Can some one explain the differances between the various types of stainless steel? I have read about 302,304, 316,18-8, 630 etc. I looked at past posts, but could not find what I was looking for. Thanks Dale
stainless steel
- Thread starter dale17781
- Start date
- Status
sandsailor - you missed 400 series s/s
That's the kind the Chinese use for all that crap they export over here. It's magnetic and will rust overnight. Put a slice of tomato on a piece of 404 stainless and watch what happens.
That's the kind the Chinese use for all that crap they export over here. It's magnetic and will rust overnight. Put a slice of tomato on a piece of 404 stainless and watch what happens.
Ross - I've been selling s/s for over 30 years.
18-8 (aka 304) s/s is what is used in quality (Oneida etc.) cutlery. 316 is what is used for surgery items. 400 series s/s would rust up in no time in a commercial application. Most surgical cutting instruments are made from high carbon steel.
18-8 (aka 304) s/s is what is used in quality (Oneida etc.) cutlery. 316 is what is used for surgery items. 400 series s/s would rust up in no time in a commercial application. Most surgical cutting instruments are made from high carbon steel.
Didn't see 404 (Chinese) grade listed.
Or did I miss it? 404 grade is the steel they use in China when manufacturing anything "stainless steel".
Or did I miss it? 404 grade is the steel they use in China when manufacturing anything "stainless steel".
So
On a trailerable boat, where the rigging is on and off all the time, and mechanical, reusable fittings, if I redo my rigging in MIL-spec 304 it's less then 1/2 the price of 316 (not counting the fittings), and stronger. If I were to replace 304 rigging once every 5 years, or the 316 once every 10, which would you consider safer?
On a trailerable boat, where the rigging is on and off all the time, and mechanical, reusable fittings, if I redo my rigging in MIL-spec 304 it's less then 1/2 the price of 316 (not counting the fittings), and stronger. If I were to replace 304 rigging once every 5 years, or the 316 once every 10, which would you consider safer?
this is from a link - should give you the answer.
The chemical and food industries alleviate these problems by adding a dash of Molybdenum (Mo). Thus 316 stainless (or A4) typically comprises 17% Cr, 11% Ni, 2 % Mo and is widely used to store and transport some very aggressive substances. So, you might think that this is the perfect stuff to use as a fastener in or through wood, and from the sole perspective of chemical attack you’d be right. But we need to reconsider the environment in which the fastener is doing its job. Imagine a bolt, nail or screw fastening a plank to a frame underwater. The head, at or near the surface, will be oxygenated enough to maintain its passive film. The shank, buried deep in the structure, is likely to be starved of oxygen but will be surrounded by various acids and chlorides. In these circumstances, the passive film may break such that the stainless becomes ‘active’. This has two effects: firstly, look back at the galvanic series and you’ll see that the difference between active and passive electropotentials in 304, and to a lesser extent in 316, is enough to cause galvanic corrosion. Like brass, stainless can form its own galvanic couple. Secondly, without the oxide layer, the stainless will corrode about as fast as steel. The upshot is that stainless fasteners below the water-line - irrespective of the grade - may be no better than mild steel. Above the water-line (more oxygen and less electrolyte) such fastenings are fine, but unless you value the extra lustre of 316, there’s little point in paying for it."
The chemical and food industries alleviate these problems by adding a dash of Molybdenum (Mo). Thus 316 stainless (or A4) typically comprises 17% Cr, 11% Ni, 2 % Mo and is widely used to store and transport some very aggressive substances. So, you might think that this is the perfect stuff to use as a fastener in or through wood, and from the sole perspective of chemical attack you’d be right. But we need to reconsider the environment in which the fastener is doing its job. Imagine a bolt, nail or screw fastening a plank to a frame underwater. The head, at or near the surface, will be oxygenated enough to maintain its passive film. The shank, buried deep in the structure, is likely to be starved of oxygen but will be surrounded by various acids and chlorides. In these circumstances, the passive film may break such that the stainless becomes ‘active’. This has two effects: firstly, look back at the galvanic series and you’ll see that the difference between active and passive electropotentials in 304, and to a lesser extent in 316, is enough to cause galvanic corrosion. Like brass, stainless can form its own galvanic couple. Secondly, without the oxide layer, the stainless will corrode about as fast as steel. The upshot is that stainless fasteners below the water-line - irrespective of the grade - may be no better than mild steel. Above the water-line (more oxygen and less electrolyte) such fastenings are fine, but unless you value the extra lustre of 316, there’s little point in paying for it."
Jimq, Good explaination!!There is another often
over looked charactaristic. That is, that often times, oxygen deprived stainless steel "looks" perfectly healthy right up to the time it fails. In some cases I prefer galvanized steel because it can look really crappy and still be strong. For below the waterline fasteners, silicon bronze is still the prefered metal.
over looked charactaristic. That is, that often times, oxygen deprived stainless steel "looks" perfectly healthy right up to the time it fails. In some cases I prefer galvanized steel because it can look really crappy and still be strong. For below the waterline fasteners, silicon bronze is still the prefered metal.
me and a buddy built a couple of plywood
dinghy's a few years back (little 6'ers) for the kids i used silicone bronze screws and he used ss screws .he noticed his screws were rusting away till the boat fell apart ,still got mine
dinghy's a few years back (little 6'ers) for the kids i used silicone bronze screws and he used ss screws .he noticed his screws were rusting away till the boat fell apart ,still got mine
grade for keel bolts ?
What would be the perfered grade of s/s for bolts on a swing keel? They say that you should change them every two years, so they will not corrode and be a problem to remove. Thanks Dale
What would be the perfered grade of s/s for bolts on a swing keel? They say that you should change them every two years, so they will not corrode and be a problem to remove. Thanks Dale
- Status