ISO K cast iron
- MC codes for cast iron
- Malleable Cast Iron (MCI) K 1.1-1.2 and Gray Cast Iron (GCI) K 2.1-2.3
- Nodular Cast Iron (NCI) K 3.1-3.5
- Compacted Graphite Iron (CGI) K 4.1-4.2
- Austempered Ductile Iron (ADI) K 5.1- 5.3
What is ISO K cast iron?
There are 5 main types of cast iron:
- Gray Cast Iron (GCI)
- Malleable Cast Iron (MCI)
- Nodular Cast Iron (NCI)
- Compacted Graphite Iron (CGI)
- Austempered Ductile Iron (ADI)
Cast iron is a Fe-C composition with a relatively high percentage of Si (1–3%). Carbon content is over 2%, which is the maximum solubility of C in the austenitic phase. Cr (Chromium), Mo (Molybdenum) and V (Vanadium) form carbides, which increase strength and hardness but lower machinability.
Machinability in general
- Short-chipping material with good chip control in most conditions. Specific cutting force: 790–1,350 N/mm²
- Machining at higher speeds, especially in cast irons with sand inclusions, creates abrasive wear
- NCI, CGI and ADI require extra attention compared to normal GCI, due to the different mechanical properties and the presence of graphite in the matrix
- Cast irons are often machined with negative types of inserts, as these provide strong edges and safe applications
- The carbide substrates should be hard and the coatings should be of thick aluminum oxide types, for good abrasive wear resistance
- Cast irons are traditionally machined dry, but can also be used in wet conditions, mainly to keep the contamination of dust from carbon and iron to a minimum. There are also grades available that suit applications with coolant supply
Influence of hardness
- The influence of hardness related to machinability for cast irons follows the same rules as for any other material
- For example, ADI (austempered ductile iron) and CGI (compacted graphite iron) as well as NCI (nodular cast iron) have hardnesses up to 300–400 HB
- MCI and GCI average 200–250 HB
- White cast iron can achieve a hardness of over 500 HB at rapid cooling rates, where the carbon reacts with the iron to form a carbide Fe3C (cementite) instead of being present as free carbon. White cast irons are very abrasive and difficult to machine
MC codes for cast iron
From a machinability point of view, cast irons are classified into malleable, gray, nodular, compacted graphite iron (CGI) and austempered ductile iron (ADI) types. Some of the higher hardnesses can be found in nodular cast irons and the ADIs.
|MC Code||Material group||Material subgroup||Manufacturing process||Heat treatment||nom||Specific force, kc1(N/mm2)|| mc|
|K1.1.C.NS||1||malleable||1||low tensile||C||cast||NS||not specified||200 HB||780||0.28|
|K1.2.C.NS||1||2||high tensile||C||NS||260 HB||1,020||0.28|
|K2.1.C.UT||2||gray||1||low tensile||C||cast||UT||untreated||180 HB||900||0.28|
|K2.2.C.UT||2||2||high tensile||C||UT||245 HB||1,100||0.28|
|K4.1.C.UT||4||CGI||1||low tensile (perlite < 90%)||C||cast||UT||untreated||160 HB||680||0.43|
|K4.2.C.UT||4||2||high tensile (perlite >= 90%)||C||UT||230 HB||750||0.41|
|K5.1.C.NS||5||ADI||1||low tensile||C||cast||NS||not specified||300 HB|||||
|K5.2.C.NS||5||2||high tensile||C||NS||400 HB|||||
|K5.3.C.NS||5||3||extra-high tensile||C||NS||460 HB|||||
The austempering heat treatment converts ductile iron (NCI) into austempered ductile iron (ADI).
Malleable Cast Iron (MCI) K 1.1-1.2 and Gray Cast Iron (GCI) K 2.1-2.3
Malleable cast iron is produced from a close-to-white iron matrix, which is then heat treated in two steps, producing a ferrite + perlite + tempered carbon structure, leading to irregular graphite grains compared to the more fracture-inducing lamellar structure in the gray cast iron. This means that the malleable material is less sensitive to cracking and its values for rupture strength and elongation are higher.
Gray cast iron has graphite in a typical flake form, and its main characteristics are low impact strength (brittle behavior); good thermal conductivity – less heat when the engine operates and low heat in cutting process; good dampening properties – absorbs the vibrations in the engine.
Components manufactured from MCI include axle bearings, track wheels, pipe fittings and high-strength gears. Components manufactured form GCI include frying pans, engine blocks, cylinders for compressors, gears and gear box cases.
Malleable cast iron has a higher tensile strength than GCI and resembles NCI in its machinability, but both generally have excellent machining properties. In general, cast iron with a perlitic structure increases the abrasive wear, while ferritic structures increase the adhesive wear.
Gray cast iron has low impact strength and generates low cutting forces, and the machinability is very good. Wear is created in the cutting process only by abrasion; there is no chemical wear. Gray cast iron is often alloyed with Cr in order to improve its mechanical properties. The higher strength then results in decreased machinability.
Nodular Cast Iron (NCI) K 3.1-3.5
Nodular cast iron has spherically shaped graphite, and the main characteristics are good stiffness (Young’s module); good impact strength = tough material, not brittle; good tensile strength; bad damping properties – does not absorb the vibrations in the engine; bad thermal conductivity – higher heat during the cutting process. In comparison to GCI, the graphite in NCI appears in the form of nodules, which contributes to higher tensile properties and toughness.
Hubs, tubing, rollers, exhaust manifolds, crankshafts, differential housings, bearing caps, exhaust manifolds, bedplates, turbo charger housings, clutch plates and fly wheels.
Turbo-charger housings and exhaust manifolds are often made of SiMo alloyed cast iron, which is more resistant to heat.
Nodular cast iron has a strong tendency to form a built-up edge. This tendency is stronger for the softer NCI materials with higher ferritic content. When machining components with high ferritic content and with interrupted cuts, adhesion wear is often the dominating wear mechanism. This can cause problems with flaking of the coating.
The adhesion problem is less pronounced with harder NCI materials that have a higher perlitic content. Here, abrasive wear and/or plastic deformation is more likely to occur.
Compacted Graphite Iron (CGI) K 4.1-4.2
CGI is a material that can meet both the increasing demands for strength and weight reduction and still retain reasonable machinability. The thermal and damping characteristics of CGI are between those of NCI and GCI. Resistance to metal fatigue is twice that of gray iron. The graphite particles in CGI are elongated and randomly oriented as in gray cast iron, but they are shorter and thicker, and have rounded edges. The coral-like morphology in CGI, together with the rounded edges and irregular bumpy surfaces of the graphite particles, provides strong adhesion between the graphite and the iron matrix. This is why the mechanical properties are so improved in CGI, relative to gray cast iron. CGI with a perlitic content below 90% is most common.
CGI is well suited for engine manufacturing, where lighter and stronger materials are needed that can absorb more power. The engine block weight alone can be reduced by approx. 20 percent compared with one made from GCI. Other examples are cylinder heads and disc brakes.
From a machinability point of view, compacted graphite iron is between gray and nodular cast iron. With two to three times the tensile strength of gray cast iron and lower thermal conductivity, machining CGI generates higher cutting forces and more heat in the cutting zone. Increased titanium content in the CGI material influences tool life negatively.
The most common machining operations are face milling and cylinder boring. Instead of cylinder boring, a change in method to circular milling can improve both tool life and productivity.
Austempered Ductile Iron (ADI) K 5.1- 5.3
Austempered ductile iron forms a family of heat-treated cast irons. The austempering heat treatment converts ductile iron to austempered ductile iron (ADI), which includes excellent strength, toughness and fatigue characteristics. ADI is stronger per unit of weight than aluminum and as wear resistant as steel. Tensile and yield strength values are twice those of standard ductile iron. Fatigue strength is 50% higher, and it can be enhanced by shot peening or fillet rolling.
ADI castings are increasingly displacing steel forgings and castings, welded fabrications, carburized steel and aluminum due to its superior performance. Its dominant uses are in the automotive industry, where it is used for suspension and transmission parts, etc. It is also used in the power/energy and the mining and construction sectors.
A 40–50% reduction in tool life compared to NCI can be expected. ADI’s tensile strength and ductility are close to steel’s, but ADI’s chip formation process classifies it as a ductile iron (segmented chip formation). The micro-hardness of ADI is higher, compared to steels of comparable hardness. Higher ADI grades contain hard particles in the micro-structure. High thermal and mechanical loads, due to high strength and ductility, will concentrate wear near the cutting edge, due to the segmented chip formation process, and wear on the top rake. Hardening during chip formation results in high dynamic cutting forces. The cutting edge temperature is a strong factor in determining wear.
ISO N non-ferrous materials
What are ISO N non-ferrous materials?
- This group contains non-ferrous, soft metals with hardnesses under 130 HB, except for high strength bronzes (> 225 HB)
- Aluminum (Al) alloys containing less than 12–13% silicon (Si) represent the largest part
- MMC (Metal Matrix Composite): Al + SiC (20–30%)
- Magnesium-based alloys
- Copper: electrolytic copper with 99.95% Cu
- Bronze: copper with Tin (Sn) (10–14%) and/or aluminum (3–10%)
- Brass: copper (60–85%) with Zinc (Zn) (40–15%)
Machinability of aluminum
- Long-chipping material
- Relatively easy chip control, if alloyed
- Pure Al is sticky and requires sharp cutting edges and high vc
- Specific cutting force: 350–700 N/mm²
- Cutting forces, and thus the power required to machine them, are low
- The material can be machined with fine-grained, uncoated carbide grades when the Si content is below 7–8%, and with PCD-tipped grades for aluminum with higher Si content
- Over eutectic Al with higher Si content > 12% is very abrasive
Engine block, cylinder head, transmission housings, casings, aerospace frame components.
MC codes for N-materials
|MC code||Material group ||Material subgroup||Manufacturing process||Heat treatment||nom||Specific cutting force, kc1 (N/mm2)||mc|
|N1.1.Z.UT||1||aluminum-based alloys||1||commercially pure||Z||cast||UT||untreated||30 HB||350||0.25|
|N1.2.Z.UT||1||2||AlSi alloys, Si <= 1%||Z||UT||60 HB||400||0.25|
|N1.2.C.NS||1||2||C||cast||NS||not specified||80 HB||410||0.25|
|N1.3.C.UT||1||3||AlSi cast alloys, Si <= 1% and < 13%||C||UT||untreated||75 HB||600||0.25|
|N1.4.C.NS||1||4||AlSi cast alloys, Si >= 13%||C||NS||not specified||130 HB||700||0.25|
|N2.0.C.UT||2||magnesium-based alloys||0||main group||C||cast||UT||untreated||70 HB|||||
|N3.1.U.UT||3||copper-based alloys ||1||non-leaded copper alloys (incl. electrolytic copper)||U||not specified||UT||untreated ||100 HB||1,350||0.25|
|N3.2.C.UT||3||2||leaded brass & bronzes (Pb <= 1%) ||C||cast||UT||90 HB||550||0.25|
|N3.3.U.UT||3||3||free cutting copper-based alloys (Pb > 1%)||U||not specified||UT||110 HB||550||0.25|
|N3.4.C.UT||3||4||high-strength bronzes (> 225 HB)||C||cast||UT||300 HB|||||
|N4.0.C.UT||4||zinc-based alloys||0||main group||C||cast||UT||untreated||70 HB|||||
ISO S HRSA and titanium
- MC codes for S materials
- HRSA materials – S 1.0-3.0
- Titanium – S 4.1-4.4
What is ISO S HRSA and titanium?
- The ISO S group can be divided into heat resistant super alloys (HRSA) and titanium
- HRSA materials can be split into three groups: nickel-based, iron-based and cobalt-based alloys
- Condition: annealed, solution heat treated, aged, rolled, forged, cast
- Properties: increased alloy content (Co more so than Ni), results in better resistance to heat, increased tensile strength and higher corrosive resistance
Machinability in general
= Stainless steels = Heat treated (aged) = Solution treatment (annealed)
- The physical properties and machining behavior of each varies considerably, due to both the chemical nature of the alloy and the precise metallurgical processing it receives during manufacture
- Annealing and aging are particularly influential for subsequent machining properties
- Difficult chip control (segmented chips)
- Specific cutting force: 2,400–3,100 N/mm² for HRSA and 1,300–1,400 N/mm² for titanium
- Cutting forces and power required are quite high
In order to achieve higher strength, heat-resistant alloys can be “precipitation hardened”.
By treating the material at elevated temperatures, i.e. aging treatment, small intermetallic particles are precipitated in the alloy. These particles will hinder movement in the crystal structure, and as a result, the material will be more difficult to deform.
MC codes for S-materials
From a machinability point of view, HRSA steels are classified into iron, nickel and cobalt-based materials. Titanium is divided into commercially pure alpha alloys and near-alpha alloys, alpha/beta alloys and beta alloys.
|MC code||Material group||Material subgroup||Manufacturing process||Heat treatment||nom||Specific cutting force,kc1 (N/mm2)||mc|
|S1.0.U.AN||1||iron-based alloys||1||main group||U|| not specified||AN||annealed||200 HB||2,400||0.25|
|S2.0.Z.AN||2||nickel-based alloys ||0||main group ||Z||forged/rolled/cold drawn ||AN||annealed||250 HB||2,650||0.25|
|S2.0.C.NS||2||0||C||cast||NS||not specified||320 HB||3,000||0.25|
|S3.0.Z.AN||3||cobalt-based alloys ||0||main group||Z||forged/rolled/cold drawn||AN||annealed||200 HB||2,700||0.25|
|S3.0.C.NS||3||0||C||cast||NS||not specified||320 HB||3,100||0.25|
|S4.1.Z.UT||4||titanium-based alloys||1||commercially pure(> 99.5% Ti)||Z||forged/rolled/cold drawn||UT||untreated||200 HB||1,300||0.23|
|S4.2.Z.AN||4||2||alpha and near-alpha alloys||Z||AN||annealed||320 HB||1,400|||
|S4.3.Z.AN||4||3||alpha/beta alloys||Z||AN||330 HB||1,400|
|S4.4.Z.AN||4||4||beta alloys||Z||AN||annealed||330 HB||1,400|||
|S5.0.U.NS||3||tungsten-based||0||main group||U||not specified||NS||not specified||120 HB|||
|S6.0.U.NS||3||molybdenum based||0||main group||U||not specified||NS||not specified||200 HB|
HRSA materials – S 1.0-3.0
High corrosion-resistant materials which retain their hardness and strength at higher temperatures. The material is used at up to 1,000°C and is hardened through an aging process.
- The nickel-based version is the most widely used – over 50% of the weight of an airplane engine. Precipitation hardened materials include Inconel 718, 706 Waspalloy and Udimet 720. Solution strengthened (not hardenable) includes Inconel 625
- Iron-based material derives from austenitic stainless steels and has the poorest hot strength properties: Inconel 909 Greek Ascoloy and A286
- Cobalt-based materials have the best hot temperature performance and corrosion resistance, and are predominantly used in the medical industry: Haynes 25 (Co49Cr20W15Ni10), Stellite 21, 31
Main alloying elements in HRSA materials
Ni: Stabilizes metal structure and material properties at high temperatures
Co, Mo, W: increase strength at elevated temperatures
Cr, Al, Si: improve resistance to oxidation and high temperature corrosion
C: increases creep strength
Aerospace engine and power gas turbines in the combustion and turbine sections, oil and gas marine applications, medical joint implants, high corrosion resistant applications.
Machinability of HRSA materials increases in difficulty in the following sequence: iron-based materials, nickel-based materials and cobalt-based materials. All the materials have high strength at high temperatures and produce segmented chips during cutting, which creates high and dynamic cutting forces.
Poor heat conductivity and high hardness generate high temperatures during machining. The high strength, work hardening and adhesion hardening properties create notch wear at maximum depth of cut and an extremely abrasive environment for the cutting edge.
Carbide grades should have good edge toughness and good adhesion between the coating and the substrate to provide good resistance to plastic deformation. In general, use inserts with a large entering angle (round inserts) and select a positive insert geometry. In turning and milling, ceramic grades can be used, depending on the application.
Titanium – S 4.1-4.4
Titanium alloys can be split into four classes, depending on the structures and alloying elements present.
- Untreated, commercially pure titanium
- Alpha alloys – with additions of Al, O and/or N
- Beta alloys – additions of Mb, Fe, V, Cr and/or Mn
- Mixed α+β alloys, in which a mixture of both classes is present
Mixed α+β alloys with type Ti-6Al-4V account for the majority of titanium alloys currently in use, primarily in the aerospace sector, but also in general-purpose applications. Titanium has a high strength to weight ratio, with excellent corrosion resistance at 60% of the density of steel. This enables the design of thinner walls.
Titanium can be used in very harsh environments that could cause considerable corrosion attacks on most other construction materials. This is due to titanium oxide, TiO2, which is very resistant and covers the surface in a layer that is approx. 0.01 mm thick. If the oxide layer is damaged and there is oxygen available, the titanium rebuilds the oxide immediately. Suitable for heat exchangers, desalting equipment, jet engine parts, landing gears and structural parts in the aerospace field.
The machinability of titanium alloys is poor compared to both general steels and stainless steels, which places special demands on the cutting tools. Titanium has poor thermal conductivity; strength is retained at high temperatures, which generates high cutting forces and heat at the cutting edge. Highly-sheared, thin chips with a tendency for galling create a narrow contact area on the rake face, generating concentrated cutting forces close to the cutting edge. A cutting speed that is too high produces a chemical reaction between the chip and the cutting tool material, which can result in sudden insert chipping/breakages. Cutting tool materials should have good hot hardness and low cobalt content, and not react with the titanium. Fine-grained, uncoated carbide is usually used. Choose a positive/open geometry with good edge toughness.
ISO H hardened steel
What is ISO H hardened steel?
- This group of materials contains hardened and tempered steels with hardnesses > 45–68 HRC
- Common steels include carburizing steel (~60 HRC), ball bearing steel (~60 HRC) and tool steel (~68 HRC). Hard types of cast irons include white cast iron (~50 HRC) and ADI/Kymenite (~40 HRC). Construction steel (40–45 HRC), Mn steel and different types of hard coatings, i.e. stellite, P/M steel and cemented carbide also belong to this group
- Typically, hard part turning falls within the range of 55–68 HRC
- Hardened steel is the smallest group from a machining point of view, and finishing is the most common machining operation. Specific cutting force: 2,550–4,870 N/mm². The operation usually produces fair chip control. Cutting forces and power requirements are quite high
- The cutting tool material needs to have good resistance to plastic deformation (hot hardness), chemical stability (at high temperatures), mechanical strength and resistance to abrasive wear. CBN has these characteristics and allows for turning instead of grinding
- Mixed or whisker reinforced ceramic is also used in turning when the workpiece has moderate surface finish demands and the hardness is too high for carbide
- Cemented carbide dominates in milling and drilling applications and is used up to approx. 60 HRC
Typical components include transmission shafts, gear box housings, steering pinions, stamping dies.
MC codes for hardened steel
|MC code||Material group||Material subgroup||Manufacturing process||Heat treatment||nom||Specific cutting force, kc1 (N/mm2)||mc|
|H1.1.Z.HA||1||steels (extra hard)||1||Hardness level 50||Z||forged/rolled/cold drown||HA||hardened (+tempered)||50 HRC||3,090||0.25|
|H1.2.Z.HA||1||2||Hardness level 55||Z||HA||55 HRC||3,690||0.25|
|H1.3.Z.HA||1||3||Hardness level 60||Z||HA||60 HRC||4,330||0.25|
|H1.4.Z.HA||1||4||Hardness level 63||Z||HA||63 HRC||4,750||0.25|
|H2.0.C.UT||2||chilled cast iron||0||main group||C||cast||UT||untreated||55 HRC||3,450||0.28|
|H3.0.C.UT||3||stellites||0||main group||C||cast||UT||not specified||40 HRC|||||
|H4.0.S.AN||4||Ferro-TiC||0||main group||S||sintered||AN||annealed||67 HRC|||||