5.8 Mild Steel Grade for Screws

Jacob, You have done a pretty fair job describing your question.

500 Mpa is 72,000 psi TS; 400 Mpa is 58,000 psi Ys.

You do not say to what standard specification you are working, so I cannot say if the requirement is for proof strength, but I will assume these properties in product after heading and roll threading.

You do not say if there is a requirement for % elongation nor % reduction in area, I bet there is...

Nor do you say if the requirement is after liquid quench and temper (heat treatment).

There are a number of standard specifications for bolt requirements Check My blog here To get a head start on which may be applicable:

http://pmpaspeakingofprecision.com/2010/01/19/three-hints-to-find-info-on-bolt-grade-steels/

To try to give you a start on grade, depending on diameter, I would suggest that if you are using electric furnace steels today, grade 1022- 1030 would easily achieve these values, after cold heading and threading, or after machining from cold drawn bar stock.

If you are purchasing hot roll rods for your headers from a Basic oxygen furnace process shop, You should ask them for the mechanical properties that you will be starting from. I do not believe that the yield strength will meet the .8 ratio unless sufficiently cold worked in BOF steels.

Unless you are doing cold work of the entire piece in your header, I do not believe that you will get the properties that you need out of say 1015 or lower grades. How much "cold working strain" will your final piece have undergone in your process from raw rod to final product?

If the bolts are to be heat treated, then the wording probably said low carbon or low carbon alloy steel. Look to the table in the standard for the maximum carbon that meets "low carbon" and choose a corresponding grade to easily assure conformance. Commercial test labs can perform a tensile test on the product. should be under $200.

The cold work will increase tensile yield and hardness; it will lower % elongation in 2" and % RA.

The tensile test will report TS,YS, %El, %RA; brinell hardness test is a separate test.

milo

Hi Milo, Thanks for your reply. I read my question again and found that still something was missing. Sorry for the confusion. Coming to my original question, I would like to clarify that I am not the screw manufacturer. We manufacture brass components. We are buying these screws completely machined by our supplier. This supplier also buy raw material from his supplier. Our screw supplier have in-house machines to manufacture these screws with in-house plating. But he does not have enough equipment for testing. He said verbally that he had used SAE1015 Grade Steel of 5.20mm Diameter, to make M6 Screws of 7mm Head Diameter with 2.5mm head width, 10mm thread length, Cheese Head Combi PZ2 BZP. Now our customer's drawing ask for Grade 5.8 Mild Steel M6 Screws, Trivalent Blue Zinc Plated (RoHS). Hence I searched about this 5.8 Grade and found the details of how 5.8 is derived. Since I have got no test certificate from my supplier I am handicapped. Also he is not technically aware completely. I have to provide our customer the proof that the screws are of 5.8 Grade. So the UTS should be above 500MPa and Yield Strength should be 400MPa. But I don't know how to test this. I approached a testing lab but they denied that small M6 Screws cannot be tested for UTS and YTS. Perhaps testing the bar out of which the screws are made would be helpful. But then need to know the quantum of stresses developed while screw-heading and during roll-thread operation, which is also unknown to me. I also came to know that by testing the hardness of these screws, we can derive the grade 5.8. Perhaps the screws might be 5.8 Grade, since our supplier is manufacturing them since decades. But I cannot take it blindly without any testing proof. Also cannot supply to our customer without any testing certificates and records. I am also looking how to certify about RoHS. I heard about Salt Spray Test, but don't understand it completely. I hope that you can now help me. Thanks JACOB

Quick first answer:"I also came to know that by testing the hardness of these screws, we can derive the grade 5.8."

Not true, Hardness testing will reflect (correlate to) Tensile, does not "certify" yield strength.

Before we invest much more time on this , it will be important for us to understnad what is the standard specidfication that your customer is asking the product to conform to that calls out the 5.8.

Milo

The drawing just ask for Mild Steel Grade 5.8 It should be trivalent zinc passivated The screw also have some dimensions, which needs to be controlled within 500microns. They want all the test reports as a proof and for records and traceability That's it. It's me who want to find the UTS and YTS to derive 5.8 Grade. Since I found that UTS should be above 500MPa and YTS to be above 416MPa and also the Rockwell Hardness on B Scale to be in the range of 85 - 95. Bottom-line is that I should be able to conduct a test on the screws received from my supplier and this test report should be provided to the customer for approval along with each batches supplied. I also need to establish a testing procedure so that I can conduct a regular inspection on our supplier for his production and supply. This also includes the Trivalent Blue Zinc Passivation tests . So the customer might need the following 1) Dimensional Inspection Report of screws 2) Material Test Reports 3) 5.8 Grade Certification 4) RoHS Confirmation 5) Trivalent Blue Zinc Coating Test Reports - 42 Hours minimum salt spray test. I am confused with 4 and 5. Wait to hear from you, Regards JACOB I hope that I am not boring you

4) RoHS is European Union Directive regarding Restriction of Hazardous Substances. It would not permit use of hexavalent Chrome or cadmium, for example. See especially the annex, Which exempts certain substances from the requirements of article 4.1: http://www.rohs.eu/english/legislation/docs/launchers/launch-2002-95-EC.html

3) Is request to certify material and mechanical properties to 5.8, BUT AGAIN WITH OUT CITING A STANDARD THAT DEFINES the applicable 5.8, Can be meaningless.

Just because everybody says 5.8 doesn't mean we have agreement on or legal provenance on what 5.8 means.

We still don't know if the 5.8 means properties by cold work or by heat treat, as I mentioned in earlier post.

We can't certify to 5.8 until we know the standard which is being cited.

We can't arrest people for speeding until we know the law.is 70 mph speeding? its fast, but legal on the autobahn... not legal in a school zone. milo

Hi Milo I understand. The customer is from Germany. Do you suggest me to ask the customer, which standard they follow for 5.8 Grade? I think its ISO 898 Part 1 How many standards specify this 5.8 Grade? Please note that this is M6 so metric series. Regards JACOB

Hi Milo, I checked your blog. The print calls this way SCREW M6 X 100LG CHEESE HEAD COMBI PZ2 BZP MATERIAL = MILD STEEL GRADE 5.8 FINISH = TRIVALENT ZINC PASSIVATION HEAD = CHEESE HEAD COMBINATION PZ2 I checked the standards and this is what it says. "Products not covered are tapping screws, thread-rolling screws, and self-drilling screws. Mechanical and material requirements for these products are covered in other SAE documents. " These screws are roll-threaded screws after the heads cold formed in headers. So it should be some other SAE Standards. Regards JACOB

OK here is what I can tell you based on M6 , 5.8 and length of 10 mm; since screw diameter is 6 mm, and length is 10mm, the screw counts as a short screw (Length of product is less than 2-1/4D).

Per sae j1199, the only mandatory tests required for short screws of all property classes are Product hardness Max; product hardness min and surface hardness;

Same if your 'cheesehead' is a special head screw; I don't know what a 'cheesehead' is in regard to the spec.

So you only need hardness compliance per SAE J199.

HOWEVER

SAE J1199 also says regarding property class 5.8:

para graph 4.2.3 " cold head unless special agreement exists to hot head;" 4.3 says "5.8 shall be roill threaded"; and 4.4.1 says "class 5.8 screws 'shall be stress relieved if necessary to assure the soundness of the head to shank junction.' When specified by purchaser, class 5.8 bolts and screws shall be stress relieved at a minimum stress relief temperature of 470 Degrees C. Where higher temperatures are necessary to relieve stresse in severely upset heads, mechanical requirements shall be agreed upon by manufacturer and purchaser."

Longer lengths can get into full size products for wedge or axial tensile testing.

Get that ISO spec.

milo

this is a catalouge for fator products

http://www.4shared.com/document/syb0t98q/fator.html
review properties of screws and bolts pg 200and studs