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The steel is usually of very fine ferrite grain structure.
The machined surface was examined to find out grain size, dislocation density, etc.
The microstructure of the specimen was mainly of finer ferrite grains with a little pearlite.
It is noted that experiment number 9 is of paramount importance since it is indexed with a higher MPCI (0.92) as per the simulation result (Table 6).
The grain pull out and partial side flow are noted (Fig. 5b).

Metallurgical graphical test revealed that from base metal to weld metal the grain diameters are changed from about 24 to 40 µm.
The columnar grain structure (Fig.2) is the characterized structure with a distance parameter d of about 40 µm between neighbouring rich delta ferrite bands.
The Fig. 1 Pipe Fig. 2 Columnar grain structure 25µm d number of replicating actions for each specimen is about 7 to 15.
This density is defined as, in the MSC regime, the average number per unit area of the short cracks in the initial zone of the DESFC and, in the PSC regime, the average number per unit area of the short cracks in the two zones ahead of the DESFC tips.

In some works [4 - 6] it was shown, that the application of rapid heat treatment (RHT) into the singlephase β-field (at rates of the order of tens or even hundreds of degrees per second) can be used to form unique microstructures comprising relatively fine β-grains (≤ 30-50 µm) with fullytransformed intragrain α+β lamellae/laths.
Local/selective heat treatment can be accomplished using a number of well-known high-energy-density methods such as those based on electromagnetic induction, electron-beam, infrared, and laser heating [8 - 10].
At the same time formed during welding deposition macro- and microstructures were characterized by presence of several zones clearly distinguishable in grain size, phase composition and intragrain features (Fig. 9a, Figs. 10a and 10b).
Weld-deposited layer had β-grains with average size of about 350-500 µm (Fig. 10a) having martensitic α" intragrain microstructure, whereas Heat Affected Zone (HAZ) was characterized by increased up to 100-150 µm β-grains with metastable β-solid solution inside, whereas base material remained in two-phase α+β globular condition (Fig. 10b).
Belov, Ultrasonic and vibromagnetic treatment of metals, Metal Science and Heat Treatment, Volume 13, Number 3 / March, 1971, p. 261

Two steps clean up procedure which consists of grain confidence index standardization and neighbour phase correlation was applied to the raw EBSD data in the TSL software.
In this procedure minimum grain tolerance angle of 5°, minimum grain size of 2 pixels and min confidence index CI >0.1 were chosen.
The bainite fraction was quantified by means of the method developed by Wu et al [7] with the assumption that the distribution of the number distribution of IQ-values is composed by a superposition of Gaussian peaks originating from the separate contribution of ferrite and bainite.
The results of this procedure are shown in Fig. 2 where the bainite fraction was associated to the number of pixels in the area locked between the abscise axis and the small Gaussian peak.
After taking into account the pixels that belong to the high angle grain boundaries (misorientation >15°) and their vicinity, the bainite fraction was determined to be 28%.

It is also still not enough to understand the main intrinsic and environment factors affecting the formation and propagation of cracks for the soils are high complex and conditioned by a large number of variables[2].
Laboratory grain analyses suggest that for the soil with largest grain size smaller than 60mm, fine particles (grain size smaller than 0.075mm) and clay particles (grain size smaller than 0.005mm) account for 4.8% and 1.4%, respectively (Fig.1).
Grain size distribution cure of the original soil sample Fig.2.
Grain size distribution cures of the soil samples in simulation experiments Image processing To make quantitative description of cracking based on the surface identification, techniques of digital image processing were used.
Therefore, a large number samples could exclude the effect of heterogeneity of particle size and particle distribution on soil cracking.

By subtracting this “mean” from the data one obtains a new function, which must have the same number of zero crossings and extrema.
A “coarse-graining” process is applied to the time series.
The length of each coarse-grained time series is N/τ. 2.
SampEn is calculated for each coarse-grained time series, and then plotted as a function of the scale factor.
Schematic illustration of the coarse-graining procedure for scale 2 and 3.

2# and 7# Fig .2 The curve of fine grain 3# and 13# When the clay content is relatively low, the cementation between the clays, accumulating disorderly around the silts, is weak.
The silts contact with each other and the basic structure is single-grained structure.
From the picture, the grading curves nearly coincide except the content of the relatively bigger grain size.
Fig. 3 The curve of fine grain 5#, 9# and 14# The m values which are approximate are 0.255, 0.204 and 0.249.
From the picture, the grading curves nearly coincide except the content of the relatively bigger grain size.

But refined grains can be obtained by adding Nb, which is favourable for high strengths after welding, and also adding Nb can reduce anisotropy in IF steels, therefore, compromises should be made in terms of the adding amount of Ti and Nb.
And the grain size of ferrite were nearly identical with size level keeping at I9 under different temperatures which explained niobium can effectively retard grain growth, and this properties would be favourable to enhance strengths of the steel after welding.
A number of steels were manufactured and samples were taken to make tensile testing.
Previously car produce had tested traditional Ti-IF steels products in spot-welding experiments which were found failed in some requirements such as tensile shear strength, nugget diameter, penetration rate and grain size.
Based on the microstructure result, the grain size was measured with around value of 90μm.

It is well known that the main effect of any severe plastic deformation (SPD) technique is strength enhancement due to grain size reduction to at least the submicrometer range.
In most investigation concerning Ti and its alloys, SPD is followed by cold rolling (CR) [4, 5]; normally the first step is performed at medium temperatures (400 – 600oC) employing a large number of ECAP passes.
The main difference consists in the directionality of deformation of the former process, and the rotation of preferential shear planes in the latter, which accounts for the grain refinement.
The equiaxed grains with d ≈ 12 μm, of sample 0X are replaced by a heavily deformed microstructure after four ECAP passes (where of course the individual grains cannot be imaged).
This outstanding result is probably due to the efficient grain refinement brought about by the eight passes, but elongation is less satisfactory, once compared with the 10% displayed by the Ti 6-4 alloy [TIMET datasheet – www.timet.com].

Compared to conventional coarse grained materials, the small grain sizes and high defect densities in UFG materials lead to high strengths and the occurrence of superplasticity [1].
The severe shearing deformation breaks the original microstructure into ultrafine or nanostructured material after a number of passes [2].
It reveals the presence of a high volume fraction of porosity, besides coarse grains.
The grain refinement promoted by ECAP is clearly shown in the micrograph of Fig. 5b.
We must stress that the grain size measurements were hindered by the presence of porosities.