HEAT TREATMENT OF 4340 1

[gill1985]

MATERIAL: ASTM A829 GR 4340
(1.75 NI .75 CR .25 MO)
MIN TENSILE STRENGTH: 125 KSI
MIN YIELD: 105 KSI
ALLOWABLE STRESS: KSI
100F=35
200F=33
300F=31.9
400F=30.6
500F=29.5
600F=28.1
700F=26.4
800F=24.2
NEED TO KNOW HEATING AND TEMERING TEMP. TO OBTAIN ABOVE MECHINICAL RESULTS.THANKS IN ADVANCE.

 

[metengr]

What are you asking? Have you read ASTM A-829? The original properties of the structural quality alloy steel plates are specified to chemical composition requirements, but tensile requirements can be used, which is what you have stated above as 125 KSI UTS and 105 Ksi yield.

The allowable stresses in your table are for design purposes to probably avoid permanent deformation in service.

So, if your question is about the original heat treatment in accordance with ASTM A-829, you want to specify Condition NT ( a normalized and tempered heat treatment for 4340 with the stated mechanical strength levels) from a steel supplier. Keep in mind, that the tensile strength requirements must be compatible with the chemical composition, heat treatment condition and plate thickness (per ASTM A-829), which I see no problems with 4340.

 

[pmkPE]

metengr and gil1985: Where did you obtain the tensile and yield properties for this particular material and grade?

 

[metengr]

pmkPE;
The specified UTS and YS, along with heat treatment condition(s) for purchase are stated in ASTM A-829.

 

[pmkPE]

ASTM A829 provides in Table 3 (Tensile Strength Ranges) the three potential "Specified Maximum Tensile Strengths" (up to 70 ksi, over 70 to 110 ksi and over 110 to 140 ksi) with the corresponding Tensile Stregth Range of 15, 20 and 25 ksi. ASTM A829 does not explicitly list for any of the 30 listed grades what the corresponding minimum yield and ultimate tensile strengths are, or could be, for any particular (heat) treatment. So I am assuming to obtain specific yield and/or ultimate strengths, one must call for them specifically or indicate what heat treatment is required along with the resulting and acceptable values for yield and ultimate strengths. If this is not correct what other ways are available for determining the properties?

I am reviewing a calculation based on a drawing that does not call out specific heat treatment, or minimum yield strength/ultimate tensile strength. The calculation calls for a yield strength of 68.5 ksi and an ultimate strength of 108 ksi - unable to speak directly with the original author - where can I find info to verify these numbers based on a bill of material calling for ASTM A826 Grade 4340 material?

 

[pmkPE]

Correction the BOM calls for ASTM A829 not 826.

 

[metengr]

So I am assuming to obtain specific yield and/or ultimate strengths, one must call for them specifically or indicate what heat treatment is required along with the resulting and acceptable values for yield and ultimate strengths.

Correct. The heat treatment condition is mentioned in A 829 - normalized and tempered.

 

[pmkPE]

metengr: What if it is not called out? What should be the default values?

 

[metengr]

pmkPE;
I am not sure I understand your question about default values. ASTM Standard Specifications do not provide mechanical property requirements tailored to specific design applications in service. The ASTM Standards are meant to assure that after selection of suitable material by a purchaser (their responsibility), the material that is purchased will meet minimum requirements in the Standard Specification.

 

[pmkPE]

metengr,

Thanks for your input- I really do appreciate your assistance.

In response to your last question if the BOM states ASTM A829 Grade 4340 ( for washer plate material) without any additional information - what would you expect the minimum yield and the minimum ultimate tensile strengths to be?

 

[metengr]

pmkPE;
Ok. Sorry about the confusion, but it is difficult to sometimes answer these types of questions without talking face to face. If your bill of material does not have any reference to a specified UTS, YS for this material grade, I cannot interpret nor specify a heat treatment for you because various strength levels can be supplied. This ASTM specification provides various Grades of material that must be ordered to a specific chemical composition, with an option to specify tensile requirements (again, if specified by the purchaser). I suppose the plate material can be specified in an annealed condition (lowest strength level with a min UTS @ 108 Ksi and min YS @ 68 Ksi) for your purposes as a conservative design approach. Keep in mind that the plate can also be supplied in a heat treated condition, as discussed in an earlier post (N&T). The bottom line is that the strength properties can be all over the map.

 

[pmkPE]

Thanks metengr!

Fortunately that is what the author used in his calculation.

My next question(s) is how did you determine these values? based on ASTM A829?

 

[metengr]

pmkPE;
The min UTS and min YS values that I referenced above were extracted from another technical publication that contains property data for annealed and normalized low alloy (4340) steel.

 

[QAFitz]

I suggest you consider purchasing the ASM "Heat Treating" guide. Not only for 4340 but for many, many other grades and heat treat information.

 

[mighoser]

For strip/sheet/plate: AMS 6395 or 6359
Tubing: AMS 6415
Forging: AMS 6415

Or Depending on form use:
ASTM A108
ASTM A 322
ASTM A 519

For Heat treat use AMS 2749/1 or 2749/2 depending on required mechanical properties.

 

[dimjim]

We used 4340 in many bearing ring for
Q&T materials and it looks like the tensile range
is for 250 BHN but the yield looks high
so I assume you would need to harden to
around 269 BHN min for that UYS. Normally I have
seen this material used for cold temperature property
materials like API designs or those materials
use in the North Sea. What is your application?