Improving the Abrasion Resistance of Nodular Cast Iron Castings by Remelting Their Surfaces by Laser Beam.

This paper presents the results of research conducted in the field of the technology of surface hardening of castings from unalloyed and low-alloy nodular cast iron using the laser remelting method. The range of studies included macro- and microhardness measurements using Rockwell and Vickers methods as well as metallographic microscopic examinations using a scanning electron microscope. Moreover, abrasive wear resistance tests were performed using the pin-on-disk method in the friction pair of nodular cast iron-SiC abrasive paper and the reciprocating method in the friction pair of nodular cast iron-unalloyed steel. Analysis of the test results shows that the casting surface layer remelting by laser for unalloyed nodular cast iron results in a greater improvement in its resistance to abrasive wear in the metal-mineral system, as compared to low-alloy cast iron. Additionally, carrying out the laser hardening treatment of the surface layer made of the tested grades of nodular cast iron is justified only if the tribological system of the cooperating working parts and allowable dimensional changes during their operation are known.

The Importance of the Geometry of the Down Sprue in the Gravity Casting Process.

This article presents the results of experiments on the optimization of down sprue geometry in the process of pouring sand molds. Theoretical assumptions and computer simulation tests are presented. The starting point was the theory and experience of gas entrapment caused mainly by a poorly designed gating system and the down sprue. Simulations were performed using Magmasoft software. First, initial studies were carried out to determine how the geometry (mainly the channel cross-section) of the sprue affects the problem, and then a detailed experiment was carried out on the so-called 'short sprue' version. The air entrapment process was analyzed, as were the parameters of the liquid alloy flow that passes through the analyzed channels. Nine geometric versions of the sprue were proposed and analyzed, and the results allowed us to conclude which sprue geometry is the best from the point of view of minimization of the gas entrapment problem.

Inhibition of Carbide Growth by Sr in High-Alloyed White Cast Iron.

Chromium cast irons have gained a well-settled position among wear-resistant materials where a low manufacturing cost is one of the key factors. The wear properties of these alloys are commonly improved by the addition of carbide-forming inoculating elements such as Ti, V, B, etc., allowing the formation of underlays for the precipitation of both M7C3 carbides and austenite. On the other hand, Sr may work as a surface-active element that adsorbs on the surface of the growing crystal, inhibiting its growth. This mechanism may support the M7C3 nucleation process. The experiment was conducted on near-eutectic chromium cast irons with 20% of Cr and 2.5-3% of C. Different amounts of strontium were used as the microstructure modifier. The improvement of carbides' stereological parameters and collocation resulted in the improvement in functional properties-wear resistance and impact strength without a significant increase in hardness as well as a decrease in carbide phase. Two types of wear studies with a modified pin-on-disc method and tests in reciprocating motion of samples in the metal-mineral system were performed. The results showed that addition modification with Sr can increase the impact strength of the alloy. EDS analysis of the samples provided results similar to hypoeutectic Al-Si alloys modified with strontium.