RU2450079C1 - Structural steel for volume-surface hardening - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains components at the following ratio, wt %: carbon 0.15 - 1.2, manganese 0.005 - 1.8, silicon 0.005 -1.8, chrome 0.005 - 1.8, nickel 0.005 - 1.8, molybdenum 0.0001 - 0.5, tungsten 0.0001 - 1.5, boron 0.00001 - 0.007, copper 0.001 - 0.3, aluminium 0.03 - 0.1, nitrogen 0.0001 - 0.1, titanium 0.001 - 0.4, vanadium 0.001 - 0.4, zirconium 0.001 - 0.4, niobium 0.001 - 0.1, tantalum 0.001 - 0.1, calcium 0.001 - 0.03, sulfur 0.0001 - 0.035, phosphorus 0.0001 - 0.035, iron and unavoidable admixtures - balance.

EFFECT: production of steels of lower and regulated hardenability with finer austenite grain, more stable level of hardenability at considerably smaller dispersion of ideal critical diametre of hardening and depth of a hardened layer, produced directly on parts exposed to strengthened volume-surface hardening, and also the possibility to process thinner and finer parts with volume-surface and through strengthening.

3 cl, 4 tbl, 3 ex

Description

The invention relates to the development of chemical compositions of structural steels, hardened by heat treatment - volume-surface hardening (SCR), carried out under the guidance of Doctor of Technical Sciences, professor, Honored inventor of the RSFSR Shepelyakovsky K.Z. [one]. The original name of the method is surface hardening with deep induction heating.

At the same time, it was shown that a high complex of mechanical properties can be achieved on carbon and low-alloy steels of low (PP) and regulated (RP) hardenability of the 1st generation [2], [3].

These are steels whose hardenability is consistent with the dimensions of the working loaded section of the parts; in this case, as a result of the SCR hardening, the surface layers of this section with an optimal value of 0.1-0.2 diameter (thickness) have a martensite structure with a hardness of HRC≈60, and in the core - HRC = 30-45.

The hardenability of steels is characterized by the value of the ideal critical diameter (Dcr.), Which determines the optimum depth of the hardened layer in relation to a specific part having the form of a cylinder, sphere or plate.

In principle, PP and RP steels have the same purpose and only conditionally differ only in the value of the ideal critical diameter (Dcr): for PP steels, as earlier, it is 8-16 mm, for modern RP steels - more than 16 mm.

The required interval Dkp. PP and RP steels for a particular type of part was achieved by the total restriction of one or a group of impurity elements to the upper limit, which reduced accuracy and increased this interval.

The closest analogue is the known structural steel PP (see patent RU 2158320), containing

carbon 0.40-0.85 manganese no more than 0.2 silicon no more than 0.2 chromium no more than 0.2 nickel no more than 0.1 copper no more than 0.1 aluminum 0.03-0.1 titanium no more than 0.1 vanadium no more than 0.4 sulfur no more than 0,035 phosphorus no more than 0,035 iron rest

A disadvantage of the known 2nd generation PP steels is that the desired low hardenability was achieved only by sharply limiting the content of all constant impurities - Mn, Si, Cr, Ni, Cu, which complicated the smelting technology, and reduced the accuracy of obtaining the specified interval Dcr . during the development of the chemical composition and, as a consequence, to a large spread in the depth of the hardened layer that goes beyond tolerances.

So, for example, steel 80PP with 0.8% C and a content of Mn, Si, Cr, Ni, Cu <0.1% each and 0.06-0.12% Ti (steel PNP) - (see patent RU 2158320 ), provides minimum hardenability - Dcr. <12 mm with austenite grain 10 points and finer (No. 11) - Dcr. <11 mm and <10 mm at No. 12, while similar steel 81pp of composition - 0.8 % C, 0.05% Mn, 0.12% Si, 0.11% Cr, 0.25% Ni, 0.3% Cu, 0.05% Al, 0.22% Ti (with a wider range of constants impurities Ni, Cu) has the same value Dcr.

The problem to which this invention is directed, is the development of steel PP (RP) of the 3rd generation.

The technical result is to obtain even finer grains of austenite No. 11-13 GOST5639 (ASTM), an even more stable predetermined hardenability level (Dкр.) With a much smaller spread thereof and which strictly corresponds to the depth of the hardened layer obtained directly on the parts subjected to thermal processing by the proposed method, the ability to process thinner, smaller and other parts with volume-surface and through hardening.

To achieve a technical result, structural steel for SCR with an ideal critical diameter of 6.0-200 mm or more is claimed, characterized in that it contains the following ratio of components, wt.%:

carbon 0.15-1.2 manganese 0.005-1.8 silicon 0.005-1.8 chromium 0.005-1.8 nickel 0.005-1.8 molybdenum 0.0001-0.5, tungsten 0.0001-1.5 boron 0.00001-0.007 copper 0.001-0.3 aluminum 0.03-0.1 nitrogen 0.0001-0.1 titanium 0.001-0.4 vanadium 0.001-0.4 zirconium 0.001-0.4 niobium 0.001-0.4 tantalum 0.001-0.1 calcium 0.001-0.03 sulfur 0.0001-0.035 phosphorus 0.0001-0.035

iron and inevitable impurities - the rest, with an ideal critical diameter defined by a mathematical expression:

·(1+4,1·Mn)·(1+0,65·Si)·(1+2,33·Cr)·(1+0,52·Ni)·(1+0,27·Cu)·(1+3,14·Mo)·(1+1,05·W)·[1+1,5(0,9-C)]·(1-0,45C')·(1-0,3Ti)·(1-0,35V)·(1-0,25Al)Dcr. = K

(1 + 4.1 · Mn) · (1 + 0.65 · Si) · (1 + 2.33 · Cr) · (1 + 0.52 · Ni) · (1 + 0.27 · Cu) · (1 + 3.14 · Mo) · (1 + 1.05 · W) · [1 + 1.5 (0.9-C)] · (1-0.45C ') · (1-0, 3Ti) · (1-0.35V) · (1-0.25Al)

where is Dkp. - ideal critical diameter, mm,

K is a coefficient the value of which depends on the actual austenite grain score on the ASTM scale, GOST5639 No. 8-13 and, accordingly, is equal to: 5.4 for the grain score No. 13; 5.8 - No. 12; 6.25 - No. 11; 6.75 -№10; 7.3 - No. 9; 7.9 - No. 8; 8.5 - No. 7; 9.2 -№6;

C, Mn, Si, Cr, Ni, Cu, Mo, W, - components, wt.%, Contained in the austenite solid solution at a final heating temperature preceding quenching cooling,

[1 + 1.5 (0.9-C)] - the factor, which is taken into account only in the case of the presence of boron in steel in an amount of 0.002-0.007 wt.%;

C ', Ti, V, Al - components, wt.%, Not contained in the austenite solid solution, but present in the form of structurally free secondary carbonitride phases at a final heating temperature preceding quenching cooling, while C' - wt.% Carbon in excess cementite of hypereutectoid steel.

Structural steel for a given chemical composition with the same grain score has an ideal critical diameter (Dcp.):

Dkp. from 6 to 15 mm with a spread of no more than 2 mm;

Dkp. from 16 to 50 mm with a spread of not more than 5 mm;

Dkp. from 51 to 100 mm with a spread of not more than 10 mm;

Dkp. over 100 mm with a spread of no more than 50 mm.

In structural steel, to prevent red brittleness, the total content of manganese, titanium and zirconium is more than six times the maximum sulfur content.

A feature of the proposed steel is that in order to achieve a given value of an ideal critical diameter, the use of formula (1) allows the limiting concentration in the steel composition of ones that more sharply increase the hardenability of these constant impurities to be limited to 0-0.05% or 0-0.1% and other less powerful ones - expand to the range of 0-0.3%, and in some cases 0-0.5% without compromising quality. This simplifies the selection of the initial charge during smelting and reduces the cost of steel, as the ultimate goal is to achieve a predetermined design Dkp. by combining the composition of residual impurity elements after steel deoxidation and the amount of alloying elements introduced in accordance with formula (1), which was based on the classical method of calculating hardenability according to Grossman [4], which turned out to be most acceptable for PP and RP steels.

Practice has confirmed its reliability for products of various shapes and sizes.

However, this calculation was clarified by the authors in connection with the prospect of its further development. So, in the formula, the ranges of the coefficient K, depending on the size of the austenite grain, were expanded to No. 11, 13. In addition, factors were added for the dependence of hardenability on tungsten and boron. The factors of the dependence of the ideal critical diameter on the modifier elements of the secondary carbonitride phases that are not included in the austenite solid solution before quenching cooling are introduced: titanium, vanadium aluminum, carbon in structurally free cementite of hypereutectoid steels, and sulfur and phosphorus are excluded from the formula, how their content in the above quantities practically do not affect the value of the ideal critical diameter (Dcp.).

In this case, first of all, from an economic point of view, it is advisable to administer dosed manganese as the most effective and relatively cheap component of one or together with inexpensive silicon in an amount of not more than 1.8% each instead of other more expensive ones that were previously unreasonably introduced into steel just to increase hardenability. The qualitative introduction of boron into steel in abnormally small amounts of 0.003-0.005% also causes an increase in hardenability, the more effective the less carbon is contained in steel (see formula 1). Using the formula allows for the development of the chemical composition of steel to ensure its optimal, and not excessive alloying.

Therefore, the introduction of other alloying elements - Cr, Ni in an amount of 0-0.5%, only with the aim of bringing hardenability (Dcp.) To a given value is less rational, since it will practically not change the mechanical properties compared with their smaller number or absence at the same value of Dcp and grain size of austenite.

Introduction to steel of modifying elements, wt.% - titanium not more than 0.4, vanadium not more than 0.4, zirconium not more than 0.4, niobium not more than 0.1, tantalum not more than 0.1, aluminum 0.03 -0.1, nitrogen not more than 0.1, calcium not more than 0.03, which are present in steel in the form of finely dispersed carbides, nitrides and other inclusions slightly dissolved in austenite helps to grind grain, increase the range of optimal heating temperatures for quenching, increase strength and plastic properties of steel PP and RP of the 3rd generation. The total content of manganese, titanium and zirconium should be more than six times the maximum sulfur content, since titanium and zirconium, like manganese, bind sulfur to refractory sulfides.

The introduction of other alloying elements, wt.% - chromium, nickel more than 0.6 (not more than 1.8 each), molybdenum and tungsten (not more than 0.5 Mo and not more than 1.5 W) individually or jointly selectively (comprehensively) also in accordance with the specified formula to achieve a predetermined design Dkp. and improvement of quality indicators - increasing mechanical properties, heat resistance, lowering the cold brittleness threshold, etc.

Below is the rationale for the chemical composition of the steels PP and RP used for the proposed method of hardening. The maximum content of manganese - 1.8 wt.% Due to the tendency of steel to overheat with a larger quantity; excess silicon content of more than 1.8-2.0 wt.% is fraught with the transfer of steel from the pearlite class to ferritic, immune to hardening by hardening; the chromium content for pearlite grade steels also does not exceed 1.8-2.0 wt.%, due to the increase in the fragility of the hardened layer with the structure of martensite; the maximum nickel content of 1.8-2.0 wt.% is selected based on its high cost in comparison with manganese, silicon, chromium and its relatively low coefficient of growth (0.52) hardenability, in addition, grinding of austenite grain to 10- 13 points in the submitted author's application of steel leads to a significant increase in ductility and viscosity, which excludes the role of nickel in the further increase in its content; copper is an ordinary practically non-removable impurity, its limit amount is usually limited by a content of 0.25%, which for a proposed steel in some cases can be increased without loss of quality to 0.3-0.5 wt.%, and taken into account when dosed steel alloying ; Molybdenum and tungsten are also expensive components; they are also metered into steel in combination with chromium and nickel, mainly to increase the heat resistance of steel; Exceeding the limited content - for molybdenum - 0.5 wt.%, for tungsten - 1.5 wt.% can, in the presence of even a small amount of manganese and chromium, transfer steel to the martensitic class, that is, to through hardening regardless of the size of the part.

Sulfur and phosphorus present in the steel in the quantities indicated above practically do not affect the value of the ideal critical diameter (Dcr.).

The content of carbide-forming elements - titanium, vanadium, zirconium niobium, tantalum within the specified limits, as well as aluminum and nitrogen forming aluminum nitride, contributes to the grinding of austenitic grain, inhibition of its growth during heating under quenching and to reduce hardenability. At the same time, the lower limit of the aluminum content range of 0.03 wt.% Guarantees a fairly complete deoxidation of steel, exceeding the upper limit of 0.1 wt.% Is impractical due to the onset of the solubility of aluminum in austenite, an uncontrolled increase in the hardenability of steel and its cost. Exceeding the maximum nitrogen content in steel - 0.1 wt.% Will cause irreversible coagulation (enlargement) of aluminum and titanium nitrides, which is an analogy for titanium, vanadium and zirconium carbides with the content of these elements in excess of 0.4 wt.%, And niobium and tantalum over 0.1%, which will also cause a rise in price of steel.

The minimum value of the ideal critical diameter of 6 mm was experimentally obtained by the authors on steel 40pp of the following chemical composition, wt.%: 0.41 C, 0.03 Mn, 0.04 Si, 0.06 Cr, 0.05 Ni, 0, 3 Cu, 0.05 Al, 0.22 Ti (the calculated value of Dcr. = 5.4 mm with an austenite grain of score No. 13).

A further decrease in the value of Dcr <6 mm leads to a sharp increase in the critical quenching rate (Dcr) to values of more than 1500 ° C / s, the use of extremely pure steels free from constant impurities, which is very difficult.

The most important distinguishing feature of the steels proposed in the method is the fact that when developing the chemical composition of the steel subjected to hardening, it is possible to theoretically predetermine the value of the ideal critical diameter (Dcp.) With a sufficient degree of accuracy.

The following are tables 1-4 of typical chemical compositions of PP and RP steels with an indication of their ideal critical diameters and examples of technological processes by the proposed method.

Example 1. Steel 81PP with a chemical composition, wt.%: 0.78 C; 0.04 Mn; 0.08 Si; 0.07 Cr; 0.15 Ni; 0.08 Cu; 0.04 Al; 0.15 Ti; 0.015 S; 0.018 P has a calculated Dcp. = 7.8 mm when processing for grain with a score of No. 12 mm.

A rolling bearing ring made of this steel with a wall thickness of 8 mm was heated through the inductor to 850 ° C for 20 s, then it was cooled with a sharp water shower and released in an oven at 150 ° C for 2 hours. As a result, the hardened layer on the outer and inner surfaces of the ring was 1.7 mm and 1.5 mm, i.e., 0.18-0.2 of the wall thickness, which corresponds to volume-surface hardening (SCR) and the real ideal critical diameter of 8 mm; the microstructure of the hardened layer is cryptocrystalline martensite (score No. 1), hardness 65-66HRC, in the core - troostite, troostosorbite, sorbitol with a hardness of 38-45HRC.

Example 2. Steel 61RP with a chemical composition, wt.%: 0.61 C; 0.5 Mn; 0.08 Si; 0.13 Cr; 0.25 Ni; 0.03 Cu; 0.04 Al; 0.05 Ti; 0.015 S; 0.018 P has a calculated Dcp. = 22.5 mm when processing for grain with a score of No. 11. A ⌀45 mm cylindrical king pin made of this steel was heated through the inductor through to 900 ° C for 50 s, then it was cooled by a sharp stream of water and released in an oven at 180 ° C for 2 hours. As a result, the hardened layer on the surface of the part was 5 mm, that is, 0.11, while the real ideal critical diameter is 21 mm; the microstructure of the hardened layer is fine-needle martensite (score No. 2), hardness 56HRC, in the core - troostite, troostosorbite, sorbitol with a hardness of 30-40HRC.

A grinding ball ⌀30 mm made of this steel was heated through the furnace through to 850 ° C, then it was cooled by a sharp stream of water with self-discharge of 180 ° C, 5 s and final cooling by a stream of water. As a result, the hardened layer on the surface of the part was 12 mm, that is, 0.4 of the diameter, which corresponds to hardening, which corresponds to the calculated values; the microstructure of the hardened layer is finely needle martensite (grade No. 2, grain grade No. 11), hardness 64HRC, troostomartensite in the core, 48-50HRC.

Example 3. Steel 50RP with a chemical composition, wt.%: 0.5 C; 0.1 Mn; 0.15 Si; l, 0 Cr; 0.8 Ni; 0.03 Cu; 0.05 Al; 0.35 V; 0.5 W; 0.015 S; 0.018 R has a calculated Dcp. = 47 mm when processing for grain with a score of No. 10. A parallelepiped-shaped part made of this steel with dimensions of 150 × 200 × 200 mm was heated through the furnace through to 850 ° C, then subjected to cooling by a sharp stream of water with a 2-time self-discharge of 180 ° C, 5 s, final cooling by a stream of water and released in an oven at 450 ° C for 3 hours. As a result, the hardened layer along the perimeter of the part’s surface was 9 mm, that is, 0.06 of the thickness (150 mm), which corresponds to the real Dcp. = 50 mm

Table 1 Steel grade, chemical composition, wt.% 41 pp 61 pp 81 pp 41 rp 110 pp carbon 0.36-0.43 0.56-0.65 0.77-0.85 0.36-0.43 1.05-1.15 manganese n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 1.8 n.b. 1.8 silicon n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 1.8 n.b. 1.8 chromium n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 1.8 n.b. 1.8 nickel n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 1.8 n.b. 1.8 copper n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 0.30 n.b. 0.30 molybdenum n.b. 0.01 n.b. 0.01 n.b. 0.01 n.b. 0.40 n.b. 0.40 tungsten n.b. 0.01 n.b. 0.01 n.b. 0.01 n.b. 1,5 n.b. 1,5 boron - - - n.b. 0.007 n.b. 0.007 aluminum 0.03-0.1 0.03-0.1 0.03-0.1 0.03-0.1 0.03-0.1 nitrogen titanium n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.04 vanadium n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.4 zirconium n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.4 n.b. 0.4 niobium n.b. 0.1 n.b. 0.1 n.b. 0.1 n.b. 0.1 n.b. 0.1 tantalum n.b. 0.1 n.b. 0.1 n.b. 0.1 n.b. 0.1 n.b. 0.1 calcium n.b. 0,03 n.b. 0,03 n.b. 0,03 n.b. 0,03 n.b. 0,03 sulfur n.b. 0,035 n.b. 0,035 n.b. 0,035 n.b. 0,035 n.b. 0,035 phosphorus n.b. 0,035 n.b. 0,035 n.b. 0,035 n.b. 0,035 n.b. 0,035 iron and unavoidable impurities rest Ideal critical diameter (Dcp.), Mm of the above steel grades 6-8 7-8 8-10 17-22 17-22 8-10 8-10 10-12 20-25 20-25 10-12 10-12 12-14 25-30 25-30 12-14 12-14 14-16 35-40 35-40 14-16 14-16 45-50 45-50 50-60 50-60 60-70 60-70 70-80 70-80 80-90 80-90 90-100 90-100 100-150 100-150 150-200 150-200

table 2 PP carbon steel FROM Mn Si Cr Ni Cu Al Ti V Mo AT S R Corn Dcr. 0.15 0.15 0.08 0.15 0.15 0.20 0.05 0.1 - - - 0,028 0,032 12 5.0 / 6.2 0.15 - “- - “- - “- - “- - “- - “- - “- - - - - “- - “- 10 5.8 / 6.5 0.15 - “- - “- - “- - “- - “- - “- - “- - - - - “- - “- 6 7.9 / 8.5 0.15 0.40 0.15 0.20 0.15 0.10 0.05 0.10 - - - 0,025 0,030 eleven 11.5 / 12 0.15 - “- - “- - “- - “- - “- - “- - “- - - - - “- - “- 6 15,6 / 16 0.8 0,03 0.05 0.02 0.1 0.15 0.05 0.22 - - 0.005 0,03 0,03 12 6.5 / 6.9 0.8 - “- - “- - “- - “- - “- - “- - “- - - - - “- - “- 10 7.5 / 8.1 0.8 - “- - “- - “- - “- - “- - “- - “- - - - - “- - “- 8 8.9 / 9.5 0.81 0.16 0.15 0.08 0,03 0.15 0.05 0.10 - - - 0,028 0,032 eleven 12.3 / 12 0.78 0.15 0.09 0.20 0.30 0.28 0.04 - 0.12 - - 0,025 0,021 12 15.1 / 15.8 1.20 0.08 0.05 0.10 0.08 0.12 0.06 0.15 - - - 0.018 0,023 12 7.6 / 7.7 1.20 0.08 0.05 0.10 0.08 0.12 0.06 0.15 - - - 0.018 0,023 8 10.3 / 11.0 1.20 0.38 0.05 0.14 0.16 0.06 0.05 - 0.15 - - 0,025 0,030 12 16.2 / 15.5

Table 3 RP steels are carbon and low alloyed FROM M Si Cr Ni Cu Al Ti V Mo AT S R Corn Dkp. 0.25 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 12 17.3 0.25 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 10 20,0 0.25 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 6 27,2 0.25 1.80 1.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 eleven 73.3 0.25 1.80 1.8 0.08 0.12 0.30 0.05 0.20 - - 0.004 0,025 0,027 eleven 145.1 0.80 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 12 31.15 0.80 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 eleven 33.64 0.80 0.50 0.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 8 42.46 0.8 0.30 0.20 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 12 17.1 0.8 1.8 1.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 12 122.6 1,2 1.8 1.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 12 100.5 1,2 1.8 1.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 10 117.0 1,2 1.8 1.8 0.08 0.12 0.30 0.05 0.20 - - - 0,025 0,027 8 136.4

Table 4 RP steel alloyed FROM Mn Si Cr Ni Cu Al Ti V Mo W S P Corn Dkp. 0.5 0.10 0.95 0.8 0.1 0.01 0.05 0.1 0.25 - - 0,022 0,027 12 25.5 0.5 0.10 0.95 0.8 0.1 0.01 0.05 0.1 0.25 - - 0,022 0,027 10 29.7 0.5 0.10 0.15 0.75 1.8 0.2 0.05 0.4 - - 0.7 0,025 0,030 10 44.1 0.5 0.12 0.15 1.8 1,0 0.18 0.05 0.1 0.38 0.5 - 0.017 0,020 10 95.6 0.8 0.11 0.12 0.80 0.3 0.25 0.05 0.1 0.35 - 0.8 0,032 0,033 12 46.5 0.8 0.15 0.08 1,2 0.08 0.15 0.05 0.2 - 0.4 1,2 0,025 0,029 eleven 174.8 0.8 1,1 1,0 1.15 0.15 0.12 0.06 0.15 - - - 0,027 0,031 12 194 1,2 0.11 0.12 0.8 0.3 0.25 0.05 0.1 0.35 - - 0,032 0,033 12 43.6 1,2 0.15 0.08 1,2 0.08 0.15 0.05 0.2 - 0.4 1,2 0,025 0,029 12 143.4 1,2 1,1 1,0 1.15 0.15 0.12 0.06 0.15 - - - 0,027 0,031 12 160.1

Literature.

1. Schepelyakovsky K.Z., Entin R.I. et al. Method for surface hardening of gears. "Bulletin of inventions." Copyright certificate No. 113770, 1958, No. 6.

2. Shepelyakovsky K.Z. Structural steel. "Bulletin of inventions." Copyright certificate No. 128482, 1960, No. 12.

3. Shklyarov I.N. Surface hardening during deep heating of the semi-axles of ZIL 130 trucks. ” "Metallurgy and heat treatment of metals", 1966, No. 7.

4. Goodremont E. Special steels., M. Metallurgizdat, Volume 1, 1959, Volume 2, 1960.

Claims (3)

1. Structural steel for volume-surface hardening, containing carbon, manganese, silicon, chromium, nickel, copper, aluminum, titanium, vanadium, niobium, tantalum, calcium, sulfur, phosphorus, iron and inevitable impurities, characterized in that it is additionally contains molybdenum, tungsten, boron, nitrogen and zirconium in the following ratio of components, wt.%:
carbon 0.15-1.2 manganese 0.005-1.8 silicon 0.005-1.8 chromium 0.005-1.8 nickel 0.005-1.8 molybdenum 0.0001-0.5 tungsten 0.0001-1.5 boron 0.00001-0.007 copper 0.001-0.3 aluminum 0.03-0.1 nitrogen 0.0001-0.1 titanium 0.001-0.4 vanadium 0.001-0.4 zirconium 0.001-0.4 niobium 0.001-0.1 tantalum 0.001-0.1 calcium 0.001-0.03 sulfur 0.0001-0.035 phosphorus 0.0001-0.035 iron and inevitable impurities rest 2. Steel according to claim 1, characterized in that its ideal critical hardening diameter for a given chemical composition has the following meanings:
Dkp. from 6 to 15 mm with a spread of no more than 2 mm;
Dkp. from 16 to 50 mm with a spread of not more than 5 mm;
Dkp. from 51 to 100 mm with a spread of not more than 10 mm;
Dcr. over 100 mm with a spread of no more than 50 mm. 3. Steel according to claim 1, characterized in that the total content of manganese, titanium and zirconium is more than six times the maximum sulfur content.