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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.

Text of Carbon and Low-Alloy Steels for Non-Metallurgists

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Presented by Weldon Mak MakelaSenior Failure Analysis EngineerMaterials Testing & Analysis Group, Element St. PaulCarbon and Low-Alloy SteelsApril 26, 2012Carbon and Low-Alloy SteelsFuture 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 CorrosionCarbon and Low-Alloy Steels2Carbon and low-alloy steelsWhat 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 Steels3What 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 Steels4Iron-Carbon Phase Diagram

Carbon and Low-Alloy Steels5Carbon and Low-Alloy SteelsCarbon SteelsThe 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%.6Low-Alloy SteelsElements 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 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 Steels7Classifications of Carbon and Low-Alloy SteelsPlain 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 Steels8Classification of SteelsClassification 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.

Carbon and Low-Alloy Steels9Carbon 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 Steels10SAE-AISI Carbon & Low-Alloy Steel NomenclatureType of Carbon/Alloy Steel GroupNumeral and Digital DesignationNominal Alloy Content, % Carbon Steels10xxC=0.05-0.95%11xxS

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