A Newly Designed High-Strength Tool Steel with High Wear and Corrosion Resistance

Abstract

In this study, a newly developed high-strength cast Fe81Cr15V3C1 (wt%) steel with a high resistance against dry abrasion and chloride-induced pitting corrosion is presented. The alloy was synthesized through a special casting process that yielded high solidification rates. The resulting fine, multiphase microstructure is composed of martensite, retained austenite and a network of complex carbides. This led to a very high compressive strength (>3800 MPa) and tensile strength (>1200 MPa) in the as-cast state. Furthermore, a significantly higher abrasive wear resistance in comparison to the conventional X90CrMoV18 tool steel was determined for the novel alloy under very harsh wear conditions (SiC, α-Al₂O₃). Regarding the tooling application, corrosion tests were conducted in a 3.5 wt.% NaCl solution. Potentiodynamic polarization curves demonstrated a similar behavior during the long-term testing of Fe81Cr15V3C1 and the X90CrMoV18 reference tool steel, though both steels revealed a different nature of corrosion degradation. The novel steel is less susceptible to local degradation, especially pitting, due to the formation of several phases that led to the development of a less dangerous form of destruction: galvanic corrosion. In conclusion, this novel cast steel offers a cost- and resource-efficient alternative to conventionally wrought cold-work steels, which are usually required for high-performance tools under highly abrasive as well as corrosive conditions.

Keywords: abrasive wear behavior; as-cast microstructure; corrosion; mechanical properties; microstructural characterization; multiphase tool steels.

Figure 1

SEM image (SE contrast) displaying the microstructure of the reference cold-work steel X90CrMoV18.

Figure 2

Microstructure of the novel Fe81Cr15V3C1 steel: (a,b) OM images of the surface after etching with Beraha I, (c) SEM images (SE contrast) of deep-etched samples revealing interdendritic carbide morphologies (inset) and their distribution as well as (d) SEM image (BSE contrast) of trails of nanocarbides (black arrows) and twinned martensite (yellow arrows).

Figure 3

Microstructural analyses by (a) a SEM image (SE contrast) with associated EDS-maps of elemental distributions of (b) iron, (c) chromium and (d) vanadium.

Figure 4

XRD patterns of the cast FeCrVC alloy after Rietveld refinement: dotted line shows the measured values and the solid line shows the calculated values, identifying the phases bcc-martensite (1a), bct-martensite (1b), fcc-austenite (2), Cr₇C₃ (3) and VC (4).

Figure 5

Characteristic engineering stress–strain curves of the studied FeCrVC cast alloy and the reference material X90CrMoV18 under a quasi-static compressive load.

Figure 6

Results of the wear tests with different abrasive counter plates: (a) average wear rate, k, of the new FeCrVC cast alloy compared to k of the reference tool steel X90CrMoV18 and (b–e) SEM images of worn surfaces displaying wedge formation in different sizes (arrows).

Figure 7

Open circuit potential transients for the novel cast steel Fe81Cr15V3C1 and the reference steel X90CrMoV18, measured in 3.5 wt % NaCl solution at room temperature.

Figure 8

Representative potentiodynamic polarization curves for (a) the novel cast steel Fe81Cr15V3C1 and (b) the reference steel X90CrMoV18, measured in 3.5 wt.% NaCl solution at room temperature after different immersion times at OCP (insets: semi-logarithmic plot of the Tafel regions near to E_corr).

Figure 9

Optical micrographs of the surface morphologies of the novel cast steel Fe81Cr15V3C1 (a) and the reference steel X90CrMoV18 (b) after immersion in 3.5 wt% NaCl solution for 24 h. SEM micrographs of the surface of the novel cast steel Fe81Cr15V3C1 after immersion for 72 h (c) with corresponding EDX line scan (see arrow): Fe—blue, Cr—indigo, V—green and C—red (d).