Prakt. Met. Sonderband 46 (2014) 307
m EFFECT OF MICROSTRUCTURE ON THE IMPACT TOUGHNESS
einer -
Sori x OF A COLD WORK TOOL STEEL
sichtlich. 1,2 n 1
\s durch das M. A. Rehan" “, B. Hdgman
vergroberung "2 Dept. of Material Technology, Uddeholms AB, SE-683 85, Hagfors, Sweden
"Dept. of Engineering Science, University West, SE-461 86, Trollhattan, Sweden
ebnis starker
zur Erzielung
stoffzustands ABSTRACT
The effect of different combination of austenitization temperatures and tempering
treatments on microstructure and impact toughness has been studied for the cold work
tool steel -Uddeholm Caldie. This is a chromium, vanadium and molybdenum alloyed tool
die Deutsche steel with approximately 0.7 wt.% C. It is used as a tool in industrial applications such as
BR 2178/15- cutting, punching, shearing, forming, drawing and extrusion. A combination of high
hardness and adequate toughness is required to withstand the common tool failure modes
of chipping and cracking.
Retained austenite content, hardness and prior austenite grain size were measured. The
impact toughness was determined for un-notched impact test specimens. The
microstructure and fracture surfaces of impact tested samples were characterized both
tainless steel macroscopically and microscopically. Scanning Electron Microscopy, Light Optical
i Engineering Microscopy and X-Ray Diffraction measurements were used. Higher austenitization
temperatures resulted in larger amounts of retained austenite and higher hardness.
ic Character- A higher austenitization temperature also caused coarsening of austenite grains and
ng”, Metallur- resulted in reduced toughness. Impact specimens austenitized and tempered at lower
temperatures were found to have better toughness than those at high austenitization and
anevicius, L.: tempering temperatures.
olycrystalline
2005, p. 262
“Lattice rota- 1.INTRODUCTION
|” Acta Mate-
, Tool steels are alloys with a wide range of carbon and metallic alloying elements. They are
of 18-8 stain- used to manufacture tools, dies, and molds that shape, form and cut other materials like
; steels, non-ferrous metals and plastics [1]. Cold work tool steels are used in industrial
> deformation applications under high stresses and therefore require high hardness, wear resistance and
Technology, ductility. The working temperature of the tool is typically below 200°C and it is used in
applications such as cutting, punching, rolling and pressing etc [2].
structure and Uddeholms Caldie is an air hardening, medium alloyed cold work tool steel. It has a
sitic. stainless martensitic structure with carbide forming elements like chromium, molybdenum and
vanadium [1]. The common tool failure mechanisms are cracking, chipping and plastic
deformation [2]. In order to overcome these failure mechanisms, the demand is to have
adequate toughness to withstand chipping and cracking while maintaining the high
hardness and good dimensional stability (i.e withstand plastic deformation).
In this paper, Caldie is examined from a microstructural point of view. The aim is to
characterize the steel with respect to retained austenite for a range of austenitizing and
tempering treatments. The microstructural characterization is complemented by impact
toughness testing and the correlation between impact toughness and microstructure is
