深圳市中科五金制品有限公司

Control on the hydrogen embrittlement

Joe Greenslade is president of Greenslade & Co, the company is located in the USA Illinois, gauge instrument sales Greenslade brand. Greenslade, inventor, writer and lecturer one. He has 11 USA patent, professional writing more than 80 articles above, and in the past 10 years often in trade and Technology Conference speech. Greenslade is a member of the 101-592 Executive Committee American public law.

On the hydrogen embrittlement, there are a few points we generally agree:

1 the hardness of the material increases, the risk of hydrogen embrittlement can increase.

2 hydrogen embrittlement electroplating, hot dip galvanizing general and relevant, but not coated or covered itself causes hydrogen embrittlement, people generally think that, causes the hydrogen embrittlement hydrogen source is from electroplating before cleaning or removal using the electroplating acid to the.

3 is generally after plating fastener after baking, obviously, can prevent to hydrogenation, but unfortunately after plating the long time to do baking, baking, roasting temperature and how long for what no consistent view? The most common is that, within an hour after plating baking 375 degrees F to 425 degrees F for 4 hours.

I'm on the hydrogenation of observations in the past thirty years have seen many suspected hydrogen embrittlement screw self tapping screws (class=a1> Tapping Screws) case, include all kinds of galvanized products, from the solution found in these cases, I learned some saving products and reduce the hydrogen embrittlement of things.

In this paper, I only want to share my observations with you, I'm not going to put forward in this paper as has been scientifically verified facts. There is a 70 year olds are very experienced metallurgist told me, his experience is the core hardness if the product does not exceed HRC36, the hydrogen embrittlement possibilities than above HRC36 products is much lower, I write down these words in order to verify his. We can use this information to hydrogen embrittlement occurs to prevent the production of screws class=a1> self tapping screws when problems, can also be used to save the suspected hydrogen embrittlement of class=a1> products, screw self tapping screws standard specification is the core hardness of HRC28 to HRC38, ISO file or even intentional hardness up to HRC40. In recent years, if someone asked me to call the hydrogen embrittlement test failed, I first asked his question is the core hardness? In all cases the answer is HRC37 to HRC40, many years ago I thought these substandard products bake for 8 to 24 hours should be eliminated hydrogen, but unfortunately there are many times this method is not effective measures. You can use this method to save the embrittlement of class=a1> screw self tapping screw when I heard the product is less than HRC36 the core hardness, resistance to hydrogen embrittlement has very strong ability, this statement, I do recommend following methods, there have been 3 cases of success.

The steps are as follows:

1 first get rid of electroplating;

2 tempering to product core hardness from HRC28 to HRC35;

3 heavy plating;

4 electroplating within an hour, the product will be baked for 8 hours, temperature 375 degrees F to 400 degrees F;

5 from the above random sampling 100Pcs the product group to do the hydrogen embrittlement test. As I mentioned, I do not know whether there can be any consumption testing methods to prove the method, but this method has successfully solved the three batch of class=a1> screw self tapping screw not qualified to remove the hydrogen embrittlement effect.

Use the following method to test the hydrogen embrittlement, I suggest the following method:

1 the gasket is sleeved on hardened product;

2 products in the test plate lock to lock the fracture, written under the maximum torque of each product value;

The 3 original 5Pcs products with a mean value of 80% of the torque, to lock the above 100Pcs products;

After 4.48 hours, and then in a clockwise direction applied the original torque value in all the tested products. If there is any product failure in applying the test torque, the batch is discarded.

My final advice to put forward the following several suggestions to the screw self tapping screw manufacturer class=a1>:

1 production to control the heat treatment process, in order to get the heart of hardness in HRC28 to HRC35, the possibility to reduce the hydrogen embrittlement from electroplating process to.

2 if you found that a batch of finished product is hydrogen embrittlement phenomenon, please according to the procedures for handling: electroplating, lowering the core hardness to between HRC28 to HRC35, baking, from electroplating, the test for at least 100Pcs, if there is any one in the final test fails, then the whole batch is destroyed. Hydrogen embrittlement is very terrible problem, I hope these suggestions can help manufacturers if you encounter this problem, can solve the problem effectively.

In order to effectively improve the elastic fasteners (spring washers, conical washer, saddle shaped washer, wave washer etc.) corrosion protective performance and decorative, mostly to the surface treatment, such as black, phosphating, electroplating processing. The electrolytic zinc plating and passivation treatment is applied more widely.

Coupled with the elastic fastener hardness between 42-50HRc in general, because of the material and the reasons of surface treatment, it is sensitive to hydrogen, in electroplating, hydrogen removal treatment did not reach the flooding of hydrogen, the residual hydrogen can cause the elastic fasteners of delayed fracture. At present, the elastic fastener fracture caused by the delayed fracture of hydrogen embrittlement in nature is a serious quality problem, people can take various techniques to reduce and prevent the hydrogen embrittlement problems of elastic fastener.

1 Effect of material defects

The harmful effect of elastic fastener material surface defects on the electro galvanized can not be ignored, such as the steel surface crack, scarring pit slightly folded inclusions and decarburized layer exceeds the allowable depth, will have a very harmful influence on the elastic fasteners galvanized, bending and forming of improper surface inserted scratch, local stress concentration will have a bad effect.

2 Effect of heat treatment process

Heat treatment process is found to have a greater impact on hydrogen embrittlement of galvanized elastic fastener after, if the hardness up to 45HRc (Tan Gang type), can induce or cause fracture elastic fastener.

In the premise of ensuring the technical parameters of heat treatment, choosing proper heating temperature, heating time reasonable, sufficient to tempering. To maximize the elimination of structure stress and thermal stress, avoid its harmful effects. Quenching heating should prevent oxidation and decarburization, mesh belt furnace carbon potential control in 0.60%-0.70%, salt bath furnace must be carefully deoxidizing slag, of the hardness testing, strict attention to the surface layer hardness causing false phenomena, so that the value of distortion of hardness test. General should be controlled at 42-44HRc is better, not more than 45HRc.

Effects of 3 electroplating process

Elastic fastener invasion often occurs due to the hydrogen hydrogen embrittlement fracture, caused heavy losses. Hydrogen hydrogen permeation is unavoidable in the whole electrolytic galvanized the hydrogen can penetrate the galvanized layer of precipitation, and even into the matrix metal. Hydrogen absorption of zinc in about 0.001%-0.100%, while the iron carbon alloy hydrogen absorption at about 0.1%. The hydrogen in the metal makes the crystal lattice distortion, have great stress, resulting in its mechanical properties reduced hydrogen evolution not only have an adverse effect on the properties of coatings, such as produce pinholes, pitting, bubbles and other defects, and can penetrate to the base metal, the metal toughness greatly reduced, causing parts of brittle fracture. The reason of hydrogen evolution except in heat treatment, higher heating temperature, hydrogen can easily penetrate into the stress concentration region, pickling and plating will occur for hydrogen evolution. Prevention of 4 hydrogen embrittlement

Electro galvanized before must strictly control the cathode electrolytic degreasing. On the elastic fasteners (especially the thickness? 1mm), not by cathodic electrolysis degreasing, instead of using the anode electrolytic degreasing, chemical degreasing or ultrasonic degreasing, also can choose metal cleaning agent degreasing (better).

Using strong acid corrosion on the elastic fasteners not, instead of using sand or shot peening treatment method to purify, surface activation of purpose. Must carry on the acid activation process, sulfuric acid is hydrochloric acid is selected. Pay attention to grasp the pickling time should not be too long (each 30-60s control), with many short time than long pickling effect is good.

Should choose galvanized electrolyte, hydrogen brittleness smaller in general, Paul compound type galvanized electrolyte hydrogen produced relatively less, the possibility of hydrogen embrittlement is small; while the cyanide zinc plating electrolyte hydrogen, hydrogen permeation hydrogen embrittlement more, the machine rate is larger.

The use of effective drive hydrogen process disperse hydrogenation, reducing hydrogen embrittlement stress. Drive hydrogen temperature of 190-230 DEG C, drive hydrogen time 6-8h. In the electro galvanized after passivation before 2h, stay more time as short as possible.