RU2510424C1 - High-strength medium-carbon fully-alloyed steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains: carbon, silicon, manganese, nickel, molybdenum, vanadium, copper, sulfur, phosphorus, iron and unavoidable components at the following ratio, in wt %: carbon - 0.18-0.24, silicon - 0.20-0.40, manganese - 1.0-1.5, nickel - 0.90-1.20, molybdenum - 0.50-0.70, vanadium - 0.10-0.20, copper - not over 0.25, sulfur - not over 0.010, phosphorus - not over 0.015, chromium - not over 3.00-3.20, iron and unavoidable components making the rest.

EFFECT: heat-treated steel feature higher ductility and mechanical strength at elongation of at least 7%.

3 tbl, 2 ex

Description

The invention relates to the field of metallurgy, namely to structural steels hardened in air, the use of which is possible for the manufacture of axisymmetric body parts.

In this case, minimizing changes in the size and shape of axisymmetric parts during heat treatment is necessary. For this purpose, heat treatment with quenching in a stressed state is used and the well-known high-strength steel grade 28X3SNM1FA TUADI 543-2002, containing, wt.%: Carbon 0.26-0.31; manganese 0.50-0.80; silicon 0.90-1.20; sulfur not more than 0.010; phosphorus no more than 0.015; chrome 2.8-3.2; nickel 0.9-1.2; molybdenum 0.75-0.85; vanadium 0.05-0.15; copper no more than 0.15.

The specified composition is not optimal, since after quenching and tempering, the relative elongation of this steel does not exceed 12% even after tempering at 600 ° C. Therefore, it cannot be used for the manufacture of housings according to the “Thermomechanical hardening” scheme, both from the point of view of insufficient elasticity after quenching and tempering, and from the point of view of accumulation of large internal stresses during cold deformation, which can lead to destruction of the material during deformation. Hence, the use of this steel is possible only by finishing hardening and tempering, which leads to a loss of geometric dimensions, despite hardening in a worn state.

Known high-strength, welded steel with high hardenability according to the patent of the Russian Federation No. 2314361, C22C 38/58, publ. January 10, 2008, adopted by the authors as a prototype containing carbon, silicon, chromium, manganese, nickel, molybdenum, vanadium, the rest is iron.

The specified steel in the selected ranges of variation of the components according to the given data at the minimum contents after quenching from rolling heating, as well as after quenching from temperatures of 950-1050 ° C, has the following minimum properties: σ _in - 130.6 kgf / mm ² , σ ₀₂ - 107.1 kgf / mm ² , δ ₅ -16%, ψ - 60%, KCU ₊₂₀ - 11.3 J / cm ² .

However, to ensure properties in the hardened state after cold deformation, the strength after thermal hardening should be at least 135 kgf / mm ² , which is provided in the technical solution according to patent No. 3214361, in which the chemical composition is presented with a minimum content of ingredients (alloying components). So, when the content of the components of the steel according to the prototype, the properties have values that do not allow obtaining after deformation of the mechanical properties not lower than 155 kgf / mm ² .

The objective of the invention is the development of high-strength medium-carbon complex alloyed steel with high ductility after quenching and tempering, allowing it to be deformed by rotational drawing in the cold state with degrees of deformation of 50-70% and providing mechanical properties in the hardened state above 155 kgf / mm ² with elongation not less than 7%.

The problem is achieved in that high-strength medium-carbon complex alloyed steel containing carbon, silicon, chromium, manganese, nickel, molybdenum, vanadium, the rest is iron, the peculiarity is that this steel contains the following components, wt.%: Carbon 0.18 -0.24; manganese 1.0-1.5; silicon 0.20-0.40; sulfur not more than 0.010; phosphorus no more than 0.015; chrome from more than 3.00 to 3.20; nickel 0.90-1.20; molybdenum 0.50-0.70; vanadium 0.10-0.20; copper is not more than 0.25, while the remainder is iron and inevitable impurities.

Compositions, heat treatment modes, properties of steel after heat treatment and various degrees of deformation by a rotary hood are presented in Tables 1, 2, 3.

Table 1 The chemical composition of the studied swimming trunks and prototype No. of swimming trunks Content Elements C Si Mn S P Cr Ni Mo V Nb Ca / Ce Cu one 0.24 0.37 1.3 0,022 0.015 3,1 0.95 0.51 0.20 0.20 2 prom melting 0.21 0.33 1.19 0.007 0.004 3.2 1.16 0.59 0.15 0.18 3 proto
type of 0.10 0.12 2.02 2.0 1.01 0.41 0.12 0.05 0.05

table 2 Mechanical properties of steels and prototype after quenching and various tempering temperatures No. of swimming trunks Temp. ° C σ ₀₂ σ _in δ ₅ ψ KCU ₊₂₀ KCU _-50 kgf / mm ² % kgf-m / cm ² one 200 126.0 152.0 14.8 57.0 9.1 7.9 500 111.0 140.0 17.1 59.0 11.5 9.6 2 200 137.1 152.0 13,2 53.0 9.0 7.3 500 118.0 130.0 14.1 56.0 12.1 8.3 3 industry. melting 450 110.0 136.0 17.7 9.5 6.47 650 78.5 89.5 21.0 22.0 15,5 4 prototype no vacation 107.0 130.6 16,0 60.0 11.3

Table 3 Mechanical properties of steel depending on the degree of deformation by a rotary hood Degree of deformation σ _in σ ₀₂ δ ₅ KCU ₊₂₀ KCU _-50 kgf / mm ² % kgf · m / mm ² t _ot 450 def. absent 80 135-137 190-195 118-121 178-181 16-19 8.0-9.6 7.9-10.0 5.0-8.45 t _temp 650 ° C def. absent 80 89.0-89.5 106.0-110.0 66.0-78.5 100.0-107.0 19.0-21.0 12.5-16.0 20.0-22.0 15.0-15.5

In the claimed range of composition values and heat treatment parameters, a tensile strength of more than 135 kgf / mm ^{2 is} provided when tempering below 500 ° C, while high ductility δ ₅ = 13.1-18.5%, ψ = 56-65% for the subsequent cold deformations. With the initial σ _in ≥135 kgf / mm ² after deformation by a rotary hood, we have σ _in ≥169 kgf / mm ² . From a comparison with the prototype, it can be seen that the composition of the declared steel specified within narrow limits allows to obtain higher characteristics of the properties both in the heat-treated and in the deformed state and, therefore, meets the criterion of "novelty."

Example 1. Steel of the proposed composition of the control heats No. 1, 2 was smelted in an induction furnace with a magnesite crucible. As the charge used charge stock, synthetic cast iron, metal chromium, nickel, aluminum, manganese, as well as ferromolybdenum, ferrosilicon, ferrovanadium.

Steel was smelted under a slag mixture consisting of calcined lime and fluorspar.

Before the introduction of cast iron and ferroalloys, metal was deoxidized by aluminum.

Steel was poured into ingots with warming profits by a sand-graphite mixture. The ingots were forged on a press with a compression force of 2000 tf to a cross section of 50 × 50 mm. The forging temperature range was 1080–1150 ° C.

Bars of ⌀16 × 500 mm, ⌀20 × 500 mm, and ⌀14 × 500 mm sizes were forged from ingots. After heat treatment, samples were made from rods to determine the mechanical characteristics of steel:

type 2-11 (for determining yield strength, tensile strength, elongation and contraction);

type 6-1 (for determining the value of impact strength).

Data on the chemical composition of the studied swimming trunks 1, and their mechanical properties are presented in tables 1 and 2.

Example 2. Steel was smelted in an electric arc furnace.

Steel was cast into a blacksmith mold to produce an ingot. The casting took place with the evacuation of the metal.

The forging ingot was heated in a furnace with a temperature of 1200 ... 1230 ° C and forged on a hydraulic press.

Forging of the ingot was carried out in 4 stages with heating the forgings in the furnace after each stage.

Forged 2 blanks with a diameter of 355 mm and a length of 4920 mm were sent for annealing at a temperature of 660-680 ° C.

After annealing, the forgings were machined on the outer surface to a diameter of 330 mm.

A pilot batch of pipes with an outer diameter of 138 mm and a wall thickness of 14 mm was made of hot-rolled steel of 20Kh3GNMFA grade.

As a tube billet, machined forgings with a diameter of 324 mm and a length of 880 mm were used.

The technological process for the production of pipes on the extrusion line includes two stages:

- production of tube blanks on a vertical press;

- manufacture of pipe sleeves on a horizontal press. The manufacturing process of liners includes the following

stages:

- drilling in the billet of the axial channel at a diameter of 30 mm;

- heating of the pipe billet to a temperature of 1080-1140 ° C;

- expansion in the press.

The manufacturing process of a pipe from a sleeve includes the following steps:

- induction heating of the sleeve;

- applying glass grease;

- pressing the liner on the press with a needle, resulting in a pipe with an outer diameter;

- pipe cooling in air;

- removal of glass grease and scale;

- annealing;

- editing pipes;

- ultrasonic and visual inspection of pipes.

Hot-deformed pipes 0 138 × 14 mm made of 20Kh3GNMFA steel were used for rotational drawing.

From annealed hot-deformed pipes, blanks (shells) were cut.

Billets (shells) for cold deformation were subjected to hardening heat treatment.

Rotary extraction was carried out on a machine model CXP2.

For the first transition, the degree of deformation was ε = 40%, for the second ε = 60%, for the third ε = 80%.

After rotational drawing with various degrees of deformation, the workpieces were subjected to low-temperature annealing.

To determine the mechanical characteristics of pipe billets and cold rolled semi-finished products at various degrees of deformation, longitudinal and radial five-fold samples were made in accordance with GOST 10006-80.

Tensile tests were performed according to GOST 1497-84. The main characteristics of mechanical properties of steel determined by tensile strength σ _B, proof stress σ _0.2 δ and elongation ₅ in the longitudinal and radial directions.

The results of the mechanical properties of 20Kh3GNMFA steel, determined on pipe billets after cold rotation drawing, depending on the tempering temperature and the degree of deformation, are presented in table 3.

From the analysis of the results presented in table 3, it follows:

- at a tempering temperature in the range of 450-550 ° C, the initial billet provides strength σ _in the range of 135-137 kgf / mm ² ;

- at a tempering temperature of 450 ° C, cold plastic deformation of steel with a degree of 40-60% provides a set of mechanical properties:

- conditional yield strength σ _pc = 170-175 kgf / mm ² ,

- temporary resistance σ _in = 177-183 kgf / mm ² ,

- elongation δ ₅ = 7-9%,

- impact strength KCU = 3.3-4.9 kgf · m / cm ² .

Thus, the obtained experimental data confirm the possibility of using the claimed steel for the manufacture of axisymmetric body parts.

Claims (1)

High-strength medium-carbon complex alloyed steel containing carbon, silicon, chromium, manganese, nickel, molybdenum, vanadium, copper, sulfur, phosphorus, iron and inevitable impurities, characterized in that it contains components in the following ratio, wt.%:
carbon 0.18 - 0.24 manganese 1.0 - 1.5 silicon 0.20 - 0.40 sulfur no more than 0,010 phosphorus no more than 0.015 chromium from more than 3.00 to 3.20 nickel 0.90 - 1.20 molybdenum 0.50 - 0.70 vanadium 0.10 - 0.20 copper no more than 0.25 iron and inevitable impurities rest