July 29, 2010

Carbon Steel Casting

Carbon steel have a good content of carbon, so it is easy to casting. especially A216 WCB.

It is important to clarify the meaning of carbon steel in the generic sense and in the more narrow context used in this report. The term steel is usually taken to mean an iron-based alloy containing carbon in amounts less than about 2%. Carbon steels (sometimes also termed plain carbon steels, ordinary steels, or straight carbon steels) can be defined as steels that contain only residual amounts of elements other than carbon, except those (such as silicon and aluminum) added for deoxidation and those (such as manganese and cerium) added to counteract certain deleterious effects of residual sulfur. However, silicon and manganese can be added in amounts greater than those required strictly to meet these criteria so that arbitrary upper limits for these elements have to be set; usually, 0.60% for silicon and 1.65% for manganese are accepted as the limits for carbon steel.

The carbon steels of interest in this report are those with carbon equal to or less than about 0.35% to facilitate welding. A further distinction can be made according to carbon content.

  • Low-carbon steels (below 0.15% carbon) contain too little carbon to benefit from hardening and are frequently used in the hot-worked or—for maximum ductility—the annealed condition. Steels of less than 0.25% carbon (often referred to as mild steel) have somewhat higher strength near the upper carbon level.
  • Medium-carbon steels (0.25–0.55% carbon) are often heat-treated (quenched and tempered) to achieve yet higher strength, but it is mainly the compositions below 0.35% carbon that are relevant to this report. Carbon steel is one of the most widely used materials in the industry. This material is used not only in many of the water- and steam-pressure containing systems in power plants but also in the supports for these systems. Although this report concentrates primarily on the pressure containing applications of carbon steels, it can also be a useful tool for structural carbon steel fabrication issues.

As the description implies, the primary alloying element of these iron based materials is carbon. Because carbon is such a powerful alloying element in steel, there are significant differences in the strength, hardness, and ductility achievable with relatively small variations in the levels of carbon in the composition. However, other important factors—such as material fabrication, heat treatment, component fabrication, and Introduction 1-2 fabrication processes—can result in significant changes to the properties of the carbon steel components.

In some cases, requirements established by codes and standards must be supplemented to achieve adequate results when working with carbon steels. It is important for the utility engineer to have access to metallurgical and properties information to aid in making decisions for projects involving carbon steels. This report is intended to provide such information on the most common boiler and piping materials used in power plants. Not all carbon steels will be covered explicitly, but the user should be able to draw relevant information needed for any required decision.



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