Study And Exploitation Of X80Pipeline Bends Steel On Composition And Process

X80pipeline bends steel is one of micro-alloy steels which are much necessarily to be studied and developed. Its application can result in large economic and social performance. Lab tests have been done to study on composition, processing and property of X80bends steel. Through the analyses, the production program has been optimized. Future thickness of22mmX80bends pipeline steels has been industrially produced. The strength-toughness, the microstructure and the phase transformation of X80bends steel have been systematically studied by mechanical test, microscopic analysis method and means of simulation technique. Moreover the heat-treated processing is firmed by the imitated heat tests and the correlation investigation of process, microstructure and property.The results of rolling tests in lab show that the existence of Mo does much effect on rising strength and increasing the rate of acicular ferrite. However it’s no much different in property when Mo content changes from0.10%to0.20%. Therefore controlling Mo content during0-0.20%in the steel is suitable and carbon equivalent of the steel without molybdenum should be0.01-0.02%higher than the one with molybdenum.Through analysis of phase transformation it can be sure that microstructure of X80bends steel with Mo is mainly made up with PF and P when the cooling rate is0.5℃/s and there will be no P in microstructure if the cooling rate reaches to1℃/s. While the rate is not lower than2℃/s the content of PF will decrease obviously. The alloying agents in the steel add stability of austenite and inhibit phase transformation of ferrite, which makes it easily to gain the microstructure mainly with low-carbon bainite and M/A in industrial production.The simulation tests of processing show that property of X80bends steel will be optimized clearly with microstructure grain refining if increasing the decrement in the temperature province without recrystallization. Meanwhile phase transformation of ferrite will be promoted with the addition of deformation.It can be concluded from the results of mechanical test and micro-analysis that the suitable microstructure of X80bends steel should be mainly composed of acicular ferrite and grain bainite. It can bring excellent strength-toughness and fine corrosion resistance to the steels.The results of heat-treated tests show that processing parameters, especially quenching temperature, have visible influence on strength-toughness of X80bends pipe. The mutation of property will appears when quenching temperature reaches to980℃, strength rises largely and toughness reduces obviously. Through the tests and analysis the proper heat treatment parameters of X80bends pipe have been defined, quenching temperature:940℃, holding time:1.35min/mm, tempering temperature:600℃, holding time:2.7min/mm.