SU1749307A1 - Steel - Google Patents

Abstract

The invention relates to the field of metallurgy, in particular to high-strength welded steel intended for welded structures in construction and engineering. In order to increase weldability, ability to change in cold condition, cold resistance while maintaining strength, the steel additionally contains titanium and calcium in the following ratio of components, wt.%: Carbon 0.09-0.15, silicon 0.15-0.6. manganese 1.0-1.9, chromium 0.5-1.0, nickel 0.5-1.4, molybdenum 0.05-0.50, vanadium 0.02-0.10, niobium 0.01- 0.06, nitrogen 0.008-0.020, aluminum 0.01-0.08, copper 0.05-0.40. titanium 0.005-0.08, calcium 0.001-0.01, iron the rest. When the following ratios are fulfilled: carbon + manganese / 6 + silicon / 24 + chromium / 5 + nickel / 40 copper / 13 + vanadium / 14 0.70, 530- 415 carbon + 90 carbon - 35 manganese - 20 nickel - 10 molybdenum 350; niobium + vanadium + (titanium - 3.4 nitrogen) 0.05–0.20. 2 tab. ate with

Description

The invention relates to metallurgy, in particular to iron-based alloys, more precisely to structural welded steels used for welded structures in construction and engineering. The closest to the proposed technical essence is steel, containing, in wt.%:

Carbon0.10-0.17

Silicon0.15-0.50

Manganese 1.0-1.6

Chrome 1.0-1.5

Molybdenum 0.2-0.5

Nickel1,6-2,3

Vanadium 0.05-0.26

Nitrogen 0,010-0,030

Aluminum0.03-0.10

Niobium 0.03-0.20

Copper0,3-1,0

Cerium0,005-0,03

IronErest

However, it has unsatisfactory weldability, ductility and cold resistance and cannot be used for critical welded structures operating at negative temperatures.

The aim of the invention is to improve the weldability and ability to form in a cold state, cold resistance while maintaining strength. The goal is achieved by the fact that steel containing carbon, silicon, manganese, chromium, molybdenum, nickel, vanadium,

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nitrogen, aluminum, niobium, copper and iron, additionally contains titanium and calcium at

the following ratio of components, wt.%:

Carbon0.09-0.15

Silicon0.15-0.6

Manganese1.0-1.9

Chrome 0.5-1.0

Nickel 0.5-1.4

Molybdenum0.05-0.50

Vanadium 0.02-0.10

Niobium 0,01-0,06

Titanium0.005-0.08

Aluminum 0.01-0.08

Nitrogen0,008-0,020

Copper0.05g-0.40

Calcium0.001-0.01

Iron Else The following relationships must be met:

1) С + Мп (6 + Si) 24 + Сг (5 + NI) 40 +

+ Cu (13 + V) 14 0.70;

2} 530-415C + 90С2 - 35 Mp-30Cr-20Ni-10Mo 350;

3) Mb + V + (Ti - 3.4N) 0.05 - 0.20.

The carbon content in the selected limits is necessary to provide the desired set of properties (strength, cold resistance). When it is contained in martensite (bainite) less than 0.09% (taking into account part of the carbon bound in niobium, vanadium and titanium carbides), the Strength level is not provided (from 700-800 N / mm2), and with a content of more than 0.15 % decreases ductility and cold resistance of steel.

The limits of the content of the elements in the solid solution: manganese, chromium, molybdenum, and nickel were chosen to provide hardenable steel and form the structure of low carbon martensite (possibly with a share of bainite). In addition, molybdenum is introduced to reduce the tendency of steel to temper embrittlement, and nickel to increase the cold resistance of steel. Increasing the content of these elements above the proposed upper limit impairs the ductility and weldability of steel.

A manganese content of less than 1%, chromium and nickel less than 0.5% of each reduces the hardenability of the steel, leads to the formation of ferrite in the structure, which adversely affects the strength properties and

cold resistance. A decrease in the molybdenum content below the lower limit of the carbon bar is a tendency of the steel to temper embrittlement and leads to embrittlement during tempering.

5 Silicon lower limit

represents the necessary minimum for steel deoxidation, the upper limit of the silicon content (0.6%) provides solid solution hardening without deterioration

0 cold resistance.

Aluminum provides deoxidation of steel, prevents waste of injected titanium and calcium. The minimum required amount of aluminum for deoxidation is 5 0.01%, an increase of more than 0.08% leads to deterioration of processability during casting, as well as to the formation of surface defects.

The minimum amount of injected copper provides an increase in the corrosion resistance of steel, and the maximum is due to the prevention of the tendency to form surface cracks.

Calcium provides a modification of sulphide inclusions, bonding sulfur to strong compounds, which provides increased impact strength and ability to deform in a cold state. In addition, formed by calcium separately,

0 and complex with titanium, sulfur and carbon (carbosulfides) hardly soluble inclusions contribute to the refinement of austenite grain, inhibit its growth during heating during rolling and in pauses between passes,

5 which also improves the impact viscosity and cold resistance of steel.

A calcium content of less than 0.001% does not provide a positive effect on the indicated properties, and an increase in its content of more than 0.01% increases the contamination of the steel with non-metallic inclusions and impairs ductility and toughness.

Nitrogen in the proposed steel is included in the composition of dispersed particles of titanium nitride and vanadium carbonitride. The lower limit of the nitrogen content provides the minimum required volume fraction of dispersed particles of titanium nitride. An increase in nitrogen content of more than 0.020%, even in the liquid state, contributes to the intensive formation of large (more than 1 micron) primary titanium nitride particles, which form accumulations, which leads to a decrease in toughness and cold resistance.

Titanium, depending on its ratio with nitrogen, plays a dual role in the proposed steel: when its content does not exceed the stoichiometry of its ratio, with nitrogen (ТК3.4Т), titanium forms

dispersed particles (TIN), which ensure the grinding of austenite grain and improve the viscosity of steel by inhibiting the growth of austenitic grain when heated for rolling and between passes in a thermal deformation processing cycle. The minimum content of titanium is due to obtaining a sufficient amount (not less than 0.004% by volume) of dispersed particles (0.02 μm) of titanium nitride.

Vanadium, niobium and titanium (with its content exceeding the stoichiometric ratio with an ezot: T 3.4M) are carbide-forming elements. They are introduced for the purpose of disperse hardening of the matrix (low carbon martensite or bainite). In addition, the doping of the above elements (primarily niobium and titanium) provides control over the process of recrystallization of austenite in the cycle of thermomechanical processing.

The minimum content of vanadium and niobium (0.02 and 0.01%, respectively) and the total content of V + IMb + (Ti-3,4N) were selected taking into account their solubility and the required carbon content in the matrix to provide the necessary proportion of reinforcing particles. The content of vanadium is more than 0.10%, niobium is more than 0.06%, the guitar is more than 0.08%, or the total content of carbide-forming materials is more than 0.2%, which causes intense dispersion strengthening, which deteriorates cold resistance, ductility and weldability.

In addition to the above limits for the content of elements and the ratios between them, in order to provide the required set of mechanical and technological characteristics, two more ratios are necessary:

r, Mn, Si, Cr, + 24 + -5 +

+ W + 7 K4 ° 530-415С + 90С2-35Мп- -30Cr-20Ni-10Mo 350.

Performing the first ratio provides satisfactory weldability and lack of tendency to cold cracks during welding.

When this ratio is exceeded (0.70), fusion welding in the near-weld zone produces martensite with high hardness and cracks in the welded joint.

The second relationship is a statistical model describing the effect of the main alloying elements on the martensitic MH point (° C). At a temperature of Mn below 350 ° C, during the martensitic transformation at thermomechanical treatment, no self / scamartensite occurs, which negatively reflects at the level of viscosity and cold resistance of the waist.

0 and can lead to the formation of three-fold. The limiting temperature ensuring the absence of cracks is 350 ° C.

Example. Steel is melted in an induction furnace and cast into ingots of mass

5 25 kg. After heating up to 1200 ° C, ingots are forged on workpieces with a section of 60x60 mm, which are subjected to hot deformation for nine passes per 10 mm thick sheet according to the scheme of thermomechanical processing: heating temperature is 1200 ° C. temperature of the end of deformation is 850 ° С, post-deformation cooling in water, tempering 650 ° С (2 h).

From the obtained sheets cut transverse round five-fold samples for

5 static tensile tests according to GOST 1497-84 and transverse impact type II samples for determining the impact strength according to GOST 9454-78 and the cold brittleness threshold. Also, imitation is carried out

0 thermal cycle welding according to GOST 23870-79 with the definition of impact strength in the simulated heat affected zone

Table 1 shows the composition of the proposed and known steels, Table 2 - their

5 mechanical properties.

As can be seen from the data obtained (see Table 2), the proposed steel provides a higher set of characteristics of cold resistance, weldability and ability

0 to be cold-formed while maintaining strength, which indicates the suitability of the proposed steel for the manufacture of welded structures of responsible purpose, including in the northern

5 performance.

With the same level of strength properties, the proposed steel contains on average 0.6% chromium and 0.95% nickel less.

Claims (1)

0 claims Steel containing carbon, silicon,  manganese, chromium, nickel, molybdenum, vanadium, niobium, aluminum, nitrogen, iron and iron, in contrast to the fact that, in order to improve5 the weldability and ability to change in cold condition, cold resistance while maintaining strength, it additionally contains titanium and calcium in the following ratio of components, wt.% : carbon-0.09-0.15; silicon - 0.15-0.6. manganese - 10-1.9, chromium - 0.5-1.0. Nickel - 0.5-1.4 Molybdenum - 0.05-0.50, Vanadium - 002-0.10 - Niobium - 0.01-0.06, Aluminum - 0.01-0.08: Nitrogen - 0.008-0.020 Copper - 0.05-0.40; titanium - 0.005-0.08 calcium - 0.001-0.01: iron - the rest when the following relationships are fulfilled: carbon + manganese / 6 + silicon / 24- hrem / 5 + nickel / 40 + copper / 13 + vanadium / 14 0.7, 530- 415 carbon + 90 carbon-squared-35margan-Zohrom-20 nickel -1 Omolybd-350; vanadium + niobium + (titanium-3,4 nitrogen) 0.05-0.20 Table 1 COOTI  1) Nb V «(Ti - 3.4N) - 0.05 - 0.20; 2) 530 - 415С 90Сг-Э5Мч - ЗОСг - Ж - ". Mechanical properties of the proposed and famous steels table 2