Method for producing high-specification ultrahigh-obdurability aging-free railway basic construction steel

Abstract

The invention relates to a method for producing high-specification ultrahigh-obdurability aging-free railway basic construction steel, belonging to the technical field of railway steels. The method comprises the steps of converter primary smelting, LF (Ladle Furnace) refining, continuous casting, continuous rolling, offline multi-section medium frequency induction heated quenching and multi-section tempering, wherein molten iron, waste steel and various alloy elements are used as raw materials, and a special smelting process is adopted; a steel billet is heated and continuously rolled by adopting an uncontrolled rolling and controlled cooling type process; and after steel is subjected to offline medium frequency induction heat treatment, the high-specification ultrahigh-obdurability aging-free railway basic construction steel is produced, wherein Rel is not less than 1,080Mpa, Rm is not less than 1,230 Mpa, A5 is not less than 6 percent, and the relaxation performance is not more than3 percent. By utilizing production smelting process equipment of the traditional steel types, approaches of reasonably proportioning chemical components of cheap alloy elements, optimizing the production process, and the like and the offline medium frequency induction heat treatment, the invention has the advantages of eliminating the influence of hot-rolling tissue inheritance on the performance of the steel, leading the steel production to reach the ultrahigh-obdurability target technical requirement in the same day and omitting the aging time.

Description

technical field [0001] The invention belongs to the technical field of railway steel, and in particular relates to a production method of large-scale ultra-high-strength toughness and aging-free railway infrastructure steel, which is suitable for the production of ultra-high-strength toughness and long-span railway infrastructure bridges. Background technique [0002] In recent years, with the large-scale construction of railways driven by domestic demand in my country, it is difficult to meet the requirements of the traditional general steel whose strength level is increased through the controlled rolling and controlled cooling process. There is an urgent need for an ultra-high-strength toughness steel for the infrastructure construction of railway cross-sea bridges. In order to ensure the service life of "permanent" buildings, the requirements for the safety, earthquake resistance and fire resistance of steel used in the infrastructure structure of ultra-high strength and t...

AI Technical Summary

Problems solved by technology

Due to the production of steel with added V and Nb alloying elements, even though they are used in small amounts, the price of V and Nb ferroalloys is relatively high, and the cost per ton of steel increases significantly

In addition, for the traditional bar rolling production, the heating temperature is unstable, and the control of the cooling equipment between the racks fluctuates greatly, resulting in the following problems in the production of large-scale (>φ25mm) high-strength finish-rolled threads in the traditional process:

[0004] 1) Due to the characteristics of the controlled rolling and controlled cooling process of traditional bar mills, even with the conditions of multi-stage water cooling and temperature control devices between stands, it is difficult to achieve low Temperature-controlled rolling (ie: final rolling temperature ≤ 700°C, deformation ≥ 30%) refines the grains, and the final structure of the steel is difficult to control, resulting in large fluctuations in the mechanical properties of the steel and instability

[0005] 2) In actual production, it is difficult to achieve low-temperature controlled rolling in general bar rolling mills. If the final rolling temperature is higher than 1000°C, the austenite grains of the steel are relatively coarse, and during the cooling process, the γ→α phase transformation The rate is low, the ferrite phase transformation is insufficient, and the phase transformation can produce a certain amount of bainite. When the proportion is greater than 20%, the Rm index is high, the yield strength Rel is not obvious, and the plasticity index (elongation A5%) Obvious reduction

[0006] 3) Hot-rolled low-alloy high-strength round steel, after the controlled cooling process, the forced cooling and self-tempering process is difficult to control, and the normal structure of the core is usually P+F type. In this metallographic state, even if the grain size Reaching ultra-fine grain, the strength index and toughness index of its comprehensive mechanical properties have reached the maximum limit, and the steel properties cannot meet the requirements of: Rm≥1230Mpa, Rel≥1080Mpa, A5≥6%, and relaxation performance≤3%

[0008] 5) For the high-strength finish-rolled thread with transverse ribs, the traditional controlled rolling and controlled cooling process can only improve the strength through the "ultra-fast cooling + self-tempering process", and the thread root of the base circle of the finish-rolled thread cross-section will bring cooling Inhomogeneous, relying on the self-tempering of steel bars on the cooling bed in the air cannot satisfy the release of high-strength residual stress

[0009] 6) With the increase of steel specification size, the specification size effect increases

The main reason is that the diameter increases, and the cooling rate from the surface to the core of the steel decreases, resulting in coarse internal grains and a decrease in yield strength

Studies have shown that if the diameter of controlled rolling and controlled cooling steel is greater than 25mm, its yield strength will be significantly reduced

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