Fatigue in Binary Alloys of bcc Iron
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I.
INTRODUCTION
O N E of the keys to designing an engineering alloy is to explore the effects of each of its constituent elements on the behavior of base metal. Since this type of investigation may be of aid in designing alloy compositions with excellent properties, it is unquestionably of practical as well as theoretical interest. As extensively reviewed by Leslie, ~ considerable work has been done on the plastic deformation behavior of ferrite, the matrix of many constructional steels. However, relatively little is known about the effects of alloying elements on the fatigue properties of a-iron (ferrite). The most systematic study performed in this field so far is the one by Epremian et al.2; however, the number of elements that they studied was limited and they determined only S-N properties. No systematic study concerning the effects of alloying elements on the fatigue crack propagation (FCP) behavior of a-iron has been performed to date. In this study the influence of various substitutional solute elements on the high cycle fatigue properties of a-iron was evaluated experimentally.
II.
EXPERIMENTAL PROCEDURE
The base material used was an electrolytic iron containing 0.002 wt pct C, < 0 . 0 2 wt pct Si, < 0 . 0 2 wt pct Mn, 0.004 wt pct P, and 0.006 wt pct S. A set of 38 binary ferrites containing A1, Co, Cr, Cu, Mn, Mo, Nb, Ni, Si, Ti, V, or W alloyed from 1 to 5 wt pct or up to the solid solubility limit of the element in a-iron was induction melted in vacuum and cast into 14 kg ingots (70 mm • 70 mm • 300 mm). High purity metals and ferro alloys were used in making the ingots of these binary alloys. Deoxidation was accomplished by adding 0.015 wt pct Si and 0.015 wt pct A1. Table I gives the chemical analysis of the ferrites in wt pct. Solid solubility limit of each alloying element at 700 ~ in a-iron 3 is also listed in the table. Throughout the subsequent text of this paper Fe-2 wt pct AI, for example, will simply be denoted as 2 AI; two wt pct in this expression indicates the nominal (not analyzed) alloy content. Each ingot was hot forged at around 1100 ~ to a plate of 45 mm in width and 10 mm in thickness. The surfaces were machined to remove oxide layers and then the thickness was HITOSHI ISHII, Associate Professor, TADASHI KAWARAZAKI, Technical Official, and YOSHINORI FUJIMURA, Professor, are all with the Department of Mechanical Engineering, Shizuoka University, 5-1, Johoku 3 chome, Hamamatsu 432, Japan. Manuscript submitted April 26, 1983. METALLURGICALTRANSACTIONS A
Table I. Concentration 'of Alloying Elements and Their Solid Solubility Limit at 700 ~ in Binary Ferrites (Wt Pct)
Alloying Element
1
Level of Element 2 3 5
A1 Co Cr Cu Mn Mo Nb Ni Si Ti V W
1.20 1.00 1.01 1.00 1.10 1.00 0.82 0.99 1.01 0.97 0.90 0.98
1.99 2.91 4.00 1.98 2.99 4.99 1.85 2.89 4.61 2.02 2.01 3.03 4.86 2.11 2.00 1.87 1.97 2.15
3.02 4.64 3.07 2.78 2.98 5.38 2.99 4.99
Solubility Limit 33.4 75.5 100 0.7 3.0 6.6 1.0 4.4 5.5 2.2 100 5.5
reduced to 4 mm by cold rolling. After process annealing at 800 ~ for one hour i
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