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How to weld the CAST IRON?
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How to weld the CAST IRON?

Views: 103     Author: Site Editor     Publish Time: 2018-03-13      Origin: www.fuchun-casting.com

Cast iron can often be repaired by welding when there are some casting defects.

There are many kinds of welding methods, which are mainly based on the material, size, thickness, complexity, type and size of defects, and the requirements of cutting and technical requirements.


What's the alloy?

Cast irons are a family of iron-carbon alloys. Their high carbon content (usually 24%) gives cast iron its characteristic hardness. However, that hardness comes at the expense of ductility. It is less malleable in comparison to steel or wrought iron. The heating and cooling cycles during welding cause expansion and contraction in the metal, inducing tensile stress. Cast irons do not stretch or deform when heated or stressedinstead, they crackmaking them extremely difficult to weld. This characteristic can be improved by adding different alloys.


To facilitate a better understanding of these materials, they can be divided into five groups, based on composition and metallurgical structure: white cast iron, malleable cast iron, grey cast iron, ductile cast iron and alloy cast iron.



Clean the casting

Regardless of the alloy, all castings must be properly prepared prior to welding. While preparing the casting for welding, it is crucial to remove all surface materials to completely clean the casting in the area of the weld. Remove paint, grease, oil, and other foreign material from the weld zone. It is best to apply heat carefully and slowly to the weld area for a short time to remove entrapped gas from the weld zone of the base metal.


A simple technique for testing the readiness of the cast iron surface is to deposit a weld pass on the metalit will be porous if any impurities are present. This pass can be grinded off, and the process repeated a few times until the porosity disappears.


Pre-Heating and Welding

If the welding is performed with electrode or oxyacetylene stick having the same chemical composition the whole workpiece should be homogenously pre-heated up to app. 600℃.

The welded piece should be cooled down slowly in furnace, hot sand or ash.


When performing "cold weld" on cast iron, the welding with short passes (20-30 mm) should be preferred and the welds should be immediately hammered. Overheating the workpiece during welding should be avoided.


It is recommended that the workpieces with complex geometry should be pre-heated to 300 - 350℃ before welding even if nickel content welding electrodes are used.

The cracks that are not outside the workpiece should be welded outside-in.

Welding technique

Welding techniques should be chosen based on their suitability to the cast iron alloy being welded. The most common welding processes are stick, oxy acetylene, and braze welding.

Stick welding, also known as shielded metal arc welding or MMA, makes use of a consumable electrode covered with a flux. Different types of electrode can be used depending on the application, the color match required, and the amount of machining to be done after welding.

Oxy acetylene welding also makes use of electrodes, but instead of an arc generated by current, an oxy acetylene torch provides the energy for welding. Cast iron electrodes, and copper zinc electrodes, are both suitable for oxy acetylene welding of cast iron.

Care must be taken not to oxidise the cast iron during acetylene welding, as this causes silicon loss and the formation of white iron in the weld. The welding rod should be melted in the molten weld pool, rather than directly by the flame, to minimize temperature gradients.


Braze welding is a common method for joining cast iron parts due to the minimal impact on the base metal itself. A welding rod provides the filler that adheres to the cast iron surface. Because of the lower melting point of the filler compared to the cast iron, the filler does not dilute with the cast iron but adheres to the surface.

welding of cast iron



  • 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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