Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
(OP)
I have to manufacture NiCrMo Alloy Steel (SAE 4340/817M40)Hex head Bolt - 12 Nos. (Silo Connecting Pins)
Bolt Length (excluding head): 555mm (21.85").
Bolt Dia: 100mm (4"). This Pin Bolt is to be Proof Load Tested at 90 tons. The Test load is not to be applied axially but radially.
I know that I have to Quench and Temper this Bolt to approx. 300-350 BHN (somewhere between "T" and "U" condition of Heat Treatment).
The end user wants this bolt to be Impact Tested at -20 degrees Centigrade. But does not know the Charpy Impact value to be specified.
I have the past data of Impact Test at -10 degree Centigrade for 7" Dia in the same material specified above and hardness of 335 BHN. The value achieved was 40 Joules.
Can anyone guide me what Impact value should I accept to supply these bolts which are Impact tested at -20 degree Centigrade?
Thanks in advance.
Bolt Length (excluding head): 555mm (21.85").
Bolt Dia: 100mm (4"). This Pin Bolt is to be Proof Load Tested at 90 tons. The Test load is not to be applied axially but radially.
I know that I have to Quench and Temper this Bolt to approx. 300-350 BHN (somewhere between "T" and "U" condition of Heat Treatment).
The end user wants this bolt to be Impact Tested at -20 degrees Centigrade. But does not know the Charpy Impact value to be specified.
I have the past data of Impact Test at -10 degree Centigrade for 7" Dia in the same material specified above and hardness of 335 BHN. The value achieved was 40 Joules.
Can anyone guide me what Impact value should I accept to supply these bolts which are Impact tested at -20 degree Centigrade?
Thanks in advance.





RE: Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
I would actually expect better than 80 Joules, but I wouldn't accept a requirement that high without prior experience with the specific heat treating equipment used. I am a bit surprised at only 40 Joules on the 7" material, but the 7" does have a much larger section size, and that will lower the CVN results.
rp
RE: Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
Thanks for your valuable advice. I shall aim at around 300 BHN with double tempering during heat treatment. Should I opt for 'Salt Bath' heat treatment process ?
In smaller diameter (2.2"), I am comfortably getting around 100-120 Joules at room temp.+25 C in SAE 4340 steel in narrow range of 290-310 BHN through 'salt bath' process.
KS.
RE: Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
rp
RE: Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
You may want to consult these two specifications or do the search under those alphanumeric strings on the net.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340
ASTM A320M is a standard for low-temperature fasteners (both alloy steels and stainless steels), and has a requirement for impact testing. Grade L43 is essentially the composition of 4340, quenched & tempered to YS725/UTS860/Elong16% and has a maximum hardness requirement of 321 HB (35 HRC). The impact requirement is a minimum of 27 J when tested at - 101 C. So, as you can see, when everything is carefully controlled, this combination offers outstanding toughness. I agree with redpicker that 54 J at - 20 C should be easily attained and is a reasonable limit for a large fastener such as this. By the way, the values that I listed above for Grade L43 ASTM A320 are for diameters up to 100 mm.
With regards to heat treating, oil quenching is the standard process for fasteners, even those as large as 100 mm in diameter. Tempering should be performed at a temperature of 1100-1150 F (595-620 C).