Volume 09 - Metallography and Microstructures Part 4 pdf

martensitic steels are more difficult to etch in this manner than medium- and high-carbon steels In the case of lath martensite, the packet size also is an important microstructure measurement The hardness and strength of martensite increase with increasing carbon content However, it also becomes more brittle Martensite has a body-centered tetragonal (bct) structure The degree of tetragonality increases with carbon content Tempering decreases the strength of martensite, but increases its toughness However, tempering of alloy steels within certain temperature ranges can reduce toughness because of embrittlement (temper martensite embrittlement or temper embrittlement) However, tempering, along with composition selections, can permit achievement of a wide range of useful strengths and toughness More information is available in the articles "Tempering of Steel" and "Martempering of Steel" in Heat Treating, Volume of ASM Handbook Pearlite is a mixture of ferrite and cementite in which the two phases are formed from austenite in an alternating lamellar pattern Formation of pearlite requires relatively slow cooling from the austenite region and depends on the steel composition Pearlite forms at temperatures below the lower critical temperature of the steel in question and may be formed isothermally or by continuous cooling As the hardenability of the steel decreases, the cooling rate can be increased without the formation of other constituents As isothermal reaction temperature decreases or the cooling rate increases, the interlamellar spacing decreases The strength and toughness of pearlitic steels increase as the interlamellar spacing decreases Because the maximum solubility of carbon in ferrite is nearly zero at room temperature and a fully pearlitic microstructure is obtained when a steel containing 0.8% C is slowly cooled from the austenite region, the volume fractions of ferrite and pearlite can be estimated In low-carbon steels, ferrite forms before the eutectoid reaction, which produces pearlite, and is termed proeutectoid ferrite Below approximately 0.4% C, the proeutectoid ferrite forms as equiaxed patches and is the continuous phase Above approximately 0.4% C, the proeutectoid ferrite generally exists as isolated equiaxed patches or as a grain-boundary layer, depending on thermal history Carbon steels are referred to as hypoeutectoid, eutectoid, or hypereutectoid when their carbon contents are below 0.8% approximately 0.8%, or above 0.8%, respectively In the case of hypereutectoid steels, excess cementite above the amount required to form pearlite will precipitate in the austenite grain boundaries before the eutectoid reaction This excess cementite is referred to as proeutectoid cementite A grain-boundary cementite network embrittles such steels The strength and hardness of ferrite-pearlite steels increase with increasing pearlite content and are further increased by reductions in the interlamellar spacing Pure ferrite (no carbon) has a hardness of approximately 70 HV; fine pearlite in a eutectoid carbon steel has a hardness of nearly 400 HV Fine pearlite is the most desirable structure for wire drawing, where extremely high strengths can be obtained Carbon steels are widely used in the hot-rolled condition The austenite grain size of the steel as it enters the final rolling pass establishes the relative sizes of the ferrite and pearlite produced during subsequent air cooling, but the cooling rate influences the fineness of the pearlite, the morphology of the proeutectoid ferrite, and the amounts of the various constituents Bainite, an austenite transformation product, is a lathlike aggregate of ferrite and cementite that forms under conditions intermediate to those that result in formation of pearlite and martensite Bainite is commonly classified as upper bainite or lower bainite Upper bainite forms isothermally or during continuous cooling at temperatures just below those that produce bainite Lower bainite forms at still lower temperatures, down to the Ms temperature or slightly below in certain cases Formation of upper bainite begins by growth of long ferrite laths devoid of carbon Because the carbon content of the ferrite laths is low, the austenite at the lath boundaries is enriched in carbon The shape of the cementite formed at the lath boundaries varies with carbon content In low-carbon steels, the cementite will precipitate as discontinuous stringers and isolated particles, but at higher carbon contents the stringers are more continuous In some instances, carbide is not precipitated, but is retained as austenite or transforms to plate martensite More information is provided in the article "Bainitic Structures" in this Volume Lower bainite has a more platelike appearance than upper bainite The ferrite plates are broader than those in upper bainite and are more similar in appearance to plate martensite As with upper bainite, the appearance of lower bainite varies with carbon content Lower bainite is characterized by formation of rodlike cementite within the ferrite plates Nonmetallic Inclusions Inclusions in steel are indigenous or exogenous in origin Indigenous inclusions form as a natural result of the decrease in solubility of oxygen or sulfur that occurs as the metal freezes Exogenous inclusions are introduced from external sources, for example, slag or refractories, that enter the steel and become trapped during solidification In most instances, these included phases are undesirable Examples of nonmetallic inclusions in carbon and alloy steels are presented in Fig 96, 97, 98, 99, 100, 101, 102, 103, and 104 in the section "Atlas of Microstructures for Carbon and Alloy Steels" in this article Carbon and Alloy Steels: Metallographic Techniques and Microstructures Arlan O Benscoter, Metallographer, Bethlehem Steel Corporation Atlas of Microstructures for Carbon and Alloy Steels Fig 45 Rimmed steel (0.08C), as rolled The structure is ferrite grains; note the slight difference in grain size from case (top) to core 3% nital 100× Fig 46 Rimmed steel (0.013% C), finish rolled at 940 °C (1720 °F) and coiled at 725 °C (1340 °F) The relatively fine ferrite grain is unusual for a steel rolled at a temperature this high Nital 100× Fig 47 Same as Fig 46, except finish rolled at 845 °C (1550 °F) and coiled at 695 °C (1280 °F) At this rolling temperature, low carbon content contributed to development of a duplex ferrite grain Nital 100× Fig 48 Rimmed steel (0.012% C), finish rolled at 820 °C (1510 °F) and coiled at 680 °C (1260 °F) Strain imparted by rolling at low finishing temperature enhances grain growth at coiling temperature Nital 100× Fig 49 Low-carbon (0.05% C) steel, showing Fe3C carbide at ferrite grain boundaries 2% nital, s, followed by Marshall's reagent, s 340 × Fig 50 Rimmed steel (0.06 %C), finish rolled at 845 °C (1550 °F) and coiled at 620 °C (1150 °F) A fine-grain ferrite developed Nital 100× Fig 51 Same material and processing as Fig 50, but at a higher magnification showing particles of cementite at the ferrite grain boundaries Picral 500× Fig 52 Same as Fig 50, except finish rolled at 790 °C (1450 °F) and coiled at 620 °C (1150 °F) The rolling temperature developed fine grains, but self-annealing caused surface grain enlargement Nital 100× Fig 53 Fig 54 Fig 55 Low-carbon (0.06% C) steel, cold rolled and annealed Fig 53: massive carbide particles Fig 54: medium size carbide particles Fig 55: small, dispersed carbides Picral All 1000× Fig 56 Rimmed steel (0.06% C), finish rolled at 890 °C (1630 °F) and coiled at 655 °C (1210 °F) Ferrite matrix contains cementite particles (light, outlined) and traces of pearlite Picral 1000× Fig 57 Same as Fig 56, except the steel was subsequently cold rolled to 60% reduction Cold rolling fragmented the cementite particles Picral 500× Fig 58 Same as Fig 57, but decarburized in wet hydrogen at 705 °C (1300 °F), The cementite particles were depleted of carbon, resulting in the formation of voids in the ferrite matrix Picral 500× Fig 59 Sheet steel (0.06C-0.35Mn-0.04Si-0.40Ti), tint etched to color ferrite grains Color depends on grain orientation Beraha's tint etchant 100× Fig 60 Fig 61 Fig 62 Capped 1008 steel, finished hot, coiled cold, then hot rolled from a thickness of mm (0.13 in.) Note increasing grain elongation as reduction increases Fig 60: 10% reduction Fig 61: 20% reduction Fig 62: 30% reduction 4% nital 250× Fig 63 Fig 64 Fig 65 Same as Fig 60, 61, and 62 Fig 63: 40% reduction Fig 64: 50% reduction Fig 65: 60% reduction 4% nital All 250× Fig 66 Fig 67 Fig 68 Same as Fig 60, 61, 62, 63, 64, and 65 Fig 66: 70% reduction Fig 67: 80% reduction Fig 68: 90% reduction 4% nital All 250× Fig 69 Low-carbon steel (0.10% C), cold rolled 90% to a thickness of 0.25 mm (0.01 in.) with HR30-T = 80 and annealed 106 s at 550 °C (1025 °F) Recrystallized 10%; HR30-T reduced to 79 Nital 1000× Fig 70 Same steel and cold rolling as Fig 69, but annealed at 550 °C (1025 °F) Recrystallization increased to 40%; HR30-T reduced to 76 Nital 1000× Fig 71 Same steel and cold rolling as Fig 69, but annealed 14.5 at 550 °C (1025 °F) Recrystallization is 80%; HR30-T reduced to 70 Nital 1000× Fig 72 Aluminum-killed 1008 steel, normalized after 60% cold reduction to a final thickness of 0.8 mm (0.03 in.) The ferritic structure contains fine pearlite (dark areas) at the grain boundaries 4% nital 1000× Fig 73 Same as Fig 72, except process annealed at 595 °C (1100 °F) after normalizing Ferritic structure contains some fine pearlite and some spheroidized cementite at the grain boundaries 4% nital 1000× Fig 74 Same as Fig 72, except process annealed at 705 °C (1300 °F) after normalizing The ferritic structure contains some cementite particles at the grain boundaries 4% nital 1000× Fig 75 Rimmed 1008 steel, coiled at 570 °C (1060 °F), cold rolled, heated rapidly in a vacuum to 690 °C (1270 °F), held 20 h, and cooled slowly Structure is ferrite and finely spheroidized cementite Picral 500× Fig 76 Same as Fig 75, except after cold rolling the sheet was heated rapidly to 740 °C (1360 °F), held 20 h, then cooled slowly Structure is ferrite, cementite particles, and pearlite Picral 500× Fig 77 Same as Fig 75, except the steel was coiled at 680 °C (1260 °F) cold rolled, heated rapidly to 690 °C (1270 °F), held for 20 h, and cooled slowly Structure is ferrite and coarse cementite Picral 500× Fig 78 Same as Fig 75, except coiled at 680 °C (1260 °F), cold rolled 70%, heated rapidly to 740 °C (1360 °F), cooled slowly to 690 °C (1270 °F), held 20 h, and cooled slowly The structure is ferrite and pearlite Picral 500× Fig 43 ASTM A572, Grade 55, steel plate, 19 mm (0.75 in.) thick, as hot rolled The structure is ferrite and pearlite Note presence of a few nonmetallic stringers in the ferrite 2% nital 100× Fig 44 ASTM A572, Grade 65, steel plate, mm (0.25 in.) thick, as hot rolled The microstructure consists of ferrite and pearlite (dark), with possibly some bainite 1% nital 250× Fig 45 ASTM A572, Grade 65, steel plate, mm (0.25 in.) thick Normalized by austenitizing at 900 °C (1650 °F) for h and cooling in air Structure is ferrite and pearlite (dark) 1% nital 250× Fig 46 ASTM A633, Grade C, 100-mm (4-in.) thick plate Austenitized at 900 °C (1650 °F) and air cooled (normalized) Fine, polygonal ferrite and fine, partially banded pearlite Nital plus picral 200× Fig 47 ASTM A710, Grade A, Class 3, 25-mm (1-in.) thick plate Austenitized at 900 °C (1650 °F), waterspray quenched, and aged at 650 °C (1200 °F) Predominantly acicular ferrite with fine, tempered carbides Nital plus picral 500× Fig 48 ASTM A737, Grade B, 38-mm (1.5-in.) thick plate Austenitized at 900 °C (1650 °F) and air-cooled normalized Fine, polygonal ferrite and banded pearlite Nital plus picral 200× Fig 49 Same as Fig 48, but austenitized at 900 °C (1650 °F), water-spray quenched, and tempered at 595 °C (1100 °F) Mixed fine polygonal and acicular ferrite with tempered carbides Nital plus picral 200× Fig 50 ASTM A808, 8-mm ( -in.) thick plate, as-rolled condition Fine-grain, slightly elongated ferrite16 pearlite Several thin, elongated MnS inclusions are evident Nital plus picral 500× Fig 51 Same as Fig 50, but 50-mm (2-in.) thick as-rolled plate Structure consists of polygonal ferritepearlite Note effect of gage dimension on grain size (compare with Fig 50) Nital plus picral 500× Fig 52 API X60, 10-mm (0.4-in.) thick plate (skelp) for line-pipe, control-rolled Fine-grain, polygonal ferrite; moderately banded pearlite Nital plus picral 200× Steel Tubular Products: Metallographic Techniques and Microstructures Donald S Dabkowski, Product Manager, Tubular Metallurgy, United States Steel Corporation; Frederick W Kern, Metallurgical Engineer, Tubular Metallurgy, United States Steel Corporation Introduction STEEL TUBULAR PRODUCTS are usually classified commercially according to common usage, as shown in Table Further subdivisions and product descriptions may be found in the article "Steel Tubular Products" in Properties and Selection: Irons, Steels, and High-Performance Alloys, Volume of ASM Handbook, formerly 10th Edition Metals Handbook Table Classification of steel tubular products Typical use Production processes Outside diameter(a), in Typical grades Usual finished status To line oil and gas wells to prevent collapse of the hole Seamless, electric resistance welding 4.5-20 H-40, J-55, K55 As-rolled C-75, L-80, N80, C-90, G-95, P-110, Q-125 Normalize or quench and temper All others Product Quench and temper H-40, J-55, N80, P-105 As-rolled Normalize or quench and temper Oil country goods Casing Tubing To convey oil or gas from the producing strata to the earth's surface Seamless, continuous welding, electric resistance welding 1.050-4.5 Rotary stem for drill bits Seamless 2.375-6.625 Line pipe Conveys oil, gas, or water 0.125(nom)80 Normalize and temper, or quench and temper Quench and temper All grades As-rolled B, X42, X46, X52, X60, X65, X70 Seamless, electric resistance welding, continuous welding, double submerged arc welding E X-95, G-105, S135 Drill pipe As-rolled Control rolled Standard pipe Plumbing, electrical conduit, low pressure conveyance of fluids, and nonstringent structural applications Seamless, electric resistance welding, continuous welding, double submerged arc welding 0.125(nom)80 All grades As-rolled Mechanical tubing Variety of round, hollow mechanical parts, such as automotive axles, bearing races, and hydraulic pistons Seamless, electric resistance welding 0.375-10.75 Carbon and alloy Hot rolled or cold drawn Pressure tubing Boiler tubes, condenser tubes, heat exchanger tubes, and refrigeration tubes Seamless, electric resistance welding 0.5-10.75 Carbon and alloy Hot rolled or cold drawn Note: Because steel tubular products manufactured in the United States are customarily produced to standard inch and fractional inch sizes, tubular product sizes are given only in inches in this article in = 25.4 mm or 2.54 cm nom: nominal (a) Property requirements for oil country goods may be found in the following American Petroleum Institute (API) Specifications: • • • 5A: "Welded or Seamless Steel Pipe for Oil or Gas Well Casing, Tubing, or Drill Pipe" 5AC: "Welded or Seamless Steel Pipe with Restricted Yield-Strength Range for Oil or Gas Well Casing or Tubing" 5AX: "High-Strength Seamless Steel Pipe for Oil or Gas Well Casing, Tubing, or Drill Pipe" Specifications for line pipe are covered by API Specification 5L, "Welded or Seamless Steel Line Pipe for Oil and Gas Transmission." The Annual Book of ASTM Standards, Section 1, Volume 01.01, contains materials specifications for standard pipe and mechanical and pressure tubing Some tubular product compositions are produced in accordance with American Iron and Steel Institute designations Typical compositions of steel tubular products depicted in the "Atlas of Micrographs" in this article are listed in Table Steels used for tubular products cover various low-carbon, medium-carbon, low-alloy, and higher alloy grades Most common, however, are the carbon and low-alloy steels Table Compositions of steel tubular products Steel Composition, % C Mn Si P S Cr Mo Nb V Ti Al B Ni ASTM and API pipe steels A 106, Grade A 0.25 max 0.270.93 0.10 min(a) A106, Grade B 0.30 max 0.291.06 0.10 min(a) A335, Grade P2 0.100.20 0.300.61 0.100.30 0.045 max 0.045 max 0.500.81 0.440.65 A335, Grade P5 0.15 max 0.300.60 0.50 max 0.030 max 0.030 max 4-6 0.450.65 A335, Grade P7 0.15 max 0.300.60 0.50-1 0.030 max 0.030 max 6-8 0.440.65 A335, Grade P11 0.15 max 0.300.60 0.50-1 0.030 max 0.030 max 1-1.50 0.440.65 A335, Grade P22 0.15 max 0.300.60 0.50 max 0.030 max 0.030 max 1.902.60 0.871.13 A381, Class Y52 0.26 max 1.40 max 0.040 max 0.050 max API X46 5L- 0.30 max 1.35 max 0.04 max 0.05 max API X60 5L- 0.26 max 1.35 max 0.04 max 0.05 max 0.05 0.02 0.03 min(b) API 5L, Grade X52 0.21 0.90 0.26 0.015 max 0.015 max 0.09 0.030 API 5A, Grade K55 0.45 1.30 0.26 0.015 max 0.015 max 0.007 API 5AX, Grade N80 0.28 1.48 0.26 0.015 max 0.015 max 0.20 0.10 0.007 API 5AX, Grade P110 0.28 1.48 0.26 0.015 max 0.015 max 0.22 0.23 0.007 API 5AC, Grade C-90 0.29 0.50 0.26 0.015 max 0.015 max 1.08 0.33 0.03 0.0015 API 5L, Grade A 0.17 0.50 0.020 0.020 API 5L, Grade X60 0.05 1.11 0.017 0.007 0.006 0.045 0.045 ASTM and AISI tube steels A161 0.100.20 0.300.80 0.25 max(a) A200, Grade T5 0.15 max 0.300.60 0.50 max 0.030 max 0.030 max 4-6 0.450.65 A209, Grade T1 0.100.20 0.300.80 0.100.50 0.045 max 0.045 max 0.440.65 A213, Grade T5c 0.12 max 0.300.60 0.50 max 0.03 max 0.03 max 4-6 0.450.65 × C (0.70 max) A254, Class I 0.050.15 0.270.63 0.050 max 0.060 max 1015 0.130.18 0.300.60 0.040 max 0.050 max 1018 0.150.20 0.600.90 0.040 max 0.050 max 1025 0.220.28 0.300.60 0.040 max 0.050 max 1215 0.09 max 0.751.05 0.040.09 0.260.35 4140 0.380.43 0.75-1 0.200.35 0.035 max 0.040 max 0.801.10 0.150.25 4620 0.170.22 0.450.65 0.200.35 0.035 max 0.040 max 0.200.30 1.65-2 5048 0.48 0.300.50 0.200.35 0.035 max 0.040 max 0.300.50 8620 0.180.23 0.700.90 0.200.35 0.035 max 0.040 max 0.400.60 0.150.25 0.400.70 (a) Also contains 0.048% max P and 0.058% max S (b) Niobium, vanadium, and titanium used at manufacturer's option Specimen Preparation Tubular products present no special problems in specimen extraction Once the tubular steel testpieces are obtained, the procedures for final sectioning, mounting, grinding, and polishing are the same as those described in the article "Carbon and Alloy Steels" in this Volume The large size of the specimens and the desired information often make mounting unnecessary Etching Nital is a widely used etchant for tubular steels It is preferred for delineating ferrite grain boundaries Picral is preferred for examining carbide particles in annealed steels and in quenched and tempered steels Vilella's reagent is used for the higher alloy of steel, such as those found in ASTM 200 and A 213 It consists of mL hydro-chloric acid (HCl), g picric acid, 100 mL ethanol and drops zephiran chloride It is usually applied by immersion Examination of Welded Joints Steel tubular products are often welded, which requires techniques for metallographic examination of welded joints These techniques are discussed in the article "Weldments" in this Volume Details on etchants used to examine welds between carbon and low-alloy steels or between carbon or low-alloy steels and stainless steels can be found in the article "Plate Steels" in this Volume Steel Tubular Products: Metallographic Techniques and Microstructures Donald S Dabkowski, Product Manager, Tubular Metallurgy, United States Steel Corporation; Frederick W Kern, Metallurgical Engineer, Tubular Metallurgy, United States Steel Corporation Atlas of Microstructures for Steel Tubular Products Fig API 5L, Grade X52, as-rolled seamless steel pipe Microstructure consists of small colonies of pearlite in a ferrite matrix Picral 500× Fig API 5A, Grade K55, as-rolled seamless steel pipe produced by press-piercing Pearlite colonies with ferrite partially outlining the prior-austenite grain boundaries Picral 500× Fig API 5AX, Grade N-80, seamless steel pipe, austenitized at 845 °C (1550 °F), water quenched, and tempered at 620 °C (1150 °F) Microstructure is tempered martensite Picral 500× Fig API 5AX, Grade P-110, seamless steel pipe, austenitized at 845 °C (1550 °F), water quenched, and tempered at 595 °C (1100 °F) Microstructure is tempered martensite Picral 500× Fig API 5AC, Grade C-90, seamless steel pipe, (24 HRC maximum), austenitized at 870 °C (1600 °F), water quenched, and tempered at 705 °C (1300 °F) Tempered martensite Picral 500× Fig API 5L, Grade A, continuous welded pipe, as-rolled Microstructure consists of large pearlite colonies in a ferrite matrix Picral 500× Fig API 5L, Grade X60, electric resistance welded pipe, as-rolled Small angular carbides in a ferrite matrix Picral and nital 500× Fig API 5L, Grade X52, double submerged arc welded pipe showing pearlite colonies in a ferrite matrix Picral 500× Fig Section through a resistance weld in API 5L-X46 steel pipe, 18-in OD by 0.375-in wall Weld is sound (NH4)2S2O8 Fig 10 Section through a two-pass butt weld (automatic gas metal arc process, CO2 shielding) in API 5L-X60 steel pipe, 30-in OD by 0.25-in wall A defective weld (note incomplete fusion, right) 4% nital 10× Fig 11 Section through a two-pass butt weld made in the same size of API 5L-X60 steel pipe as in Fig 10 and by the same process (automatic gas metal arc, CO2 shielding) Fusion is complete A defective weld (note shrinkage crack in the weld bead, which occurred during solidification) 4% nital 15× Fig 12 ASTM A106, Grade A, seamless steel pipe, 0.84-in OD, 0.147-in wall, normalized by austenitizing at 870 °C (1600 °F), air cooling Longitudinal midwall section Ferrite (light areas) and pearlite (dark) Nital 250× Fig 13 ASTM A106, Grade A, seamless steel pipe, 1.315-in OD by 0.179-in wall, as hot drawn Specimen was longitudinal at midwall thickness Structure is ferrite (light gray) in a matrix of pearlite (gray and black) Nital 275× Fig 14 ASTM A106 Grade B, seamless steel pipe, 3-in OD by 0.43-in wall, as-fabricated Specimen was taken in longitudinal direction Structure consists of ferrite (light areas) and pearlite (dark areas) Nital 100× Fig 15 ASTM A106, Grade B, seamless steel pipe, 12-in OD by 1.3-in wall, as-fabricated Specimen was taken in longitudinal direction Light areas are ferrite; dark areas are pearlite Nital 100× Fig 16 ASTM A106, Grade B, steel pipe, 28-in OD by 1.22-in wall, as-extruded Specimen taken near surface Ferrite at grain boundaries and as plates in grains Nital 100× Fig 17 Same grade and size of pipe as for Fig 16, but normalized by austenitizing at 870 °C (1600 °F) and air cooling Specimen was taken near surface Note absence of decarburization Nital 100× Fig 18 Same grade and size of pipe as for Fig 16, but normalized by austenitizing at 1095 °C (2000 °F) for h and air cooling Surface shows decarburization (light gray areas near top) The light areas near bottom of micrograph are ferrite; the matrix is pearlite Nital 100× Fig 19 Same grade and size of pipe as for Fig 16, and same heat treatment as for Fig 18, but specimen was taken from center of pipe wall Structure consists of ferrite (light) at prior austenite grain boundaries and as plates within grains in a matrix of pearlite Nital 100× Fig 20 Same grade and size of pipe as for Fig 16, but normalized by austenitizing at 1315 °C (2400 °F) for h and air cooling The light areas in the structure are ferrite along boundaries of very coarse prior austenite grains and as plates within grains; the matrix is pearlite Nital 100× Fig 21 ASTM A335, Grade P2, seamless steel pipe, cold drawn and stress relieved at 690 °C (1275 °F) Specimen was taken in longitudinal direction Light areas are blocky ferrite; dark areas, containing ferrite plates Nital 100× ... 0.20C-1.0Mn steel, as-quenched The structure is pearlite (dark), martensite (light), and ferrite (white) 10% Na2S2O5 1000× (M Scott) Fig 109 Steel specimen (Fe-0.22C-0.88Mn-0.55Ni-0.50Cr-0.35Mo)... areas are ferrite; gray and black areas, pearlite with fine and coarse lamellar spacing Nital 500× Fig 1 64 25-mm (1-in.) diam 41 40 steel bar, austenitized h at 845 °C (1550 °F) and water quenched... (Fe-0.75C) that was held 2A h at 1095 °C (2000 °F) and air cooled Slow cooling from the austenite region produced this pearlite structure 4% picral 500× Fig 158 Dual-phase steel (0.11C-1 .40 Mn-0.58Si-0.12Cr-0.08Mo),