Steels age-hardening

Maraging steels are a class of high strength steels of very low carbon content. Strengthening is achieved by the use of substitutional elements to produce age hardening in the martensitic iron-nickel matrix. The term maraging was thus coined from the words martensite and age hardening . 

The discussion so far has been limited to the structure of pure metals, and to the defects which exist in crysteds comprised of atoms of one element only. In fact, of course, pure metals are comparatively rare and all commercial materials contain impurities and, in many cases also, deliberate alloying additions. In the production of commercially pure metals and of alloys, impurities are inevitably introduced into the metal, e.g. manganese, silicon and phosphorus in mild steel, and iron and silicon in aluminium alloys. However, most commercial materials are not even nominally pure metals but are alloys in which deliberate additions of one or more elements have been made, usually to improve some property of the metal examples are the addition of carbon or nickel and chromium to iron to give, respectively, carbon and stainless steels and the addition of copper to aluminium to give a high-strength age-hardenable alloy. 

ASTM A561 Hot rolled and cold finished age hardening stainless and heat resisting steel bars, wire and shapes G4303 G4309... 

Hawley(Ref 8) give an example of wrought "age-harden able" alloys which are modifications of Duralumin or of castable alloys containing Al and ca 12%. Other industrial products of Al alloys are granules of various sizes used for adding to molten steel, for Thermite reactions and for expls. F.equire-... 

Hawley(Ref 8) give an example of wrought "age-hardenable" alloys which are modifications of Duralumin or of castable alloys containing Al and ca 12%. Other industrial products of Ai aiioys are granules of various sizes used for adding to molten steel, for Thermite reactions 3nd for expls, Renulre ments of the most important alloy of Al(Mg-Al) used in expls are described in a joint Army-Navy Spec(Ref 3). The tests and detns are listed under Aluminum (Analytical Procedures). The aiioy of Ai with Mg is used in pyrotechnic compositions and as a metal additive to some fci h explosives... 

T. Nelson, R. Steel, and W. Arbegast, In Situ Thermal Studies and Post-Weld Mechanical Properties of Friction Stir Welds in Age Hardenable Aluminum Alloys, Sci. Technol. Weld. Joining, Vol 8 (No. 4), 2003, p 283-288... 

Cu rich alloys having high strength and high electrical conductivity, and age-hardenable Fe rich alloys can be developed through consideration of the Cu-Fe-Mo phase diagram. Molybdenum is added to steels traditionally in order to improve their mechanical properties, in particular ductility, since molybdenum promotes grain refinement. The additions of copper to steels increase their corrosion resistance and improve formability. 

Table 2 lists n values for several materials [1]. Typically, the n values for most metals vary between 0.1 and 0.5. The n values of aluminum alloy sheets decrease sharply with an increase in the tensile strain and are lower than those of steel sheets. The n value of commercial HSLA steels decreases with increasing strength and its low n value makes it less formable than mild steel [38]. There are different strain hardening behaviors for mild steels and high-strength steels. The strain distribution ability of steels increases with the increase in overall n value. The peak n value at a low strain level increases the strain distribution ability of the steel. Aging of rimmed steels causes the n value to decrease with time. Additionally, excessive temper rolling beyond that required to eliminate YPE (Cv) will also reduce the n value. 

Hsi] Hsiao, C.N., Yang, J.R., Age Hardening in Martensitic/Bainitic Matriees in a Copper-Bearing Steel , Mater. Trans., JIM, 41(10), 1312—1321 (2000) (Experimental, Morphology, Meehan. Prop., 25)... 

Mey] Meyer, L., On the Dissolution, Precipitation, and Age Hardening Effect ofNiobium in Plain Carbon Steel (in German), Z. Metallkd., 58(5), 334-339 (1967) (Experimental, Morphology, Phase Relations, Thermodyn., 21)... 

In addition to hydrogen embrittlement, brittle failure can occur as a result of stress corrosion, liquid metal attack, or strain-age hardening. The last mentioned cause is well known and can occur on strained steel of any strength but seldom actually occurs in modem steels it is adequately documented in Appendix E of BS 729 (British Standards Institution, 1971 reaffirmed in 1986) users often erroneously refer to this effect as hydrogen embrittlement. This clearly states that strain-age embrittlement is the only type of embrittlement that can be aggravated by the hot dip galvanizing process. 

Alloys having litde or no sensitivity are claimed to be 7075-T6 aluminum Haynes 188 (cobalt-base) beryllium copper (copper-base) Types 304, 316, and 310 austenitic stainless steels Type 430 high-hardness ferritic steel and age-hardened austenitic A286 steel. Titanium-base alloy T1-6A1-4V exhibits moderate sensitivity. Alloys with high sensitivity are Haynes 25 (cobalt-base) and iron-base alloys, including medium- and high-strength steels. 

Additions of aluminum enhance high temperature oxidation resistance. Aside from corrosion performance, this element is added to some precipitation-hardening stainless steels to promote age hardening (e.g., S13800). In contrast, a small amount of aluminum is present in Type 405 stainless (S40500) to prevent hardening by stabilizing the ferrite phase. 

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