So, what is wanted is the relationship between temperature and yield stress for these two different materials.

Try Kempe's Engineers' Year Book, any edition, looking for the chapters on properties of engineering materials.

_{(Dunno why this is in Instrumentation. It would get a better response in Mechanical Engineering)}

Both materials have the same chemical composition except the addition of Mo in 316. Due to the addition of 2-3% Mo in SS316 it has better corrosion resistance and less chances of weld decay (welding defect due to chromium carbide precipitates). Mechanical Properties are almost similar. For allowable stresses and other physical/mechanical properties check allowable stress table at various temperatures. At room temperature both materials have the value of 137.9 MPa for allowable stress. Allowable stress value decreases with the increase in temperature.

Tehseen

From experience - Temperature and pressure about the same. 306 will show corrosion, main use of 316 is food/pharmaceuticals or ourdoor in salt spray atmosphere

Main difference as already posted is the Mo content.

According to ASME Code, for unfired vessels (pipes) the maximum design temperature is 1500ºF (815ºC) for both types of SS. Maximum allowable stresses are similar:

For 304SS: 18.9 ksi @ 200ºF and 1.4 ksi @ 1500ºF

For 316SS: 20 ksi @ 200ºF and 1.3 ksi @ 1500 ºF

Regarding maximum pressure, there are no requirements: You just have to calculate the stresses due to internal/external pressure as well as any other design load and keep it below the allowable values.

Kind regards

In general I agree with your (Kwetz) information except that ASME requires that when the operating temperature is over 1000°F the user must use 304H or 316H or as a minimum 304 or 316 with a .04% minimum carbon content. That requirement precludes the use of 304 or 316 dual certified materials i.e. 304/304L or 316/316L as designated on the material marking and certifications.

Other contributers stated (not Kwetz) that 304 & 316 were the same except for addition of Mo. That is not the only difference 304 sst is an 18Cr-8Ni Austinetic Stainless steel while 316 is a 16Cr-12Ni-Mo Austinetic material, the 316 being more corrosion resistant and less "magnetic" and less suceptable to carbide precipitation in the weld & heat affected zone. As a result there is less less chance of the slight "rusting" seen near welds on the 304 materials than on 316 material. Passivation can eliminate that rusting but it does not make 304 as corrosion resistant as 316.

well pointed out!

I also agree with your other post relating to that strange matter of low temperature toughness of SS.

Cheers

304ssl was made to be, a wet instrument steel.

316ssl was made to be a protected constructiion instrument steel, that is put in a case after each use and not allowed to rust, because,316ssl does allow fine pockets of rust 2um large to form.

Neither are allowed to be used for roofing sheet metals, or as containers for halogens & acids,as in rail & truck tank cars, because they fracture from blows,torque or side stress.

I don't know the history but I can tell you that eiher 304 or 316 stainless steel are quite resistant to impact even at very low temperatures.

In the field of cryogenics resistance to impact is an issue because we build vessels that operate to temperstures down to 4.2 Kelivns, near absolute zero, and the material still has excellent impact properties so I am puzzled by the comment regarding " they fracture from blows, torque or side stress". Many Liquid Oxygen, liquid Hydrogen and Liquid Helium trailers and dewars ( inner vessels) are manufactured using 304 stainless steel although the trend is to aluminum due to weight.

Further, in th process and sanitary industries, 304 & 316 ( 316 more so in sanitary applications) stainless steel is used for vessels containng lethal substances including Ozone. I have done that recently and one of my customers use it for wet petrochemical applications from room temperature up to 1000°F.

Your statement may be true in the construction industry, however, I believe that 300 series Stainless steel was used for the skin of Gateway Arch in St Louis Missouri, clearly a construction application as are many buildings and monuments.

I don't know if your query was fully answered, although the demand and supply of 304H is quite specific. I know that with greater lab-testing the high temperature requirements 4 some batches of the 316 and 316L grade can satisfy from an engineering perspective all temperature boundary characteristics, of the non-mass produced 304H.

Did you get all the information you required? we seek forgings supplied to/from the UK for a particular application.....? Any favourites...?