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Carbon and Low-Alloy Steels for Non-Metallurgists


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This presentation will provide the non-metallurgist with a basic understanding of carbon and low alloy steels. First we'll describe the carbon and low alloy steels by examining the iron-carbon binary phase diagram and understand the basic microstructures as related to carbon content. We'll discuss the nomenclature of the different carbon and alloy steel groups. We will then examine how mechanical properties are influenced through carbon content, alloy additions and heat treatment. We will also discuss the differences in carbon and low alloy steels that are specified as structural steels and high strength-low alloy (HSLA) steels. Finally, we will address the issues of material selection, processing and finishing.

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Carbon and Low-Alloy Steels for Non-Metallurgists

  1. 1. Carbon and Low-Alloy SteelsPresented by Weldon ‘Mak’ MakelaSenior Failure Analysis EngineerMaterials Testing & Analysis Group, Element St. Paul April 26, 2012 Carbon and Low-Alloy Steels
  2. 2. Future Topics for webinars• Metallurgical Failure Analysis for Problem Solving-Dec. 4, 2011• Carbon and Low-Alloy Steels-April 26, 2012• Heat Treating• Stainless Steels• Tool Steels• Aluminum Alloys• Surface Engineering• Corrosion Carbon and Low-Alloy Steels 2
  3. 3. Carbon and low-alloy steels• What is steel?• Iron-carbon phase diagram.• Carbon and low-alloy steel classifications.• Mechanical properties.• Microstructure.• Application.• Structural Steels.• Specifications and selection of carbon and low-alloy steels.• This presentation will not cover cast steels, coated products, forgings, cast irons, ultra-high strength or other specialty steels.• Tool steels and stainless steels will be covered in separate presentations.Source: Metals Handbooks, 10th Edition, ASM International. Carbon and Low-Alloy Steels 3
  4. 4. What is steel?• Steel is iron with small amounts of carbon and other elements added to impart unique properties in the material.• Pure iron is soft, ductile and has low strength.• Steel is made by reducing iron ore to iron, which contains carbon and other impurities. Further refining reduces the impurities, controls carbon and other element content.• Steels consist of iron with varying amounts of carbon: – Carbon content varies from 0.02-1.25%. – Carbon is the primary elemental addition to increase strength. – Carbon allows for heat treatment to increase strength.• Other elemental additions improve properties: – Manganese-up to 2.00%. – Silicon-up to 1.0%. – Chromium, nickel, molybdenum, and other elements in varying quantities. Carbon and Low-Alloy Steels 4
  5. 5. Iron-Carbon Phase Diagram Carbon and Low-Alloy Steels 5
  6. 6. Carbon Steels• The most common metal used to manufacture products. - Low-carbon steels: Carbon content varies from 0.05% to 0.30%. - Medium-carbon steels: Carbon content varies from 0.30% to 0.60%. - High-carbon steels: Carbon content varies from 0.60% to 0.95%.• Other elements commonly found in carbon steels: - Manganese is controlled to less than 2.0%. - Sulfur is controlled to 0.35% maximum. - Phosphorous is controlled to 0.12% maximum. - Silicon is usually controlled to less than 0.60%. - Lead, when added is controlled to less than 0.35%. - Other elements are not controlled but are usually held to less than 2.0%. Carbon and Low-Alloy Steels 6
  7. 7. Low-Alloy SteelsElements are added to modify the basic carbon steel compositions toprovide superior properties.• Manganese, silicon, chromium, nickel and molybdenum are the most common additions to form low-alloy steels.• Vanadium, niobium, aluminum, tungsten, copper and other elements are added to provide additional specific characteristics.• Total elemental additions are less than 10%.Properties enhanced by alloying:• Hardenability - the ability to be strengthened through heat treatment.• Toughness - the ability to withstand impact loads.• Environmental resistance - weathering and other corrosive environments.• Elevated temperature resistance. Carbon and Low-Alloy Steels 7
  8. 8. Classifications of Carbon and Low-Alloy Steels• Plain carbon Steels: Carbon, manganese, phosphorous and sulfur are controlled. Other elements are not controlled.• Resulfurized, rephosphorized or leaded steels: Sulfur, phosphorous or lead are intentionally added to improve machineability.• Low-alloy steels: Controlled additions of elements are utilized to enhance properties and to provide specific characteristics.• Structural steels: All steels could be used as structural steels but we will focus on a group called the High-Strength Low-Alloy (HSLA) Steels. Carbon and Low-Alloy Steels 8
  9. 9. Classification of SteelsClassification can depend on:• Composition―carbon, low-alloy, tool or stainless steels.• Manufacturing method―open hearth, basic oxygen, electric furnace, vacuum processed.• Finishing method―hot or cold rolled, cold finished, cold drawn.• Product form―bar, plate, sheet, strip, wire, tubing, or structural shape.• Deoxidation practice―killed, semikilled, capped or rimmed.• Microstructure―ferritic, pearlitic, or martensitic.• Strength level―specified in ASTM or other standards.• Heat treatment―annealed, normalized, spherodized or quenched and tempered.• Quality descriptors―commercial, forging, drawing, or aircraft quality. Carbon and Low-Alloy Steels 9
  10. 10. Carbon Steel NomenclatureSAE-AISI: Four digit designation.• First 2 digits define the alloy group. For example: – A 10 in the front indicates the group is a plain carbon steel. – Resulfurized carbon steels start with 11, followed by the carbon content. – Resulfurized and rephosphorized carbon steels will start with a 12, followed by the carbon content. – High manganese carbon steels will start with a 15, followed by the carbon content for manganese contents between 1.00-1.65%.• Last 2 digits indicate the nominal carbon content. – Plain carbon steels will have the designation of: SAE 1005 – SAE 1095. This indicates the nominal carbon content will vary from 0.05%-0.95%.• AISI – American Iron and Steel Institute designation is slowly disappearing.• SAE – Society of Automotive Engineers is more common.• UNS – Unified Numbering System is a worldwide designation for composition of metals and alloys. For example: UNS G10200 is the designation for SAE 1020 carbon steel. Carbon and Low-Alloy Steels 10
  11. 11. SAE-AISI Carbon & Low-Alloy Steel Nomenclature Type of Carbon/Alloy Steel Group Numeral and Digital Designation Nominal Alloy Content, %Carbon Steels 10xx C=0.05-0.95% 11xx S<0.33% 12xx S<0.35, P=0.12% 15xx 1.00<Mn<1.65%Manganese Steels 13xx 1.60<Mn<1.90%Nickel Steels 23xx Ni=3.50% 25xx Ni=5.00%Nickel-Chromium Steels 31xx Ni=1.25, Cr=0.65 & 0.80 32xx Ni=1.75, Cr=1.07 33xx Ni=3.50, Cr=1.50 & 1.57 34xx Ni=3.00, Cr=0.77Molybdenum Steels 40xx Mo=0.20 & 0.25 44xx Mo=0.40 & 0.52Cr-Mo Steels 41xx Cr=0.50, 0.80, 0.95, Mo=0.12, 0.20, 0.25, 0.30Ni-Cr-Mo Steels 43xx Ni=1.82, Cr=0.50 & 0.80, Mo=0.25 43BVxx Ni=1.82, Cr=0.50, Mo=0.12 & 0.25, V=0.03 Min. 47xx Ni=1.05, Cr=0.45, Mo=0.20 & 0.35 81xx Ni=0.30, Cr=0.040, Mo=0.12 86xx Ni=0.55, Cr=0.50, Mo=0.20 87xx Ni=0.55, Cr=0.50, Mo=0.25 88xx Ni=0.55, Cr=0.50, Mo=0.35 93xx Ni=3.25, Cr=1.20, Mo=0.12 94xx Ni=0.45, Cr=0.40, Mo=0.12 97xx Ni=0.55, Cr=0.20, Mo=0.20 98xx Ni=1.00, Cr=0.80, Mo=0.25 Carbon and Low-Alloy Steels 11
  12. 12. SAE-AISI Carbon & Alloy Steel Nomenclature, continued Type of Carbon/Alloy Steel Group Numeral and Digital Designation Nominal Alloy Content, %Ni-Mo Steels 46xx Ni=0.85 & 1.82, Mo=0.20 & 0.25 48xx Ni=3.50, Mo=0.25Cr Steels 50xx Cr=0.27, 0.40, 0.50, 0.65 51xx Cr=0.80, 0.87, 0.92, 0.95, 1.00, 1.05Cr - Bearing Steels 50xxx C=1.0% Min., Cr=0.50 51xxx C=1.0% Min., Cr=1.02 52xxx C=1.0% Min., Cr=1.45Cr - Vanadium Steels 61xx Cr=0.60, 0.80, 0.95, V=0.10 %, 0.15 % Min.Tungsten-Cr Steels 72xx W=1.75, Cr=0.75Si-Mn Steels 92xx Si=1.40 & 2.00, Mn=0.65, 0.82, 0.85, Cr=0 and 0.65 %High-Strength Low-Alloy Steels 9xx Various SAE GradesBoron Steels xxBxx B denotes boron steelLeaded Steels xxLxx L denotes leaded steel Carbon and Low-Alloy Steels 12
  13. 13. Mechanical Properties of Carbon and Low-AlloySteels• Mechanical properties vs. carbon content.• Mechanical properties vs. manganese content.• Mechanical properties vs. cold work.• Mechanical properties vs. heat treatment.• Impact properties.• Fatigue properties. Carbon and Low-Alloy Steels 13
  14. 14. Typical Stress/Strain Curve for Steel Carbon and Low-Alloy Steels 14
  15. 15. Mechanical Properties vs. Carbon Content HOT ROLLED CARBON STEEL BARS, MANGANESE <1.0% 140 120 100 80 KSI Tensile Strength 60 Yield Strength 40 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 15
  16. 16. Mechanical Properties vs. Manganese Content HOT ROLLED CARBON STEEL BARS, MANGANESE >1.0% 120 100 80 KSI 60 Tensile Strength Yield Strength 40 20 0 0.25 0.36 0.41 0.48 0.52 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 16
  17. 17. Tensile Strength vs. Manganese Content EFFECT OF MANGANESE CONTENT ON TENSILE STRENGTH 140 120 100 80 KSI 60 Mn <1.0% Mn >1.0% 40 20 0 0 0.2 0.4 0.6 0.8 1 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 17
  18. 18. Yield Strength vs. Manganese Content EFFECT OF MANGANESE CONTENT ON YIELD STRENGTH 80 70 60 50 KSI 40 Mn <1.0% 30 Mn >1.0% 20 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 18
  19. 19. Mechanical Properties vs. Cold Work COLD DRAWN CARBON STEEL BARS 120 100 80 KSI 60 Tensile Strength Yield Strength 40 20 0 0.1 0.2 0.3 0.4 0.5 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 19
  20. 20. Tensile Strength vs. Cold Work EFFECT OF COLD WORK ON TENSILE STRENGTH 140 120 100 80 KSI Hot Rolled 60 Cold Drawn 40 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 20
  21. 21. Yield Strength vs. Cold Work EFFECT OF COLD WORK ON YIELD STRENGTH 90 80 70 60 50 KSI 40 Hot Rolled Cold Drawn 30 20 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 NOMINAL CARBON CONTENT, % Carbon and Low-Alloy Steels 21
  22. 22. Quenched & Tempered Hardness vs. Carbon Content Rockwell C Ultimate Tensile Hardness, HRC Strength, ksi. 55 301 50 255 45 214 40 182 35 157 30 136 25 120 20 108 Carbon and Low-Alloy Steels 22
  23. 23. General Comments on Impact Properties of Carbonand Low-Alloy Steels1. Carbon and low-alloy steels have a ductile-to-brittle transition temperature: - Above the DBTT the material will fail in a ductile manner and the absorbed impact energy is high. - Below the DBTT the material will fail in a brittle manner (cleavage) with low absorbed energy.2. The transition temperature can be shifted by alloy additions: - Manganese and silicon will lower the DBTT. - Sulfur and phosphorous will raise the DBTT.3. The energy absorbed can be altered by alloy additions: - Nickel will increase the toughness at low temperatures. - Chromium, molybdenum and copper indirectly increase absorbed energy through hardenability enhancement. Carbon and Low-Alloy Steels 23
  24. 24. Impact Properties vs. Carbon Content Carbon and Low-Alloy Steels 24
  25. 25. General Statements about FatigueFatigue is a progressive, localized and permanent change in a material subjected tofluctuating strains, at stresses with maximum values less than the ultimate tensile strength ofthe material.1. The stress can be substantially less than the ultimate tensile strength.2. The alternating strains can lead to crack initiation and propagation.3. As the crack grows in size, final failure can occur catastrophically when the remaining cross section can no longer support the applied load.4. Steels have a fatigue limit, which is approximately 50% of the ultimate tensile strength.5. The following variables will affect the fatigue limit: - Surface roughness - Temperature - Decarburization, carburizing, nitriding - Designs that create stress risers - Microstructure and grain size - Material discontinuities - Processing discontinuities - Residual stress - Corrosion or erosion - Service-induced nicks or gouges - Material properties, carbon content Carbon and Low-Alloy Steels 25
  26. 26. Typical S-N Curve for Steel Carbon and Low-Alloy Steels 26
  27. 27. SAE 1005 Low Carbon Steel Carbon and Low-Alloy Steels 27
  28. 28. SAE 1018 Low Carbon Steel Carbon and Low-Alloy Steels 28
  29. 29. SAE 8620 Low Carbon Alloy Steel Carbon and Low-Alloy Steels 29
  30. 30. SAE 1045 Medium Carbon Steel Carbon and Low-Alloy Steels 30
  31. 31. SAE 1144 Resulfurized Steel Carbon and Low-Alloy Steels 31
  32. 32. SAE 1060 Medium Carbon Steel Carbon and Low-Alloy Steels 32
  33. 33. SAE 5150 Alloy Steel Carbon and Low-Alloy Steels 33
  34. 34. Applications for Low-Carbon SteelsLow-carbon steels: Carbon content less than 0.30%.• Products are sheet, strip, plate, wire, bar, tubing and structural shapes.• Can be purchased in hot or cold-rolled, cold-finished, annealed, cold drawn condition.• Typical applications: - Body panels for vehicles, appliances, etc. - Coated products such as galvanized sheet, strip or wire. - Low strength wire products. - Structural shapes. - Chain• Weldable, formable, heat treatable to moderate strength levels.Note: Low-carbon steels are often referred to as ‘mild’ steels. Carbon and Low-Alloy Steels 34
  35. 35. Applications for Medium-Carbon SteelsMedium-carbon steels-carbon content between 0.30-0.60%.• Increased carbon and manganese allow the medium-carbon steels to be quenched and tempered to high strength levels.• Purchased in many forms.• Typical uses: - Shafts, couplings, crankshafts, gears and other high-strength applications. - Rails, railway wheels, rail axles. - Forgings, castings.• Can be welded if properly pre-heated and post-heated. Carbon and Low-Alloy Steels 35
  36. 36. Applications for High-Carbon SteelsHigh-carbon steels: Carbon content between 0.60-1.00%.• High carbon allows heat treatment to very high strength levels.• Cold working produces products with very high strength levels.• Typical uses: - Springs. - High strength wire such as music wire. - Tool applications-water hardening tool steels are commonly high - carbon steels. - Other products requiring high strength with a minimum of processing.• Normally not weldable because of high-carbon content. Carbon and Low-Alloy Steels 36
  37. 37. Applications for Low-Alloy SteelsLow-alloy steels: Carbon varies from 0.10-1.00%. Elements are added toproduce unique capabilities.• Heat-treatable to high strength and toughness.• Elemental additions can improve environmental degradation under certain conditions.• Elemental additions up to 10% can improve oxidation and corrosion resistance at elevated temperatures.• Common uses: - Bearings and bearing races. - Weathering steels. - A myriad of parts and products that must be heat-treated to high- strength or high-toughness.Note: Low-alloy steels gain strength through heat treatment. Carbon and Low-Alloy Steels 37
  38. 38. Structural SteelsHigh-strength carbon and low-alloy steels having yield strengths greaterthan 275 MPa (40 ksi) and can be classified as follows:• As-rolled carbon-manganese steels (13XX and 15XX).• Heat-treated carbon steels.*• Heat-treated low-alloy steels.*• As-rolled high-strength low-alloy (HSLA) steels, also know as microalloyed steels.*Notice that we have been talking about carbon and low-alloy steels, butnow they are heat treated for use as high-strength structural steel. Carbon and Low-Alloy Steels 38
  39. 39. High-Strength Low-Alloy Steels (HSLA)Primarily utilized for structural applications requiring:• High strength: HSLA steels utilize low carbon content with small amounts of alloying elements and a variety of controlled processing parameters to obtain high yield strengths, greater than 275 MPa (40 ksi.).• Good toughness, weldability, formability and atmospheric and other corrosion resistance.• Availability as hot-rolled sheet, strip, and plate; hot-rolled and cold-finished bar; tubing, pipe and structural shapes. Can also be furnished as cold- rolled sheet and forgings.Applications include construction of bridges, buildings, drilling rigs, vehicleparts, piling, ships, etc.Described in at least 18 ASTM specifications, which provide chemicalcomposition, mechanical properties, forms available and intended uses.Many of these specs list several grades with different strength levels. Carbon and Low-Alloy Steels 39
  40. 40. Specifications for HSLA SteelsASTM Specification Available Forms Special Characteristics Intended Uses A242 Plate, Bar, Shapes ≤ 4 in. Atmospheric weathering Welded, bolted or riveted construction A572 Plate, Bar, Shapes ≤ 6 in. 6 grades with YS ≥ 42 ksi Bridges and buildings A588 Plate, Bar, Shapes ≤ 8 in. Atmospheric weathering, YS ≥ 50 ksi Welded bridges and buildings A606 HR & CR Sheet and Strip Atmospheric weathering Weight savings and durability A607 HR & CR Sheet and Strip 6 grades with YS ≥ 45 ksi Weight savings and durability A618 Welded and Seamless Tubing 3 grades with different characteristics Welded, bolted or riveted construction A633 Plate, Bar, Shapes ≤ 6 in. 5 grades with YS ≥ 42 ksi Service down to -50°F A656 Plate ≤ 5/8 in. YS ≥ 80 ksi Truck, crane, railroad car frames A690 Piling Corrosion resistance Sea water exposure applicationsA709, Gr 50 & 50W Plate, Shapes ≤ 4 in. Minimum YS = 50 ksi Bridges A714 Pipe, welded and seamless 1/2 to 26 in. Pipe Piping A715 HR Sheet, Strip 4 grades, YS = 50-80 ksi Structural, formability & weldability A808 HR Plate ≤ 2 1/2 in. CVN 30-45 ft-lb @ -50°F Railway tank cars A812 Coiled sheet YS = 65-85 ksi Welded pressure vessels A841 Plate ≤ 4 in. YS = 45-50 ksi Welded pressure vessels A847 Welded and Seamless Tubing YS ≥ 50 ksi Bridges and buildings A860 Welded fittings YS ≥ 70 ksi Gas, oil transmission lines A871 Plate ≤ 1 3/8 in. Atmospheric weathering Tubular structures and poles Carbon and Low-Alloy Steels 40
  41. 41. Specifications for Carbon & Low-Alloy SteelsSpecifications are written statements defining product requirements.• Describes both technical and commercial requirements.• Controls procurement.• May cover any or all of the following parameters: - Scope defines product classification, size range, processing, or other information deemed useful to both supplier and user. - Chemical composition of the carbon or low-alloy steel. - Quality statement describes special requirements such as steel quality, type and processing methods. - Quantitative requirements identify chemical composition ranges, mechanical and physical properties and test methods germane to the application. - Additional requirements may include such items as size and straightness tolerances, surface and edge finish, packaging and loading instructions. Carbon and Low-Alloy Steels 41
  42. 42. Specifications, continuedMost existing specifications have been prepared by engineeringsocieties, associations, and institutions whose membersmake, specify, purchase and/or use steel products. Some common ones arelisted below:• Association of American Railroads – AAR• American Bureau of Shipbuilding – ABS• American Railway Engineering Association – AREA• American Society of Mechanical Engineers – ASME• American Petroleum Institute – API• American Society for Testing and Materials – ASTM• Society of Automotive Engineers – SAE• Aerospace Material Specifications (of SAE) – AMS• Federal and Military Specifications – FED and MILForeign countries have their own material and process specificationsystems, such as the DIN, JIS, BS, AFNOR, UNI, etc. Many of thesespecifications reference some ASTM specifications. Carbon and Low-Alloy Steels 42
  43. 43. Specifications, continuedASTM is the most widely used specification system because they arecomplete for procurement purposes. Most ASTM specs includecomposition, mechanical, dimensional, quality and testingrequirements, or reference other ASTM specs that cover specific aspectsof a material.• ASTM specifications are used worldwide.• Some federal and military procurements are gradually transitioning to ASTM specifications.• Material descriptions use common SAE-AISI designations but also include the UNS system to identify a material composition.A common ASME specification is referred to as the Boiler and PressureVessel Code. This code is the authority for any application involving thedesign and construction of boilers, pressure vessels and associatedpiping, including nuclear applications. Many ASME material specificationsclosely parallel ASTM. Carbon and Low-Alloy Steels 43
  44. 44. Carbon and Low-Alloy Steel SelectionMaterial and process selection should always be based on the followingconsiderations:• Material strength with reference to operational loads, vibration, temperature and environmental exposures.• Processing parameters such as formability, weldability, machineability and other fabrication considerations to produce the product.• Form of material to most economically fabricate the product whether it be sheet, strip, plate, bar, or structural shape.• Availability of the material in the required form, quantity and price.• Finishing processes such as painting, plating, heat treatment, etc.Always use a material and/or process specification to procure or finish aproduct. Carbon and Low-Alloy Steels 44
  45. 45. Some General Comments1. Resulfurized, rephosphorized or leaded steels are not generally weldable or heat treatable.2. The above materials should not be used in dynamic or cyclical applications, especially in cold weather environments.3. When designing products, ensure the maximum load is no greater than 1/3 of the yield strength of the material and well below the fatigue limit.4. Never use a steel in the ‘as quenched’ condition. Always temper the steel.5. When welding, always use pre-heat and/or post-heating when the carbon content is more than 0.30%.6. A low-alloy steel is not significantly stronger than a plain carbon steel with the same carbon content, in the same condition. Low-alloy steels provide high-strength, only after heat treating. Save money if you don’t need high-strength. Carbon and Low-Alloy Steels 45
  46. 46. Contact us for further information Weldon ‘Mak’ Makela Josh Schwantes Senior Failure Analyst Metallurgical Engineering Manager 651 659 7275 651 659 7205 Craig Stolpestad Mark Eggers Sales Manager Inside Sales, NDT & Metals 651 659 7206 651 659 7349 Carbon and Low-Alloy Steels 46