Materials Research Center Leoben Austria Bohler Austria University

Materials Research Center, Leoben Austria Bohler Austria University of Brescia, Italy Bohler, Austria Institute of Metals and Technology, Ljubliana, Slovania

Shanghai University and Zhengda Mould, China Politecnico Torino and Cogne Acciai Specially, Italy Politecnico Torino and AQMsrl, Italy Uddeholm Sweeden Metallurgical Research Institute, Bucharest, Romania

Portland State University, US, Intensive Technology, Kyev, Ukraine University of Zagreb, Croatia Aubert Duval, France Edelstahl Witten-Krefeld, Germany TTN and Politecnico Torino Schmeltz and Bohler-Uddeholm, Germany

Ecole de Mines, France University of Ljubliana , Ljubliana, Slovania and Politecnico Torino, Italy University of Ljubliana , Ljubliana, Slovania and Universidad Politecnica de Madrid, Spain Uddeholm Tooling, Sweeden

Bohler Edelstahl, Austria Ecole de Mines, France Shanghai University, China Ecole de Mines, France

EXTENDED ABSTRACT Two years activity of a technical working group named “Comitato per la Qualità degli Acciai da Stampi per Pressocolata” (Committee for the Quality of Steels devoted to Die Casting Dies). This group is a part of the larger “Comitato Pressocolata” (Die Casting Committee) belonging to the Associazione Italiana di Metallurgia (AIM), Italian Association for Metallurgy. The technical group started its activity on 2003 and worked to provide the die casting world end users (such as die designers & manufacturers and foundries) with a comprehensive technical specification, defining the tool steels requirements that are necessary to be achieved so as to guarantee satisfying service performance levels for the tool.

The steel properties characterization is defined on the base of three quality levels which ensure increasing service performances, defined as follows: Top, Medium and Standard Quality. The steel classification is based only on the measurable final minimum characteristics, those that have to be clearly guaranteed, and not on the specific fabrication route selected by each steel producer. The steel quality is in particular measured through the following features: · chemical composition · hardness · microcleanliness · microstructure homogeneity · carbides distribution · impact toughness This steel characteristics are defined both in the annealed and quenched and tempered conditions. All the aforementioned properties have to be investigated on the transverse section of the original semiproduct.

The standard proposes a control methodology and procedure for the impact toughness evaluation, using both V-notched (ISO-KV) and unnotched (KVW) impact specimens. Currently the impact toughness is considered one of the most characteristic property of materials quality. The impact test is performed on quenched and tempered specimens machined directly from the annealed parent block of the die (testing treatment) and on specimens removed from the quenched and tempered die. The specimens removal and heat treatment conditions are specified for specimens removed from the parent block prior the heat treatment and those being removed from the as-quenched and tempered die. Starting from the Tool 06 Conference, the current version of the specification will be opened to discussion, revisions and adding on since the technological and scientific evolution of the die casting sector is in continuous progress.

Development of W 360 Objective: Develop thermally stable tool steel W 360 ISOBLOC with outstanding ductility at a working hardness of 52 – 56 HRc. Method: ESR of optimized composition • Higher carbon content of 0. 5 % t o increase hardenability by formation of fine carbides. • Molybdenum increased to 3% obtaining thermally stable carbides for hot hardness. • Chromium decreased by a half percent to 4. 5%, reducing the quantity of thermally unstable carbides without a loss in throughhardenability. • Carbide-forming element vanadium was specified at about 0. 55 %. This guarantees a refined grain structure. • Lower silicon and manganese contents are responsible for a significant high toughness and ductility level.

W 360 H 11

GOAL Identify heat treating conditions that improve performance of die casting dies. OBJECTIVE • Compare between austempered and oil quenched H 11, all tempered in the range of 42 -44 HRC: - Structure examination - Mechanical properties evaluation: hardness, impact strength and thermal fatigue resistance

Typical Austempering TTT

EXPERIMENTAL

Step 2 –Austempering and tempering procedure 21 cylindrical samples were cut (D=32 mm and L=65 mm) from the same original bar. A 1: Austempered at 310°C for 5 hours; Quadruple temper at 1000°C for 40 min A 2: Austempered at 340°C for 5 hours; Quadruple temper at 1000°C for 40 min Q: traditionally oil quenched and tempered specimens. Triple temper at 1000°C for 40 min For austempered and oil quenched samples the final tempered hardness was 42 -43 HRC.

1 J=0. 737562 ft-lb

CONCLUSIONS • The bainite nucleation and growth are faster when the isothermal transformation temperature is as close as possible to the Ms point. • The temper resistance of the A 2 austempered and tempered structure appears to be higher than that of the oil quenched and tempered morphology. • The impact strength produced by drastic oil quenching is still higher (average 27 J) than the austempering (average 17 or 15 J). These latter values of 17 or 15 J, however, are not low for the steel used considering that the annealed condition was at the lowest limit of the acceptance area.