RU1775490C - Steel - Google Patents

Abstract

The invention relates to ferrous metallurgy, in particular to the production of steel, and can be used in the manufacture of cold-rolled structural sheet for stamping parts of automobiles, tractors, agricultural machines. Steel contains, wt.%: Carbon - 0.02-0.07; Manganese - 0.15-0.30; silicon - 0.01-0.10; phosphorus - 0.04-0.10; aluminum - 0.02-0.07; calcium - 0.0005-0.001; copper - 0.02-0.30; boron - 0.0005-0.005; iron - the rest. The proposed steel has increased fatigue strength (endurance 248-260 N / mm) while maintaining the formability. 2 tab.

Description

The invention relates to the field of ferrous metallurgy, in particular to production, and can be used in the manufacture of cold-rolled structural sheet for stamping parts of automobiles, tractors, agricultural machines.

At present, low-carbon steel steels are used for the manufacture of mechanical parts by cold stamping, which are characterized by high ductility but do not meet the requirements of operational reliability and durability, in particular under conditions of alternating loads due to low fatigue strength.

Known steel containing, wt.%: Carbon Not more than 0.07

Manganese 0.20-0.35

Sulfur: Not more than 0.025

Phosphorus Not more than 0,020

Aluminum

Silicon

Chromium

Nickel

Copper

Iron

0.02-0.07 No more than 0.01 No more than 0.03 No more than 0.06 No more than 0.06 Else

The disadvantage of this steel is its low strength under static loading and alternating loads due to the low content of hardening alloying elements.

The closest to steel of the claimed composition in terms of technical nature and the achieved effect is known steel, containing, wt.%:

Carbon 0.03-0.10

Manganese 0.20-0.40

Silicon 0.05-0.20

Phosphorus 0.015-0.08

Aluminum0.01-0.06

-ch VI ate che about

Calcium 0.001-0.025

Zirconium 0.01-0.05

IronOther

The disadvantage of this steel is its low fatigue strength due to the presence of zirconium nitrides (carbonitrides) in the structure. The high thermodynamic activity of zirconium and its affinity for nitrogen and carbon makes it possible to form these inclusions in liquid steel and during crystallization, which are highly stable upon reheating, do not dissolve upon heating of the slabs for rolling, and remain in the final structure after processing . These inclusions are acute-angled and can serve as effective stress concentrators, causing a decrease in fatigue strength.

The purpose of the invention is to increase fatigue strength while maintaining a shampuemost.

This goal is achieved in that the steel containing carbon, manganese, silicon, phosphorus, aluminum, calcium and iron, additionally contains copper and boron in the following ratios of components, wt.%:

Carbon 0.02-0.07

Manganese 0.15-0.30

Silicon 0.01-0.10

Phosphorus 0.04-0.10

Aluminum 0.02-0.07

Calcium 0.0005-0.001

Copper 0.02-0.30

Bor0,0005-0.00

IronOther

The proposed steel contains carbon, manganese, silicon, phosphorus, aluminum, calcium and iron, differs from the prototype in that it additionally contains copper and boron in the following ratio of components, wt.%: Carbon 0.02-0.07; manganese 0.15-0.30; silicon 0.01-0.10; phosphorus 0.04-0.10; aluminum 0.02-0.07; calcium 0.0005-0.001; copper 0.02-0.30 ;. boron 0.0005-0.005; iron is the rest.

The composition of the proposed steel includes silicon and phosphorus, which alloy the ferrite and grind the ferrite grain, causing hardening of the steel. This should help increase the endurance limit under cyclic loads. However, silicon and phosphorus when used separately or jointly intensively increase the tendency to aging, accelerate the precipitation of dispersed carbide inclusions within ferrite grains and at the boundaries, and phosphorus also forms segregation at the grain boundaries. This leads to an increase

yield strength, a decrease in the ultimate amplitude of the stress cycle and, as a result, can cause a decrease in fatigue strength. For this, in order to take advantage of the positive effect of hardening elements - silicon and phosphorus on hardening and to prevent their negative effect on aging and embrittlement along grain boundaries, it is necessary to bind carbon (as well as nitrogen) in the solid solution. This is achieved by adding boron to the sagal. It is known that boron intensively binds these impurities at high temperatures, reducing the possibility of aging, and

5 also prevents grain boundaries from phosphorus segregation and embrittlement. But, like a surface-active element, boron, in turn, can form a precipitate along the grain boundaries. Prevent this

0 allows the addition of copper. A combination of boron and copper is known to increase the ductility of structural steel.

In steel of the claimed composition, the additive

5 boron and copper are used together with silicon and phosphorus, and in this combination, a new effect is obtained - an increase in fatigue strength. A comparison of the known technical solutions and the claimed steel composition did not reveal the joint use of copper-boron-silicon-phosphorus elements in low-carbon structural steel for cold stamping. Therefore, the proposed solution has

5 is a sign of significant scientific novelty and allows us to ensure the most effective achievement of the goal — an increase in fatigue strength while ensuring resilience to cold folding of sheet steel.

In the inventive steel, the lower limits (wt.%) Of carbon (0.02), manganese (0.15), silicon (0.01) and phosphorus (0.04) are taken to provide the minimum required level of strength and the upper limits of these elements (0.07, 0.30, 0.10 and 0.10, respectively) to prevent deterioration of the formability.

Lower aluminum limit

0 (0.02) are subtracted to achieve sufficient deoxidation, and an upper limit (0.07) to prevent a decrease in ductility and fatigue resistance from the formation of large non-metallic inclusions

5 (aluminates, alumina).

The lower limit of calcium content (0.0005) is taken to increase the efficiency of the deoxidizing action of aluminum and to improve the shape (globularization) of inclusions of aluminum oxides and the upper limit

(0.001) - to prevent a decrease in phosphorus when reacted with calcium.

A lower limit of copper content (0.02) is chosen to prevent the enrichment of grain boundaries with boron, the formation of boundary inclusions of borides and to reduce fatigue strength. The upper limit of the copper content (0.30) is selected from the limitations of increasing the yield strength and deterioration of formability.

A lower limit of boron content (0.0005) is chosen to increase the endurance limit due to the suppression of aging associated with the addition of silicon and phosphorus and to prevent embrittlement of the grain boundaries by phosphorus. An upper limit of boron content (0.005) has been selected to prevent embrittlement of grain boundaries with boron and to reduce formability.

Example. Steel was smelted in an induction furnace with a capacity of 100 kg, cast into ingots, hot rolled into strips of 5.0 mm thick, cold rolled into strips of 2.0 mm thick, annealed according to the continuous mode - heating at a speed of 10 degrees C / s to 850 ° C, exposure 100 s, cooling to 600 ° C at a speed of 10 degrees C / s, then to 20 ° C in water, heating to 400 ° C at a speed of 10 degrees C / s, exposure 200 s , cooling in air, followed by training by 1%.

8 melts were smelted, of which 5 melts of the inventive steel of the proposed composition — No. 2, 3, 4, of the transverse composition — No. 1, 5 and 3 of the melting of known composition (Mg 6, 7, 8). The chemical composition of steels is given in table 1.

Tensile properties were tested according to GOST 11701-84. for extrusion according to GOST 10510-74, on us0

5

0

5

0

5

0

Claims (1)

taly according to GOST 25502-72. Fatigue tests were carried out on an EDC-20 din hydro-pulsation testing machine with a one-sided asymmetric cycle with an asymmetry coefficient of -0.2 with a 3F10 / cycle test base. The results of the mechanical properties tests are presented in Table 2. The data presented show that the embedded steel has a higher fatigue strength than steel is known. In addition, it differs from the prototype steel in higher distance strength characteristics, while maintaining stampability at the same level. This should ensure good processability in processing, increased reliability in operation, reduced metal consumption of parts when using replaceable steel instead of the well-known prototype steel. Manufacturing methods for installed steel are not fundamentally complicated in comparison with the known steel and do not worsen environmental conditions. SUMMARY OF THE INVENTION Steel containing carbon, manganese, silicon, phosphorus, aluminum, calcium and iron, characterized in that, in order to increase fatigue strength while maintaining stampability; it additionally contains copper and boron in the following ratio of components, wt.%: Carbon Manganese Silicon Phosphorus Aluminum Calcium Copper Boron Iron 0.02-0.07 0.15-0.30 0.01-0.10 0.04-0.10 0.02-0.07 0.0005-0.001 0.02-0.30 0.0005-0.005 Rest Table 1 Continuation of the table. 1 table 2