Comprehensive Investigations of the Supersolidus Liquid-Phase Sintering of Two Plastic Mold Steels

Abstract

The processing of plastics, particularly reinforced composites, necessitates the use of corrosion-and wear-resistant materials for tools that come into contact with the polymer. For such applications, plastic mold steels were developed that offer not only a good wear resistance due to the presence of carbides in a martensitic matrix, but also good corrosion resistance provided primarily by a sufficient amount of dissolved chromium. The common processing route for these high-alloyed materials is the hot isostatic pressing (HIP) of gas-atomized powders (PM-HIP). In this context, sintering plays an insignificant role, except for the processing of metalmatrix composites (MMCs). The development of novel wear-and corrosion-resistant MMCs based on plastic mold steels requires knowledge of the sintering behavior of prealloyed powders of such tool steels. It is well known that alloyed powders can be processed by supersolidus liquidphase sintering (SLPS), a method leading to almost full densification and to microstructures without significant coarsening effects. In this work, two different gas-atomized powders of plastic mold steels were investigated by computational thermodynamics, thermal analysis, sintering experiments, and microstructural characterization. The results show that both powders can be sintered to almost full density (1 to 3 pct porosity) by SLPS in a vacuum or a nitrogen atmosphere. Experimental findings on the densification behavior, nitrogen uptake, and carbide volume fractions are in good agreement with calculations performed by computational thermodynamics.

Correlation of processing route and heat treatment with the abrasive wear resistance of a plastic mold steel

“…This effect was already found in similar investigations [11]. Additionally, there is a precipitation of chromium rich carbides which are thermodynamically stable at a temperature of 1070 8C in this kind of steel [22]. In contrast, the formation of silicon rich oxides is based on the amount of silicon in the chemical composition Table 1 and the oxygen uptake during thermal spraying [24].…”

“…However, Figure 2b exhibits on the one hand a homogeneous distribution of vanadium rich MC-carbides but on the other hand there are eutectic M7C3 carbides leading to a net-like distribution. This fact is known from literature [22]: due to the comparatively high processing temperatures accompanied by a fully liquid state this carbide distribution is generated in the course of solidification.…”

Influence of Heat Treatment on the Performance Characteristics of a Plastic Mold Steel

“…Hardening was immediately followed by a two‐step tempering (see Table 2) with subsequent air cooling. Tempering at 200°C was performed to achieve a low tempered state containing retained austenite while tempering at 540°C was chosen to obtain maximum secondary hardness 11, 13. The investigated heat treatment with tempering at 650°C is not likely to be used in application, but it was used for determining the effect of a soft matrix and carbide precipitation on the resulting mechanical properties.…”

Metallic materials for tribocorrosion systems

“…Another possibility that has arisen during the past years is the liquid-phase assisted sintering of prealloyed steels in nitrogen atmosphere (super-solidus liquid phase sintering, SLPS). Here, nitrogen is used to lower the process temperature, but inevitably, nitrogen gets also dissolved during the process, which could be taken advantage of if controlled properly (Hill et al, 2010b). In many cases the surface treatment of a bulk part, however, is sufficient because tribocorrosion attacks the surface and not the core.…”