The alloying elements of low alloy steel are less than 5%. The low alloy steel is added one or several alloy elements on the basis of carbon steel to improve the performance. Such as manganese, silicon, aluminum, nickel, copper, boron, phosphorus, rare earth, etc. A709 grade 50W bridge steel plate Steel with one or more of these elements will have the advantages of high strength and toughness. Due to the addition of few alloy elements, it is called low alloy high strength steel.
In addition, according to customs statistics, from January to February, 7.81 million tons of A709 grade 50W bridge steel plate and so on steel were exported, 2.04 million tons of imported steel, and 6.01 million tons of net exported steel were converted into crude steel, a year-on-year decrease of 33.7%. According to the above data, the average daily supply of crude steel in China from January to February was 2478200 tons, down 5.09% from December of last year, up 3.70% year on year. Compared with the situation of delayed demand, steel production keeps growing, and the market presents a situation of supply exceeding demand.
The outer diameter of the hot-rolled seamless pipe is generally larger than 32mm, and the wall thickness is 2.5-75mm. The diameter of the cold-rolled seamless pipe can be 6mm, the wall thickness can be 0.25mm, the outer diameter of the thin-walled pipe can be 5mm, and the wall thickness is less than 0.25mm. The size accuracy of the cold-rolled seamless pipe is higher than that of the hot-rolled seamless pipe, A709 grade 50W bridge steel plate.
Normalizing is to heat the steel parts to 30~80℃above the critical temperature for a period of time. Then the parts are taken out of the furnace and cooled in air. Since the cooling rate of normalizing is faster than that of annealing, the strength and hardness of normalized A709 grade 50W bridge steel plate are higher than that of annealed A709 grade 50W bridge steel plate, but the elimination of internal stress is not as good as annealing. The normalizing operation of A709 grade 50W bridge steel plate is simple, the cost is low, the productivity is high, and it is widely used in actual production.
