Steel casting

Cast steel is the starting material for castings made ​​of steel (as opposed to castings from other casting materials and the block and / or continuous casting). Carbon steel cast includes iron-carbon alloys with a maximum of 0.60% silicon and 1% manganese, up to 0.5 %, the strength properties determined the carbon content significantly. Low - to high-alloy cast steel also contains in varying proportions alloying elements such as chromium, nickel, molybdenum, vanadium, tungsten and others. When cast steel, the advantageous properties of steel and the design advantages of the casting design are combined in the final product (steel casting ). Most forging steels be shed to castings, but are then provided with a GS or G before the steel brand name (example: G42CrMo4 ).

Cast steel is mainly because of two reasons in producing much more demanding than other cast iron materials such as cast iron:

  • A look at the iron-carbon diagram is sufficient to deduce that the melting temperature significantly higher (melting point of iron 1538 ° C compared to gray cast around 1150 ° C). The higher liquidus leads the cast steel to a much higher casting temperature (approx. 1600 ° C ) than cast iron. These elevated temperatures make much greater demands on the melting technique, the refractory materials of the furnace linings, crucible and casting tools, and finally to the mold materials.
  • When cast steel shrinkage is two percentage is about twice as large as in gray cast iron.
  • Since the steel castings are solidified brittle, coarse-grained and dendritic as-cast, these parts must be subjected to heat treatment ( normalizing, tempering, annealing, stress relieving ).

Due to the large difference between the specific volumes of the material just below the solidification temperature and at room temperature cast steel is more prone to the formation of voids as cast iron, also has to be considered a higher shrinkage. Without special countermeasures ( feeder ) would produce steel castings unprofitable by voids or unusable by extensive production welding. The feeder on steel castings are removed with autogenous flame cutting, by taking advantage of the heat of oxidation burned by the oxygen supplied to the material in the so-called kerf and removed. For smaller feeder diameters and special steel alloys tee feeders are preferred. Through the mechanical- thermal effect of flushing Stahlgießstrahls ceramic inserts ( fireclay) are to increase the surface resistance in the gating system of the larger forms used ( control). By means of gouging ( gouging ) the material is further eroded synclinal for exposing and removing casting defects and to model the surfaces and prepared for any repair welds.

The far hypoeutectic composition of steel alloys leads to a very viscous melt and therefore to poor conformability, whereby fine structures can be produced only by subsequent machining.

For products of steel castings have better mechanical properties, cast steel is ductile and weldable. To use all the usual types of steel can come, even stainless steels.

Large steel castings can weigh several hundred tons, such as housing for steam turbines. In Germany, the largest and heaviest steel castings are manufactured to a delivery mass of 52,000 kg of steel castings Groeditz currently.

For future high-temperature reactors (HTR ) is thinking about pre-stressed container made ​​of cast steel or ductile iron as the reactor pressure vessel.

The first successful attempts to cast intricate parts made of steel in one piece, undertook born Dunningen Jacob Mayer as technical director of the Bochum Association in 1841. His method he had patented on 16 December 1851.

Experiments at the Helmholtz -Zentrum Dresden -Rossendorf show that magnetic brakes melting in steel castings can specifically influence. The quality of cast materials can be increased when stir the still liquid metal melts externally applied magnetic fields, slow or calm.

Machining allowances

The determination of the machining allowance takes place depending on the maximum size of the casting and the applied cast (form ) method. The standard works on this material give guidance to the applied values ​​, however, are based on the experience of each steel foundry. For areas that form the upper limits in the mold, the price fixed values ​​of the machining allowance will be increased by 2 to 10 mm. Even when applying for weld- the additions should be selected from 20 to 50 percent larger to compensate for the welding variations in the finished part can. Holes and grooves, which are considered to be small relative to the casting are often full cast and introduced by machining. To deliver the required quality cast, all provided with editing artboards the drawing are usually delivered pre-processed by the foundry with an average addition of 3 to 8 mm per area. All tolerances should be agreed by the DIN EN ISO 8062-3 in the tolerance ranges DCTG 11 to 14.

Standardization

  • German standard steel castings for pressure purposes EN 10213; January 2008
  • German standard corrosion -resistant cast steel DIN EN 10283; December 1998
  • German standard steel castings for general applications DIN EN 10293; June 2005
  • German standard cast steel for the construction industry DIN EN 10340; January 2008
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