Getting Your Metallurgical/Historical Geek On

Notice the pattern

We have an interesting article on Damascus steel from 1998. (Also called Wootz, Bulat, Pulad, Fuladh, and Bintai)

The hypereutectoid (high carbon) steel is known for its strength, toughness, and a water like surface finish.  (Most of the stuff that you see today called "Damascus" is pattern welded, a completely different type of steel.)

While it is named for Damascus, the steel, a crucible steel, was actually made in South Asia, specifically India and Sri Lanka.

The secret of making this steel was lost in the 1800s, and we now have an explanation as to why.

The short version is that this was less of a secret than it was an loss of access to very specific materials.

The steel was created from ore that contained minute traces of elements like (primarily) vanadium, manganese, and tungsten, which facilitated the formation of carbide spheres in the steel.

Then with precise control of heat while forging these spheres become stretched, creating the patterns. (OK, that part is a bit of a secret)

With the suppression of steel production in by British colonial authorities, they wanted the Indians to buy British steel, not make their and the possible exhaustion of the original mines.

INTRODUCTION

The arms and armor section of most large museums display examples of Damascus steel weapons. These steels are of two different types, pattern-welded Damascus and wootz Damascus, both of which were apparently first produced prior to around 500.^1,2 These steels have in common an attractive surface pattern composed of swirling patterns of light-etched regions on a nearly black background. The pattern-welded steels were produced by forge welding alternating sheets of high- and low-carbon steels. This composite was then folded and forge-welded together, and the fold/forge cycle was repeated until a large number of layers was obtained.

This article is concerned with the second type of Damascus steel, sometimes called oriental Damascus. The most common examples of these steels are swords and daggers, although examples of body armor are also known. The name Damascus apparently originated with these steels. The steel itself was produced not in Damascus, but in India and became known in English literature in the early 19th century³ as wootz steel, as it is referred to here. Detailed pictures of many such wootz Damascus swords are presented in Figiel's book,⁴ and the metallurgy of these blades is discussed in Smith's book.⁵

Unfortunately, the technique of producing wootz Damascus steel blades is a lost art. The date of the last blades produced with the highest-quality damascene patterns is uncertain, but is probably around 1750; it is unlikely that blades displaying low-quality damascene patterns were produced later than the early 19th century. Debate has persisted in the metallurgy community over the past 200 years as to how these blades were made and why the surface pattern appeared.^6-8 Research efforts over the years have claimed the discovery of methods to reproduce wootz Damascus steel blades,^9-12 but all of these methods suffer from the same problem—modern bladesmiths have been unable to use the methods to reproduce the blades. The successful reproduction of wootz Damascus blades requires that blades be produced that match the chemical composition, possess the characteristic damascene surface pattern, and possess the same internal microstructure that causes the surface pattern.

DAMASCUS STEEL

Wootz steel was produced as roughly 2.3 kg ingots, commonly referred to as cakes, that are solidified in a closed crucible. It was a relatively high-purity iron steel with 1.5% carbon. The cakes were shipped to Damascus, Syria, where bladesmiths learned to forge them into the swords that displayed a beautiful surface pattern. The hypereutectoid carbon level of these steels plays a key role in producing the characteristic surface pattern, because the pattern results from alignment of the Fe₃C particles that form in such steels on cooling. When western Europeans first encountered these patterned weapons, they adopted the name Damascus steel. Wootz Damascus blades possessing the highest-quality damascene patterns were produced in the 16th-17th century.⁴

Both the internal microstructure and the chemical composition of these steels were well established early in this century.^11,13 The internal microstructure of a wootz Damascus blade possessing a high-quality damascene surface pattern is a unique metallurgical microstructure.⁸ It consists of bands of small (generally around 6 mm diameter) particles of Fe₃C (cementite) clustered along the band centerline. The bands have a characteristic spacing in the 30-70 mm range and are contained in a steel matrix. The structure of the steel matrix varies depending on how the smith heat-treated the blade, but it is generally found to be pearlite. The bands lie parallel to the forging plane of the blades. By manipulating the angle of the blade surface relative to the plane of the bands, the smith can produce a variety of convoluted patterns of intersection of the bands with the blade surface. With polishing and etching, the Fe₃C particles cause the bands to appear white and the steel matrix nearly black; thus, the surface pattern is created.

Reproducing Wootz Damascus Blades

In recent work, a technique to produce blades that match the best museum-quality wootz Damascus blades in both surface appearance and internal microstructure has been developed. Figure 1 presents a blade recently made by one of the authors, A.H. Pendray, showing the characteristic damascene surface pattern. It has been specially prepared to include the famous Mohammed's ladder pattern that appears on many of the higher-quality museum swords and blades. The circular pattern between the ladders is often termed the rose pattern, and it is also sometimes found on high-quality museum blades.⁴ A longitudinal section from an adjoining piece of this blade is also shown, which illustrates the aligned bands of clustered cementite particles typical of the better quality museum blades.

A detailed picture description of the production process for this blade has recently been published.¹⁴ In addition, the technique has been fully described in the literature,^15-17 and it has been shown that blades possessing high-quality damascene patterns can be repeatedly produced utilizing the technique. The technique is, in essence, a simple reproduction of the general method described by the earlier researchers. A small steel ingot of the correct composition (Fe + 1.5C) is produced in a closed crucible and is then forged to a blade shape. However, some key factors are now specified. These include the time/temperature record of the ingot preparation, the temperature of the forging operations, and the type and composition level of impurity elements in the Fe + 1.5C steel. It appears that the most important factor is the type of impurity elements in the steel ingot. Recent work^17-18 has shown that bands of clustered Fe₃C particles can be produced in the blades by the addition of very small amounts (0.03% or less) of one or more carbide-forming elements, such as V, Mo, Cr, Mn, and Nb. The elements vanadium and molybdenum appear to be the most effective elements in causing the band formation to occur. An obvious question raised by these results is, are these elements also present at low levels in the 16-18th century wootz Damascus blades?

This is a seriously fun read. 

Well, it is a fun read for me, and I apologize for nothing.