RU2756671C1 - Method for production of grinding balls (options) - Google Patents

Abstract

FIELD: grinding equipment.

SUBSTANCE: invention relates to a method for producing grinding balls made of steel containing, by wt. %: C 0.75-0.80, Mn 0.80-0.90, Si 0.25-0.35, Al less than 0.020, P less than 0.015, S less than 0.020, Cr 0.35-0.40, Ni 0.15-0.25, Cu less than 0.030, V 0.10-0.15, Mo 0.03-0.05, N less than 0.015, H less than 0.0003, Fe being the rest. The method includes the production of balls with a nominal diameter of 80-100 mm, after rolling, the balls are cooled to a temperature of 740-800°С, the balls are quenched in a quenching medium with an exposure time of 3.0 to 4.0 minutes, and the subsequent tempering is carried out at a temperature of 180-260°С and an exposure time of 180 to 320 minutes, while after tempering, self-release is carried out with an exposure time of 12 to 48 hours. The method includes the production of balls with a nominal diameter of 110-140 mm, after rolling, the balls are cooled to a temperature of 740-800°С, the balls are quenched in a quenching medium with an exposure time of 3.5 minutes to 5.0 minutes, and the subsequent tempering is carried out at a temperature of 180-260°С and an exposure time of 180 to 320 minutes, while after tempering, self-release is carried out with an exposure time of 12 to 48 hours.

EFFECT: increase in the operational resistance of the balls, obtaining grinding balls with a volumetric hardness characterized by group 5 of hardness according to GOST 7524-2015 on a production scale.

6 cl, 2 dwg, 2 tbl, 1 ex

Description

The invention relates to rolling production, in particular to heat treatment of grinding balls.

Known inventions of obtaining steel for the production of grinding balls: patent RU No. 2415194 C1 "Steel" MPK6 C22C 38/38; C22C 38/34; C22C 38/32, published on March 27, 2011, bulletin 9 [1], patent RU No. 2425168 C2 "Steel" MPK6 C22C 38/26, published on July 27, 2011, bulletin 21 [2], patent RU No. 2425169 "Steel" MPK6 C22C 38/40, published on 07/27/2011, bul. 21 [3], as well as copyright certificates, copyright certificate SU1497262 A1 "Steel" MPK6 C22C 38/14, convention priority 01/13/1988 [4], copyright certificate SU1446189 A1 " Steel "MPK6 C22C 38/16, published on 23.12.1988 [5].

A known method for the production of steel grinding balls patent RU No. 2596737 C1 MPK6 C21D 9/36; B21H 1/14; C21D 1/02; B23P 15/00; C22C 38/40, published 10.09.2016, bul. 25 [6], including heating of a continuously cast billet, rolling on a hot section mill of round billets of an appropriate size, then heating them in an induction device, rolling balls from them on a helical rolling mill at a temperature of 950-1050 ° C, cooling the balls before quenching, quenching and self-tempering of balls in containers, while a square continuously cast billet is made with a section of (100-150) × (100-150) mm from steel with the following ratio of components, wt%: carbon 0.6-1.05; silicon 0.15-2.0; manganese 0.2-1.2; chromium 0.03-0.5; copper 0.03-0.40; iron and inevitable impurities, and the rest, and heating of round billets is carried out in an induction device to a temperature at the outlet of the inductors of 1070-1140 ° C, the balls are cooled to a quenching temperature of 840-900 ° C in a cooling drum with a rotation speed in the range of 6.0- 22.0 rpm with equalization of the temperature of the balls over the section due to the rotation of the balls in the drum for less than 2 minutes, and the quenching of the balls is carried out in the quenching drum at a speed of its rotation in the range of 0.4-2.5 rpm with running water with a temperature 25-42 ° C to a ball temperature after quenching 125-160 ° C.

The disadvantage of this method is that this method does not allow to obtain the 5th group of hardness with continuous hardenability, but only partial hardenability corresponding to the 4th group, and has a lower gradient.

Known device and method for heat treatment of balls, patent RU 2455369 C1 MPK6 C21D 9/36, published 10.07.2012, bulletin 19 [7], including after stamping or rolling heating, cooling the balls from the temperature of stamping or rolling to the temperature of quenching, quenching by cooling balls from the temperature of quenching in water and tempering, while before quenching, the temperature of the balls is equalized, and then they are cooled with water at a cooling rate of no more than 12 deg / s 150-200 ° C below the temperature of the end of rolling or stamping.

The disadvantage of this method is that it lacks the technology for producing balls of hardness group 5. Also, a significant difference in the technology is the temperature of the balls before quenching, which is 830-900 ° C, which implies the use of target steels below the 5th hardness group.

The known method of heat treatment of grinding balls patent No. 2113513 MPK6 C21D 9/36; B21H 1/14, published 10.09.2016, bul. 25 [8], including rolling, cooling to the hardening temperature for 2-15 minutes. and hardening.

There is a known method of heat treatment of grinding balls copyright certificate No. 1344793 A1 MPK6 C21D 9/36, published on 10/15/1987 [9], including heating to the austenitizing temperature, holding, cooling, and quenching in water, while cooling is carried out at a speed of 20-50 ° C / s until the average temperature across the cross section of the balls reaches 600-70 ° C.

The disadvantage of these methods is that the modes of heat treatment do not allow obtaining continuous hardenability of the balls.

The closest (prototype) in technical essence to the claimed method, in terms of the number of similar features, is patent RU 2634541 C1 "Method and device for heat treatment of balls" IPC6 C21D 9/36, published on 31.10.2017, bullet 31 [10], including alignment the temperature of the balls from the temperature of stamping or rolling to the temperature of air quenching when they are placed on the conveyor, cooling in water from the quenching temperature in a rotating quenching drum and tempering, while the balls temperature equalization to the air quenching temperature is carried out for more than 40 s when placed on a conveyor made with the possibility of placing one ball in each of its structural elements, and the balls are cooled in water to a temperature below the point of the beginning of the martensitic transformation Mn, while the balls are evenly and one by one placed in the cells of the quenching drum, into which water is supplied for washing balls, then the balls are tempered by heating and thermostating in a furnace and Subsequent final cooling.

The disadvantage of this method is that according to the technology of heat treatment on the proposed steel grades, after continuous hardenability of the balls, residual stresses remain, which contribute to their further destruction during operation.

The technical result, which the alleged invention is aimed at, is: increasing the operational durability of the balls, obtaining grinding balls with a volumetric hardness characterized by the 5th hardness group according to GOST 7524-2015 on a production scale.

The technical result is achieved by the fact that in the method of producing grinding balls with bulk hardness from steel containing, wt%: C 0.75-0.80; Mn 0.80-0.90; Si 0.25-0.35; Al less than 0.020; P less than 0.015; S less than 0.020; Cr 0.35-0.40; Ni 0.15-0.25; Cu less than 0.030; V 0.10-0.15; Mo 0.03-0.05; N less than 0.015; H is less than 0.0003, Fe is the rest, including rolling, cooling of balls, quenching, tempering, according to the invention after rolling or after stamping or after reheating, the balls are cooled to a temperature of 740-800 ° C and then quenched in a quenching environment, in this case, the holding time is, respectively: for balls with a nominal diameter of 80-100 mm from 3.0 to 4.0 min, for balls with a nominal diameter of 110-140 mm from 3.5 min to 5.0 min, followed by tempering, respectively: for balls with a nominal diameter of 80-140 mm at a temperature of 180-260 ° C and a holding time from 180 to 320 minutes, and further self-release with a holding time from 12 to 48 hours.

In addition, water or other medium with a specific heat capacity from 3800 to 4000 J / kg · deg. Is used as a quenching medium. thermal conductivity coefficient from 0.4 to 0.7 W / m · deg., and also due to the fact that the subsequent tempering is carried out either only at low-temperature or at multi-stage tempering.

The essence of the inventions is illustrated by the following drawings:

fig. 1 - Test results for bulk hardness, HRC of balls from a trial heat;

fig. 2 - Macrostructure of samples of balls from an experimental melt;

The essence of the invention is as follows.

The use of the proposed method provides a martensitic structure throughout the depth of the grinding balls. The martensitic structure in steels is formed at a high cooling rate, with a phase transition below the AC3 point (the point of onset of austenitization) until the end of the transformation, according to the transformation kinetics from the diagrams of supercooled austenite. Obtaining continuous hardenability is possible at a high cooling rate of both the surface and the core (center) of the balls. It is especially difficult to achieve such a transformation with large ball diameters.

The ball is a figure with the maximum mass of the object (the ratio of mass to volume), therefore the heat transfer mirror in the medium is as small as possible. According to Fourier's law, heat transfer starts from the surface of the ball and ends with the center of the ball, so the maximum effect can be obtained on those materials in which the transformation kinematics occurs with the maximum thermal conductivity inside the object.

In addition, continuous hardenability creates internal stresses (the intensely cooling surface has a denser structure than the inner part of the material and upon further cooling, a layer-by-layer completion of the transformation is created), which, due to the difference in state, cause the appearance of dislocations and then can lead to the appearance of cracks on the balls, which unacceptable according to GOST 7524-2015.

The chemical composition of steel for the production of grinding balls, containing, wt.%: With 0.75-0.80; Mn 0.80-0.90; Si 0.25-0.35; Al less than 0.020; P less than 0.015; S less than 0.020; Cr 0.35-0.40; Ni 0.15-0.25; Cu less than 0.030; V 0.10-0.15; Mo 0.03-0.05; N less than 0.015; H less than 0.0003, allows to solve this contradiction, to ensure high hardness of both the surface and the inner zone of the finished balls, to exclude the occurrence of internal stresses, and also to determine the heat treatment modes for balls of large diameters (80-140).

Cooking grinding balls to a temperature of 740-800 ° C after rolling, or after stamping, or after reheating allows you to provide the required temperature for the start of hardening. Deviation from the specified temperature range, both above 800 ° C and below 740 ° C, does not allow starting quenching of balls from temperatures that ensure complete quenching, with incomplete quenching, a mixed structure of troostite and martensite or bainite and martensite is formed, which reduces the hardness of the balls below the established standard ...

The duration of the hardening process is regulated depending on the diameter of the balls, the group of their hardness and the chemical composition of the steel. For example, when receiving grinding balls of the 5th group of hardness, the duration of quenching of balls with a nominal diameter of 80-100 mm is 3.0 - 4.0 minutes, for balls with a nominal diameter of 110-140 mm - 3.5 - 5.0 minutes.

Increasing the residence time of the grinding balls in the quenching medium beyond the established limits is impractical, since this time is sufficient for the volumetric hardenability to pass.

A decrease in the residence time of the grinding balls in the quenching medium below the established limits will lead to insufficient hardenability of the ball and the absence of obtaining bulk hardness.

The subsequent tempering of grinding balls with a nominal diameter of 80-140 mm is carried out at a temperature of 180-260 ° C, which makes it possible to remove surface stresses arising during the hardening process.

A deviation from the specified temperature range below the set temperature value will lead to a lack of surface heating and, in the future, to the possibility of cracking, and an excess of the set temperature value will lead to the beginning of transformations in the grains (typical temper brittleness of the first kind) and the appearance of surface embrittlement.

The duration of the holding process for grinding balls of any nominal diameter is 180-320 minutes. in the furnace and further self-tempering in the bunker is 12-48 hours, which ensures the sufficiency of the tempering process.

The method of obtaining grinding balls with bulk hardness works as follows.

Obtaining grinding balls with nominal diameters from 80 mm to 140 mm that meet the requirements of the 5th group of hardness is possible using the material of the balls from steel grade 70HGFN-2: C 0.75-0.80; Mn 0.80-0.90; Si 0.25-0.35; Al less than 0.020; P less than 0.015; S less than 0.020; Cr 0.35-0.40; Ni 0.15-0.25; Cu less than 0.030; V 0.10-0.15; Mo 0.03-0.05; N less than 0.015; H less than 0.0003, with appropriate heat treatment.

Heat treatment technology consists of the following stages:

1. Rolling, or stamping, or reheating of grinding balls at a temperature of 950-1050 ° C.

2. Cooking grinding balls with a nominal diameter of 80-120 mm to temperatures of 740-800 ° C, and with a nominal diameter of 130-140 mm to temperatures of 740-880 ° C after rolling or stamping, or reheating the balls to the specified temperatures, \

3. Quenching of grinding balls in water:

- with a nominal diameter of 80-100 mm at a temperature range from 40 ° C to 55 ° C, with a holding time:

- for balls with a nominal diameter of 80-100 mm from 3 minutes to 4 minutes,

- for balls with a nominal diameter of 110-140 mm from 3.5 min to 5 min,

or in another medium with a specific heat capacity from 3800 J / kg · deg to 4400 J / kg · deg. and the coefficient of thermal conductivity from 0.4 W / m · deg to 0.7 W / m · deg, observing the same temperature and time parameters.

1. Subsequent low-temperature one or multi-stage tempering of balls with a nominal diameter of 90-140 at a temperature of 180-260 ° C with a holding time from 180 to 320 minutes.

2. Further self-tempering of balls with a holding time from 12 to 48 hours.

An example of a specific implementation of the method.

Testing according to the technology of the proposed invention was carried out at the section of the ball rolling mill of the rail and structural shop of JSC "EVRAZ NTMK" in the production of balls ∅100 and 120 mm steel grade 77HGFMN.

Grinding balls with nominal diameters of 100 mm and 120 mm were rolled in a helical rolling mill at a temperature of 950-1050 ° C. Then the grinding balls were cooled in air to a temperature of 780 ° C. After that, the grinding balls were quenched in quenching drums in running water at a temperature of 45-50 ° C for a holding time:

- for balls with a nominal diameter of 100 mm from 3 min

- for balls with a nominal diameter of 120 mm from 3.5 min

Next, a low-temperature tempering was carried out in a continuous gas tempering furnace with 7 working zones for balls with a nominal diameter of 100 mm at a temperature of 180 ° C with a holding time of up to 200 min, and then self-tempering for 40 hours in closed bins.

The determination of the hardness of the grinding balls on the surface and the depth of ½ the radius of the ball was carried out in accordance with GOST 9013-59.

The chemical composition of the steel is shown in Table 1.

The test results showed that the proposed method for the production of grinding balls by chemical composition from Table 1 ensures the production of finished balls with a hardness corresponding to group 5 according to GOST 7524-2015 and are presented in Table 2. The bulk hardness indicated in Table 2 was determined by the method of finding the hardness gradient by the depth of calcination in the ball (Fig. 1), while the bulk hardness (OT) is calculated by the formula:

OT = 0.289Tpov + 0.436T0.25 + 0.203T0.5 + 0.63T0.75 + 0.009Tts,

where Tпов - the value of the hardness of the surface of the ball,

Tts - the value of the hardness of the center of the ball,

T0.25, T0.5, T0.75 - hardness value at a distance from the ball surface.

Quenching cracks on the surface of the test balls (left and right) are absent (Fig. 2), on both balls there is an axial segregation of 1.5 points, which is caused by the characteristics of the rolled metal from a round billet and is not a rejection feature. The appearance of quenching cracks occurred when the temperature of the water (quenching medium) fell below 45 ° C, and when the tempering time was less than 180 minutes in the tempering furnace or the subsequent self-tempering time in the bins was less than 12 hours.

Application of the proposed method of manufacturing grinding balls provides grinding balls with bulk hardness, characterized by the 5th hardness group according to GOST 7524-2015 [11] on a production scale for balls from 80 to 140 mm.

Thus, this technical solution meets the "novelty" criterion.

Analysis of patents and scientific and technical information did not reveal the use of new essential features used in the proposed solution. Therefore, the proposed invention meets the criterion of "inventive step".

It has been confirmed by experience that the use of the proposed invention allows:

- to obtain grinding balls of the 5th group of hardness with diameters from 100 to 120 mm;

- in 2020, balls of the 5th group of hardness from this steel grade were shipped to the consumer ∅100 - 436.6 tons and ∅120 - 676 tons.

Sources of information

[1] patent RU No. 2415194 C1 "Steel" MPK6 C22C 38/38; C22C 38/34; C22C 38/32, published 03/27/2011, bulletin 9;

[2] patent RU No. 2425168 C2 "Steel" MPK6 C22C 38/26, published on July 27, 2011, bullet 21;

[3] patent RU No. 2425169 "Steel" MPK6 C22C 38/40, published on July 27, 2011, bullet 21;

[4] copyright certificate SU 1497262 A1, "Steel" MPK6 C22C 38/14, convention priority 01/13/1988;

[5] Copyright certificate SU 1446189 A1 "Steel" MPK6 C22C 38/16, published on 23.12.1988;

[6] patent RU No. 2596737 C1 "Method for the production of steel grinding balls" MPK6 C21D 9/36; B21H 1/14; C21D 1/02; B23P 15/00; C22C 38/40, published 10.09.2016, bul. 25;

[7] patent RU 2455369 C1 "Device and method for heat treatment of balls" IPC6 C21D 9/36, published 10.07.2012, bulletin 19;

[8] patent RU 2113513 C1 "Method of heat treatment of grinding

balls "MPK6 C21D 9/36; B21H 1/14, published 10.09.2016, bul. 25;

[9] Inventor's certificate SU No. 1344793 A1 "Method of thermal

processing of grinding balls copyright certificate MPK6 C21D 9/36, published on 15.10.1987;

[10] patent RU2634541 C1 "Method and device for thermal

processing balls "IPC6 C21D 9/36, published on 31.10.2017, bul. 31.

[11] GOST 7524-2015.

Table 1.

Chemical composition of steel grade 70HGFN-2

WITH, % Мn,% Si,% Al,% P,% S,% Cr,% Ni,% Cu,% V,% Mo,% Ti,% H, ppm Fe 0.71-0.75 0.90-1.0 0.25-0.35 <0.01 <0.015 <0.01 0.40-0.45 0.10-0.14 <0.02 0.08-0.12 <0.01 <0.015 <3.0 rest

Table 2.

Regulated and actual values of hardness of grinding balls of group 5

Nominal ball diameter, mm Hardness, HRC / HB according to GOST, not less Hardness, HRC on test balls actual Ball surface Volumetric Ball surface Volumetric From 80 to 100 incl. 58/567 48/453 58.6-59.9 52.1-52.8 From 110 to 120 incl. 56/545 43/401 56.1-58.3 49.6-49.7

Claims (6)

1. Method for the production of grinding balls from steel containing, wt%: C 0.75-0.80, Mn 0.80-0.90, Si 0.25-0.35, Al less than 0.020, P less than 0.015, S less than 0.020, Cr 0.35-0.40, Ni 0.15-0.25, Cu less than 0.030, V 0.10-0.15, Mo 0.03-0.05, N less than 0.015, H less 0.0003, Fe - the rest, including rolling, quenching, tempering, characterized in that balls with a nominal diameter of 80-100 mm are produced, after rolling the balls are cooled to a temperature of 740-800 ° C, the balls are quenched in a quenching environment with exposure to for 3.0 to 4.0 minutes, and the subsequent tempering is carried out at a temperature of 180-260 ° C and a holding time for 180 to 320 minutes, while after the tempering, self-tempering is carried out with a holding time for 12 to 48 hours. 2. The method according to claim 1, characterized in that water or a medium with a specific heat capacity of 3800 to 4000 J / kg⋅grad and a coefficient of thermal conductivity from 0.4 to 0.7 W / m2grad is used as the quenching medium. 3. The method according to claim 1, characterized in that a multi-stage vacation is carried out as a vacation. 4. Method for the production of grinding balls from steel containing, wt%: C 0.75-0.80, Mn 0.80-0.90, Si 0.25-0.35, Al less than 0.020, P less than 0.015, S less than 0.020, Cr 0.35-0.40, Ni 0.15-0.25, Cu less than 0.030, V 0.10-0.15, Mo 0.03-0.05, N less than 0.015, H less 0.0003, Fe - the rest, including rolling, quenching, tempering, characterized in that balls with a nominal diameter of 110-140 mm are produced, after rolling the balls are cooled to a temperature of 740-800 ° C, the balls are quenched in a quenching environment with exposure to for 3.5 minutes to 5.0 minutes, and the subsequent tempering is carried out at a temperature of 180-260 ° C and a holding time from 180 to 320 minutes, while after the tempering, self-tempering is carried out with a holding time of 12 to 48 hours. 5. The method according to claim 3, characterized in that water or a medium with a specific heat capacity of 3800 to 4000 J / kg⋅grad and a coefficient of thermal conductivity from 0.4 to 0.7 W / m2grad is used as the quenching medium. 6. The method according to claim 3, characterized in that a multi-stage vacation is carried out as a vacation.

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