CZ303595A3 - Steel for railway wheels and wheel flanges - Google Patents

Abstract

The steel contains up to 0.8% C, at least 0.2% Si, at least 0.5% Mn, less than 0.003 Al and max. 0.0015% oxygen produced by degassing. The steel compsn. can be: (1) 0.4-0.7 C, 0.2-0.5% Si, 0.7-1.2% Mn, max. 0.025% P, 0.30% Cr, 0.30% Cu, 0.08% Mo, 0.30% Ni, 0.05% V, and balance Fe plus melting impurities; (2) 0.4-0.7% C, 0.2-0.5% Si, 0.6-0.9% Mn, max. 0.025% P, and balance iron plus melting impurities; and (3) 0.2-0.8% C, 0.2-1.2% Si, 0.6-1.3% Mn, max. 0.025% P, 0.7-1.2% Cr, max. 0.4% Mo, max. 0.25% V, max. 0.003% B, and balance Fe plus melting impurities. The steel may also contain 0.02-0.05% Nb and/or 0.05-0.1% V.

Description

Steel for railway wheels and wheel flanges

2512 3 5 _ £ i i.

The invention relates to steel which is suitable as a mass for railway wheels, railway wheel disks, railway wheel flanges and other objects which are subjected to mechanical and dynamic rolling stress and which are hereinafter referred to as wheel flanges.

Current_technologies

Wheel flange steels are subject to high static and dynamic stresses on their running and friction surfaces due to the weight of the car as well as the braking and accelerating forces. In addition, especially in the case of railway wheels braked by brake blocks, a substantial thermal load can occur, which, depending on the frictional heat generated during braking and starting, may cause a change in the structure with the mobile surface hardening due to martensite formation in the heated mobile surface area. Due to the high rolling impact stress, railway wheels often lead to cracking and peeling at the interface.

__ ___ This danger is particularly high due to the inhomogeneity of the mass, in particular uoxidic inclusions. Such inclusions give rise to a considerable deleterious effect which promotes crack formation and crack expansion. Such inclusions are generally 'alumina residues from aluminum deoxidation that serve to reduce | It is intended to prevent the formation of carbon monoxide CO bubbles when the steel solidifies. Such subsurface bubbles lead to surface defects during further processing, which then appear as flaws in the running surface. Another advantage of aluminum deoxidation lies in the stable solidification of the released nitrogen nitrogen to the aluminum nitride in the liquid steel and the resulting resistance to aging, as well as the suppression of grain coarsening during possible heat treatment or also under local frictional heat stress during braking and starting.

Conventional wheel flange steels therefore contain, in addition to about 0.2 to 0.7% carbon, normally 0.009 to 0.063% aluminum.

These cracks, which are often the cause of fatigue damage and fatigue fractures, arise further as a result of thermal shock stresses due to slip during acceleration and braking, or also local exceedance of the permanent oscillation resistance in the area of high impact and sliding stresses on and below the running surface .

To improve mechanical properties such as high wear resistance, fatigue crack resistance, brittle fracture safety, durable vibration resistance and resistance to thermal shock, wheel flange steels often have alloy elements such as 0.3% carbon, up to 1, 0% chromium, up to 0.20% molybdenum and up to 0.20% vanadium. In this way, the individual properties of the material can be improved, but it is not possible to prevent those damage to the running surface which are caused by alumina inclusions from aluminum deoxidation.

% Of the invention to

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SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a steel having a higher degree of purity than conventional wheel flange steels and therefore less sensitive to fatigue cracking.

The solution to this problem is that the usual aluminum deoxidation does not take place and the steel, preferably the continuously cast steel, is instead deoxidized in vacuum by forming carbon monoxide CO in order to reduce the oxygen content to a maximum of 0.0015% preferably The aluminum content should not exceed 0.003%, preferably 0.002%, and the steel should have a value of not more than 1, preferably 0, perpendicular to the running surface according to DIN 50 602, in a longitudinal section.

The invention is described in detail

Alumina-free, vacuum-deoxidized steel has 0.4 to 0.7% carbon, 0.20 to 0.50% silicon, 0.60 to 1.30% manganese to 0.30% chromium, at most 0.025 # phosphorus, and maximum®

0.025% sulfur. 3 preferably does not have titanium, since titanium produces undesirable sharp-edged carbonitrides which can lead to fatigue damage.

However, the alumina-free flange steel according to the invention may also contain 0.60 to 0.80% of carbon, 0.50 to 1.20% of silicon, 0.80 to 1.30% of manganese, not more than 0.025% of phosphorus and 0%. 40 to 1.50% chromium or even to 0.08% molybdenum, and / orin di _and; - - - - _: .....

The composition of the steel can be altered by means of said alloys to provide particularly favorable properties, such as elevated temperature Acl or martensite, increased crack resistance and reduced rate of crack continuation, or certain composition states after normal alignment or improvement. This is without prejudice to alumina-free deoxidation.

All these steels are suitable for rolling rail components such as wheels, wheel flanges and wheel discs in a vacuum-treated state. The corresponding steel composition must be matched to the corresponding target size, as determined, for example, by UIC 810-1 and 312-3 for wheel flanges and solid wheels, see Table 24.3.

The wheel flange steel according to the invention has a wear resistance as usual steel and, due to its purity, has a high fatigue crack resistance. This is shown by the bending fatigue limit tests carried out using three steels in accordance with Table 1, residual iron, the position and properties of which are shown in the drawing.

and Fig. 1 shows the test position in longitudinal section of the wheel; Fig. 2 shows a cross-section of the wheel in a plane along the line I in Fig. 1 and Fig. 3 the test shape.

Table I

- - - State Tensile strength ketuna- you in alternating bending stress [N / mm · ² ] C (¾) Si (%) Mn (¾) p (%) WITH (%) Al (%) - and. 0.46 0.35 0.92 0,032 0.019 0,025 N ¹ ' 695 230 O 2. 0.53 .0,30 0.70 0,022 0.017 0.020 M 820 275 • i U 3. . 0.52 0.36 0.74 0.020 0,021 0,021 S ² > 920 340 ’Λ 4, 0, 47 0.32 0.91 0.020 0, 020 0,002 N 697 270 (+ 17%) 0 3. 0.52 0.33 0.72 0.018 0.019 0.001 N . 815 337 (+ 22%) 0 6. 0.54 0.36 0.72 0,022 0.018 0.001 WITH 918 390 (+15%). 1

1) Normally annealed

2) wheel rim

The data of the individual experiments including the oxidation degree of purity K2 of the longitudinal test specimens are compiled more. They clearly show an increase in the bending fatigue strength of alternating bending stresses of steels 4 and 5 according to the invention by approximately 15 to 22% _by comparison with conventional steels 1 to 3.

In order to obtain such an increase in fatigue fatigue under alternating bending stress in conventional steels, their tensile strength would have to be increased by approximately 18% by technical measures of the alloys. However, this would be associated with a substantial loss in toughness and resistance to thermal shocks, since an increase in tensile strength can only be attributed to toughness and resistance to thermal shocks.

In the steels according to the invention, the greater resistance to fatigue limit in alternating bending stresses is an indicator for

It is resistant to fatigue cracks resulting largely from the lack of alumina inclusions and the associated notch effects, as well as the surrounding tensile stress field resulting from cooling and shaping and heat treatment temperatures.

Silicates and sulphides are less harmful due to their lower notch effect. Due to their greater flexibility and due to their greater thermal expansion coefficients, they are also not surrounded by the stress fields.

When the steel according to the invention is used as a wheel flange material, stress peaks which are otherwise connected to alumina inclusions and which are the starting points for fatigue cracks on and under the running surface are also based on the tensile stress resulting from rolling stress.

Since the desoxidation of aluminum is avoided according to the invention, steels with 0.02 to 0.05% niobium and / or 0.02 to 0.1% vanadium can be recommended in order to improve the aging resistance and to prevent grain size increase due to thermal conditions.

Claims (6)

PATENT CLAIMS « - · = LV * steel railway wheels and wheel flanges and for the dynamic rollably loaded objects, characterized in that t has up to 0.8% carbon, less than 0,2% of silicon, at least 0.5% manganese ^Rt less % of the aluminum content, and the oxygen content produced by vacuum degassing of not more than 0.0015%. Steel according to claim 1, characterized in that it has 0.40 to 0.70% carbon, 0.20 to 0.50% silicon, 0.70 to 1.20% manganese and at most 0.025 fc of phosphorus. 30 ib of chromium, 0.30 ib of copper, 0.03 ib of molybdenum, 0.30% nickel, 0.05% of vanadium, the remainder of the iron, including melt contaminants. Steel according to claim 1, characterized in that it has 0.40 to 0.70% carbon, 0.20 to 0.50 Tb of silicon, 0.60 to 0.90 ib of manganese and at most 0.025 phosphorus, the rest of the iron including by melting conditional impurities. Steel according to claim 1, characterized in that it has 0.20 to 0.30% carbon, 0.20 to 1.20 Tb of silicon, 0.60 to 1.30 Tb of manganese, at most 0.025% phosphorus, and 0, 70 to 1.20% chromium, up to 0.40% molybdenum, up to 0.25% vanadium, up to 0.003% boron, the remainder of the iron including melting contaminants Steel according to one of Claims 1 to 4, characterized by _{il = J =} ^^ g = .e = - = t- "i = n - = _j " = ^ that = has "'0702" to "" 0v05 "^ '' nroba 'á' / n b o “005“ * áz · '“ ¹ ™ - 0.1 £> vanadium. Use of steel according to one of Claims 1 to 5 as material ii. (J for railway wheels, wheel flanges and dynamically rolling> objects.