Quick Answer: Which Steel Grade Should I Use?
A steel grade is a standardized alloy (set by SAE/AISI or ASTM) that fixes the carbon and alloy content, so its strength, hardness and machinability are known. For most CNC machined parts, 4140 pre-hard alloy steel is the go-to, often called the "6061 of steels." Pick 4340 when you need more strength, 12L14 for the fastest machining and D2 tool steel for wear resistance.
This chart compares 12 steel grades by SAE/AISI number across: tensile strength (ksi), yield strength (ksi), hardness (HB or HRC), machinability, weldability and corrosion resistance. Grades cover carbon steel, alloy steel, tool steel and high-speed steel, with the best common use for each.
Tensile strength range: 1018 carbon 63 ksi | 4140 alloy 95 ksi | 4340 alloy 108 ksi | D2 tool steel 248 ksi (hardened) · 4140 pre-hard ships at 28–34 HRC, ready to machine.
How to Pick the Right Steel Grade
Steel comes in many grades. Each one trades off strength, hardness, machinability, and cost. The right pick depends on your part's job.
Carbon Steels
Carbon steels (1018, 1045, 12L14) are cheap and easy to get. 1018 welds well and machines fast. 1045 is stronger and works for gears and bolts. 12L14 is the fastest to machine. Use it for high-volume screw machine parts.
Alloy Steels
Alloy steels (4130, 4140, 4340, 8620) add chromium, molybdenum, or nickel. These elements boost strength and wear resistance. 4140 is the most popular. Think of it as the "6061 of steels." It handles most jobs well.
4340 is stronger and tougher. Use it for landing gear, crankshafts, and other high-stress parts. 8620 is the go-to for case hardening. Its soft core absorbs shock while the hard surface resists wear.
Tool Steels
Tool steels (A2, D2, O1, S7, M2) are made for hardness. They hold an edge and resist wear. But they are hard to machine. Most shops cut them in the soft state, then heat treat.
D2 has the best wear resistance. S7 handles impact best. M2 stays hard at high cutting temperatures.
4140 pre-hard is the best all-around steel for CNC machining. It arrives heat treated to 28-34 HRC. You skip the heat treatment step and save time and money.
Quick Decision Guide
- Need to weld? → 1018 or 4130
- Need strength? → 4340
- Need machinability? → 12L14
- Need wear resistance? → D2 Tool Steel
- Good all-around? → 4140 pre-hard