A comparison of powder metallurgical and conventional processing of tungsten-alloyed high boron tool steels

High boron tool steels (HBTS) offer excellent mechanical properties at low cost and reduced ecological impact. Powder metallurgical (PM) processing yields highly homogeneous microstructures but is time and cost intensive, whereas casting and hot forming offers a more efficient alternative but is generally associated with lower microstructural uniformity. This study investigates whether the typical refined PM microstructure, characterized by rounded, finely dispersed hard phases, can be reproduced through conventional methods. It further addresses discrepancies between predicted and observed phase types and fractions in boron steels alloyed with refractory elements such as tungsten by producing a near equilibrium condition. The question shall be answered whether casting and swaging can replicate the homogeneous microstructural and mechanical characteristics of HBTS on the example of a tungsten-alloyed PM HBTS. Thus, PM material was produced through gas atomization, hot isostatic pressing, swaging, and heat treatment. Microstructures were characterized using scanning electron microscopy, X-ray diffraction, and wavelength-dispersive spectroscopy, and compared to those of cast and swaged counterparts. Compression testing was conducted to evaluate mechanical performance. The results show that both processing routes yield highly similar microstructures in diffusion annealed condition, each containing equal fractions of tetragonal M 2 B borides and cubic M 3 (C,B) carboborides, despite conflicting thermodynamic predictions. Mechanical properties after hardening and tempering were also comparable, with both materials exhibiting a hardness of approx. 610 HV10 and compressive strengths close to 3 GPa. These findings demonstrate that a microstructure, closely resembling a PM microstructure, can be achieved by swaging and heat treatment of cast HBTS. • The microstructure of powders of the alloy Fe0.4C1B2.5Cr2W is composed of primary γ -Fe dendrites and carboborides of the M 23 (C,B) 6 and M 3 (C,B) types within the interdendritic regions. • The microstructure of cast W-alloyed tool steels can be transformed through swaging and diffusion annealing to strongly resemble a diffusion-annealed PM microstructure. • In an application-oriented quenched and low-tempered condition, the PM samples reach the same compressive strength as the cast and swaged samples with a higher compressive strain. • It is shown, that the influence of refractory alloying elements on the microstructures and properties of powder metallurgical high boron tool steels can be well approximated by a conventional casting and swaging route.