Fracture toughness is one of the main material properties used when selecting and optimizing heat treatment of tools. However, fracture toughness data alone is not sufficient and need to be supported by other material properties and features. The aim of the present research work was to correlate fracture toughness properties of hot-work tool steel, especially its variation to the local microstructure, microhardness, and composition and to establish methodology for proper evaluation of tool steel's fracture toughness. Results show that the pressure of any weak point, either in a form of non-metallic inclusions and/or large undissolved eutectic carbide clusters, located in the region of positive segregation with high microhardness will lead to considerable reduction in fracture toughness.
COBISS.SI-ID: 1001898
The development of design guidance for stainless steel structures requires more tests on ferritic grade connections. This paper deals with a series of lap shear tests which have been carried out on various configurations of bolted and screwed connections. The tests demonstrate net section failure, bearing failure and block tearing failure. The material is a ferritic stainless steel of grade 1.4509 (AISI 441) with a thickness of 0.5-4.5 mm. The results are utilized in developing design guidance in accordance with Eurocodes.
COBISS.SI-ID: 1067946
Over the last decades considerable efforts are made to develop high performance spring steels, which would allow vehicles weight reduction. One way of improving steel properties is by refining its microstructure and reducing amount of inclusions. In the presented work the effect of cleaner and more uniform microstructure obtained through electro-slag remelting (ESR) on the mechanical and dynamic properties of spring steel was investigated. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. Results show that while ESR gives some improvement, especially in terms of better repeatability and reduced scattering, it has negative effect on fatigue properties of the spring steel.
COBISS.SI-ID: 1015210
Limited load-carrying capacity and impact loading resistance greatly restrict the use of hard coatings in forming applications, making substrate hardness and resistance to crack initiation and propagation very important. By using different combinations and parameters of vacuum heat treatment effect of the substrate fracture toughness and hardness on the load-carrying properties was determined under progressively loading dry sliding conditions, while ball-on-plate impact fatigue test was employed to investigate impact wear resistance. Results clearly show, that substrate hardness is the most important property influencing load-carrying capacity and impact wear resistance of the coated surface. However, with increased hardness and brittleness of the coating increase in fracture toughness although on the expense of the reduced hardness becomes beneficial.
COBISS.SI-ID: 28797479
Currently the best overall appraisal of tool and high-speed steel applicability seems to be a combination of fracture toughness, bending, or compression testing and in specific cases of impact or small-punch creep test. This paper clearly demonstates usability of a single KIc-test specimen for determination of a wide range of properties being important for tool and high-speed steels, and their vacuum-heat-treatment optimization. In the case of ESR AISI M2 high-speed steel low tempering and austenitizing temperature are preferable in terms of ductility and toughness, high tempering and lower austenitizing temperatures in terms of bending strength and high-speed machinability, while high austenitizing and mid tempering temperatures in terms of hardness, compression strength and grindability.
COBISS.SI-ID: 1001642
We have studied the transformation of carbides in AISI M42 high-speed steels in the temperature window used for forging. The annealing was found to result in the partial transformation of the large, metastable M2C carbides into small, more stable grains of M6C, with an associated change in the crystal orientation. In addition, MC carbides form during the transformation of M2C to M6C. The results also show an interesting difference in the carbide-transformation reactions on the surface versus the bulk of the alloy, which has implications for in-situ studies of bulk phenomena that are based on surface observations.
COBISS.SI-ID: 1171882
The main challenge in realizing the immense potential of nano-engineered steels is to manufacture large components and quantities at low costs, where homogeneous dispersion of ceramic nano-particles in molten metals is extremely hard to achieve. Investigation was performed on the conventional 51CrV4 spring steel, where different types of nano-particles were added into the melt. Effect of nanoparticles alloying was investigated after hot rolling, soft annealing and vacuum heat treatment using typical processing parameters. Research was focused on the yield and ultimate tensile strength, fracture toughness and fatigue properties. Results of this investigation indicate that nano-particles reinforcement of spring steel is feasible even by using simple liquid metal casting routes, with the nano-particles type and size having impact on ultimate tensile strength and fatigue limit. Finer and more uniform is the distribution of nano-particles better fracture toughness, fatigue properties and flexibility can be expected together with high hardness and improved tensile properties, which is between 10 and 20%.
COBISS.SI-ID: 1128874
The aim of our research work was to investigate the effect of deep cryogenic treatment on fracture toughness, wear resistance and load-carrying capacity of cold work tool steel and to determine the effectiveness of deep cryogenic treatment depending on the tool steel type and chemical composition. The type and chemical composition of the tool steel considerably affect the way how deep cryogenic treatment changes mechanical, tribological and load-carrying capacity of the tool steel. For lower carbon and higher W and Co containing cold work tool steel properties can be improved for up to 70%, but are very limited in the case of high-speed steel. At high carbon and vanadium contents properties of cold work tool steels can even be deteriorated after deep cryogenic treatment. In terms of abrasive wear resistance and load-carrying capacity increasing the hardness is the most decisive factor.
COBISS.SI-ID: 1171370
Cr2N0.61-7Ag nanocomposite coatings were deposited on substrates made of Cr-V ledeburitic tool steel Vanadis 6 using reactive magnetron sputtering at a deposition temperature of 500 °C. Investigations of as-deposited films and annealing experiments in closed-air atmosphere at temperatures of 300, 400 and 500 °C and the durations up to 24 h, followed by quantitative scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray diffraction revealed that the films were composed of Cr2N0.61 matrix and individual silver agglomerates located along columnar crystals of the matrix. The maximal size of Ag-agglomerates was 80 nm. The surface population density of silver agglomerates increased with prolonging the annealing time up to 2 h and then decreased. The increase was more pronounced at lower annealing temperatures. This behaviour was referred to the competition between three phenomena, namely the transport of detached Ag atoms to the free surface, formation of oxide layer on the surface and sublimation of silver from the surface. At lower temperatures and/or shorter annealing times, the Ag-transport to the free surface was determined to be prevalent, thus, an increase in population density of silver agglomerates was determined. On the other hand, for higher temperatures and/or longer annealing times the population density of Ag-agglomerates rather decreased due to retarding effect of thicker oxide layer and sublimation of silver.
COBISS.SI-ID: 1171114
Optimization of tool steel properties and corresponding heat treatment is mainly based on trial and error approach, which requires tremendous experimental work and resources. The aim of the present work was to explore the potential and possibilities of artificial neural network based modelling to select and optimize vacuum heat treatment conditions depending on the hot work tool steel composition and required properties. Results show that this type of modelling can be successfully used for detailed and multifunctional analysis of different influential parameters as well as to optimize heat treatment process of hot work tool steels depending on the composition. In terms of composition V was found as the most beneficial alloying element increasing hardness and fracture toughness of hot work tool steel, Si, Mn and Cr increase hardness but lead to reduced fracture toughness, while Mo has the opposite effect. Optimum concentration providing high KIc/HRC ratios would include 0.75% Si, 0.4% Mn, 5.1% Cr, 1.5% Mo and 0.5 % V, with the optimum heat treatment performed at lower austenitizing and intermediate tempering temperatures.
COBISS.SI-ID: 1249194