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!important}.entry-content[class] h2{font-size: 25px !important}.entry-content[class] h3{font-size: 20px !important}.entry-content[class] h4{font-size: 17px !important}.entry-content[class] p,.entry-content[class] li{font-size: 16px !important}.entry-content[class] table th,.entry-content[class] table td{font-size: 14px !important;padding: 11px 12px !important}.entry-content[class] .aobo-hero{padding: 30px 22px}.entry-content[class] .aobo-final-cta{padding: 26px 22px}.entry-content[class] .aobo-final-cta .aobo-btn{width: 100%}}\n<\/style>\n<section class=\"aobo-ht-ref ts-props\">\n<div class=\"aobo-wrap\">\n\n<div class=\"ts-hero\">\n<div class=\"ts-hero-top\">\n<div class=\"ts-kicker\"><span><\/span>Tool Steel | Chemical Analysis | Mill Certificate<\/div>\n<h1 style=\"--h1-max:40px\">How the Chemistry of a Tool Steel Heat Is Tested<\/h1>\n<p>A mill certificate carries a column of numbers for carbon, chromium, molybdenum, vanadium and the rest, and everything a buyer relies on rests on those numbers being right. They are not produced by one instrument. Four different methods cover the chemistry of a steel heat, each of them measures a different set of elements on a differently prepared sample, and each of them has a documented failure mode. This page covers what each method measures, how the sample is taken and prepared, and which elements a certificate can and cannot be checked against.<\/p>\n<\/div>\n<\/div>\n\n<div class=\"ts-tool-area\">\n\n<h2 class=\"ts-h2\">Four methods, not one<\/h2>\n<p class=\"ts-p\">The elements that define a tool steel grade are split across techniques. The alloying elements and the common impurities are reported by spark emission spectroscopy, which is the workhorse of a steelworks laboratory. Carbon and sulphur are measured by high-temperature combustion, which is the reference method for those two elements because emission sources struggle with them. Oxygen, nitrogen and hydrogen are measured by inert gas fusion, and no emission method reaches them at all. X-ray fluorescence sits alongside as an independent technique that needs no standards for a semiquantitative answer.<\/p>\n<div class=\"ts-table-wrap\" style=\"width:fit-content;max-width:100%\">\n<table class=\"ts-table\" style=\"min-width:960px;\">\n<thead><tr><th>Method<\/th><th>Elements it reports<\/th><th>Sample it needs<\/th><th>Time<\/th><\/tr><\/thead>\n<tbody>\n<tr><td class=\"ts-type\">Spark optical emission spectroscopy<\/td><td class=\"ts-safe\">The alloying elements and most metallic impurities, reported against an iron line as an internal standard<\/td><td class=\"ts-safe\">A conducting solid with a flat ground or sanded face, which becomes one electrode of the spark<\/td><td class=\"ts-safe\">A few minutes from sampling to a result at the furnace<\/td><\/tr>\n<tr><td class=\"ts-type\">Glow discharge emission spectroscopy<\/td><td class=\"ts-safe\">The same elements as the spark, and it can be set up to reach carbon, phosphorus and sulphur, with detection limits quoted from 0.002 % for sulphur to 0.014 % for carbon<\/td><td class=\"ts-safe\">A clean, flat ground surface that will seal against an O ring at low pressure<\/td><td class=\"ts-safe\">Not stated for the routine case, and it is a slower sample changeover than the spark<\/td><\/tr>\n<tr><td class=\"ts-type\">High-temperature combustion<\/td><td class=\"ts-safe\">Carbon and sulphur, reported as a percentage of specimen weight<\/td><td class=\"ts-safe\">A weighed solid, chip or powder sample of 1 g or less, in a ceramic crucible with accelerators<\/td><td class=\"ts-safe\">Sample preparation 2 to 3 minutes, analysis 40 seconds to 2 minutes<\/td><\/tr>\n<tr><td class=\"ts-type\">Inert gas fusion<\/td><td class=\"ts-safe\">Oxygen, nitrogen and hydrogen, each as a total content<\/td><td class=\"ts-safe\">A solid, chip or powder sample, usually 2 g or less<\/td><td>1 to 10 minutes after sample preparation<\/td><\/tr>\n<tr><td class=\"ts-type\">X-ray fluorescence<\/td><td class=\"ts-safe\">Elements from sodium upward, and semiquantitative results on many samples without any standards at all<\/td><td class=\"ts-safe\">Bulk solid, powder, pressed pellet, glass, fused disk or liquid, typically 32 mm across<\/td><td class=\"ts-safe\">Counting time plus sample preparation, which is the dominant cost<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p class=\"ts-tcap\"><em>The four methods that between them cover the chemistry of a steel heat. Compiled from the three source articles in ASM Handbook, Volume 10.<\/em><\/p>\n<p class=\"ts-p\">The consequence for a certificate is that its rows came from different methods on different sample forms, and that is normal. Where it matters is when a customer has one of the rows rechecked. Carbon, for example, can be reported by emission, by combustion or by a dedicated glow discharge set-up, and those three routes do not have the same uncertainty.<\/p>\n\n<h2 class=\"ts-h2\">How the heat is sampled and analysed<\/h2>\n<p class=\"ts-p\">Spark emission is the fastest route to an elemental analysis of a metal, and the steel industry&#8217;s use of it explains why. During production of a heat, the metal is sampled and the molten sample is allowed to cool. A flat surface is ground or sanded onto the cooled sample, which then goes into the spark source with no further preparation. The analysis runs, and the result goes straight back to the furnace so the alloying additions can be trimmed into range. Sampling and analysis together take a few minutes at most.<\/p>\n<p class=\"ts-p\">That speed is the reason the method is trusted at the furnace, and it is also the reason its limits matter. The sample forms one electrode of the spark and a tungsten pin forms the other, so the material has to conduct. The spark is normally run in a flowing argon sheath, which makes the discharge strike much more reproducibly and reduces the burn area by a factor of ten compared with an unstabilised spark. The light is not recorded immediately. A preburn period of about a minute conditions a fresh electrode surface, after which the emission for most elements stays reasonably constant for the 30 seconds needed to record a spectrum.<\/p>\n<p class=\"ts-p\">The reason for that preburn is worth knowing, because it is the mechanism behind a discrepancy a customer will occasionally see. Emission from a spark train changes within minutes as the spark conditions the surface, a behaviour called sparking-off. Its exact shape depends on the spark parameters, the sample composition, the sample phase structure, the surface condition, the sparking atmosphere and the burn area. Because the composition and phase structure of the electrode are among the inputs, the emission result for an element is matrix dependent, and the correction used in practice is to ratio the line intensities of the minor elements against a line from iron, the major constituent. That compensates for variations in sampling and excitation between samples, and it carries an assumption with it. The assumption is that the reference element is sampled and excited the same way as the minor constituents, which is not always safe in a steel carrying inclusions whose composition differs sharply from the bulk.<\/p>\n\n<h2 class=\"ts-h2\">Calibration is where an emission result is won or lost<\/h2>\n<p class=\"ts-p\">None of that produces a usable number unless the instrument has been calibrated against standards that match the unknown closely, in both chemical composition and physical form. A laboratory running spark analysis has to hold a set of standards for every type of material it analyses, and the article is blunt that spark standards are not easily produced and generally have to be bought, from the national reference material supplier or from a private company. A tool steel heat checked against a low alloy steel standard is being measured on a curve that does not describe it.<\/p>\n<p class=\"ts-p\">Emission spectroscopy also has a hard limit on which elements it can see. Nitrogen, oxygen, hydrogen, the halogens and the noble gases are listed as difficult or impossible to determine by optical emission. Every emission method also carries the same general caveat, which is that its response depends on the matrix. That is why the certificate row for a tool steel&#8217;s nitrogen or oxygen content cannot have come from the same instrument as the chromium row.<\/p>\n\n<h2 class=\"ts-h2\">Carbon and sulphur by combustion<\/h2>\n<p class=\"ts-p\">Combustion analysis reverses the logic of the other methods. Instead of exciting the sample, it burns it. A weighed sample of 1 g or less goes into a ceramic crucible with an accelerator and is brought to between 1370 and 1425 &deg;C in a stream of oxygen. The carbon leaves as carbon monoxide and carbon dioxide, the sulphur as sulphur dioxide, and both are measured by infrared absorption or thermal conductivity and reported as a percentage of specimen weight. Analysis takes 40 seconds to two minutes once the sample is prepared.<\/p>\n<p class=\"ts-p\">The accelerators are not optional, and their selection rules are specific enough to be a useful check on whether a laboratory knows what it is doing.<\/p>\n<div class=\"ts-table-wrap\" style=\"width:fit-content;max-width:100%\">\n<table class=\"ts-table\" style=\"min-width:860px;\">\n<thead><tr><th>Accelerator<\/th><th>What it is used for<\/th><\/tr><\/thead>\n<tbody>\n<tr><td class=\"ts-type\">Copper chip<\/td><td class=\"ts-safe\">A combustion aid for steel, iron and nonferrous alloys in a high-frequency furnace for the determination of carbon. It may be combined with iron chips for nonferrous alloys, or with tin chips on some systems for sulphur. Copper cannot be used alone for sulphur, because the sulphur combines to form copper sulphate and is lost<\/td><\/tr>\n<tr><td class=\"ts-type\">Copper strip<\/td><td class=\"ts-safe\">The same guidelines as copper chips, used with resistance furnace systems<\/td><\/tr>\n<tr><td class=\"ts-type\">Iron chip<\/td><td class=\"ts-safe\">An accelerator for combusting steel, iron or nonferrous metals and alloys for carbon or sulphur. Where the target is below 0.05 % carbon and 0.002 % sulphur, high-grade iron chips are specified, and they must be used when combusting nonferrous materials in a high-frequency system<\/td><\/tr>\n<tr><td class=\"ts-type\">Tin chip<\/td><td class=\"ts-safe\">An additive accelerator with a low combustion point, which raises the temperature early in the burn and so assists the initial stages of combustion<\/td><\/tr>\n<tr><td class=\"ts-type\">Tungsten<\/td><td class=\"ts-safe\">An accelerator for most steels, irons and nonferrous materials, giving excellent combustion when combined with tin chips, and used mainly where very low carbon and sulphur contents are being determined<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p class=\"ts-tcap\"><em>Combustion accelerators and what each contributes. Source, Table 1 of <em>High-Temperature Combustion<\/em>, in ASM Handbook, Volume 10.<\/em><\/p>\n<p class=\"ts-p\">Two further details decide whether a low figure is real. The blank, defined as carbon or sulphur arriving from anywhere other than the sample, can come from the oxygen supply, the crucible or boat, and the accelerators, and it runs between 0.010 and 0.0005 % depending on the system and the grade of consumables. Automatic analysers compensate for it, and manual or semiautomatic ones require it to be subtracted. And the specimen has to be homogeneous, because the method is destructive and reports a total for the piece that was burned.<\/p>\n\n<h2 class=\"ts-h2\">Oxygen, nitrogen and hydrogen by inert gas fusion<\/h2>\n<p class=\"ts-p\">Inert gas fusion is the method for the three gases. A sample of 2 g or less is fused in a graphite crucible, heated to between 2500 and 3000 &deg;C by an impulse current or by high-frequency induction. At that temperature the bonds between the gas and the metal break down, and the crucible itself supplies the carbon that takes up the oxygen. Hydrogen and nitrogen leave as H<sub>2<\/sub> and N<sub>2<\/sub>, oxygen leaves as carbon monoxide, and an inert carrier gas sweeps them to a thermal conductivity or infrared detector. Helium is the usual carrier for nitrogen or nitrogen and oxygen, and nitrogen or argon for oxygen or hydrogen on their own.<\/p>\n<div class=\"ts-table-wrap\" style=\"width:fit-content;max-width:100%\">\n<table class=\"ts-table\" style=\"min-width:880px;\">\n<thead><tr><th>Gas<\/th><th>How it enters the steel<\/th><th>What it does<\/th><\/tr><\/thead>\n<tbody>\n<tr><td class=\"ts-type\">Hydrogen<\/td><td class=\"ts-safe\">Physically and chemically adsorbed from the atmosphere, and taken up again during drawing, rolling, heat treating or annealing, then diffused during cooling or aging<\/td><td class=\"ts-safe\">Internal cracks that generally appear during cooling in drawing, rolling or forging. A large cross section can break under high or continuous stress because of them, and hydrogen embrittlement is the service side of the same problem<\/td><\/tr>\n<tr><td class=\"ts-type\">Nitrogen<\/td><td class=\"ts-safe\">Absorbed from the melt, deliberately added to austenitic manganese steels for yield strength, or introduced later by nitriding<\/td><td class=\"ts-safe\">Increases yield strength and, by nitriding, hardenability, and it can decrease ductility<\/td><\/tr>\n<tr><td class=\"ts-type\">Oxygen<\/td><td class=\"ts-safe\">The hardest of the three to control because it is available from many sources and reacts with many metals<\/td><td class=\"ts-safe\">Inclusions and blowholes, and an increase in hardness with age when it combines with the carbon and nitrogen in the steel<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p class=\"ts-tcap\"><em>The three gases measured by inert gas fusion, why they get into a tool steel and what they do there. Compiled from <em>Inert Gas Fusion<\/em>, ASM Handbook, Volume 10.<\/em><\/p>\n<p class=\"ts-p\">Sample handling for this test has a rule that is easy to break. Material has to be cut to size, and the cut has to be kept cool for oxygen and hydrogen work specifically, because heating during sectioning drives hydrogen out of the sample and oxidises the surface, and either one moves the number. The specimen must also not be contaminated with nitrides, oxides or hydrides on the way in. For a tool steel the hydrogen figure is the one with a service consequence, since the internal cracking that hydrogen causes appears during cooling after drawing, rolling or forging, which is to say during the processes that made the bar.<\/p>\n\n<h2 class=\"ts-h2\">X-ray fluorescence as the independent check<\/h2>\n<p class=\"ts-p\">X-ray fluorescence works on a different physical principle from emission, which makes it useful as a second opinion. It measures the characteristic x-rays a sample emits when it is irradiated, it works on bulk solids, powders, pressed pellets, glasses, fused disks and liquids, results are semiquantitative on many samples with no standards at all, and its detection limits for bulk work run from a few parts per million to a few tens of parts per million depending on the x-ray energy and the matrix.<\/p>\n<p class=\"ts-p\">Its limits are just as well documented. It is not suitable for elements below sodium in atomic number unless special equipment is fitted, and then only down to carbon at best, so it cannot be the method behind a carbon figure on a tool steel certificate. Sample preparation is described as the single most important step in the analysis and the one most often neglected. Surface roughness is usually allowed to reach 100 &mu;m for higher energy radiation but has to come down to 20 to 40 &mu;m below about 2 keV, and soft metals smear across the surface during polishing, which coats the sample with the element being measured and returns a high result. A laboratory that polishes a leaded or free machining steel the same way it polishes a tool steel is measuring its own preparation.<\/p>\n<p class=\"ts-p\">A glow discharge source is the third option for the same job, and it does better than the spark on two counts that matter for routine control. Its working curves are more linear and less matrix dependent, and it produces cleaner spectra with narrower lines on a source that is simpler electronically. Against that it needs a clean sample ground flat enough to hold a vacuum at the O ring, while the spark runs at atmospheric pressure on a sample that has only been coarse sanded.<\/p>\n\n<h2 class=\"ts-h2\">What this means for a tool steel order<\/h2>\n<p class=\"ts-p\">The chemistry on a certificate is a set of results, and the elements that decide a grade are not all measured the same way. Carbon, the element that separates one tool steel from another more than any other, is a combustion measurement or a dedicated glow discharge measurement, not a routine spark reading. Chromium, molybdenum, vanadium and tungsten come from emission. Oxygen, nitrogen and hydrogen, which govern cleanliness and the risk of internal cracking, come from inert gas fusion and will be reported separately or not at all.<\/p>\n<p class=\"ts-p\">So when a composition has to be checked, the two questions worth asking are which method produced each row and which standard was used to calibrate it. The composition ranges for the common tool steel families are tabulated in the <a href=\"https:\/\/aobosteel.com\/tool-steel-composition-chart\/\">tool steel composition chart<\/a>, with the individual grade sheets at <a href=\"https:\/\/aobosteel.com\/d2-steel-composition\/\">D2 steel composition<\/a> and <a href=\"https:\/\/aobosteel.com\/h13-steel-composition\/\">H13 steel composition<\/a>, and the melting route that decides how low the gas and inclusion levels can go is covered in <a href=\"https:\/\/aobosteel.com\/esr-tool-steel\/\">ESR tool steel<\/a>. The powder metallurgy grades, where a carbon figure is central to the specification, are collected in <a href=\"https:\/\/aobosteel.com\/pm-high-speed-steel-composition\/\">PM high speed steel composition<\/a>. How the numbers are handled on the way out of our own warehouse is set out in <a href=\"https:\/\/aobosteel.com\/tool-steel-quality-verification\/\">how we control tool steel quality<\/a>, the grades with their composition ranges sit under <a href=\"https:\/\/aobosteel.com\/cold-work-tool-steels\/\">cold work<\/a> and <a href=\"https:\/\/aobosteel.com\/high-speed-steels\/\">high speed<\/a> tool steels, the catalogue is at <a href=\"https:\/\/aobosteel.com\/tool-steels\/\">tool steels<\/a>, and a certificate question can be put to us directly through the <a href=\"https:\/\/aobosteel.com\/contact\/\">contact page<\/a>.<\/p>\n\n<div class=\"ts-disclaimer\">\n<h3>Before you act on a composition figure<\/h3>\n<p>A reference page, it is not an Aobo Steel specification. Composition data is for general reference only, and actual values vary by standard, mill and heat number, so confirm against the material test certificate or ask Aobo Steel. The figures above are also the published measurement limits and procedures of the methods named, not a statement about the capability of any particular laboratory.<\/p>\n<\/div>\n\n<p class=\"ts-source\">Source: ASM Handbook, Volume 10, Materials Characterization, ASM International, 1986.<\/p>\n\n<\/div><\/div><\/section>\n","protected":false},"excerpt":{"rendered":"<p>Tool Steel | Chemical Analysis | Mill Certificate How the Chemistry of a Tool Steel Heat Is Tested A mill certificate carries a column of numbers for carbon, chromium, molybdenum, vanadium and the rest, and everything a buyer relies on rests on those numbers being right. They are not produced by one instrument. Four different [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_uag_custom_page_level_css":"","site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"disabled","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-21151","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO 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