In addition to material specifi cation, one of the procedures most commonly dictated by steel casting customers is welding.
• T e Unifi ed Numbering System (UNS). UNS was developed by technical societies and govern- ment agencies to clear up the confusion surrounding steel material specifi cation. T e system uses a letter followed by fi ve digits to cover all steel types. T e system incorporates the AISI/ SAE system (AISI/SAE 1040 is G10400) and includes a number of additional classifi cations. (T e letter “G” is used for plain carbon and alloy steels; cast steels are designated by the letter “F” or “J.”) However, the system is not yet widely used.
The American Society for Test- ing and Materials (ASTM) system is based on the steel product and ap- plication, rather than composition. The specifications, which might be for railroad rails, boiler tubes, plate or bolts, contain within them composition, mechanical properties and other required characteristics. According to the Steel Founders’ Society of America, the steel casting industry most commonly uses the ASTM system.
The Big Four In the metalcasting arena, many
grades of carbon and low alloy steel meet specifi c end-use requirements, such as structural strength, wear resistance, high temperature properties
and corrosion resistance. While such material is generally ordered to ASTM requirements for steel castings, other specifi cations may be used. T e most common ASTM specifi cations are: • ASTM A 781/A 781M-97— Covers mandatory requirements for steel and alloy castings in general industrial use.
• ASTM A 703/A 703M-97— Covers common requirements that apply to steel castings for pressure-containing parts.
• ASTM A 957-96—Covers requirements for steel and alloy castings produced via the invest- ment casting process.
• ASTM A 985-98—Covers common requirements for steel investment castings used in pressure-containing applications. T e process and procedures most
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commonly specifi ed by the customer in addition to material are heat treat- ment (which may enhance the proper- ties of specifi c alloys) and welding. T ese processes have the greatest eff ect on casting metallurgical quality and serviceability, and both are routinely performed by steel casting facilities. T e temperature-control and record- ing equipment on heat treatment furnaces should be calibrated at speci- fi ed intervals. T e metalcasting facility can be required to submit procedures and qualifi cations for review before starting an order.
Alloying Elements Understanding the eff ects of diff er-
ent alloying elements on steel can help designers select a steel composition that meets the component’s require- ments. Elements that can be added
Carbon and low alloy steels generally are classifi ed based on composition. The higher-alloy steels (stainless, heat-resistant, wear-resistant, etc.) can be classifi ed according to composition, microstructure, application or specifi cation.
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