Distinguish from professional knowledge
In terms of professional knowledge, the expression methods of general ductile iron in the national standard are QT400-15, QT400-18, etc., where QT is the abbreviation of the first capital letter of ductile iron, 400 refers to the tensile strength of the part, 15, 18 refers to elongation. There are many representation methods of ductile iron in foreign countries, EN-GJS-400-15/18 in European standard, GGG40/GGG40.3/GGG50 in German standard and so on.
The general expression method of gray cast iron in the national standard is HT150, HT200, HT250, etc., where HT is the abbreviation of the first capital letter of gray cast iron, 150 refers to the tensile strength of the part, and the expression method of gray iron parts in German standard is GGG15 /GGG20/GGG25/GGG30 and so on.
The graphite in the gray cast iron structure exists in flakes, and the graphite in the nodular cast iron structure exists in a spherical shape; the gray cast iron has low strength and plasticity (flaky graphite splits the matrix, causing stress concentration), high brittleness, and good vibration damping performance. It is mainly used to produce some parts that do not require high strength; the splitting effect of spherical graphite on the matrix is minimized, and the stress concentration is minimized, which can give full play to the performance of the matrix, and has certain plasticity and good toughness.
