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Presented by Weldon Mak Makela

Senior Failure Analysis Engineer

Materials Testing & Analysis Group, Element St. Paul

Carbon and Low-Alloy Steels

April 26, 2012 Carbon and Low-Alloy Steels


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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


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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, castirons, 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.



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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 andother impurities. Further refining reduces the impurities, controlscarbon 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.



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Iron-Carbon Phase Diagram



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Carbon and Low-Alloy Steels

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%.

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Low-Alloy Steels

Elements are added to modify the basic carbon steel compositions to

provide 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 elementsare 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 corrosiveenvironments.

Elevated temperature resistance.



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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 orlead are intentionally added to improve machineability.

Low-alloy steels: Controlled additions of elements are utilized toenhance 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.



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Classification of Steels

Classification can depend on:

Compositioncarbon, low-alloy, tool or stainless steels. Manufacturing methodopen hearth, basic oxygen, electric furnace,

vacuum processed.

Finishing methodhot or cold rolled, cold finished, cold drawn.

Product formbar, plate, sheet, strip, wire, tubing, or structural shape.

Deoxidation practicekilled, semikilled, capped or rimmed.

Microstructureferritic, pearlitic, or martensitic.

Strength levelspecified in ASTM or other standards.

Heat treatmentannealed, normalized, spherodized or quenched and

tempered. Quality descriptorscommercial, forging, drawing, or aircraft quality.



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Carbon Steel Nomenclature

SAE-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 thecarbon 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. Thisindicates 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 SAE1020 carbon steel.



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SAE-AISI Carbon & Low-Alloy Steel NomenclatureType of Carbon/Alloy Steel Group Numeral and Digital Designation Nominal Alloy Content, %

Carbon Steels 10xx C=0.05-0.95%

11xx S


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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=0.25

Cr Steels 50xx Cr=0.27, 0.40, 0.50, 0.65

51xx Cr=0.80, 0.87, 0.92, 0.95, 1.00, 1.05

Cr - Bearing Steels 50xxx C=1.0% Min., Cr=0.50

51xxx C=1.0% Min., Cr=1.02

52xxx C=1.0% Min., Cr=1.45

Cr - Vanadium Steels 61xx Cr=0.60, 0.80, 0.95, V=0.10 %, 0.15 % Min.

Tungsten-Cr Steels 72xx W=1.75, Cr=0.75

Si-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 Grades

Boron Steels xxBxx B denotes boron steel

Leaded Steels xxLxx L denotes leaded steel



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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.



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Typical Stress/Strain Curve for Steel



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Mechanical Properties vs. Carbon Content

0

20

40

60

80

100

120

140

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

KSI

NOMINAL CARBON CONTENT, %

HOT ROLLED CARBON STEEL BARS, MANGANESE


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Mechanical Properties vs. Manganese Content

0

20

40

60

80

100

120

0.25 0.36 0.41 0.48 0.52

KSI


HOT ROLLED CARBON STEEL BARS, MANGANESE>1.0%

Tensile Strength

Yield Strength



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Tensile Strength vs. Manganese Content

0

20

40

60

80

100

120

140

0 0.2 0.4 0.6 0.8 1

KSI


EFFECT OF MANGANESE CONTENT ON TENSILESTRENGTH

Mn 1.0%



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Yield Strength vs. Manganese Content

0

10

20

30

40

50

60

70

80

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

KSI


EFFECT OF MANGANESE CONTENT ON YIELD

STRENGTH

Mn 1.0%



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Mechanical Properties vs. Cold Work

0

20

40

60

80

100

120

0.1 0.2 0.3 0.4 0.5

KSI


COLD DRAWN CARBON STEEL BARS

Tensile Strength

Yield Strength



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Tensile Strength vs. Cold Work

0

20

40

60

80

100

120

140

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

KSI


EFFECT OF COLD WORK ON TENSILE STRENGTH

Hot Rolled

Cold Drawn


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Yield Strength vs. Cold Work

0

10

20

30

40

50

60

70

80

90

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

KSI


EFFECT OF COLD WORK ON YIELD STRENGTH

Hot Rolled

Cold Drawn



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Quenched & Tempered Hardness vs. Carbon Content

Rockwell CHardness, HRC

Ultimate TensileStrength, ksi.

55 301

50 255

45 21440 182

35 157

30 136

25 120

20 108



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General Comments on Impact Properties of Carbonand Low-Alloy Steels

1. Carbon and low-alloy steels have a ductile-to-brittle transitiontemperature:- 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 absorbedenergy through hardenability enhancement.



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Impact Properties vs. Carbon Content



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General Statements about Fatigue

Fatigue is a progressive, localized and permanent change in a material subjected tofluctuating strains, at stresses with maximum values less than the ultimate tensile strength of

the 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



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Typical S-N Curve for Steel



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SAE 1005 Low Carbon Steel



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SAE 1018 Low Carbon Steel



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SAE 8620 Low Carbon Alloy Steel



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SAE 1045 Medium Carbon Steel



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SAE 1144 Resulfurized Steel



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SAE 1060 Medium Carbon Steel



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SAE 5150 Alloy Steel



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Applications for Low-Carbon Steels

Low-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.



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Applications for Medium-Carbon Steels

Medium-carbon steels-carbon content between 0.30-0.60%.

Increased carbon and manganese allow the medium-carbon steels tobe 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.



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Applications for High-Carbon Steels

High-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.



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Applications for Low-Alloy Steels

Low-alloy steels: Carbon varies from 0.10-1.00%. Elements are added to

produce unique capabilities. Heat-treatable to high strength and toughness.

Elemental additions can improve environmental degradation undercertain 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.



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Structural Steels

High-strength carbon and low-alloy steels having yield strengths greater

than 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.



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High-Strength Low-Alloy Steels (HSLA)

Primarily utilized for structural applications requiring:

High strength: HSLA steels utilize low carbon content with small amountsof alloying elements and a variety of controlled processing parameters toobtain high yield strengths, greater than 275 MPa (40 ksi.).

Good toughness, weldability, formability and atmospheric and othercorrosion 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.



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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 -50F

A656 Plate 5/8 in. YS 80 ksi Truck, crane, railroad car frames

A690 Piling Corrosion resistance Sea water exposure applications

A709, 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 @ -50F 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



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Specifications for Carbon & Low-Alloy Steels

Specifications 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 otherinformation deemed useful to both supplier and user.- Chemical composition of the carbon or low-alloy steel.

- Quality statement describes special requirements such as steelquality, type and processing methods.- Quantitative requirements identify chemical composition ranges,mechanical and physical properties and test methods germane to theapplication.- Additional requirements may include such items as size andstraightness tolerances, surface and edge finish, packaging andloading instructions.



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Specifications, continued

Most existing specifications have been prepared by engineering societies,associations, and institutions whose members make, specify, purchase and/or

use steel products. Some common ones are listed 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 MIL

Foreign countries have their own material and process specification systems,such as the DIN, JIS, BS, AFNOR, UNI, etc. Many of these specificationsreference some ASTM specifications.



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Specifications, continued

ASTM is the most widely used specification system because they arecomplete for procurement purposes. Most ASTM specs includecomposition, mechanical, dimensional, quality and testing requirements,or reference other ASTM specs that cover specific aspects of a material.

ASTM specifications are used worldwide.

Some federal and military procurements are gradually transitioning toASTM specifications.

Material descriptions use common SAE-AISI designations but alsoinclude 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 the

design and construction of boilers, pressure vessels and associatedpiping, including nuclear applications. Many ASME material specificationsclosely parallel ASTM.



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Carbon and Low-Alloy Steel Selection

Material and process selection should always be based on the following

considerations: Material strength with reference to operational loads, vibration,

temperature and environmental exposures.

Processing parameters such as formability, weldability, machineabilityand other fabrication considerations to produce the product.

Form of material to most economically fabricate the product whether itbe 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.


C


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Some General Comments

1. 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 greaterthan 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 thecarbon content is more than 0.30%.

6. A low-alloy steel is not significantly stronger than a plain carbon steelwith the same carbon content, in the same condition. Low-alloy steelsprovide high-strength, only after heat treating. Save money if youdont need high-strength.


C f f h i f i


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Contact us for further information

Weldon Mak MakelaSenior Failure Analyst651 659 [email protected]

Josh SchwantesMetallurgical Engineering Manager651 659 7205

[email protected]

Craig StolpestadSales Manager651 659 [email protected]

Mark EggersInside Sales, NDT & Metals651 659 [email protected]

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