Research On The Influence And Action Echanism Of Bauschinger Effect Within High Gradepipeline Steel

The most economical and favourable way to transport oil and natural gas is pipeline steel transportation Shougang Jingtang United Iron&Steel Co.,Ltd.(abbreviation:Jingtang company)product positioning to meetthe needs of national economic development and national industrial policy to the principle of market-oriented,the 21st century international advanced level of quality sheet metal base,so the development of high grade pipeline steel smelting technology has important significance.Since2011,Jingtang company start production of high-grade pipeline steel X80,management and technology has improved continuously,X80 pipeline steel production capacity of 45,000 tons per month.However,It due to fierce competition in the market,each steel plant think for the product cost control and more stringent quality requirements,the development of high grade pipeline steel products is critical for Jingtang conpanies.The pipeline level of X80,X90,X100 as well as X120 have entered the application stage.However,as the complex deformation processes which lead to the work-so fling due to Bauschinger Effect there exists a great mechanical properties defference after deformation compared to before.The complex phase composition within the pipeline steel matrix lead to a big reduction of yield strength among the deformation processes.Thus hidden safety concern appear in the use process.There fore,a thorough knowledge of the influence and the mechanisms of Bauschinger Effect to high grade pipeline steel are of great significance.In this article three chemical composition of X100 pipeline steel are designed.Simulation of rolling and coiling were tested to these steels in the laborary.The steels of each chemical conposition were coiling at 300℃,350℃,400℃ respectively.The mechanical properties were tested with the means of scanning electron microscopy and tension testing etc.The favourable chemical composition scheme was chosen.Tension testing were tested on the qualified X90 and X100 pipeline steels.With he application of SEM,TEM etc.The influences and mechanisms of Bauschinger Effect were analysised.The results showed that:with the coiling tenperature increase from 300℃,350℃ to 400℃ the composition of steel’s phase are acicular ferritemixed feature.The grain size increases with the raise of coiling temperature.Howener,the experimental steel with 0.25%Cr content showed a less coarse tendency,The results of 0.25%content steel coiling at 300℃,350℃,400℃ showed that:when coiling at 300℃ the yield strength is750MPa.When coiling at 400℃ the yield strength is 400MPa.The coiling temperature’s influence is intenser on yield strength than tensile strength.The grain boundary is composited with the boundary smaller than 15 degree and larger than 50 degree.The precipitates are mianly composited with Nb/Ti(C/N)within 50～200nmThe Bauschinger Effect tests’results of X100 pipeline steel show that the metallographic phases are consist of acicular ferrite laths and a small amount of polygonal ferrite.The pretension-compression test indicates that with the precompression increase the Bauschinger Effect value reaches to 194MPa,Bauschinger Energy Parameter reaches to 1.455,and Bauschinger Stress Parameter reaches to 0.409.Saturation phenomenon was viewed in the test accompanied by the increase of pretension.Preconpression-tension test shows that:with the precompression level reach 1.5%the Bauschinger Effect value reaches to 142MPa in reverse tension process.The twice compression process after pretension showed a decrease in Bauschinger Effect value which indicates there exists a inheritance in numerous reverse deformation.Cyclic loading test shows that there appeared a decease from 0.895 to 0.422 in Bauschinger Energy Parameter.A reverse tendency of Bauschinger Effect value was observed in cyclic loading test compared with pretension and precompression tests.