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Why did Goujian sword not rust for thousands of years? What was the advanced manufacturing technology at that time?
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Why did Goujian sword not rust for thousands of years? What was the advanced manufacturing technology at that time?

Views: 119     Author: Site Editor     Publish Time: 2018-10-31      Origin: www.fuchun-casting.com


Fifty years ago, a rare and unusual sword was found in a tomb in China. Despite being well over 2,000 years old, the sword, known as the Goujian, did not have a single trace of rust.The blade drew blood when an archeologist tested his finger on its edge, seemingly unaffected by the passage of time.  Besides this strange quality, the craftsmanship was highly detailed for a sword made such a long time ago. The sword measures 22 inches in length and has beautiful repeating dark rhombi patterns on both sides of the blade. In addition, there are delicate embellishments of blue crystals and turquoise, as well as concentric circles designed around the handle. Exquisitely forged from copper and tin, the markings on the sword also remain in excellent condition.

 

 goujian sword


Surprisingly, the bronze sword  has traversed more than 2,000 years of history, but there is no rust on its body. What is the reason why it has been stainless for thousands of years?

 

We put sword of Goujian under a 500-fold microscope and took thousands of microscopic photos. We can see a yellow part, which is the blade of the sword. We can also see the dense structure like a branch. This is called "dendrite". This is the cell of the sword, which is the "metallographic tissue" inside the metal. Through this metallographic structure called dendrite, we can speculate and study its casting technology  and alloy composition.

 

According to the observation, this sword contains about 80% - 83% copper, 16% - 17% tin, and a small amount of lead and iron. Copper is a kind of inert metal. It is not easy to rust under daily conditions. This is first reasons why the sword is stainless.

 

Then look at the external environment of the sword: the tomb is buried several meters underground, the coffins cover each other, and the coffins are filled with a fine white clay around the coffin chamber, which has good compactness. In addition, the upper part of the grave pit has been compacted and filled with earth, which makes the tomb chamber almost a closed space. So many sealing layers basically isolate the air exchange between the tomb chamber and the outside world. Modern scientific research shows that steel will not rust even in neutral or slightly acidic water under completely oxygen-insulated conditions. This is the second reason why the sword is stainless.

 

The groundwater level of the tomb is relatively high, and the air content in the tomb room is less after being immersed in groundwater for a long time. This is the third reason.


gold metallurgy

 

The successful casting of Goujian sword, embodied the crystallization of the labor cooperation of moulding, model making, roasting, casting and mechanical processing at that time, which included the wisdom and creativity of the ancient Chinese people.


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FAQS

  • What is 'multiple certification'?

    This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.

    For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.

  • What surface finishes are available on stainless steels?

    There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.

    The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.

  • Can I use stainless steel at high temperatures?

    Various types of stainless steel are used across the whole temperature range from ambient to 1100 deg C. The choice of grade depends on several factors:

    1. Maximum temperature of operation
    2. Time at temperature, cyclic nature of process
    3. Type of atmosphere, oxidising , reducing, sulphidising, carburising.
    4. Strength requirement

    In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.

    Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.

  • Can I use stainless steel at low temperatures?

    Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.

    Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.

    Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.

    In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.

    Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite. 

  • Is stainless steel non-magnetic?

    It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. 

    It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.

    In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.

    Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.

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