Thermal Fatigue Properties of H13 Hot-Work Tool Steels Processed by Selective Laser Melting

Currently, selective laser melting (SLM) is gaining widespread popularity as an alternative manufacturing technique for complex and customized parts, especially for hot-work and injection molding applications. In the present study, as the major factors for the failure of H13 hot-work die steels during hot-working, thermal fatigue (TF) properties of H13 processed by SLM and a conventional technique were investigated. TF tests (650 °C/30 °C) were conducted on the as-selective laser melted (As-SLMed), thermally treated selective laser melted (T-SLMed), and forged (Forged) H13. Results show that the As-SLMed H13 exhibited the best TF resistance properties among the specimens herein (the shortest total crack length and highest hardness of 687 ± 12 HV5), whereas the Forged H13 exhibited the poorest TF resistance properties (the longest total crack length and lowest hardness of 590 ± 11 HV5) after TF tests. TF resistance properties were closely related to the initial and final hardness. Further microstructural investigations revealed that the typical cell-like substructures, increased amount of retained austenite, and most importantly, refined grain size were the main reasons for the improved TF resistance properties in the As-SLMed H13 compared to the Forged counterparts.

THE DETERMINATION OF CHARACTERISTICS OF TEMPORAL PULSATING CAVITY WITH GUNSHOTS FIRED FROM FORT-12 GUN

The article presents the analysis of morphological peculiarities of temporal pulsating cavity under the experiment conditions using ballistic gel. In the course of the experiment there was used Fort-12 gun and standard ammunition of 9*18 mm caliber. A 250 Bloom ballistic gel (recommended by the leading researchers) was chosen as a simulator. The preparation of gel blocks was conducted using a classical methods suggested by Fackler and Malinowski, the concentration is 10 %, cooled down to the temperature of 4 °C (the exposition time is 48 hours). The visualization of a wound tract and cracks in gel left by the gunshot projectile and liquidation of the temporary pulsating cavity was conducted with the use of a contrasting water-soluble dye. After that the blocks were photographed and cut across the wound tract into plates of 1 cm width. Each section was scanned individually with the use of a flatbed scanner. In order to evaluate the damaging effect of the wounding projectile there are used standard calculation methods: Fackler’s wound profile (WP), the total crack length method (TCL), the polygonprocedure (PP).

Weathering of Radial and Tangential Wood Surfaces of Pine and Spruce

Summary The development of cracks and changes in appearance have been investigated on radial and tangential surfaces of pine (Pinus silvestris L.) and spruce (Picea abies Karst.) which have been exposed outdoors for 33 months. The degradation of the surfaces has also been studied at the micro-level. Untreated samples, samples impregnated with a CCA-agent and samples surface treated with linseed oil have been tested. The annual ring orientation is the most important factor for crack development on weathering. The type of wood, impregnation treatment and surface treatment with linseed oil have only a marginal effect on the crack development. No relation has been found between the density of the samples and the crack development. After 33 months of outdoor exposure, tangential surfaces of pine have 13 times more total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces is 6 times greater than on the radial surfaces. Tangential surfaces of both pine and spruce have a greater number of cracks per unit area and wider cracks than the corresponding radial surfaces. Tangential and radial surfaces show the same colour change in the surface as a result of weathering. On the micro-level, tangential surfaces have more and deeper cracks than radial surfaces. The cracks on the tangential surfaces occur frequently in both earlywood and latewood. On radial surfaces, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage. Decomposition of the cell wall takes place on both radial and tangential surfaces. Cracks arise which follow the S2 fibril orientation in the cell-wall. Delamination in the middle lamella is especially noticeable in the latewood on tangential surfaces. No differences have been observed regarding linseed oil treatment, impregnation or type of wood.