Advice for Impact value at -20 degrees Centigrate for Bolt in SAE4340

[karma281053]

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.

 

[redpicker]

You should be able to achieve 54 Joules (40 Ft-Lbs), or better, at -20C with this material at this hardness. If you don't, there is something wrong. Of course, as with most cases when you have to meet impact requirements, you should try to stay away from the upper end of the hardness range.

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

 

[karma281053]

Hi Redpicker,
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.

 

[redpicker]

I would think a 4" section size a bit large for the 'Salt Bath' treatment to be more effective than an oil quench, but maybe not. The real question is what is needed? I can't imagine that 54 Joules at -20C is not going to be enough to prevent brittle failure in a 4" bolt. But, you will really need to know what the customer is going to specify before you decide on the process.

rp

 

[Cockroach]

Regardless of bolt size, Notch Toughness or Charpy Impact are conducted at -45C with 20J energy absorption. This is a pipeline and valve specification as per CSA Z245.15 which is a tighter than API 6D. I can't recall the ISO specification off the top of my head, something like 59598......

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

 

[TVP]

KS,

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).