This research is conducted to study the thermal fatigue resistance of different hot-work tool steels; AISI H11 and H13, special tool steel and 18% Ni maraging steel. The maraging steel is surface cladded by GTA welding to study the thermal fatigue resistance of surface layer. An influence of mechanical and microstructural properties on thermal fatigue resistance is evaluated. An innovative apparatus for thermal fatigue testing is developed to study the thermal fatigue resistance. The test specimens are subjected to cyclic heating in bath of molten Aluminum Alloy 226 and cooling in bath of water-based lubricant. They are continuously internally cooled with cold water. The specimens are periodically analyzed after completion of particular number of cycles. The microstructure, hardness profile and the surface cracks developed are analyzed. Temperature transients at different locations of test specimen are measured and used in computation of transient stresses performed by finite elements. The specimens of special geometry are developed using finite element modeling to improve testing efficiency. An optimal set of thermal fatigue testing parameters are developed to establish efficient testing. The influence of thermal loading on tempering of hot work tool steel and on aging of maraging steel claddings during testing is determined. The results showed significant differences in thermal fatigue resistance of tested materials and their heat treatments. The best thermal fatigue resistance achieved special tool steel due to its high thermal stability. The resistance of AISI H11 tool steel is slightly superior to that of maraging steel weld.

Thermal fatigue of materials for die-casting tooling

Indexable insert tools for machining operations are in service exposed to high temperatures and cyclic mechanical loads. Secondary hardening steels such as hot-work steels are commonly used for tools subjected to thermal exposure. However, these steels, highly alloyed with strong carbide forming elements as Cr, V and Mo, are generally difficult to machine and machining represents a large fraction of the production cost of a tool. Thus, the present study concerns the development of a new steel with improved machinability and meeting the requirements for high-temperature properties. Softening resistance of the THG2000 and QRO90 tool steels, commonly used in hot-work applications, and a newly developed tool steel MCG2006 with lower alloying content of carbide forming elements, was investigated by tempering and isothermal fatigue testing. Mechanisms of high-temperature softening of the tested tool steels were discussed with respect to their microstructure and high-temperature mechanical properties. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis. No difference in softening behaviour was found among the QRO90 and MCG2006 regarding hot hardness measurements. The THG2000 indicated some stabilization of the hardness between 450 and 550 °C and a considerable hardness decrease at higher temperatures. The short-time cyclic softening in isothermal fatigue was controlled by dislocation rearrangement and annihilation. The alloying composition of the steels presently tested had no influence on the dislocation density decrease. The long-time softening was affected by the material's temper resistance and strongly depended on the carbide morphology and their over-ageing resistance. The QRO90 with greater molybdenum and lower chromium contents than in the THG2000 show the best resistance to softening among the tested grades at all temperatures. The MCG2006, leaner alloyed with the carbide forming elements and alloyed with 4 wt% nickel, has better temper resistance than THG2000 at higher temperatures and longer tempering times.

High-temperature properties and microstructural stability of hot-work tool steels

Thermo fatigue cracking of die casting dies

Microstructure and crystallography of borides and secondary precipitation in 18 wt.% Cr–4 wt.% Ni–1 wt.% Mo–3.5 wt.% B–0.27 wt.% C steel

This paper assesses how simple small-angle scattering particle size evaluation models, such as Porod or Guinier radii, which have a normally limited validity range, may see this range extended to larger q values. This is shown to be particularly true for metallic systems, where the dispersion in particle size is always large. Because of the size dispersion, the relationship between the average particle size and the Guinier radius is shown to change. For systems with relatively large size dispersion, the paper shows that the Porod and Guinier radii, and simple extensions thereof, give valuable information on particle size and particle size distribution. This is demonstrated to be valid for particles with moderate aspect ratios. These simple evaluations are quick and very well adapted to large data sets, such as those originating from time-resolved or scanning small-angle experiments.

https://hal.archives-ouvertes.fr/hal-00591218/document

On the validity of simple precipitate size measurements by small-angle scattering in metallic systems

https://hal.archives-ouvertes.fr/hal-01715082/document

The effect of the addition of alloying elements on carbide precipitation and mechanical properties in 5% chromium martensitic steels

Influence of chemical composition on the precipitation of secondary carbides in modified AISI H11 hot-work tool steels


 In the WAAM process, the accuracy of the toolpath is of prime importance for the mechanical properties of the final part because of the material defects that could be generated. This paper deals with the motion analysis of the end effector nozzle of a robot dedicated to the WAAM process. The movement of the nozzle to create a rectangular layer was experimentally analyzed without physically depositing material (trajectory definition only). Various strategies, nozzle speeds and layer areas were compared in terms of travel time and length over different sections of the toolpath in order to identify various problems, in particular associated with acceleration and deceleration phases when changing direction. The consequences of a discontinuous deposition were also studied, revealing a complex interaction between cold metal transfer equipment and robot controllers. The results enable a better understanding of this interaction, which is important for deposition quality and performance. Finally, a model was proposed to calculate the manufacturing time of any layer area based on a preliminary identification for a single area.

/pdf/complex-interaction-between-cmt-equipment-and-robot-2y9c3gso.pdf

Pierre Michaud

Papers

The effect of the addition of alloying elements on carbide precipitation and mechanical properties in 5% chromium martensitic steels

Influence of chemical composition on the precipitation of secondary carbides in modified AISI H11 hot-work tool steels

Complex Interaction Between CMT Equipment and Robot Controllers During the WAAM Process: Consequences for Toolpath Accuracy