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THE BASICS OF MOLTEN SALT QUENCHANTS Molten salt is an ideal he wide operating temperature nonuniform hardness or cracks. This range and other characteristics of tendency increases with increasing medium for interrupted molten salts make them ideally hardenability of the steel. Causes of suited to low-distortion quench- distortion usually can be traced to un- quenching processes. ing of iron, steel, and tool steel. even or nonuniform quenching, Nitrate-based salt, the Thanks to advances in salt thermal stresses, and phase transfor- T quality, pollution abatement, and mation stresses. most widely used, material handling, salt bath These causes can be largely over- blankets the quench quenching is more efficient and eco- come by interrupting the quenching nomical than ever before. process with a salt bath. This is temperature range of 150 A properly selected salt can be used achieved by rapidly cooling the parts to 595°C (300 to 1100°F). for processes such as martempering from the austenitizing temperature to and austempering in a single bath. Ex- a point above the martensite forma- by Gajen P. Dubal* cellent thermal stability and tolerance tion or start temperature (Ms). The for contaminants make salt quenching parts are held at that temperature for a Heatbath/Park Metallurgical Corp. systems almost maintenance-free. And specified time, and then cooled (usu- Detroit, Mich. baths can provide satisfactory per- ally in air) to room temperature. The formance for many years simply by interruption in quenching consider- adding salt to replace that which is ably reduces thermal stresses and, dragged out. thereby, distortion. Processes in this The focus of this article is on nitrate- category are martempering, austem- based salts for quenching iron and pering, and their variations. steel parts, since this constitutes the For most carbon and low-alloy largest portion of molten salt steels, the temperature at which the quenching applications. Chloride- quench is interrupted is usually in the based salts used for quenching tool 175 to 370°C (350 to 700°F) range. A steels also are briefly covered. nitrate-based salt is the best choice here. A chloride-based salt is selected Controlling distortion for high-alloy and tool steels, where Quenching in water, brine, a water- the interruption temperature range based polymer solution, or oil can is 480 to 705°C (900 to 1300°F). cause distortion and in some cases, Continued

Automated salt bath furnace line for heat treating high-speed steel tools includes a salt quench furnace and air-cool conveyor. Source: ASM Handbook, Vol. 4, Heat Treating: ASM Interna- * Member of the ASM Heat Treating Society tional, Materials Park, Ohio, 1991, p. 728. HEAT TREATING PROGRESS • AUGUST 2003 81 heatbath.qxd 7/24/03 8:11 PM Page 2

Cooling rate, °F/s (°C/s) Molten salt’s advantages measuring quench severity, as well as 80 (44) 160 (89) 240 (133) 320 (178) The most distinct ad- for understanding the quenching vantage of salt quenching mechanism and studying the effects 1600 is its wide operating tem- of quench variables. (871) perature range — 150 to Typical cooling and cooling rate Cooling rate 595°C (300 to 1100°F) for curves for a nitrate-based salt bath are 1200 1 (649) a typical nitrate-based shown in Fig. 1. The cooling rate salt, which is unmatched curve clearly shows that no vapor 60.5 °F/s (33.6 °C/s) 800 by any other quench phase is present and that the cooling (427) medium. rate varies uniformly with tempera- Temperature, °F (°C) 400 The quenching mecha- ture. This is in sharp contrast to oil, (204) Cooling nism also is considerably polymer, or brine quenchants. different. In most liquid The main operating variables in salt

20 40 60 80 quenchants, heat extrac- quenching processes are temperature, Cooling time, s tion occurs throughout agitation, water content, and residence Fig. 1 — Typical cooling and cooling rate curves for a nitrate- the three stages of vapor, time. based molten salt bath at 255°C (495°F). The cooling rate curve boiling, and convection. Temperature: Although primarily shows that no vapor phase is present and that the cooling rate Salt quenching has no governed by the Ms temperature of varies uniformly with temperature. No agitation or water addi- vapor phase, so problems the steel, there is some room for tion. Average cooling rate from 650 to 260°C (1200 to 500°F): with vapor phase barriers varying salt bath temperature. In gen- 33.6°C/s (60.5°F/s). Ref. 1. are avoided. Most of the eral and regardless of medium, the heat extraction is by con- lower the bath temperature, the faster vection. As a result, distortion is min- is the cooling rate. In salt bath 100 (56) imized and the hardness achieved is quenching, the effect of this variable more uniform and consistent. is marginal, but it still can be opti- 80 mized. The recommended practice is (44) Other important advantages of salt quenching include: to start at the lowest temperature and 60 • Quench severity can be controlled incrementally increase it until the best (33) by varying the temperature, agitation, combination of hardness and distor- 40 tion is obtained. (22) and water content of the salt bath.

Cooling rate, °F/s (°C/s) • Productivity in salt quenching is In some cases, salt bath temperature 20 high because parts rapidly attain tem- can be manipulated to achieve re- (11) perature equalization. markable results. For example, large sections can be martempered by first 50 (25) 100 (51) 150 (76) • Due to excellent thermal and Flow rate, ft/min (cm/s) chemical stability, salt baths can pro- quenching in water or brine for a short vide consistent quenching perform- time and then transferring them to a Fig. 2 — Increasing agitation results in con- ance for many years. Ordinarily, the salt bath. This helps achieve higher siderable increase in quench severity (cooling hardness to a greater depth. Similarly, rate). Temperature of the low-melting-point only maintenance required is to re- salt bath: 175°C (350°F). The cooling rate place salt that is dragged out. low-hardenability steels can be plotted on the vertical axis is the average of the • Salt can be easily washed off with austempered by using two salt baths, rates determined at every 55.5°C (100°F) in- water and recovered for reuse. the first bath at a lower temperature terval between 650 and 260°C (1200 and Choosing to recover salt eliminates than the second.2 With such manipu- 500°F). Ref. 1. disposal and reduces operating costs. lations, cooling curves satisfy a key re- • The same salt bath can be used for quirement of quenching: avoiding the tempering. pearlite nose of the TTT (time-tem- Limitations: Salt has to be used perature-transformation) diagram. above its melting point of about 150°C In most production setups, heat (300°F), and, because of its oxidizing input to the salt from the work ex- nature, combustible or incompatible ceeds heat losses by radiation, neces- materials should definitely be kept out sitating a cooling system to maintain of the salt bath to avoid the possibility bath temperature within the required of violent reactions. range. Solutions include external Salt used to present safety and en- cooling fins and/or a heat exchanger vironmental problems, but technology inside the bath. for dealing with them is now well de- Agitation: The effect of bath agita- veloped and they are no longer con- tion is greater than that of tempera- sidered deterrents to its use. ture. Increasing agitation results in a considerable increase in quench Quench process variables severity, as shown in Fig. 2.1 The Quench severity is a measure of the cooling rate plotted on the vertical axis ability of a quenchant or quenching is the average of the cooling rates de- system to extract heat from a test spec- termined at every 55.5°C (100°F) in- imen, part, or workload. Among the terval between 650 and 260°C (1200 various methods, cooling curve and 500°F). This temperature range is analysis is the most useful tool for chosen because it spans the pearlite 82 HEAT TREATING PROGRESS • AUGUST 2003 heatbath.qxd 7/24/03 8:12 PM Page 3

nose of the TTT diagram for most tortion. Water content of the bath typ- peratures up to 900°C (1650°F). steels. ically varies from 2 to 3% at 150°C Quenching from a higher temperature Agitation can be provided by pro- (300°F) to about 0.5% at 315°C (600°F). is not recommended unless parts are peller-type agitators or by a pump Safety considerations dictate that small and well separated. Even then, with a draft tube. As many as four water is added only to a bath having parts should first pass through a neu- propellers with single or dual im- sufficient agitation — never to a still tral salt bath maintained at a lower pellers may be required, depending bath — and it should be added very temperature. A chloride-based salt is on bath size. If a pump is used, salt slowly, as a fine stream or spray, di- recommended when quenching from flow from bottom to top is preferable. rectly into the vortex created by agita- high austenitizing temperatures like Agitation should not be provided by tion. Instead of fresh water, salt solu- 980 to 1315°C (1800 to 2400°F), as are bubbling air into the salt bath, because tion from the washing operation or required for tool steels. it is inefficient and will cause undesir- low-pressure steam also can be used. If parts are austenitized in an at- able carbonate buildup. Note that agitation also helps disperse mosphere, air, or vacuum furnace, In some instances, vigorous agita- the water uniformly throughout the either type of salt can be used for tion increases distortion considerably. bath. quenching, depending on the required Thus, mild agitation is often used in A fringe benefit of water addition quench temperature. But if the aus- combination with a water addition to is that it lowers salt’s freezing point, tenitization process is carried out in a minimize distortion without sacri- further increasing its working range. salt bath, the following selection cri- ficing hardness. Agitation must be For example, a 1% water addition teria are recommended: maintained while water additions are lowers the freezing point by 11°C • When quenching from a barium- made. (20°F), while 2% water lowers it by chloride-based neutral salt bath, a Like temperature, agitation also can 19°C (35°F). chloride-based quenching salt is the be manipulated to advantage. An ex- Residence time: The time that parts appropriate choice. If nitrate-based ample: austempering of thin-walled remain in the bath depends on steel quenching salt is used, barium chlo- parts such as cylinder liners. To mini- composition, section thickness, quench ride carryover thickens the bath, af- mize thermal shock, agitation is not severity, and the process being per- fecting its quench severity. And sep- used during the first 15 to 20 seconds formed. In martempering, a few min- aration and removal of barium of the quench. It is then initiated au- utes are generally sufficient for tem- chloride from a nitrate-based bath is tomatically and continued until com- perature to equalize throughout the difficult. But if parts are austenitized pletion of the standard austempering section. A water addition significantly in a barium-chloride-free, chloride- operation. This procedure helps min- reduces this time, increasing produc- based bath, then a nitrate-based imize distortion without adversely af- tivity. Too long a residence time may quenching salt should be chosen. fecting mechanical properties.3 produce a microstructure other than • If quenching is to follow carbur- Water content: A small addition of the required martensite, resulting in izing or carbonitriding in a cyanide- water to a salt bath produces a signif- lower hardness and mechanical prop- based salt bath, safety is the primary icant increase in its quench severity, erties. In austempering, on the other concern. Quenching directly from a as shown in Fig. 3.1 Note that the com- hand, up to a few hours may be cyanide-based bath into a nitrate- bination of agitation (50 cm/s [100 needed to complete the transforma- based bath causes a violent explosion ft/min]) and a water addition (~3%) tion of austenite to bainite. Although and must never be done. The safe increases quench severity three-fold, a longer time is not harmful, it will in- practice is to transfer parts from the compared with that of a nonagitated, crease processing costs. cyanide bath into a neutral salt bath “dry” salt bath. The practical result is Other factors: Successful salt bath and then quench them into a nitrate- significantly increased surface hard- quenching also requires consideration base bath. This practice causes a ness and depth of hardness. Achieving of steel composition, austenitizing gradual buildup of cyanide in the neu- similar results with increased agita- temperature, and the section thickness tral salt bath — cyanide content tion alone would cause greater dis- and configuration of parts. However, should not exceed 5% for safe opera- these are not quenching variables. tion. Alternatively, parts can be air cooled, washed to completely remove 140 (78) Salt selection considerations cyanide salt residues, austenitized in 120 The selection of a quenching salt is a neutral salt bath, and quenched. (67) governed primarily by the austeni- • If carburizing is carried out in 100 tizing temperature, austenitizing a cyanide-free salt bath, then direct (56) medium, and quenching temperature. quenching into a nitrate-based bath 80 There are two main categories of can be performed without risking an

Cooling rate, °F/s (°C/s) (44) quenching salts: nitrate-based and explosion. chloride-based, having working 1 2 3 4 5 6 ranges of 150 to 595°C (300 to 1100°F) Nitrate-based salts Water content, % and 425 to 705°C (800 to 1300°F), re- Once you’ve settled on the type of spectively. Hydroxide- and carbonate- quenching salt, selection of a specific Fig. 3 — Increasing water content also in- based salts are not recommended for salt within that category is also im- creases quench severity (cooling rate). Salt bath temperature: 175°C (350°F). Flow rate (agita- quenching or austenitizing, because portant. Nitrate-based salts are either tion): 50 cm/s (100 ft/min). The cooling rate is these materials adversely affect sur- binary or ternary mixtures of nitrate the average of the rates determined at every face chemistry. and nitrite of sodium and potassium. 55.5°C (100°F) interval between 650 and A nitrate-based salt is suitable for There are nearly a dozen compositions 260°C (1200 and 500°F). Ref. 1. quenching from austenitizing tem- available, varying primarily in melting HEAT TREATING PROGRESS • AUGUST 2003 83 heatbath.qxd 7/24/03 8:12 PM Page 4

point, but also by degree of purity and Table 1 — Physical properties of nitrate-based quenching salt physical form. Melting point: Nitrate-based salts Property Value have melting points that span the 135 Specific gravity 1.84–1.92 to 330°C (275 to 630°F) temperature Specific heat 0.35–0.40 range. Selection of a specific salt de- 2 pends on the lowest temperature at Thermal conductivity 0.571 W/m•K (0.33 Btu•ft/h•ft •°F) which it will be operated and its Heat transfer coefficient 4.5–16.5 kW/m2•K (800–2900 Btu/h•ft2•°F) melting point. The difference between Dragout rate 50–100 g/m2 (1–2 lb/100 ft2) the two temperatures should be at least 55°C (100°F). Selecting a salt having the lowest possible melting stantially affect quench severity. But hours from a bath at 205°C (400°F). temperature, however, offers several if its level exceeds the solubility limit, Such observations in combination advantages: quench speed begins to drop. with periodic hardness checks help in • It provides the flexibility to If the austenitizing medium is a adjusting the rate of water addition. change quench severity simply by neutral salt bath, chloride gradually A recently introduced water controller changing its operating temperature. builds up in the quench bath due to eliminates manual adjustments by au- • The same salt bath can be used for carryover. Here, too, quench severity tomatically maintaining water content a high-temperature process as well as is little affected within the solubility at a preset level. a low-temperature process, including limit but will start to decline if the limit Melting point: This needs to be tempering. is exceeded. checked only occasionally, since it • Dragout losses could conceivably These contaminants, both soluble changes very little over time. A sig- be low, since salt would take longer to and insoluble, can be at least partially nificant increase in melting point may freeze after the parts are removed removed by desludging the bath. The indicate gross contamination or from the bath. best method is to reduce bath tem- thermal breakdown of the salt, usu- Product form: Quenching salts perature as much as possible so as to ally due to accidental overheating. In were formerly available only in gran- lower the solubility limits. This helps either case, depending upon the salt ular or crystalline form, which caused in precipitating excess carbonate and analysis, partial or complete replace- dusting when added to a quench bath, chloride. Agitation and heating are ment may become necessary. In case and also caused frothing and scum. turned off and the contaminants are of overheating, its causes should be Quench severity was adversely af- allowed to settle to the bottom of the investigated and properly rectified. fected until the bath stabilized. These salt quench tank, from where they are Salt bath safety: Quenching salt is problems can now be avoided by se- removed. nonflammable and relatively nontoxic, lecting salt in briquette or flake form. Contaminants can also be continu- and no toxic or hazardous fumes are Once molten, all nitrate-based ously removed, if the furnace is given off by a salt quench bath. How- quenching salts have nearly the same equipped with a separating chamber. ever, there are potential safety con- physical properties (Table 1). Contaminated salt is circulated cerns related to the relatively high bath through this chamber, where the con- temperature, bath overheating, and Salt system maintenance taminants settle to the bottom and are incompatible materials. Precautions Salt quenching systems are gener- periodically removed. that should be taken to help ensure ally maintenance-free, due primarily Continuous filtration is another safe salt bath quenching are listed in to salt’s excellent thermal stability and method of removing insoluble con- Table 2. ability to tolerate contaminants. A salt taminants. In this method, salt is con- bath can provide consistently satis- tinuously passed through filter bas- Post-quenching operations factory performance for many years kets, which are periodically removed After quenching, parts are im- simply by adding new or recovered and emptied. mersed in an agitated hot water bath, salt to replace that dragged out. The Water content: If addition of water where most of the salt is dissolved. amount of dragout depends on the to the salt bath is a common practice, This helps remove salt from blind mass and configuration of the parts its content should be periodically holes, crevices, ledges, and other re- and the fixtures or conveying system, checked and adjusted to ensure the cesses. Parts are then rinsed in a hot but generally is in the range of 50 to required quench severity. Water con- water spray to wash off any remaining 100 g/m2 (1 to 2 lb/100 ft2). tent can be determined by weighing salt. High-pressure steam also can be Contaminants: If general cleanli- a small salt sample both before and used. ness guidelines are not followed, soot, after drying it in a laboratory oven at Racks, baskets, fixtures, and the con- scale, metallic debris from parts, or 370 to 425°C (700 to 800°F). Water con- veyor system should be thoroughly other foreign materials may get into tent generally varies from 2 to 3% at washed and dried before they reenter the bath and accumulate over time. 150°C (300°F) to about 0.5% at 315°C the austenitizing furnace or salt bath. Fine contaminants remain in suspen- (600°F). Otherwise, carry-back of quenching sion due to bath agitation, and when The rate of water addition depends salt can contaminate the austenitizing they exceed about 0.5%, quench se- on the size and temperature of the medium and cause pitting or decar- verity decreases. bath, the amount of work being burization of parts. It can also damage Formation of carbonate is another quenched, and the desired quench the furnace interior. concern, particularly if salt is used at severity. It also depends on the evap- Salt recovery: Salt from wash water a high temperature. Within its solu- orative loss. It has been observed that can be recovered by evaporation of its bility limit, carbonate does not sub- about 1 to 2% water evaporates in 24 water content. What results is molten 84 HEAT TREATING PROGRESS • AUGUST 2003 heatbath.qxd 7/24/03 8:12 PM Page 5

Table 2 — Guidelines for safe salt bath quenching* Area of concern Recommendations Accidental burns Although quenching salt is nonflammable and relatively nontoxic, concern for personnel safety arises due to the temperature at which it is used. Adequate precautions should therefore be taken to protect operating personnel from accidental burns. Personnel safety can be enhanced further by totally enclosing the entire salt quenching operation. Fume exhaust Although no toxic or hazardous fumes are given off by a salt quench bath, good exhaust around the bath is highly recommended. This is particularly helpful when charging with fresh salt and during the quenching operation, especially when the bath contains water. Dry parts Parts, fixtures, and conveyors should be absolutely dry and free of moisture, oil, or other liquid when entering the quench bath. Otherwise, rapid vaporization of such liquid may cause a sudden expulsion of molten salt, which could result in injury and damage. Adding water If water is added to increase quench severity, it should be trickled or atomized onto the surface of the bath. It should never be introduced below the surface or under pressure. Otherwise, spattering or eruption of molten salt can occur. Extinguishing fires Water sprinklers should not be installed in or around any molten salt system. There should be a clearly visible sign warning that water or any liquid-type extinguisher should not be used in case of fire. Carbon dioxide-type extinguishers and sand are the best means of fighting and containing fires in the vicinity of molten salt baths. Overheating The salt bath should be protected from accidental overheating by installing audio/video alarms that signal when temperatures exceed a preset limit. If the temperature of a nitrate-based salt continues to rise beyond 595°C (1100°F), it may break down, and reactions between the products of the breakdown and the bath container could result in leakage of salt. Freezing and remelting A steel wedge should be inserted to the bottom of the bath and maintained in position until salt is solidified. When remelting, heat salt slowly and remove the wedge as soon as the salt surrounding the wedge melts. Incompatible materials Combustible and incompatible materials such as cyanide salt should never be introduced into a nitrate-based salt quench bath to avoid possible violent reactions which may result in an explosion. Storage Salt should be stored in well-marked, closed containers, which should be kept in a dry location segregated from incompatible materials such as cyanide salts. * Applies to both nitrate- and chloride-based quenching salts, except where noted. However, concern for personnel safety is greater for chloride-based salt due to its higher operating temperature and toxicity. Chloride-based salt also rapidly absorbs moisture. salt that is then transferred into metal Chloride-based salts is undesirable to have moisture or containers, where it freezes into blocks. Chloride-based quenching salts are water in a chloride-based salt. How- When salt is needed, entire blocks or eutectic mixtures of chlorides of cal- ever, due to the hygroscopic nature of portions of them are added to the cium, barium, sodium, and potassium. this salt, it is probable that some mois- bath. Although there are many composi- ture may be present in a freshly Recovery and reuse of salt elimi- tions in this category, the two most melted salt bath. Most of the moisture nates disposal of wash water. The commonly used have melting points evaporates out in a few hours. drawback is that undesirable contam- of 455°C (850°F) and 495°C (920°F) “Drying” of the bath can be inants will build up in the bath, with respective working ranges of 495 speeded up by using the “aluminum making periodic adjustment of salt to 675°C (925 to 1250°F) and 540 to sheeting” technique. Sheets of alu- chemistry a requirement for main- 705°C (1000 to 1300°F). Here too, the minum are placed in the bath and ex- taining uniform quenching perform- lower melting salt has clear advan- amined after 20 minutes. If the surface ance. This explains why many heat tages over the higher melting compo- has darkened or has a heavy white treaters still prefer to dispose of their sition. These salts have a specific layer on it, it means that moisture is wash water. gravity of 2.24 to 2.40 and a specific still present in the bath and has reacted Disposal: Although nitrate-based heat of about 0.27. with the aluminum. The sheet is then quenching salt is relatively nontoxic Maintenance: Quenching from a cleaned by shot blasting or pickling, and nonflammable, it is classified as a high-temperature salt bath at 980 to dried, and again immersed in the bath. hazardous material due to its oxidizing 1315°C (1800-2400°F) brings barium- The process is repeated until the alu- nature. When salt is contained in wash chloride-rich salt into the quenching minum no longer reacts with the bath water, the hazard is reduced consider- salt. This upsets the eutectic composi- (no dark or white layer is produced). ably, and many local waste treatment tion and increases the melting point. The aluminum sheeting technique also authorities permit discharge of wash The imbalance can be corrected by pe- helps remove metallic contaminants. water into their drainage systems. If riodic additions of “melting point re- In some instances, a black material permission cannot be obtained, the ducer,” a salt specifically formulated may be seen floating on or near the handling of wash water can be dele- for this purpose. Frequently, after the surface of freshly melted chloride- gated to a waste disposal company. initial meltdown, only appropriate ad- based salt. This is the thermal degra- Sludge can be used for chemical land- ditions of melting point reducer are dation product of the organic anti- fill, where permitted. Otherwise, it can required. The additions also restore caking agent used in raw-material be dissolved in water and treated the quench bath fluidity. production, and can accumulate to same way as the wash water. In contrast to a nitrate-based salt, it form a crust. The scum or crust usu- HEAT TREATING PROGRESS • AUGUST 2003 85 heatbath.qxd 7/24/03 8:13 PM Page 6

ally can be eliminated by holding the Salt selection in a nutshell 3. “Salt Bath Austempering and Martem- bath at 560°C (1040°F) for about an In summary, Molten salt is an ideal pering,” by Q.D. Mehrkam: Machinery, hour. quenching medium for interrupted June 1969. Safety: The precautions listed in quenching processes using a nitrate- Table 2 also apply to chloride-based based salt in the 150 to 595°C (300 to For more information: Mr. Dubal is quenching salt. However, concern for 1100°F) temperature range, and a chlo- quenching specialist, Heatbath/Park Met- personnel safety is greater due to the ride-based salt in the 425 to 705°C (800 allurgical, 8074 Military Ave., Detroit, MI salt’s higher operating temperature to 1300°F) range. Most quenching re- 48204; tel: 313/895-7215; fax: 313/895-4844; and toxicity. quirements are met by nitrate-based e-mail: [email protected]. Chloride-based salt also rapidly ab- salt, and selection of the lowest- Heatbath/Park Metallurgical offers oil sorbs moisture. Consequently, a melting-temperature composition is quenchants, molten salt products, polymer “frozen” bath should be well covered recommended. The salt’s quench quenchants, and post-heat treating prod- to minimize moisture pick-up, and severity can be adjusted to suit any ucts, and is the only manufacturer of gen- restarting a solidified bath should be process by altering temperature, agi- uine Park salt bath products. Products done slowly and carefully to avoid tation, and water content. And excel- produced under the Park name by foreign entities are not warranted by Heat- boiling and spattering. Salt containers lent thermal stability means that con- bath/Park Metallurgical for quality, per- should be kept tightly closed and sistent quenching performance can be formance, or safety. Park Metallurgical is a stored in a dry location. maintained for many years simply by subsidiary of Heatbath Corp., Indian Or- Washing and disposal: Due to the adding new or recovered salt to re- chard, Mass. (www.heatbath.com). hygroscopic nature of chloride-based place that which is dragged out. Spent quenching salt, parts should be salt is safe to work with and easy to washed soon after quenching to avoid recover or dispose of. HTP rusting. The most suitable washing medium is agitated hot water with no cleaning agent added. Before dis- References charging the wash water, it should be 1. “New Developments in Salt Bath Quenching,” by R.W. Foreman: Industrial treated to convert soluble and toxic How useful did you find the information Heating, March 1993, Vol. 60, No. 3, p. presented in this article? barium chloride into insoluble and 41–47. nontoxic barium sulfate. Recovery of Very useful, Circle 296 2. “Salt Bath Quenching,” by G.P. Dubal: Of general interest, Circle 297 salt from the wash water does not Advanced Materials & Processes, December Not useful, Circle 298 seem practical at present. 1999, Vol. 156, No. 6, p. H23–H28.

Corrosion: New ASM Handbook High-temperature solutions The purpose of ASM Handbook, Vol. 13A, Corrosion: Fundamentals, Testing, Alloy Engineering (AE) has added to its heat- and Protection is to help engineers and designers understand corrosion so and corrosion-resistant products by pur- that they can solve existing corrosion problems and prevent future ones. chasing the fabrication business of TEI/ The coverage of the volume has been completely revised Rolock. “This acquisition enhances our ability to ensure that it is the most comprehensive, practical, and to provide engineered solutions to high-tem- up-to-date resource available. Each article is indexed to perature challenges.” says president Lou other appropriate sections of the ASM Handbook, and Petonovich. AE now offers atmosphere gen- each provides a road map to the thousands of individual erators and ammonia dissociators in addi- bibliographical references that were used to compile the tion to its other heat treating products. information. Alloy Engineering Co., 844 Thacker St., ASM International, Customer Service Center, Materials Berea, OH 44017; tel: 440/243-6800; fax: 440/ Park, OH 44073-0002; tel: 440/338-5151 ext. 5900; fax: 243-6489; e-mail: sales@alloyengineering. 440/338-4634; email: [email protected]; com; Web: www.alloyengineering.com Circle 401 Web: www.asminternational.org. Circle 400 Electronic Device Failure Journal of Materials Engineering Analysis News and Performance Quarterly newsletter packed with case his- Focuses on industrial performance meas- tories and contract lab reviews. Written by urement. Primarily comprised of real-world technicians, engineers, and managers. Also engineering applications; contains some contains backside analysis, industry news, original research. Presents a clear under- training, and ask the experts. Official publi- standing of the relationships between ma- cation of the Electronic Device Failure terial selection, processing, applications, and Analysis Society. Call and mention code performance. 5900020-TEIFSJGR for a FREE issue. ASM International, Customer Service ASM International, Customer Services Center, Materials Park, OH 44073; tel: 800/ Center, Materials Park, OH 44073; tel: 800/ 336-5152 or 440/338-5151 ext. 5900; fax: 440/ 336-5152 or 440/338-5151; fax: 440/338-4634; 338-4634; e-mail: cust-srv@asminternational. e-mail: [email protected]; Web: org; Web: www.asminternational.org. Circle 403 www.asminternational.org. Circle 402 SPECIAL ADVERTISING SECTION For more information contact: Suzanne Campbell, editorial assistant, Advanced Materials & Processes ASM International, Materials Park, OH 44073-0002; tel: 440/338-5151, ext. 5672; fax: 440/338-4634 e-mail: [email protected]; website: www.asminternational.org

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