Seasonal cracking of brass

Many of the alloys of copper are more resistant to corrosion than is copper itself, owing to the incorporation either of relatively corrosion-resistant metals such as nickel or tin, or of metals such as aluminium or beryllium that would be expected to assist in the formation of protective oxide films. Several of the copper alloys are liable to undergo a selective type of corrosion in certain circumstances, the most notable example being the dezincification of brasses. Some alloys again are liable to suffer stress corrosion by the combined effects of internal or applied stresses and the corrosive effects of certain specific environments. The most widely known example of this is the season cracking of brasses. In general brasses are the least corrosion-resistant of the commonly used copper-base alloys. 

Two of the earliest and classic examples of stress corrosion are the seasonal cracking of brass cartridge cases and the caustic embrittlement of riveted steel locomotive steam boilers. Ammunition becomes worthless during the wet seasons, and boilers explode because of cracks that started near the rivets or stressed areas. 

Season-cracking" of brass as intergranular corrosion Moore, Beckinsale... 

The first recognized case of environmentally induced corrosion was that of seasonal cracking of brass in the rainy season. It was a classical example of SCC of brass in ammoniacal environment. Soon upon being realized as a major mechanism, it became the subject of intense research and a brief review of literature would show that thousands of papers have been written on the subject. The most intriguing is the mechanism of stress corrosion cracking and stress corrosion crack propagation. A full discussion of the mechanism is beyond the scope of this chapter. An online search would reveal thousands of articles and update references. Four basic categories of mechanisms have been proposed ... 

What is the seasonal cracking of brass How it is caused and prevented ... 

The two classic cases of stress-corrosion cracking are the season cracking of brass, and the caustic embrittlement of steel. Both of these obsolete terms describe the environmental conditions... 

Season Cracking—stress corrosion cracking of brass. 

Season Cracking cracking resulting from the combined effect of corrosion and stress, which is usually confined to the stress-corrosion cracking of brass in ammoniacal environments. 

Season cracking of high zinc brasses is a severe form of embrittlement resulting in cracking or disintegration. Somewhat similar forms of stress-corrosion cracking occur in many other metals and alloys. Embrittlement of boiler plate, discussed below, may be considered a special case. 

T.C. Wilson, G. Edmunds, E.A. Anderson, and W. Peirce, Effect on Season Cracking of Alloy Additions to Cartridge Brass, Sym-... 

Seasonal cracking This refers to the cracking of brass in ammoniacal environment. 

Seasonal cracking This is the cracking of brass and copper alloys in ammoniacal environment. This particularly happens in rainy seasons in the tropics. 

Minor additions of arsenic (0.02—0.5%) to copper (qv) and copper alloys (qv) raise the recrystaUization temperature and improve corrosion resistance. In some brass alloys, small amounts of arsenic inhibit de2incification (22), and minimise season cracking. 

Nitrogen compounds These also arise from both natural and synthetic sources. Thus ammonia is formed in the atmosphere during electrical storms, but increases in the ammonium ion concentration in rainfall over Europe in recent years are attributed to increased use of artiflcial fertilisers. Ammonium compounds in solution may increase the wettability of a metaland the action of ammonia and its compounds in causing season cracking , a type of stress-corrosion cracking of cold-worked brass, is well documented. 

Failure of copper alloys may occur by cracking due to the combined influence of tensile stress and exposure to a corrosive environment. When the stresses are produced in components during manufacture the trouble is usually known as season cracking and failures of brass components due to this form of stress corrosion have been known for many years ... 

Typical examples of this form of corrosion include seasonal cracking in cold-formed or rolled brass in environments containing ammonia and the cracking of austenitic stainless alloys in the presence of chlorides. 

Failure of copper alloys may occur by cracking due to the combined influence of tensile stress and exposure to a corrosive environment. When the stresses are produced in components during manufacture the trouble is usually known as season cracking and failures of brass components due to this form of stress corrosion have been known for many years Only certain specific environments appear to produce stress corrosion of copper alloys, notably ammonia or ammonium compounds or related compounds such as amines. Mercury or solutions of mercury salts (which cause deposition of mercury) or other molten metals will also cause cracking, but the mechanism is undoubtedly different. Cracks produced by mercury are always intercrystalline, but ammonia may produce cracks that are transcrystalline or intercrystalline, or a mixture of both, according to circumstances. As an illustration of this, Edmunds" found that mercury would not produce cracking in a stressed single crystal of brass, but ammonia did. 

The residual stress in a metal, or more commonly an alloy, wiU, in certain corrosive environments, result in mechanical failure by cracking. It first became apparent at the end of the nineteenth century in brass (but not copper) condenser tubing used in the electric power generating industry. It was then called season cracking. It is usually prevalent in cold-drawn or cold-roUed alloys which have residual stress. Heat treatments to relieve this stress were developed to solve the problem. It was soon realized that there were three important elements of the phenomenon the mechanical, electrochemical, and metallurgical aspects. 

Although the susceptibility to SCC is decreased by annealing the brasses, they are still sensitive to seasonal cracking in ammonia contaminated environments, particularly the agricultural land. Literature is abundant on the subject and the readers may refer to some of the references cited at the end of the chapter. 

During the rainy season, the British Army in India did not often go out and stored weapons and ammunition in the stables. At the end of the monsoon, when taking up arms again, the soldiers saw that many cartridges in brass 70/30 were unusable because of cracks. Since these problems were related to the season and did not occur during the dry season, corrosion experts in the UK coined the term season cracking for this type of corrosion. It was not until 1921 that an explanation could be given for this phenomenon ... 

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