In metal cutting, there are different workpiece materials. Different materials have different cutting formation and removal characteristics. How do we master the characteristics of different materials? ISO standard metal materials are divided into 6 different type groups, each type has unique characteristics in terms of machinability, and this article will summarize them separately.
Metal materials are divided into 6 categories:
(1) P-steel
(2) M-stainless steel
(3) K-cast iron
(4) N-Nonferrous metals
(5) S-heat-resistant alloy
(6) H-hardened steel
picture
↑↑Cutting characteristics of different materials↑↑
01-P steel
What is steel?
- Steel is the largest material group in metal cutting.
- Steel can be unhardened steel or quenched and tempered steel (hardness up to 400HB).
- Steel is an alloy with the element iron (Fe) as its main component. It is manufactured through a smelting process.
- The carbon content of non-alloy steel is less than 0.8%, only Fe and no other alloying elements.
- The carbon content of alloy steel is less than 1.7%, and alloying elements such as Ni, Cr, Mo, V, W, etc. are added.
picture
Areas of application: Within the scope of metal cutting, group P is the largest material group, as it covers several different industrial areas.
Materials are typically long-chip materials that form continuous, relatively uniform chips. The specific chip pattern usually depends on the carbon content.
– Low carbon content = tough, sticky material.
– High carbon content = brittle material.
Processing characteristics:
- Long-chip materials.
- 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 for processing ISO P materials are within a limited range.
picture
02-M stainless steel
What is stainless steel?
- Stainless steel is an alloy material with at least 11%~12% chromium.
- Carbon content is usually very low (as low as 0.01% maximum).
- The main alloys are Ni (nickel), Mo (molybdenum) and Ti (titanium).
- Forms a dense layer of Cr2O3 on the steel surface, making it corrosion resistant.
picture
Areas of application: In group M, most applications belong to the oil and gas, pipe fittings, flanges, process industries and the pharmaceutical industry.
Chip Shape: The material forms irregular, flaky chips that allow higher cutting forces than ordinary steel. There are many different types of stainless steel. Chip breaking performance (from easy to nearly impossible) varies depending on alloy properties and heat treatment.
Processing characteristics:
- Long-chip materials.
- Chip control is relatively smooth in ferrite and more difficult in austenite and duplex.
- Unit cutting force: 1800~2850 N/mm²
- High cutting forces, built-up edge, heat and work hardening during machining.
picture
03-K cast iron
What is cast iron?
- There are 3 main types of cast iron: gray cast iron (GCI), ductile iron (NCI) and compacted graphite iron (CGI).
- Cast iron is mainly composed of Fe-C and has a relatively high silicon content (1%~3%).
- 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.
picture
Application fields: Group K is mainly used in automobile parts, machine manufacturing and ironmaking industries.
Chip Shape: Materials vary in chip shape, from nearly powdery chips to long chips. The power required to process this material group is usually small.
*Note: There is a big difference between gray cast iron (usually the chips are almost powdery) and ductile iron, the chip breaking of the latter is often similar to steel.
Processing characteristics:
- Short chip materials.
- Good chip control in all operating conditions.
- Unit cutting force: 790~1350 N/mm²
- Machining at higher speeds produces abrasive wear.
- Medium cutting force.
picture
04-N nonferrous metals
What are non-ferrous metal materials?
- This category includes non-ferrous metals, soft metals with a hardness below 130 HB.
- Non-ferrous metal (Al) alloys containing nearly 22% silicon (Si) form the largest part.
- Copper, bronze, brass.
picture
Application fields: Aircraft manufacturing and aluminum alloy automobile wheel manufacturers occupy a major position in Group N.
Although the power required per cubic inch is low, to obtain high metal removal rates, it is still necessary to calculate the maximum power required.
Processing characteristics:
- Long-chip materials.
- In the case of alloys, chip control is relatively easy.
- Non-ferrous metals (Al) are sticky and require the use of sharp cutting edges.
- Unit cutting force: 350~700 N/mm²
- The cutting force and power required to process ISO N materials are within a limited range.
picture
05-S heat-resistant alloy
What is heat-resistant alloy?
- Heat-resistant alloys (HRSA) include many high-alloy 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.
Properties: Higher alloy content (cobalt than nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.
picture
Application areas: Group S materials that are difficult to process are mainly used in the aerospace, gas turbine and generator industries.
The range is wide, but high cutting forces are usually present.
Processing characteristics:
- Long-chip materials.
- Difficulty in chip control (jagged chips).
- A negative rake angle is required for ceramics and a positive rake angle is required for carbide.
- Unit cutting force:
For heat-resistant alloys: 2400~3100 N/mm²
For titanium alloy: 1300~1400 N/mm²
- Requires high cutting forces and power.
picture
06-H hardened steel
What is hardened steel?
- From a machining perspective, hardened steels are the smallest grouping.
- This group includes quenched and tempered steels with hardness >45~65 HRC.
- Generally, the hardness range of the hard parts being turned is generally between 55~68 HRC.
picture
Areas of application: Hardened steels in group H are used in a variety of industries, such as the automotive industry and its subcontractors, as well as machine building and the mold business.
Chip shape: usually continuous, red-hot chips. This high temperature helps reduce kc1 values, which is important to help solve application challenges.
Processing characteristics:
- Long-chip materials.
- Relatively good chip control.
- Requires negative rake angle.
- Unit cutting force: 2550~4870 N/mm²
- Requires high cutting forces and power.
