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Mechanical properties of P.W. Steel

Updated August, 6th, 2002

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Mechanical properties of Modern Fabricated Pattern Welded Damascus Steels

Abstract

The works of modern fabricated Pattern Welded Damascus steel by two of the best Russian bladesmiths has been investigated. The energy absorbed in fracturing and the corresponding bend angle (in Charpy test), as well as hardness has been measured. The data of tension test is adduced. Fractography, metallography, qualitative X-ray and spectral analysis have been conducted. A dilatometer was used to check position of polimorfic points. It has been shown, mechanical properties of such material are on a level with standard tool carbon and low alloyed steels.

Key words: damascus steel, mechanical properties, toughness.

• Abstract
• Introduction
• Experimental
• Result and Discussion
• Conclusion
• Acknowledgment
• References

 Introduction

There are two sorts of Damascus steels: "Genuine" or Wootz Damascus and Mechanical, Pattern or Welded Damascus (we do not mention False or Imitation Damascus here). In Russia the first one is named as Bulat (from Persian "Pulad"), while the second is named as Damascus steel simply.

Many of investigators have been occupied with Bulat/Wootz Damascus. In the middle of the last century the Russian metallurgist A. P. Anosov restored the technology of producing Bulat blades [1], and this production was glimmering at Zlatoust Arm Factory up to the end of 1919 [2]. Thorough works by Russian scientists N. I. Belaiew and N. T. Belaiew were published in the beginning of the century [3-5]. In our days the bladesmiths V. I. Basov (USSR) [6] (the first mentioning [7]) and A. H. Pendray (USA) were the first to make Bulat/Wootz Damascus blades. In his beautiful studies J. D. Verhoeven with co-workers laid the foundation for the theory of Wootz Damascus ([8], for example).

Welded Damascus steel was fabricated and now is worked out in greater quantities than Wootz Damascus steel. However, in scientific respect the previous always was in the shadow of the latter. The author knows a couple of the papers on mechanical properties of genuine antique Bulat/Wootz Damascus blades [9, 10]. Of course, there are works devoted to the mechanical properties of modern fabricated Bulat steels ([11] for example). But mechanical characteristics of Welded Damascus steels are known worse.

As long ago as 20's barrels of hunting rifles of Welded Damascus steel were fabricated in Tula (Russia) (so name the "red hardware"). Such barrels were expensive and it was found they had not advantages in strength. In addition they were more prone to occlusion (penetration and trapping of gunpowder gases in the material). So, fabrication of such barrels was stopped. However we could not find the quantity data of those tests.

The scope of the present work is to determine the mechanical properties of modern fabricated Welded Damascus steels from the best of Russian bladesmiths.

Experimental

The samples were taken from works by bladesmith V. D. Koptev (Tula, Russia) and "patriarch" of Russian bladesmiths V. I. Basov (Suzdal', Russia). We had got the Basov's work in fully heat-treated state (quenched and tempered). The Koptev's work had been quenched only (not tempered).

The specimens were cut with specimen axis in the longitudinal direction. There are not blades with thickness of 10 mm, sure. So, for impact test we used the U-notched specimens LxBxH=55x10x5 mm (N 3 by Russian standard GOST 9454-78). We determined the absorption energy and bend angle in Charpy test. As soon as the impact test data are not invariant to dimensions of specimens, we used control ones of 1.0%C-1.5%Cr-Fe steel.

The specimens were tempered at 400 °C for 2 h. This temperature is above standard tempering temperature for blades (bladesmiths temper them at about 300-350 °C usually). It had been done to simplify the comparison with reference data. Besides, temperature at 300 °C lies in region of tempered-martensite embrittlement.

The several specimens of Koptev's Damasc were sequence tempered at 150, 250, 400 °C. Thus we were able to determine effect of tempering temperature on hardness. The load in microhardness test was 1 and 10 N.

Chemical composition of the samples was measured by optical spectroscopy. Because of heterogeneity and severe texture we restricted ourselves to the quality X-ray diffraction phase analysis. It was conducted after electrolytic polishing and etching on base (in solution 65%H₃PO₄, 15%H₂SO₄, 4.5%CrO₃, 0.5%FeCl₃, 15%H₂O). Also, etching in Nital was employed.

For the tension test we used specimens with dimensions of working sections 3.6x5.8x26 mm ("short") and 2.65x3.65x74 mm (in the latter case, the elongation was taken on 35 mm gage length, which correspond to "long" specimen for such cross section). The first of this specimens was prepared from the Basov's work, while the second - from the Koptev's one.

The one of the fractured parts of the second specimen had sufficient gage length and it was tested again after new tempering. Cross head speed was 2 mm/min, 10 mm/min and 1 mm/min correspondingly. Yield strength, tensile strength, elongation and reduction of area had been determined by standard methods. Also, mean true strain e_u = ln ( l_u / l₀ ) away necked region was been measured.

It is known, very strong plastic deformation can depress polymorphic points [12]. So, Basov's assertion to the effect that Welded Damascus steel must be quenched from lower temperatures [6], would be grounded. To check this hypothesis, we invoked dilatometry. The specimen for the test was prepared from the Basov's work. The rate of heating in the dilatometer was about 60 °C/min. So high rate was needed to prevent dislocation annealing.

Result and Discussion

Chemical composition

Besides carbon and sure iron, the Koptev's work contained about 0.25% Mn. The Basov's work contained 0.5% Mn and 0.3% Cr. In this way, they fit plan carbon steels by chemical composition.

Phase analyses

Before the tempering the works had dual a - and g -phase sttructure. g -phase disappeared after 400 °C tempering. This is normal for carbon steels, where the temperature of full decomposition of retained austenite is about 300 °C.

Dilatometer test

We have not detected any shift of the Ac₁ point in the Welded Damascus steel as compared with low carbon steel: in both case the transformation began at 750 °C, what is normal for such rate of heating. The temperature of the Ac₃ point was not detected because high rate of heating in dilatometer, used by us, and heterogeneity of the Damascus steel.

It should be noted, we tested the heat treatment specimen, i.e. after quenching and 400 °C tempering. Such processing can abolish the effect [12]. Unfortunately, we had not get a specimen of Damascus steel in fresh hammered condition.

Macrostructure

Microstructure of tested works are shown in Fig. 1.

	Koptev's work
	Koptev's "Ni-damascus"
	Macrostructure of the fragment from Basov's work
Fig. 1. Macrostructure of Damascus steels

Mechanical properties

Fig. 2. Hardness in versus tempering temperature: DB - Basov's; DK - Koptev's Damascus work; index t - near the tip, h - near the handletennon; U10 - 1.0 %C steel

Hardness

Very uneven hardness was observed in Damascus works. Even within a strand. Generally speaking, this is quite natural. The hardness in versus tempering temperature is presented in Fig. 1. As it is easy to see, there is no appreciable difference between hard strands of Koptev's work and 1.0% C steel. Behavior of the soft strands fit more to 0.35% C steel than to wrought iron, which usually used to fabricate Welded Damascus steel. Obviously, this was due diffusion carbon during fabrication.

Hardness of the zones in Basov's work differed considerably: at low hardness of strands, there are "spots" with high hardness (up to 6.3 Gpa after tempering at 400 °C). This is considerable more, than hardness of plan carbon steels after such tempering. The optical spectrometry confirmed absence of alloy elements in the "spots". Possibly, this is result of high forging strain hardening. But causes of that have not been ascertaining in details.

Charpy test

Data of Charpy test have been summarized in table 1. In the same table typical hardness of the specimens is cited. For reference, the extract from some corresponding standards is given in table 2. It may be seen, notch toughness of Damascus steel are close to the notch toughness of tool carbon and low allowed steels. For reference, data on some typical modern steels summarized in table 2 [13].

1. strands with high / low hardness;
2. (HRc) numbers were received by conversion of HV;
3. there were areas with HV 6.3 GPA;
4. the standard deviation.

* - this steel and its alloyed varieties used in the past for mass production of many sorts of cold arms (including sabers, dirks, etc.).

Tension test

Data of the tension test are summarized in table 3. The "short" specimen fractured away of the working part (near the grip) and some exfoliation was observed on its fractured surfaces. So its results, especially R.A., can not be considered as reliable. Unfortunately, we could not repeat the test because limited amount of material.

* - broke out of the working part and there is exfoliation in the neck;
** -

It may be seen from received data, the tensile strength of the tested Welded Damascus steels are some inferior to tempered at the same temperature quenched carbon steel with 0.7% C at essentially equal plasticity.

It may be noted also, the tensile strength of the testing Welded Damascus steels is below strength of the genuine Wootz Damascus steel [10] at nearly equal plasticity (tensile strength of the latter was 1100 ±  50 MPa). Hardness of the characterized in [10] Wootz Damascus steel was Ra = 62 (HRc 23) only. Apparently, perfect cutting properties of Wootz Damascus steel [14] are dictated by other causes and are not associated with hardness of the matrix. The most probably, the carbides serve as cutting elements in the latter.

Fractography

Fracture surfaces of the Charpy specimens had stepped configuration. Some exfoliation into plates at about 0.7 mm was observed. According to masters, stepwise fracture is typical for Damascus steel. This indicates insufficiently high quality of the welding applicable in final stage of its fabrication.

Koptev's work fractured in transcrystalline, brittle manner. The Basov's work had brittle-ductile fracture. Nevertheless, there was not a great differences in toughness between them.

Conclusion

The samples of modern fabricated Welded Damascus steel (at list, the samples tested by us) do not exceed up-to-day high-carbon and low alloyed steels in combination hardness-toughness and they are considerably inferior to supersteels.

In future, the author plans to fulfill the research of modern fabricated Bulat steels. Unfortunately, for the time being it is look like as impossible to investigate Bulat and Damascus by ancient fabrication. And the author will be very grateful to anybody who can help him with this.

Acknowledgment

Finally, I should like to acknowledge V. I. Basov and V. D. Koptev for granted me their works for the research.

References

1. ?
   1a.) ?
   There are brief translations:
   1b.) Anosof. Memoire sur l'acier damasse.-"Annuaire du Journal des mines de Russie". Annee 1841. S-Petersbourg. 1844.
   1c.) Anosoff. Ueber Damascenerstahl.-"Politechnisches Journal", Bd 93, Stuttgart, 1844, S. 58-62.
2. ?
3. ?
4. N. Belaiew. Damascene steel. J Iron Steel Inst. 97: 417-439 (1918).
5. ?
6. ?
7. ?
8. J. D. Verhoeven, A. H. Pendray and E. D. Gibson. Wootz Damascus Steel Blades. Materials characterization, 1996, v. 37, p. 9-22.
9. ?
10. D. T. Peterson, H. H. Baker and J. D. Verhoeven. Damascus Steel, Characterization of One Damascus Steel Sword // Materials Characterization, 1990, v. 24, p. 355-374.
11. V. R Nazarenko, V. F Yankovskii, M. A Dolginskaya, P. M. Yakovenko. Damascus Steel - Myths and Reality // Metal science and heat treatment (English Translation of Metallovedenie i Termicheskaya Obrabotka Metallov). 1992, v. 34, n. 6, p. 402-410.
12. ?
13. ?
14. J. D. Verhoeven, A. Pendray, W. E. Dauksch. Wootz vs. conventional steels: the silk scarf test // Blade, 1995, March, p. 60-63.