RU2238338C1 - Method for producing from continuously cast rolled bar with spheroidal structure of low-carbon steel for cold bulk pressing of high-strength fastening parts of compound shape - Google Patents

Abstract

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

SUBSTANCE: method involves melting steel in electric furnace, said steel containing, wt%: carbon 0.27-0.32; manganese 0.30-0.65; silicon 0.01-0.17; sulfur 0.005-0.020; chromium 0.01-0.25; niobium 0.005-0.02; calcium 0.001-0.010; iron the balance, with ratios of 12/C-Mn/0.03≥20; Ca/S2≥.0650 being met; providing processing beyond furnace and continuous pouring of steel while protecting metal flow with argon; providing hot rolling of continuous bar at hot rolling initial temperature of 900-950⁰C and hot rolling final temperature of 740-850⁰C at deformation extent of at least 20% in final passes; providing cold gauging deformation at deformation extent of 20-25% and spheroidizing annealing including high-speed inductive heating in intercritical temperature range of cold deformed metal, with following controlled cooling within temperature range of 650-730⁰C at cooling rate of 0.5-1.0⁰C/min and further cooling in thermal chamber at temperature of 100-200⁰C. Microalloying of steel with niobium inhibits recrystallization process at temperature of 1,000-1,100⁰C and provides for fine-grained structure of austenite favorable for steel spheroidization process.

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

3 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products from low carbon steel for cold die forging fasteners of particularly complex shapes.

(SU 1703709 A, 07.01.1992 г.)Known structural steel containing (wt.%): Carbon 0.17-0.20%, manganese 0.65-1.0%, silicon 0.17-0.37%, chromium 0.55-0.70%, vanadium 0.05-0.08%, niobium 0.02-0.04%, the rest is iron in the following ratio of components, wt.%:

(SU 1703709 A, 01/07/1992)

The most important requirement for long products of low carbon steel for cold forming for complex 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 . 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.

The closest analogue to the claimed invention is a known method for the production of long products from low carbon steel for cold forging of complex profile fasteners, including steelmaking in an electric furnace, out-of-furnace processing, continuous casting, hot rolling of a continuously cast billet and cooling (RU 2156313 C1, C 21 D 8 / 02, 09/20/2000).

The basis of the invention is the task of developing steel with high deformability and a method for the production of long products from it. The technical result of the invention is to obtain the structure of long products, guaranteeing rational conditions for cold forging of complex profile fasteners.

To achieve a technical result in the known method for the production of long products from low carbon steel for cold forging of complex profile fasteners, including steelmaking in an electric furnace, out-of-furnace processing, continuous casting, hot rolling of a continuously cast billet and cooling, steel is melted in the following ratio of components, wt.% :

Carbon 0.27-0.32

Manganese 0.30-0.65

Silicon 0.01-0.17

Chrome 0.01-0.25

Sulfur 0.005-0.020

Niobium 0.005-0.02

Calcium 0.001-0.010

Iron rest

when the ratios 12 / C - Mn / 0.03 ≥ 20; Ca / S ≥ 0.065,

where C is carbon, Mn is manganese, Ca is calcium, S is sulfur, hot rolling starts at 900-950 ° C and ends at 740-850 ° C with a degree of deformation of at least 20% in the last passes, then cold deformation is carried out by calibration with a degree of deformation of 20-25% and spheroidizing annealing by high-speed heating in the temperature range A _сl + (10-30) ° С followed by regulated cooling in the temperature range 650-730 ° С with a cooling rate of 0.5-1.0 ° С / min and further cooling in a heat chamber at an ambient temperature of 100-200 ° C.

Deoxidizing agents and alloying elements with a low nitrogen content are used. During continuous casting, the metal stream is protected from contact with air.

The given combinations of alloying elements (item 1) make it possible to obtain a uniform finely dispersed structure of spheroidized perlite with a favorable combination of strength and ductility characteristics after accelerated spheroidizing annealing in the proposed steel (bar up to 25 mm in diameter).

Carbon and carbide-forming elements (niobium) are introduced into the composition of this steel in order to provide a finely dispersed grain structure, which will increase both its strength level and provide a given level of ductility, as well as expand the range of annealing of steel. The upper limit of the carbon content (0.32%) and niobium (0.02%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.27% and 0.005%, respectively - to ensure the required level of strength of this steel.

Manganese and chromium are used on the one hand as solid solution hardeners, on the other hand, as elements that significantly increase the stability of supercooled austenite. At the same time, the upper level of manganese — 0.65% and chromium — 0.25% is determined by the need to ensure the required level of steel ductility, and the lower — 0.30% and 0.01%, respectively, by the need to provide the required level of strength and technological ductility 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.

Calcium is an element that modifies non-metallic inclusions. The upper limit (0.010%), as in the case of sulfur, is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.001%) limit is due to issues of manufacturability.

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 related to the manufacturability of production.

определяют условия обеспечения заданных характеристик пластичности и упрочняемости стали при холодной объемной штамповке сложнопрофильных крепежных деталей, используют раскислители и легирующие с низким содержанием азота.The ratio

they determine the conditions for ensuring the specified characteristics of ductility and hardenability of steel during cold forging of complex-profile fasteners, use deoxidizers and alloys with a low nitrogen content.

An example of the method

The smelting of low-carbon steel of the following composition: carbon - 0.30%, manganese - 0.45%, silicon - 0.10%, chromium - 0.20%, sulfur - 0.011%, niobium - 0.012%, calcium - 0.001%, is carried out in 150-ton arc steel furnaces using 100% metallized pellets in the charge, which ensures that the mass fraction of nitrogen before release from the particleboard is not more than 0.003%, as well as a low content of color impurities. The preliminary alloying of the metal with manganese and silicon is carried out in the ladle upon discharge from the particleboard. After the release, the metal was purged with argon through the bottom purge unit during which the steel was deoxidized by aluminum. After that, the metal enters the integrated steel processing unit (AKOS), where it is possible to heat the metal to the required temperature, purge it with argon through the bottom blowing unit, dosed the necessary ferroalloys and treat the steel with flux-cored wire with various fillers. At AKOS, refining slag is imposed with an additive of lime and fluorspar, slag is deoxidized with granulated aluminum, the metal is alloyed with aluminum to a content of 0.050%, the metal is refined according to the manganese content, and it is heated to a temperature that ensures further processing. After processing at AKOS, the metal is subjected to vacuum treatment at a batch vacuum. During evacuation, a final adjustment of the chemical composition is made. After evacuation, the metal is treated with silicocalcium and transferred to casting. Casting is carried out on radial four-strand UNRS in an ingot 300 × 360 mm in size with a drawing speed of 0.6-0.7 m / min, with metal protection from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and argon feed. It also provides a low nitrogen and oxygen content and metal purity from non-metallic inclusions. After casting and cutting to a measured length, the continuously cast billets obtained were cooled in controlled cooling furnaces. Hot rolling of long products starts at a temperature of 900-950 ° C, and ends at a temperature of 740-850 ° C, with a deformation of at least 20% in the last passes. This is followed by etching of hot-rolled steel in a solution of sulfuric acid (concentration of 180-200 g / l) at a temperature of 80 ° C for 30 minutes, followed by applying a lubricating coating. This is followed by cold deformation by calibration with a deformation of 20-25% and spheroidizing annealing, including high-speed induction heating in the intercritical temperature range (A _Cl + 10-30 ° C) of a cold-deformed metal with subsequent regulated cooling in the temperature range 650-730 ° C, with speeds 1.0-1.5 ° C / min and further cooling in a heat chamber at an ambient temperature of 100-200 ° C, which reduces the duration of the spheroidization process by 5-10 times.

Fulfillment of the ratio of alloying elements made it possible to provide the required level of ductility of steel directly in the hot-rolled state at a level of δ = 28%, and the level of cold precipitation of a sample with a diameter of 20 mm at 75% of the height.

при содержании марганца - 0.45%, углерода - 0.30%

when the manganese content is 0.45%, carbon is 0.30%

при содержании серы - 0,011%, кальция - 0.001%.

when the sulfur content is 0.011%, calcium is 0.001%.

Implementation of the proposed method for the production of long products from low carbon steel of high technological ductility, which provides the structure of long products, guaranteeing rational conditions for cold forming for complex profile fasteners.

Claims (3)

1. Method for the production of long products from low carbon steel for cold forming of complex profile fasteners, including steelmaking in an electric furnace, after-furnace treatment, continuous casting, hot rolling of a continuously cast billet and cooling, characterized in that the steel is melted in the following ratio of components, wt.% : Carbon 0.27-0.32 Manganese 0.30-0.65 Silicon 0.01-0.17 Chrome 0.01-0.25 Sulfur 0.005-0.020 Niobium 0.005-0.02 Calcium 0.001-0.010 Iron Else when the relations 12 / C - Mn / 0.03 ≥ 20; Ca / S ≥ 0.065, where C is carbon; Mn is manganese; Ca is calcium; S is sulfur hot rolling starts at 900–950 ° С and ends at 740–850 ° С with a degree of deformation in the last passes of at least 20%, then cold deformation is carried out by calibration with a degree of deformation of 20–25% and spheroidizing annealing by high-speed heating in the temperature range A _s1 + (10-30) ° C, subsequent regulated cooling in the temperature range 650-730 ° C with a cooling rate of 0.5-1.0 ° C / min and further cooling in a heat chamber at an ambient temperature of 100-200 ° C. 2. The method according to claim 1, characterized in that use deoxidizers and alloying elements with a low nitrogen content. 3. The method according to claim 1, characterized in that during continuous casting, the metal stream is protected from contact with air.