University of Cambridge

Pearlite: patented steel wire


A. R. Waugh, S. Paetke and D. V. Edmonds

Pearlite can have a very fine interlamellar spacing if it forms at a low transformation temperature. "Patenting" involves heating a steel of approximately eutectoid composition (0.84 wt% carbon, 0.21Si 0.64Mn) into an austenitic state, followed by transformation at a temperature of about 450°C to achieve an interlamellar spacing of 100 nm or less.

The patented wire is then cold-drawn with a 98% reduction in area, to further strengthen the steel to levels in excess of 2 GPa.

Photographs courtesy of Dr Sally Waugh.

As-drawn wire

The imaging atom-probe pictures are taken at about 65 K.
pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Transmission electron micrograph showing severely deformed structure.
See Paetke for more detail.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field ion image of severely deformed structure.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field-ion image of the as-drawn wire.
.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding Fe2+ image.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding C2+ image. The concentration of carbon is either close to
25 at.% (cementite) or 1-2 at.% in the ferrite.

The as-drawn wire has a 0.2% proof strength of about 1400 MPa. Plastic deformation of cementite can sometimes cause its dissolution, with carbon being introduced into the ferrite. This is because the carbon prefers to be at dislocations in ferrite than in the cementite lattice. Furthermore, if the cementite particle size is reduced to less than that of a critical nucleus, it will dissolve.



pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation

More pictures from as-drawn wire.


As-drawn and tempered wire

Imaging atom-probe pictures taken at about 20 K in order to enhance resolution. The samples are, after patenting and cold-drawing, tempered at 200°C for 30 min.
pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field-ion image taken at an "optimum" imaging voltage.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field-ion image taken at a voltage which enhances the visibility of the dislocation cell boundaries.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding Fe2+ image.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding C2+ image. The distribution of carbon is not significantly different from the as-drawn state, but the strength increases dramatically to about 2 GPa on tempering, indicating that it is the dislocation cell-structure created by heat treatment that is responsible for strengthening.


Imaging atom-probe pictures taken at about 20 K in order to enhance resolution. The samples are, after patenting and cold-drawing, tempered at 200°C for 30 min.
pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field-ion image taken at an "optimum" imaging voltage.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Field-ion image taken at a voltage which enhances the visibility of the dislocation cell boundaries.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding Fe2+ image.

pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation, A. R. Waugh

Corresponding C2+ image. The distribution of carbon is not significantly different from the as-drawn state, but the strength increases dramatically to about 2 GPa on tempering, indicating that it is the dislocation cell-structure created by heat treatment that is responsible for strengthening.


pearlite, drawn pearlite, patented steel wire, wire, strong steel, segregation

More pictures from as-drawn and tempered wire.







4th edition
4th edition, 2017
3rd edition
3rd edition, 2015
1st edition
1st edition, 2017


PT Group Home Materials Algorithms