Mathematical modelling of hot formability of steels

24.00; Translated from Czech. (Hutn. Listy 1989 v. 44(11) p. 783-787)Available from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4570)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Examination of the thermal conditions in the hot torsion test

19.00; Translated from Czech (Hutn. Listy 1987 v. 42(8) p. 544-551)SIGLEAvailable from British Library Document Supply Centre- DSC:9023.19(VR--3504)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Study of thermal conditions during the hot torsion test

17.50; Translated from German (Neue Huette 1986 v. 34(6) p. 233-238)Available from British Library Document Supply Centre- DSC:9022.06(BISI-Trans--26230)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Introduction

http://dx.doi.org/10.1177/000276421348735

Vliv kování za tepla na strukturu HS 6-5-2 rychlořezné oceli

Microstructure analysis was performed on rolled bars of high-speed steel after two and three forging cycles, each cycle comprising one upsetting and one drawing out operation. High-speed steels belong to difficult-to-form materials with a narrow forging temperature interval. Forging above the maximum forging temperature may lead to grain coarsening. Below the minimum forging temperature, deformation resistance of the material increases, and the workpiece may fail. Using numerical modelling, special forging dies were designed and effective strain distribution was calculated for an axial cross-section plane in specimens after two and three forging cycles. The purpose of the analysis was to identify the relationship between the amount of effective strain and the shape and size of austenite grain and the volume fraction and density of carbidesafter forging. The size of prior austenite grains was measured using the linear intercept method which is based on the Snyder-Graff method. Grain shapes were characterized in terms of circularity, which is the difference between the shape in question and a circle. With increasing amount of strain, the grains in the materialbecame finer, as undissolved carbides impeded grain growth. In as-received rolled condition, the austenite grain size was G9. After three forging cycles, it was smaller, G11 (the higher the number, the smaller the grains). Circularity characterizes the complexity of a grain shape.Micrographs of carbide particles were taken using a scanning electron microscope and examined with NISElements image analysis software. The majority of carbides were sized between 0.2 and 2μm.The carbides which are less than 1μm in size do not shrink in response to increasing strain and their quantity does not change appreciably. Carbides with a size of 1-2μm show a different behaviour. In the central region of specimens, where strain is the largest, their amounts are much larger than in less-worked regions