Q550D Steel Description
Q550D representation method: "Q" as the first letter of the Chinese character Pinyin of the yield strength of steel; "550" as the yield strength value, in MPa; D-quality grade is D grade (quality grade is divided into C, D , E).
Q550D When the customer needs to have the thickness direction performance of the steel plate, add the symbol representing the thickness direction (Z-direction) performance level after the above-mentioned specified grade, for example: Q550D-Z15, Q550D-Z25, Q550D-Z35.
Q550D steel standards: GB/T 16270-2009; GB/T1591-2018
Q550D Steel Plate Main Chemical Elements
a.
Carbon (C): The carbon content in the steel increases, the yield point and tensile strength increase, but the plasticity and impact resistance decrease. When the carbon content exceeds 0.23%, the weldability of the steel deteriorates, so it is used for welding. For low-alloy structural steels, the carbon content generally does not exceed 0.20%. The high carbon content also reduces the atmospheric corrosion resistance of the steel, and the high carbon steel in the open yard is apt to rust; in addition, carbon can increase the cold brittleness and time sensitivity of the steel.
b.
Silicon (Si): Silicon is added as a reducing agent and a deoxidizing agent during the steel making process, so the killed steel contains 0.15-0.30% of silicon. If the silicon content in the steel exceeds 0.50-0.60%, silicon is an alloying element. Silicon can significantly improve the elastic limit of steel, yield point and tensile strength, so it is widely used as spring steel. Adding 1.0-1.2% silicon to the quenched and tempered structural steel increases the strength by 15-20%. Silicon combined with molybdenum, tungsten, chromium, etc., has the effect of improving corrosion resistance and oxidation resistance, and can manufacture heat-resistant steel. Silicon-containing 1-4% low carbon steel, with a very high magnetic permeability, used in the electrical industry to make silicon steel sheet. An increase in the amount of silicon will reduce the weldability of the steel.
c.
Manganese (Mn): In the process of steel making, manganese is a good deoxidizer and desulfurizer, and the general steel contains 0.30-0.50% of manganese. When adding more than 0.70% of carbon steel, even if it is "manganese steel", it has more toughness than ordinary steel, and has higher strength and hardness, improves the quenchability of steel, and improves the hot workability of steel. For example, 16Mn steel is 40% higher than the A3 yield point. 11-14% manganese containing steel has extremely high wear resistance, used in excavator buckets, ball mill liners, etc. The increase in the amount of manganese reduces the corrosion resistance of the steel and reduces the welding performance.
d.
Phosphorus (P): Under normal circumstances, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates the welding performance, reduces the plasticity, and deteriorates the cold bending performance. Therefore, it is usually required that the phosphorus content in the steel is less than 0.045%, and the demand for high-quality steel is lower.
e,
sulfur (S): sulfur is also a harmful element under normal circumstances. The steel is made to be hot brittle, reduce the ductility and toughness of the steel, and cause cracks during forging and rolling. Sulfur is also detrimental to weldability and reduces corrosion resistance. Therefore, the sulfur content is usually required to be less than 0.055%, and the high-quality steel is required to be less than 0.040%. The addition of 0.08-0.20% sulfur to the steel improves the machinability and is commonly referred to as free-cutting steel.
Q550D steel smelting method: steel is smelted by converter or electric furnace, and refined outside the furnace if necessary.
Q550D delivery status: Q550D steel plate is usually delivered in quenched and tempered condition.
Q550D steel plate main application: mainly used in important (low temperature) high-strength structural parts, engineering machinery, mining steel structural parts.
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