RU2562719C1 - Roll stock with round cross section for producing of high-strength fasteners - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: to improve plastic characteristics at keeping of high strength properties the steel is produced which contains, wt %: carbon 0.30-0.35, manganese 0.50-0.70, silicon 0.20-0.37, phosphorus less than 0.020, silicon less than 0.010, chrome 0.40-0.70, nickel no more than 0.15, copper no more than 0.20, aluminium 0.015-0.035, titanium 0.03-0.05, boron 0.002-0.005, calcium 0.0001-0.005 and iron the rest.

EFFECT: composition for fabrication of roll stock with round cross section for producing of high-strength fasteners will allow to increase profitability of trading of hot roll with improved consumer properties.

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Description

The invention relates to the metallurgy of steel and can be used in the production of long products of circular cross section, for cold precipitation containing chromium and manganese, mainly for the manufacture of high-strength fasteners.

Steels with a high chromium content, as a rule, have increased strength, sufficient ductility, which allows them to be used in conditions of dynamic loads and increased friction (for example, fasteners, crankshafts, gears). Features of steels are described, for example, in the reference book of V.N. Zhuravleva and O.N. Nikolaev "Engineering Steel", ed. 3rd M., "Mechanical Engineering", 1981, p. 101-106.

Known alloy steel containing chromium, titanium and vanadium, which additionally contains aluminum, which increases wear resistance during impact-abrasive wear (see AS USSR No. 969779, class C2C 38/38, publ. In BI No. 40, 1982 g.).

The disadvantage of this steel is its low ductility. The closest analogue to the claimed object is steel 30X, described in GOST 4543-71 "Rolled products from alloy structural steel." It contains carbon, silicon, manganese, sulfur, phosphorus, chromium, nickel, copper, and iron and is characterized by the content of these components in the ratio, wt.%:

Carbon 0.24 ... 0.32 Manganese 0.50 ... 0.80 Silicon 0.17 ... 0.37 Phosphorus no more than 0,035 Sulfur no more than 0,035 Chromium 0.80 ... 1.10 Nickel no more than 0.30 Copper no more than 0.30 Iron rest

Known steel does not guarantee the required upsetting ability, expressed through the absence of guaranteed provision of defect-free cold draft by 66% after heat treatment in connection with the hereditary coarse grain of this steel.

The expected technical result is the obtaining of good plastic characteristics of rolled products while maintaining high strength properties, allowing them to withstand cold draft in accordance with the requirements of GOST 10702 for draft group 66.

To solve this problem, round-rolled products for the manufacture of high-strength fasteners are made of steel containing carbon, silicon, manganese, sulfur, phosphorus, chromium, nickel, copper and iron, characterized in that it additionally contains aluminum, titanium, boron and calcium at the following ratio, wt.%:

Carbon 0.30 ... 0.35 Manganese 0.50 ... 0.70 Silicon 0.20 ... 0.37 Phosphorus up to less than 0,020 Sulfur less than 0.010 Chromium 0.40 ... 0.70 Nickel no more than 0,15 Copper no more than 0.20 Aluminum 0.015 ... 0.035 Titanium 0.03 ... 0.05 Boron 0.002 ... 0.005 Calcium 0.0001 ... 0.005 Iron rest

All of the above limits for the content of components in the proposed steel were obtained as a result of processing experimental data.

The essence of the proposed technical solution is to optimize the content of individual components in chromium-containing steel. As a result of this, the plastic properties of the steel are improved while maintaining strength, which is especially important during its subsequent processing by the consumer.

During crystallization, boron captures hydrogen and limits the saturation of steel with it, stabilizes the subcortical zone of the continuously cast billet, and suppresses the segregation of sulfur and other impurities - that is, it significantly reduces shrinkage segregation. In addition, boron nitride BN eliminates the occurrence of aging processes over time due to the complete binding of nitrogen. The lower strength and increased ductility of the rolled stock with boron, which compared with the similar rolled stock from steel without boron, is due to the influence of boron, which contributes to a more uniform distribution of base and impurity elements between the components of the structure. In addition, as a result of the binding of nitrogen atoms to boronitrides and carboboronitride compounds, martensite in the structure of rolled metal with boron has a lower nitrogen concentration and, as less solid and durable, acquires a greater tendency to deformation deformation.

The silicon content of 0.20-0.37% allows you to get a well-deoxidized metal and reduce the content of brittle silicates, as well as to avoid a sharp decrease in plastic properties during subsequent cold deformation (due to the fact that a higher silicon content prevents the movement of dislocations).

The introduction of titanium reduces the contamination of steel by non-metallic inclusions, especially oxides, increases ductility and provides a given degree of hardenability of strip products.

The limitation of the upper limit of the aluminum content allows to minimize the content of non-metallic inclusions, to improve the quality of continuously cast billets.

Due to the low oxygen activity, calcium reacts with sulfur and is released in the form of calcium sulfides. Calcium also reacts with aluminum and primary deoxidation products to form liquid calcium aluminates, which improves the spillability of the metal. Thus, calcium can reduce the inclusion of alumina and manganese sulfides. The introduction of calcium into the metal allows one to change the morphology of the constituents of nonmetallic inclusions, transferring it from “dangerous” to more favorable, globular, and to clear grain boundaries from carbonitrides.

The addition of calcium to the metal, in addition to reducing the contamination of the metal with non-metallic inclusions, can significantly increase the number of crystallization centers, which in subsequent processing leads to good metal stampability.

An experimental verification of the proposed technical solution was carried out in the production of 30XP steel in the electric steel-smelting shop of OJSC Magnitogorsk Metallurgical Plant, followed by its rolling at mill 170. The experimental results were evaluated by the results of mechanical tests of round steel.

The best results (yield of rolled products in the range of 99.0-99.7 after tests for cold draft in accordance with the requirements of GOST 10702 for precipitation group 66T) were obtained using the proposed steel.

Deviations from the required chemical composition and obtaining the optimal microstructure led to the marriage of mechanical properties.

So, when the content in steel (wt.%) Al <0.015 (but with the recommended content of the remaining elements), C <0.30, Mn <0.50, Si <0.20, Cr <0.40, Ca <0 , 0001 (under the same condition), it was not possible to obtain the required yield after tests for cold draft in accordance with the requirements of GOST 10702 for the draft group 66T in 10-25% of round steel. When the content in steel (wt.%) Al> 0.035 (but with the recommended content of the remaining elements), C> 0.35, Mn> 0.70, Si> 0.37, Cr> 0.70 and Ca> 0.005, and also the increased content of S, P, Ni and Cu (respectively, more than 0.010, 0.020, 0.15 and 0.20), insufficient plastic properties did not allow to obtain a circle with a given surface quality of round steel due to contamination of the metal with non-metallic inclusions and coarse austenitic grain obtained after heat treatment.

When receiving round rolled steel, the chemical composition of which had at least one component with a different (from the declared) value, the sorting of finished rolled products by unacceptable deviations from the specified norm of tests for cold draft in accordance with the requirements of GOST 10702 for draft group 66T was not less than 1.8-4.2%, and in some cases, the ductility was unsatisfactory.

Comparative tests of steel 30X, chosen as the closest analogue, led to sorting for the above reason from 20.0-35.0% of finished steel. Thus, an experimental verification confirmed the acceptability of the technical solution found to fulfill the goal and its advantage over a known object.

The implementation of the invention in the production of chromium-containing steel will increase profits from the sale of rolled products with improved consumer properties.

Concrete example

Round rolling of chromium-containing steel with a diameter of 13 mm

contains (wt.%):

C = 0.31; Si = 0.24; Mn = 0.61; S = 0.004; P = 0.012; Cr = 0.58; Ni = 0.06; Cu = 0.05; Al = 0.019; Ti = 0.041; Ca = 0.0025, B = 0.0029, the rest is iron.

Claims (1)

Steel for rolled round cross-section for the manufacture of high-strength fasteners containing carbon, silicon, manganese, sulfur, phosphorus, chromium, nickel, copper and iron, characterized in that it additionally contains aluminum, titanium, boron and calcium in the following ratio, wt. %:
carbon 0.30-0.35 manganese 0.50-0.70 silicon 0.20-0.37 phosphorus less than 0,020 sulfur less than 0.010 chromium 0.40-0.70 nickel no more than 0,15 copper no more than 0.20 aluminum 0.015-0.035 titanium 0.03-0.05 boron 0.002-0.005 calcium 0.0001-0.005 iron rest