FAS Membership Community

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

John,

Before retirement I was responsible for an accredited (ISO 17025) fastener testing laboratory.  While we didn't see very many austenitic stainless steel set screws we did supply quite a few Hex Head Cap Screws and we did run into problems with meeting tensile strength (110,000 psi min).  The root cause of the issue was the grip length tolerance.  In order to meet that requirement, we needed to have wire that was strain hardened before forming or we needed to supply a fully threaded length screw (zero grip length).

Moving to you issue, there appears to be an error in ASTM F880 in that it has the cold worked (rolled) threads at a lower strength that an annealed machined thread.  If the threads are rolled from pitch diameter wire there should be an increase in strength at the cup point.  Having said that I looked up ASTM F593 for proof.  Table 2 list the machined parts with a lower hardness (Designation A - 65-95 HRB, YS 20ksi, UTS 70ksi) that the cold worked (Designation CW B95-C32, YS 60ksi, UTS 95ksi) has.

I hope this information has value for you.

Sincerely,
Michael B. Connelly, FASM, CQE

------------------------------
Michael Connelly
Connelly Consulting
Chicago IL
(312) 972-8556
------------------------------

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

I had the same thoughts as Michael when I saw the post first, but did not respond as it did not make sense. The cup point of a cold rolled thread gets maximum deformation (work hardening) and should have the highest hardness. I would suggest confirm that the set screw threads are actually cold rolled by macro section checking the grain flow and measuring microhardness at the cup point tip.
Hope the issue is resolved by now.

------------------------------
Prabir Chaudhury
President
Education and Consulting LLC
Phoenix AZ
(480) 577-0772
------------------------------

Original Message:
Sent: 12-04-2022 11:25
From: Michael Connelly
Subject: Set screw hardness standards

John,

Before retirement I was responsible for an accredited (ISO 17025) fastener testing laboratory.  While we didn't see very many austenitic stainless steel set screws we did supply quite a few Hex Head Cap Screws and we did run into problems with meeting tensile strength (110,000 psi min).  The root cause of the issue was the grip length tolerance.  In order to meet that requirement, we needed to have wire that was strain hardened before forming or we needed to supply a fully threaded length screw (zero grip length).

Moving to you issue, there appears to be an error in ASTM F880 in that it has the cold worked (rolled) threads at a lower strength that an annealed machined thread.  If the threads are rolled from pitch diameter wire there should be an increase in strength at the cup point.  Having said that I looked up ASTM F593 for proof.  Table 2 list the machined parts with a lower hardness (Designation A - 65-95 HRB, YS 20ksi, UTS 70ksi) that the cold worked (Designation CW B95-C32, YS 60ksi, UTS 95ksi) has.

I hope this information has value for you.

Sincerely,
Michael B. Connelly, FASM, CQE

------------------------------
Michael Connelly
Connelly Consulting
Chicago IL
(312) 972-8556

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

Maybe my use of the term cup point caused some confusion. I am referring not to the threads themselves but the tip of the fastener that engages another component. I am not sure how this feature is manufactured.


------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

Original Message:
Sent: 12-05-2022 09:48
From: Prabir Chaudhury
Subject: Set screw hardness standards

I had the same thoughts as Michael when I saw the post first, but did not respond as it did not make sense. The cup point of a cold rolled thread gets maximum deformation (work hardening) and should have the highest hardness. I would suggest confirm that the set screw threads are actually cold rolled by macro section checking the grain flow and measuring microhardness at the cup point tip.
Hope the issue is resolved by now.

------------------------------
Prabir Chaudhury
President
Education and Consulting LLC
Phoenix AZ
(480) 577-0772

Original Message:
Sent: 12-04-2022 11:25
From: Michael Connelly
Subject: Set screw hardness standards

John,

Before retirement I was responsible for an accredited (ISO 17025) fastener testing laboratory.  While we didn't see very many austenitic stainless steel set screws we did supply quite a few Hex Head Cap Screws and we did run into problems with meeting tensile strength (110,000 psi min).  The root cause of the issue was the grip length tolerance.  In order to meet that requirement, we needed to have wire that was strain hardened before forming or we needed to supply a fully threaded length screw (zero grip length).

Moving to you issue, there appears to be an error in ASTM F880 in that it has the cold worked (rolled) threads at a lower strength that an annealed machined thread.  If the threads are rolled from pitch diameter wire there should be an increase in strength at the cup point.  Having said that I looked up ASTM F593 for proof.  Table 2 list the machined parts with a lower hardness (Designation A - 65-95 HRB, YS 20ksi, UTS 70ksi) that the cold worked (Designation CW B95-C32, YS 60ksi, UTS 95ksi) has.

I hope this information has value for you.

Sincerely,
Michael B. Connelly, FASM, CQE

------------------------------
Michael Connelly
Connelly Consulting
Chicago IL
(312) 972-8556

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

Original Message:
Sent: 12/5/2022 10:03:00 AM
From: John Merrill
Subject: RE: Set screw hardness standards

Maybe my use of the term cup point caused some confusion. I am referring not to the threads themselves but the tip of the fastener that engages another component. I am not sure how this feature is manufactured.


------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

Original Message:
Sent: 12-05-2022 09:48
From: Prabir Chaudhury
Subject: Set screw hardness standards

I had the same thoughts as Michael when I saw the post first, but did not respond as it did not make sense. The cup point of a cold rolled thread gets maximum deformation (work hardening) and should have the highest hardness. I would suggest confirm that the set screw threads are actually cold rolled by macro section checking the grain flow and measuring microhardness at the cup point tip.
Hope the issue is resolved by now.

------------------------------
Prabir Chaudhury
President
Education and Consulting LLC
Phoenix AZ
(480) 577-0772

Original Message:
Sent: 12-04-2022 11:25
From: Michael Connelly
Subject: Set screw hardness standards

John,

Before retirement I was responsible for an accredited (ISO 17025) fastener testing laboratory.  While we didn't see very many austenitic stainless steel set screws we did supply quite a few Hex Head Cap Screws and we did run into problems with meeting tensile strength (110,000 psi min).  The root cause of the issue was the grip length tolerance.  In order to meet that requirement, we needed to have wire that was strain hardened before forming or we needed to supply a fully threaded length screw (zero grip length).

Moving to you issue, there appears to be an error in ASTM F880 in that it has the cold worked (rolled) threads at a lower strength that an annealed machined thread.  If the threads are rolled from pitch diameter wire there should be an increase in strength at the cup point.  Having said that I looked up ASTM F593 for proof.  Table 2 list the machined parts with a lower hardness (Designation A - 65-95 HRB, YS 20ksi, UTS 70ksi) that the cold worked (Designation CW B95-C32, YS 60ksi, UTS 95ksi) has.

I hope this information has value for you.

Sincerely,
Michael B. Connelly, FASM, CQE

------------------------------
Michael Connelly
Connelly Consulting
Chicago IL
(312) 972-8556

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

By sectioning the screw and mounting it in bakelite, a hardness scan of the screw threads and cup tip should reveal whether the strength called for in the ASTM standard is met.  Make sure that the A370 hardness conversion table is used for austenitic stainless steels, and not for bcc carbon steels.

------------------------------
Christopher Hahin
Engineer of Structural Materials & Bridge Investigations
Illinois Department of Transportation
Springfield IL
(217) 522-4023
------------------------------

Original Message:
Sent: 12-05-2022 09:48
From: Prabir Chaudhury
Subject: Set screw hardness standards

I had the same thoughts as Michael when I saw the post first, but did not respond as it did not make sense. The cup point of a cold rolled thread gets maximum deformation (work hardening) and should have the highest hardness. I would suggest confirm that the set screw threads are actually cold rolled by macro section checking the grain flow and measuring microhardness at the cup point tip.
Hope the issue is resolved by now.

------------------------------
Prabir Chaudhury
President
Education and Consulting LLC
Phoenix AZ
(480) 577-0772

Original Message:
Sent: 12-04-2022 11:25
From: Michael Connelly
Subject: Set screw hardness standards

John,

Before retirement I was responsible for an accredited (ISO 17025) fastener testing laboratory.  While we didn't see very many austenitic stainless steel set screws we did supply quite a few Hex Head Cap Screws and we did run into problems with meeting tensile strength (110,000 psi min).  The root cause of the issue was the grip length tolerance.  In order to meet that requirement, we needed to have wire that was strain hardened before forming or we needed to supply a fully threaded length screw (zero grip length).

Moving to you issue, there appears to be an error in ASTM F880 in that it has the cold worked (rolled) threads at a lower strength that an annealed machined thread.  If the threads are rolled from pitch diameter wire there should be an increase in strength at the cup point.  Having said that I looked up ASTM F593 for proof.  Table 2 list the machined parts with a lower hardness (Designation A - 65-95 HRB, YS 20ksi, UTS 70ksi) that the cold worked (Designation CW B95-C32, YS 60ksi, UTS 95ksi) has.

I hope this information has value for you.

Sincerely,
Michael B. Connelly, FASM, CQE

------------------------------
Michael Connelly
Connelly Consulting
Chicago IL
(312) 972-8556

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------

I did some FA  work on set screws and the client was trying to replace a domestic producer with overseas that was "not working" in application - the US producer had a specialized method of rolling the tip of a stainless steel set screw to cold work hardened -as I was able to confirm via micro indentation hardness testing.- the overseas producer had no idea and simple machined them from pre-hardened (heavily drawn) stainless steel barstock (Free machining to boot!) - that caused obvious thread rolling issues - yes thread rolling a free machining steel - story gets even deeper.

------------------------------
Edward Vojcak
Senior Metallurgical Engineer
SGS North America
Blue Island IL
(708) 595-8734
------------------------------

Original Message:
Sent: 12-02-2022 11:47
From: John Merrill
Subject: Set screw hardness standards

ASTM F880 and ISO 3506-3 both specify hardness for stainless steel cup point set screws. Both recognize this depends on whether the screw is machined or cold worked. But cold working does not occur at the cup point edges, which is where hardness is the most important. Has anyone had to research this?

------------------------------
John Merrill
Principal Engineer
EagleBurgmann
Matthews NC
7048407045
------------------------------