Charpy (ISO V test piece) Values of low carbon, cold rolled, bar stock

[green29]

We are working on obtaining CE marking for the Pressure Equipment Directive of a valve. One of the requirements is the bending rupture energy measured on ISO V test piece is no less than 27J at the lowest scheduled operating temperature. The standard product uses 12L14, 1215 etc. which I am pretty sure will not meet this specification. I have called several mills and they have no idea what impact values are obtainable for 1018 or any other low carbon steel. Ideally looking for a material that meets this specification at -20 Celsius and has decent screw machine machinability (1018 not really ideal). If someone knows a place where rough Charpy numbers are available this would be great also. I have seen the general carbon content vs. transition curves.

Thanks for your help.

 

[TVP]

First, you are correct that free machining grades like 12L14 and 1215 will not meet this requirement. Not even close. Standard cold drawn bar steel grades like 1018 or 1020 may be close, but as you have already learned, mills probably will not be willing to make any guarantees. Usually in order to meet this type of requirement, you either need an alloy steel (> 1%Mn, some Ni, etc.), or the steel needs to be thermomechanically rolled so that the grain size is very fine in the hot-rolled condition, or the steel must be normalized as a final heat treatment. Here is a reference that shows some general trends for various compositions, etc.:

http://collab.asminternational.org/gm/document-1.9.28286/autb2001p123.pdf

I recommend that you contact Timken regarding one of their microalloy grades like MicroTec 2W65. They can also make controlled additions of S and Ca in order to improve machinability without producing elongated sulfide stringer-type inclusions that drastically reduce fracture toughness, especially at lower temperatures. Here are some links with basic information (no Charpy data):

http://www.timken.com/en-us/Knowledge/engineers/handbook/Pages/pdm021.aspx

http://www.timken.com/en-us/products/Steel/Documents/4190.pdf

 

[metengr]

If this is for PED for a valve, why don't you consider one of the ASTM specifications for carbon steel that are endorsed for code acceptance? For example, if you look at ASME B&PV Code, Section II there are carbon steel wrought products that have been grouped for service at -20 deg C or higher?

You need to consider formability and possibly weldability issues if used in a valve.

 

[green29]

I am waiting for someone at Timken to get back to me. That might be a good idea.

I reviewed the ASME B&PV Code earlier. From what I could understand, the table that exempts impact testing was all for plate stock grades. The valves are screw-in cartridge valves without any welds, all features are turned. I also had a 4140 quoted but added to much cost to work.

 

[metengr]

I reviewed the ASME B&PV Code earlier. From what I could understand, the table that exempts impact testing was all for plate stock grades

No, this is not true. There are bar grades as well for service down to -20 deg C. Look at SA 675 bar grades.

 

[green29]

metengr

I don't have the code available in front of me (I will need to go back to the university library.)

I was looking at the impact test exemption curves and notes excerpted from UCS-66 of VIII-1. Do SA 675 bar grades fall under "Curve B applies to except for cast steels, all materials of Curve A if produced to fine grain practice and normalized which are not listed in Curves C and D below." or should I be looking somewhere else in the code? I am unfamilar with the ASTM material grade specifications and have not been able to find much on the internet so I will need to head to the library for that also.

Timken had some recommendations but did not have specific Charpy test data to know for sure.

If a heat treatment is not specified, will the impact values be all over the map from lot to lot of materials for a cold drawn or hot rolled bar stock?

 

[metengr]

green29;
Yes, the following Grades of bar for SA 675 would fall under Curve A

Grade 45,50,55,60,65,70

 

[TVP]

green29,

Yes, impact values will be all over the map from lot-to-lot if you do not specify composition limits, heat treatment parameters, grain size, etc.