Thixoforming : Semi-solid Metal Processing

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ageing or controlled, continuous cooling due to the element distribution in the liquid and solid phases. Due to these, mechanical properties can be achieved that are superior to those of conventional hardening. For example, the application temperature of steel X210CrW12 can be raised considerably by means of the described heat treatments. To consolidate the industrial application of steel 100Cr6 in the thixoformed state, further systematic examinations have to be conducted and applicable heat-treatment strategies have to be developed. Important for this is the avoidance of a connected carbide network on the grain boundaries. Based on the examinations up to this point, a transformation of the segregated grain-boundary areas has to take place in such a way that a structural compound of austenite, martensite and finely distributed carbides can form. The necessary transformations can be reached either by means of specific cooling directly following the transformation process or by means of a special heat treatment by heating from the cooled state, so that no degradation of the global mechanical properties of the material occurs. Table 3.9 shows the element contents of the separate phases with a fraction of 50% solid and 50% liquid phase. The M s temperatures calculated from this are given in the last column. For the purpose of comparison, the respective values for the conventional hardening of the materials are also given. In Table 3.10, the summarized measured microhardness of the separate structural components of steels X210CrW12 and 100Cr6 are given. The values in these two tables clarify that due to the strong reallocation of the elements chromium and carbon in both materials, a multiphase structure is formed which exhibits potential for new material properties due to its different transformation behaviour. For steel X210CrW12, this was already Table 3.9 Thermo-Calc calculated carbon and chromium contents of the solid and liquid phases at equilibrium with phase contents of 50 mol% and of the austenite at conventional hardening temperatures; calculated Ms temperatures as a function of the annealing temperature using the empirical equation M s ¼ 635 – 475[mass% C(g)] 17[mass% Cr(g)] 33[mass% Mn(g)] [64]. C (mass%) 3.6 Microstructure Analysis and Material Propertiesj99 Cr (mass%) Mn (mass%) Ms ( C) X210CrW12 Solid (austenite) 1.23 9.16 0.23 112.6 1285 C Liquid 3.07 14.85 0.37 (eutectic transformation) f s ¼ 50% Near 970 C Austenite 0.76 4.62 0.30 185.5 100Cr6 Solid (austenite) 0.55 1.36 0.24 342.7 1418 C Liquid 1.46 1.65 0.36 98.5 f s ¼ 50% 850 C Austenite 1.00 1.50 0.30 124.6
100j 3 Material Aspects of Steel Thixoforming Table 3.10 Measured microhardness of the structural components of different material conditions of the steels X210CrW12 and 100Cr6. Heat treatment Phase Hardness X210CrW12, after quenching from 1270 C Solid (austenite) 300 HV0.1 Liquid (eutectic) 450–700 HV0.1 X210CrW12, microstructure after adapted Different carbides, 750–800 HV10 heat treatment acicular pearlite, martensite and retained austenite X210CrW12, after conventional hardening (970 C) Austenite 760 HV10 100Cr6, after quenching from 1400 C Martensite, carbides, retained austenite 750 HV30 100Cr6, after conventional Martensite, carbide, 830 HV30 hardening (850 C/oil) retained austenite examined in detail in the scope of this research, whereas for the steel 100Cr6 further test series have to be conducted. Only after completing these examinations can a final statement about the thixoformability of steel 100Cr6 be made. 3.7 Conclusions Thixoforming of steel is in general possible, but still remains in an early and far from mature development stage. Not least because of the high process temperatures and the oxidation aptness of partial liquid steels, this procedure is still faced by great challenges and much optimization is needed before it can be applied industrially. The preconditions for selecting suitable alloys for thixoforming are well understood: it is mainly the temperature sensitivity and the particular liquid-phase development during heating and soaking. High-alloyed steels with precipitates that stabilize the microstructure at high process temperatures seem to be more suitable than lean-alloyed steel concepts. Thixoforming requires a thorough understanding of the microstructure development during semi-solid processing. It has been shown that this is not possible in a highly accurate manner by metallographic examination of quenched samples alone. Proper process control will therefore need instantaneous microstructure state monitoring by online numerical modelling. Characteristic features are observed in thixoformed specimens which are inherent to the thixoforming process; for example the alloy decomposition due to significant different solubilities of liquid and solid phases and due to the sponge effect in the liquid–solid suspension or the occurrence of pores and inhomogeneous grain size distributions.
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Thixoforming Semi-solid Metal Proce
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Further Reading Herlach, D. M. (ed.
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The Editors Prof. Dr. G. Hirt Insti
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VI Contents 1.3.5.2 Other Aluminium
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VIII Contents 4.6.1 Thixocasting 13
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X Contents 7.4.2 Isothermal Non-ste
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XII Contents 9.4.1.3 Simulation Res
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Preface Semi-solid forming of metal
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XVIII List of Contributors Andreas
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XX List of Contributors Alexander S
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2j 1 Semi-solid Forming of Aluminiu
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10j 1 Semi-solid Forming of Alumini
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Table 1.1 Overview of semi-solid pr
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Part One Material Fundamentals of M
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32j 2 Metallurgical Aspects of SSM
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44j 3 Material Aspects of Steel Thi
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46j 3 Material Aspects of Steel Thi
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here it can be assumed that the dat
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Figure 5.2 Calculated temperature v
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Figure 5.4 Composition profiles of
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It is clear that C has by far the s
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Figure 5.7 The density of X210CrW12
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5.3 Calculations for the Bearing St
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Figure 5.11 Composition profiles of
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Figure 5.14 The density of 100Cr6.
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area which is available for heat tr
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Part Two Modelling the Flow Behavio
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170j 6 Modelling the Flow Behaviour
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7 A Physical and Micromechanical Mo
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3. Macroscopic averages or homogeni
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displacement boundary conditions or
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and liquid are both assumed to be i
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are the strain rate concentration t
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Semi-solid viscosity (Pa s) into cl
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Load (kN) strain to rupture, leadin
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Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
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adius R radius of the spherical inc
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Part Three Tool Technologies for Fo
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242j 8 Tool Technologies for Formin
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9 Rheocasting of Aluminium Alloys a
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Figure 9.2 Processes for the semi-s
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Two Italian companies gained the fi
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9.2 SSM Casting Processesj317 For t
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Figure 9.7 Oil pump cover for Honda
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Figure 9.9 Middle temperature cours
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Figure 9.12 Components of cartridge
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Figure 9.15 Process adapted multipa
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step-shot experiments. It is also s
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Figure 9.18 (a) Meander tool for fl
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Figure 9.19 (a, b) Wear appears in
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Table 9.2 Temperature determination
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and are plausible on the left. Furt
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Figure 9.27 Development of the micr
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some places can be observed as smal
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Figure 9.31 Simulation of the metal
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Figure 9.33 So-called Constant Temp
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Figure 9.35 Comparison of the micro
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9.4 Rheoroutej347 If rounding of th
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9.4.1.2 Parameters: Cooling to the
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Figure 9.36 Results of the 2D-MICRE
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homogeneous microstructure and no d
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grain fragment density [mm -1 ] 200
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can be considered for rheocasting o
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Figure 9.44 Microstructure of Zr/Sc
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Figure 9.45 MAGMAsoft simulation: c
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The cooling to the process temperat
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D grain diameter of a circle DGM De
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27 Doppelbauer, M. (2003) Wirtschaf
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10 Thixoforging and Rheoforging of
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1970s [7]. Also, the quality of the
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10.3 Heating and Forming Operations
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With the solution of the Equations
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10.3.1.2 Modelling of Inductive Hea
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material properties have to be cons
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10.3 Heating and Forming Operations
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Figure 10.9 Experimental results, d
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Figure 10.12 Segregation in compone
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10.3.4 Thixoforging of Steel In thi
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10.3.5 Thixojoining of Steel In the
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einforcing element. The possibiliti
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Figure 10.20 The robot controller a
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Figure 10.21 Experimental results w
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Figure 10.24 Design and working pri
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The investigations show that the rh
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Figure 10.31 Scheme of the heat tra
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Table 10.2 Definition of boundary c
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Figure 10.35 Experimental and simul
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References 1 Koesling, D., Tinius,
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steel billets into the semi-solid s
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412j 11 Thixoextrusion The followin
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414j 11 Thixoextrusion channel with
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416j 11 Thixoextrusion parameter co
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418j 11 Thixoextrusion Both concept
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420j 11 Thixoextrusion should be ju
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422j 11 Thixoextrusion Figure 11.8
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424j 11 Thixoextrusion Table 11.4 C
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426j 11 Thixoextrusion Temperature
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428j 11 Thixoextrusion impacts. Ext
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432j 11 Thixoextrusion shell format
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436j 11 Thixoextrusion Table 11.6 P
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440j 11 Thixoextrusion solidificati
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442j 11 Thixoextrusion GPa pressure
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444j Index arbitrary volume element
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446j Index equilibrium tests 141 eq
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448j Index - importance 273 ion flu
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450j Index oxygen-sensitive element
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452j Index - thixoforming 241 semi-
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454j Index - high pressure 131 - sc
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Thixoforming : Semi-solid Metal Processing

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