100Cr6: Steel Technical Specifications

01100Cr6 Bearing Steel: Introduction and General Characteristics

100Cr6 steel (material number 1.3505) is a rolling bearing steel defined by EN ISO 683-17:2023, the standard that divides the steels for bearing rings and rolling elements into five groups. It belongs to the through-hardening group, which the standard itself describes as steels with about 1% carbon and 1 to 2% chromium: unlike a case-hardening steel, which hardens in a carbon-enriched surface layer, 100Cr6 carries its high carbon content through the whole section and takes its hardness from hardening alone.

Of the requirements the standard sets, those that describe the material are the chemical composition, the maximum hardness in the delivery condition, the spheroidisation of the carbides in the annealed conditions and a degree of inclusion cleanliness, whose verification is agreed at the time of order; the others concern surface, dimensions, testing and documents.

1.1What Is 100Cr6: the Designation and the Two Elements That Define It

The designation states the nominal composition: 100 stands for carbon of around 1% and Cr6 for chromium of around 1.5%, in line with the bands of the standard, 0.93-1.05% carbon and 1.35-1.60% chromium. These are the two elements that make the grade: carbon determines the hardness attainable after hardening and the amount of carbides, chromium raises the hardenability and takes part in the carbides. The same group of the standard holds grades that vary chromium, manganese, silicon and molybdenum; 100CrMo7 is one of them.

1.2100Cr6 vs 100CrMo7: What Changes Between the Two Grades

100CrMo7 (1.3537) belongs to the same group of EN ISO 683-17. It has the same carbon, 0.93-1.05%, and the same silicon and manganese bands; what changes is chromium, which rises to 1.65-1.95%, and molybdenum, which goes from a 0.10% maximum to a prescribed alloying element, 0.15-0.30%. In the spheroidise-annealed condition (+AC) the standard allows it a higher maximum hardness: 217 HBW against 207.

The standard gives no measure of what the extra chromium and molybdenum change in hardening, because it tabulates the hardenability of neither grade: the comparison is made on the part and on the cast, at equal geometry and equal cycle. What some manufacturer datasheets say about the thicknesses at which it pays to move from one to the other is collected on the bearing steels page, and it holds for the quenching medium and the cycle it was derived with.

1.3Reference Standard and Inspection Certificate for 100Cr6

The reference standard for 100Cr6 is EN ISO 683-17:2023, part 17 of ISO 683, which sets the technical delivery conditions for ball and roller bearing steels. It is the fourth edition of an international standard first issued in 1976 and rewritten in 1999, 2014 and 2023. Adopted as a European standard in 1999, between 1999 and 2001 it replaced the national standards still found on older drawings: DIN 17230 in Germany, UNI 3097 in Italy and NF A35-565 in France.

For inspection documents the standard refers to ISO 10474, with the inspection certificates 3.1 and 3.2: the certificate reports the cast analysis of all the elements specified for the grade. Every product must be traceable to the cast.

02Chemical Composition of 100Cr6 Steel: Alloying Elements and Standard Specifications

The chemical composition of 100Cr6 is fixed by EN ISO 683-17:2023 on the cast analysis. Alongside the carbon and chromium bands, silicon and manganese sit in narrow bands, while phosphorus and sulphur have low ceilings; sulphur, which forms sulphides, also weighs on inclusion cleanliness.

The deviations on product analysis in the third column are not a second specification: they are the tolerance allowed when the delivered product is analysed. For each element, within one cast, the deviation is allowed on one side only, above the upper limit or below the lower one, never both. Product analysis is carried out only when it is requested at the time of order.

By agreement at the time of order the standard allows two variants: sulphur up to 0.030% when machinability is the priority, and silicon no higher than 0.15% for cold forming. The first comes at a cost: more sulphur means more sulphides, that is, an inclusion cleanliness different from that of the base grade.

Beyond the elements in the table, the standard specifies requirements on calcium, titanium and oxygen, the contents most closely tied to the cleanliness of the steel: for their values the text of the standard is authoritative.

2.1Inclusion Cleanliness and Carbide Structure

For a bearing steel cleanliness is a front-line requirement, and the standard says so: non-metallic inclusions are decisive for the fatigue life of bearings, so every steel in the standard must have a certain degree of cleanliness. The requirements on the content of microscopic inclusions apply to every delivery; it is their verification that needs an agreement at the time of order, with the methods the standard refers to, among them ISO 4967 and JIS G 0555. For macroscopic inclusions, if verification is requested, the method and the acceptance limits are agreed.

Besides cleanliness, structure counts. In the condition annealed to spheroidise the carbides, +AC, and in the spheroidised and cold-worked condition, +AC+C, the standard requires the carbides of the through-hardening steels to be spheroidised. The degree of spheroidisation and the distribution of the carbides are agreed at the time of order when they matter, with reference-image methods such as ISO 5949 and SEP 1520: spheroidisation alone does not rule out carbide networks at the grain boundaries or segregation banding.

2.2100Cr6 International Equivalents

100Cr6 equivalents come in two kinds: correspondences written in a standard, collected in the table, and commercial pairings. Outside Europe, EN ISO 683-17 lists the Japanese SUJ2 of JIS G 4805 as comparable to 100Cr6: comparable, not identical, because the Japanese standard sets composition bands of its own.

Manufacturer datasheets often pair 100Cr6 with other designations. For UNI 3097, the Italian standard replaced in 2001, they give the same designation, 100Cr6. 100C6 is the French designation they associate with NF A35-565, replaced by NF EN ISO 683-17 in 1999. 52100 is the American designation, from another system of standards: before substituting it for 100Cr6 in a specification, the pairing has to be checked by comparing the two standards.

03Mechanical Characteristics of 100Cr6 Steel: What the Standard Prescribes

Of the mechanical characteristics of 100Cr6 the standard prescribes a single quantity: the maximum Brinell hardness in the delivery condition. 100Cr6 is bought to be machined annealed and then hardened, and the properties of the finished component depend on the heat-treatment cycle applied to the part.

3.1100Cr6 Hardness in the Delivery Conditions

The hardness of 100Cr6 that can be demanded on delivery depends on the condition ordered. In the condition annealed to spheroidise the carbides, +AC, the maximum is 207 HBW; in the spheroidised and cold-worked condition, +AC+C, it rises to 241 HBW. The values do not depend on the diameter, and the test is Brinell to ISO 6506-1.

One practical consequence concerns the order: without an agreement the standard provides for delivery in the untreated condition, which has no hardness requirement, so the spheroidise-annealed condition, +AC, has to be stated explicitly in the order.

The surface has rules of its own. Unless otherwise agreed, products are delivered with a hot-worked surface, and the standard sets no maximum depth of decarburisation: ground, peeled or machined products must be free of it, while for hot-rolled, forged, cold-reduced or rough-machined products intended for peeling or grinding the machining allowance is agreed at the time of order. Alternatively, for round bars and rod, the permissible depth of surface discontinuities can be specified to ISO 9443.

3.2Hardness After Hardening: a Requirement of the Part, Not of the Standard

The hardness sought on hardened 100Cr6, the hardness of the raceways and of the rolling elements, is not a requirement of the steel standard: EN ISO 683-17 prescribes none, neither as a minimum nor as a range. It is set by the specification of the component, together with the hardening and tempering cycle that produces it, and it is verified on the treated part. The values given in some manufacturer datasheets refer to cycles and test pieces that differ from one another, and they are not a requirement of the steel.

3.3Tensile Strength and Yield Strength: Values Not Prescribed

For the tensile strength of 100Cr6, its yield strength, elongation and impact strength the standard gives no values, in any condition: neither on the annealed bar nor on the hardened and tempered steel. If a delivery has to guarantee mechanical requirements, the standard allows other delivery conditions to be agreed, and with them the values to be met.

04Physical Characteristics of 100Cr6 Steel: Density and Elastic Constants

The physical characteristics of 100Cr6 are not a matter for its standard. The table gives the design values that the Eurocodes set for structural steel, with the standard each value is taken from. For weight calculation the steel convention applies, 7.85 kg/dm³: it is the same value DIN 17230 prescribed for the nominal weight of through-hardening bearing steels, and the same one used by the site's bar weight calculator. It is not the measured density of the grade, which some manufacturer datasheets give as slightly lower.

The modulus of elasticity at room temperature is 210 GPa and the shear modulus 81 GPa, consistent with a Poisson's ratio of 0.30; the coefficient of thermal expansion is 12 × 10⁻⁶/K, a mean value valid up to 100 °C. Thermal conductivity, specific heat and electrical resistivity change with the condition, annealed or hardened, and with temperature. The Eurocodes give the first two for structural steel, which a steel with 1% carbon and 1.5% chromium does not resemble, and some manufacturer datasheets give values that differ from one another: in the table they are left without a value, because a thermal calculation needs values referred to the condition of the part.

05Heat Treatments of 100Cr6 Steel: Annealing, Hardening and Tempering

The heat treatments of 100Cr6 are two distinct moments in the life of the material: spheroidise annealing, which makes it machinable, gives it the structure hardening will start from and is the condition to state in the order when it is to be machined from bar; and hardening followed by tempering, carried out on the machined part before finishing, which gives it its service hardness.

5.1Spheroidise Annealing and the +AC Condition

Spheroidise annealing brings the carbides of 100Cr6 into the form of globules dispersed in the ferritic matrix: it is the structure the standard prescribes for the +AC condition, together with the maximum hardness. The cycle that achieves it is mill practice, and the temperature windows given in some manufacturer datasheets do not agree with one another.

5.2100Cr6 Hardening: Guide Temperatures, Quenching Medium and Hardenability

For the hardening of 100Cr6 a historical reference remains: DIN 17230 of 1980, withdrawn in 2000, gave, for 100 Cr 6, hardening in oil from 830-870 °C, declaring it a guide value and specifying that the actual temperatures and conditions are to be chosen so as to obtain the required properties. Some manufacturer datasheets still give the same range; the actual cycle, however, is set by the specification of the part.

The standard does not tabulate the hardenability of 100Cr6: for through-hardening steels there is no Jominy band, and the grade is not ordered with the +H suffix, with which the standard's case-hardening and induction-hardening grades can be ordered to a prescribed hardenability. Up to what section 100Cr6 hardens through depends on the hardenability of the cast and on the austenitising conditions, as well as on the thickness and geometry of the part at the time of hardening and on the quenching medium, and it is verified on the part.

5.3Tempering of 100Cr6

Tempering of hardened 100Cr6 is a low-temperature tempering, which relieves the hardening stresses and improves toughness while keeping most of the hardness. DIN 17230 gave it as 150-180 °C, again as a guide value; the actual temperature is set by the heat-treatment specification of the part.

5.4Cycles and Critical Points the Standard Does Not Fix

Normalising, hot forming, stress relieving, bainitic hardening, sub-zero treatments: these are cycles the standard does not cover, and their parameters are set on the part with whoever machines and treats it. The standard does not publish the critical points Ac1 and Accm or the martensite start temperature Ms, which in any case are not constants of the grade: they depend on the cast and on the cycle, which is why some manufacturer datasheets give values that differ from one another.

06Industrial Applications of 100Cr6 Steel: Bearings and Contact-Loaded Components

The applications of 100Cr6 all come from the same problem: a surface that rolls or slides under a concentrated load, repeated over the whole life of the component. The standard defines its steels by their use: steels for the rings and the rolling elements of bearings.

6.1Rings, Balls and Rollers for Rolling Bearings

Inner and outer rings, balls, rollers and needles are what the grade exists for: they are made from bar, wire or tube in the spheroidised condition, through-hardened, tempered and then ground. Rings produced by forging or hot rolling lose the spheroidised structure of the bar and are spheroidise annealed again after forming. The choice between 100Cr6 and the more highly alloyed grades of the same family depends on how far the core of the part has to harden, with the factors described in the section on hardening.

6.2Other Uses: Components Subject to Wear and Contact Pressure

Outside the bearing, 100Cr6 is used wherever the same combination of hardness and wear resistance is needed on a through-hardened part: guide pins and bushes, rollers and cams, components of pumps and injection systems, gauges and measuring instruments, punches and die parts for small-section cold working.

6.3Machinability in the Spheroidise-Annealed Condition

The machinability of 100Cr6 is decided by the delivery condition. In the spheroidise-annealed +AC condition the structure of globular carbides allows turning, drilling and milling; after hardening what remains is grinding, hard turning with suitable tools and finishing operations. When machinability is the priority, the standard allows by agreement the higher-sulphur variant described in the section on composition.

07Frequently Asked Questions about 100Cr6 Steel: Technical Answers for Professionals

Short answers to the most common technical questions on 100Cr6.

7.1What is the difference between 100Cr6 and 100CrMo7?

They are two grades of the same group of EN ISO 683-17, with the same carbon. 100CrMo7 has more chromium, 1.65-1.95% against 1.35-1.60%, and molybdenum as an alloying element, 0.15-0.30%, and in the spheroidise-annealed condition it allows 217 HBW instead of 207. The standard tabulates the hardenability of neither. The choice depends on how far the core of the part has to harden, and it is verified on the part and on the cast.

7.2Does 100Cr6 correspond to 52100, 100C6 or SUJ2?

Of the three, only SUJ2 of JIS G 4805 has a correspondence written in EN ISO 683-17, as a comparable grade, not an identical one: the composition bands of the two standards do not coincide. 100C6 and 52100 are pairings found in manufacturer datasheets: the first is the designation they associate with the French standard replaced in 1999, the second belongs to the American system. In a specification the grade is ordered with its standard, and any substitution is checked by comparing the two standards.

7.3What hardness does 100Cr6 reach after hardening?

The steel standard does not guarantee one: EN ISO 683-17 prescribes no hardness after hardening, neither as a minimum nor as a range. The hardness of the component is set by its specification and by the hardening and tempering cycle, and it is verified on the treated part. The hardness that can be demanded on delivery is a different one: 207 HBW max in the spheroidise-annealed +AC condition.

7.4Is 100Cr6 stainless?

No. With 1.35-1.60% chromium it is far from the threshold that defines a stainless steel, at least 10.5% chromium according to EN 10020, and in a humid environment it rusts like a carbon steel: it has to be protected with a film of oil or with a surface treatment. For bearings that have to resist corrosion, EN ISO 683-17 itself provides a separate group, the stainless bearing steels.

7.5Is 100Cr6 weldable?

It is not a steel for fusion welding. With carbon around 1% the heat-affected zone hardens to a high-carbon martensite, hard and brittle, and the risk of cracking remains high even with preheating; the steel standard does not deal with weldability and gives neither preheat nor carbon equivalent. As a rule, 100Cr6 components are joined mechanically, or the zone to be welded is designed in a different grade.

7.6Can 100Cr6 be carburised?

There is no point in carburising it. Carburising enriches with carbon the surface layer of a steel that has little of it, whereas 100Cr6 already has around 1% throughout the section and takes its hardness from hardening alone. For bearings that need a hard layer on a tough core, EN ISO 683-17 provides a separate group of case-hardening steels. Carbonitriding is a different matter: on through-hardening steels it is used to modify the surface layer, the standard does not cover it, and the parameters are set by the specification of the part.

7.7Which standard does 100Cr6 comply with?

EN ISO 683-17:2023, the part of ISO 683 for ball and roller bearing steels. Older drawings may still cite the national standards that its first European edition replaced: DIN 17230, UNI 3097 and NF A35-565.

7.8Which delivery conditions does the standard provide for 100Cr6?

Annealed to spheroidise the carbides, +AC, 207 HBW max, and spheroidised and cold-worked, +AC+C, 241 HBW max; treated for cold shearability, +S, with requirements to be agreed; untreated, which applies when the order states nothing else. The standard allows others to be agreed.

7.9What is the density of 100Cr6?

7.85 kg/dm³, which is not the measured density of this grade but the conventional value with which the weight of steels is calculated. The same number sits behind the bar weight calculator, where the profile and the dimensions are enough to obtain the weight per metre and the total weight.

08The Siderticino Offer for 100Cr6 Steel: Annealed Bars for Bearings and Components to Be Hardened

Siderticino supplies 100Cr6 steel (1.3505) in compliance with EN ISO 683-17:2023, in hot-rolled round bars in the spheroidise-annealed +AC condition - the condition the grade is machined in before hardening - in diameters from 20 to 220 mm. Cutting is carried out to size on the lengths required, and the EN 10204 inspection documentation accompanies the supply, with a 3.1 inspection certificate on request.

For diameters and a quote request see the product page: 100Cr6 steel products. For the related grade see the 100CrMo7 products and the category page for bearing steels; to estimate the weight of semi-finished products the steel bar weight calculator is available.

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