Steels for monobloc tyres for railways and the like

Abstract: Steels for tyre rims and monobloc tyres for railways, tramways and underground railways, comprising two types of C-Mn-Ni-Mo steels micro-alloyed with B, Zr, Nb, V and Al.

Description: This invention relates to a steel, utilizable for the fabrication of monobloc tyres for railways, tramways and underground railways. It is known that one of the more critical problems in the field of rolling stock is constituted by the phenomenon of tyre fluting, which is a phenomenon of local deterioration of the rolling surface of rim, which, following localized wear, transforms in time its circular starting profile into a multiside polygonal profile. During the running of the vehicle, such deterioration becomes a source of noise and, in order to restrain the sound emission within the limits provided for by the law, it is necessary to perform frequent profile grindings on the traditional materials used at present, in order to restore the original circular profile, which involves high costs and consumptions. Object of this invention is to obviate the aforementioned drawbacks. In its more general aspect, this invention allows to reach this object through the utilization, for the fabrication of monobloc railway tyres, of a C-Mn-Mo steel in which small amounts of elements (oligoelements) have been added comprising B, Zr, Nb, V and Al. The contemporaneous presence of such oligoelements, in well defined ratios relatively to one another and to the other elements comprised in the steels, allows to realize a synergetical activity which allows to obtain a good hardening, necessary to reach a remarkable hardness and wear resistance, higher than those of the traditional steels used at present for railway tyres, preserving at the same time toughness. The composition is shown in the following table, where, besides oligoelements, also all the other elements comprised are indicated, stressing for some of them the extreme minimum and maximum percent contents foreseen. MICROALLOYED STEEL FOR MONOBLOC TYRES 0.43 - 0.45 ≤0.005 ≤0.015 0.73 - 0.78 ≤0.10 0.20 - 0.25 0.40 - 0.45 ≤0.25 0.30 - 0.35 ≤0.020 ≤0.025 ≤0.010 0.0010 - 0.0018 0.015 - 0.020 0.025 - 0.030 0.03 - 0.05 In the case of micro-alloyed steel for monobloc railway tyres, the following mechanical properties are ensured in the tyre plate and the rim crown. Side plate Rim crown Ultimate tensile strength (N/mm2) ≤850 940-1020 Yield point (N/mm2) ≥700 Elongation (%) ≥15 ≥14 Striction (%) ≥45 ≥40 CHARPY U resilience temp. = 20°C (Joule) ≥20 Said monobloc tyres undergo a differential hardening treatment in a suitable plant having known characteristics. Such heat treatment comprises the following steps: NORMALIZATION by heating at 870-930°C and following maintenance for 2-4 hours at such temperature, followed by spontaneous air cooling up to room temperature. ROUGH MACHINING; AUSTENIZITING by heating at 870-900°C and following maintenance for 2-4 hours at such temperature, followed by cooling in the differential hardening plant; TEMPERING through heating at 500-540°C, and following maintenance for 8-12 hours at such temperature, followed by spontaneous air cooling up to room temperature. The tempering temperature of 500-540°C ensure, also in this case, that high toughnesses are reached and reduces the problems of surface hardness decline during shoe braking. Also the conditions that promote wear resistance throughout the life of the monobloc tyre and the good homogeneity of the rolling surface hardness are ensured.

Claims: A steel for monobloc tyres for use on railways, tramways and underground railways consisting of a C-Mn-Mo type steel micro alloyed with B, Zr, Nb, V and Al, which steel comprises the following elements in percent by weight: C 0.43 - 0.45 S ≤ 0.005 P ≤ 0.015 Mn 0.73 - 0.78 Cr ≤ 0.10 Ni 0.20 - 0.25 Mo 0.40 - 0.45 Cu ≤ 0.25 Si 0.30 - 0.35 Sn ≤ 0.020 As ≤ 0.025 Ti ≤ 0.010 B 0.0010 - 0.0018 Zr 0.015 - 0.020 Nb 0.025 - 0.030 V 0.03 - 0.05 balance Fe apart from impurities. A monoblock tyre for railways, tramways and underground railways made by the steel according to claim 1 and comprising a side plate and a rim crown which, after a differential hardening treatment comprising: normalization by heating at 870 - 930°C for 2 - 4 hours and spontaneous air cooling up to room temperature; rough machining; austeniziting by heating at 870 - 900°C for 2 - 4 hours and cooling in a differential hardening plant ; tempering by heating at 500 - 540°C for 8 - 12 hours and spontaneous air cooling up to room temperature, exhibit the following mechanical properties: Properties Units Side plate Rim crown Ultimate tensile strength N/mm 2 ≤ 850 940 - 1020 Yield point N/mm 2 ≥ 700 Elongation % ≥ 15 ≥ 14 Striction % ≥45 ≥ 40 CHARPY U resilience (temp. = 20°C) Joule ≥ 20

Inventors: AMICI GIAMPIERO, GHIDINI ANDREA, AMICI, GIAMPIERO, GHIDINI, ANDREA
Applicants: LUCCHINI SIDERURGICA S P A, LUCCHINI SIDERURGICA S.P.A.
Application year: 1995
Main classification: C22C38
IPC codes: C22C38, C21D1, C21D9