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How to choose casting materials?
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How to choose casting materials?

Views: 96     Author: Site Editor     Publish Time: 2017-10-17      Origin: www.fuchun-casting.com

Corrosion Resistant - Stainless Steel Alloys 

Castings are classified as “corrosion resistant” if they are used in aqueous environments and vapours below 650°C. To perform well in a corrosive environment the carbon content should be low and usually below 0.20% and sometimes below 0.03%. Based on microstructure Corrosion resistant cast alloys are grouped as Martensitic, Austenitic, or Duplex.

High Strength to Weight Ratio and Corrosion Resistance

Titanium offers a high strength to weight ratio and extraordinary corrosion resistance, making it an ideal choice for medical, marine, hand tools, sporting goods, and high performance automotive applications.

Wear and Abrasion Resistant

Castings are classified as wear and/or abrasion resistant if during applications where constant or high friction occurs the alloys have minimal loss in mass and do not deform due to friction force. These alloys are almost always of high hardness. This hardness is achieved by the formation of carbides within the metal which are very abrasion resistant.

Heat Resistant Alloys 

Castings are classified as heat resistant if they are capable of sustained operation while exposed, either continuously or intermittently to operating temperatures that result in material temperatures in excess of 650°C. The application of heat resistant alloys depends on

  • Resistance to corrosion at elevated temperature

  • Stability - resistance to warping, cracking, thermal fatigue at elevated temperature.

  • Creep strength

Alloys for Cryogenic Applications

The austenitic stainless steels and titanium alloys possess a unique combination of properties which makes them useful at cryogenic (very low) temperatures, such as are encountered in plants handling liquefied gases. These materials at cryogenic temperatures have tensile strengths substantially higher than at ambient temperatures while their toughness is only slightly degraded.

Low Magnetic Permeability

Supreme can produce a range of alloys that have low magnetic permeability's of 1.05 Mu or lower. We have the capability to report the magnetic permeability of alloys in accordance with ATSM A342 method 3. Supreme can produce and measure the magnetic permeabiltiy of alloys to lower than 1.01 Mu.

Non Sparking Alloys

Supreme can produce a range of alloys that can be used in environments where fires and explosions are a concern. These include industries where fluids both vapour and liquids, and particulates such as dust and residue are present and can be ignited.



  • 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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