RU126003U1 - HIRE REDUCED HIGHER STRENGTH FOR THE PRODUCTION OF NUTS OF CLASS DURABILITY 8 AND 9 - Google Patents

Abstract

1. Converted rolled products of increased strength from low carbon steel for the production of nuts of strength class 8 and 9, characterized in that it is made in the form of a rod formed in a skein with a smooth round profile of low carbon steel with a content, wt.%: Carbon 0.15-0 35, of manganese 0.5-1.6, having a yield strength of at least 360 N / mm, a tensile strength of at least 480 N / mm, a relative elongation (δ) of at least 28% and a relative narrowing of at least 60% .2 . Rolled according to claim 1, characterized in that the rod is made of steel by hot rolling with an end in the range from 950 to 1050 ° C and heat treatment from rolling heating by interrupted quenching to a mass-average temperature of 660-760 ° C. 3. Rental according to claim 1, characterized in that the rod is made with a diameter of from 6.0 to 22.0 mm and is formed into a skein with a mass of up to 5.0 tons.

Description

The proposed solution relates to metallurgy and metal forming, and more specifically to the manufacture of rolled round smooth profile of increased strength (wire rod) from low carbon steel for the production of fasteners, for example, nuts, mainly hexagonal strength classes 8 and 9.

Known carbon steel wire rod for subsequent processing into hardware products according to patent No. 2292247, IPC ⁷ В21В 1/16, "Method for rolling wire rod" (published in 2007), which is obtained by heating a steel billet to the austenitizing temperature, subsequent multi-pass compression in vertical and horizontal rolls with calibers with a regulated temperature of the end of rolling equal to 970 ÷ 1050 ° С and water cooling from the temperature of the end of rolling to a temperature of 730 ÷ 790 ° С. Technology parameters provide improved quality and yield of wire rod, as well as the required degree of study of the carbon steel microstructure, eliminating the formation of defects in the strip. The latter favorably affects the manufacturability of wire rope production.

However, the use of such wire rod for the production of fasteners by cold forming is not possible due to the unfavorable combination of its strength and plastic properties, as well as the increased carbon content in it.

Also known for rental products according to patent No. 2336316, IPC ⁷ C21D 8/06, C21C 38/60, C21C 38/54 "ROLLED ROUND FROM BORNE-BASED STEEL FOR COLD VOLUME STAMPING" (published in 2006), which is used to provide rational conditions for cold volume stamping of highly specialized high-strength fasteners is obtained from steel containing, wt.%: C - 0.06-0.35; Mn 0.60-1.40; Si - 0.001-0.37; Cr - 0.001-0.35; V - 0.001-0.05; Nb - 0.005-0.02; Ti - 0.01-0.04; B - 0.0005-0.0050; Al - 0.02-0.06; N is 0.005-0.015; As - 0.0001-0.03; Sn - 0.0001-0.02; Pb - 0.0001-0.01; Zn - 0.0001-0.005. Rolled products have regulated parameters for metal inclusions (sulfides, oxides, silicates and nitrides), structure, actual grain size and decarburized layer. The diameter from 10 to 25 mm is made in the rods and is characterized by the following indicators of mechanical properties - the value of cold draft is not less than 1/3 of the height, the tensile strength is not more than 580 N / mm ² , the yield strength is not more than 540 N / mm ² , the elongation is not less than 18%, relative narrowing of at least 55%. High-strength fasteners of strength class 900 MPa and higher are obtained from this product during cold stamping and subsequent heat treatment, however, due to the complex alloying of steel, the cost of such products is high. The use of such rolled products for the manufacture of products of mass use, which is a nut of strength class 8 and 9, is unacceptable due to non-competitiveness.

The prototype of the proposed utility model, as the closest in its technical essence and the achieved result, is rolled according to patent No. 2330891, IPC ⁷ C21D 8/06, C21C 38/60, C21C 38/14 "ROLLED ROUND FROM LOW-CARBON HIGH-PLASTIC SODIUM FOR STAMPS ”(published in 2008), which is manufactured with a diameter of 12 to 36 mm in the form of rods of measured length. The technical result of the invention is to obtain improved characteristics of technological ductility and viscosity of rolled products to ensure rational conditions for cold forming for complex profile fasteners. The technical result is achieved by the fact that long products are obtained from steel containing components in wt.%: C - 0.04-0.11; Mn 0.25-0.60; Si - 0.01-0.055; Al - 0.03-0.05; S is 0.005-0.015; P - 0.005-0.02 ;, N - 0.005-0.015; O ₂ - 0.001-0.015; As - 0.0001-0.03; Sn - 0.0001-0.02; Pb - 0.0001-0.01; Zn - 0.0001-0.005, iron and inevitable impurities - the rest. The rental has a macrostructure - central porosity, point heterogeneity, segregation square - not more than 3 points for each type, shrinkable segregation - not more than 3 points; segregation strips - not more than 1 point, non-metallic inclusions for sulfides, oxides, silicates and nitrides with a size not exceeding 3 points for each type of inclusions, a uniform spheroidized structure in length, consisting of at least 60% granular perlite, the size of the actual grain is 5- 10 points, the amount of cold draft - not less than 1/3 of the height and mechanical properties: σ _в - not more than 460 MPa, δ ₅ - not less than 28%, ψ - not less than 65%.

A disadvantage of the known steel is its low strength properties, which do not provide fasteners with a strength of 800 MPa and without finish heat treatment (quenching with tempering) due to the low content of carbon, manganese and silicon in steel, the main reinforcing components. Also unfavorable is the delivery format of rolled products, which are manufactured with a diameter of 12 to 36 mm in the form of rods of measured length. This circumstance complicates its use in modern high-tech nut production based on the use of rolled products in coils, which minimizes metal loss. The cost of rolled products (steel) and energy costs for the subsequent heat treatment of fasteners (class 8 and 9 strength nuts) lead to a significant increase in the cost of finished products and the inability to compete with similar products supplied from Southeast Asia.

The proposed utility model solves the problem of producing rolled steel (wire rod) of increased strength from ordinary low-carbon steel grades for the production of nuts of class 8 and 9, which eliminates the heat treatment of the finished product and ensures its cost reduction.

The problem is achieved in that the proposed rolled products of increased strength of a smooth round profile for the production of nuts of strength class 8 and 9, made in the form of a rod formed into a coil, has a yield strength (σ _t ) of at least 360 N / mm ² , temporary tensile strength (σ _in ) not less than 480 N / mm ² , relative elongation (δ ₅ ) not less than 28%, relative narrowing (ψ) not less than 60% and made of low carbon steel containing 0.15 ... 0.35% carbon, 0 , 5 ... 1.6% manganese, the rest is iron and inevitable impurities, when the carbon equivalent _(eq C) not less than 0.23% determined by the formula: C _eq = C + Mn / 20 where: C, Mn - weight fraction of carbon and manganese in%. The process of its production includes steel smelting, hot rolling and heat treatment, while the temperature of the end of hot rolling is limited in the range from 950 to 1050 ° C, the heat treatment is carried out from rolling heating by interrupted quenching to a mass-average temperature of 660 ... 760 ° C; and the hire itself is made in the form of a rod with a diameter of 6 to 22 mm formed into a skein weighing up to 5.0 tons.

The technical result of the proposed utility model is to obtain rolled steel (wire rod) of increased strength with a diameter of 6.0 ... 22.0 mm formed into a skein weighing up to 5 t for the production of nuts of class 8 and 9. The presence of such a rolling stock reduces the cost of production of the nut through the use of ordinary low-carbon steel grades and reducing heat treatment costs by eliminating hardening and tempering operations. The latter greatly enhances the competitiveness of damage base products to ensure quality and mechanical properties.

To achieve a technical result, rolled steel of increased strength from low carbon steel for the production of nuts of strength class 8 and 9 is made in the form of a rod formed into a coil with a smooth round profile of low carbon steel with a content, wt.%: Carbon 0.15-0.35, manganese 0.5-1.6, having a yield strength of at least 360 N / mm ² , a temporary tensile strength of at least 480 N / mm ² , an elongation of (65) of at least 28% and a relative narrowing of at least 60%. The rod was obtained from steel by hot rolling with an end in the range from 950 to 1050 ° C and heat treatment from rolling heating by means of interrupted quenching to a mass-average temperature of 660 ÷ 760 ° C. The rod is made with a diameter of 6.0 to 22.0 mm and is formed into a skein with a mass of up to 5.0 tons.

All the distinguishing features of the claimed utility model are interconnected and contribute to the achievement of the task.

So, if the rolled product has a yield strength of at least 360 N / mm ² , a temporary tensile strength of at least 480 N / mm ² , an elongation of (85) of at least 28%, a relative narrowing of at least 60%, then the raw materials themselves are already laid higher mechanical properties that are inherited by the finished product, which will be made from it. The resulting hardware products, such as a nut, will have a higher strength class and there is no need for the nut itself to be hardened. The use of rolled products with a yield strength of less than 360 N / mm ² and a temporary tensile strength of less than 480 N / mm ² does not provide the required properties of the resulting nut. Rolled products with the indicated properties, despite the increased strength in comparison with annealed or hot-rolled products, remain sufficiently plastic (δ ₅ ≥28%, ψ≥60%), and when the nut is cold stamped, no cracks form on the finished product. If the characteristics of the ductility of rolled products - the relative elongation (δ ₅ ) is less than 28%, and the relative narrowing (ψ) is less than 60%, then when the nut is stamped, cracks form, which is a rejection sign. The manufacture of rolled steel with a carbon content of less than 0.15% and manganese less than 0.5% does not ensure the strength properties of rolled products at the claimed level due to the insufficient amount of pearlite component in the metal structure. The manufacture of rolled steel with carbon content of more than 0.35% and manganese more than 1.6% will lead to the need for cold forming to subject it to spheroidizing annealing to transfer an increased amount of perlite from plate to globular form and subsequent etching, which increases the cost of production and energy costs. The total effect of carbon and manganese, as the main alloying elements in ordinary pisco-carbon steels that increase the strength and hardness of products, is indirectly estimated through the carbon equivalent (C _eq ) determined by the above formula. Moreover, the technical result is achieved when the carbon equivalent is at least 0.23%. With a value of less than 0.23%, the final properties of the rental will not correspond to the claimed level of properties. In steel, one or more alloying elements from the group of silicon, chromium, copper, molybdenum, vanadium, and nickel in insignificant amounts that are not specially introduced into the steel, but from the scrap during smelting, can be present as inevitable impurities. These elements also contribute to improving the strength and hardness of rolled products by hardening the solid solution and increasing the proportion of carbides.

The process of obtaining rolled products of increased strength includes several phased technological operations, which also contribute to the achievement of the task. Steel smelting and billet production can be carried out using any of the currently used technologies. Hot rolling is carried out in a continuous mill stream to the finished rolling size with the end in the temperature range from 950 to 1050 ° C. At the end of rolling at temperatures below 950 ° C, equipment operation is hindered due to a decrease in the ductility of the metal and an increase in the load on the rolling stands. The completion of rolling at a temperature above 1050 ° C leads to the formation of an unfavorable coarse-grained metal structure and hindering the process of subsequent cooling of the rolling steel before winding. Heat treatment from rolling heating is carried out by means of interrupted quenching of rolling steel by streams of water in special wiring devices to a mass-average temperature of 660 ... 760 ° C. The mass average temperature (temperature of self-tempering) depends on the duration of cooling (interrupted quenching) and significantly affects the formation of the mechanical properties of rolled products. When ensuring the average bulk temperature of rolled products below 660 ° C, mechanical properties are formed with an unsatisfactory plasticity level (δ ₅ less than 28% and ψ less than 60%), which complicates the use of such rolled products for further processing. When ensuring the average bulk temperature of rolled products above 760 ° C, strength properties (σ _t , σ _c ) are formed below the declared ones, which does not provide high-quality hardware products. The manufacture of rolled products in the form of a rod with a diameter of 6.0 to 22.0 mm formed into a skein, the mass of which can reach 5.0 tons, provides several advantages for its subsequent processing into fasteners. So at the metallurgical redistribution, the production of rolled products in coils is carried out on high-performance equipment with minimal loss of metal for trimming during the formation of a uniform level of mechanical properties. At the hardware redistribution, the use of rolled stock of this assortment and format (skein weighing up to 5.0 tons) allows us to produce a nut of strength class (8 and 9) of a wide assortment from M4 to M18 with minimal metal loss without quenching of the finished product.

A comparative analysis of the invention with the prototype allows us to identify differences in that the inventive steel has a higher level of strength properties, which are achieved by using ordinary low-carbon steel of a certain composition, as well as a specific set of manufacturing operations. Production Example

In the conditions of metallurgical production, round rolling (wire rod) with a diameter of 6.0 ... 22.0 mm was made of steel grades 16G2, 20G2, 20 and 35, which was subjected to heat treatment from the temperature of the end of rolling by interrupted quenching by water flows to a mass-average temperature of 650 ... 770 ° С, cooling in air and the subsequent collection of turns into a coil. In the manufacture of rolled products, the process parameters were changed (rolling temperature, duration of cooling of the rolled products with water), which made it possible to maintain the mass-average temperature in a given interval and to obtain finished steel with a different level of mechanical properties. From rolled coils were taken samples which were tested for tensile GOST 1497 with definition characteristics σ _r, σ _in, δ ₅ and ψ. The test results are presented in table 1.

An example of manufacturing a nut.

In the conditions of hardware production, rolled metal (wire rod) according to Nos. 2, 3, 5 and 6 from table 1 was processed into a nut with a size of M10 mm. Before processing, scale was removed from the surface of the wire rod and the technological operation of applying a lubricant layer to the surface of the wire rod (phosphating) was carried out.

When hauling the wire rod on the AZTM 1/750 drawing mill onto a workpiece with the diameter necessary for the manufacture of the nut, a single calibration was used with a diameter of 13.3 mm. The manufacture of the M10 hex nut in accordance with GOST 5927 was carried out on a cold heading six-position automatic press. The nuts were tested with a test load in accordance with clause 8.1 of GOST R 52628 by axial tension using the FP-100/1 testing machine. Separately, the load was determined at which the nut thread breaks down (test until the nut breaks). The results of testing the production of nuts are shown in table 2.

table 2 Rolled Properties, Mechanical Properties, and Nut Strength Class No. p / p from table 1 steel grade The mechanical properties of the rental Nut Properties Note σ _t , N / mm ² δ ₅ ,% Stall load, KN Stress thread breakdown, N / mm ² Strength class 2 16G2 350 34.0 70,2 832 6 - 3 16G2 360 34.0 74.8 887 8 - 5 20G2 450 27.0 89.5 1062 10 Crack marriage 6 20G2 415 29.5 82.8 982 9 -

The results indicate that the proposed technical solution provides rolled products (wire rods) from ordinary low-carbon and low-alloy steels of increased strength for the subsequent production of fasteners, for example, nuts of strength class 8 and 9. In this case, the rolled metal in its strength characteristics exceeds properties similar to products supplied for the hardware industry in accordance with GOST 30136 (Rolled wire of carbon steel of ordinary quality. Technical conditions) and GOST 10702 (Rolled products from high-quality structural carbon and alloy steel for cold extrusion and upsetting. Technical conditions). Products made from rolled products of increased strength are characterized by higher consumer properties, and also have lower cost due to the use of cheap steel grades and reduce the cost of initial rolling and heat treatment (excluding operations of annealing of raw materials and / or heating the nut for hardening).

Converted rolled products of increased strength of a smooth round profile can be widely used for the manufacture of class 8 and 9 nuts for mechanical engineering, automotive industry and other industries.

Table 1 Steel grade and composition, rolled diameter, production parameters, mechanical properties No. p / p steel grade Diameter of hire, mm FROM, % Mn,% С _equiv ,% The temperature of the end of rolling, ° C Temperature of hire after T / O (mass average), ° С The mechanical properties of the rental σ _t , N / mm ² σ _in , N / mm ² δ ₅ ,% ψ,% one 10 14.0 0.11 0.60 0.14 1000 - 205 380 35.0 69.0 2 ∗) 16G2 14.0 0.14 1.42 0.21 950 650 350 470 34.0 68.0 3 16G2 14.0 0.15 1,60 0.23 950 660 360 480 34.0 67.0 four 16G2 6.0 0.15 1,60 0.23 950 680 380 505 33.0 64.5 5 ∗∗) 20G2 14.0 0.21 1.39 0.28 980 650 450 560 27.0 58.0 6 20G2 14.0 0.21 1.39 0.28 980 690 415 535 29.5 61.5 7 ∗) 20G2 14.0 0.21 1.39 0.28 980 770 350 460 34.0 65.0 8 20G2 22.0 0.21 1.39 0.28 980 760 385 515 32,0 62.0 9 twenty 18.0 0.20 0.66 0.23 1000 760 365 490 30,0 62.0 10 35 22.0 0.35 0.68 0.38 1050 760 370 525 29.5 61.5 1 - According to the prototype, ∗∗) - reduced strength properties, ∗∗∗) - reduced plastic properties

Claims (3)

1. Converted rolled products of increased strength from low carbon steel for the production of nuts of strength class 8 and 9, characterized in that it is made in the form of a rod formed into a skein with a smooth round profile of low carbon steel with a content, wt.%: Carbon 0.15-0 , 35, manganese 0.5-1.6, having a yield strength of not less than 360 N / mm ² , temporary tensile strength of not less than 480 N / mm ² , elongation (δ ₅ ) of not less than 28% and relative narrowing of not less than 60 % 2. Rolled according to claim 1, characterized in that the rod is made of steel by hot rolling with an end in the range from 950 to 1050 ° C and heat treatment from rolling heating by interrupted hardening to a mass-average temperature of 660-760 ° C. 3. Rental according to claim 1, characterized in that the rod is made with a diameter of from 6.0 to 22.0 mm and formed into a skein with a mass of up to 5.0 tons.