UNS S45000 Precipitation Hardening Steel Round Bar, UNS S45000 Rods & UNS S45000 Bars

Product Description

1. Microstructure and Phase Transformation

UNS S45000 relies on a carefully balanced martensitic-austenitic matrix.

• In the Solution Annealed State (+A / Condition A): The material is predominantly a low-carbon martensite. Unlike traditional 400-series martensitic steels, it does not become excessively brittle or prone to cracking in this state because the carbon content is restricted to a maximum of $0.05\%$.

• During Aging (Precipitation Hardening): When heated to a specific temperature range ($482^\circ\text{C}$ to $621^\circ\text{C}$ / $900^\circ\text{F}$ to $1150^\circ\text{F}$), sub-microscopic copper-rich phases precipitate out of the solid solution. These precipitates distort the crystal lattice, acting as barriers to dislocation movement and dramatically increasing the steel's yield strength.

2. Commercial Supply Formats & Tolerances

Depending on your downstream manufacturing steps (e.g., forging, direct CNC machining, or centerless grinding), UNS S45000 bars are typically ordered in the following variations:

• Cold Finished (Drawn or Ground) Rods: Typically available in smaller diameters (usually up to $2$ or $3\text{ inches}$). They offer excellent dimensional control (often conforming to ASTM A484 tolerances like h9 or h11) and a smooth surface finish, which minimizes tool chatter and setup time in high-speed CNC Swiss or turning lathes.

• Hot Rolled / Smooth Turned Bars: Usually specified for larger diameter structural rods or shafts ($>3\text{ inches}$). These bars are often bought in Condition A, rough-machined, heat-treated to the desired H-condition, and then finished via grinding to eliminate any minor surface oxidation from the aging furnace.

3. Comparing UNS S45000 to UNS S17400 (17-4 PH)

If you are deciding between UNS S45000 and the more common UNS S17400 for a bar application, consider this direct comparison:

4. Quality Control & Testing Requirements

When validating an Inbound Material Test Report (MTR) for UNS S45000 bars to ensure compliance with ASTM A564 or AMS 5773, look for the following verification checks:

1. Macroetch Testing: Ensuring freedom from dangerous segregation, bursts, or heavy porosity (critical for aerospace and high-pressure oil/gas stems).

2. Ultrasonic Inspection: Frequently mandated for bars over $2\text{ inches}$ in diameter to detect internal cooling cracks or inclusions.

3. Hardness vs. Tensile Correlation: Ensuring that if the bar is ordered pre-heat treated (e.g., H1000 or H1050), both the surface Brinell/Rockwell hardness and the core tensile pull tests match the specification windows uniformly.