What is the difference between different metal materials while cutting?


In metal cutting, there will be different workpiece materials, and the cutting formation and removal characteristics of different materials are different. How can we grasp the characteristics of different materials? ISO standard metal materials are divided into 6 different types of groups; each type has unique characteristics in terms of workability.
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-Non-ferrous metals

(5) S-heat-resistant alloy

(6) H-hardened steel

(1) P - Steel

What is steel?
– Steel is the largest material group in metal cutting.
– Steel can be non-hardened steel or quenched and tempered steel (up to 400HB).
– Steel is an alloy based on the element iron (Fe). It is manufactured through a smelting process.
– The carbon content of non-alloyed steels is less than 0.8%, with 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 are added.
In the ​​metal cutting, the P group is the largest material group because it covers several different industrial areas.
The material is usually a long chip material capable of forming continuous, relatively uniform chips. The specific chip form usually depends on the carbon content.
– Low carbon content = tough, sticky material.
– High carbon content = brittle materials.

Processing characteristics:

• Long chip material. 

• Chip control is relatively easy and stable. 

• Low carbon steel is sticky and requires sharp cutting edges. 

• Unit cutting force kc: 1500–3100 N / mm2 

• The cutting forces and power required to process ISO P materials are within a limited range.


(2) M - Stainless Steel

What is stainless steel?
– Stainless steel is an alloy material with a minimum of 11–12% chromium.
– The carbon content is usually very low (down to 0.01% max).
– The alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
– Forms a dense layer of Cr2O3 on the steel surface to make it corrosion resistant
In Group M, most applications are in the oil and gas, pipe, flange, processing, and pharmaceutical industries.

Processing characteristics:

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

(3) K - Cast Iron

What is cast iron?
– There are 3 main types of cast iron: grey cast iron (GCI), nodular cast iron (NCI) and vermicular graphite cast iron (CGI).
– Cast iron is mainly composed of 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, increasing strength and hardness, but reducing machinability.
Group K is mainly used in automotive parts, machine manufacturing and ironmaking.
The chip formation of the material varies, from approximately powdery chips to long chips. The power required to process this material group is usually small.
Note that there is a big difference between gray cast iron (usually chip-like powdery) and nodular cast iron, which in many cases is more similar to steel.

Processing characteristics:

– Short chip material.
– Good chip control in all conditions.
– Unit cutting force: 790-1350 N / mm2
– Abrasive wear occurs at higher speeds.
– Medium cutting force.

(4) N - Nonferrous Metals

What is non-ferrous metal material? – This category contains non-ferrous metals and soft metals with a hardness of less than 130 HB.
– Non-ferrous metal (Al) alloys containing nearly 22% silicon (Si) make up the largest portion.
– Copper, bronze, brass. Aircraft manufacturing and aluminum alloy automotive wheel manufacturers dominate the N group. Although the power required per mm3 (cubic inches) is low, to obtain higher metal removal rate, it is still necessary to calculate the maximum power rate required.

(5) S - Heat Resistant Alloy

What is a 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.
– Higher alloy content (cobalt is higher than nickel) ensures better heat resistance, higher tensile strength and higher corrosion resistance.
Group S materials that are difficult to process are mainly used in the aerospace, gas turbine and generator industries.
The range is wide, but higher cutting rates.

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 carbides.
– Unit cutting force:
For heat resistant alloys: 2400–3100 N / mm2
For titanium alloy: 1300-1400 N / mm2
– High cutting forces and rates are required.

(6) H - Hardened Steel

What is hardened steel?
– For machining, hardened steel is the smallest group.
– This group contains hardened and tempered steels> 45–65 HRC.
– Normally, the hardness range of hard parts being turned is between 55–68 HRC.
Hardened steels in Group H are used in various industries, such as the automotive industry and its subcontractors, as well as machine building and mold operations.
Usually continuous, red-hot chips. This high temperature helps reduce the kc1 value and is important to help solve application challenges.

Processing characteristics:

– Long chip material.
– Relatively good chip control.
– Requires negative rake angle.
– Unit cutting force: 2550-4870 N / mm2
– High cutting forces and power are required.