There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Enhanced ductility and toughness in an ultrahigh-strength Mn-Si-Cr-C steel: The great potential of ultrafine filmy retained austenite

The effect of different microstructures on the tensile and toughness properties of a low alloy medium carbon steel (0.28C–1.4Si–0.67Mn–1.49Cr–0.56Mo wt%) was investigated, comparing the properties obtained after the application of selected quenching and partitioning (Q&P) and quenching and tempering (Q&T) treatments. After Q&T the strength–toughness combination was the lowest, whereas the best combination was achieved by Q&P, as a result of the carbon depletion of the martensite and the high stabilization of the austenite. Nonetheless, the presence of islands of martensite/austenite (MA) constituents after Q&P treatments prevented the achievement of toughness levels comparable to the ones currently obtainable with other steels and heat treatments.

Microstructure, tensile and toughness properties after quenching and partitioning treatments of a medium-carbon steel

There has long existed a controversy regarding the formation of the bainite phase in steels. Nonetheless, following the clear identification of bainite in 1930, several characteristic features associated with the bainite transformation became well established. These features include: the classification into upper and lower bainite; the existence of a bainite start temperature; and the incomplete reaction phenomenon. Accordingly, two competing theories have been developed to explain the bainite transformation. However, no overriding consensus has been reached as to which is correct. The first theory invokes a diffusion controlled transformation, describing the growth of bainite via the propagation of ledges – a series of steps on the transformation interface. The second interpretation favours a displacive, diffusionless transformation. Bainite growth occurs via the autocatalytic nucleation and growth of successive subunits or platelets. Over time, a wealth of techniques has been implemented in orde...

The Bainite Controversy

Three-body abrasive wear of carbide-free bainite, martensite and bainite-martensite structure of similar hardness

Seamless pipes are usually quenched and tempered after manufacture in order to obtain the desired properties. The possibility of avoiding this heat treatment is explored here, by designing steels which transform into an carbide free bainitic microstructure during cooling from the hot processing phase of the pipe. The cooling conditions studied are appropriate for the manufacturing process and care has been taken to ensure that the correct microstructure is generated for the range of cooling rates experienced in industrial practice. The alloy design has been validated by kinetic and microstructural studies.

Air cooled bainitic steels for strong, seamless pipes Part 1 – alloy design, kinetics and microstructure

Embodiments of the present disclosure are directed to coiled steel tubes and methods of manufacturing coiled steel tubes. In some embodiments, the final microstructures of the coiled steel tubes across all base metal regions, weld joints, and heat affected zones can be homogeneous. Further, the final microstructure of the coiled steel tube can be a mixture of tempered martensite and bainite.

High performance material for coiled tubing applications and the method of producing the same

A high strength bainitic steel and a process for producing seamless pipes for OCTG applications are described. In particular, the advantages ensuing to the steel of the invention are the improvement in strength-toughness over tempered martensitic steels, and a simplified thermal treatment. Quenching is not necessary and by avoiding the quenching treatment the microstructure results far more homogeneous, which allows thick walled tubes to be produced. For the same steel composition, in comparison to conventional tempered martensitic structures, a better combination of strength and toughness can be achieved, in particular by tempering as rolled carbide-free bainitic structures.

High strength bainitic steel for octg applications

Embodiments of the present disclosure comprise carbon steels and methods of manufacture. In one embodiment, quenching and tempering procedure is performed in which a selected steel composition is formed and heat treated to yield a slightly tempered microstructure having a fine carbide distribution. In another embodiment, a double austenizing procedure is disclosed in which a selected steel composition is formed and subjected to heat treatment to refine the steel microstructure. In one embodiment, the heat treatment may comprise austenizing and quenching the formed steel composition a selected number of times (e.g., 2) prior to tempering. In another embodiment, the heat treatment may comprise subjecting the formed steel composition to austenizing, quenching, and tempering a selected number of times (e.g., 2). Steel products formed from embodiments of the steel composition in this manner (e.g., seamless tubular bars and pipes) will possess high yield strength, e.g., at least about 165 ksi, while maintaining good toughness.

High strength steel having good toughness

Steel compositions contain micro-alloying additions of boron and titanium, with yield strength of at least 100 ksi (690 MPa), excellent toughness and good weldability. Boron additions are used to increase hardenability. Strong nitride formers, such as titanium, may be added to the steel composition in order to prevent boron nitrides from forming. These compositions may be cooled from hot rolling in air or using accelerated cooling. After air cooling, the composition may be quenched or quenched and tempered. The compositions are suitable for high strength line pipes (for example, X100 in API 5L standard) and other applications.

Gonzalo Gomez

Papers

Air cooled bainitic steels for strong, seamless pipes Part 1 – alloy design, kinetics and microstructure

High performance material for coiled tubing applications and the method of producing the same

High strength bainitic steel for octg applications

High strength steel having good toughness

Bainitic steels with boron