How do different metal materials cut differently?

In metal cutting, there are 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, each with unique characteristics in terms of machinability. 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

Cutting characteristics of different materials
01-P steel
What is steel?
-Steel is the largest material group in the field of metal cutting.
-Steel can be non quenched and tempered steel or quenched and tempered steel (with a hardness of up to 400HB).
-Steel is an alloy primarily composed of iron (Fe). It is manufactured through a melting process.
-The carbon content of non alloy steel is less than 0.8%, with 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.

Within the range of metal cutting, the P group is the largest material group as it covers several different industrial fields.
The material is usually a long chip material that can form continuous and relatively uniform chips. The specific form of chips 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 stable.
-Low carbon steel has viscosity and requires sharp cutting edges.
-Unit cutting force kc: 1500-3100 N/mm2
-The cutting force and power required to process ISO P materials are within a limited range of values.

 

02-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 (as low as a maximum of 0.01%).
-The main alloys are Ni (nickel), Mo (molybdenum), and Ti (titanium).
-Form a dense layer of Cr2O3 on the surface of the steel to make it corrosion-resistant.

In Group M, most applications belong to the oil and gas, pipe fittings, flanges, processing industry, and pharmaceutical industry.
The material forms irregular flake shaped chips, which have higher cutting force compared to ordinary steel. There are many different types of stainless steel. The chip breaking performance (from easy to almost impossible to break) varies depending on the alloy characteristics and heat treatment.
Processing characteristics:
-Long chip material.
-Chip control is relatively smooth in ferrite, but difficult in austenite and duplex.
-Unit cutting force: 1800-2850 N/mm2
-High cutting force, chip buildup, heat, and work hardening are generated during machining.

 

03-K cast iron
What is cast iron?
-There are three main types of cast iron: gray cast iron (GCI), nodular cast iron (NCI), and nodular cast iron (CGI).
-Cast iron is mainly composed of Fe-C and has a relatively high silicon content (1-3%).
-The carbon content exceeds 2%, which is the maximum solubility of C in the austenite phase.
-The addition of Cr (chromium), Mo (molybdenum), and V (vanadium) forms carbides, which increase strength and hardness, but reduce machinability.

The K group is mainly used in automotive components, machine manufacturing, and ironmaking industries.
The chip formation of materials varies, from approximately powdered chips to long chips. The power required to process this material group is usually small.
Note that there is a significant difference between gray cast iron (usually with chips resembling powder) and ductile iron, with the latter often having chips similar to steel.
Processing characteristics:
-Short chip material.
-Good chip control in all operating conditions.
-Unit cutting force: 790-1350 N/mm2
-Processing at a higher speed will result in abrasive wear.
-Medium cutting force.

 

04-N Nonferrous Metals
What is non-ferrous metal material?
-This category includes non-ferrous metals and soft metals with a hardness below 130 HB.
-The largest part is composed of non-ferrous metal (Al) alloys containing nearly 22% silicon (Si).
-Copper, bronze, brass.

The aircraft manufacturing industry and aluminum alloy car wheel manufacturers dominate the N group.
Although the power required per mm3 (cubic inch) is low, to achieve high metal removal rates, it is still necessary to calculate the maximum power required.
Processing characteristics:
-Long chip material.
-If it is an alloy, chip control is relatively easy.
-Non ferrous metals (Al) have viscosity and require the use of sharp cutting edges.
-Unit cutting force: 350-700 N/mm2
-The cutting force and power required for processing ISO N materials are within a limited range of values.

 

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

The difficult to process S-group materials 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.
-Difficulty in chip control (serrated chips).
-For ceramics, a negative lead angle is required, while for hard alloys, a positive lead angle is required.
-Unit cutting force:
For heat-resistant alloys: 2400-3100 N/mm2
For titanium alloys: 1300-1400 N/mm2
-The required cutting force and power are very high.

 

06-H Hardened Steel
What is hardened steel?
-From a processing perspective, quenched steel is the smallest group.
-This group includes quenched and tempered steel with a hardness>45-65 HRC.
-Usually, the hardness range of hard parts being turned is between 55-68 HRC.

The hardened steel in Group H is applied in various industries, such as the automotive industry and its subcontractors, as well as the machine manufacturing and mold business.
Usually continuous, red hot chips. This high temperature helps to reduce the kc1 value, which is important for solving application problems.
Processing characteristics:
-Long chip material.
-Relatively good chip control.
-Negative front corner required.
-Unit cutting force: 2550-4870 N/mm2
-The required cutting force and power are very high.