Corrosion properties of a plastic mould steel with special focus on the processing route

Abstract

Applications in plastics processing bear increased requirements for the used materials, especially with respect to their corrosion and wear resistance. For this reason, special powder metallurgical tools steels were developed that fulfil these demands. The common processing route for their production is hot isostatic pressing (HIP) of pre-alloyed powders which is followed by hot working if semi-finished parts are to be produced. As an alternative to HIP, super solidus liquid phase sintering (SLPS) permits the consolidation of pre-alloyed tool steel powders to near net-shape parts. It can be performed in different sintering atmospheres. In this work, the plastic mould steel X190CrVMo20-4 was processed by SLPS in vacuum as well as under nitrogen atmosphere. The resulting materials were analysed with respect to their microstructure, tempering behaviour and corrosion resistance in 0.5 molar sulphuric acid in dependence of the heat treatment. As a reference, the HIPed and the HIPed and worked state were also investigated. The results show that different heat treatments alter the ranking of the sintered and the HIPed state with respect to corrosion resistance. As expected, a high tempering for maximum secondary hardness causes a significant loss of corrosion resistance. The experimental findings were supported by thermodynamic calculations based on slight alterations in chemical composition that result from the different manufacturing processes.

New Developments in Martensitic Stainless Steels Containing C + N

“…If N is dissolved in V-rich precipitates in martensitic stainless steels (e.g., X190CrVMo20-4-1), it cannot contribute to a higher corrosion resistance, which was shown in ref. [33] Furthermore, C is pushed into the austenite resulting in increased RA or austenitization temperatures, which would make a cryogenic treatment mandatory. Based on Thermo-Calc 1 calculations Hill reported Supersolidus Liquid Phase Sintering (SLPS) of X190CrVMo20-4-1 under N 2 atmosphere should result in an increase amount of N in the matrix as well as in the V-rich precipitates.…”

Influence of Heat Treatment on the Microstructure and Corrosion Resistance of 13 Wt Pct Cr-Type Martensitic Stainless Steel

“…After being austenitized for 45 minutes, the samples were quenched to room temperature in oil. Since the working temperature for most of the plastic molds is below 573 K (300°C) and in some cases, tempering between 753 K and 793 K (480°C and 520°C) is also used for surface heat treatment of MSSs, [8] the experimental steel samples were tempered at 573 K (300°C), above the working temperature of injection molds), 773 K and 923 K (500°C and 650°C) for 2 hours, respectively. Followed by air cooling to room temperature [~298 K, (25°C)].…”

“…[7] 30Cr13 martensitic stainless steels (MSSs), which possess excellent mechanical properties and good corrosion resistance, are widely used as corrosion-resistant plastic mold steel. [8,9] However, the 13 wt pctCr-type MSSs are sensitive to localized corrosion, especially the pitting corrosion, when such confined anionic species as Cl À is in presence. [10,11] In these cases, the progressive consumption of oxygen cannot be halted and the cathodic reaction of oxygen reduction is still in process on the metal surface, thus the metal surface becomes anode and is consistently dissolved in Cl À solution, [11] which consequently leads to the depassivation of the protective films on MSSs' surface and would cause a severe corrosion, which is harmful to the surface quality and the service life of injection molds.…”

“…[8,12] Generally, the austenitizing temperature mainly affects the distribution of undissolved carbides in steel matrix, whereas the tempering temperature strongly determines the formation and distribution of the precipitates after tempering, which degrades the corrosion resistance and is known as the main factor for the sensitivity to pitting corrosion of MSSs. [13,14] In another words, the passive film that formed on MSSs surface can greatly improve the resistance of MSSs to general corrosion, but is often susceptible to localized breakdown, which could cause the dissolution of underlying metal in consequence.…”

Cavitation erosion and hydroabrasion resistance of cold work tool steels produced by powder metallurgy

“…The influence of processing on the microstructure as well as corrosion resistance of carbide-rich steels has been investigated in detail in the past [45][46][47]. The larger size of carbides in X190S and X245S compared to X190H and X245H, which can be seen in Figs 10-13a, is caused by the higher sintering temperatures during SLPS, which, in combination with the liquid phase leads to more distinct mass transport.…”