RU2340699C2 - Steel for grinding balls - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains carbon, manganese, silicon, aluminum, boron, copper, titanium, chrome, nickel, nitrogen, iron and admixtures, at following ratio of components, wt %: carbon 0.65-0.75, manganese 0.70-0.80, silicon 0.20-0.35, aluminum 0.010-0.025, nitrogen 0.005-0.025, titanium 0.005-0.010, chrome 0.40-0.50, nickel 0.01-0.30, boron 0.001-0.003, iron is the rest, at that admixtures are in following numbers: sulphur - not more than 0.030%, phosphorus - not more than 0.030% and copper - not more than 0.30%.

EFFECT: increasing of endurance and hardness of grinding balls.

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Description

The invention relates to ferrous metallurgy, in particular to steel used for the production of grinding balls.

Known selected as a prototype steel [1], containing (in wt.%):

carbon 0.45-0.65 manganese 0.60-1.00 silicon 0.60-1.20 aluminum 0.01-0.06 boron 0.0025-0.0040 copper 0.06-0.36 titanium 0.02-0.06 iron rest

A significant disadvantage of this steel is the low hardness and service life of balls made of this steel.

The desired technical results of the invention are to increase the wear resistance and hardness of grinding balls.

To achieve this, steel containing carbon, manganese, silicon, aluminum, boron, copper, titanium and iron additionally contains chromium, nickel and nitrogen in the following ratio of components (in wt.%):

carbon 0.65-0.75 manganese 0.70-0.80 silicon 0.20-0.35 aluminum 0.010-0.025 nitrogen 0.005-0.025 titanium 0.005-0.010 chromium 0.40-0.50 nickel 0.01-0.30 boron 0.001-0.003 iron rest

while the impurities are contained in the following amounts: sulfur - not more than 0.030%, phosphorus - not more than 0.030% and copper - not more than 0.30%.

The inventive chemical composition of steel for grinding balls is selected based on the following premises.

The carbon content is selected based on ensuring sufficient hardness and hardenability of the steel. When its concentration in steel is less than 0.65%, the hardness of the balls decreases, and with an increase in carbon concentration of more than 0.75%, their tendency to crack formation increases.

The ratio of manganese is selected based on the fact that when the manganese content is up to 0.80%, an increase in hardness, hardenability and resistance to cracking is provided. The lower limit is chosen based on the fact that manganese with a content of less than 0.70% does not affect hardenability.

Silicon within the claimed limits eliminates the split balls during shock loads. At a silicon concentration of less than 0.20%, the tendency of the balls to crack during impact loads significantly increases. In the manufacture of steel balls above the upper declared limit of the silicon content (0.35%), the tendency of the balls to crack formation increases.

With an increase in the chromium content to 0.50%, the hardness and hardenability of steel increases, which in turn leads to an increase in the wear resistance of grinding balls. When the chromium content is less than 0.40%, a decrease in hardenability of steel and, consequently, wear resistance of balls is observed.

The established nickel concentration limit (0.01-0.30%) has a positive effect on reducing the tendency of balls to crack during impact loads and increases the hardenability of steel. When the nickel content is less than the specified limit, the required hardenability of the steel is not provided. A nickel content of more than 0.30% is not economically feasible.

The aluminum content (0.010-0.025%) was selected based on the one hand, on the basis of the need to obtain fine real grain, and on the other, on the exclusion of the formation of unacceptable alumina non-metallic inclusions, which increase the tendency of the balls to crack under impact loads.

Titanium is used as a deoxidizing agent and protects boron from binding to nitrides, which increases the hardenability of steel. Based on this, the optimum values for titanium are its content of 0.005-0.010%. The upper limit of the concentration of titanium is selected based on economic considerations.

A nitrogen concentration of less than 0.005% does not lead to the formation of nitrides, which ensures the grinding of the actual grain, and as a result, a decrease in the tendency of balls to crack during impact loads. With an increase in nitrogen of more than 0.025%, there may be cases of spotted segregation and the formation of bubbles in steel as a result of "nitrogen boiling".

The limitation of the content of sulfur, phosphorus and copper is selected based on ensuring the quality of the surface of the finished grinding balls.

A series of experimental swimming trunks with the claimed chemical composition was smelted in DSP-100N10 arc furnaces. The chemical composition is shown in table 1. After casting the steel at the continuous casting machine, the balls were rolled and heat treated from the rolling mill using the two-stage cooling technology with self-tempering. The test results are shown in table 2. Thus, the inventive chemical composition provides increased hardness and wear resistance of the balls.

Table 1. The chemical composition of steel, wt.% Structure FROM Si Mn Cr Ti Al N AT Ni S R Cu Fe one 0.46 0.20 0.70 0.40 0.005 0.015 0.005 0.001 0.01 0.005 0.015 0.05 rest 2 0.70 0.28 0.78 0.40 0.011 0.015 0.008 0.001 0.14 0.008 0.019 0.06 rest 3 0.71 0.24 0.76 0.42 0.009 0.018 0.010 0.003 0.30 0.016 0.019 0,07 rest four 0.58 0.33 0.69 0.45 0.007 0.016 0.013 0.002 0.28 0.005 0,028 0.12 rest 5 0.57 0.26 0.79 0.48 0.013 0,020 0,022 0.003 0.25 0,020 0,023 0.20 rest 6 0.75 0.35 0.80 0.50 0.010 0,020 0,025 0.003 0.30 0,030 0,030 0.30 prototype 0.45-0.65 0.60-1.20 0.60-0.80 - 0.02-0.06 0.01-0.06 - 0.0025-0.0040 - - - 0.06-0.36 rest

table 2 Mechanical properties of steel Structure Hardness, MPa Wear, g The number of balls with cracks After heat treatment After a 10-fold drop one 495 0.44 0 0 2 575 0.31 2.6 4.1 3 578 0.29 3 4.8 four 517 0.37 2.9 4,5 5 524 0.35 3.0 4.1 6 595 0.27 2,5 4.0 prototype 440-560 0.31-0.45 3.2-7.0 5.8-10.0

Information sources

1. A.S. USSR No. 1446189, C22C 38/16.

Claims (1)

Steel for grinding balls containing carbon, manganese, silicon, aluminum, boron, copper, titanium and iron, characterized in that it additionally contains chromium, nickel and nitrogen in the following ratio, wt.%: carbon 0.65-0.75 manganese 0.70-0.80 silicon 0.20-0.35 aluminum 0.010-0.025 nitrogen 0.005-0.025 titanium 0.005-0.010 chromium 0.40-0.50 nickel 0.01-0.30 boron 0.001-0.003 iron rest, while the impurities are contained in the following amounts: sulfur - not more than 0.030%, phosphorus - not more than 0.030% and copper - not more than 0.30%.