The standard "ASTM A48/A48M-22 Standard Specification for Gray Iron Castings" developed by the American Society for Testing and Materials (ASTM) describes the requirements for gray iron castings intended for general engineering use where tensile strength is an important consideration. Castings are classified according to the tensile strength of the iron in individually cast test bars. This standard subjects chemical composition to tensile strength.
Castings produced to this standard are graded according to the minimum tensile strength achieved on special test coupons designed to standardize the cooling rate. The tensile strength developed in specific casting sections may differ from the test coupon values.
Definitions of many terms commonly used in gray cast iron castings are included in the standard “ASTM A644-14 Standard Terminology for Iron Castings”.
Castings ordered and manufactured in accordance with this standard are divided into a number of classes based on the properties of the individually cast test bars. These classes are shown in the tables given in the standard. Each class is indicated by a number followed by a letter. The number indicates the minimum tensile strength of the individually cast test bar and the letter indicates the size of the test bar.
Orders for materials complying with this standard must include the following information:
Castings may need to meet special requirements such as hardness, chemical composition, microstructure, pressure tightness, radiographic soundness, dimensions, surface finish, etc. when agreed in writing between the manufacturer and purchaser.
Test bars representing castings conforming to this standard shall meet the tensile strength requirements described in the tables contained within the standard.
Castings must conform to dimensions or drawings supplied by the purchaser or, if no drawings are available, to dimensions predicted by pattern equipment supplied by the purchaser.
The surface of the casting must be free from adhering sand, scale, cracks and hot tears as determined by visual inspection. Repairs by plugging or welding of any kind will not be permitted unless written permission is given by the Purchaser.
A lot consists of one of the following:
Test bars shall be separate castings cast from the same batch as the castings they represent and shall have the dimensions shown in the table. Allowances for reasonable pattern outline may be made within the tolerances shown in the table. Test bars A, B and C are standard test bars in the form of simple cylinders. Test bar S is special and designed for use where standard bars are not satisfactory.
Test rods shall be cast into dried, baked or chemically bonded moulds made primarily of siliceous sand aggregate with suitable binders. The average grain size of the sand shall be close to the size of the sand from which the castings are cast. Moulds for test rods shall be at approximately room temperature when cast. More than one test rod may be cast into a single mould, but each rod in the mould shall be surrounded by a thickness of sand not less than the diameter of the rod.
Test bars intended to represent castings cooled to below 480 degrees before mold shaking should be cooled to below 480 degrees in their molds. They may then be cooled to room temperature in still air.
Test bars intended to represent castings hotter than 480 degrees when shaken from their molds shall be cooled as described above or (by agreement between the manufacturer and purchaser) shaken from their molds at approximately the same temperature as the castings they represent.
When castings are stress relieved, annealed or otherwise heat treated, the test bars should be subjected to the same heat treatment and treated alongside the castings they represent.
Tensile testing is conducted in accordance with ASTM E8-04. A tensile test is performed on each batch and must meet the specified tensile requirements.
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