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Log In Sign Up. Analytical modeling of the thermomechanical behavior of ASTM F high nitrogen austenitic stainless steel used as a biomaterial under multipass deformation. Alberto M Jorge Junior. Bernardes a, Samuel F. Silva a, Gedeon S.

Reis a, Mariana B. Silva b, Alberto M. Ast interactions in ASTM F austenitic stainless steel were studied by means of Received 22 September hot torsion tests with multipass deformation under continuous cooling, simulating an industrial laminating pro- Received in revised form 14 January cess. Samples were deformed asstm 0.

The tests indicate that the stress level depends on deformation tempera- Qstm online 25 February ture and the slope of the equivalent mean stress EMS vs. Below the Tnr, strain-induced precipitation of Z- Biomaterial phase NbCrN occurs in short interpass times tpass b 30 sinhibiting recrystallization and promoting stepwise Recrystallization stress build-up with strong recovery, which is responsible for increasing the Tnr. At interpass times longer than Precipitates 30 s, the coalescence and dissolution of precipitates promote a decrease in the Tnr and favor the formation of re- Z-phase crystallized grains.

Introduction the friction, lubrication and heat transfer conditions are different, in- cluding ast, plastic f15886 determined in the simulation of the hot Austenitic stainless steels are being used as a material for orthopedic conformation physical equations of each process leading to optimal re- implants. ASTM F steel is currently the one most widely used by sults.

Thus, it is possible to evaluate the role of the Z-phase and the soft- Brazil’s National Health Service SUSbut it presents unsatisfactory me- ening mechanisms that occur during microstructural evolution, and to chanical and corrosion properties. Steels containing Mn, N and a low concentration of Ni, such as routes. ASTM F, have been developed to mitigate these problems. This In the manufacture of orthopedic prostheses, e. However, ing of prostheses [4,5].

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In the case of steels not subjected to phase trans- the interaction between precipitation and recrystallization of this steel formation during cooling after hot forging, controlled processing is is still not fully established. This characteristic makes it a promising sub- more restricted. One possibility is to zstm repeated recrystallization stitute of ASTM F steel in more critical applications of more severe of the austenite and prevent grain growth in the intervals between loading and longer periods within the human body.

A second alternative would be to accumulate strains below the Physical simulations of thermomechanical processing by miniaturized non-recrystallization temperature Tnrthereby increasing the number devices allow for the execution of designs with multipass deformation ap- of nucleation sites. Different microalloying elements have different erate during deformation and in the intervals between passes. However, effects on Tnr. The microalloying element present in the composition of the ASTM F steel under study is niobium Nbwhich is the most effective element for increasing the Tnr.

The aim is to determine the Tnr and its depen- steel, Z-phase is present at room temperature and is dissolved dence on the applied deformation per pass and the waiting time, ana- partially or totally during reheating at high temperatures.


This phase lyzing the action of softening mechanisms and the occurrence of is a little known complex nitride, f11586 tetragonal crystal structure precipitation, as well as its role in the shape of the curves. Material and method The Z-phase precipitation potential is determined from the solubility product by calculating the supersaturation of the microalloying ele- The austenitic stainless steel studied here is ASTM F used in ments at a given temperature, comparing the amount of dissolved the manufacture of orthopedic implants.

Table 1 describes the composition of this steel. The technique developed by Boratto et al. The test specimens were induction heated asfm a tempera- luted concentrations of elements in solution.

The temperature was controlled by o o means of an optical pyrometer. Cr, Nb and N in solution, one obtains the equation of the solubility prod- uct, which, according to Giordani [10], is expressed by: This interaction is important etching and supported on a mesh Cu grid.

Thin foil samples were because it determines the axtm mechanisms that act during hot processing, and therefore, the resulting microstructural evolution. Note that the curves are clearly separable into two regions with different slopes in EMS. Equivalent mean stress EMS vs.

Geminga Medical: Materials

This increase causes the slope of the EMS vs. The steeper slope of the line in region II is an indication that, in addition to the increased strength of the material in response to EMS MPa stress built up through the decrease in deformation temperature, another hardening mechanism is activated simultaneously, leading to the onset of strain-induced precipitation.

Thus, Tnr represents the temperature at which recrystallization is no longer completed in the intervals between passes. Therefore, the change in inclination, and hence, in the level of stress is associated with the microstructural evolution taking place during and between multipass deformations. This increase is due to the decrease in deformation temperature and the longer time required for the softening phenomena to act when Fig.

This is deformed grains, characterizing the subsequent softening, with short interpass times not affecting the EMS, which thus becomes only a func- tion of temperature. Finally, in the low tem- perature region below Tnr, note the stress build-up with intense recov- ery, and partial interpass recrystallization with strong hardening high EMS and high incidence of strain-induced precipitation, changing the slope of the curve.

At high temperatures the precipitates are more stable, such as Z-phase and NbN, which are the ones most likely to interact with the recrystallization kinetics, where a delay in the recrystallization kinetics with an increase in EMS, Fig. Analysis by TEM of carbon replicas and thin foils under the conditions: Thereafter, tron diffraction, Fig.

Note the precipitates coarsening when the time the Tnr decreases as the interpass time increases. Also note that the Tnr in- between passes is increased. As can be seen, the Tnr reaches a The increase in EMS in the initial deformation passes above Tnr at maximum at about 30 s, presenting basically two regions: At temperatures below Tnr, recrystallization is due to strain-induced precipitation, which is time-dependent, such that delayed by the presence of strain-induced precipitation of Z-phase par- the effect of Tnr retardation increases in these deformation conditions.

As the tem- comes less effective due to coalescence and dissolution of the precipitates, perature decreases, the recrystallization phenomenon decreases and thus increasing the extent of recrystallization and reducing Tnr. It should be noted that the effect of solute N, Mo, Nb and stacking interpass time increases, see Fig. Energy dispersive X-ray spectroscopy: Note that, unlike the data obtained by previous methods, precipitation may occur at higher 3. Precipitation will probably always occur below this temperature, as already observed in the previ- In Fig.


In these experi- directly from the EMS vs. Considering that complex, since the tests were performed under continuous cooling. Using these equations, corrections in question. The result of these corrections is depicted in Fig. Starting from the second and third reloadings, there is The curves shown in Fig. In the second reloading, the perature.

Dependence of non-recrystallization temperature Tnr on interpass time tpass and applied strain per pass. The microstructure in Fig. However, this does not cause dynamic recrystallization DRX of this steel because of interpass precipitation. From the mechanical standpoint, a comparison of the multipass curves corrected at constant temperature and those obtained from the continuous isothermal runs Fig.

With the increase in deformation during reloading, the curve reaches stress levels above the curves obtained in the contin- uous isothermal runs [20]. Calculation of the supersaturation through the solubility product of grains and twinning. Tests with multipass deformations under continuous cooling indi- However, the stored energy increases with applied deformation, i.

In from the matrix by the precipitates that are formed, decreasing its me- other words, this material cannot withstand an increase in loading, chanical strength and corrosion resistance [17]. When the interpass time is short less than 30 sre- [1] M.

Planell, Biomaterials in orthopaedics, J. Interface 5 — At interpass times of more [2] E. Balancin, Proportion of recovery and recrystallization during inter-pass times at high temperatures on a Nb- and N-bearing austenitic than 30 s, the coalescence and dissolution of precipitates reduce stainless steel biomaterial, Scr.

Vannevik, Characterization of a nitrogen-rich austenitic stainless steel used for osteosynthesis devices, J. Cohen, Niobiun carbonitride precipitation and austenite recrystallization in hot-rolled microalloyed steels, Metall. Giordani, Evidence of strain-induced precipitation on a Nb- and N-bearing aus- tenitic stainless steel biomaterial, Mater.

Forum — — Grong, Analytical modelling of grain growth in metals and alloys in the presence of frowing and dissolving precipitates—I. Normal grain growth, Acta Metall. Agren, Precipitation reac- tions caused by nitrogen uptake during service at high temperatures of a niobium stabilised austenitic stainless steel, Acta Mater. Jonas, Effect deformation parameters on the no- recrystallization temperature in Nb-beating steels, Metall. A 24A — Physical Metallurgy of Fig.

A austenite and on strain induced precipitation kinetics, Scr.

Medina, Evolution of austenite static recrys- [14] E. Jonas, A one-parameter approach to determining the critical condi- tallization and grain size during hot rolling asrm a V-microalloyed steel, Mater.

Norma ASTM Fe1

aztm Jonas, Dynamic and post-dynamic f15866 [15] S. Yue, The necessity of dynamic precipitation for the occurrence of crystallization under hot, cold and severe plastic deformation conditions, Prog.

A 69— Balancin, Dynamic recovery and dynamic recrystallization competition on a Nb- and N-bearing austenitic stainless. Remember me on this computer. Enter the email address you signed up with and we’ll email you a reset link. Click here to sign up. Help Center Find new research papers in: