A material callout affects more than strength. It changes machinability, heat treatment, finish and lead time. Compare the service load and required properties before choosing a grade.
Fe
01Carbon and alloy steels
Grade
Carbon
Hardness after treatment
Properties and uses
S15C / SS400
S15C: about 0.15%; SS400: not specified by grade
—
Common structural grades; verify strength and heat-treatment needs separately
S45C
0.45%
HRC 45 ～ 55
The most general-purpose medium-carbon steel: shafts, gears, fixtures
SCM440
0.40% + Cr-Mo
HRC 30 to 35 (quenched and tempered)
High strength, good hardenability; drive shafts
SNCM439
Ni-Cr-Mo
HRC 32 ～ 38
Large-section high-strength parts
SCM415
0.15% + Cr-Mo
Surface HRC 58 to 62
For carburising: gears, cams
Carbon content affects achievable hardness; low-carbon steel may need surface hardening for wear resistance.
02Stainless steels
Grade
Series
Magnetic
Properties
SUS304
Austenitic
None
The most general-purpose; good corrosion resistance, work-hardens badly
SUS303
Austenitic
None
Sulphur added for machinability; slightly less corrosion resistant
SUS316
Austenitic
None
Molybdenum added; resists chlorides, for food and marine use
SUS420J2
Martensitic
Yes
Hardenable to HRC 50+; tooling, dies
SUS440C
Martensitic
Yes
HRC 58+; bearings, blades
SUS630 (17-4PH)
Precipitation hardening
Yes
Precipitation hardened; high strength with corrosion resistance
Austenitic stainless steels are not hardened by conventional quenching; choose a grade and process for the required properties.
Why SUS304 is particularly difficult to cut
Work hardening. A cut surface can go from HB 180 to above HB 350.
Poor thermal conductivity. The heat stays in the edge, about a third that of carbon steel.
High toughness. Chips do not break easily and wrap around the tool.
What to do. Cut deep enough to get under the hardened layer, do not feed too lightly, keep the edge sharp, flood with coolant, and prefer inserts with good chip breaking.
03Aluminum alloys
Grade
Series
Heat treatable
Properties
A1050
1000 pure aluminium
No
Excellent conductivity, soft, poor for machining
A5052
5000 Al-Mg
No
The workhorse for sheet metal; bends well, corrosion resistant
A6061-T6
6000 Al-Mg-Si
Yes
The most machined grade; balanced strength and machinability
A6063
6000
Yes
For extrusion; good surface, anodises beautifully
A7075-T6
7000 Al-Zn
Yes
Strength approaching steel, but poor corrosion resistance and weldability
ADC12
Die casting
No
Die-cast parts; high silicon content, abrasive on tooling
T6 denotes solution treatment and artificial aging; plan machining and dimensional checks around the treatment.
04Tool steels and others
Grade
Type
Hardness
Uses
SKD11
Cold work tool steel
HRC 58 ～ 62
Blanking dies, shear blades, wear parts
SKD61
Hot work tool steel
HRC 45 ～ 52
Die-casting dies, forging dies
SKH51
High-speed steel
HRC 62 ～ 65
Cutting tools, punches
FC250 / FCD450
Grey cast iron / ductile iron
HB 180 ～ 250
Machine bases, housings
C3604
Free-cutting brass
—
Turned parts, fittings
POM / PEEK
Engineering plastics
—
Wear bushings, insulating parts
Precision tool-steel parts may need stock for grinding after heat treatment.
05Questions before choosing
What does it have to withstand? Tension, bending, impact, wear, fatigue, each maps to different properties.
What is the environment? Dry indoors, outdoors, chlorides, high temperature, food contact, these set the corrosion class.
Does it have to be hard? Hard means hardenable, so check the carbon content or the option of carburising first.
Can you buy it, can you make it? Lead time and minimum order on a special grade often affect a project more than the properties do.