Cold work, percent

Ferritic stainless contains 15 to 30 percent Cr, with low carbon content (0.1 percent). The higher chromium content improves its corrosive resistance. Type 430 is a typical example. The strength of ferritic stainless can be increased by cold working but not by heat treatment. Fairly ductile ferritic grades can be fabricated by all standard methods. They are fairly easy to machine. Welding is not a problem, although it requires skilled operators. 

It is sometimes convenient to express the degree of plastic deformation in metals as the percent cold work, CW%, rather than as strain ... 

The types of stainless steel included in the 300 series are hardenable only by cold-working those included in the 400 series are either nonhardenable or hardenable by heat-treating. As an example, type 410, containing 12 percent chromium and no nickel, can be heat-treated for hardening and has good mechanical properties when heat-treated. It is often used as a material of construction for bubble caps, turbine blades, or other items that require special fabrication. 

At room temperature the yield and ultimate strengths were in the range of 250,000 psi for both sizes of wire, with the 0.005-in.-diameter wire possessing somewhat higher values. The ductility, as determined by percent reduction in area, was appreciably higher for the 0.010-in.-diameter samples as compared-to the 0.005-in.-diameter wires (51 % vs. 18%) because of the additional cold work contained in the latter samples. 

According to the systematic study by Ross (1967) of the effect of cold rolling on the hardness of yttrium and twelve of the lanthanide metals, the hardness of all metals except La, Nd, Er, Y, and perhaps Sm tends to increase rapidly during the initial 20-25 percent reduction. Further hardening does not occur until reductions of the order of 60 percent (see fig. 8.5). This is in agreement with the earlier work by Love (1960) on erbium and dysprosium shown in fig. 8.6. A comparison of the effect of 50 percent cold work by swaging (Love, 1959) or... 

Fig. 8.9. Effect of annealing temperature and rate of cooling from annealing temperature on the hardness of 30 percent cold worked yttrium. From Bohlander (1961).

Percent cold work-dependence on original and deformed cross-sectional areas... 

FigMre 7.19 For 1040 steel, brass, and copper, a) the increase in yield strength, b) the increase in tensile strength, and (c) the decrease in ductihty (%EL) with percent cold work. 

It is first necessary to determine the percent cold work resulting from the deformation. This is possible using Equation 7.8 ... 

Figure 7.23 The variation of recrystallization temperature with percent cold work for iron. For deformations less than the critical (about 5%CW), recrystallization will not occur.

Degree of plastic deformation may be expressed as percent cold work, which depends on original and deformed cross-sectional areas as described by Equation 7.8. 

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