RU2425896C1 - Procedure for fabrication of double tee for mine mono-rail ways - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: process of fabrication of double tee for mine mono-rail ways consists in heating work-piece, in rolling at temperature 1040-1100C to summary reduction 80-85% of area of cross section of roll, in successive conditioning during 12-18 sec and in forming finished profile, in successive preliminary accelerated simultaneous cooling flanges along centre form external side and in places of flanges conjugation with wall of profile during 0.35-0.45 sec, in conditioning during 0.05-0.07 sec and in interrupted quenching of flanges simultaneously on external and internal sides during 0.60-0.75 sec. ^ EFFECT: high plastic characteristics and impact resilience at negative temperature at maintaining strength characteristics and uniformity of their distribution along cross section of double tee. ^ 1 ex, 2 tbl, 2 dwg

Description

The invention relates to ferrous metallurgy, in particular to the manufacture of complex sections of rolled products using heat from rolling heating with accelerated cooling of rolled products in a stream of continuous medium-graded mills, in particular an I-beam for mine monorails.

A known method of heat treatment of shaped sections of rolled products in the manufacture of channels and beams of various steel grades, including preliminary accelerated cooling of thin elements with a speed of 150-300 ° C / s to a mass average temperature of 750-600 ° C, followed by interrupted quenching of the entire profile and cooling in air (SU No. 933736, class C21D 8/00, 1/02, publ. 06/07/1982, BI No. 21).

The closest to the claimed method in terms of technical nature and the achieved positive result is a method of manufacturing rolled products of an angular profile, including austenization, hot rolling, bending the top of the corner to a temperature of self-tempering of 500-750 ° C, holding for at least 30 s, baking the whole product to temperatures of 700 -950 ° C and air cooling (SU No. 440426, class C21D 1/02, 7/14, 9/06, publ. 08/25/1974, BI No. 31).

A disadvantage of the known methods is the inability to provide a high level of consumer properties and mechanical characteristics of the finished product, such as five-fold elongation at break and toughness at low temperatures. This is due to the fact that the known methods are used to ensure the properties of shaped profiles with a shelf thickness of 1.3-1.7 times the wall thickness, and for an I-beam this ratio is 2-2.3.

The task of the invention is to increase the impact strength at negative temperatures and plastic characteristics of the I-beam, while maintaining the strength characteristics and uniformity of their distribution over its cross section.

The problem is achieved in that in a method of manufacturing rolled products, including heating the billet, rolling at a temperature of 1040-1100 ° C, preliminary accelerated cooling of individual profile elements from the temperature of the end of rolling, holding, interrupted hardening to a mass-average temperature of 740-790 ° C and final cooling in air, according to the invention, rolling is carried out to a total compression of 80-85% of the roll cross-sectional area, followed by exposure for 12-18 s and the formation of a finished profile, after which about, for 0.35-0.45 s, carry out preliminary accelerated cooling of the shelves in the center from the outside and in the places of interfacing of the shelves with the profile wall, then, after holding for 0.05-0.07 s, interrupted hardening is carried out shelves simultaneously from the inside and outside for 0.60-0.75 s.

The technical result of the invention is to obtain high plastic properties while maintaining high strength characteristics of the finished rolled product of a complex profile, which can be achieved by controlling the recrystallization processes, starting from the formation of the finished profile using hot deformation and the subsequent accelerated cooling mode.

Achieving the specified technical result is ensured by the fact that rolling is carried out to a total compression of 80-85% of the roll cross-sectional area, followed by exposure for 12-18 s and the formation of a finished profile, after which simultaneously, for 0.35-0.45 s carry out preliminary accelerated cooling of the shelves in the center from the outside and in the places of interfacing of the shelves with the profile wall, then, after holding for 0.05-0.07 s, interrupted hardening of the shelves is carried out simultaneously from the inside and the outside for 0.60 -0.75 s

The proposed method of manufacturing an I-beam for mine monorails with a specified set of features, a sequence of operations and a choice of intervals of values of signs in the specified range of their changes ensures the achievement of a technical result, which consists in providing high plastic characteristics and impact strength at negative temperatures while maintaining strength characteristics and uniformity of them distribution of the I-section for mine monorail from low alloy OF DATA steels.

It was experimentally established that the total reduction of more than 85% at the indicated rolling temperatures can lead to a disruption of the metal continuity, which is unacceptable. To ensure strain hardening at temperatures above 1000 ° C, rolling must be carried out with a total compression of at least 80% of the roll cross-sectional area. To relieve strain stresses and conduct the process of static recovery and static recrystallization after hot deformation with the indicated reductions, an exposure time of at least 12 s is required, which will ensure restoration of the ductility of the metal. To stop the recrystallization process, the shutter speed before final rolling should be no more than 18 s. In addition, when holding for more than 18 s in the range of the indicated temperatures, rapid grain growth begins, which negatively affects the strength characteristics of the metal. Such a process of deformation will provide a highly dispersed structure that is uniform over the entire cross section of the profile, the preservation of which during subsequent heat treatment will provide an increase in ductility while maintaining high strength in the finished product.

It is known that at temperatures above 1000 ° C, the primary recrystallization process takes fractions of a second, and the process of collective recrystallization quickly develops, which leads to rapid grain growth, respectively, to softening of the metal and a decrease in its plastic characteristics. In this regard, immediately after rolling, it is necessary to carry out preliminary accelerated cooling for at least 0.35 from massive parts of the profile — shelves in the center from the outside at the same time as the shelves mate with the wall, as shown in Fig. 1. Preliminary accelerated cooling lasting more than 0 , 45 s and subsequent exposure less than 0.05 s will lead to a large temperature imbalance between the shelves and the wall and, accordingly, to warping of the profile. To ensure a combination of high strength characteristics with high ductility, the shutter speed before interrupted quenching should be no more than 0.07 s. The process of interrupted quenching of the shelves simultaneously from the inner and outer sides (Fig. 2), in the second stage of cooling, provides accelerated heat removal from the central layers of the shelves during cooling for at least 0.60 s, which will prevent high tempering in the transitional layers of the shelves at equalization of temperatures between the center and the surface. Interrupted quenching for a period of not more than 0.75 s will make it possible to obtain a finely dispersed bainitic structure in the transition layers of the shelves, providing high plastic characteristics of the metal and impact strength at low temperatures.

The drawing (Fig. 1) shows a diagram of the simultaneous accelerated cooling of massive parts of the profile — the shelves in the center from the outside, with the interface between the shelves and the wall, and FIG. 2 shows a diagram of the interrupted hardening of the shelves simultaneously from the inside and the outside.

Example. Industrial testing of the inventive method for manufacturing an I-beam for monorail mine roads was carried out in a mid-grade workshop of OJSC West Siberian Metallurgical Plant at mill 450 in the manufacture of a DP155 I-beam from industrial melting steel 09G2S. For this purpose, hot rolling of continuously cast billets with a cross section of 200 × 150 mm at a temperature of 1080 ° C was carried out to a total compression of 84% of the roll cross-sectional area, then exposure was carried out for 16 s and the finished profile was formed, after which preliminary accelerated cooling was simultaneously carried out on the shelves to the center from the outside and at the interface between the shelves and the profile wall for 0.40 s, followed by exposure for 0.06 s. After exposure, the shelves were quenched simultaneously from the inner and outer sides for 0.65 s. Hardening was interrupted when the mass-average temperature of the I-beam reached 760 ° C, and the final cooling was carried out in air.

According to the proposed method, several modes were tested, providing for a change in the total reduction during hot rolling, the shutter speed before forming the finished profile and after preliminary accelerated cooling, accelerated cooling and interrupted quenching, the temperature range of hot rolling and mass average temperature before final cooling in air in the claimed the range of their changes with going beyond the boundary values. Modes of implementation of the proposed method are shown in table 1.

After the implementation of these modes, the tensile strength σ _B , yield strength σ ₀₂ , fivefold elongation δ ₅ and impact strength at −40 ° C KCU were determined. The results of industrial tests are shown in table 2.

So, upon reaching a temporary tensile strength of 530-550 N / mm ^2, an I-beam with high five-fold elongation and impact strength of 170-190 J / cm ^{2 was} obtained, which is 1.4-1.5 times higher compared to the prototype.

Table 1 The modes of implementation of the proposed method of thermomechanical processing No. at measure Tempera
rolling round, ° С Σ
tie,% Exposure after Σ compression, s Accelerated
cool
s Aging
ka before temper
Coy, with Interrupted
quenching, s Mass average temperature after hardening, ° С one 1040 85 12 0.45 0.05 0.60 740 2 1100 80 eighteen 0.35 0,07 0.75 790 3 1080 84 16 0.40 0.06 0.65 760 four 1030 79 eleven 0.50 0.04 0.55 730 5 1110 86 19 0.30 0.08 0.80 800

table 2 Mechanical properties of high strength bar reinforcement No. at measure Tensile strength σ _V , N / mm ² Yield strength σ _0.2, N / mm ² Five-fold elongation δ ₅ ,% Impact strength at -40 ° C KCU, J / cm ² Proposed solution one 550 400 32 176 2 530 345 33 180 3 540 385 34 189 four 560 430 29th 121 5 500 325 thirty 136 Prototype 510 330 28 125

From these tables it can be seen that in the manufacture of a double tee for mine monorail DP155 by the proposed method, better results were obtained in terms of plasticity and impact strength at low temperatures at a high level of strength than in the prototype.

The proposed method is industrially applicable at metallurgical enterprises having continuous section rolling mills and producing complex shaped sections. For example, the implementation of the proposed method for the manufacture of high-strength and plastic I-beams on 450 continuous rolling mill ZSMK OJSC showed high technology efficiency and allowed to obtain high plastic characteristics and impact strength at low temperatures while maintaining strength characteristics and uniformity of their distribution over the I-section for mine monorails from low alloy steels.

Currently, the I-beam is in high demand in the mining and coal industries.

Claims (1)

A method of manufacturing an I-beam for monorail mine roads, including heating the billet, rolling at a temperature of 1040-1100 ° C, preliminary accelerated cooling of individual profile elements from the temperature of the end of rolling, holding, interrupted hardening to a mass-average temperature of 740-790 ° C and final cooling in air, characterized in that the rolling is carried out to a total compression of 80-85% of the cross-sectional area of the roll, followed by exposure for 12-18 s and the formation of the finished profile, and then simultaneously, during 0.35-0.45 s, carry out preliminary accelerated cooling of the shelves in the center from the outside and at the points of interfacing of the shelves with the profile wall, and then, after holding for 0.05-0.07 s, interrupted hardening of the shelves is carried out simultaneously with internal and external sides for 0.60-0.75 s.

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