Round-profiled rolled iron from low-alloyed steel for cold die forging of high-strength geometrically complex fastening members

FIELD: ferrous metallurgy.

SUBSTANCE: invention provides round-profiled iron smelted from steel containing, wt %: carbon 0.10-0.15, manganese 0.90-1.40, silicon 0.001-0.37, sulfur 0.005-0.020, chromium 0.001-0.35, 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 unavoidable impurities - the balance. When following relationships are fulfilled: 500(Ti/24-N/7)+0.2 ≥ 0; 40 ≥ C/0.01+B/0.0001 ≥ 3.0, rolled iron has following characteristics: maximum degree of pollution with nonmetal inclusions, in particular sulfides, oxides, silicates, and nitrides, does not exceed 3 points for each type of inclusions; longitudinally uniform spheroidized structure composed of at least 80% perlite; effective grain size 5-10 points; diameter of wire 10-23 mm; carbon-free layer not exceeding 2.5% diameter; cold setting value at least 1/3 height; throughout hardenability in circles up to 15 mm in diameter; point of maximum load not higher than 520 MPa; relative elongation at least 20%; and relative contraction at least 65%.

EFFECT: ensured optimal conditions for cold die forging of high-strength geometrically complex fastening members and simultaneously improved steel hardenability characteristics.

 

The invention relates to the field of metallurgy, in particular to the production of rolled, round, low-carbon boron steel for cold massive forming high strength of geometrically-complex fasteners particularly complex form.

Known rolled round of micro steel containing carbon and alloying elements having a defined structure, such as cold-deformed martensite, tensile strength, not less than 1800 MPa, and the wire diameter is 0.1-0.5 mm [1].

Famous bars, all from low-carbon boron steel, containing (wt.%): carbon 0,15-0,30%, silicon 0.5 to 0.8%manganese and 0.7 to 1.5%, phosphorus 0,02-0,10, copper, 0.1 to 0.4, boron 0,001-0,005%, titanium of 0.01-0.05%, aluminum from 0.01 to 0.05%, the rest of the iron with specified mechanical properties [2]. The disadvantages of this steel are the broad limits of the content of alloying elements, which can lead to instability of the mechanical properties, its low efficiency and insufficient hardenability.

Closest to the technical essence and the achieved effect of the present invention is rolled, round, low-carbon boron steel, containing (wt.%): carbon 0,10-0,20%, silicon 0,15-0,30%, manganese from 0.90-1.40 per cent, molybdenum 0,01-0,30%, boron from 0.005 to 0.005%, titanium 0.01 to 0.04, nitrogen 0,005-0,015%, the rest of the iron, when, after the corresponding ratios ; Mn+5×Mo≥2.15, having defined the structure and mechanical properties [3]. The disadvantage of this method is that when a relatively high level of variation in the carbon content is not taken into account the protection factor of boron from binding in the nitrides that will not allow you to get increased hardenability characteristics.

The objective of the invention is the provision of efficient conditions for cold massive forming geometrically-complex high-strength fasteners while providing uniform mechanical properties across the section of the car and high performance hardenability of steel.

The most important requirement of rolled steel, round, boron steel for cold massive forming of high-strength fasteners particularly complex form, is, on the one hand, the high technological plasticity and low coefficient of strain hardening in the state of delivery and, on the other hand, the ability to provide the specified level of consumer properties after the final heat strengthening.

The problem is solved by the fact that known rolled, round, low-carbon boron steel having a specified structure, ultimate strength and hardness, according to the invention is made of steel containing the following relation is of komponentov in wt.%:

carbon 0,10-0,15

manganese 0,90-1,40

silicon 0,001-0,37

sera of 0,005 0,020

chrome 0,001-0,35

Nickel from 0.005 to 0.10

niobium 0,005-0,02

titanium 0.01 to 0.04)

Bor 0,0005-0,0050

aluminum 0,02-0,06

nitrogen 0,005-0,015

iron and

inevitable impurities else

And:

the maximum score of contamination of steel, non-metallic inclusions in sulfides, oxides, silicates and nitrides of not greater than 3 points for each type of inclusions, car has a homogeneous spheroidizing structure in length, consisting of not less than 80% granular perlite, the amount of the actual grain - 5-10 points, the diameter is from 10 to 23 mm, has a de-carbonized layer is not more than 1.5% of the diameter, the amount of cold upsetting of not less than 1/3 of the height, end-to-end (90%) hardenability in circles with a diameter of 15 mm, an ultimate strength of not more than 520 MPa, elongation not less than 20%the relative narrowing of at least 65%.

Given the combination of alloying elements (1) allow to obtain in the finished product (bolt, nut, stud diameter up to 23 mm) after thermolysine (tempering temperature of not less than 920°C, followed by tempering temperature not lower than 620° (C) a homogeneous fine structure of martensite leave with a favorable combination of strength and ductility.

is glared and carbonitrides elements (niobium) are entered into the composition of this steel to ensure a fine grain structure, that will increase as the level of its strength, and to provide a given level of ductility. While niobium and vanadium manage the processes in the austenitic region (determines the tendency to grain growth of austenite, stabilizes the structure during thermomechanical processing, increases the temperature of recrystallization and, consequently, affects the character γ-α- transformation. Niobium and vanadium also contributes to hardening of the steel during thermolysine. The upper limit of carbon content (0.15%), niobium (0.02%) due to the need to ensure the required level of ductility of steel, and the bottom, respectively, 0.10%, 0.005%, providing the required strength level of the steel.

Manganese and chromium is used, on the one hand, as a solid solution hardener, on the other hand, as an element, substantially increasing the stability of the supercooled austenite and increases the hardenability of steel. The upper levels of manganese, - 1.40%, chromium (0.35%) is determined by the need to ensure the required level of ductility of steel, and the lower - 0.90%, 0.001% by the need to provide an appropriate level of strength and hardenability of the steel.

Silicon belongs to territooriumil elements. The lower limit for silicon - 0.001% caused by the deoxidation of steel. The silicon content higher 0.37% adversely ska is placed on the characteristics of ductility of steel.

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

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

Nitrogen is an element that participates in the formation of carbonitrides, while lower levels (0.005%) is determined by the requirement to provide a given level of strength, and the upper level (0.015%) - requirement to provide a given level of ductility and hardenability.

Nickel within the specified limits (0.005-0.10%) affect the properties of the hardenability and toughness of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.020%) due to the necessity of obtaining a given level of ductility and toughness of steel, and the lower limit (0.005%) - questions-tech production.

To ensure complete bonding of nitrogen in the nitride type TiN and AlN as the result of reactions:

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

requires the following ratios of elements, otherwise protection boron from tying it in nitrides and decrease characteristics of the hardenability of steel.

Ratio:define storage conditions in more than 50% effective boron, which provides a set of characteristics of the hardenability of steel.

Therefore, the claimed set of characteristics meets the criterion of "substantial differences".

Below is an example implementation of the present invention, not excluding other in the scope of the claims.

Melting boron steels produced in shaft furnace “Fuchs”. For guaranteed low nitrogen content developed special technology, including melt blending liquid cast iron up to 40% of the total volume of the mixture. Oxidative period provides a high rate of oxidation of carbon within 0,05-0,07%/min electric mode involves shutting off the furnace when the carbon content of 0.2-0.4 percent above the lower limit specified, dodavku the carbon produced without arcing. The temperature of the discharge from the furnace 1640-1680°C. Enter ferroalloys, steel treatment to remove non-metallic inclusions is made at the ladle furnace, equipped with a system e is antropologia or hinotori. The temperature of the steel before casting on 60°C above the liquidus temperature of the brand. Casting is done in extended to the top of the mold. The mass of the ingot 7.85 so To ensure a low content of nitrogen in the casting is the protection of the jet of metal with argon through a special ring device. Heating of the ingots in the blooming shop is regenerative wells before the temperature started rolling 1250-1270°C. Rolling of ingots produced at the blooming mill (mill 1300) and then on a continuous billet mill on the billet cross section of 100×100 mm For removing the formed during heating of ingots de-carbonized layer of the workpiece are subjected to abrasive blasting." Then he made hot rolling the resulting workpiece on a wire mill 150 or small-section mill 250 in diameters from 5.5 to 23 mm in coils. To ensure the value of de-carbonized layer is not more than 1% of the diameter of the limited rate of billets from the furnace is not less than 100 t/h for 150 mill and at least 56 t/h to 250 mill. The onset temperature rolling of billets 1220-1240° (C) to 250 mill and 1270-1290° (C) to 150 mill. Hot rolling of the rolled finish at a temperature of 1000-1050°With, then are accelerated cooling to 880-900°C, followed by cooling to 300°and then winding the coils.

In the hot rolling is received from the postal car with a diameter of 15 mm with the structure of granular perlite (95%), bezplatny layer depth of 0.18 mm, the score of the actual grain - 8, cold sludge wire with a diameter of 15 mm by 75%, the temporary strength of 500 MPa, an elongation of 22%, narrowing 69%..

Ratio

The introduction of the proposed product - rolled, round, boron steel of high hardenability provides obtaining directly into the mill stream (without additional spheroidizing annealing) patterns of rolled guaranteeing the rational conditions of cold massive forming geometrically-complex high-strength fasteners.

SOURCES of INFORMATION

1. EN 2177510 C2, 21 D 8/06, 27.12.2001.

2. SU 901331, C 22 C 38/16,21.04.1980,

3. EN 2127770 C1, With 22 38/14, 20.03.1999, (prototype).

Rolled, round, made of alloy steel containing carbon and alloying elements with the given parameters of quality steel non-metallic inclusions, structure, mechanical properties and hardenability and technology of plasticity, characterized in that the steel contains the following ratio of components, wt.%:

Carbon 0,10-0,15

Manganese 0,90-1,40

Silicon 0,001-0,37

Sera of 0,005 0,020

Chrome 0,001-0,35

Nickel from 0.005 to 0.10

N is Obi 0,005-0,02

Titanium 0.01 to 0.04)

Bor 0,0005-0,0050

Aluminum 0,02-0,06

Nitrogen 0,005-0,015

Iron and inevitable impurities Else

when performing correlations

the maximum score of contamination of steel, non-metallic inclusions in sulfides, oxides, silicates and nitrides of not greater than 3 points for each type of inclusions, car has a homogeneous spheroidizing structure in length, consisting of not less than 80% granular perlite, the amount of the actual grain 5-10 points, diameter from 10 to 23 mm, has a de-carbonized layer is not more than 1.5% of the diameter of the rent, the amount of cold upsetting of not less than 1/3 of the height, through 90%hardenability of steel with a diameter up to 15 mm, ultimate strength of not more than 520 MPa, elongation not less than 20%, the relative narrowing of at least 65%.



 

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