Round-profiled rolled iron from low-carbon steel for cold die forging of high-strength especially high-profiled fastening members

FIELD: ferrous metallurgy.

SUBSTANCE: invention provides round-profiled iron smelted from low-carbon steel composed of, wt %: carbon 0.17-0.25, manganese 0.30-0.65, silicon 0.01-0.17, sulfur 0.005-0.020, vanadium 0.005-0.07, niobium 0.005-0.02, calcium 0.001-0.010, iron and unavoidable impurities - the balance. When following relationships are fulfilled: 12/C-Mn/0.02 ≥ 27; 0.46 ≥ 6V+8Nb ≥ 0.22; Ca/S ≥ 0.065, 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% grainy perlite; effective grain size 5-10 points; diameter 10-25 mm; carbon-free layer not exceeding 1.5% of diameter; cold setting value at least 1/3 height; point of maximum load not higher than 550 MPa; relative elongation at least 20%; and relative contraction at least 60%.

EFFECT: ensured optimal conditions for cold die forging of high-strength geometrically complex fastening members and simultaneously ensured improved characteristics of in-process plasticity and low level of stray hardening.

 

The invention relates to the field of metallurgy, in particular to the production of rolled, round, highly ductile low carbon steel for cold massive forming fasteners particularly complex form.

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

Famous bars, all of nizkouglerodistoi steel containing, wt.%: carbon 0,17 of 0.20%, si 0,17-0,37%, manganese of 0.65 to 1.00%, chromium 0,55-0,70%, vanadium of 0.05-0.08%, niobium 0,02-0,04%, iron rest, when the ratio (chrome/carbon)(vanadium/niobium)2=16,4-65,9 [2]

Closest to the technical essence and the achieved effect of the present invention is rolled, round, steel, containing, wt.%: carbon 0.18-0.22%, manganese 0.27-0.67%, silicon 0,17-0,37%, vanadium of 0.05-0.10%niobium, 0.01 to 0.04%, the rest of the iron in the following ratio, wt.%: 6V+8Nb≥ 0.56 and 100000VNb28.0 [3]. Disadvantages in 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.

Task izopet the tion is the provision of efficient conditions for cold massive forming geometrically-complex fasteners while providing uniform mechanical properties across the section of the car and high performance technological plasticity.

The most important requirement of rolled steel, round, high-ductility low carbon steel for cold massive forming 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.

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

carbon 0.17-0.25

manganese 0.30-0.65

silicon 0.01-0.17

sera of 0,005 0,020

vanadium 0.005-0.07

niobium is 0.005-0.02

calcium, 0.001-0.010

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 point, the wire diameter ranges from 10 to 25 mm, it is no 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, ultimate strength, not more than 550 MPa, elongation not less than 20%, relative narrowing of at least 60%.

Given the combination of alloying elements (1) allow to obtain in the finished product (bolt, nut, stud diameter up to 23 mm), post-cold massive forming a homogeneous fine structure of martensite leave with a favorable combination of strength and ductility.

Carbon and carbonitrides elements (vanadium, niobium) are entered into the composition of this steel to ensure a fine grain structure, which 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 (determine the propensity for the grain growth of austenite, stabilize the structure during thermomechanical processing, increase the recrystallization temperature and, consequently, affect the character γ -α - transformation. Niobium and vanadium also contributes to hardening of the steel during thermolysine. The upper limit of carbon content (0.25%), niobium (0.02%) and vanadium (0.07%) due to the need to ensure the required level of ductility of steel, and the bottom, respectively, 0.17%, 0.005% and 0.005% by providing the required strength level of the steel.

Manganese, 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. The upper level of the manganese content is 0.65%, is determined by the need to ensure the required level of ductility of steel, and the lower - 0.30%, the need to ensure the required level of strength of the steel.

Silicon belongs to territooriumil elements. The lower limit for silicon - 0.01%, caused by the deoxidation of steel. The silicon content higher than 0.17% will adversely affect the characteristics of ductility 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.

Calcium is an element, modifying nonmetallic inclusions. The upper limit (0.010%), as in the case of sulfur caused by the necessity of obtaining a given level of ductility and toughness of steel, and the lower (0.001%) limit - questions-tech production.

Ratiosdefine the conditions ensure the specified characteristics of plasticity and proclaimeth cold steel at the drop-forging of geometrically-complex fasteners

Therefore, the claimed owls is the synergy signs meets the criterion of ″ significant differences″ .

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

Smelting high-ductility low carbon steel 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 an electric heating system 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 a 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 ingots p is otvoditsya on 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 rapid cooling to 880-900° C, followed by cooling to 300° and then winding the coils.

In the hot rolling get rolled diameter of 21 mm with the structure of granular perlite (99%), bezplatny layer depth of 0.12 mm, the score of the actual grain - 9, cold sludge wire with a diameter of 21 mm, 90%, temporary tear resistance of 500 MPa, an elongation of 22%, narrowing 70%..

Ratio

C=0,20%, Mn=0,50%

V=0,01%, Nb=0,01%

Ca=0,0011%, S=0,008%

The introduction of the proposed product - rolled, round, low-carbon steel high plasticity of especial getting directly into the mill stream (without additional spheroidizing annealing) patterns of rolled, ensuring rational conditions of cold massive forming geometrically-complex fasteners.

SOURCES of INFORMATION

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

2. SU 1703709, With 22 38/54, 07.01.1992.

3. SU 1772208, With 22 38/12, bull. No. 40, 30.10.1992 (prototype).

Rolled, round, produced from low-carbon steel containing carbon and alloying elements that have the specified quality parameters become non-metallic inclusions, structure, mechanical properties, proclaimest deformation and technology of plasticity, characterized in that the steel contains the following ratio of components, wt.%:

Carbon 0,17-0,25

Manganese between 0.30 to 0.65

Silicon, from 0.01 to 0.17

Sera of 0,005 0,020

Vanadium from 0.005 to 0.07

Niobium 0,005-0,02

Calcium 0,001-0,010

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 25 mm, de-carbonized layer is not more than 1.5% of the diameter, the amount of cold upsetting of not less than 13 height, ultimate strength of not more than 550 MPa, elongation not less than 20%, relative narrowing of at least 60%.



 

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