Volume 18 - Friction, Lubrication, and Wear Technology Part 19 pot

Fig. 8 Dry pin-on- ring test used to evaluate effect of microstructure on the wear resistance and the hardness of pearlitic steel pins. Test parameters: pressure, P, 34.71 MPa (5.033 ksi); velocity, v, 0.4 m/s (1.3 ft/s); atmosphere, dry air. P, pearlite; P/F, pearlite and ferrite. Source: Ref 6 In lubricated block-on-ring wear experiments with pearlitic carbon steel where deformation wear was the principal wear mode, pearlite was observed to minimize the depth of extreme plastic deformation (Ref 8). During heavy working, the interlath spacing in pearlite will decrease and the ferrite will work harden. Thus, the hardness of pearlite increases with decreased lamellae spacing (Fig. 9) and the structure tends to resist recrystallization (Ref 9). The result is a thinner zone of heavy working and a smaller volume of metal extruding out of the contact zone. Fig. 9 Abrasive wear resistance and bulk hardness of 0.7% C steel as a function of pearlite interlamellar spacing. Abrasion data obtained using pin abrasion test apparatus with pressure, P, of 710 kPa (105 psi); two different 220-mesh abrasives (flint [96 to 99% Si] and silicon carbide) used in separate tests. Source: Ref 6 Under boundary lubrication conditions, where heavier loads are possible than under dry conditions, a pearlitic structure with tight interlamellar spacing in the pearlite phase is appropriate to minimize the depth of shear instability. Shear instability (Ref 10) below the contact surface is the source for deformation wear. Austenitic steels with varying manganese content show wear resistance to be a function of manganese content. The resistance depends on the transformation of the unstable austenite to martensite (that is, the hard wear-resistant phase). Manganese tends to promote the retention of room-temperature austenite in carbon steel. The retained austenite is unstable and will transform to martensite under heavy deformation. The room-temperature austenite becomes more stable as the manganese content of the alloy is increased. Pin-on-disk experiments performed by Jost and Schmidt (Ref 11) showed that the amount of austenite transformation decreased with increasing manganese content. Figure 10 shows an almost linear increase in wear resistance with decreasing concentration of manganese in the alloy. Fig. 10 Plot of wear resistance versus unstable austenite content as a function of manganese content. Pin-on- disk test specimens had 4 to 8% Mn content Fe-Mn- C steel pins rubbed against a steel disk. Test parameters, pressure, 4.2 MPa (610 psi); velocity, 0.18 m/s (0.59 ft/s). Source: Ref 6 References 1. G. Krauss, Physical Metallurgy and Heat Treatment of Steel, Metals Handbook Desk Edition, H.E. Boyer and T.L. Gall, Ed., American Society for Metals, 1985, p 28-2 to 28-10 2. Properties and Selection of Irons and Steels, Vol 1, 9th ed., Metals Handbook, 1978, p 606 3. D.E. Diesburg and F. Borik, Optimizing Abrasion Resistance and Toughness in Steels for the Mining Industry, Symposium on Material for the Mining Industry, Climax Molybdenum Co., 1974 4. M.M. Khruschov, The Principles of Abrasive Wear, Wear, Vol 28, 1974, p 97-99 5. E. Hornbogen, The Role of Fracture Toughness in the Wear of Metals, Wear, Vol 33, 1975, p 251-259 6. K.H. Zum Gahr, Abrasive Wear of Metallic Materials, Metallurgical Aspects of Wear, DGM, 1981, p 73- 104 7. P. Clayton, The Relationship between Wear Behavior and Basic Material Properties for Pearlitic Steels, Proceedings of the International Conference on Wear of Materials, American Society of Mechanical Engineers, 1979, p 395-396 8. W.A. Glaeser, High Strain Wear Mechanisms in Ferrous Alloys, Wear, Vol 123, 1988, p 155-169 9. N. Jost and I. Schmidt, Friction Induced Martensite in Austenitic Fe-Mn-C Steels, Proceedings of the International Conference on Wear of Materials, American Society of Mechanical Engineers, 1985, p 205- 214 10. G. Langford, Deformation of Pearlite, Metall. Trans. A, 1977, p 861-875 11. A.A. Rosenfield, A Shear Instability Model of Sliding Wear, Wear, Vol 116, 1987, p 319-328 Wear of Stainless Steels John H. Magee, Carpenter Technology Corporation Introduction STAINLESS STEELS are primarily used to resist corrosive attack in environments that are as mild as kitchen sinks or as severe as piping used in the chemical process industry. They are broadly defined as steels that contain at least 10.5% Cr. A wide range of corrosion resistance can be achieved by increasing the chromium content and adding other elements, especially nickel. In addition, high tensile yield strength (>1400 MPa, or 205 ksi) can be accomplished through martensite formation, precipitation hardening, or cold work. Because of the broad definition used, stainless steels are further divided into five families, each with a unique microstructure, alloying element additions, and range of physical, mechanical, and corrosion properties. The selection of a particular type of stainless steel for an application involves the consideration of such factors as the corrosion resistance of the alloy, mechanical properties, fabricability, and cost. However, for applications such as pumps, valves, bearings, fasteners, and conveyor belts, where one contacting metal surface moves relative to the other, the wear and galling resistance of the metals in contact should also be considered in the selection process. Stainless steels are characterized as having relatively poor wear and galling resistance, but are often required for a particular application, because of their corrosion resistance. Therefore, finding the most effective alloy to withstand wear and galling can be a difficult problem for design engineers. Lubricants and coatings are often used to reduce wear, although lubricant use is precluded in may applications, such as high-temperature environments, in which they can break down, or food and pharmaceutical processing equipment, which require sanitation. Additionally, a critical part, such as a valve in a power plant, must resist galling or seizing, because it can shut down or endanger the entire plant (Ref 1, 2). This article discusses each stainless steel family, specifically in terms of wear resistance. Information on wear and galling, laboratory wear and galling tests, and the associated data from these tests is presented. Applications and design considerations are also discussed. Classification of Stainless Steels. In the United States, grades of stainless steels are generally designated by one or more of these methods: the American Iron and Steel Institute (AISI) numbering system, the Unified Numbering System (UNS), and proprietary name of designation. In addition, designations have been established by most of the major industrial nations. Of the two institutional numbering systems, AISI is the oldest and most widely used. Most of the grades have a three-digit designation; the 200 and 300 series are generally austenitic stainless steels, whereas the 400 series are either ferritic or martensitic. Some of the grades have a one- or two-letter suffix that indicates a particular modification of the composition. The UNS system is a broader-based system that comprises a list of metal alloys, including stainless steel. This system includes a considerably greater number of stainless steels than AISI, because it incorporates all of the more recently developed stainless steels. The UNS designation for a stainless consists of the letter S, followed by a five-digit number. For those alloys that have an AISI designation, the first three digits of the UNS designation usually correspond to an AISI number. When the last two digits are 00, the number designates a basic AISI grade. Modifications of the basic grades use two digits other than zeroes. Table 1 provides the compositional limits for select stainless steels, listed by UNS and AISI type designations and separated into the basic families. Where AISI type designations are not available, common trade names are listed in parentheses. These names, the third commonly used identification of stainless steels, have often become the popular means of identifying a particular alloy. A complete listing of all stainless alloys available is provided in Ref 3. Table 1 Composition of selected standard and special stainless steels Composition, wt% max UNS designation AISI type C Mn Si P S Cr Ni Mo N Others Ferritic alloys S40500 405 0.08 1.00 1.00 0.040 0.030 11.50- 14.50 . . . . . . . . . 0.10-0.30 Al S40900 409 0.08 1.00 1.00 0.045 0.045 10.50- 11.75 0.50 . . . . . . 6 × C-0.75 Ti S43000 430 0.12 1.00 1.00 0.040 0.030 16.00- 18.00 . . . . . . . . . . . . S43020 430F 0.12 1.25 1.00 0.060 0.1 (a) 16.00- 18.00 . . . 0.60 . . . . . . S43023 430FSe 0.12 1.25 1.00 0.060 0.060 16.00- 18.00 . . . . . . . . . 0.15 min Se S43400 434 0.12 1.00 1.00 0.040 0.030 16.00- 18.00 . . . 0.75- 1.25 . . . . . . S44200 442 0.20 1.00 1.00 0.040 0.030 18.00- 23.00 . . . . . . . . . . . . S44300 443 (b) 0.20 1.00 1.00 0.040 0.030 18.00- 23.00 0.50 . . . . . . 0.90-1.25 Cu S44400 444 (b) 0.025 1.00 1.00 0.040 0.030 17.50- 19.50 1.00 1.75- 2.50 0.025 [0.20 + 4 (C + N)]-0.80 Ti + Nb S44600 446 (b) 0.20 1.50 1.00 0.040 0.030 23.00- 27.00 . . . . . . 0.25 . . . S18200 18-2FM (c) 0.08 1.25- 2.50 1.00 0.040 0.15 (a) 17.50- 19.50 . . . 1.50- 2.50 . . . . . . Martensitic alloys S40300 403 0.15 1.00 0.50 0.040 0.030 11.50- 13.00 . . . . . . . . . . . . S41000 410 0.15 1.00 1.00 0.040 0.030 11.50- 13.00 . . . . . . . . . . . . S41400 414 0.15 1.00 1.00 0.040 0.030 11.50- 13.00 1.25- 2.50 . . . . . . . . . S41600 416 0.15 1.25 1.00 0.060 0.15 (a) 12.00- 14.00 . . . 0.60 . . . . . . S41610 416 Plus X (d) 0.15 1.50- 2.50 1.00 0.060 0.15 (a) 12.00- 14.00 . . . 0.60 . . . . . . S41623 416Se 0.15 1.25 1.00 0.060 0.060 12.00- 14.00 . . . . . . . . . 0.15 min Se S42000 420 0.15 (a) 1.00 1.00 0.040 0.030 12.00- 14.00 . . . . . . . . . . . . S42010 TrimRite (e) 0.15- 0.30 1.00 1.00 0.040 0.030 13.50- 15.00 0.25- 1.00 0.40- 1.00 . . . . . . S42020 420F 0.15 (a) 1.25 1.00 0.60 0.15 (a) 12.00- 14.00 . . . 0.60 . . . . . . S42023 420FSe (b) 0.30- 0.40 1.25 1.00 0.060 0.060 12.00- 14.00 . . . 0.60 . . . 0.15 min Se; 0.60 Zr or Cu S43100 431 0.20 1.00 1.00 0.040 0.030 15.00- 17.00 1.25- 2.50 . . . . . . . . . S44002 440A 0.60- 0.75 1.00 1.00 0.040 0.030 16.00- 18.00 . . . 0.75 . . . . . . S44003 440B 0.75- 0.95 1.00 1.00 0.040 0.030 16.00- 18.00 . . . 0.75 . . . . . . S44004 440C 0.95- 1.20 1.00 1.00 0.040 0.030 16.00- 18.00 . . . 0.75 . . . . . . S44020 440F (b) 0.95- 1.20 1.25 1.00 0.040 0.10- 0.35 16.00- 18.00 0.75 0.40- 0.60 0.08 . . . S44023 440FSe (b) 0.95- 1.20 1.25 1.00 0.040 0.030 16.00- 18.00 0.75 0.60 0.08 0.15 min Se Austenitic alloys S20100 201 0.15 5.50- 7.50 1.00 0.060 0.030 16.00- 18.00 3.50- 5.50 . . . 0.25 . . . S20161 Gall- Tough (e) 0.15 4.00- 6.00 3.00- 4.00 0.040 0.040 15.00- 18.00 4.00- 6.00 . . . 0.08- 0.20 . . . S20300 203EZ (f) 0.08 5.00- 6.50 1.00 0.040 0.18- 0.35 16.00- 18.00 5.00- 6.50 0.50 . . . 1.75-2.25 Cu S20910 22-13-5 (c) 0.06 4.00- 6.00 1.00 0.040 0.030 20.50- 23.50 11.50- 13.50 1.50- 3.00 0.20- 0.40 0.10-0.30 Nb; 0.10-0.30 V S21000 SCF19 (e) 0.10 4.00- 7.00 0.60 0.030 0.030 18.00- 23.00 16.00- 20.00 4.00- 6.00 0.15 2.00 Cu S21300 15-15LC (e) 0.25 15.00- 18.00 1.00 0.050 0.050 16.00- 21.00 3.00 0.50- 3.00 0.20- 0.80 0.50-2.00 Cu S21800 Nitronic 60 (g) 0.10 7.00- 9.00 3.50- 4.50 0.040 0.030 16.00- 18.00 7.00- 9.00 . . . 0.08- 0.20 . . . S21904 21-6-9LC (c) 0.04 8.00- 10.00 1.00 0.060 0.030 19.00- 21.50 5.50- 7.50 . . . 0.15- 0.40 . . . S24100 18-2Mn (c) 0.15 11.00- 14.00 1.00 0.060 0.030 16.50- 19.50 0.50- 2.50 . . . 0.20- 0.45 . . . S28200 18-18 Plus (e) 0.15 17.00- 19.00 1.00 0.045 0.030 17.00- 19.00 . . . 0.50- 1.50 0.40- 0.60 0.50-1.50 Cu . . . Nitronic 30 (g) 0.10 7.00- 9.00 1.00 . . . . . . 15.00- 17.00 1.50- 3.00 . . . 0.15- 0.30 1.00 Cu S30100 301 0.15 2.00 1.00 0.045 0.030 16.00- 18.00 6.00- 8.00 . . . . . . . . . S30200 302 0.15 2.00 1.00 0.045 0.030 17.00- 19.00 8.00- 10.00 . . . . . . . . . S30300 303 0.15 2.00 1.00 0.20 0.15 (a) 17.00- 19.00 8.00- 10.00 0.60 . . . . . . S30310 303 Plus X (d) 0.15 2.50- 4.50 1.00 0.20 0.25 (a) 17.00- 19.00 7.00- 10.00 0.75 . . . . . . S30323 303Se 0.15 2.00 1.00 0.20 0.060 17.00- 19.00 8.00- 10.00 . . . . . . 0.15 min Se S30330 303 Cu (b) 0.15 2.00 1.00 0.15 0.10 (a) 17.00- 19.00 6.00- 10.00 . . . . . . 2.50-4.00 Cu; 0.10 Se S30400 304 0.08 2.00 1.00 0.045 0.030 18.00- 20.00 8.00- 10.50 . . . . . . . . . S30403 304L 0.03 2.00 1.00 0.045 0.030 18.00- 20.00 8.00- 12.00 . . . . . . . . . S30430 302 HQ (b) 0.10 2.00 1.00 0.045 0.030 17.00- 19.00 8.00- 10.00 . . . . . . 3.00-4.00 Cu S30431 302 HQ- FM (e) 0.06 2.00 1.00 0.040 0.14 16.00- 19.00 9.00- 11.00 . . . . . . 1.30-2.40 Cu S30452 304 HN (b) 0.08 2.00 1.00 0.045 0.030 18.00- 20.00 8.00- 10.50 . . . 0.16- 0.30 . . . S30500 305 0.12 2.00 1.00 0.045 0.030 17.00- 19.00 10.00- 13.00 . . . . . . . . . S30900 309 0.20 2.00 1.00 0.045 0.030 22.00- 24.00 12.00- 15.00 . . . . . . . . . S30908 309S 0.08 2.00 1.00 0.045 0.030 22.00- 24.00 12.00- 15.00 . . . . . . . . . S31000 310 0.25 2.00 1.50 0.045 0.030 24.00-19.00 . . . . . . . . 26.00 22.00 S31008 310S 0.08 2.00 1.50 0.045 0.030 24.00- 26.00 19.00- 22.00 . . . . . . . . . S31600 316 0.08 2.00 1.00 0.045 0.030 16.00- 18.00 10:00- 4.00 2.00- 3.00 . . . . . . S31603 316L 0.030 2.00 1.00 0.045 0.030 16.00- 18.00 10.00- 14.00 2.00- 3.00 . . . . . . S31620 316F 0.08 2.00 1.00 0.20 0.10 (a) 17.00- 19.00 12.00- 14.00 1.75- 2.50 . . . . . . S31700 317 0.08 2.00 1.00 0.045 0.30 18.00- 20.00 11.00- 15.00 3.00- 4.00 . . . . . . S31703 317L 0.030 2.00 1.00 0.045 0.030 18.00- 20.00 11.00- 15.00 3.00- 4.00 . . . . . . S32100 321 0.08 2.00 1.00 0.045 0.030 17.00- 19.00 9.00- 12.00 . . . . . . 5 × C min Ti S34700 347 0.08 2.00 1.00 0.045 0.030 17.00- 19.00 9.00- 13.00 . . . . . . 10 × C min Nb S34720 347F (b) 0.08 2.00 1.00 0.045 0.18- 0.35 17.00- 19.00 9.00- 12.00 . . . . . . 10 × C-1.10 Nb S34723 347FSe (b) 0.08 2.00 1.00 0.11- 0.17 0.030 17.00- 19.00 9.00- 12.00 . . . . . . 10 × C-1.10 Nb; 0.15-0.35 Se S38400 384 0.08 2.00 1.00 0.045 0.030 15.00- 17.00 17.00- 19.00 . . . . . . . . . N08020 20Cb-3 (e) 0.07 2.00 1.00 0.045 0.035 19.00- 21.00 32.00- 38.00 2.00- 3.00 . . . 8 × C-100 Nb; 3.00-4.00 Cu Duplex alloys S31803 2205 (c) 0.30 2.00 1.00 0.030 0.020 21.0- 23.0 4.50- 6.50 2.50- 6.50 0.08- 0.20 . . . S32550 Alloy 255 (c) 0.04 1.50 1.00 0.04 0.03 240- 27.0 4.50- 6.50 2.00- 4.00 0.10- 0.25 1.50-2.50 Cu S32900 329 0.20 1.00 0.75 0.040 0.030 23.00- 28.00 2.50- 5.00 1.00- 2.00 . . . . . . S32950 7-Mo Plus (e) 0.03 2.00 0.60 0.035 0.010 26.0- 29.0 3.50- 5.20 1.00- 2.50 0.15- 0.35 . . . Precipitation-hardenable alloys S13800 PH13-8 Mo (g) 0.05 0.20 0.10 0.010 0.008 12.25- 13.25 7.50- 8.50 2.00- 2.50 0.01 0.90-1.35 Al S15500 15-5PH (g) 0.07 1.00 1.00 0.040 0.030 14.00- 15.50 3.50- 5.50 . . . . . . 0.15-0.45 Nb; 2.50-4.50 Cu S15700 15-7PH (g) 0.09 1.00 1.00 0.040 0.030 14.00- 16.00 6.50- 7.25 2.00- 3.00 . . . 0.75-1.50 Al S17400 17-4PH (g) 0.07 1.00 1.00 0.040 0.030 15.50- 17.50 3.00- 5.00 . . . . . . 0.15-0.45 Nb; 3.00-5.00 Cu S17700 PH 17-7 (g) 0.09 1.00 1.00 0.040 0.040 16.00- 18.00 6.5-7.75 . . . . . . 0.75-1.50 Al S35000 633 (b) 0.07- 0.11 0.50- 1.25 0.50 0.040 0.030 16.00- 17.00 4.00- 5.00 2.50- 3.25 0.07- 0.13 . . . S35500 634 (b) 0.10- 0.15 0.50- 1.25 0.50 0.040 0.030 15.00- 16.00 4.00- 5.00 2.50- 3.25 0.07- 0.13 . . . S45000 Custom 450 (e) 0.05 1.00 1.00 0.030 0.030 14.00- 16.00 5.00- 7.00 0.50- 1.00 . . . 8 × C min; 1.25-1.75 Cu S45500 Custom 455 (e) 0.05 0.50 0.50 0.040 0.030 11.00- 12.50 7.50- 9.50 0.50 . . . 0.10-0.50 Nb; 1.50-2.50 Cu 0.80-1.40 Ti S66286 A286 (c) 0.08 2.00 1.00 0.040 0.030 13.50- 16.00 24.0- 27.0 1.00- 1.50 . . . 0.35 Al; 0.0010-0.010 B 1.90-2.35 Ti; 0.10-0.50 V Note: All compositions include Fe as balance. (a) Minimum, rather than maximum wt%. (b) Designation resembles AISI type, but is not used in that system. (c) Common trade name, rather than AISI type. (d) Trade name of Crucible Inc. (e) Trade name of Carpenter Technology Corporation. (f) Trade name of Al-Tech Corp. (g) Trade name of Armco Inc. Families of Stainless Steels On the basis of microstructure, there are five major families of stainless steels: ferritic, austenitic, martensitic, precipitation-hardenable (PH), and duplex (austenite and ferrite). Ferritic stainless steels are so named because their body-centered-cubic (bcc) crystal structure is the same as iron at room temperature. These alloys are magnetic and cannot be hardened by heat treatment. In general, ferritic stainless steels do not have particularly high strength. Their annealed yield strengths range from 275 to 350 MPa (40 to 50 ksi), and their poor toughness and susceptibility to sensitization limit their fabricability and the usable section size. Their chief advantages are their resistance to chloride stress-corrosion cracking, atmospheric corrosion, and oxidation, at a relatively low cost. Ferritic stainless steels contain between 11 and 30% Cr, with only small amounts of austenite-forming elements, such as carbon, nitrogen, and nickel. Their general use depends on their chromium content. The low-chromium (11%) alloys (S40500 and S40900) have fair corrosion and oxidation resistance and good fabricability at low cost. They have gained wide acceptance for use in automotive exhaust systems. The intermediate-chromium (16 to 18%) alloys (S43000 and S43400) are used for automotive trim and cooking utensils. These alloys are not as readily fabricated as the lower Cr alloys, because of their poor toughness and weldability. The high-chromium (19 to 30%) alloys (S44200 and S44600) are used for applications that require a high level of corrosion and oxidation resistance. These alloys often contain either aluminum or molybdenum and have a very low carbon content. Their fabrication is possible because of special melting techniques that can achieve very low carbon, as well as very low nitrogen contents. Stabilizing elements, like titanium and niobium, can be added to prevent sensitization and to improve as-welded properties. Austenitic stainless steels constitute the largest stainless family, in terms of number of alloys and usage. Like the ferritic alloys, they cannot be hardened by heat treatment. However, their similarity ends there. The austenitic alloys are nonmagnetic, and their structure is face-centered-cubic (fcc), like high-temperature (900 to 1400 °C, or 1650 to 2550 °F) iron. They possess excellent ductility, formability, and toughness, even at cryogenic temperatures. In addition, they can be substantially hardened by cold work. Although nickel is the chief element used to stabilize austenite, carbon and nitrogen are also used, because they are readily soluble in the fcc structure. A wide range of corrosion resistance can be achieved by balancing the ferrite-forming elements, such as chromium and molybdenum, with austenite-forming elements. Austenitic stainless steel can be subdivided into two categories: chromium-nickel alloys, such as S30400 and S31600, and chromium-manganese-nitrogen alloys, such as S20100 and S24100. The latter group generally contains less nickel and maintains the austenitic structure with high levels of nitrogen. Manganese (5 to 20%) is necessary in these low-nickel alloys to increase nitrogen solubility in austenite and to prevent martensite transformation. The addition of nitrogen also increases the strength in austenitic alloys. Typical chromium-nickel alloys have tensile yield strengths from 200 to 275 MPa (30 to 40 ksi) in the annealed condition, whereas the high-nitrogen alloys have yield strengths up to 500 MPa (70 ksi). As previously mentioned, austenitic alloys can be substantially hardened by cold working. The degree of work hardening depends on alloy content, with increasing alloy content decreasing the work-hardening rate. Figure 1 depicts the higher work-hardening rate of type 301 (7% Ni) versus type 305 (11.5% Ni), which is primarily due to its lower nickel content. Austenitic stainless steels that have a low alloy content, such as S20100, S20161, S30100, and S30400, often become magnetic because of the transformation to martensite when sufficiently cold worked or heavily deformed in machining or forming operations. The rapid work hardening of S20161 is a major advantage in sliding wear. In S30430, copper is intentionally added to lower the work-hardening rate for enhanced headability in the production of fasteners. Fig. 1 Effect of cold working on mechanical properties of stainless steels. (a) Type 301. (b) Type 305. Source: Ref 4 Another property that depends on alloy content is corrosion resistance. Molybdenum is added to S31700 and S31600 to enhance corrosion resistance in chloride environments. High-chromium grades (S30900 and S31000) are used in oxidizing environments and high-temperature applications, whereas a high-nickel grade (N08020) is used in severe reducing acid environments. To prevent intergranular corrosion after elevated-temperature exposure, titanium or niobium is added to stabilized carbon in S32100 or S34700. Also, lower-carbon grades (AISI L or S designations), such as S30403 (type 304L), have been established to prevent intergranular corrosion. Martensitic stainless steels are similar to iron-carbon alloys that are austenitized, hardened by quenching, and then tempered for increased ductility and toughness. These alloys are magnetic, and their heat-treated structure is body- centered tetragonal. In the annealed condition, they have a tensile yield strength of about 275 MPa (40 ksi) and are generally machined, cold formed, and cold worked in this condition. The strength obtained by heat treatment depends on the carbon content of the alloy. Increasing carbon content increases strength, but decreases ductility and toughness. The most commonly used alloy in this family is S41000, which contains about 12% Cr and 0.1% C. This alloy is tempered to a variety of hardness levels, from 20 to 40 HRC. Both chromium and carbon contents are increased in alloys S42000, S44002, S44003, and S44004. The first of these contains 14% Cr and 0.3% C and has a hardness capability of 50 HRC. The other three alloys contain 16% Cr and from 0.6 to 1.1% C. These alloys are capable of 60 HRC, and a tensile yield strength of 1900 MPa (280 ksi). The amount of primary carbides increases with increased carbon content in these three alloys. Wear resistance for martensitic stainless steels is very dependent on carbon content. S44004 (1.1% C) has excellent adhesive and abrasive wear, similar to tool steels, whereas S41000 (0.1% C) has relatively poor wear resistance. The key to adhesive wear resistance is a high hardness. Abrasive wear resistance requires both high hardness and primary carbides. Molybdenum and nickel can be added to martensitic stainless steel to improve corrosion and toughness properties. However, the addition of these elements is somewhat restricted, because higher amounts results in a microstructure that is not fully martensitic. PH stainless steels are chromium-nickel grades that can be hardened by an aging treatment. These grades are classified as austenitic (such as S66286), semi-austenitic (such as S17700), or martensitic (such as S17400). The classification is determined by their solution-annealed microstructure. The semi-austenitic alloys are subsequently heat treated, so that the austenite transforms to martensite. Cold work is sometimes used to facilitate the aging reaction. Various alloying elements, such as aluminum, titanium, niobium, or copper, are used to achieve aging. They generally form intermetallic compounds, but in S17400, fine copper precipitates are formed. Like the martensitic stainless steels, PH alloys can attain high tensile yield strengths, up to 1700 MPa (250 ksi). However, these alloys have superior ductility, toughness, and corrosion resistance, compared with the martensitic alloys. These properties are related to their higher chromium, nickel, and molybdenum contents, as well as their restricted carbon (0.040 max.) levels. The low carbon content of the martensitic PH stainless steels is especially critical for toughness and good ductility. However, this low carbon content reduces the wear resistance of these alloys. Duplex stainless steels are chromium-nickel-molybdenum alloys that are balanced to contain a mixture of austenite and ferrite, and are magnetic, as well. Their duplex structure results in improved stress-corrosion cracking resistance, compared with the austenitic stainless steels, and improved toughness and ductility, compared with the ferritic stainless steels. They are capable of tensile yield strengths ranging from 550 to 690 MPa (80 to 100 ksi) in the annealed condition, which is approximately twice the strength level of either phase alone. The original alloy in this family was the predominantly ferritic S32900. The addition of nitrogen to duplex alloys, such as S32950 and S31803, increases the amount of austenite to nearly 50%. In addition, nitrogen improves aswelded corrosion properties, chloride corrosion resistance, and toughness. The improvement in toughness is probably related to the higher amount of austenite present, which makes it possible to produce heavier product forms, such as plates and bars. Physical and Mechanical Properties of Stainless Steels The physical and mechanical properties of stainless steels are quite different from those of aluminum and copper alloys. However, when comparing the various stainless families with carbon steels, many similarities in properties exist, although there are some key differences. Like carbon steels, the density of stainless steels is 8.0 g/cm 3 , which is approximately three times greater than that of aluminum alloys (2.7 g/cm 3 ). Like carbon steels, stainless steels also have a high modulus of elasticity (200 MPa, or 30 ksi), which is nearly twice that of copper alloys (115 MPa, or 17 ksi) and nearly three times that of aluminum alloys (70 MPa, or 10 ksi). Differences between these materials are evident in thermal conductivity, thermal expansion, and electrical resistivity, as well. Figure 2 shows the large variation in thermal conductivity between various types of materials: type 6061 aluminum has a very high thermal conductivity, followed by aluminum bronze, 1080 carbon steel, and then stainless steels. For stainless steels, alloying additions, especially nickel, copper, and chromium, greatly decrease thermal conductivity. [...]... cobalt-base alloys and cadmium-plated alloys resist galling while titanium alloys tend to gall Factors Affecting Wear and Galling The factors that affect wear and galling can be design, lubrication, environmental, and material related Component design is probably the most critical factor When stainless steels are required, proper design can minimize galling and wear Similar applications, like valve parts,... conclusion of the test, corrosive wear versus time is plotted for the alloys being evaluated Block-on-ring is an ASTM standard test (Ref 19) for determining the resistance of materials to sliding wear The test utilizes a block-on-ring friction and wear testing machine to rank pairs of materials according to their sliding wear characteristics under various conditions Rotational speed and load can be varied to... as riveted joints This type of wear is a combination of oxidation and abrasive wear Oscillation of two metallic surfaces produces tiny metallic fragments that oxidize and become abrasive Subsequent wear proceeds by mild adhesive wear in combination with abrasive wear Fretting wear is influenced by contact conditions, environmental conditions, and material properties and behavior These factors may interact... the sulfur-bearing stainless steels, such as types 303 and 416, have better galling resistance, but poorer adhesive wear resistance than their non-sulfur-bearing parent alloys, types 304 and 410 Another alloy example is Waukesha 88, which contains a tin- and bismuth-bearing second phase that results in excellent galling resistance, despite the high nickel content of the alloy (Ref 16) Hardness and microstructure... resulting in low wear rates This form of wear is called mild wear, or oxidative wear, and can be tolerated by most moving components When the applied load is high, metallic bonds will form between the surface asperities, and the resulting wear rates are high The load at which there is a transition from mild to severe wear is called the transition load Adhesive wear is more prevalent in parts where a lubricant... test) Fig 9 Key components of a block-on-ring test apparatus The coefficient of sliding friction, using the equation sf = (friction force)/(applied load) Source: Ref 2 sf, is calculated Crossed-cylinder is an ASTM standard test (Ref 20) for determining the resistance of metallic materials to metal-to- metal wear This test ranks the adhesive wear resistance of materials and evaluates the compatibility of... Abrasion-resistant steel 7 (250) 25 25 25 6 47 47 23 23 48 (failed in 18 months) Source: Ref 11 Adhesive Wear The metal-to-metal wear resistance of stainless steels can be determined by using the crossed-cylinder wear test Unlike low-stress abrasion resistance, austenitic stainless steels generally have superior resistance, compared with martensitic stainless alloy (Table 6) The excellent wear resistance... have the highest tensile ductility and toughness The latter two alloys, S20161 and S 2180 0, were specifically developed to have superior resistance to galling and metal-to-metal wear for stainless steels Alloy N08020 is a high-nickel (33%) stainless alloy for use in harsh corrosive environments Table 2 Properties of selected stainless steels relative to various ferrous and nonferrous alloys UNS or AISI... quenched from 1010 °C (185 0 °F) and tempered: at 250 °C (500 °F) at 593 °C (1100 °F) Annealed Oil quenched from 1038 °C (190 0 °F) and tempered at 316 °C (600 °F) Annealed Oil quenched from 1038 °C (190 0 °F) and tempered at 316 °C (600 °F) 82 HRB 276 40 517 75 35.0 70.0 43 HRC 26 HRC 92 HRB 52 HRC 97 HRB 57 HRC 1089 724 345 1482 448 189 6 158 105 50 215 65 275 1337 827 655 1724 758 197 5 193 120 95 250 110... loss is determined for both the stationary and rotating specimens, and the total volume loss is recorded When dissimilar materials are being tested, it is recommended that each alloy be tested in both the stationary and rotating positions Fig 10 Typical crossed-cylinder test apparatus Source: Ref 21 Pin-on-disk is an ASTM standard test for determining the wear of material during sliding (Fig 11) The . S24100 1 8- 2Mn (c) 0.15 11.0 0- 14.00 1.00 0.060 0.030 16.5 0- 19. 50 0.5 0- 2.50 . . . 0.2 0- 0.45 . . . S28200 1 8- 18 Plus (e) 0.15 17.0 0- 19. 00 1.00 0.045 0.030 17.0 0- 19. 00 . . . 0.5 0- 1.50. 0.10 7.0 0- 9.00 3.5 0- 4.50 0.040 0.030 16.0 0- 18. 00 7.0 0- 9.00 . . . 0.0 8- 0.20 . . . S 2190 4 2 1-6 -9 LC (c) 0.04 8.0 0- 10.00 1.00 0.060 0.030 19. 0 0- 21.50 5.5 0- 7.50 . . . 0.1 5- 0.40 Gall- Tough (e) 0.15 4.0 0- 6.00 3.0 0- 4.00 0.040 0.040 15.0 0- 18. 00 4.0 0- 6.00 . . . 0.0 8- 0.20 . . . S20300 203EZ (f) 0.08 5.0 0- 6.50 1.00 0.040 0 .1 8- 0.35 16.0 0- 18. 00 5.0 0- 6.50