RU2265066C2 - Method of heat treatment of large-sized articles - Google Patents

Abstract

FIELD: metallurgy of iron.

SUBSTANCE: method comprises heating articles up to austenitic condition, soaking, cooling, and tempering. The articles whose wall thickness does not exceed 30 mm are cooled in two stages. First, the articles are submerged into the hot water with a temperature of no less than 80°C or cold water with a temperature no more than 40°C. Second, the articles are cooled in air. The articles whose wall thickness exceeds 30 mm are cooled in three stages. First, they are submerged into hot water with a temperature no less than 80°C or cold water with a temperature of no more than 40°C. Second, short-term submerging into the cold or hot water. Third, short term submerging into the hot or cold water and/or in air.

EFFECT: reduced deformation of article faces.

2 dwg, 2 tbl

Description

The invention relates to the field of hardening heat treatment of large-sized products such as connecting parts of pipelines or thick-walled large-diameter pipes of strip steels.

A known method of hardening heat treatment of pipes by heating them in continuous sectional furnaces to a predetermined temperature and cooling with dispersed water or an air-air mixture when they exit the furnace in sprayers, followed by tempering in continuous sectional furnaces at a temperature of 550-650 ° C (see. Thermal hardening of rolled products) / Edited by K.F. Starodubov, M., Metallurgy, 1970, p. 170).

The disadvantage of this method is the inability to obtain metal with the desired bainitic or ferritic-bainitic structure for products with a thickness of 25-30 mm and above due to the limited cooling rate of the metal. In addition, the connecting parts of pipelines, having a different shape, cannot, like pipes, be heated in sectional furnaces and cooled in sprayers in a continuous mode, when transportation is carried out by roving rolls with simultaneous rotation of the products.

The closest in technical essence, the achieved effect and selected as a prototype is a method of heat treatment of large-sized products, including heating the products to an austenitic state, aging, cooling in a tank with a quenching medium and tempering. Cooling is carried out in two stages. In the first stage, the product is cooled in water with a temperature of (t _boiling. -10 ° C) -t _boiling. or aqueous solutions of salts with a temperature (t _boiling. -50 ° C) -t _boiling. until the product surface acquires a temperature of 180-550 ° C. At the second stage, cooling is carried out by intermittent bathing or cooling in air (see USSR AS No. 1576578, class C 21 D 1/56, application. 4.05.88, publ. 7.07.90 “Method for the heat treatment of large-sized products” )

The wall thickness of large-sized products, in particular connecting parts of pipelines, varies from 9 mm to 80 mm. Obviously, in order to obtain the optimal structural state of the metal of such products, namely, bainitic or ferrite-bainitic structure, it is necessary to carefully select processing parameters depending on the product wall thickness, steel grade, type and temperature of the quenching medium. The disadvantage of the prototype method is the lack of reliable criteria for choosing the parameters of hardening heat treatment of the product. This leads to an uneven flow of processes of structure and carbide formation and, therefore, the difficulty of ensuring a satisfactory level of warping of the ends of the products.

The objective of the present invention is to ensure the uniformity of the processes of structure- and carbide formation in products with different wall thicknesses.

The technical result obtained by the implementation of this invention is to reduce warpage of the ends of the products.

This problem is solved due to the fact that in the known method of heat treatment of large-sized products, including heating the products to an austenitic state, aging, cooling stages of products and tempering, according to the invention, products with a wall thickness of not more than 30 mm are cooled in two stages, first by immersion in hot water with a temperature of at least 80 ° C or cold water with a temperature of not more than 40 ° C, and in the second stage in air, products with a wall thickness of more than 30 mm are cooled in three stages, first by immersion in hot water with a temperature of a swarm of at least 80 ° C or into cold water with a temperature of not more than 40 ° C, in the second stage - intermittent bathing in cold or hot water, and in the third stage - intermittent bathing in hot or cold water and / or air, in the first stage, cooling in hot water is carried out to a surface temperature of the product of at least 180 ° C, and in cold water - to a surface temperature of the product of at least 300 ° C, in the second stage, cooling is carried out at an average temperature over the cross section of the product wall (M _n - 550 ° C), where M _n - transformed martensite start temperature tions and cooling duration, at least until complete transformation of austenite to ferrite-bainite or bainitic structure according to thermokinetic diagram decay austenite steel grade for a particular product.

Studies conducted on the sources of patent and scientific and technical information have shown that the claimed method is unknown and does not follow explicitly from the studied prior art, i.e. meets the criteria of novelty and inventive step.

The method can be carried out at any enterprise specializing in this industry, because this requires well-known materials and standard equipment, and is widely used in the heat treatment of metal products, i.e. is industrially applicable.

To obtain a large number of particles of the secondary phase (carbides, carbonitrites) uniformly distributed in the matrix, it is necessary to rapidly cool the product from a uniform austenitic state at a rate sufficient to prevent the release of dissolved interstitial atoms (carbon and nitrogen) from the solid solution. In this case, the temperature of the end of accelerated cooling plays an important role in creating a supersaturated solid solution in which the process of carbon and nitrogen evolution is suppressed. This is due to the fact that these elements, even at low metal temperatures, have significant diffusion ability. It was experimentally established that the claimed optimally selected temperature ranges and the type of quenching medium make it possible to obtain a ferrite-bainitic or bainitic metal structure for each range of wall thickness of the product due to the uniform occurrence of structural and carbide formation processes. This provides a reduction in warpage of the ends of the products.

When selecting the optimal processing parameters, both the surface temperature of the product and the average temperature over the cross section of the product wall were taken into account, i.e. the temperature acquired by the wall as a result of heating in air (due to warmer deep layers) after dipping into the quenching medium.

The proposed method of heat treatment of large-sized products was tested under industrial conditions when hardening the connecting parts of pipelines, namely die-welded tees with a diameter of 530 mm and 1020 mm, made of steel 10G2FBYu. In identical conditions, the prototype method was tested.

The heat-treated products were heated in an oven to 950–980 ° C, held at this temperature, and then cooled. The cooling characteristics and the obtained metal properties are presented in table 1.

Measurements to determine the degree of warpage of the tee were carried out after various modes (characteristics of the modes are given in table 1) processing. The measurement results to determine the degree of warpage of the products according to the claimed method and the prototype method are shown in table 2.

The invention is illustrated by drawings, in which:

Figure 1 Front view (from the side of the end) on the connecting piece of the pipeline - a tee / this figure shows the position of the measuring points of the diameter of the end of the tee /.

Figure 2 Cooling curves of the proposed method:

dashed line - cooling according to mode 3 (the characteristic of the mode is given in table 1) for a die-welded tee with a diameter of 530 mm and a wall thickness of 26 mm from steel grade 10G2FBY

solid line - cooling according to mode 6 (the characteristic of the mode is given in table 1) for a die-welded tee with a diameter of 1020 mm and a wall thickness of 40 mm from steel grade 10G2FBYu.

Analysis of the data given in the tables shows that the proposed method allows to reduce warpage of the ends of the products.

In addition, the proposed method ensures the achievement of a high level of mechanical properties of the product and increases the resistance of the metal to softening during subsequent heating (for example, during tempering and welding).

Table 1 No. by processing mode Type of method After quenching cooling circuit Product wall thickness, mm Mechanical properties of metal products Yield Strength, MPa Tensile strength, MPa Relative extension, % Impact strength KCV ^-20 MJ / m ² one


Prototype method Cooling in water with a temperature of 96 ° C to a surface temperature of the product of 150 ° C

Bathing in water with a temperature of 96 ° C until the product raised to air reaches a temperature of 500 ° C

Air cooling

26

610

706

17

0.35 2
40
490
640
nineteen
0.5 3 The inventive method Cooling in hot water with a temperature of 80 ° C to a surface temperature of the product 180 ° C

Air cooling with temperature averaging over the wall section up to 430 ° С and holding for 80 s. until austenite is completely converted to bainite according to the thermokinetic diagram 26 600 710 21 0.75 4 Cooling in hot water with a temperature of 80 ° C to a surface temperature of the product 180 ° C

Bathing (3.5 min in water, 1.0 min in air) in hot water with a temperature of 80 ° C at an average temperature over the wall section of 550 ° C for 80 s until the austenite is completely converted to bainite according to the thermokinetic diagram

Air cooling 40
500
620
25
1,2
5
Cooling in cold water with a temperature of 30 ° C to a surface temperature of the product 300 ° C

Cooling in air with averaging the temperature of the metal over the cross section up to 450 ° C and holding for 80 s for the complete conversion of authenite to bainite according to the thermokinetic diagram 26
620
760
twenty
0.5



6

Cooling in cold water with a temperature of 30 ° C to a surface temperature of the product 300 ° C

Bathing (1.5 min in water, 0.5 min in air) in cold water with a temperature of 30 ° C at an average temperature over the wall section of 550 ° C for 80 s

Cooling by bathing (1 min in water, 0.5 min in air) in cold water with a temperature of 30 ° C at an average temperature over the wall section of 300 ° C and further cooling in air 40

540

670

23

11.1 Note: The temperature of the onset of martensitic transformation for a given composition of 10G2FBYu steel (Mn) is 420 ° C.

table 2 Processing mode Absolute dimensions of the diameter of the end of the tee after various processing modes, mm Section 1-1 Section 2-2 Section 3-3 Production + calibration of the ends, i.e. the initial state
(numerator - for wall thickness 26 mm, denominator - for wall thickness 40 mm) 530/1020 530/1020 530/1020 Heat treatment according to mode 1, i.e. in accordance with the prototype 526 533 527 Heat treatment according to mode 2 i.e. in accordance with the prototype 1017 1024 1018 Heat treatment mode 3 529 530 529 Heat treatment mode 4 1019 1020 1019 Heat treatment mode 5 529 531 529 Heat treatment mode 6 1020 1019 1021

Claims (1)

A method of heat treatment of large-sized products, including heating the products to an austenitic state, aging, cooling stages of products and tempering, characterized in that products with a wall thickness of not more than 30 mm are cooled in two stages, first by immersion in hot water with a temperature of at least 80 ° C or cold water with a temperature of not more than 40 ° C, and in the second stage in air; products with a wall thickness of more than 30 mm are cooled in three stages, first by immersion in hot water with a temperature of at least 80 ° C or in cold water with a temperature of not more than 40 ° C, in the second stage by intermittent bathing in cold or hot water, and at the third stage - intermittent bathing in hot or cold water and / or in the air; at the same time, in the first stage, cooling in hot water is carried out to a surface temperature of the product of at least 180 ° C, and in cold water - to a surface temperature of the product of at least 300 ° C, in the second stage, cooling is carried out at an average temperature over the cross section of the product wall (M _n - 550 ° C), where M _n - martensite start temperature, and cooling duration, at least until complete transformation of austenite to ferrite-bainite or bainitic structure according to thermokinetic diagram decay austenite steel grade for CONCRETE Nogo product.

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