With the introduction of modern low-weight high-strength materials, tools and dies in hot metal forming are exposed to increasingly demanding contact conditions. This requires use of surface ...engineering techniques and proper balance between core hardness and fracture toughness. However, it is not very straight forward which combination to use in terms of wear resistance. The aim of this work was to investigate the effect of Si content on properties of AISI H11-type hot work tool steel in relation to austenitizing and tempering temperature. Work was focused on the core fracture toughness and fracture toughness versus hardness ratio and how they affect galling and wear resistance of plasma nitrided hot work tool steel. In the case of high Si content, increased austenitizing temperature results in high core hardness but considerable drop in fracture toughness and wear resistance. However, for low Si content, increased core hardness is accompanied with improved fracture toughness and greatly improved wear resistance. Galling resistance on the other hand is more or less independent of the substrate properties and mainly depends on surface conditions and plasma nitriding process.
One of the most influential microstructure constituents in creep resistant steels are carbide particles. Carbide particles act as obstacles to dislocations movement, therefore the creep rate strongly ...depends on their size and distribution. At elevated temperatures to which creep resistant steels are exposed, carbide morphology is altered by the coarsening mechanism, consequently deteriorating the creep resistance of these steels. The aim of this work is to study the role of size and distribution of carbide particles on creep rate. Different distributions and size of carbides were obtained by different heat treatment conditions. The effect of different carbide morphology on the creep resistance was evaluated by uniaxial constant load creep tests.
Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are ...different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. 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. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.
The aim of this research was to determine the effect of vacuum-heat-treatment process parameters on the material properties and their correlations for low-Si-content AISI H11-type hot-work tool steel ...using a single Circumferentially Notched and fatigue Pre-cracked Tensile Bar (CNPTB) test specimen. The work was also focused on the potential of the proposed approach for designing advanced tempering diagrams and optimizing the vacuum heat treatment and design of forming tools. The results show that the CNPTB specimen allows a simultaneous determination and correlation of multiple properties for hot-work tool steels, with the compression and bending strength both increasing with hardness, and the strain-hardening exponent and bending strain increasing with the fracture toughness. On the other hand, the best machinability and surface quality of the hardened hot-work tool steel are obtained for hardness values between 46 and 50 HRC and a fracture toughness below 60 MPa√m.
Specimens of high chromium creep resistant steel were tempered at 800 °C for different times and examined in SEM. After short tempering stringers of cementite particles are formed at ferrite grain ...boundaries. By longer tempering, the content of chromium and molybdenum increase up to Cr18Fe3Mo2C6 and the number of stringers decreases what gradually increase the creep rate.
In this study two new tests were developed, i.e., with continuous internal water cooling as well as discontinuous internal water and air cooling. It was proved that the first type of testing is ...appropriate for simulating the time course of the temperature at a selected depth of a thermally loaded, hot-working die surface layer, i.e., the temperature field on the die surface layer. The second type of testing is appropriate for a study of the thermal fatigue resistance of a tool material.
The effect of grain space orientation and particle-matrix stress transfer on dislocation movement forces with difference of acting stress components in slip plane in climb direction is discussed. A ...modified equation for calculation of creep rate of creep resistant steel including M
23
C
6
particles size and spacing is proposed. Small differences of experimental and calculated creep rates are obtained by stress exponent n = 3·65.
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