RU2016127C1 - Steel - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: in order to improve cooling resistance of high-strength steel in the state after hot rolling with accelerated cooling while maintaining the at least 600 N/mm², steel further comprises nickel and niobium, the ratio of the components being as follows (wt %): 0,06-0,15 carbon; 0.1-0.5 silicon; 1.5-2.2 manganese; 0.3-0.8 chromium; 0.02-0.10 vanadium; 0.01-0.05 titanium; 0.01-0.08 aluminium; 0.001-0.010 calcium; 0.006-0.014 nitrogen; 0.3-0.7 nickel; 0.01-0.05 niobium; and iron, the balance, the ratio of the components being as follows: 600≥ 830-270 carbon: 90 manganese : 37 nickel : more than 550 chromium; 0.13≥ carbon : 12/93 niobium : 12/51 vanadium 12/48 (titanium 3.4 nitrogen) > 0.03. EFFECT: improved properties of the steel. 2 tbl

Description

 The invention relates to metallurgy, and more particularly to structural steels used for high-strength cold-resistant welded building structures.

The closest to the proposed technical essence, the greatest number of similar features and the achieved effect is steel, containing, wt.%: Carbon 0.08-0.22 silicon 0.12-0.40 manganese 0.80-1.80 chromium 0 90-2.20 molybdenum 0.20-0.50 vanadium 0.05-0.15 nitrogen 0.005-0.015 aluminum 0.01-0.01 calcium 0.001-0.01 REM 0.005-0.05 titanium 0.01 -0.06 boron 0.001-0.005 iron rest
This steel has high strength characteristics (σ _0,2 = 600-1100 N / mm ²⁾ after the hot rolling and accelerated cooling to 500-550 ^{° C,} but has low viscosity and high threshold and cold brittleness can not be used for structures northern execution.

The aim of the invention is to increase the cold resistance of steel in the state after hot rolling with accelerated cooling while maintaining a yield strength of at least 600 N / mm ² .

The goal is achieved in that the steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, titanium, calcium, nitrogen, iron, additionally contains nickel and niobium in the following ratio, wt.%: Carbon 0.06-0.15 silicon 0.1-0.5 manganese 1.5-2.2 chromium 0.3-0.8 nickel 0.3-0.7 vanadium 0.02-0.10 niobium 0.01-0.05 titanium 0 01-0.05 aluminum 0.01-0.08 calcium 0.001-0.01 nitrogen 0.006-0.014 iron rest
In this case, the following relations should be fulfilled:
600 ≥ 830 - 270 C = 90Mn - 37Ni - 70 Cr≥ ≥ 550
0.13 ≥ C - 12/93 Nb - 12/51 V - 12/48 (Ti-3.4N) ≥ 0.03
The carbon content in the selected range is necessary to ensure the required set of properties of strength, ductility and cold resistance, taking into account the part bound to the carbides of niobium, vanadium and titanium. A carbon content of less than 0.06% does not provide a bainitic structure in steel and, accordingly, the required strength properties, and more than 0.15%, leads to a decrease in impact strength and cold resistance.

Limits chromium, manganese and nickel in the proposed steel are selected to provide at least 80% bainitic structure when cooled steel at a rate ^of 6-8 C / s. The content of these elements above the upper limit impairs the cold resistance of steel due to the formation of a martensitic structure, and when they are contained below the lower limit, the strength properties of steel are not ensured.

 The vanadium content in the specified range allows to increase the strength characteristics due to the formation of dispersed carbonitrides, strengthening the ferrite phase. An increase in the content of vanadium above the specified limit leads to coarsening of the carbonitride phase and worsening of the binding properties, and when the content of vanadium is less than 0.02%, the amount of carbonitrides sufficient to harden the ferrite phase is not formed, which does not allow the required yield strength to be reached.

 The limits of the content of titanium and nitrogen provide the formation of dispersed particles of titanium nitride, providing grinding of austenitic grain, which leads to an increase in the ductility and toughness of steel. The lower limits of the content of titanium and nitrogen are selected from the need to ensure the minimum required proportion of dispersed particles of titanium nitride. An increase in the nitrogen content of more than 0.014% and titanium of more than 0.05% promotes the intensive formation of large (1-3 μm) particles of titanium nitride, which reduces the toughness and worsens the cold resistance.

 The niobium content limits are selected from the conditions for controlling the processes of austenite recrystallization in the thermomechanical treatment cycle during rolling. The niobium content below 0.01% does not provide a sufficiently effective increase in the temperature of recrystallization, which leads to an increase in austenitic grain in the intervals between rolling stands and a decrease in the cold resistance of steel. A niobium content of more than 0.05% leads to a deterioration in the viscosity of steel due to dispersion hardening.

 The lower limits of the content of silicon and aluminum are chosen to ensure deoxidation of the metal, and the upper ones in order to prevent contamination of the steel with aluminates and deterioration of the rolled surface for aluminum and embrittlement of ferrite for silicon.

 Calcium provides the modification of sulfide inclusions, binding sulfur to strong compounds, which provides increased toughness and cold resistance. A calcium content of less than 0.001% does not provide a positive effect on these properties, and an increase in its content of more than 0.01% increases the contamination of steel with non-metallic inclusions and impairs ductility and toughness.

In addition to the above content limits of elements, to ensure the required complex of mechanical properties, it is necessary to fulfill two more relations: 600 ≥ 830 - 270С - 90Mn - 37Ni - 70 Сr ≥ 550 0.13 ≥ С - 12/93 Nb - 12 / 51V-12 / 48 (Ti - 3.4 N) ≥ 0.03
The first relation is a statistical model that describes the effect of the main alloying elements on the temperature of the onset of bainitic transformation, V _n ( ^o C). When B _n above 600 ^C in the steel structure appears more than 20% of ferrite, which lowers the strength characteristics of steel, and when B _n of less than 550 ^{° C} - the conditions of continuous cooling do not allow for complete decomposition of austenite in the bainite region which entails the formation of martensite component in the structure and leads to a decrease in toughness and cold resistance.

 The second ratio is the amount of carbon in bainite and ferrite, i.e. not bonded to carbides of vanadium, niobium and titanium. The carbon content in bainite in excess of 0.13% leads to embrittlement of the matrix and deterioration in cold resistance, and less than 0.003% to a decrease in strength characteristics.

Steel was smelted in an induction furnace and cast into ingots weighing 10 kg. Ingots after heating to 1150 ^{° C} for forged billets 60x60 mm, which was hot rolled in 9 passes on a sheet with a thickness of 10 mm by thermal deformation processing circuit:
heating temperature ^of 1150 C;
the temperature of the end of the deformation of 800 ^about ;
cooling to 580 - 550 ^о С at a speed of 6 ^о С / s;
further cooling in calm air.

 Transverse round five-fold specimens for static tensile testing in accordance with GOST 1497-84 and transverse impact specimens of type 11 for determining impact strength in accordance with GOST 9454-78 and cold brittleness threshold in accordance with GOST 4543-71 were cut from the obtained sheets.

 Table 1 shows the compositions of the proposed and known steel, and in table. 2 - their mechanical properties.

As can be seen from the obtained data, the proposed steel provides a higher impact strength (KCV ^-40 ≥ 60 J / cm ² ) and a low cold brittleness threshold (T ₅₀ <-70 ^о С) with sufficiently high strength properties (σ _0.2 > 600 N / mm ² ).

When calculating the expected economic effect from the use of the proposed steel, 09G2FB steel used for similar purposes was taken as the base object. The proposed steel has a yield strength of at least 600 N / mm ² ; steel - the base object - not less than 450 N / mm ² . This increase in yield strength saves more than 25% of the metal in the finished product (taking into account the expenditure coefficient).

Claims (1)

STEEL containing carbon, silicon, manganese, chromium, vanadium, aluminum, titanium, calcium, nitrogen and iron, characterized in that, in order to increase the cold resistance in the state after hot rolling with accelerated cooling while maintaining a yield strength of at least 600 N / mm ² , it additionally contains nickel and niobium in the following ratio of components, wt.%:
Carbon 0.06 - 0.15
Silicon 0.1 - 0.5
Manganese 1.5 - 2.2
Chrome 0.3 - 0.8
Vanadium 0.02 - 0.10
Titanium 0.01 - 0.05
Aluminum 0.01 - 0.08
Calcium 0.001 - 0.010
Nitrogen 0.006 - 0.014
Nickel 0.3 - 0.7
Niobium 0.01 - 0.05
Iron Else
the following ratios should be fulfilled: 600 ≥ 830 - 270 carbon - 90 manganese - 37 nickel - 70 chrome>550; 0.13 ≥ carbon - 12/93 niobium - 12/51 vanadium - 12/48 (titanium - 3.4 nitrogen) ≥ 0.03.

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