Development of high-strength steel surfacing technology

Abstract

Railway crossings belong to the most exposed components of a track structure. Operational load presents very complicated complex of adhesive, abrasive, and mainly contact-fatigue affect, which leads to preferential wear and tear primarily in the point and stock rail area depending on many external factors (such as crosswise and lengthwise slip, actual geometry relation in contact with a real worn wheel profile and the like) in the final result. The possibility of continuous reprofiling of the worn segments is an essential requirement on the material applied. The selection of material analyses results presented herein refer to the surfacing technology proposal of progressive bainitic steel for railway crossings casting. This material, industrial termed as Lo17MnCrNiMo, is intended for the most load-carrying segments particularly. Its chemical composition together with heat treating leads to the comparison with the original alternative (already applied Lo8CrNiMo) to modification of phases represented and later-on higher yield value mechanical parameters, fracture and notch toughness. Development holder of this material and as well the surfacing technology is DT - Výhybkárna a strojírna, a.s, Prostějov company. Surfacing technology solved herein came from experimental verification of some filler material alternatives, while the common background was following: • overlay quality associated with original characteristics of the base material; • demanded quality of join without a degradation of overlays characteristics; • all without a need of pre-heat and after-heat of created overlays. This technology is so attractive primarily because of reducing the problematic heat-cycle requirements that are to be obeyed. From the results – the crucial zone of transition follows from line of joint to the surface travel area. In this zone direct contact between base material and surfacing metal – no interlayer. This situation present a direct source of weld joint harm in interpreted combinations, simultaneously the absence of interlayer can cause higher inner press on weld boundaries. The positive influence of repeated heating of following layers surfacing on HAZ, as well as on the inner shape (grain) of surfacing metal, does not take effect. Manual impact load testing results in austenitic material of Cr/Mn type, which is manually able to harden above its original hardness of base material – without a phase transformation. Bainitic surfacing metal of Cr/Ni/Mo type does not yield to dynamic hardening under load. Large amount of dispersion of hardening was identified in area under the surfacing lengthwise the created weld deposits. In coincidence with this “sensitivity” to implementation it is proper to think of automatic surfacing appliance. Automation brings the advantage of stabilized process with and thus also the quality performance, simultaneously there is the possibility for layer preservation by flux and the positive impact regime of surfacing layers cooling. On principal it is necessary to lean the development of contact-fatigue load, where outstanding impact rate of load occurs in addition, against two basic moments: 1. The increase of lifetime in a given regime of load requires an optimal drift into the range of high cycle fatigue, where the influence of fore fatigue process stadium is principally real, which is possible to put together with increase of yield point from the characteristic material impress point of view. 2. Practically running processes of cumulative microscopic deformation (ratcheting) pose claims on the development conditions of surface layers plasticity. That together with anaclastic behaviour of a material influences the circumstances of already initiated damage, i.e. safety in regard of a dynamic load.