Steels continued high-alloy continued


Iron—Silicon Alloys. Iron—siHcon alloys, commercially known as siHcon steel, contain siHcon up to about 4%. The addition of siHcon to iron results ia several beneficial effects (/) siHcon iacreases the electrical resistivity, thereby reduciag the eddy-current loss and enhancing the a-c use of the alloy. This iacrease, together with the changes ia some magnetic properties, is illustrated ia Figure 3 (10). A fairly good approximation (13) relating the siHcon content and resistivity p ia fiQ-cm ia commercial alloys is p = 13.25 + 11.3 (% Si). (2) Because Si reduces the size of the y loop (fcc-phase field), high temperature heat treatment for purification and orientation control is possible without the deleterious effect of the CC- y-phase transformation. (J) Si decreases the value of the magnetocrystaUine anisotropy energy (Fig. 3) and thus tends to enhance the permeabiHty and to decrease the core loss. The  [c.369]

In steelmaking, various elements are added to the molten metal to effect deoxidation, control of grain size, improvement of the mechanical, physical, thermal, and corrosion properties, and other specific results. Originally, the chemical element to be incorporated into the steel was added to the bath in the form of an alloy that consisted mainly of iron but was rich in the desired element. Such alloys, because of their high iron content, became known as ferroalloys and were mosdy produced in iron blast furnaces. Later, the production of alloys for steelmaking was carried out in electric-reduction and other types of furnaces, and a number of these alloys contain very Httle iron. For this reason, the term addition agent is preferred when describing the materials added to molten steel for altering its composition or properties ferroalloys are a special class of addition agents.  [c.379]

Low—medium alloy steels contain elements such as Mo and Cr for hardenabiHty, and W and Mo for wear resistance (Table 4) (7,16,17) (see Steel). These alloy steels, however, lose their hardness rapidly when heated above 150—340°C (see Fig. 3). Furthermore, because of the low volume fraction of hard, refractory carbide phase present in these alloys, their abrasion resistance is limited. Hence, low—medium alloy steels are used in relatively inexpensive tools for certain low speed cutting appHcations where the heat generated is not high enough to reduce their hardness significantly.  [c.197]

High speed steels contain significant amounts of W, Mo, Co, V, and Cr in addition to Fe and C (18,19). The presence of these alloying elements strengthens the matrix beyond the tempering temperature, increasing the hot hardness and wear resistance. The materials are readily available at reasonable cost and exhibit the following desirable features through hardenabihty higher hardness than carbon steel and low—medium alloy steels good wear resistance high toughness (a feature especially desirable in intermittent cutting) and the abiUty to alter hardness appropriately by suitable heat treatment. This last facihtates manufacturing complex tools in the soft aimealed condition followed by suitable heat treatment for hardening and grinding of tools and cutters to final shape. Associated with the advantages are the following limitations hardness decreases sharply beyond 540°C, limiting these tools to low speed cutting operations (<30 m/min) wear resistance, chemical stabiUty, and propensity to interact chemically with the chip and the machined surface are limited and the chips tend to adhere to the tool.  [c.198]

The submitters employed a nickel autoclave and noted that product from Step D may contain a small amount of hydrogen chloride or chlorinated material than can adversely affect a stainless steel pressure vessel. Hastelloy C is a high-nickel alloy.  [c.154]

For erosive wear. Rockwell or Brinell hardness is likely to show an inverse relation with carbon and low alloy steels. If they contain over about 0.55 percent carbon, they can be hardened to a high level. However, at the same or even at lower hardness, certain martensitic cast irons (HC 250 and Ni-Hard) can out perform carbon and low alloy steel considerably. For simplification, each of these alloys can be considered a mixture of hard carbide and hardened steel. The usual hardness tests tend to reflect chiefly the steel portion, indicating perhaps from 500 to 650 BHN. Even the Rockwell diamond cone indenter is too large to measure the hardness of the carbides a sharp diamond point with a light load must be used. The Vickers diamond pyramid indenter provides this, giving values around 1,100 for the iron carbide in Ni-Hard and 1,700 for the chromium carbide in HC 250. (These numbers have the same mathematical basis as the more common Brinell hardness numbers.) The microscopically revealed differences in carbide hardness accounts for the superior erosion resistance of these cast irons versus the hardened steels.  [c.270]

Another approach for speeding PF resin cure utilizes faster phenolics as accelerators. The most popular of these has been resorcinol. Many different approaches have been tried. Resorcinol has often been cooked into the PF resin. This is probably the least effective approach available. Depending on the amount of resorcinol used and other reaction conditions, different results are obtained. If enough resorcinol is added to the beginning of the cook, a resorcinol-formaldehyde polymer will rapidly form. This polymer will contain little or no phenol. Thus, in a viscosity-limited system, the resin may hit the viscosity endpoint while still containing large quantities of raw phenol and formaldehyde. Meanwhile, the resorcinol-formaldehyde polymer will have exhausted all of the resorcinol functionality during its formation. Such a polymer will not show the rapid curing characteristics hoped for and will have high VOC emissions. If only a small amount of resorcinol is used, it will become thoroughly incorporated into the phenolic polymer and will show no special reactivity in cure. Sometimes, the resorcinol polymer made in the first case will break down in the presence of the excess phenol to give the same result as the second case. This will only happen if the reaction time and conditions are sufficient to allow it.  [c.918]

The scope of the term stainless steel has not been precisely defined, but for general purposes it may be considered to include alloys whose main constituent is iron but which also contain not less than 10% Cr. As with low-alloy steels, a distinction between low or medium carbon grades and high carbon grades must also be drawn, the latter being more in the nature of alloy cast irons. These are used mainly for oxidation resistance at high temperatures and for applications where abrasion resistance allied to a certain amount of corrosion resistance is required, and will not be considered in this section.  [c.518]

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.  [c.1270]

Increased use of galvanised steel for corrosion protection and alloy steels for weight reduction ia automobile manufacturiag are changing the character of prompt iadustrial scrap and shredded scrap. Prompt iadustrial scrap from automobile stamping plants contain increa sing amounts of siac-coated scrap which may be as high as 40—50% of the scrap generated. Scrapped autos also have higher zinc content ia the ferrous fractioa. About two-thirds of aew plant galvanising capacity is for the automotive market the test is for the building and constmction iadustries and appHances (21). Also, shipments of galvanised sheet by the domestic steel iadustry iacreased steadily siace 1991 to about 13 million t ia 1994. Imports of galvanised sheet have been substantial also, totaling about 1.7 million t ia 1994 (22). Zinc content of galvanised sheet may vary from <1% to at least 10% depending on sheet thickness and coating weight used. A rough estimate based on total sine used for galvanising and total galvanised sheet shipments, without accounting for sine losses during production, indicates an iadustry average of about 4%. Other sinc-containing coatings include Galvalume (Bethlehem Steel Corporation) and Zincrometal. Galvalume coating is an aluminum—sine alloy having <50% sine and, for a given coating weight, contains less total sine than galvanised steel. Zincrometal is a sine-based paint coating. The sine content of the coated steel is about 0.5%. The use of Zincrometal declined in the early 1990s. Remelting of sinc-coated scrap results in high loadings of sine and, to some extent, associated lead and cadmium, in the furnace dust. EAF furnace dust, listed as a hasardous waste, is receiving considerable research attention. Some of the dust is commercially processed for sine recovery and safe disposal.  [c.555]

High-chromium cast irons contain between 12 and 30 percent chromium, 1.5 to 3.5 percent carbon, and frequently contain molybdenum and nickel as secondary constituents. They have become standard in most secondary and tertiary dry-grinding apphcations (Durman, loc. cit.). These alloys form a metastable austenite structure on casting. Subsequent thermal processing forms secondary chromium-carbide particles dispersed through the matrix. This depletes the austenite of alloy content and facihtates transformation to martensite on quenching. The chromium carbide results in a slightly higher level of toughness than Ni-hard, and higher wear resistance because of greater hardness of chromium carbide. Molybdenum may be added to increase hardenabihty in heavy sec tions. Elimination of austenite in the structure can improve resistance to spalling, although spalling limits the range of uses. Hardness can range from 52 to 65 Rockwell. For ball mill balls the diy wear rate is often Mo that of cast or forged steel. The cost is 2-3 times as great, so there is an economic advantage. In wet grinding, however, the wear rate of chrome alloys is greater, so the cost may not be competitive. For ring-roll mills, high-chromium molybdenum parts have improved wear costs over use of Ni-hard, and also reduced labor costs for maintenance.  [c.1830]

All too frequently lubricants containing sulphur are exposed to more severe operating conditions than intended, and staining and corrosion results. This has given sulphur compounds and sulphur-containing additives, particularly those of the dithiosphosohate type, a bad name. Silver bearings are still used in certain diesel and aero-engines and if the lubricants for these engines contain sulphur compounds with too much chemical activity, severe corrosion ensues . A more widespread problem is the corrosion of phosphor-bronze alloys (containing about 10% tin) particularly in little-end bushes in diesel engines where temperature can exceed 200° C. Some engine builders and operators hold sulphur additives entirely responsible, but this opinion cannot be substantiated, for corrosion can occur with lubricants containing only natural sulphur compounds . Two important metallurgical factors, affecting the corrosion resistance of phosphor-bronze alloys are the amount of alloying element in solution in the copper-rich phase and the porosity of the alloy. For example, if the amount of tin in solution can be increased by special casting techniques or heat treatments the corrosion resistance is greatly increased. Similarly, zinc or silicon in solution also increases the resistance of copper to sulphur corrosion. If the alloy is porous the lubricant is drawn into the pores where it stagnates, and, at high temperatures, becomes very corrosive, e.g. copper catalyses oil oxidation with the consequent formation of corrosive sulphur compounds.  [c.451]

Applications The method can be adapted to barrel plating and to the mirror-spray technique The development of printed circuitry has stimulated demand for means of rendering parts of insulating surfaces conducting and solderable. Developments seem to be confined to deposition of single metal species e.g. Sn, Ni, Co, Ag, Cu, Pd and Au. The hypophosphite methodgives deposits which contain 8-10% of phosphorus. Such deposits are hard (e.g. 500 Hy) and brittle they are relatively pore-free and have good corrosion resistance, particularly if heat-treated. In general, the corrosion resistance is proportional to the phosphorus content, and such coatings can comply with Fed. Spec. QQ-N-290. Exposure tests have shown that 0.012 mm thick Ni-P coatings give better protection to steel than 0.025 mm of electrodeposited nickel. Their high resistance to wear has been proved by their application in, for example, surfacing moulding dies. These coatings have been used to protect a low-alloy pearlitic steel from corrosion in air at 650° C, and in superheated steam for up to l(X)0h (see also Section 13.7).  [c.437]


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Corrosion, Volume 2 (2000) -- [ c.0 ]