Research On Process Optimization Of Offshore Platform Steel E690

The E690 offshore platform steel is a kind of super high strength steel plate with yield strength can be up to 690 Mpa. The manufacturing technique of E690 is well developed abroad, while it is relatively poor inland, only few enterprises can produce offshore platform steel. This project study the basic features of pilot product E690 from Xinyu iron and Steel Group, and put forward relevant process optimization methods, the details are as follows:Theoretical calculation of second phase precipitate, the effects of the key elements(Ni,Cu, Ti) on precipitation and calculation of temperature fator effect on the elements contents of different precipitation are performed by software Thermo-calc. Which afforded proof of process optimization on composition and continuous casting process. The results show that the precipitation order is: Ti4C2S2,FCC_A1#2,Mn S,B2 M,M3B2,BN_HP4,FCC_A1#3,Al N,HCP_A3#2,KSI_CARBIDE,MC_ETA,M23C6,M7C3,MC_SHP,M3 P, and the contents of alloy elements(Ni、Cu、Ti) have a certain effect on the precipitation. The copper content can increase to 0.2% moderately.Designing orthogonal experiments to conculate various factors which effect the austenite dynamic recrystallization, such as deformation temperature 、 deformation quantity 、deformation rate. Study the effect of different deformations on the dynamic recrystallization of austenite by performing single channel test on the sample steel via Gleeble-3800 thermal simulation measurement. The analysis methods include rating grain size based on the austenite morphology of treated sample and conjoint analyzing the true stress-true strain curve.The results show that the most effective factor on the austenite recrystallization is deformation temperature, and then the deformation quantity, the last is deformation rate. The extremely low deformation rate can easily lead to intermittent dynamic recrystallization of austenite,which should be avoided as far as possible in production. A reasonable process parameters need to be controlled to produce crystalline grain of high granularity and well uniformity. The granularity can be up to 9.7 on the best treatment process(deformation temperature 950℃,deformation 50% and deformation rate 0.1s-1).Combined the achievements from studying high temperature plasticity、phase transition laws and thermal treatment process of E690(another project of our research team), as well as dynamic recrystallization laws of austenite. The optimize process include ingredients,continuous casting process, TMCP and thermal treatment of E690. The best processoptimizations are as follows: firstly, reduce the Nickel content to 2.00%, relatively increase the copper content no more than 0.2%, and increase the titanium content to 0.02%.Secondly, in order to reduce the mass precipitation of Al N、BN and Nb(C、N) on the grain boundary, as well as associated precipitation of BN and Mn S, the fluctuation of longitudinal and transverse temperature should be reduced during continuous casting process. The Slab straightening temperature should be controlled between 950℃ and 990℃ to avoid the third brittle zone. Thirdly, the accumulate deformati-on should be achieved to more than 50%, the deformation rate should be close to 0.1s-1under the conditions of rolling mill during TMCP.Lastly, set the hardening heat、temper temperature and temper time be 880℃、630℃ and120 min respectively and co-ntroll the cooling rate between 1 to 3℃/s on the thermal treatment process. The industrial test proved that these process optimizations have certain effect on the promotion of product performance.