{"id":1965,"date":"2018-10-15T09:22:51","date_gmt":"2018-10-15T09:22:51","guid":{"rendered":"https:\/\/aboutfoundry.com\/?p=1965"},"modified":"2026-08-27T15:33:53","modified_gmt":"2026-08-27T15:33:53","slug":"annealed-cast-iron","status":"publish","type":"post","link":"https:\/\/aboutfoundry.com\/en\/annealed-cast-iron\/","title":{"rendered":"Annealed cast iron"},"content":{"rendered":"\n

Annealed cast iron<\/strong> (malleable cast iron) is a special type of cast iron that gains its toughness and ductility through controlled heat treatment: cast as hard, brittle white cast iron, then annealed for hours at 900 to 1000 degrees Celsius, which converts the embedded cementite into temper carbon. Used above all where strength and impact resistance are required.<\/p>\n\n\n\n

Production process<\/h2>\n\n\n\n

Annealed cast iron is produced in two clearly defined steps. First, a white cast iron is formed that is extremely hard but brittle. In a second process step, heat treatment takes place \u2014 also called “annealing” or “tempering”. Here the material is heated to temperatures between 900 and 1000 degrees Celsius for several hours. During this process, the cementite embedded in the cast iron transforms into temper carbon. This gives annealed cast iron its typical combination of strength and toughness, which makes it particularly valuable in production and processing.<\/p>\n\n\n\n

Types of annealed cast iron<\/h2>\n\n\n\n

A basic distinction is made between black and white annealed cast iron. Black annealed cast iron is produced by annealing under low-oxygen conditions, which converts the cementite into temper carbon more uniformly across the cross-section. It is named after its dark fracture surface and is characterised by particular toughness and ductility. White annealed cast iron, by contrast, is treated in an oxidising atmosphere, which decarburises the edge zone of the component and leaves few carbon deposits at the surface. It offers good weldability and is ideally suited to thin-walled, precision engineering components.<\/p>\n\n\n\n

Applications and advantages of annealed cast iron<\/h2>\n\n\n\n

Thanks to its robust yet ductile properties, annealed cast iron is particularly suited to applications in the automotive industry, mechanical engineering, and fittings and pipe connections in plumbing technology. Its key advantage is that annealed cast iron products combine very high mechanical strength with lasting resistance to vibration and impact loads. This makes them well suited to the requirements for stable, reliable and durable components.<\/p>\n\n\n\n

In practice: what the foundry engineer needs annealed cast iron for<\/h2>\n\n\n\n

For the engineer, annealed cast iron is the material of choice when a component allows the complex geometries typical of cast iron but needs the impact resistance and ductility of steel in service \u2014 for example pipe fittings, brackets, or agricultural machinery components. Production requires two clearly separated process steps: first the part is cast as white cast iron with a high proportion of bound carbon (cementite), then it undergoes an annealing treatment of several hours at 900 to 1000 \u00b0C, which converts the cementite into temper carbon. In practice, the annealing atmosphere determines the outcome: an oxidising atmosphere produces white annealed cast iron with a decarburised edge zone and good weldability, while a low-oxygen atmosphere produces black annealed cast iron with a more uniform carbon distribution across the cross-section. Wall thickness is a hard limit here: in overly thick-walled components the core no longer solidifies fully white, so graphite forms instead of cementite already during casting, and the later annealing treatment no longer works.<\/p>\n\n\n\n

Annealed cast iron grades under DIN EN 1562<\/h2>\n\n\n\n
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Designation<\/th>Type<\/th>Test piece diameter<\/th>Tensile strength Rm (min.)<\/th>Elongation A (min.)<\/th><\/tr>\n<\/thead>\n
EN-GJMW-400-5<\/td>white annealed cast iron<\/td>12 mm<\/td>400 MPa<\/td>5 %<\/td><\/tr>\n
EN-GJMB-350-10<\/td>black annealed cast iron (ferritic)<\/td>12-15 mm<\/td>350 MPa<\/td>10 %<\/td><\/tr>\n
EN-GJMB-700-2<\/td>black annealed cast iron (pearlitic)<\/td>12-15 mm<\/td>700 MPa<\/td>2 %<\/td><\/tr>\n<\/tbody>\n<\/table><\/figure>\n\n\n\n

Values according to DIN EN 1562:2019-06, rounded and given as examples; the standard also covers further intermediate grades. The properties for EN-GJMW-400-5 apply to the 12 mm test piece; at 6 mm the same grade reaches only 300 MPa and 12%.<\/p>\n\n\n\n

Frequently asked questions about annealed cast iron<\/h2>\n\n\n\n

What is annealed cast iron?<\/h3>\n\n\n\n

Annealed cast iron is a cast iron material that is first cast as a hard, brittle white cast iron and then converted, through an annealing treatment of several hours, into a tough, readily formable microstructure. It combines the castability of cast iron with an impact resistance approaching that of cast steel.<\/p>\n\n\n\n

What is white annealed cast iron?<\/h3>\n\n\n\n

White annealed cast iron (EN-GJMW) is produced by annealing in an oxidising atmosphere. This decarburises the edge zone of the component while temper carbon forms in the core. It can be readily galvanised and welded and is preferred for thin-walled, smaller components.<\/p>\n\n\n\n

What is the difference between annealed cast iron and nodular graphite iron?<\/h3>\n\n\n\n

In nodular graphite iron<\/a>, the spherical graphite shape forms already during solidification, by inoculating the melt with magnesium. In annealed cast iron, the graphite shape (temper carbon) only forms afterwards, through annealing of cast iron that first solidified white. For large wall thicknesses, nodular graphite iron is more economical, because no additional annealing treatment is needed.<\/p>\n\n\n\n

Standard reference<\/h2>\n\n\n\n

DIN EN 1562:2019-06<\/strong> sets out grades, designations and minimum properties for annealed cast iron, divided into white (EN-GJMW) and black (EN-GJMB) annealed cast iron.<\/p>\n\n\n\n

Related terms<\/h2>\n\n\n\n