Cold-working hardening

The Brinell test range is limited, by the capabUity of the hardened steel baU indenters used, to HBN 444. This range can be extended upward to HBN 500 by using special cold work-hardened steel baUs and to as high as HBN 627 by using special tungsten carbide bads. 

Fig. 8. Microhardness profile across interfaces of two types of explosion clads that show widely divergent response resulting from the inherent cold-work hardening characteristics where Q represents the 3.2-mm type 304L stainless/28.6-mm, A 516-70 control (before cladding) ( ) = clad + flat ...

In swaging, the material has an almost constant cold work hardening over the entire cross-section. Nevertheless, even at the highest deformation ratios, a residual strain remains that is sufficient for a follow-up forming process. 

Suitable for severe cold heading or cold forming lower cold-work-hardening rate than type 305. Bolts, rivets, screws, instrument parts. 

CH Cold work hardened HK Knoop hardness number... 

CHA Cold work hardened, aged HLLW High level liquid waste (nuclear)... 

Too much cold working hardens steel, and harder steel cracks more easily than soft. Perhaps some of our knives, the cracked ones, were overworked by an overzealous hammer operator, or perhaps they were stamped too hard by a super-patriot. Another source of cracks could have been a slip of the polishing wheel or serration cutter or any such tool capable of introducing a nick or nucleus from which a fatigue or other type of crack could get a head start and grow prematurely. Or the knives may have been cooled unevenly or too rapidly, and this could have left residual manufacturing stresses in the blade. 

Steels iu the AISI 400 series contain a minimum of 11.5% chromium and usually not more than 2.5% of any other aHoyiag element these steels are either hardenable (martensitic) or nonhardenable, depending principally on chromium content. Whereas these steels resist oxidation up to temperatures as high as 1150°C, they are not particularly strong above 700°C. Steels iu the AISI 300 series contain a minimum of 16% chromium and 6% nickel the relative amounts of these elements are balanced to give an austenitic stmcture. These steels caimot be strengthened by heat treatment, but can be strain-hardened by cold work. 

Properties. Table 1 hsts many of the physical, thermal, mechanical, and electrical properties of indium. The highly plastic nature of indium, which is its most notable feature, results from deformation from mechanical twinning. Indium retains this plasticity at cryogenic temperatures. Indium does not work-harden, can endure considerable deformation through compression, cold-welds easily, and has a distinctive cry on bending as does tin. 

Mechanical Properties. An advantage of the two corrosion-resistant alloys is that they may be strengthened considerably by cold working. MP35N alloy is iatended for use ia the work-hardened or work-hardened and aged condition, and the manufacturers have suppHed considerable data concerning the mechanical properties of the alloy at different levels of cold work. Some of these data are given ia Table 8. 

Most wrought alloys are provided in conditions that have been strengthened by various amounts of cold work or heat treatment. Cold worked tempers are the result of cold rolling or drawing by prescribed amounts of plastic deformation from the annealed condition. Alloys that respond to strengthening by heat treatment are referred to as precipitation or age hardenable. Cold worked conditions can also be thermally treated at relatively low temperatures to affect a slight decrease in strength (stress rehef annealed) to benefit other properties, such as corrosion resistance and formabiUty. 

Demonstrations Take a strip — 0.25 mm X 1 cm X 15 cm of cold-rolled (work-hardened) brass and bend it (on edge) on the overhead until permanent deformation takes place. Anneal brass strip at bright red head for — 0.5 min to soften it. After cooling replace on overhead and show that permanent deformation takes place at a much smaller deflection than before. This illustrates the importance of large Uy in springs. 

Work hardening is achieved by cold rolling. The yield strength increases with strain (reduction in thickness) according to... 

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