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Iron, Carbon Steel, and Alloy Steel by H. S. link and R. J. Schmitt, Applied Research Laboratory, U . S. Steel Corp., Monroeville, Pa. Improved compositions and more economical processing procedures have lowered product costs Marked weight reduction is now possible in many structures by use of higher strength iron and steel Carbon and low alloy steels may be practical for boiling water nuclear power plants D u n m c 1959 AND 1960, a major effort of the iron and steel industry has been directed toward lowering costs of ferrous products. I n the design of many structures, higher allowable stresses are used to take full advantage of the weight-saving potential of high-strength steels and constructional alloy steels. Increased interest in higher yield-strength steels has led to lower cost versions, so that even greater economies are now possible in certain applications. Savings are also made by using improved carbon-steel products and iron castings for many items that previously required more expensive steels. Porcelain-enameling steels that do not require a ground coat are examples. Iron and steel have maintained their position as basic materials of construction in the chemical and petroleum industries and have expanded into new areas. Preliminary corrosion studies have shown that steel will probably be the best allaround construction material for economical saline water conversion plants. Steel is already the basic material of construction for many plants utilizing sea water, Extensive corrosion testing has shown that steel may be practical for use in boiling water nuclear power plants. Steel has the necessary high-strength properties at ambient and elevated temperatures required for high-speed aircraft and missiles and is being used more extensively than ever before in these applications. Also, development of an inexpensive, high current capacity potential controller has made anodic protection of immediate value in controlling corrosion of iron and steel chemical process and storage equipment. This review covers literature published during 1959 and 1960. Iron Nodular iron castings are being used more extensively in applications that previously required forgings or weldments of carbon steels (74A). I n studies to de-
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velop more economical techniques of promoting graphite nodule formation, one investigator (6A) found that magnesium halides in combination with NaCl and/or CaSin were effective spheroidizing agents for relatively low-sulfur gray irons. To obtain reasonable efficiency, the salt was added immediately after slag removal. I n calcium-spheroidized iron, the spheroidizing action was restricted by residual titanium in the melt (8A). Additions of misch metal, along with metallic calcium, counteracted this effect. A relationship among tensile properties, hardness, and composition of ductile iron was shown by regression analysis of data from production heats (73A). Equations for predicting tensile properties from this relationship had 95% confidence limits for as-cast iron but were less applicable for heat-treated castings. I n contrast to a general belief that structure and properties of cast iron are impaired by tin, additions of small amounts were found to be beneficial to both gray and nodular irons ( 3 A , 72A). The main effect was to eliminate ferrite and promote pearlite formation, with no change in graphite form attributed to tin. ‘4more realistic specification of grayiron castings is made possible by a recent revision ( 7 7.4) of ASTM A 48 which takes into account the size factor of castings and provides instructions for obtaining the test bar. -4program for standardizing procedures for impact testing of gray cast iron is being sponsored by the International Committee on Methods of Testing Cast Iron, and a procedure for this type of testing has been proposed ( 7 A ) . A new cast-pin tear test for evaluating susceptibility of castings to cracking during solidification was proposed ( 7 A ) . In studies of the effects of various elements on properties of gray cast iron, lead was found ( 4 A ) to cause a loss in transverse strength because of the formation of a Widmanstatten type of graphite. This is believed to be a cause of premature cracking sometimes exhibited by heavy castings. Improved high tempera-
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ture properties-both short-time tensile and creep rupture-of gray-iron castings were attributed to addition of up to about 2.OyO molybdenum (77A),and improved crystal structure, strength, and hardness resulted from copper additions ( Z A ) . Ductility of high-carbon gray irons was markedly lowered when manganese content was greater than about 0.5% (76A). However, with manganese content less than about O.6%, ductility was significantly increased by inoculation. Calcium was the most effective inoculant for hypoeutectoid gray irons ( 9 A ) , improving graphite distribution and mechanical properties. Graphitization of malleable cast iron was reported to be improved by additions of CaSi? (IOA) and boron ( 7 5 A ) and by vacuum degassing ( 5 A ) . Calcium silicide effectively promoted graphitization, even in irons that contained less than 0.5% silicon. Although boron caused a loss in tensile strength, this could be counteracted by separate addition of copper. Additional benefits from vacuum degassing were elimination of blow holes and microporosity defects.
Carbon and low-Alloy Steels Until recently, the highest available minimum yield points in carbon steels for general structural applications have been 32,000 or 33,000 p.s.i,, in accordance with ASTM Specification A 373 or A 7, respectively. A new ASTM Specification, A36-60T, makes available carbon steel with a minimum yield point of 36,000 p.s.i. for these applications (7B). Yield-point increase is obtained by increasing the manganese content. New lightweight wide-flange beams are now being produced by the steel industry in all rolled-beam depths of 12 inches and larger. Savings in weight from 3 to 18% can be obtained. Weight savings provided by new section sizes, together with those of A 36 steel, will improve the competitive position of carbon steel in construction.
High-strength low-alloy steels (50,000 p.s.i. minimum yield point) are being applied more extensively in construction of buildings, bridges, and vehicles to obtain either appreciable weight reductions or greater durability at the same weight (9B). In the last review (September 1959, Pt. 11, p. 1178), niobium-bearing carbon steels with improved yield points and notch toughness were described. Since then, they have been marketed as economical high-strength steels by most major steel companies. However, because it is now generally recognized that niobium impairs the notch toughness of hot-rolled product (5B), the new steels have been largely confined to light-gage material (less than 0.5 inch thick) in which adequate notch toughness can be obtained by controlling composition within specific limits. Two tentative standards concerning high-strength steels for plates, bars, and structural shapes were issved by ASTM ( I B , 2B). These standards provide specifications for high-strength steels for bolted and riveted structures (A44059T) and for welded structures (A4416OT) ; the A 441 steels are characterized by minimum 0.02y0 vanadium content. Because of the growing stockpiles of depleted uranium, efforts are being made to find nonnuclear uses for this product (GB). Experiments to utilize uranium for alloying of steels have been reported, but specific test results have not been published. A marked increase in strength, toughness, and corrosion resistance has been claimed for addition of uranium to plain carbon steel. Although the experimental steels are reportedly not radioactive, development of commercial processes for uraniumbearing steels is not imminent. T h e suitability of niobium-bearing carbon-manganese steels for hot-rolled and cold-expanded line pipe is being investigated (72B). Present results indicate that minimum yield strength of 60,000 p.s.i. could be attained. However, further studies are required to determine whether pipe has satisfactory weldability and notch toughness. The use of deformed steel bars with minimum yield points of 60,000 and 75,000 p.s.i. for reinforcing concrete is now permitted by the American Concrete Institute building code. Although demand is low, increased use is expected especially in larger concrete columns. Tentative ASTM specifications for bars are A432-60T and A434GOT, respectively (7B). Cold extruding (4B, 7 8 ) is finding increased favor for certain carbon-steel and alloy-steel automotive parts that formerly required forging or machining. More commercial use will be made of this versatile technique when additionah technical and production knowledge is gained. Elevated-tem-
perature drawing techniques, discussed more completely under Alloy Steels, are also used to obtain increased strength in carbon steel bars (7OB). An annealing method utilizing loosely wound coils is gaining wide acceptance for processing sheet and strip steels (3B). Marked reductions in time required to anneal cold-rolled product are obtained with this new method which also provides decarburization or gas alloying, of coiled product as desired. Improved techniques continue to be developed. With regard to gas alloying, a recent study (73B) showed that chromiumdiffusion treatments provide a surface alloy layer on plain carbon steel that resists oxidation without appreciably affecting bulk properties. Thus, such treatment can upgrade the oxidation properties of carbon steel to those of high-alloy steels. Research in Russia (77B) has indicated that surface hardness and corrosion resistance of steel can be improved by boronization. I n the past, porcelain enamelers found two coats of enamel necessary for the regular low-metalloid enameling steels available to them. Recently developed special enameling steels do not require the conventional ground-coat, but new pretreatments are needed to promote direct white-enamel adherence. Development and use of steel sheets with decorative vinyl protective coating has advanced rapidly. Improved forming and joining techniques (8B), as well as improved properties of the material itself, have been responsible for a substantial increase in applications for the product, which may have a galvanized or uncoated steel base.
Alloy Steels The trend toward higher allowable stresses in structural design is especially apparent in alloy steels (75C). Heattreated constructional alloy steels with minimum yield strengths of 80,000 to 100,000 p.s.i. are now available from several sources. As the result of design improvements, light-gage plate and sheet material of these high-yield-strength steels is being used in applications where heavier gages of carbon steel were formerly used. I n the field of astronautics, the need for weight savings is obvious, and the search for satisfactory higher strength materials is intense. Efforts to develop an improved sheet material for rocketmotor cases of solid-fuel missiles have been of particular importance. The material generally used has been quenched and tempered sheets of medium-carborl alloy steels. Although performance of sheets with yield strengths up to about 220,000 p s i . has been satisfactory, those with higher strengths have shown poor fracture toughness. Efforts to improve fracture toughness
of ultra-high-strength steel sheet include evaluation of procedures such as vacuum-consumable electrode melting, controlled decarburization, cladding, and warm working. Sheets of AIS1 Type 41XX steels modified with additions of cobalt are reported (ZC, 8C) to have yield strengths as high as 235,000 p.s.i., low notch sensitivity, and satisfactory weldability and formability for rocket motor cases and other missile and airframe applications. Techniques involving variations of so-called warm working or hot-cold working procedures (5C, 77C, 72C) for developing higher strengths and other desirable mechanical properties in alloy steels have received much attention during the past several years. Yield strengths of 320,000 p.s.i. and higher, together with good tensile ductility, have been exhibited by some mediumcarbon and high-carbon alloy steels after the steels had been deformed in the metastable austenite condition and then quenched and tempered. Although promising results are being obtained, commercialization does not appear likely in the near future. However, commercial use is being made of a warm-drawing process that reportedly develops tensile properties in hot-rolled alloy steel bars equivalent to those expected in quenched and tempered product. This process, less costly than conventional heat-treatment, is also supposed to provide machining characteristics better than bars quenched and tempered to the same strength level. Increased industrial, military, and medical use of liquefied gases has emphasized the need for moderate-strength steels with good notch toughness at temperatures as low as -320" F. At present, the most promising alloy steel for cryogenic applications is the 9% nickel steel (ASTM A 353) used either in the double-normalized and tempered or quenched-and-tempered conditions. Recent burst tests of refrigerated full-size cylindrical and rectangular vessels indicated (4C, 70C) that welded 9% nickel steel vessels apparently do not require stress-relieving treatments as now specified by the ASME pressure-vessel code. Continuing work on brittle fracture of large rotors has led to a better understanding of relationships between conventional notch-toughness tests and fracture behavior of notched spin-disks and full-size forgings under high-speed rotation (IGC, 77C). Improvements in the notch toughness of rotor steels have continued, with V-notch Charpy 507, shear transition temperatures of many recent Ni-Mo-V steel forgings being within the range of 35' to 75' F. Widespread use has been made of vacuum-casting techniques in commercial production of alloy steels. By late 1959, all domestic producers of heavy forgings had installed facilities for VOL. 53, NO. 7
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vacuum casting. Because dissolved bydrogen is reduced to low levels by this process, problems of thermal flaking and poor tensile ductility (long associated with hydrogen) have been eliminated in vacuum-cast forgings (73C, 1 4 2 ) . Furthermore, lengthy heat treatments required to minimize thermal flaking in air-cast forgings can be considerably shortened or eliminated in processing vacuum-cast forgings. Vacuum casting, in conjunction with the Perrin process, is reported (6C) to have produced forgings with very low sulfur contents and with few inclusions. I n vacuum casting forging ingots, the mold is generally located in an evacuated chamber, and the steel is teemed from a seated ladle through a sealed fitting. Simpler and more flexible vacuum casting (7C? 9C) consists of placing the ladle of as-cast steel in a chamber, which is then sealed and evacuated, and injecting helium under pressure to provide required agitation. A Cr-Mo-V hot-work-die steel produced by this type of' ladle degassing is reported to have improved heat and abrasion resistance, hardness, and hardenability. Variations of vacuum casting in which alloying elements with an affinity for oxygen are not added until degassing is complete, or partially complete, have been developed ( I C , 3C, 78C) and are already used commercially to a limited extent in this country. When steel in the undeoxidized or unkilled condition is cast in a vacuum: carbon in the steel acts as a strong deoxidation agent and removes most of the oxygen as C O . Thus, when oxidizing alloying elements are later added, the steel is already deoxidized or killed and oxides (inclusions) are not formed.
Welding Of several neiv welding processes introduced, the adaption of inert-gas consumable-electrode welding to make it suitable for joining thin materials is of particular importance ( 5 0 - 7 0 ) since the advent of high-yield-strength alloy steels in sheet thicknesses. With this process, which employs small-diameter filler wires and special constant-potential power sources, sheet steels ranging in thickness from 0.015 to 0.125 inch can be welded a t high production rates. Conventional inert-gas shielded-arc welding was not suitable for thin materials because of unstable arcs and irregular filler-wire melting a t low amperages. Applications that require all-position welding have been successfully joined. The plasma torch ( I D , 3 0 ) for cutting offers tremendous advantages over conventional chemical flames for many applications. This new heat source with its unusually high temperature (up to
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50,000' K.), performs many tasks not possible heretofore and produces heat a t lower cost than oxy-fuel gas combinations. The plasma torch was first used to cut metals faster; and its latest use has been for simulating severe conditions of missile nose-cone re-entry. Electron-beam welding (20,4 D ) , a process that utilizes a narrow beam (3 microns in diameter) of high-energy electrons in a vacuum, can be used to join metals ranging in thickness from 1 inch to that of foils. Such welds exhibit a fusion area averaging only 0.030 inch in width. With high-precision, work-locating devices and a wide range of electrical-power inputs, this process has considerable potential. Corrosion Iron. Corrosion of tubes in exhaust heat exchangers of sewage-gas engines is associated with condensation and H2S content of the sewage gas (29E). Tube failures always occur at points where exhaust-gas temperatures are lowest. Hydrogen sulfide severely attacks copper and brass tubes, whereas iron tubes were satisfactory for this service. Iron sulfide periodically forms on the surface of the iron tubes as tubercles in masses, and the tubes need occasional hammering and flushing to loosen these deposits. Corrosion of the tubes can be avoided by removing H2S from the gas or by maintaining temperatures above the acid dew point (250' to 300' F.). Ethylene glycol solutions containing 1.5y0sodium benzoate plus 0.1% SaNoz are reported (76E) to protect cast iron in automotive cooling systems only when solutions are initially heated. When the mixture is added to antifreeze solution in vehicle cooling systems, this limitation introduces no particular difficulty, since the engine is running when the cooling system is filled to mix the solution, and this automatically heats the solution. High-silicon cast-iron anodes are at least equal to graphite anodes in groundbed applications where coke-breeze backfill is utilized and are superior in marshland and other areas where backfill is impractical (77E). I n fresh-water applications, high-silicon cast-iron anodes perform very well so long as the temperature does not exceed 125' F. In salt or brackish water, molybdenum additions are beneficial, especially at high temperatures. Contrary to expectations, increasing the silicon content of pearlitic flakegraphite cast irons does not always increase corrosion resistance. Corrosion of cast-iron cylinder liners and piston rings in diesel engines by acids in combustion gases occurs a t a maximum rate when the silicon content is about 2%
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(6E). Reduction to 1% ' silicon markedly improves in corrosion resistance. Steel. A comprehensive review of iron, carbon steel, and alloy steel use in the chemical industry has been prepared by Schmitt (25E). Steel is satisfactory for handling concentrated H z S 0 4 , mixtures of HNOs and H2SOt, and HCr04. I n general, cast iron and steel are usually not suitable for handling organic acids, such as acetic and citric: and for handling fatty acids such as palmitic and stearic. Steel is very resistant to alkaline solutions at moderate temperatures, but corrosion is a problem with concentrated alkalies at high temperatures. In handling dry gases, steel is usually satisfactory at atmospheric and subzero temperatures. However, alloy steels are often required because of their improved physical properties. Steel tank cars and cylinders are normally used for transporting and storing liquefied gases such as chlorine, SOS, and "3. Cast-iron distillation equipment has also been widely used in the recovery of NH3 from coke-oven gas. Steel equipment is also widely used for handling organic solvents, including dry CCld and other chlorinated solvents up to the boiling point, benzene, and petroleum products such as gasoline and kerosine. Cast iron, carbon steel, and low-alloy steels are construction materials for most of the equipment used in producing of steam from water. I n addition, the use of steel can be expanded to handle more corrosive chemicals through use of corrosion inhibitors: protective coatings, and cathodic protection. Important design factors have been reviewed (33E). Basic material of construction for refinery equipment is carbon steel, and substitution of a more highly alloyed steel must be justified on a cost us. performance comparison (28E). At temperatures above about 950' F., however, addition of chromium to steel is required to prevent excessive scaling; the amount needed is roughly proportional to anticipated temperature. Firebox-quality steel, ASTM -428.5, was found (70E) to be the best carbon steel now available for sulfate-digester construction after studying data on 61 vessels. Corrosion resistance of rimmcd steel was no better or worse than that of semikilled steels in sulfate-digester service. Firebox-quality rimmed-steel digesters carefully sandblasted showed no improvement over vessels from which mill scale was not removed. Cathodic protection has proved effective for controlling corrosion of processing equipment in. the chemical industry (78E). Although laboratory development is usuall'y required, this method may provide a n economical solution to many corrosion problems. Cathodic
an 4protection equipment has been employed in handling brackish water, highly chlorinated water, and concentrated brines. Other metals protected in chemical media include copper alloys, lead, and stainless steels. Anodic protection, in which the equipment is the anode with respect to a platinum cathode, is applicable only to highly conductive solutions establishing a passive range with the metal. A reference electrode and a potentiostat to maintain potential in the passive range are also needed. Development of an inexpensive high current-capacity potential controller by Sudbury and others (37E) has made anodic protection of immediate value in controlling chemical process and storage problems caused by corrosive liquids. This technique has been found useful in minimizing corrosion of carbon steel and stainless steel equipHzS04, and ment handling "03, H3P04, nitrate and sulfate salts, and NaOH (23E, 27E). Anodic protection of equipment used in acid-base neutralization and acid-hydrocarbon reactions is possible so long as adequate conductivity is maintained. Control of corrosion has been established a t temperatures as high as 500' F. Chemical factors affecting the high corrosion rate of carbon steel (AIS1 1020) by liquid-phase fuming "01 were studied by Rittenhouse and Mason (24E). Corrosion rates decreased with increasing N O z concentration i n fuming " 0 3 in the range 0 to 12 wt. % and also decreased with increasing water content in the range 0 to 3.5 wt. 70. This behavior indicates that the nitroB be innium ion (NO*+) or N ~ O may volved in the rate-controlling step. Factors affecting corrosion of steel by mixtures of oil, brine, and H S have been studied by Shannon and Boggs (26E). Initial corrosion rate of steel specimens is dependent on the HzS concentration. After about 1 day's exposure, the rate becomes diffusion controlled and independent of HeS concentration. At high HzS concentrations. Corrosion rate is lowered by formation of an FeS coating through which diffusion is slower. U p to 1 wt. yo NaCl increases corrosion rate by preventing formation of this coating; above 1 wt. 70NaCl, corrosion rate decreases, possibly because NaCl acts as an inhibitor and is adsorbed on the surface. Atmospheric stress-corrosion tests on alloy and stainless steels for use in highspeed aircraft and missiles conducted by Phelps and Loginow (27E) showed that very high strength alloys hardened by heat treatment are susceptible under certain conditions to atmospheric stresscorrosion cracking, like many nonferrous alloys in conventional aircraft. Protective coatings anodic to steel appear
to be very effective in preventing stress corrosion. A correlation between tests and actual service performance has not been established, Stress-corrosion cracking of ferrous materials other than austenitic stainless steels has been reviewed by Phelps (22E). The method of manufacture of the steel, deoxidation practice, and residual elements present affect susceptibility. Stress-corrosion cracking of steel in alkaline solutions is prevented in the chemical and process industries by use of stress-relieving treatments and design to reduce stresses, by maintaining temperature and concentration of caustic solutions in a range where cracking does not occur, and in some cases by the use of coatings. Stress-corrosion cracking of structural carbon steel in hot concentrated nitrate solutions has been associated with carbon and nitrogen content, degree of deoxidation, grainboundary carbides, and tendency toward strain aging. Widespread use of stressrelieved pressure vessels has minimized stress-corrosion cracking of steel in agricultural ammonia service. Recently, it has been found that water added to ammonia acts as an inhibitor and prevents stress-corrosion cracking. Three reports (7E, 5E, 75E)describing current research on stress-corrosion cracking of steel formed part of a conference on the physical metallurgy of stresscorrosion cracking. Bastien ( 7 E ) reported that cracking and failure of steel under stress in contact with moist HzS results from embrittlement of the metal by hydrogen. The tendency of steel toward hydrogen embrittlement depends largely on its microstructure. Structures with fine spheroidal carbides dispersed in a ferrite matrix are least susceptible to the effect of hydrogen and usually perform satisfactorily in the presence of moist HzS04, even when subjected to high mechanical stresses. Stress-corrosion cracking of decarburized and undecarburized low-carbon steels in boiling 20% aqueous N H 4 N 0 3 solution was studied by Logan (75E). Extensive plastic deformation occurred in fine-grain steel before stress-corrosion cracking developed. Less plastic deformation occurred in large grained decarburized steel and in specimens made anodic using a n externally applied electric current. I n all cases, stress corrosion cracks were intercrystalline. Engell and Baume1 (5E) have studied the electrochemical mechanism of stress-corrosion cracking of carbon steel in nitrate solutions. Current-potential curves of iron single crystals and polycrystalline iron show that the ferrite crystal becomes passivated in hot concentrated nitrate solutions, the grain boundaries remaining active. I n dilute nitrate solutions, passivation of the grain occurs as a result of
Materials of Construction Review anodic polarization that leads to attack of the grain boundaries. Purity and heat-treatment of the metals have a pronounced influence on this type of intercrystalline corrosion. The effect of alloying carbon steel upon its resistance to stress-corrosion cracking has been studied by Parkins and Brown (ZOE). Copper-bearing steels, although useful in resisting certain types of corrosion, are more prone to cracking in nitrate solutions than unalloyed carbon steels. Experiments with copper specimens and with partially copper-plated steel specimens in nitrate solutions indicate that copper so coupled can increase the cracking tendency of an unalloyed steel. If copper-bearing steel corrodes to the extent that copper dissolves and then deposits on the surface of the steel to form a galvanic couple, a n increase in cracking tendency would be expected. Chromium and aluminum additions increase the resistance of steel to cracking in nitrate solutions. Immunity of steels containing aluminum to cracking may be related to oxide film formation. Additions of aluminum to steel (up to 1%) prevent grain-boundary attack by nitrate solutions. Preliminary investigations have shown that steel will probably be the best allaround material for the construction of economical saline-water conversion plants (7E). The rate of attack for steel under immersed conditions in clean sea water at ambient temperatures averages about 5 mils per year. Pitting is frequently reported to be a t a rate of about 10 to 15 mils per year, but this rate often drops off with continued exposure. The presence of mill scale on the steel can increase pitting rate. Use of a deaerator to remove the ouygen in sea water will make it possible to use steel a t temperatures u p to 250" F., according to Standiford (3OE). Deaeration is by far the most practical way of reducing sea-water attack. After heating the incoming sea water in a deaerator, oxygen scavengers such as NaZS03 or hydrazine can be used to provide further protection. The conclusion that the lower-cost carbon and low alloy steels may be pi actical for use in water-cooled atomic power plants was reached after extrnsive corrosion testing by Vreeland and others (32E). Tests were conducted with several commercially available steels in environments simulating those in a nuclear boiling water reactor. The temperature during the tests was 546' F., and pressure was 1000 p.s.i. Corrosion of carbon and low-alloy steels in neutral water or steam containing both oxygen and hydrogen was lower than for similar materials in alkaline water containing hydrogen but no oxygen, as would exist in a pressurized-water reactor. The low VOL. 53, NO. 7
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corrosion observed is believed to be due to the presence of oxygen or of oxygen and hydrogen, which may help form a more protective adherent oxide on the steel. No difference in corrosion was noted among steels containing u p to 570 chromium. Corrosion of a variety of steels in liquid lead and bismuthin the 1112’ to 1652’ F . range was studied by James and Trotman (77E) by measuring w-eight losses of steel specimens after immersion in the hot side of a thermal convection loop. I n bismuth, low-alloy steels are more resistant to corrosion than AIS1 Type 410 or 304 stainless steel. Nickel and manganese have an equally deleterious effect on the corrosion resistance of 2.25% chromium, 1% molybdenum alloy steel. I n bismuth inhibited \vith zirconium, the best steels tested had extrapolated corrosion rates of less than 0.005 inch per year at 1292’ F Corrosion of steels in lead is about 40 times less than in bismuth under similar conditions and is reduced by addition of 500 p,p.m. of titanium. Initial rusting of steel in the atmosphere can be explained by the electrochemical theory, according to Larrabee (74E). Once rusting has started. however, it does not progress at a uniform rate. Depending upon the amount of pollution in the atmosphere and the composition of the steel, the oxide film is more or less protective. Of all the common pollutants, NaCl, typified by sea salt, is the greatest destroyer of the protective rust film on carbon steel. Ovides of sulfur are a poor second, and when both pollutants are nearly absent. atmospheric corrosion of steel is not significant. When dew is deposited on steel. rusting as evidenced by discoloration soon takes place, but in the absence of chlorides or sulfates, this film quicklv assumes a protective nature and corrosion extends for only a few ten thousandths of a n inch into the surface. Underwater corrosion data on 10 structural steels in tropical sea water and fresh water (Gatum Lake) environments were reported by Forgeson and others (QE). The corrosion of unalloyed low-carbon steel in tropical sea water a t Panama is of the same magnitude as that in temperate sea water a t Kure Beach, N. C., and less than that at Port Hueneme, Calif. No significant difference in the type or magnitude of corrosion was found between copperbearing steel and unalloyed low-carbon steel in sea and fresh water and at mean tide. The inclusion of 2 and 5% nickel in structural steel did not increase its corrosion resistance in fresh water or a t mean tide, but in sea water nickel addition increased weight loss and pitting. Tests to determine whether steel structures buried in soil and placed
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under cathodic protection could be embrittled by hydrogen as a consequence of such cathodic protection were conducted by Bruckner and Myler ( 2 E ) . ‘4 reducible iron oxide present in the mill scale delayed hydrogen absorption. Embrittlement of two steels occurred because of notch formation when adherence of iron oxide to base metal was destroyed during cathodic protection. Under conditions of low p H with and without sulfide ions present, cathodic protection induced hydrogen absorption. ’\Vith sulfide ions present, embrittlement was severe. ,4 normalized steel was insensitive to embrittlement during cathodic protection. Coated Products. Comparative performance of paint coatings on mild steel and low-alloy steels has been reviewed by Copson and Larrabee ( 3 E ) . Both field tests and service experience have shown that paint coatings ar- more durable on high-strength low-alloy steels than on carbon steel or on copper steel. Any rust that forms at breaks or discontinuities or underneath the paint film is less voluminous on the low-alloy steels, and consequently there is less rupturing of the paint film and less moisture reaches the steel to promote further corrosion. Thus, the extra durability of the paint is due to the better atmospheric corrosion behavior of the highstrength low-alloy steels. As a protective coating for steel, zinc occupies the leading position among the metals (7QE). Zinc is readily applied by a variety of techniques suitable for any type of steel product and has a century of tested service. Related chemically to zinc, cadmium shows differences in behavior that sometimes make it preferable as a coating metal; it has better resistance to alkalis and to marine industrial atmospheres and is less affected by high humidities. Under acid conditions, lead is superior; where a high temperature resistance is sought, aluminum-coated steel is a natural choice. For the storage of foodstuffs and potable liquids, tinplate is unexcelled. In recent pears, work has been directed toward understanding the corrosion mechanism and interrelation of the three reactions that occur in the corrosion of tinplate: dissolution of the tin, dissolution of the steel base, and evolution of hydrogen. Frankenthal and others (88)have shown that in grapefruit and tomato juice, dissolution of the tin coating is accompanied by evolution of hydrogen; in prunes: hydrogen is not evolved when the tin dissolves: but only when the steel base is attacked. Koehler and others (7323) have reported that the corrosion mechanism encountered in carbonated beverage cans is one of attack on the steel base stimulated by reduction processes occurring at areas
INDUSTRIAL AND ENGINEERING CHEMISTRY
of exposed tin or other cathodic regions. Factors affecting the painting of steel welds were studied by Keane and Bigos ( 7 2 E ) . I t was found that residues caused by electrode coating should be removed from the weld area before painting, preferably by blast cleaning. When this is not possible, several types of pretreatments were helpful. Tests conducted by Edwards and others ( 4 E ) with steel panels confirm that acetylenic alcohols when used as inhibitors in pickling baths, prior to coating, provide a substrate that will increase the corrosion inhibition of epoxy-phenolic systems under severely corrosive conditions. The substrate formed on the steel surface provided protection equal to or superior to that provided by light-weight zinc phosphate pretreatment. The mechanism for this phenomenon is believed to b e related to the acid and hydrogen embrittlement inhibitive properties OF acetylenic alcohol. Literature Cited Iron
(IA) de Sy, A., Modern Castings 35, No. 6, 41 (1959). (2A) Ibid., 37, No. 3, 126 (1960). (3A) Ellwood, E. C . ! Zbid.: 36, No. 1, 73 (1959). (4A) Evans: E. R., Brit. Cart Iron Reictirch Assoc. J . Research and Develop. 8 , 340 (May 1960). (5A) Gallo, S., D’Alessandro, G., Fondirrin ’ itul. 8, 397 (Novembcr 1959) (6A) Hlousek. C.. Sle‘vhrensfd 7 , 425 (October 1759). (7A) Hull, F. C.. Welding J . (’1’. I - . ) , Research Suppl. 38, No. 4, 176s (1959). (8A) Kusakawa, T., Iijimi, S., ./spa'! Foundrymen’s Soc. J . 31, 26 (Octobrl. 1959). (9A) McGrady. D. D., Langenherg. C. C.. others, Modern Casfings 38, KO. 4. 133 (1960). (10A) Maruyama, M., Ito, M., J a p a n Foundr.ymen’s SOG.J . 32, 261 (April 1960). (11.4) Materials in Design Eng. 52, No. 2. 10 (1960). (12A) Metal B o y . 77, No. 6, 67 (1960). (13A) Rauch, A. H., Peck, J. B., McCullough, E. M., Modprn Castings 35, No. 3, 111 (1959). (14A) Salbaing, J. L., Ibid., 36, No. 3. 61 (1959). (15A) Shimomura, T., Mizunumu, S., Jafian Fnundrymen’s Soc. J . 31, 781 (September 1959). (16A) Stein, E. M.. McIntire, H. 0 . : Modern Ca&q 35, No. 3. 103 (1959). (17A) Turnhuli, G. K.. Wallace, J. F., Zbid.. 34, N o . 1, 81 (1959). Carbon and Low Alloy Steels (IB) Am. SOC.Testing Materials, Philadelphia, Pa., “ASTM Standards,” Pt. I (1960 Suppl.). 2B) Zbid., (1959 Suppl.). 3B) Arnold, J., Iron Steel Engr. 37, No. 8, 91 (1960). (4B) Automobile Enqr. 49, No. 2, 74 (1959). (5B) Beiser. C. A., Am. SOC. Metals, ‘ Preprint ‘No. 138, 1959. (6B) Donahue, J. E., Hegenbotham, A. E.. U. S. At. Energy Comm. Tech. Rept. MIT-OR-5, November 1959.
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(7B) Garwood, M. F., Metal Progr. 78, No. 4, 115 (1960). (8B) Metal Progr. 7 5 , No. 3, 126 1959). (9B) Mogerman, W. D., Consu ting Engr. 13, N o . 4, 96 (1959). flOB’1 Nachtman. E. S.. Materials in ‘ &sign Eng. 49,’No. 3, 98 (1959). (11B) Pchelkina, M. A., Lakhtin, Y . M., ‘ Mktalloved. i Termischesk. Orabotka Metal. 1960 (Julv). D . 40. (12B) Pipe LIne‘News 32, N o . 5, 38 (1960). (13B) Samuel, R. L., Hoar, T. P., MetallurEia 60, No. 359, 75 (1959).
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Alloy Steels (1C) Bennett, G. H., Protheroe, H. T., Ward, R. G., J. Zron Steel Znst. (London) 195, No. 2, 174 (1960). (2C) Bhat, G. K., Metal Progr. 77, No. 6, 75 (1960). (3C) Harders, F., Knuppel, H., Brotzmann, K., J. Metals 12, No. 5, 398 (1960). (4C) ZNCO (International Nickel Co.) 27, 2 (1960). (5C) Kula, E. B., Dhoai, J. M., Trans. Am. SOC.Metals 52. 321 11960). (6C) Levaux, J., Nepp;r, bk., J . Zron SteeZ Znst. (London) 192, No. 5, 77 (1959). 17C) Metal Proer. 76. No. 3. 111 (1959). ’ ’ i8C\ Zbid.. 7 7 . h o . 3. 65 (I960\. ‘ (9Cj Ibid.; N d . 5, 107. (1OC) Zbid., 7 8 , No. 6, 65 (1960). (11C) Schmatz, D. J., Shyne, J. C., Zackav. V. F.. Trans. Am. Soc. Metals 52, 34g (1960).‘ (12C) Schmatz, D. J., Zackay, V. F., Zbid., 51, 476 (1959). (13C) Steiner, J. E., Metal Progr. 76, No. 1. 72 11959). (14C) S’tool,’ J. H., J. Zron Steel Znst. (London) 191, No. 1, 67 (1959). (15C) Stout, R. D., Welding J. ( N . Y.) 39, No. 7, 273s (1960). (16C) Thum, E. E., Metal Progr. 76, No. \
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[l%~o?b!~,~%. 3, 121 (1959). 18C) Wooding, P. J., Sieckman, W., Zbid., 77, No. I , 116 (1960).
Welding (1D) Browning, J. A., Welding J . ( N . Y . ) 38, No. 1, 28 (1959). (2D), Burton, G., Jr., Frankhouser, W. L., Zbzd., 38, No. 10, 401s (1959). (3D) Gage, R. M., Zbid., 38, No. 10, 959 (1959). (4D) GFeene, W. J., Banks, R. R., Niedzielski, R. M., Zbid.,. 39.. No. 8. 791 (196oj. (5D) McElrath, T., Zbid., 38, No. 1, 28 (1959). \ - - - - I .
(6D) Orr, H. J., Headapohl, J. H., Zbid., 39, No. 6, 600 (1960). (7D) Tuthill, R. W., Zbid., 38, No. 10, 976 (1959). Corrosion (1E) Bastien, P. G., in “Physical Metallurgy of Stress Corrosion Fracture,” Thorn. Rhodin, ed., Vol. IV, p. 311, Interscience, New York-London, 1959. (2E) Bruckner, W. H., Myler, K. M., Corrosion 15. No. 11. 591t (1959’1. (3E) Copson,’ H. R:, Lar;abe< C. P., A S T M Bull. N o . 242, 68 (1959). (4E) Edwards. K. N.. Nowacki. L. J.. ‘ Mueller, E. R., Corrosion 15, 275t (1959): (5E) Engell, H. J., Baumel, A., in “Physical Metallurgy of Stress Corrosion Fracture,” Thorn. Rhodin, ed., Vol. IV, p. 341, Interscience, New York-London, 1959. ‘ gept., 1960. . (8E) Frankenthal, R. P., Carter, P. R., Laubscher, A. N., J . Agr. Food Chem. 7, 441 (1959). (9E) Forgeson, B. W., Southwell, C. R., Alexander, A. L., Corrosion 16, No. 3, 10% (1960’1. (IOEj-Harris: H. B., Park, L. H., Tappi 43, No. 5, 225A (1960). (11E) James. J. A.. Trotman. J.. J . Zron ‘ Steh Znst. (London)’l94, 63, 319 (1960). (12E) Keane, J. D., Bigos, J., Corrosion ‘ 16, No. 12, 6Olt (1960). (13E) Koehler, E. L., Daly, J. J., others, Zbid., 15, No. 9, 477t (1959).
(14E) Larrabee, C. P., Zbid., 15, No. 10, 526t (1959). (15E) Logan, H. L., in “Physical Metallurgy of Stress Corrosion Fracture,” Thorn. Rhodin, ed., Vol. IV, p. 295, Interscience, New York-London, 1959. (16E) Mercer, A. D., Wormwell, F., J . Apjl. Chemistry (London) 9, 577 (1959). 117E) Natl. Assoc. Corrosion Encrs.. Tech. ‘ Uhit Committee Rept., CoGosibn 16, No. 2, 65 (1960). (18E) Zbid., 15, No. 3, 123t (1959). 119E) Nicholls. J. H.. Corrosion Technol. ’ 6 , No. 9, 275 (,1959).’ (20E) Parkins, R. N., Brown, A., J . Zron Steel Znst. (London) 193, Pt. 1, 45 (1959). (21E) Phelps, E. H., Loginow, A. W., Corrosion 16, No. 7, 325t (1960). (22E) Phelps, E. H., Proc. Ann. Water Conf., Engrs. SOC.Western Penn.: 20th, 1959. (23E) Riggs, 0. L., Hutchinson, M., Conger, N. L., Corrosion 16, No. 2, 58t (1960). (24E) Rittenhouse, J. B., Mason, D. M., Zbid., 15, No. 5, 245 (1959). (25E) Schmitt, R. J., Proc. Short Course Process Industry Corrosion, Ohio State University, Natl. Assoc. Corrosion Enws.. D. 31. 1960. (26E)” Shinnon, D. W., Boggs, J. E., Corrosion 15, No. 6, 299t (1959). (27E Shock, D. A., Riggs, 0.L., Sudbury, J. il.. Zbid., 16. No. 2. 55t (1960). f28E\ Skinner. ‘E. N:. Mason.’ J. F.. ‘ Mbran, J. J., Ibid., ’ 1 6 , No. ’12, 593f (1960). (29E) Sperry, W. A., Public Works 90, No. 4, 101 (1959). (30E) Standiford, F. C., Jr., Bjork, H. F., Advances in Chemistry Ser. No. 27, 115 (1960). (31E) Sudbury, J. D., Riggs, 0. L., Shock, D. A., Corrosion 16, No. 2, 47t (1960). (32E) Vreeland, D. C., Gaul, G. G., Pearl, h’. L., Natl. Assoc. Corrosion Engrs. Publ. 60-13, 1960. (33E) Whitney, F. L., Am. SOC. Mech. Engrs. Publ. No. 59-SA-58, 1960.
IN THE W O R K S . . . Manuscripts Accepted for Publication within the Next Three Issues of IIEC Crystallization Theory and Fundamentals
Application of Crystallizer Equipment
Radiation Applications Inc., long Island City, N. Y.
D. E. Garrett Associated Chemicals Co., Pomona, Calif.
Successful crystal production depends on complex relationships between many variables. Although crystallization is based partly on know-how, scientific principles should guide the process-designer
Choice of crystallization equipment is particularly important, since product quality often depends on design. Suitable applications of the most common industrial crystallizers are given here
H. M. Schoen
Crystallizer Design
Stlrred Tanks and Mixers for Liquid Extraction
W. C. Saeman
R. E. Treybal
Olin Mathieson Chemical Corp., New Haven, Conn.
New York University, New York,
Crystallizer design is outlined to aid the equipment user, rather than the equipment manufacturer. The problems of paying for the equipment, operating it, and controlling it must also enter into equipment choice Application of Nonllneor Regression to Reaction Kinetics
N. L. Cull and H. H. Brenner
N.Y. In 1958, the author suggested an approach to estimating stage efficiency i n extraction. The information which has become available since that time is reviewed, and the method is brought up-to-date
A N e w Equilibrium Still
Humble Oil & Refining Co., Baton Rouge, La.
C. H. Bloom, C. W. Clump, and A. H. Koeckert Lehigh University, Bethlehem, Pa.
The kinetics of hexane isomerization were successfully represented by a mathematical model. This statistical technique coupled with a digital computer will be a powerful tool for handling complex chemical kinetics
Vapor-liquid equilibria and latent heats of vaporization can be measured simultaneously in this still. Design and construction details of the apparatus are given, with confirming data VOL 59, NO. 7
0
JULY 1961
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