RU2790722C1 - Grinding ball production method - Google Patents

Abstract

FIELD: production of grinding balls.

SUBSTANCE: steel is poured into billets of square section, then these billets are rolled into billets of round section, the diameter of which corresponds to the conditional diameter of the final balls in the range of 30–40 mm. Round billets are heated to a temperature of 1010–1160°C. Produce cross-helical rolling with a temperature of the end of rolling 950-1100°C. The balls are chilled to 770–890°C. Then they are hardened to a temperature of 100–150°C, and then the balls are subjected to self-tempering for at least 12 hours.

EFFECT: abrasive resistance of the balls is increased.

4 cl, 2 tbl, 1 ex

Description

The invention relates to rolling production, in particular to a method for the production of grinding balls used in drum-type mills used in the mining industry and cement production plants.

A known method for the production of steel grinding balls, including heating a continuously cast billet, rolling on a section hot rolling mill of round billets of the appropriate size, their subsequent heating in an induction device, rolling balls from them on a helical rolling mill at a temperature of 950-1050 ° C, cooling the balls before hardening, hardening 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 0.03-1.5; copper 0.03-0.40; iron and unavoidable impurities remain the rest, and heating of round blanks is carried out in an induction device to a temperature at the outlet of the inductors of 1070-1140°C, cooling of the balls to a hardening temperature of 840-900°C is carried out in a cooling drum with a speed of its rotation in the range of 6.0- 22.0 rpm with equalization of the temperature of the balls over the cross section due to the rotation of the balls in the drum for less than 2 minutes, and the hardening of the balls is carried out in a hardening drum with a speed of its rotation in the range of 0.4-2.5 rpm with running water at a temperature of 25-42°C to the temperature of the balls after hardening 125-160°C [Patent RU No. 2596737, IPC C21D9/36, B21H1/14, C21D1/02, B23P15/00, C22C38/48, 2016].

The disadvantage of this method is that this method does not allow to obtain balls of the fifth hardness group with through hardenability.

The closest to the proposed invention in terms of technical essence is a method for the production of grinding balls, including the production of balls with a nominal diameter of 80-100 mm, after rolling the balls are cooled to a temperature of 740-800 ° C, the balls are quenched in a quenching medium with holding for 3, 0 to 4.0 min, and subsequent tempering is carried out at a temperature of 180-260°C and a holding time of 180 to 320 minutes, while after tempering, self-tempering is carried out with a holding 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°C, the balls are hardened in a hardening medium with holding for 3.5 min to 5.0 min, and the subsequent tempering is carried out at a temperature of 180-260°C and a holding time of 180 to 320 minutes, while after the holiday, self-tempering is carried out with a holding time of 12 to 48 hours [Patent RU No. 2756671, IPC C21D9/36, C22C38/24, B21H1/14, 2021].

The disadvantage of this method is the increased cost of steel production due to the presence of a larger number of alloying components.

The technical result of the proposed technical solution is to develop a method for the production of steel grinding balls with a nominal diameter of 30 to 40 mm, characterized by increased abrasive resistance.

The specified technical result is achieved by the fact that in the method for the production of grinding balls, including steel smelting, rolling of balls and their heat treatment, according to the invention, steel is smelted, while the content of carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, copper, molybdenum, vanadium , niobium, nitrogen in steel are the following, wt.%:

carbon 0.6–0.8 silicon 0.15–0.4 manganese 0.6–1.4 phosphorus no more than 0.04 sulfur no more than 0.04 chromium 0.1-0.4 nickel no more than 0.3 copper no more than 0.3 molybdenum no more than 0.015 vanadium no more than 0.015 niobium no more than 0.015 nitrogen no more than 0.015

at the same time, the carbon equivalent of steel is 0.77–1.13, then the steel is poured into square-section blanks, then these blanks are rolled into round-section blanks, the diameter of which corresponds to the conditional diameter of the final balls in the range of 30–40 mm, the blanks are heated round section to a temperature of 1010–1160 °С, cross-helical rolling is performed with a temperature of the end of rolling of 950–1100 °С, the balls are chilled to a temperature of 770–890 °С, then they are quenched to a temperature of 100–150 °С, and then balls are self-tempered for at least 12 hours.

The hardness of the grinding balls on the surface is 61–70 HRC, at a depth of 0.5 of the ball radius 55–70 HRC, and the bulk hardness is 55–65 HRC.

On the ball surface, the microstructure consists of martensite, and at a depth of 0.5 of the ball radius it consists of 95–100% martensite and no more than 5.0% residual austenite.

The actual grain size of the ball austenite before hardening is 6 - 8 points.

The essence of the proposed method is as follows.

This chemical composition and the structure obtained after the claimed heat treatment make it possible to reduce the consumption coefficient for customers when processing steel grinding balls in mills.

When the carbon content is less than 0.6%, the hardness of the balls decreases below the permissible values.

With a carbon content of more than 0.8%, the fragility of the balls increases and, after heat treatment, cracking is possible.

Silicon is a steel deoxidizer, and also helps to increase its strength and elasticity after the final heat treatment. When the silicon content is less than 0.1%, the steel will not be sufficiently deoxidized. A silicon content of more than 0.4%, combined with a high carbon content, leads to an increase in the fragility of the balls.

Manganese acts as a steel deoxidizer and a sulfur-binding element. Also, manganese increases the strength of steel after the final heat treatment, increases the hardenability. The manganese content of less than 0.6% in steel leads to a decrease in strength and to insufficient hardenability of the balls. The manganese content of more than 1.4%, with a high content of carbon and silicon, can lead to a decrease in steel ductility.

Sulfur and phosphorus are harmful impurities that degrade the quality of steel, so the content of these chemical elements should be limited to less than 0.04% each.

Chromium in the amount of 0.1–0.4% provides the hardness and strength of steel, provides corrosion resistance of the ball and resistance to abrasive wear. A further increase in the chromium content leads to an increase in the cost of steel.

Mass fractions of copper, molybdenum, vanadium, niobium in the established ranges make it possible to provide the necessary hardness of the balls. Their increase above the declared values will lead to the formation of non-metallic inclusions and is not economically feasible.

Nitrogen is present in steel in the form of brittle non-metallic inclusions and degrades the mechanical properties of the grinding balls. The maximum nitrogen content in steel is permissible in an amount of not more than 0.015%.

The metal should be free of macrostructure defects, the number and size of non-metallic inclusions should be minimal, there should be no grid along the grain boundaries, it is required to minimize the amount of harmful impurities.

Obtaining a carbon equivalent in the claimed range makes it possible to obtain balls without the formation of cracks on the surface and provides increased abrasive resistance.

When the workpiece is heated above a temperature of 1160°C, austenite grain growth is observed, which leads to a decrease in the impact resistance of the ball and an increase in abrasive wear. When the billet is heated below a temperature of 1010°C, the loads on the rolls increase, which leads to their premature wear, the need for frequent adjustments, and the risk of chipping the flanges.

At a temperature of the end of rolling above 1100°C, it becomes difficult to grip the workpiece with rolling rolls, the balls after rolling have an oval shape that goes beyond the permissible values according to GOST 7524.

At the temperature of the end of rolling below 950°C, the loads on the rolling rolls increase, which leads to their premature wear, the need for frequent adjustments, and the risk of chipping the flanges.

When hardening starts from a temperature below 770°C, hardening occurs from a two-phase region, which does not allow obtaining the target microstructure and the required hardness on the ball surface according to GOST 7524. When hardening starts at a temperature above 890°C, internal stresses increase significantly after hardening, which can lead to to the appearance of cracks on the surface of the balls.

With an increase in the temperature of the end of hardening above 150°C, there is a risk of not achieving the required hardness and the required structure of the metal. At the temperature of the end of hardening below 100°C, the mass-average temperature of the grinding balls is not sufficient to relieve internal stresses, which can provoke the appearance of cracks.

Self-tempering is an important component of the technology of thermal hardening of balls. At the stage of self-tempering, the completion of structure formation in the balls occurs, as well as the relaxation of stresses that arise in products during the hardening process. To achieve the required properties of the balls, their self-release must take place for at least 12 hours.

The size of the actual austenite grain should be 6–8 points - this provides high abrasive and impact resistance of the balls.

The metal should be free of macrostructure defects, the number and size of non-metallic inclusions should be minimal, there should be no grid along the grain boundaries, it is required to minimize the amount of harmful impurities.

Implementation example.

Table 1 shows the options for the chemical composition of steel. Table 2 shows the controlled characteristics of technological parameters.

According to the data presented in tables 1 and 2, subject to the specified heat treatment modes, the grinding balls have the required characteristics: microstructure, hardness, sizes of non-metallic inclusions, fine grain, and, therefore, are well amenable to heat treatment and have low abrasive wear.

Table 1

Chemical composition of steels ^*

No. p / p Mass fraction of elements, % C Si Mn P S Cr Cu Ni Seq 1 0.60 0.15 0.60 0.01 0.01 0.15 0.10 0.06 0.77 2 0.70 0.30 0.80 0.015 0.015 0.25 0.14 0.15 0.93 3 0.75 0.40 1.00 0.02 0.02 0.40 0.20 0.26 1.06

* - the content of copper, molybdenum, vanadium, niobium and nitrogen was 0.014%.

table 2

Controlled parameters

No. p / p consumer goods Tkp Tsubst. Tzak. t otp, min Surface hardness, HRC Hardness per ½ radius, HRC Bulk hardness, HRC 1 1010 950 780 100 1200 70 65 65 2 1090 1030 830 130 1200 65 63 61 3 1160 1100 890 150 1200 62 60 58

Claims (6)

1. A method for the production of grinding balls, including steel smelting, ball rolling and heat treatment, characterized in that steel is smelted, while the content of carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, copper, molybdenum, vanadium, niobium, nitrogen in steel the following, wt.%: carbon 0.6–0.8 silicon 0.1–0.4 manganese 0.6–1.4 phosphorus no more than 0.04 sulfur no more than 0.04 chromium 0.1–0.4 nickel no more than 0.3 copper no more than 0.3 molybdenum no more than 0.015 vanadium no more than 0.015 niobium no more than 0.015 nitrogen no more than 0.015, in this case, the carbon equivalent of steel is 0.77–1.13; sections to a temperature of 1010–1160°C, cross-helical rolling is performed with a temperature of the end of rolling of 950–1100°C, the balls are cooled to a temperature of 770–890°C, then they are quenched to a temperature of 100–150°C, and then the balls self-release for at least 12 hours. 2. The method according to claim 1, characterized in that the hardness of the grinding balls on the surface is 61–70 HRC, at a depth of 0.5 of the ball radius 55–70 HRC, and the bulk hardness is 55–65 HRC. 3. The method according to claim 1, characterized in that on the surface of the ball the microstructure consists of martensite, and at a depth of 0.5 of the radius of the ball from 95–100% martensite and not more than 5.0% residual austenite. 4. The method according to claim 1, characterized in that the size of the actual austenite grain of the ball before hardening is 6–8 points.