November 2020 Volume 2

EQUIPMENT & TECHNOLOGY MATERIALS

forge back to the starting shape effects another 2:1 forging reduction. This 4:1 degree of forge work is sufficient to eliminate the ingot dendritic condition with essentially no net deformation to inclusions, avoiding grain flow effects from elongation. • Very tight temperature control during pouring (teeming) of the ingot: By using theminimum temperature necessary to ensure a properly solidifying ingot, any excess heat that extends the solidification time is avoided. Quicker solidification reduces segregation effects and minimizes grain flow effects from banding. Implementing these metallurgical processes in the manufacture of die steel significantly reduces grain flow effects, and greatly improves the overall strength of dies. The next article will offer some quantitative evidence of improved die strength from these procedures and note strategies for reducing grain flow effects on vulnerable cracking areas in dies and peripheral equipment. ■

Nick Cerwin

Benjamin Ritchey

Nick Cerwin is the retired Director of Technical Services at Finkl Steel. Benjamin Ritchey is the Technical Director for Finkl Steel and can be reached at BRitchey@Finkl.com.

Transverse CVN

Longitudinal CVN

Grain Flow Direction

Photomicrograph at 200X original magnification of actual MnS inclusions in steel elongated in the grain flow direction. If the concentration of such inclusions is high, the mechanical properties can be adversely affected in the transverse direction. The overlaid Charpy V-notch test bars (not to scale) provide an exaggerated example of how these inclusions would be expected to influence impact strength: in the transverse orientation, the elongated inclusions align with the direction of crack propagation from the V-notch, resulting in reduced impact strength. If not well controlled, nonmetallic inclusions can reduce impact strength in the transverse direction to less than one-half the longitudinal value Photomicrograph at 200X original magnification of actual MnS inclusions in steel elongated in the grain flow direction. If the concentration of such inclusions is high, the mechanical properties can be adversely affected in the transverse direction. The overlaid Charpy V-notch test bars (not to scale) provide an exaggerated example of how these inclusions would be expected to influence impact strength: in the transverse orientation, the elongated inclusions lign with the direction of crack propagation from the V notch, resulting in reduced impact strength. If not well controlled, nonmetallic inclusions can reduce impact strength in the transverse direction to less than one-half the longitudinal value.

FIA MAGAZINE | NOVEMBER 2020 13