6 Types of Metal Cutting Difference

In the metal cutting process, there are different materials of the workpieces.

Different materials have different cutting formation and removal characteristics. How do we master the features of different materials?

ISO standard metal materials are divided into 6 different types of groups, each of which has unique properties in terms of processability.

This article will summarize them separately.

6 categories of metal materials:

(1) P-steel

(2) M-stainless steel

(3) K-cast iron

(4) N-non-ferrous metals

(5) S-heat resistant alloy

(6) H-hardened steel

6 categories of metal materials

Cutting characteristics of different materials

01-P Steel

What is steel?

  • Steel is the largest group of materials in the field of metal cutting.
  • Steel can be non-hardened steel or quenched and tempered steel (hardness up to 400HB).
  • Steel is an alloy containing iron (Fe) as the main component. It is manufactured through a smelting process.
  • Non-alloy steel has a carbon content of less than 0.8%, only Fe and no other alloying elements.
  • The carbon content of the alloy steel is less than 1.7%, and alloying elements such as Ni, Cr, Mo, V, W, etc. are added.
ISO MC Material
P P1 Non-alloy steel
P2 Low alloy steel (alloy element ≤ 5%)
P3 High alloy steel (alloy element > 5%)
P4 Cast steel

Within the metal cutting range, the P group is the largest material group because it covers several different industrial fields.

The material is typically a long chip material that is capable of forming continuous, relatively uniform chips. The specific form of the chip usually depends on the carbon content.

– Low carbon content = Tough viscous material.

– High carbon content = brittle material.

Processing characteristics:

  • Long chip material.
  • Chip control is relatively easy and smooth.
  • Mild steel is sticky and requires a sharp cutting edge.
  • Unit cutting force kc: 1500–3100 N/mm2
  • The cutting force and power required to process ISO P materials are within a limited range.

Steel Processing Characteristics

02-M Stainless Steel

What is stainless steel?

  • Stainless steel is an alloy with a minimum of 11–12% chromium.
  • The carbon content is usually very low (down to a maximum of 0.01%).
  • The alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
  • Form a layer of dense Cr2O3 on the steel surface to make it resistant to corrosion.
ISO MC Material
M P5 Ferritic/martensitic stainless steel
M1 Austenitic stainless steel
M2 Super austenitic stainless steel, Ni≥20%
M3 Duplex stainless steel (austenitic/ferritic)

In Group M, most applications are in the oil and gas, pipe fittings, flanges, processing industries, and pharmaceutical industries.

The material forms an irregular flaky chip, which has a higher cutting force than ordinary steel. There are many different types of stainless steel. Chip breaking performance (from easy to almost impossible to break) varies depending on alloy properties and heat treatment.

Processing characteristics:

  • Long chip material.
  • Chip control is relatively smooth in ferrite and difficult in austenite and duplex.
  • Unit cutting force: 1800-2850 N/mm2
  • High cutting forces, built-up edges, heat and work hardening during machining.

Stainless Steel Processing Characteristics

03-K Cast Iron

What is cast iron?

  • There are three main types of cast iron: grey cast iron (GCI), ductile iron (NCI) and compacted graphite cast iron (CGI).
  • Cast iron is based on Fe-C with a relatively high silicon content (1–3%).
  • The carbon content exceeds 2%, which is the maximum solubility of C in the austenite phase.
  • Cr (chromium), Mo (molybdenum) and V (vanadium) are added to form carbides, which increase strength and hardness but reduce machinability.
ISO MC Material
K K1 Malleable cast iron
K2 Gray cast iron
K3 Ductile iron
K4 Vermicular graphite cast iron
K5 Austempered ductile iron

The K group is mainly used in the automotive parts, machine manufacturing and iron making industries.

The chip formation of the material varies from approximately powdered chips to long chips. The power required to process this set of materials is typically small.

Note that grey cast iron (usually the chip is approximately powdery) differs greatly from ductile cast iron, which is often similar to steel in many cases.

Processing characteristics:

  • Short chip material.
  • Good chip control under all conditions.
  • Unit cutting force: 790-1350 N/mm2
  • Processing at higher speeds can result in abrasive wear.
  • Medium cutting force.

Cast Iron Processing Characteristics

04-N Non-ferrous Metals

What is non-ferrous metals?

  • This class contains non-ferrous metals and soft metals with a hardness of less than 130 HB.
  • The largest part of the non-ferrous (Al) alloy containing nearly 22% silicon (Si).
  • Copper, bronze, brass.
ISO MC Material
N N1 Alloy based on non-ferrous metals
N2 Magnesium based alloy
N3 Copper base alloy
N4 Zinc-based alloy

Related reading: Ferrous vs Non-ferrous Metals

Aircraft manufacturing and aluminum alloy wheel manufacturers dominate the N group.

Although the power required per mm3 (cubic inches) is low, it is still necessary to calculate the maximum power required in order to achieve high metal removal rates.

Processing characteristics:

  • Long chip material.
  • If it is an alloy, chip control is relatively easy.
  • Non-ferrous metal (Al) is sticky and requires a sharp cutting edge.
  • Unit cutting force: 350-700 N/mm2
  • The cutting force and power required to process ISO N materials are within a limited range.

Non-ferrous Metals Processing Characteristics

05-S Heat Resistant Alloy

What is heat resistant alloy?

Heat resistant alloys (HRSA) include many high alloyed iron, nickel, cobalt or titanium based materials.

Group: iron-based, nickel-based, cobalt-based

Working conditions: annealing, solution heat treatment, aging treatment, rolling, forging, casting.

Features: higher alloy content (cobalt over nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.

ISO MC Material
N S1 Iron-based alloy
S2 Nickel-based alloy
S3 Cobalt based alloy
S4 Titanium based alloy
S5 Tungsten-based alloy
S6 Molybdenum based alloy

S-materials with difficult processing are mainly used in the aerospace, gas turbine and generator industries.

The range is wide, but there is usually a high cutting force.

Processing characteristics:

  • Long chip material.
  • Difficult chip control (serrated chips).
  • A negative rake angle is required for ceramics and a positive rake angle is required for cemented carbide.
  • Unit cutting force:
  • For heat resistant alloys: 2400–3100 N/mm2
  • For titanium alloy: 1300-1400 N/mm2
  • High cutting force and power required.

Heat Resistant Alloy Processing Characteristics

06-H Hardened Steel

What is hardened steel?

  • From a processing point of view, hardened steel is the smallest grouping.
  • This group contains quenched and tempered steel with a hardness > 45–65 HRC.
  • Typically, the hardness of a hard part being turned is typically between 55–68 HRC.
ISO MC Material
H H1 Steel (45-65HRC)
H2 Chilled cast iron
H3 Tungsten chromium cobalt alloy
H4 Ferro-TiC

Hardened steel in Group H is used in a variety of industries, such as the automotive industry and its subcontractors, as well as machine manufacturing and mold business.

Usually continuous, red hot chip. This high temperature helps to reduce the kc1 value and is important to help solve application challenges.

Processing characteristics:

  • Long chip material.
  • Relatively good chip control.
  • Require a negative rake angle.
  • Unit cutting force: 2550-4870 N/mm2
  • High cutting force and power required.

Hardened Steel Processing Characteristics

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