ML35 and ML45 cold heading steel are widely used in the production of metal products, combined with the production process and product development of each steel mill, and the relevant situation of ML35 steel is specifically introduced.
Mechanical properties of ML35 steel
Project yield strength σs/MPa Tensile strength σb/MPa Elongation δ5/% Section shrinkage ψ/%
Standard ≥ 315 ≥ 530 ≥ 20 ≥ 45
Shougang optimization target 380 575 31 60
Shougang and Baotou Steel use ML35 steel for converters, Laiwu Steel and Jiangyin Xingcheng to produce ML35 steel by electric arc furnace. The production of ML35 steel is produced in accordance with the GB6478-86 standard and is mainly used to manufacture 8.8 high-strength standard parts.
Shougang proposed that the average yield strength of ML35 cold heading steel is 380MPa, the qualified yield strength is ≥380MPa; the average tensile strength of ML35 cold heading steel is 576MPa, the qualified tensile strength is ≥576MPa; the shrinkage of ML35 cold heading steel section The average is 56% and the acceptable face shrinkage is ≥56%.
Shougang and Baotou Steel produced ML35 cold heading steel using 80 tons converter smelting. The slag-making system of Baotou Steel is a single slag method. The oxygen supply system determines the oxygen pressure and changes the gun position. The end point control is to pull the carbon to make the blowing and increase the carbon after the furnace. The loading system is to make slag batching and multiple additions, strictly control the process temperature and prevent the steel from being peroxidized. The molten steel in the ladle is refined under the entire argon blowing state. Use a low-speed to high-speed to gradually increase the heating rate to heat and timely add slag-forming material, add CaC215~30kg, Al grain 25~50kg. Deep desulfurization under a reducing atmosphere, the average desulfurization rate was 59.2%.
Jiangyin Xingcheng Steel Co., Ltd. developed ML35 steel and formed mass production. 30t electric arc furnace smelting → 40t ladle furnace refining → R8m continuous casting 140 billet → billet fine integration grid and then rolled into a material. The steel mill measures to provide molten steel with high purity, temperature and uniform composition: (1) Strengthen the arc furnace tapping process and pre-deoxidation work in the pre-refining period. When the electric arc furnace is tapped, 1kg of silicon germanium is added in the downstream of the steel, and 0.3kg of aluminum wire is fed to the LF in the early stage of the LF. At the same time, the refining temperature of about 1600 °C is ensured, so that the deoxidation product has time to fully float. (2) The aluminum wire is replenished at the later stage of refining. Since the oxygen content of the molten steel is low at this time, most of the aluminum to be fed exists in the form of dissolved aluminum in the steel. (3) After adding aluminum, feed 1kg of silicon calcium per ton of steel to prevent nodulation during continuous casting and improve the shape and distribution of inclusions.
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