Tomaž Vuherer

Study of the Simulated Heat Affected Zone of Creep Resistant 9–12% Advanced Chromium Steel

Global warming leads to research-development attempts worldwide with a view to reduce CO2 emission. Therefore, in the energy supply sector, a special focus has been directed to further development of steels that can endure the ultra-supercritical steam conditions. Our article presents the basic study on weldability of the advanced 9–12% chromium steel applying the thermomechanical simulation of the heat affected zone (HAZ). The changes of microstructures and material properties of HAZ before and after postweld heat treatment (PWHT) have been analyzed and compared by light microscopy, scanning electron microscopy (SEM), hardness measurements, and impact toughness testing. Microstructures at representative points during typical welding cycle and PWHT were studied in details.

Low temperature impact toughness of the main gas pipeline steel after long-term degradation

The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper.

DEFORMATION AND ENERGY PARAMETERS OF FRACTURE OF STEEL OF THE MAIN GAS PIPELINE

By example of steel 17G1S, the regularities in the impact fracture of Charpy specimens at normal and low temperatures are described. The relationship between the energy parameters of fracture (impact toughness) and the deformation response of the material (the height of shear lips) of the specimens from the pipe steel is established. The micromechanisms of impact fracture of the material are described. At 20 °C and –30 °C, focal splitting of the material was observed on the fracture surface of specimens; at –60 °C, the material failed in a brittle manner by the mechanism of cleavage.

Influence of kinematic factors of friction stir welding on the characteristics of welded joints of forged plates made of EN AW 7049 A aluminium alloy

Original scientific paper In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min to 850 min and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow.

Application of semantic technology for calculation of welding time in the development of new products

Determining the time of execution is very important in the early stages of each project (e.g. making offers, design phase etc.), especially in the stage of planning. This paper presents our approach to estimating the welding time for the purposes of planning the manufacturing processes. The approach is based on the knowledge of welding experts from the Nieros metal d.o.o. company and standards of welding (international and internal). An expert system was developed based on semantic web technologies for calculating the welding time in the product design phase and it is strongly integrated with the main ERP system of the Nieros metal d.o.o. company. Test results are presented at the end of this article.

Optimization of Single Pass Welding of High Carbon Bainitic Steel

Single pass welds have been made on a newly developed high carbon bainitic steel with the process of A-Tig welding. Despite the high carbon content, welding could be performed without the requirement of preheating, as a fully carbide free bainitic microstructure forms within the weld from the initially spheroidized condition. Therefore the welds are not susceptible to cold cracking upon cooling to room temperature. The single pass welds were performed by varying the heat input through changes in the welding speed, all the welds produced show a greatly uniform hardness of about 640HV1. This strongly suggests that the precipitates required for bainite formation in the new steel grade are only slightly influenced by the spheroidization annealing.

Analysis of deformation induced martensite in AISI 316L stainless steel

Abstract Metastable austenite stainless steel AISI 316L is sensitive to cold deformation, where transformation from austenite to martensite occurred. The bending deformation as the formation process leads to tensile and compression troughout the thickness of the billet. Tensile testing of the specimen causes differences in the true stress-strain along the contraction neck prior to fracture as well. The aim of the paper is to find correlation between microhardness as brief inspection parameters and extension of martensitic transformation. The total equivalent plastic strain extend diagram obtained by numerical simulation of bending was compared with tensile true stress-strain diagram. Results show very good correlation between hardness, true strain and martesite content. Therefore, one can conclude that by hardness measurement, it is possible to measure the level of equivalent plastic strain until ultimate tensile stress as a linear correlation between hardness, true strain and martesite content.

Metallographic Analysis of Kinetically Activated Bainite (KAB) Welds

Abstract Weldability of kinetically activated bainite steels with the process of activated tungsten inert gas welding was evaluated by means of mechanical testing and metallographic techniques. The latter were used to identify which phases formed and to determine their volume fractions as well as formation mechanisms. Based on this information, correlations were established between the welding parameters and the observed metallurgical phenomena. Particular emphasis was put on the morphology and the amount of retained austenite and the local formation of martensite. All tests were performed without preheating or post weld heat treatment of the high-carbon steel.

An Evaluation of Steel Embrittlement Caused by Welding

Abstract The fracture toughness of the HAZ in welds on a HSLA structural steel was assessed by using two types of precracked small-scale fracture-mechanics specimens. The microstructure of the single- and double-pass HAZs was simulated on a Gleeble machine at two different cooling rates. A direct measurement of K Ic was not possible due to the limited size of both kinds of specimens. A suitable adaptation of the loading diagrams was performed in order to produce relevant data about the fracture properties of the investigated sub-zones of the HAZ.