RU2238333C1 - Method for producing of rolled bars from boron steel for cold bulk pressing of high-strength fastening parts - Google Patents

Abstract

FIELD: metallurgy, in particular, production of high-strength parts of specifically compound shape.

SUBSTANCE: method involves melting steel containing, wt%: carbon 0.17-0.32; manganese 0.90-1.40; silicon 0.01-0.17; sulfur 0.005-0.020; chromium 0.01-0.30; vanadium 0.005-0.07; molybdenum 0.005-0.10; nickel 0.005-0.10; niobium 0.005-0.02; titanium 0.01-0.04; boron 0.0005-0.0050; aluminum 0.02-0.06; nitrogen 0.005-0.015; iron the balance, with 12/C-Mn/0.055≤20; 500x(Ti/24-N/7)+0.2≥0; 40≥C/0.01+B/0.001≥33; providing processing beyond furnace; pouring in casting molds while protecting flow; providing hot rolling of ingot to produce blank; rolling blank; providing controlled cooling and winding of rolled product into rolls; finishing hot rolling at temperature of 1,000-1,0500C; providing controlled accelerated cooling to 880-900⁰C with following cooling in air to temperature of up to 300⁰C. Method allows additional spheroidizing annealing process to be avoided.

EFFECT: provision for producing of rolled bars of structure enabling advantageous conditions for cold bulk pressing of compound shape fastening parts and improved characteristics of hardenability of steel.

1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products from boron-containing steel for cold forming for high-strength fasteners of especially complex shape.

(патент РФ).Known structural steel containing (wt.%): Carbon 0.18-0.24%, manganese 0.90-1.30%, silicon 0.17-0.37%, boron 0.0005-0.0050%, nitrogen 0.005-0.015%, vanadium 0.01- 0.08%, titanium 0.01-0.04%, the rest is iron in the following ratio of components, wt.%:

(RF patent).

The most important requirement for long products made of boron-containing steel for cold forging of high-strength fasteners of particularly complex shape is, on the one hand, high technological ductility and low coefficient of strain hardening in the delivery state and, on the other hand, the ability to provide a given level of consumer properties after the final hardening. This steel from the batch to the finished long products undergoes a fairly lengthy redistribution, which includes the following operations: smelting, hot rolling, spheroidizing annealing, calibration. The task of providing the necessary set of mechanical properties, indicators of technological plasticity and a low coefficient of strain hardening of rolled metal in the delivery state is currently being successfully solved by a number of techniques used at various stages of steelmaking.

A known production method (patent JP 61-163210, 07.23.1986, C 21 D 8/06), including heating the rods to 950 ° C, which provides the release of aluminum nitride and boron, followed by cooling with water at a speed of 25 ° / min to room temperature. This method does not provide the required level of spheroidization of the structure of the used steel class.

A known method of production of reinforcing bars (patent DE 3434744 A1, 04/03/1986, C 21 D 8/06), including heating to 1150 ° C, rolling at from 1150 to 800 ° C in order to obtain a ferrite-pearlite structure. Further heating to 1000 ° C followed by cooling to room temperature.

The closest analogue is the method of production of long products from boron-containing steel for cold forming of high-strength fasteners, including steelmaking in electric furnaces, after-furnace treatment, casting into molds, hot rolling of the ingot and cooling (RU 2042734 C1, C 22 C 38/54, 27.08 .1995 g.).

The basis of the invention is the task of developing steel of high hardenability and a method for the production of long products from it, which ensures production directly in the mill stream (without additional spheroidizing annealing). The technical result is to obtain a spheroidized structure of long products, guaranteeing rational conditions for cold forming for complex profile high-strength fasteners, as well as increased values of hardenability characteristics.

The technical result is achieved by the fact that in the method for producing long products from boron-containing steel for cold forming of high-strength fasteners, including smelting steel in an electric furnace, out-of-furnace processing, casting into molds, hot rolling of an ingot and cooling, steel is melted in the following ratio of components, wt. %:

Carbon 0.17-0.32

Manganese 0.90-1.40

Silicon 0.01-0.17

Sulfur 0.005-0.020

Chrome 0.01-0.30

Vanadium 0.005-0.07

Molybdenum 0.005-0.10

Nickel 0.005-0.10

Niobium 0.005-0.02

Titanium 0.01-0.04

Boron 0.0005-0.0050

Aluminum 0.02-0.06

Nitrogen 0.005-0.015

Iron and inevitable impurities

When performing the ratios:

hot rolling is completed at a temperature of 1000-1050 ° C and is cooled in a regulated manner, first accelerated to a temperature of 880-900 ° C, and then in air to 300 ° C.

The above combinations of alloying elements (p. 1) make it possible to obtain a uniform finely divided martensite structure in tempering steel (in a finished product with a diameter of up to 25 mm) after thermal improvement (quenching from a temperature of at least 920 ° C and subsequent tempering from a temperature of at least 620 ° C) with a favorable combination of strength and ductility characteristics.

Carbon and carbonitride-forming elements (vanadium, niobium) are introduced into the composition of this steel in order to provide a fine grain structure, which will increase both its strength level and provide a given level of ductility. In this case, niobium and vanadium control processes in the austenitic region (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the temperature of recrystallization, and, as a result, affects the nature of the γ-α transformation). Niobium and vanadium also contribute to the hardening of steel during thermal improvement. The upper limit of carbon content (0.32%), niobium (0.02%) and vanadium (0.07%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.17%, 0.005% and 0.005%, respectively - to ensure the required level of strength of this steel.

Manganese, molybdenum and chromium are used, on the one hand, as a solid solution hardener, and on the other hand, as an element that significantly increases the stability of supercooled austenite and increases the hardenability of steel. The upper level of manganese - 1.40%, chromium (0.30%), molybdenum (0.10%) is determined by the need to ensure the required level of ductility of steel, and the lower - 0.90%, 0.005% and 0.005%, by the need to provide the required level of strength and hardenability of steel.

Silicon refers to ferrite-forming elements. The lower limit on silicon - 0.01% is due to steel deoxidation technology. A silicon content above 0.17% will adversely affect the ductility characteristics of steel.

Boron contributes to a sharp increase in the hardenability of steel. The upper limit of boron content is determined by considerations of ductility of steel, and the lower - by the need to ensure the required level of hardenability.

Aluminum and titanium are used as deoxidizers and protect boron from binding to nitrides, which contributes to a sharp increase in the hardenability of steel. So, the lower level of the content of these elements (0.02 and 0.01, respectively) is determined by the requirement to ensure hardenability of steel, and the upper level (0.06 and 0.04) is determined by the requirement to ensure a given level of ductility of steel.

Nitrogen, an element involved in the formation of carbonitrides, while the lower level of its content (0.005%) is determined by the requirement to ensure a given level of strength, and the upper level (0.015%) is determined by the requirement to ensure a given level of ductility and hardenability.

Nickel in the specified range (0.005-0.10%) affects the characteristics of hardenability and toughness of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.020%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.005%) is due to issues of manufacturability.

To ensure complete binding of nitrogen to nitrides such as TiN and AlN as a result of reactions:

[Ti] + [N] = TiN, [Al] + [N] = AlN

the following ratio of elements is required; otherwise, boron is not protected from binding to nitrides and the hardenability characteristics of steel are sharply reduced.

The ratio

determine the conditions for maintaining in steel more than 50% of the effective boron, which provides the specified characteristics of hardenability of steel.

The following is an example implementation of the method.

The smelting of boron-containing steel containing carbon 0.29%, manganese 1.22%, silicon 0.17%, sulfur 0.010%, chromium 0.15%, vanadium 0.02%, molybdenum 0.009%, nickel 0.04%, niobium 0.01%, titanium 0.03%, boron 0.0034% , aluminum 0.043%, nitrogen 0.010%, produced in the Fuchs mine electric furnace. For guaranteed low nitrogen content, a special technology has been developed, including: batch melting with molten iron up to 40% of the total volume of the charge. The oxidation period provides for high rates of carbon oxidation in the range of 0.05-0.07% / min. The electric mode provides for turning off the furnace with a carbon content of 0.2-0.4% above the lower limit for a given one, carbon blowing is carried out without an electric arc. The temperature of the exhaust from the furnace 1640-1680 ° C. Ferroalloys are introduced, steel is treated to remove non-metallic inclusions at the ladle furnace equipped with an electric heating or chemical heating system. The temperature of the steel before casting is 60 ° C higher than the liquidus temperature of the brand. Steel casting is carried out in molds broadened up. The weight of the ingot is 7.85 tons. To ensure a low nitrogen content during casting, the metal stream is protected by argon through a special ring device. The ingots are heated in a crimping workshop in recuperative wells to a rolling start temperature of 1250-1270 ° C. The ingots are rolled on blooming (mill 1300) and then on a continuous billet mill for a workpiece with a section of 100 × 100 mm. To remove the decarburized layer formed during heating of the ingots, the workpieces are subjected to abrasive cleaning. Then, the obtained workpiece was hot rolled at wire mill 150 or small mill 250 in diameters from 5.5 to 23 mm in coils. To ensure the size of the decarburized layer is not more than 1% of the diameter, the rate of delivery of billets from the furnace is limited to not less than 100 t / h for mill 150 and not less than 56 t / h for mill 250. The temperature of the start of rolling of billets is 1220-1240 ° C for mill 250 and 1270-1290 ° C for mill 150. Hot rolling of long products is completed at a temperature of 1000-1050 ° C, then accelerated cooling to 880-900 ° C, followed by cooling in air to 300 ° C and subsequent winding into riots.

углерод 0.29%, марганец 1.22%,

carbon 0.29%, manganese 1.22%,

титан 0.03%, азот 0.009%,

titanium 0.03%, nitrogen 0.009%,

углерод 0.29%, бор 0.0044%.

carbon 0.29%, boron 0.0044%.

Implementation of the proposed method for the production of long products from boron-containing steel of increased hardenability, which ensures the production of high-quality steel structures directly in the mill stream (without additional spheroidizing annealing), which guarantees rational conditions for cold forging of complex-profile high-strength fasteners.

Claims (1)

Method for the production of long products from boron-containing steel for cold forging of high-strength fasteners, including steelmaking in electric furnaces, after-furnace treatment, casting into molds, hot rolling of an ingot and cooling, characterized in that steel is smelted in the following ratio of components, wt.%: Carbon 0.17-0.32 Manganese 0.90-1.40 Silicon 0.01-0.17 Sulfur 0.005-0.020 Chrome 0.01-0.30 Vanadium 0.005-0.07 Molybdenum 0.005-0.10 Nickel 0.005-0.10 Niobium 0.005-0.02 Titanium 0.01-0.04 Boron 0.0005-0.0050 Aluminum 0.02-0.06 Nitrogen 0.005-0.015 Iron Else when fulfilling the ratios 12 / С-Mn / 0,055 ≤ 20; 500 · (Ti / 24-N / 7) + 0.2≥0, 40≥ (C / 0.01 + V / 0.001) ≥33, hot rolling is completed at a temperature of 1000-1050 ° C and controlled cooling is accelerated to 880-900 ° C followed by cooling in air to 300 ° C.