical composition range of X100 hot-rolled strips is obtained on the basis of X80 by increasing contents of C,Mn,Ni and Mo of X80.The granular bainite microstructure could be refined and the volume fraction and size of M-A islands could be controlled in a reasonable range by reasonably regulating cooling rate and coiling temperature of X100 pipeline steel,which ensure high strength and toughness of X100 pipeline steel.展开更多
基金Item Sponsored by National Key Technologies Research and Development Program of China(2006BAE03A15)
文摘The austenitization behaviors of two high niohium-containing X80 pipeline steels with different titanium contents, including the dissolution of microalloying precipitates and the austenite grain growth, were investigated by using physical-chemical phase analysis method and microstructural observation. The results illustrated that most niobium could be dissolved into austenite during soaking at 1 180 ℃, whereas little amount of titanium could be dissolved. It was found that during soaking, the austenite grain growth rate was initially high, and then decreased after soaking for 1 h; moreover, the austenite grains grew up more rapidly at temperatures above 1 180 ℃ than below 1 180 ℃. The results show that the steel with titanium content of 0. 016% has a larger austenite grain size than that with titanium content of 0. 012% under the same soaking conditions, which is explained by considering the particle size distribution.
文摘In order to ensure the safety of long-distance oil and natural gas transmission pipeline installed in seismic and/or permafrost region, high strength pipeline steel with excellent deformability has been developed. The ferrite and bainite dual phase pipeline steel is a very important kind of high deformability pipeline steel. Polygonal ferrite is a key microstructure in ferrite and bainite dual phase deformability pipeline steel. Ferrite evolution during isothermal process at 700 ℃ after 50% deformation at 800 ℃ was conducted by using a Gleeble-3800 thermal simulator, and microstructure was characterized by using an optical microscope, a scanning electron microscope and a transmission electron microscope. There are two types of ferrite, ferrite with high density dislocation and ferrite with a little dis location. There is about 7% （volume percent） deformation induced ferrite （DIF） for compression of 50% at 800 ℃ and strain rate of 1 s-1. During the isothermal process at 700 ℃, with the holding time increasing, ferrite volume percent, ferrite grain number and average ferrite grain size increase. As the holding time is prolonged, dislocation re-covery occurs in DIF. There are secondary phases in ferrite when the holding time is too long, and secondary phases and dislocation formation in dislocation pinning.
文摘The influence of alloying design,controlled rolling technology and cooling system of X100 hot-rolled strips on microstructure and micro-hardness has been discussed in detail in this paper.The results show that optimal chemical composition range of X100 hot-rolled strips is obtained on the basis of X80 by increasing contents of C,Mn,Ni and Mo of X80.The granular bainite microstructure could be refined and the volume fraction and size of M-A islands could be controlled in a reasonable range by reasonably regulating cooling rate and coiling temperature of X100 pipeline steel,which ensure high strength and toughness of X100 pipeline steel.
