I've been reading some of the past posts on stainless steel. It seems that there is some lower grade stainless that is made in korea or china that we should not use on areas that need superior strength. I need to replace the bolt in the hounds for the forestay, why can't I use a grade 8 bolt? Will this bolt rust? It's for my 85 Mac. With all that stress on the forestay, I would feel safer with a stronger bolt. Thanks, Mac
Replacing bolts
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Two types..
What is "18-8" stainless steel? 300 series stainless steel has approximately (not exactly) 18% chromium and 8% nickel. The term "18-8" is used interchangeably to characterize fasteners made of types 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the "18-8" types, but slight differences in chemical composition do make certain grades more resistant than others against particular chemicals or atmospheres. You never really know what you'll get from different manufacturerers but most are similar in composition. 18-8 is roughly the strength of a grade 2 bolt & while steel bolts are graded for strength, such as Grade 2, 5, and 8 - stainless steel bolts are not. There are places on the internet that sell 18-8 and 304 bolts as meeting steel Grade 5 specification's, but they do not and you should be very wary of these claims. So what's 316 stainless steel? While 304 contains 18% chromium and 8% nickel. 316 contains 16% chromium, 10% nickel and 2% molybdenum. The "moly" is added to help resist corrosion to chlorides like sea water. Type 316 is the main stainless used in the marine environment, with the exception of fasteners and other items where strength and wear resistance are needed, then Type 304 (18-8) is typically used for this because it is stronger. I guess the question is what did the factory supply for that fastener? My 36 footer that weighs almost 18k pounds loaded uses all stainless steel fasteners including on the mast, stays etc. So I think it will be fine for your Mac and yes grade 8 bolts rust on boats.... Most all marine grade fasteners you buy at West Marine, Boat US or your local supplier will be of the 18-8 type for strength. You can find and buy 316 but you really need to specify it or you'll get 18-8..
What is "18-8" stainless steel? 300 series stainless steel has approximately (not exactly) 18% chromium and 8% nickel. The term "18-8" is used interchangeably to characterize fasteners made of types 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the "18-8" types, but slight differences in chemical composition do make certain grades more resistant than others against particular chemicals or atmospheres. You never really know what you'll get from different manufacturerers but most are similar in composition. 18-8 is roughly the strength of a grade 2 bolt & while steel bolts are graded for strength, such as Grade 2, 5, and 8 - stainless steel bolts are not. There are places on the internet that sell 18-8 and 304 bolts as meeting steel Grade 5 specification's, but they do not and you should be very wary of these claims. So what's 316 stainless steel? While 304 contains 18% chromium and 8% nickel. 316 contains 16% chromium, 10% nickel and 2% molybdenum. The "moly" is added to help resist corrosion to chlorides like sea water. Type 316 is the main stainless used in the marine environment, with the exception of fasteners and other items where strength and wear resistance are needed, then Type 304 (18-8) is typically used for this because it is stronger. I guess the question is what did the factory supply for that fastener? My 36 footer that weighs almost 18k pounds loaded uses all stainless steel fasteners including on the mast, stays etc. So I think it will be fine for your Mac and yes grade 8 bolts rust on boats.... Most all marine grade fasteners you buy at West Marine, Boat US or your local supplier will be of the 18-8 type for strength. You can find and buy 316 but you really need to specify it or you'll get 18-8..
SAE Grades
SAE Grade 5 bolts have 3 marks or lines on the head that are in the shape of a “Y”. Grade 8 bolts have 6 marks on the head. Mark’s Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8’s as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, someone can figure out how much load that fastener can carry in both tension and shear. Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum Grade 8 bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum Grade 5 bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum Grade 5 bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum More info’: http://www.americanfastener.com/technical/grade_markings_steel.asp
SAE Grade 5 bolts have 3 marks or lines on the head that are in the shape of a “Y”. Grade 8 bolts have 6 marks on the head. Mark’s Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8’s as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, someone can figure out how much load that fastener can carry in both tension and shear. Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum Grade 8 bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum Grade 5 bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum Grade 5 bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum More info’: http://www.americanfastener.com/technical/grade_markings_steel.asp
Think about what
The bolt is attatched to, fiberglass and a 1500lb test cable, the most important characteristic is corrosion resistance not strength. Do buy good quality bolts from a reputable supplier, but don't worry about the bolt breaking. Tim
The bolt is attatched to, fiberglass and a 1500lb test cable, the most important characteristic is corrosion resistance not strength. Do buy good quality bolts from a reputable supplier, but don't worry about the bolt breaking. Tim
grade 8
Have you ever looked at the bolts used on the frame of a pcikup truck? The ones that you cut/grind off because they are too rusty- those are grade 8. And a note about those strength rating for the bolts. First off, you didnt mention what size bolt your calculations are for, which would hav been nice. Second - the bolt isn't any weaker in shear versus axial strain...in fact if i put a bolt in a block of steel and gave it exessive axial strain by overgithening it (which stretches the bolt in tension) I would expect it to break at a low force level, as opposed to shear which involves ripping the entire bolt in half, not just the threads. Yield strength: this is how much stress the bolt can take with *permanently* stretching. The zone between yield strength and tensile strength, the bolt begins to deform permenently. Beyond tensile strength..stuff breaks.
Have you ever looked at the bolts used on the frame of a pcikup truck? The ones that you cut/grind off because they are too rusty- those are grade 8. And a note about those strength rating for the bolts. First off, you didnt mention what size bolt your calculations are for, which would hav been nice. Second - the bolt isn't any weaker in shear versus axial strain...in fact if i put a bolt in a block of steel and gave it exessive axial strain by overgithening it (which stretches the bolt in tension) I would expect it to break at a low force level, as opposed to shear which involves ripping the entire bolt in half, not just the threads. Yield strength: this is how much stress the bolt can take with *permanently* stretching. The zone between yield strength and tensile strength, the bolt begins to deform permenently. Beyond tensile strength..stuff breaks.
grades
Have you ever looked at the bolts used on the frame of a pcikup truck? The ones that you cut/grind off because they are too rusty- those are grade 8. And a note about those strength rating for the bolts. First off, you didnt mention what size bolt your calculations are for, which would hav been nice. Second - the bolt isn't any weaker in shear versus axial strain...in fact if i put a bolt in a block of steel and gave it exessive axial strain by overgithening it (which stretches the bolt in tension) I would expect it to break at a low force level, as opposed to shear which involves ripping the entire bolt in half, not just the threads. Yield strength: this is how much stress the bolt can take with *permanently* stretching. The zone between yield strength and tensile strength, the bolt begins to deform permenently. Beyond tensile strength..stuff breaks.
Have you ever looked at the bolts used on the frame of a pcikup truck? The ones that you cut/grind off because they are too rusty- those are grade 8. And a note about those strength rating for the bolts. First off, you didnt mention what size bolt your calculations are for, which would hav been nice. Second - the bolt isn't any weaker in shear versus axial strain...in fact if i put a bolt in a block of steel and gave it exessive axial strain by overgithening it (which stretches the bolt in tension) I would expect it to break at a low force level, as opposed to shear which involves ripping the entire bolt in half, not just the threads. Yield strength: this is how much stress the bolt can take with *permanently* stretching. The zone between yield strength and tensile strength, the bolt begins to deform permenently. Beyond tensile strength..stuff breaks.
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