Specifications_4340_steel.pdf

Specifications

4340 Steel

Compositional and melting requirements:

1. The Contractor shall provide AISI 4340 steel bars, from a single heat to minimize compositional and microstructural variation. Because steel plants produce steel in different heat sizes (inherent to their facilities), ACMD will allow some flexibility in our contract by bracketing the quantity of the steel to be purchased and setting a maximum of $100,000 for the purchase. We prefer to purchase the maximum quantity of steel possible.

2. The steel shall be produced using either a double-vacuum-melting procedure (vacuum-induction-melt vacuum-arc-remelt, VIM-VAR), or arc furnace melting followed by argon-oxygen-decarburization (AOD) refining to produce electrodes which are vacuum arc re-melted (ARC-AOD-VAR).

3. The steel shall meet the compositional requirements of AISI-SAE alloy 4340. Refer to http://www.steelforge.com/alloy-steel-4340/ for compositional information.

4. The steel must also meet the stricter requirements of AMS6414 (see http://standards.sae.org/ams6414/), which describes steel production by a vacuum-melting procedure.

5. ACMD also requires that the phosphorus, sulfur, vanadium, niobium, titanium, and copper contents of the steel to be low. The maximum concentrations (in mass %) allowed for these elements shall be: (1) P = 0.010, (2) S = 0.010, (3) V = 0.030, (4) Nb = 0.005,

(5) Ti = 0.003, and (6) Cu = 0.35.

6. The composition shall be certified using standard analytical procedures (such as optical emission spectroscopy or x-ray fluorescence), and the equipment shall be calibrated by standards traceable to NIST. The composition shall be measured at the top and bottom of the re-melted ingot. These two measurements shall be included in the documentation with the order, meet our compositional requirements, and meet the limits on residuals given in

5. above. Deviations between the two measurements (in mass percent between the top and bottom of VAR ingot) cannot exceed 0.030 for C, Si, and Mo; 0.10 for Mn; 0.030 for Cr; 0.050 for Ni; 0.003 for P; and 0.001 for S.

7. The ingots shall be forged, rolled to billet, conditioned, then hot rolled to bar (if an alternate process has not been mutually agreed upon). The goal of the processing is to have bar from one procurement to have inclusion distributions and sizes that are similar to batches produced from other procurements. With this objective in mind, it is required that the steel be processed in a manner agreed upon prior to the processing of the steel, such as:

a. VAR ingots at 1093 °C (2000 °F) are forged to 12 by 11 inch billets that are http://www.steelforge.com/alloy-steel-4340/ http://standards.sae.org/ams6414/ rolled to 2 ¼ inch diameter billets.

b. These billets are then solution annealed (1100 °C/2012 °F for 1 hour, minimum) prior to rolling to ½ inch square bar (1093 °C/2000 °F).

c. If the solution treatment is performed as a separate process, controlled cooling

(fans, quenching, etc.) is required down to a temperature of 500 °C (930 °F).

d. If the solution treatment is performed as part of the re-heating cycle prior to rolling, the process shall be described in adequate detail to indicate/estimate holding and cooling times.

8. The bar shall be finished to 0.50-inch square bar (+0.15 inch, -0.00 inch).

a. The corner radius of the finished bars cannot exceed 0.03 inches.

b. The microstructure shall be uniform through the thickness, with a maximum acceptable grain size of ASTM number 7.

c. In other attributes (decarburization, segregation, surface condition, etc.), the steel must be suitable for use as 10 mm square Charpy V-notch specimens.

9. The 0.50-inch bar shall be fully annealed to a hardness of RB-95 max.

a. The bar shall be annealed at 850 °C (1550 °F) for 1 hour, furnace cooled at

10 °C/hr (50 °F/hr) to 315 °C (600 °F), then air cooled to room temperature.

b. It is critical to produce a uniform hardness bar (no hard spots), because hard spots result in significant machining issues.

c. ACMD will accept alternate heat-treating schedules by mutual agreement.

The bar is required to be machine straightened (for twist and bow), and shipped in lengths of no more than 6 feet.

4340 Steel