Advantages and Applications of 45 Steel CNC Machining

GB 45 is a plain carbon steel with a nominal carbon content of 0.42–0.50%. Manganese runs 0.50–0.80%, silicon stays under 0.37%, and there are no deliberate alloying additions. In the Chinese GB system the number is simply the carbon content in hundredths of a percent, so 45 means 0.45% C. That single number explains most of its behavior: harder and stronger than low-carbon steel, but still soft enough to cut freely with carbide tooling.

The nearest North American equivalent is AISI 1045. They are close enough that drawings often cross-reference them, though the sulfur and phosphorus limits differ slightly and heat-treat response is not identical. If a print calls out 1045 and the shop stocks GB 45, ask for the mill certificate before you accept the substitution.

Compared with 1018, this grade carries more carbon and therefore more strength after heat treatment. Compared with 4140, it lacks chromium and molybdenum, so it hardens shallower and loses strength faster at elevated temperature. That trade is usually worth it when the part does not see high stress or heat.

At around 170–210 HB in the normalized or annealed condition, the material cuts with a clean chip and leaves a good as-machined finish. We typically run it at Ra 1.6–3.2 μm straight off the tool, and Ra 0.8–1.6 μm when the finish matters. No special coolant chemistry is needed. Standard flood coolant handles it.

Turning and milling both behave predictably. The chip is ductile but not gummy, so it breaks without wrapping around the tool. That matters on long shafts and on parts with deep pockets, where a stringy chip costs cycle time. Threading is straightforward too, and rolled threads hold up well.

The catch is heat treatment distortion. A 0.45% carbon steel quenches hard, and thin or asymmetric parts can move during the quench. If your part has tight tolerances on two features that are far apart, plan a finish-machining pass after hardening. We hold ±0.005 mm (±0.0002 in) on features we cut after heat treatment.

Welding is possible but not friendly. Preheating and post-weld stress relief are usually required, and the weld zone will not match the base metal hardness. If the design relies on welded joints, consider a low-carbon steel instead.

• 1
  Good forShafts, spindles, gears, bolts, pins, bushings, mold bases, jigs and fixtures.
• 2
  HardeningWater or oil quench, then temper. Common range is 25–50 HRC depending on tempering temperature.
• 3
  Watch outDistortion on thin walls and long slender parts. Leave stock for a post-hardening pass.
• 4
  Not idealHigh-stress springs, parts above 300 °C in service, or anything needing deep hardenability.

Automotive and EV work uses this grade for transmission shafts, steering components, and non-critical engine hardware. It takes induction hardening on a wear band while the rest of the part stays machinable. That combination is why it shows up on so many rotating parts.

Industrial machinery is the biggest user. Think spindles, lead screws, coupling hubs, pump shafts, and hydraulic rod ends. These parts need strength, a decent surface finish, and a price that holds up across a 500-piece run. A medium-carbon steel delivers all three.

In tooling and fixtures, it is common for mold bases, jig plates, locating pins and clamp bodies. The material is stable enough after stress relief to hold position, and it takes black oxide or electroless nickel without trouble.

Medical and robotics work uses it less often, mainly for brackets and structural links where stainless is not required. If the part touches a patient or sees washdown, move to 304 or 316L instead.

For prototypes, the low cost and fast cutting make it a good first article material. You can validate geometry, then switch to a heat-treated alloy for production if the load case demands it.

Hardening is usually done to 25–35 HRC for structural parts and 40–50 HRC for wear surfaces. Above 50 HRC, machining gets expensive and grinding becomes the better option. Tell us the target hardness and whether it applies to the whole part or just a band.

For corrosion resistance, black oxide and electroless nickel are the common choices. Neither is a substitute for stainless in a wet environment. Zinc plating works for indoor hardware. Bead blasting gives a uniform matte look before plating.

We inspect 100% of parts before shipment. That includes a raw material certificate check, in-process monitoring on critical dimensions, and a final inspection report on request. Tolerances down to ±0.005 mm are routine on turned features.

Our 127 CNC machines include 16 simultaneous 5-axis centers, 16 mill-turn centers, and a Ø400 mm rotary table. Maximum processing size is 4,000 mm. The 5-axis and mill-turn capacity matters most for this material because it lets us cut complex features in one setup, which reduces the distortion risk from rechucking.