Steels for bearing production from Ovako

Steels for bearing production from Ovako

Contents: Metallurgy of bearing steels Steel grades Research and developemnt For bars, tubes, rings and wire rod, see brochures: Bar products from Ovako, also available in German, French, Polish, Finnish and Swedish Seamless Tubes from Ovako, also available in German, French, Finnish and Swedish Rolled and forged rings from Ovako Wire rod for a broad scope of applications, also available in German, French and Polish These brochures can be ordered or printed as PDF from our website. 2

vako is one of the world s largest manufacturers of through-hardening bearing steel. We will maintain this leading position as the bearing industry continuously challenges us to make further technical and logistical improvements. As a supplier to most of the leading bearing producers, we have acquired unique knowledge and experience in this field. Total Control Ovako is a fully integrated bearing steel producer. We control the whole chain of production, from melting the steel through rolling to producing a finished component. Our product range of tube, bar, ring and wire accommodates all the main components of a rolling bearing. And we meet all the requirements specified irrespective of the type of steel used for rolling bearing manufacture. Total Partnership Our objective is to be a true partner with our customers, from both a technical and business point of view. Our technical specialists are dedicated to working closely with those of our customers. This allows us to optimise the use of steel both from a product and a production perspective. We can develop new and better steels, tailor-make products and improve machinability and heat treatment responses. By co-operating with our key customers we are able to establish long-term business agreements and customise logistical and EDI solutions. We support them in their global sourcing strategies and contribute with multiple product packages that keep administration to a minimum. We also have experience in joint cost- reduction activities. Total Quality Total Quality Management is a central concept within Ovako. All our activities aim at producing and delivering products and services to fulfil customer s needs. Our quality policy and comprehensive quality assurance help us to achieve the highest standards. Ovako s quality system conforms to ISO/TS 16949 and ISO 9001. The company is also ISO 14001 certified. 3

Metallurgy of bearing steels The demand for increased reliability of rolling bearings in service is continuous. Bearings are expected to last longer and endure higher stress under adverse conditions. This poses higher demands on the steel used by bearing manufacturers. Our long-standing cooperation with the world s leading rolling bearing manufacturers has given Ovako a unique understanding of material development for rolling bearing applications. By optimising and making full use of these skills in each production step we can achieve high quality bearing steel with optimum mechanical properties. Each step must be controlled with a high degree of precision to minimise the content of harmful non-metallic inclusions. By controlling cleanliness carefully and through the use of a number of key technologies, such as magnetic induction stirring and vacuum degassing in the the secondary metallurgy, and controlled casting, it has been possible to increase the fatigue strength of our bearing steels considerably. The objective is to produce steel, which is optimised regarding properties, quality and economy. Clockwise from top left: Steel melting, continuous casting, billet rolling and oxygen scarfing. 4

Steel making and billet production Ovako has four steel works, three of which have a scrap melting electric arc process and one blast furnace oxygen converter process. Like most other producers of bearing steel, Ovako uses scrap melting process as its basis for bearing steel production. The blast furnace oxygen converter process is also a possibility to make bearing steels. Raw material Like most other producers of bearing steel, Ovako uses scrap as its basic raw material. The selection and procurement of scrap is of great importance to the quality of the end product. For that reason we have high demands and tight control over the scrap we use. Used ferroalloys and other additions, too, are carefully controlled. Melting The melting process requires complete control of all parameters, from liquid raw melt to furnace control, so that the melt has the correct properties when it goes to the next stage of production. At this stage, a number of the most important properties inherent in the cast are already fixed. Secondary metallurgy This process stage determines the final metallurgical quality, i.e. the final chemical composition and the cleanliness of the steel. The metallurgical unit operations in this part of the production process include: control of alloy content deoxidation (reducing the oxygen content and inclusion count in the steel) desulphurisation (reducing the sulphur content of the steel) degassing (elimination of other harmful gases) temperature adjustment (to reach the appropriate temperature for teeming). soft induction stirring During this secondary metallurgy treatment the molten steel is stirred by an induction coil or by argon bubbling to create the best possible uniformity, removing oxide inclusions, sulphur and undesirable gases. Casting There are two ways to solidify bearing steels in Ovako: the traditional ingot casting and continuous bloom casting. The uphill teeming of ingots is Ovako s traditional casting technique. It creates large forging reductions, so as to achieve the desired final quality requirements. For some bearing steel products it is the only accessible casting method. Uphill teeming ensures a minimum of inclusions and a good surface finish. The design of the ingot mould has been optimised to reduce segregation in the steel during solidification, and during teeming the molten steel is shrouded by inert gas to protect it from reacting with the air around it. Once solidified, the ingots are stripped from the moulds and taken directly to the soaking pits and brought to an adequate temperature before primary rolling. The soaking is introduced to avoid harmful segregation in the steel. Ovako has also a very long experience in continuous casting. The first concast facility was started up in 1965 at Imatra Steel Works. The bloom caster, which was modernised recently, represents the latest concast technology. The large bloom size of 370 310 mm results in a good deformation in rolling. Naturally all molten surfaces are protected and the mould stirring is standard Ovako practice. The solidified blooms are hot charged into the reheating furnace for rolling. This beneficial process provides clear advantages in surface quality and low level of segregations, resulting in good production economy. Ingot casting Scrapping Melting Secondary metallurgy Continuous casting Rolling Billet rolling The entire metallurgical process at Ovako, from the steel melting to the finished billet, is carried out in a hot flow in order to minimise the risk of surface defects. Billets can be surface conditioned by oxygen scarfing after the first stages of primary rolling, or by grinding. Before the billets are transferred for secondary rolling, i.e. tube, bar, wire or rings, they are subject to magnetic particle testing testing, and, if needed, to grinding to remove the possible surface defects. Magnetic particle testing 5

Steel grades Ovako mainly produces through-hardening steels for bearing applications, and is one of the world s leading companies in this segment. We also produce a significant quantity of carburising steel grades for this application. Listed below are some of our standard grades for bearing applications. Through-hardening bearing steels Ovako specialises in high-strength through-hardening bearing steels. These grades exhibit high fatigue and wearresistance, good machinability, high hardness and good dimensional stability. A hardness of 60-65 HRC can be achieved through martensitic hardening and tempering, making these steels ideal for bearing products. This distinguishing property package is also suitable for other market segments and applications that have the same high quality requirements as the bearing industry. 100Cr6 type (SAE 52100) Used mainly for small and medium-sized bearing components. The 100Cr6 steel grades have high fatigue strength and hardness, and good wear resistance. There are several different versions of this grade. For example: Designation acc. to EN 10027-1 Ovako designation 100Cr6 803J Standard. 100Cr6 mod. F 803F With a controlled sulphur concontent for consistent machining properties. 100Cr mod. Q 803Q Isotropic properties and better fatigue strength due to higher cleanliness levels, and a finer size and distribution of non-metallic inclusions. 100Cr6 mod. Z 803Z Better cold forming properties due to reduction of the silicon content. 100Cr6 mod. D 803D Better machinability due to the higher sulphur content. Air hardening type A steel grade specifically designed for air or gas quenching. By using gas cooling or air hardening it is possible to reduce the amount of quench distortion. The use of quenching mediums such as oil and salt can also be avoided. Hardenability corresponds to a bar with approx. Ø 40 mm (cooled in still air). The Ovatec 677 series demonstrate very good mechanical performance, and is often recommended for the most demanding applications. Designation acc. to EN 10027-1 Ovako designation 70SiCrMnMo6-5 Ovatec 677L Standard. 65SiCrMnMo6-5 Ovatec 677Q Isotropic properties and better fatigue strength due to higher cleanliness and a finer size and distribution of non-metallic inclusions. 6

Through-hardening bearing steels for bainitic hardening These grades are used for bainitic hardened medium and large-sized bearing components. They all have a high fatigue strength, good toughness and excellent wear resistance. The through-hardenability corresponds to a ring with wall thickness T, quenched in oil. Designation acc. to EN 10027-1 Ovako designation 100CrMo7 824B Through hardenability corresponds to T< 20 mm (~ Ø 35 mm bar) 100CrMo7-3 825B Through hardenability corresponds to T< 30 mm (~ Ø 50 mm bar) 100CrMo7-4 826B Through hardenability corresponds to T< 50 mm (~ Ø 80 mm bar) Through-hardening bearing steels for martensite hardening These grades are used for the martensite hardening of large- and medium-sized bearing components. They have high fatigue strength, high hardness and good wear resistance. The through hardenability corresponds to a ring with wall thickness T, quenched in oil. T Definition of ring wall thickness The T section is defined as the material thickness that is the controlling factor in the heat treatment process, sometimes called the ruling section. Designation acc. to EN 10027-1 Ovako designation 100CrMnSi4-4 831B Through hardenability corresponds to T< 20 mm (~ Ø 35 mm bar) 100CrMnSi6-4 837B Through hardenability corresponds to T< 30 mm (~ Ø 50 mm bar) Case-hardening bearing steels Ovako s case-hardening bearing steels are adjusted to offer good machinability and minimal dimensional change after hardening. The hard surface generated from casehardening provides high fatigue strength and high wearresistance, while the softer core gives the component a high toughness. Ovako produces a number of casehardening steels suitable for bearing applications. For example: Designation acc. to EN 10027-1 Ovako designation 20MnCr6-3 126H Standard carburising steel with good toughness and high fatigue strength. 20NiCrMo2-2 152G Increased toughness due to a higher nickel content. Also available with normal sulphur content for better machinability. 17MnCr5 234K Controlled hardenability due to a tighter chemical composition. 18CrNiMo14-6 255G Excellent toughness and high fatigue strength, due to a higher cleanliness specification and a high nickel content. 18CrMnMoNi9-5-5 277L Air-hardening carburising steel with high toughness and high fatigue strength. 18CrMnMoNi9-5-5 mod. 277Q Same as above, but higher cleanliness level. 7

Average chemical composition Steel designation according to Quality C Si Mn S max. Cr Ni Mo EN 10027-1 Ovako level % % % % % % % 100Cr6 803J BQ 0.97 0.25 0.35 0.015 1.50 - - 100Cr6 mod. F 803F BQ 0.97 0.27 0.35 0.015 1.50 - - 100Cr mod. Q 803Q IQ 0.95 0.30 0.30 0.002 1.50 - - 100Cr mod. Z 803Z BQ 0.97 < 0.15 0.35 0.015 1.45 - - 100Cr mid. D 803D BQ 1.02 0.30 0.35 0.025 1.50 - - 70SiCrMnMo6-5 677L BQ 0.70 1.55 1.40 0.015 1.10-0.25 65SiCrMnMo6-5 mod. Q 677Q IQ 0.65 1.50 1.40 0.002 1.10-0.25 100CrMo7 824B BQ 0.97 0.30 0.30 0.015 1.80-0.20 100CrMo7-3 825B BQ 0.97 0.30 0.70 0.015 1.80-0.30 100CrMo7-4 826B BQ 0.97 0.35 0.70 0.015 1.80-0.45 100CrMnMoSi8-4-6 827B BQ 0.97 0.50 0.90 0.015 1.90-0.55 100CrMnSi4-4 831B BQ 0.97 0.60 1.10 0.015 1.00 - - 100CrMnSi6-4 837B BQ 1.00 0.60 1.10 0.015 1.50 - - 26MnCr6-326 126H BQ 0.20 0.27 0.80 0.025 0.50 - - 20NiCrMo2-2 152G BQ 0.21 0.25 0.75 0.015 0.50 0.55-17MnCr5 234K BQ 0.16 0.25 1.15 0.035 0.95 - - 18CrNiMo14-6 255G PBQ 0.16 0.27 0.55 0.005 1.45 3.50 0.20 18CrMnMoNi9-5-5 277L BQ 0.18 0.35 1.30 0.030 2.20 0.50 0.50 18CrMnMoNi9-5-5 mod. Q 277Q PBQ 0.18 0.35 1.30 0.030 2.20 0.50 0.50 Comparable standards EN ISO 683-17 Ovako ASTM AFNOR DIN BS SAE SS NF A35-565:1970 17230:1980 100Cr6 803J A732 100 C 6 100 Cr 6 2 S.135 52100 2258 100Cr6 803F A732 100 C 6 100 Cr 6 2 S.135 52100 2258 100Cr6 803Q A732 100 C 6 100 Cr 6 2 S.135 52100 2258 803Z 100Cr6 803D A732 100 C 6 100 Cr 6 2 S.135 52100 2258 677L 677Q 100CrMo7 824B 100 CD 7 100 CrMo 7 100CrMo7-3 825B 100 CrMo 7-3 100CrMo7-4 826B 100CrMnMoSi8-4-6 827B 100 CrMnMo 8 100CrMnSi4-4 831B A485 100CrMnSi6-4 837B 100 CM 6 100 CrMn 6 126H A534 20NiCrMo2 152G A322 20 NCD 2 805 A 20 2506 17MnCr5 234K 16 MC 5 16 MnCr 5 590 A 17 18NiCrMo14-6 255G A757 17 NiCrMo 14 277L 8

Typical mechanical properties Steel designation according to Structure Hardness R m (MPa) R eh (MPa) A 5 (%) Z (%) EN 10027-1 Ovako 100Cr6 803 Martensite 61-64 HRC 2300 1700 2 2 Bainite 58-61 HRC 2300 2100 5 7 70SiCrMnMo6-5 677L Martensite 61-64 HRC 2300 1700 2 2 65SiCrMnMo6-5 mod. Q 677Q Martensite 61-64 HRC 2300 1700 2 2 100CrMo7 824B Bainite 58-61 HRC 2300 2100 5 7 100CrMo7-3 825B Bainite 58-61 HRC 2300 2100 5 7 100CrMo7-4 826B Bainite 58-61 HTC 2300 2100 5 7 100CrMnMoSi8-4-6 827B Bainite 58-61 HRC 2300 2100 5 5 100CrMnSi4-4 831B Martensite 61-64 HRC 2300 1700 2 2 100CrMnSi6-4 837B Martensite 61-64 HRC 2300 1700 2 2 26MnCr6-3 126H Case hardened 300-430 HB 980-1370 800-900 10-12 20NiCrMo2-2 152G Case hardened 300-430 HB 980-1370 800-900 10-12 17MnCr5 234K Case hardened 250-350 HB 880-1180 640 9 18CrMnMoNi9-5-5 277L Case hardened 350-370 HB 1100-1300 850-950 10-12 The properties correspond to typical values of core after hardening or case-hardening. 9

Cleanliness specifications Ovako s continuous development of its steel making practice over the last decade has made it possible to further control the oxygen and sulphur content in our products. The maximum inclusion levels have been significantly lowered, thereby ensuring steels with consistently high cleanliness and superior fatigue properties. In addition to bearing quality level (BQ) Ovako has three more quality categories for bearing steels. CQ The Customer Quality level. Limits are defined according to specific customer requests and agreed mutually. PBQ The Premium Bearing Quality is intended for more demanding applications that require extra clean steel grades. IQ The Isotropic Quality for applications requiring exceptional fatigue properties, and cleanliness levels comparable to Electro Slag Re-melt (ESR) and Vacuum Arc Re-melt (VAR) steels. 10

Typical microscopic inclusions A-type inclusion. B-type inclusion. D-type inclusion. Titanium inclusion. Fatigue testing equipment. 11

Research and development The art of making steel requires an understanding of steel and an ability to predict what will happen to the steel in various situations. It is essential for Ovako as a supplier to the rolling bearing industry that we increase our knowledge and understanding about the steel and the products made from it, thereby improving and meeting the increasing market demands and expectations. It is our explicit policy to continue to strengthen our position within this market segment, so it is not by chance that we are the company that has developed and applied for more patents for bearing steels and heat treatment variants than any other company in the Western world. Ovako has developed and introduced many new steel grades. Neither is it by chance that we were the first in the world to actively control the hardenability of the steel during the production. We were also the first to achieve inclusion levels in conventionally produced steels comparable with those of re-melted steels. Today, our research and development activities are concentrating on a greater understanding of steel and how it performs from a metallurgical point of view and how that affects the material properties. Our ultimate target is to optimise the steel performance for every application and to come up with entirely new, cost effective material solutions. We are active in developing and improving our products. For instance, we are improving tolerances on diameters, surface roughness, machinability and heat treatment properties. Ovako co-operates closely with a number of research institutes and universities to widen our competence and knowledge base so as to ensure success in our development projects. 12

Material development Ovako continuously strives to obtain a better knowledge and understanding of the behaviour of our bearing steel materials through scientific research. Fatigue testing Fatigue testing is a useful tool for understanding and determining the service life of bearing steels. At Ovako we have test rigs for rolling contact, rotational bending and axial loading, which all generate valuable information about the properties of fatigue. A steel grade s fatigue property is determined by fatigue life testing in combination with a measurement of inclusion size and count. SEM analysis Ovako uses several ultra-modern Scanning Electron Microscope (SEM) for investigating microstructure, inclusion characteristics and crack properties. A Field Emission Gun (FEG) makes it possible to generate quality pictures at very high resolutions. Analysing systems that uses back scatter mapping in combination with X-ray spectroscopy are the most useful tool available for inclusion counting, providing information about inclusion composition and the size distribution. One microscope is also equipped with an Electron Back Scatter Diffraction (EBSD) detector, which provides information about the crystallographic orientation and material grain structure. A study of fatigued fracture surface in a bearing steel. The SEM-microscopes are continuously used for many kinds of investigations. An Al 2 O 3 inclusion. A study inside the inclusion. 13

Ultrasonic testing Immersion ultrasonic testing is used as routine method of quality control in many cases. The typical frequency range when investigating bars and billets is 10 to 25 MHz. Immersion ultrasonic scanning of samples makes it possible to see how different manufacturing stages affect the occurrence of macro inclusions. This means that the product integrity is improved and changes in the production process can be followed. Ovako has gone further, improving and developing immersion ultrasonic testing methods by the use of focused, high frequency probes 25 to 80 MHz. This gives Ovako the possibility to map both macro and meso inclusions in our steel. Our ultrasonic test equipment gives us a quick and reliable testing tool for continuous research and development. High frequency ultrasonic scanning of a billet sample. No./mm 2 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 22 24 26 28 30 32 34 Size, d (µm) A test piece scanned with a high-frequency (80 MHz) probe. A few larger inclusions can be seen in the C-scan image. The results of the evaluation are presented in a histrogram (left). Inclusion distribution diagram. Results from 80 MHz. 14

Ovako is a leading European producer of long special steel products for the automotive, heavy vehicle and engineering industries. Production consists of low alloy and carbon steels in the form of bars, wire rod, tubes, rings and pre-components. The company has 16 production sites and several sales companies in Europe and the USA. Total steel production is 2 million tonnes. SALES UNITS: Finland: Ovako Bar Oy Ab Teollisuuskuja 1 FI-142 00 Turenki Tel: +358 (0)3 570 26 00 Fax: +358 (0)3 570 26 02 France: Ovako France S.A.S. 14, rue de Mirande FR-21000 Dijon Tel: +33 (0)3 80 54 15 15 Fax: + 33 (0)3 80 50 14 67 Germany/Austria: Ovako GmbH Postfach 1255 40672 Erkrath Tel: +49 (0)211-2504-0 Fax: +49 (0)211-2504-244 Netherlands: Ovako Bar BeNeLux Bedrijvenpark Twente 295 NL-7602 KK Almelo Tel: +31 (0)546-588 360 Fax: +31 (0)546-588 366 Ovako Wire b.v. Postbus 3 NL-2950 AA Alblasserdam Tel: +31 (0)78 692 3100 Fax: +31 (0)78 692 3192 Poland: Ovako Polska Sp. z.o.o. ILMET Building 15 Jana Pawla II Avenue PL-00-828 Warsaw Tel: +48 (0)22 6976464 / 65 / 66 Fax: +48 (0) 22 6976467 Russia: OOO Ovako Office 1812 Savelkinskiy proezd, d.4 124482 Zelenograd Moscow Tel: +7 (4)95 228 07 80 Fax: +7 (4)95 228 07 81 United Kingdom: Ovako Ltd. Unit 2, Britannia Park Trident Drive Wednesbury WS10 7XA Tel: 0121 502 1010 Fax: 0121 505 0019 PRODUCITON: Sweden: Hofors Steelworks: Ovako Steel AB SE-813 82 Hofors Tel: +46 (0)290 250 00 Fax: +46 (0)290 250 25 Hällefors Rolling Mil: Ovako Steel AB SE-712 80 Hällefors Sweden Tel: +46 (0)591 600 00 Fax: +46 (0)591 606 06 Finland: Imatra Steel Works: Ovako Bar Oy Ab Terästehtaantie 1 FI-55100 Imatra Tel: +358 (0)5 680 21 Fax: +358 (0)5 680 22 11 Netherlands: Ovako Wire b.v. Postbus 3 NL-2950 AA Alblasserdam Tel: +31 (0)78 692 3100 Fax: +31 (0)78 692 3192 USA: Ovako North America, Inc. 1096 Assembly Drive Suite 312 Fort Mill, SC 29708 Tel: +1-803 1802 1500 Fax: +1-803-1802-1501 CO-12GB 08.03 1000 Copyright Ovako 2008 www.ovako.com