RU2238339C1 - Method for producing of spheroidal rolled bar from low-carbon steel for cold bulk pressing of compound-profiled fastening parts - Google Patents

Abstract

FIELD: metallurgy, in particular, production of rolled parts of specifically complex shape from low-carbon steel.

SUBSTANCE: method involves melting steel in electric furnace; providing processing beyond furnace; pouring into casting molds while providing protection of flow; hot rolling of ingots and obtaining blank; providing controlled rolling of blank; winding rolled product into rolls; gauging rolled products at deformation extent of 15-20% and providing spheroidizing annealing process; melting steel at following ratio of components, wt%: carbon 0.27-0.32; manganese 0.30-0.65; silicon 0.01-0.25; sulfur 0.005-0.020; niobium 0.005-0.02; calcium 0.001-0.010; iron the balance, with following ratios being provided:12/C - Mn/0.03 equal to or exceeding 20; Ca/S equal to or exceeding 0.065. Process of microalloying of steel with niobium inhibits steel recrystallization process at rolling finishing temperature of 950-1,000⁰C to allow controlled rolling on existing equipment and formation of fine-grained structure. Spheroidizing annealing process is performed by high-speed heating of cold deformed metal at intercritical temperature range, followed by regulated cooling within temperature range of 650-730⁰C at cooling rate of 1.0-1.5⁰C/min and further cooling in thermal chamber at temperature of cooling medium of 100-150⁰C. Method allows spheroidizing process time to be reduced by 5-10 times.

EFFECT: increased efficiency and provision for producing of rolled bars having structure providing adequate conditions for cold bulk pressing of compound profiled high-strength fastening parts from steel with improved ductility and toughness.

2 cl, 1 ex

Description

(Авторское свидетельство СССР 1703709 от 07.01.1992 г., бюл. №1, С 22 С 38/26).The invention relates to the field of metallurgy, in particular to the production of long products from low carbon steel for cold die forging of complex profile fasteners of particularly complex shape. Known structural steel containing, wt.%: Carbon 0.17-0.20%, manganese 0.65-10%, 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.%:

(USSR author's certificate 1703709 of 01/07/1992, bull. No. 1, C 22 C 38/26).

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 complex 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 electric furnaces, out-of-furnace processing, casting into molds, hot rolling of an ingot to produce a workpiece and cooling (RU 2042734 C1, C 22 C 38/54, 08/27/1995).

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 electric furnaces, out-of-furnace processing, casting into molds, hot rolling of an ingot to produce a workpiece, steel is smelted 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 relations

after hot rolling, cold deformation is carried out by calibration with a degree of deformation of 15-20% and spheroidizing annealing of the cold-formed workpiece by high-speed induction heating in the intercritical temperature range and subsequent regulated cooling in the temperature range 650-730 ° C with speeds of 1.0-1.5 ° C / min and further cooling in a heat chamber at an ambient temperature of 100-150 ° C to reduce the duration of the annealing process. When casting steel into the molds, the metal stream is protected.

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

Carbon and carbonitride-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. In this case, niobium controls processes in the austenitic region (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical treatment, increases the temperature of recrystallization and, as a result, affects the nature of the γ-α transformation. Niobium also contributes to the hardening of steel during thermal improvement. The upper limit of the content carbon (0.32%), niobium (0.02%) due to the need to ensure the required level of ductility of steel, and the bottom - respectively 0.27%, 0.005% - to ensure the required level of strength of this steel .

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

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.

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%) due to issues of manufacturability.

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 due to issues of manufacturability.

определяют условия обеспечения заданных характеристик пластичности и упрочняемости стали при холодной объемной штамповке сложнопрофильных крепежных деталей.The ratio

determine the conditions for ensuring the specified characteristics of ductility and hardenability of steel during cold forging of complex profile fasteners.

An example implementation 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%, 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 when the carbon content is 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 outlet from the furnace 1640-1680 ° C. The introduction of ferroalloys, the processing of steel to remove non-metallic inclusions are carried out on a 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. Ingot rolling is performed 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 a wire mill 150 or a small-grade 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 950-1000 ° C and wound into riots. 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 lubricant coating. This is followed by cold deformation by calibration with a deformation of 15-20% 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 100-150 ° 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 the 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 with increased stampability provides a spheroidized structure of long products, guaranteeing rational conditions for the cold forging of complex profile fasteners.

Claims (2)

1. A method for the production of long products from low carbon steel for cold forging of complex profile fasteners, including steelmaking in an electric furnace, after-furnace treatment, casting into molds, hot rolling of an ingot to produce a workpiece 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 after hot rolling, cold deformation is carried out by calibration with a degree of deformation of 15-20% and spheroidizing annealing of the cold-formed workpiece by high-speed induction heating in the intercritical temperature range and subsequent regulated cooling in the temperature range 650-730 ° C with speeds of 1.0-1.5 ° C / min and further cooling in a heat chamber at an ambient temperature of 100-150 ° C to reduce the duration of the annealing process. 2. The method according to claim 1, characterized in that when casting into the molds, the metal stream is protected.