Usually, the microstructure of the steel consists of bainite
, martensite, and retained austenite in a matrix of soft ferrite .
Metallurgists have discovered that bainite
, a microconstituent that forms in steel under certain conditions, is the best candidate to produce tough and reliable weld joints.
0.6 mm are bainite
martensitic structures, and deeper is bainite
Q690 steel is known as a typical low carbon bainite
steel with excellent mechanical properties, and it is widely used in offshore engineering industry [1, 2].
Moreover, small amounts of granular ferrite and upper bainite
were observed; see Figure 4(b).
Slowing down the cooling rate from 16[degrees]C/s to 1 [degrees]C/s in sequence 2 has led to a larger bainite
fraction and higher elongation: 10% (Fig.
SEM and TEM studies of the phase composition of as-received specimens of 15Kh2NMFAA steel have shown that the tempered bainite
matrix contains initial hardening phases: [Me.sub.7][C.sub.3], [(Mo, Cr).sub.2]C-type carbides, V(C, N) carbonitrides, and nonmetallic inclusions (manganese sulfides MnS and silicon oxides Si[O.sub.2]).
Chen  observed the fracture failure process in industrial steel-grit bainite
structure with microcracks under uniaxial tension by scanning electron microscopy (SEM), and the results revealed that the major fracture mechanism involved the formation, growth, and connection of microvoids.
For the former they changed a ferritic bainite
beam to a boron beam and the latter from a DP500 to a dual-phase 980.
Instead of elongated grains and upper bainite
(or pearlite), the microstructure (Figure 2) contains a mixture of ferritic grains with (probably) small islands of martensite.
Another example of DSTL intellectual property being reworked for commercial application is a relationship with industrial giant Tata to market a super bainite
steel that was originally developed for the protection of armoured vehicles.
The microstructure analysis indicates that a small amount of graphite precipitated flaky hard martensite, and lower bainite
remains in this area.