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A Design Study in Steel - Spokane Industries Steel Snubber Arm

Steel Alloy Selection

Spokane Industries casting engineers considered two Cr-Ni-Mo steel alloys for the snubber arm -  AISI 8620 and  AISI 4320. 
Both of these alloys are used for moderate section sizes which require medium hardenability, strength, and impact shock resistance. 

AISI 8620 (0.18-0.23C, 0.70-0.90 Mn, 0.15-0.30 Si, 0.40-0.60Cr, 0.40-0.70 Ni, 0.15-0.25 Mo) 
AISI 4320 (0.17-0.22C, 0.45-0.65 Mn, 0.15-0.30 Si, 0.40-0.60Cr, 1.65-2.00 Ni, 0.20-0.30 Mo) 
The mechanical properties of these two alloys depend on selecting a heat-treatment for the specified section thickness.  With an appropriate heat-treatment for the snubber arm the properties of the two alloys are --  

AISI 8620 (HT A)		 AISI 4320 (HT B)
 Minimum Ultimate Tensile Strength  98 ksi  130 ksi 
 Minimum Yield Strength  71 ksi  85 ksi 
 Minimum % Elongation 21% 22%
Minimum % Reduction in Area 54% 56%
Impact Toughness (-40F) - ft-lbs 35 40
 Brinell Hardness Range 270 BHN  255 BHN
The AISI 4320 meets all the mechanical property requirements goals and was the alloy chosen for casting the snubber arm. 


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Copyright 2011  by the Steel Founders' Society of America   All rights reserved. 
Address comments to: blairr@sfsa.org
Last Modified:August, 2011 by STG

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In cooperation with
Spokane Industries - Steel Castings Division