Historical Version s - view previous versions of standard. Work Item s - proposed revisions of this standard. More A This specification covers steel castings, general requirements, for pressure-containing parts.
|Genre:||Health and Food|
|Published (Last):||16 December 2008|
|PDF File Size:||8.50 Mb|
|ePub File Size:||10.90 Mb|
|Price:||Free* [*Free Regsitration Required]|
What is the purpose of this requirement? When steel is melted, oxygen and nitrogen can be dissolved in the molten steel. When the metal is poured into the casting mold, the oxygen can come out of the solution and form gas porosity in the castings. In order to avoid castings with excessive gas porosity, the foundry may add deoxidizing elements to the melt. The presence of these elements results in the formation of oxide compounds, which mitigates the formation of oxygen gas bubbles during solidification.
One of the elements that is sometimes added as a deoxidizer is aluminum, which creates a potential for the formation of aluminum nitride. This compound tends to precipitate in the prior austenite grain boundaries and can result in castings that display loss of ductility that could result in brittle failure of the casting if it is shock-loaded in service. If fracture occurs, it has a rock-candy appearance due to fracture along the prior austenite grain boundaries.
The fracture is often very shiny due to the presence of aluminum nitride platelets on the surface. Most foundries have the equipment necessary to analyze and report aluminum content. Although some foundries monitor nitrogen levels in their steel, many do not have the necessary equipment to do this. The specifications for the common cast steels used in valve bodies do not require analysis or reporting of nitrogen as a standard requirement. Therefore, the nitrogen content of the steel is often not known or reported, and it is possible that enough nitrogen is present to form aluminum nitride.
Certain elements are known to inhibit the formationof aluminum nitride. It has also been found thathigher levels of phosphorus, sulfur,boron, molybdenum and copper inhibitaluminum nitride embrittlement.
The thickness of the casting orportion of the casting is an obviousfactor influencing whether embrittlementoccurs, since thicker casting sectionswill cool more slowly through thecritical temperature range than thinsections. The casting configuration can also influence the cooling rate. A complex casting with relatively thin walls may experience slower cooling rates than a simple casting with the same wall thickness because the complex casting will lose heat through the mold less effectively.
The mold material can also influence the cooling rate. For example, air-set sand is known to inherently produce molds that cool slower than green-sand molds.
For heats with aluminum content greater than 0. The resulting etched specimen is compared with 10 reference macrographs. Heats with severity levels 4 and lower are acceptable. Looking for a career in the Valve Industry? Renewable Energy Consumption Surpasses C.
Latest Web Only. Sections New! Industry 4. Latest Articles. Latest Products. Post: 01 June Upcoming Valve Industry Events Reprints. Secret Key. Remember Me. Variables That Influence Embrittlement There are a number of variables that influence the potential for this type of embrittlement: 1 The steel must contain enough aluminum and nitrogen to support the formation of enough aluminum nitride to cause a significant embrittling effect.
Latest Post Popular Links Events. Visit VMA. Emerson: Virtual Valve Repair Service.
Active, Most Current. Prices subject to change without notice. About Us. Contact Us. Sign In. Standards Store.