Effect of cooling temperature on the microstructure and corrosion behavior of X80 pipeline steel

Dual-phase accelerated cooling(DPAC) was applied to X80 pipeline steel to obtain its microstructure with different amounts of bainite and ferrite. The microstructure, hardness, and polarization behaviors of the steel, cooled to different temperatures, were investigated. Results showed that, with decreasing cooling temperature, the amount of polygon ferrite(PF) increased while that of acicular ferrite(AF) decreased. The amount of bainite correspondingly decreased, except when cooled to 760°C. Moreover, the grain size of ferrite increased. The corrosion behaviors of different phases were distinct. Martensite/austenite(M/A) islands presented at the grain boundary of the PF phase caused small pits. Numerous micro-corrosion cells were formed in the AF and bainite phases, where micropores were prone to form. X80 pipeline steel cooled to 700°C had the best corrosion resistance in the simulated seawater. The decreased amount of the PF phase reduced the area of cathode, resulting in slight corrosion. About 40 vol% of the bainite phase provided strength while the PF phase provided adequate ductility to the X80 steel. It was concluded that the appropriate cooling temperature was 700°C for ideal corrosion resistance and mechanical properties.

Cost reduction of alloying element in high strength steel plate by optimization of controlled cooling technology

Controlled cooling technology is getting more and more attention with the development of thermal-mechanical control process. In the past decade, achieving the given finish cooling temperature was the sole goal for the technology. However ,with the research and development of new steels such as super high strength steel, researchers have in recent years realized the determinate effects that different cooling paths have on the finish cooling temperature and paid more attention to the control of the cooling rate. This paper focuses on not only the optimization of the controlled cooling system with high precision and fast cooling rate, but also the research and development of the high strength steel plate with reduced alloying component.

Properties and homogeneity of 550-MPa grade TMCP steel for ship hull

Ultra low carbon steels by the thermal mechanical control process（TMCP） with less Ni,Cr,and Mo contents have been developed for 550 MPa grade heavy gauge ship hulls and offshore structures.The relationships among microstructures,process,and properties of the studied steel have been investigated.A series of accurate control technologies have been developed for this kind of steel.Cu microalloying and TMCP＋relaxation precipitation control（RPC）＋accelerated cooling process were employed to optimize the mechanical properties and ensure the homogeneity of the 80-mm thick plate.The microstructures of thin plates slightly changed from surface to center,but the micro-structures of the heavy gauge plate（80 mm） changed notably.Adopting the simple composition,it can meet the requirement of thin plates by adopting a few microalloys.As for thick plates（80 mm）,a little higher Cu and Ni contents should be adopted.These steels can meet the needs without tempering.By these ways,the properties of the steels can be optimized,and the cost can be decreased notably.

Research on TMCP technology for the manufacture of SUS 304 L austenitic stainless steel plates

Two thermo-mechanical controlled processes （TMCP） including controlled rolling and accelerated cooling are proposed for the production of heavy gauge SUS 304 L austenitic stainless steel plates with different strengths and other characteristics. Based on the recrystallization mechanism and carbide precipitation behavior of SUS 304 L austenitic stainless steel ,TMCP provides a powerful means to control the microstructure and precipitation of the hot rolled steel plate by the controlled rolling and accelerated cooling process. The dislocation density and grain size are the main factors in determining the strength of the stainless steel plates. Therefore ,it is necessary to strictly control the hot rolling parameters, including parameters such as the finish hot rolling temperature in the recrystallization temperature region and the total reduction in the non-recrystallization region. Furthermore, in order to avoid carbide precipitation and guarantee the intergranular corrosion resistance of TMCP SUS 304 L austenitic stainless steel, a critical cooling rate after rolling is determined.

Microstructure Characterization of High-heat-input Welding Joint of HSLA Steel Plate for Oil Storage Construction

In this paper, microstructure and mechanical properties of welding metals in 610 MPa high strength low alloy （HSLA） were studied after high-heat-input welding. Both the base material and the weld joint proved excellent strength and toughness by vibratory electrogas arc （VEGA） welding under 90 to 100 kJ/cm heatinput. The heat-affected zone （HAZ） was comprised of fine-grain zone （FGZ） and coarse-grain zone （CGZ）, which characterizes fine granular structure and lathing-bainite substructure, It has found that large quantity of dispersed TiN and M23E6 precipitates restrain structure growing in HAZ and strengthen the weldment together with dislocations in the welded joint.

Combined Effects of Nb and B MicroAlloying in Molybdenum Based Ultra Low Carbon Bainitic (ULCB) Steels

ULCB steels have a great potential for structural as well as automotive applications due to the lean alloying concept and the favorable combination of strength and ductility.These steels are being considered as the material of choice for many advanced applications where yield strength above 500 MPa is required to reduce component weight.Traditionally Mo has been a key alloying element in producing such steels.In order to push the property envelope of ULCB steels it is interesting to combine Mo alloying with the microalloying elements Nb and B.Cross effects between these elements bear synergies that cannot be achieved by single alloying.The paper demonstrates how these synergies can be beneficially used in combination with appropriate processing.

Microstructure Refinement and Precipitation Characteristics of TMCP-Processed Plates for Pipeline Applications

The influence of technological parameters of controlled rolling and accelerated cooling (TMCP-processing) on microstructure and mechanical properties of plates with thickness of 25 mm and more at the mill "5000" of OJSC "Мagnitogorsk Iron and Steel Works" were investigated.The necessity of formation of fine-grained ferrite-bainite microstructure without elongated areas of coarse lath bainite for achievement of DWTT properties is proved.Precipitation conditions and type of Nb(C,N) and (Nb,V)(C,N) particles with the size of less than 10 nm in the process of rolling and additional tempering are defined.