RU2280700C1 - Method of heat treatment of rails - Google Patents

Abstract

FIELD: ferrous metallurgy; methods of heat treatment of railway rails.

SUBSTANCE: proposed method makes it possible to obtain maximum hardness (HB288) at depth of 22 mm from head rolling surface and high resistance of rails due to sufficient depth of hardened layer at homogeneous sorbitic structure. Rail is slightly cooled down after rolling heating to temperature of 820-870°C; it is cooled in two media: first with compressed air from head surface for 20-30 s at air flow rate of 3000-4000 m³/h, air temperature of 10-25°C and pressure of 0.55 Mpa; then, head is cooled with water-and-air mixture at flow rate of water of 25-30 l/min, water temperature of 10-30°C and pressure of 0.3-0.4 Mpa. Simultaneously with cooling the head, rail base is cooled with the same water-and-air mixture at temperature of 10-30°C, flow rate of 6-7 l/min and pressure of 0.08-0.09 Mpa.

EFFECT: enhanced efficiency.

2 tbl

Description

The invention relates to ferrous metallurgy, in particular to methods for heat treatment of railway rails.

A known method of hardening rails with rolling heating by differentially cooling the profile elements with compressed air [1]. Significant disadvantages of this method are the limited ability to obtain maximum values of hardness (HB388) on rails made of steel with a carbon content of 0.71-0.82%, insufficient depth of the hardened layer in the rail head.

There are also known methods of heat treatment of rails, including heating for hardening and surface cooling of the rail head with jets of water and a water-air mixture [2, 3]. The disadvantages of these methods are the heterogeneity of the structure along the depth of the hardened layer, the formation of unacceptable structures (upper bainite, martensite) in the near-surface layer of the head, insufficient straightness of the rails due to uneven cooling of all elements of the rail profile, and the need for cold dressing.

There is also known a method of heat treatment of rails [3], a prototype in which cooling of the head is carried out continuously to 100-400 ° C with an increase in the flow rate of the cooler from 1 to 50 volumes per second, after which controlled cooling of all profile elements is performed. A significant drawback of this method is the heterogeneity of the microstructure from the surface of the rail head, the possibility of the formation of unacceptable structures in the surface layer of the head (upper bainite, martensite), the inability to obtain maximum hardness values (HB388) at a distance of 22 mm from the head rolling surface.

The desired technical results of the invention are: increasing the set of mechanical properties, obtaining maximum hardness (HB388) at a depth of 22 mm from the head rolling surface, as well as increasing the operational stability of rails by obtaining a sufficient depth of the hardened layer with a uniform sorbitol structure.

To do this, the rail from rolling heating is cooled to a temperature of 820-870 ° C, then it is cooled in two environments: initially compressed air from the surface of the head for 20-30 seconds at an air flow of 3000-4000 m ³ / h, air temperature 10-25 ° C and a pressure of 0.55 MPa; then the head is cooled with a water-air mixture at a water flow rate of 25-30 l / min, a water temperature of 10-30 ° C and a pressure of 0.3-0.4 MPa, while the rail head is cooled, the sole is cooled with a water-air mixture at water temperature 10-30 ° C, a flow rate of 6-7 l / min and a pressure of 0.08-0.09 MPa.

The cooling of the rail head in two environments allows at the initial time by cooling the head surface to a temperature of 600-550 ° C for 20-30 seconds, ensuring the formation of sorbitol with a lamellar form of the carbide phase, which completely eliminates the possibility of formation in the surface layers of the head of unacceptable structures of upper bainite and martensite. Moreover, an increase in the cooling time with compressed air (more than 30 seconds) leads to a sharp decrease in hardness on the rolling surface, and with a decrease in cooling time (less than 20 seconds), the likelihood of the formation of martensite and bainite increases. The subsequent use of a water-air mixture with a constant flow rate of water helps to increase the depth and hardness of the hardened layer of the head to the required limits. The cooling of the rail sole with a water-air mixture is carried out to ensure its straightness. In this case, the water content in the mixture supplied to the sole should be four times less than on the head.

The claimed limits are selected experimentally based on the requirements for microstructure, straightness, mechanical properties and hardness of carbon steel.

The method was implemented in semi-industrial conditions on full-profile samples 1500 mm long, taken from a rail of type P65 made of steel grade NE76F. Heated to a temperature of 820-870 ° C, the samples were quenched in a cooling device, which consists of two sections, consisting of eight receivers, two of which are located above the rolling surface, four from the side of the side surfaces of the head, and two under the sole of the rail sample. The receivers have gratings formed by rows of holes with a diameter of 1.5 mm and located at a fixed distance (50 mm) from the rail surface. After heat treatment, the microstructure of the hardened metal was investigated, and the mechanical properties and hardness were determined.

The technological parameters of the heat treatment of rail samples are shown in table 1. The results of mechanical tests and studies of the microstructure in table 2.

The proposed method of heat treatment made it possible to increase the complex of mechanical properties, the hardness of steel, and also to increase the operational stability of the rails by obtaining a uniform sorbitol structure and increasing the depth of the hardened layer.

Information sources

1. V.V. Polyakov, A.V. Velikanov. Fundamentals of technology for the production of railway rails - M .: Metallurgy, 1990. 416 p.

2. A.S. USSR No. 518970, class C 21 D 9/04.

3. A.S. USSR No. 350843, class C 21 D 9/04.

4. A.S. USSR No. 522751, class C 21 D 9/04.

Table 1.
Technological parameters of heat treatment of a rail sample in a cooling unit consisting of two sections (length 1500 mm) No. Rail temperature, ° С Rail head heat treatment mode Outsole Cooling Mode Stage I II stage Compressed air pressure, MPa Compressed air consumption, m ³ / h Air temperature ° C Cooling time, sec Water pressure, MPa Water consumption, l / min Water temperature, ° С Cooling time, min Water pressure, MPa Water consumption, l / min one 840 0.15 1000 10 60 0.10 8 fourteen 5 0,03 one 2 820 0.25 1000 twenty 40 0.15 12 17 5 0.04 2 3 860 0.35 2000 10 thirty 0.20 16 26 four 0.05 3 four 850 0.45 2500 fourteen thirty 0.25 19 fourteen four 0.06 four 5 830 0.50 3000 eighteen twenty 0.30 23 twenty 3 0,07 5 6 820 0.50 3000 10 thirty 0.35 25 thirty 3 0.08 6 7 870 0.55 4000 25 twenty 0.40 thirty 10 2 0.09 7 8 870 0.55 4000 12 fifteen 0.40 thirty eighteen 2 0.09 7

Table 2.
Results of physical and mechanical tests and microstructure studies No. Microstructure of hardened rail head layer Depth of hardened layer (hardening sorbitol), mm Microstructure of the neck and sole of the rail The hardness of the rail, HB σ _t σ _in δ ₅ , φ KCU, J / cm ² PKG 10 22 neck sole N / mm ² % + 20 ° С -60 ° C one Sorbitol hardening 5-6 Perlite 341 331 321 293 293,283 710 1160 fifteen 44 27 12 2 Sorbitol hardening 7-8 Perlite 341 341 331 283 293,283 740 1180 13 37 28 fourteen 3 Sorbitol hardening 9-15 Perlite 375 341 331 302 293.302 840 1190 12 37 thirty 16 four Sorbitol hardening 18-23 Perlite 375 352 341 302 302,302 900 1280 12 35 thirty 22 5 Sorbitol hardening 24-26 Perlite 388 363 341 311 311,302 910 1290 eleven 36 33 24 6 Sorbitol hardening 25-28 Perlite 388 375 363 321 311,321 960 1320 12 35 thirty 25 7 Sorbitol hardening 27-30 Perlite 388 388 375 331 311,341 990 1340 12 34 32 24 8 Sorbitol quenching with martensite patches 27-30 Perlite 388 388 375 331 311,341 1040 1360 10 32 25 16 prototype Sorbitol hardening 25 363-388 352-363 321-331

Claims (1)

A method of heat treatment of rails, including continuous cooling of the head, followed by controlled cooling of the rail profile elements, characterized in that the rail from rolling heating is cooled to a temperature of 820-870 ° C and cooled in two environments: initially compressed air from the surface of the head for 20-30 s at an air flow rate of 3000-4000 m ³ / h, at an air temperature of 10-25 ° C and a pressure of 0.55 MPa, then the head is cooled with a water-air mixture at a water flow rate of 25-30 l / min, water temperature is 10-30 ° C and a pressure of 0.3-0.4 MPa, simultaneously but with cooling of the rail head, the sole is cooled with a water-air mixture at a water temperature of 10-30 ° C, a flow rate of 6-7 l / min and a pressure of 0.08-0.09 MPa.