Control method of center loosening of φ280mm 35crmo round tube billet

Abstract

The invention discloses a center porosity control method for 35CrMo round steel casting blooms with cross section diameter being 280 mm. The method comprises the following steps: converter smelting, LF molten steel refining, RH refining and continuous casting of molten steel, and is characterized in that crystallizer electromagnetic stirring and solidification end electromagnetic stirring are combined in the continuous casting step. The method has the benefits that first, in the molten steel smelting step, control is carried out according to reasonable parameters, so as to improve the impurity of molten steel and ensure that the discharging conditions of the molten steel are optimal; and then, in the molten steel casting step, crystallizer electromagnetic stirring and solidification end electromagnetic stirring are combined to ensure that molten steel ingredients and temperature are homogenized, a blank shell grows uniformly, and columnar crystal structures are consistently scoured and fused in the stirring process, so that the areas of center porosity in the casting blooms are reduced, and the density is improved.

Description

technical field [0001] The invention relates to the field of iron and steel metallurgy, in particular to a method for controlling looseness in the center of a 35CrMo round tube steel billet with a section of φ280mm. Background technique [0002] 35CrMo billet steel is mainly used for the production of steel for oil well pipes used in oil and gas exploitation and transportation. P≤0.020%, S≤0.010%, V≤0.015%, Cr: 0.85%~1.05%, Mo: 0.17%~0.24%, Cu≤0.15%, Ni≤0.20%, Alt: 0.020%~0.040%, Residual element requirements: Nb≤0.010%, Ti≤0.010%, B≤0.005%, and V+Nb+Ti+B+Zr≤0.15%; As≤0.015%, Sn≤0.010%, Sb≤0.010%, Pb≤0.008 %, Bi≤0.010%, and As+Sn+Sb+Pb+Bi≤0.045%, and the balance is Fe. Under the joint action of stress and hydrogen sulfide gas during use, brittle fracture (called hydrogen sulfide stress corrosion) will occur suddenly when the stress is much lower than its own yield strength, which will easily cause problems such as production leakage, which is harmful to production and adv...

AI Technical Summary

Problems solved by technology

In particular, defects such as the loose center of the slab will have an adverse effect on the processing of the slab rolling through the pipe and the quality of the finished product

[0003] For 35CrMo tube billet steel, the high chromium and molybdenum content in the steel composition itself determines that the columnar crystals of the cast slab have a relatively large development trend. Moreover, because the cast slab has a relatively large section and is a round billet, its specific surface area is small. The heat transfer efficiency of the slab is lower, the solidification and cooling are slow, and the control of the crystallization structure is more difficult

During the continuous casting production process, the columnar crystals of the billet are developed, which often leads to the bonding between the columnar crystal dendrites, forming a closed space, and the molten steel continues to cool and solidify, shrinking in volume, and the liquid steel outside the space cannot be fed in time, resulting in loose and other defects. Defects cannot be effectively eliminated in the subsequent rolling process, affecting product quality