The United States Nibo Ke is the United States the largest rated pressure ductile iron valve manufacturer. The NIBCO multi-turn valve is ideally suited for many applications: where cast iron or cast steel valves can be installed in industries such as hydrocarbons, chemicals, ships, fire protection, pulp and paper. As a replacement for steel, humans developed ductile iron in 1949. Cast steel carbon content of less than 0.3%, while the cast iron and ductile iron carbon content is at least 3%. The low carbon content in the cast steel allows the carbon present as free graphite to not form structural flakes. The natural form of carbon in cast iron is free graphite flake form. In ductile iron, this graphite sheet is modified into tiny spheres by special treatment. This improved ball makes the ductile iron more excellent in physical properties than cast iron and steel. It is this carbon's spherical microstructure that makes ductile cast iron more ductile and impact resistant while the sheet form inside the cast iron results in no ductile cast iron. The best ductility is achieved with a ferritic matrix, so all pressure-loaded components of NIBCO ductile iron are treated in a ferritic annealing cycle. The spherical structure inside the ductile iron can also eliminate the cracks that easily result from the flaky graphite inside the cast iron. In the microscopic picture of ductile iron, you can see the crack march to the graphite ball after the termination. In the ductile iron industry, these graphite balls are called "Crack Terminators" because they have the ability to stop cracking. Sometimes, ductile iron is called "the best of both worlds," meaning ductile iron has the strength of cast steel, and cast iron has excellent corrosion resistance. Nodular cast iron and cast iron (gray cast iron) compared with cast iron, ductile iron in terms of strength has an absolute advantage. Tensile strength of ductile iron is 60k, while the tensile strength of cast iron is only 31k. Ductile iron has a yield strength of 40k, whereas cast iron does not show yield strength and eventually breaks. Ductile iron strength - cost ratio is far superior to cast iron. (See page 83 for a complete comparison of mechanical properties). Ductile iron has the same corrosion resistance as cast iron. Ductile iron and cast steel comparison The strength of ductile iron and cast steel strength is comparable. Ductile iron has a higher yield strength, the lowest yield strength of 40k, while the yield strength of cast steel is only 36k. (See page 83 for a complete comparison of mechanical properties). In most municipal applications, such as water, salt water, steam, etc., ductile cast iron is more resistant to corrosion and oxidation than cast steel. Due to the spheroidal graphite microstructure of nodular cast iron, ductile iron is superior to cast steel in terms of its ability to attenuate vibrations and is therefore more conducive to stress reduction. An important reason for choosing ductile iron is that ductile iron is less expensive than cast steel. The low cost of nodular cast iron makes this material more popular, more efficient casting, and less machining costs for ductile iron.