Thixoforming : Semi-solid Metal Processing

424j 11 Thixoextrusion
Table 11.4 Comparisonof hardnessandYoung smodulusvalues[GPa]of X210CrW12duringprocessing.
Sample state Hardness Young s modulus
untreated 5.2 (0.5) 220 (34)
thixoextruded 7.4 (3.1) 233 (21)
thixoextruded and annealed 7.8 (0.5) 220 (8)
Standard deviations are given in parentheses.
values for hardness and Young s modulus are determined if the primary globulitic
phase is indented, whereas high-level values are measured in the intergranular
phase.
According to metallurgical investigations on microstructure formation of
X210CrW12 processed in the semi-solid state (see Chapter 3), samples of extruded
bars are heat treated at 540 C for 10 h in air. Comparison of the respective
mechanical properties of untreated X210CrW12, thixoextruded bars and thixoextruded
bars after annealing (Table 11.4) provides evidence that a significant improvement
in hardness may be achieved by thixoforming this alloy. Hardness values are
preserved after annealing, which is encouraging with a view to the industrial
application of X210CrW12 parts produced by thixoforming. Young s modulus values
increase to a lesser extent and decrease to the initial values after heat treatment.
11.4.3
Upscaling of Isothermal Thixoextrusion
Results on thermal and mechanical process parameters obtained in thixoextrusion
experiments on the INSTRON laboratory testing machine were transferred to an
upscaled and improved tool setup implemented in an SMS Meer open die forging
press. The tool and billet dimensions and also the geometric complexity of the die
were considerably increased. The applied tool setup allows for higher die temperatures,
owing to the improved heating system. Additionally, a water cooling tube was
provided directly below the forming table in order to quench the extruded bars
rapidly. A mechanism to carry the weight of the extruded bar was not installed. The
tool setup is depicted in Section 8.6.4.2, tool dimensions are given in Table 11.5 and
the die cross-section is shown in Figure 11.11. The thixoextrusion trials were
performed at a punch velocity of 15 mm s 1 . The billets used had a diameter of
76 mm and a height of 100 mm.
The temperature evolution of the tool during preheating is shown in Figure 11.12.
The die land temperature was selected as the working set point with a target value of
1250 C, leading to temperatures of approximately 1340 C in the container.
In addition to the tool heating, a reproducible and homogeneous temperature
distribution in the billet for thixoextrusion experiments (isothermal and the
following non-isothermal – see Section 11.5) of the steel alloy X210CrW12 used is