Some little things you have to know about stainless steel fasteners

First, why does Stainless Steel rust?

A: Stainless steel will rust under certain conditions. Stainless steel has the ability to resist atmospheric oxidation - that is, rust, but also has the ability to resist corrosion in the medium containing acid, alkali, salt - that is, corrosion resistance. However, the size of its corrosion resistance is changed with the chemical composition of the steel itself, the mutual state, the conditions of use and the type of environmental media. The stainless steel fastener products of Huishang technology meet the standard requirements of 304 and 316. In the laboratory brine spray test 304 material guaranteed to reach more than 48 hours, 316 material guaranteed to reach more than 72 hours. Due to the assembly with the twist caused by the surface of the Screw or due to different external conditions of use, the surface may appear red rust, but the chromium in the material and the outside air reaction to produce chromium oxide protective layer, although the surface of the rust but not like carbon steel rust rot, rust can be wiped off with cloth. Therefore, stainless steel fasteners do not guarantee rust caused by assembly.

Second, why is stainless steel magnetic? A: Stainless steel materials are non-magnetic only in the vacuum state of solid solution, after cold drawing or cold processing deformation will produce magnetism and even some magnetism is more obvious. The magnetic permeability of a material in a magnetic field is measured relative to the magnetic permeability of the material in a vacuum, and if the magnetic permeability is close to 1, the material has lower magnetic properties. For example, A2 (304) : magnetic permeability ≈1.8; A4 (316) : Magnetic permeability ≈1.015; A4 (316L) : Magnetic permeability ≈1.005; So stainless steel fasteners with magnetic is a normal phenomenon.

Third, stainless steel 304, 316 material fastener assembly why will bite to death.

A: Because stainless steel has good ductility, when stainless steel fasteners are locked, the pressure and heat generated between the teeth will destroy and erase the chromium oxide layer between them, making the metal teeth directly blocked/cut, and then the phenomenon of adhesion will make the stainless steel fasteners completely locked and can no longer be removed or locked. That is, "lock" commonly known as "bite to death".

Stainless steel bolts and nuts with thread locking cause analysis:

1. The essential reason of the material

2, the internal reasons for locking:

① The probability of thread locking will increase when bolts and nuts produced by the same furnace number material are assembled.

The influence of the accuracy of the thread, the external thread grade 6h and the internal thread 6H will increase the friction force, (excessive coordination) the external thread is 6g, (gap coordination), and the thread diameter is the lower limit within the tolerance range.

③ The higher the copper Cu content in the material composition, the higher the locking probability of the thread with the corresponding increase, but some fasteners do not use materials with higher copper content due to the cold heading deformation. The material used by our company will cause the locking probability of thread matching from large to small: 302HQ≥304HC≥304

3. External causes of locking:

If the product is not correctly selected, it should be confirmed whether the mechanical properties of the product can meet the needs of use (such as the tensile strength of the screw and the safety load of the Nut) before use. In addition, the length of the screw should be selected appropriately, with 1-3 tooth spacing of the nut exposed after tightening.

(2) The teeth are rough or have foreign bodies sticking, such as solder joints and other metal chips sandwiched between the teeth, often lead to locking.

③ Too much force or too fast locking speed as far as possible to choose a torque wrench or socket wrench, avoid using an adjustable wrench or electric wrench, because the electric wrench often leads to too fast locking speed, rapid rise in temperature and lock.

④ The direction of force Angle is not reasonable, the nut must be perpendicular to the axis of the screw for spinning, do not tilt.

⑤ No gasket is used, and the use of gasket can effectively prevent the problem of over-locking. It is recommended to use tight anti-lock nuts (waxing, boiling oil treatment).

4, locking solution

Wax anti-locking treatment and oil anti-locking treatment, and these two processes are available on our side.

What is the difference between A4-50, A4-70, A4-80 and A4L-50, A4L-70, A4L-80?

A: According to GB/T3098.6-2014 Fasteners mechanical properties of stainless steel bolts, screws and studs:

1, the group mark of steel is composed of letters and a number, the letter represents the category of steel, the number represents the

Chemical composition range of steel. Among them, A represents austenitic steel, A2 represents 304 material, A4 generation

Table 316 material, A4L represents 316L material;

2, the performance grade mark is composed of two numbers, and represents 1/10 of the tensile strength of the fastener.

5. What kind of process does A4-80 adopt?

A: Cold heading bolts require A4-80 to use 316 material, by increasing the amount of deformation in the process of material drawing to improve the tensile strength of the material to reach more than 800MPa, the conventional process of 316 material bolts, we guarantee to reach more than 700MPa tensile strength.

Nut requirements A4-80 Even using 316 raw materials or soft wire directly warm upsetting processing can ensure that the nut guaranteed load strength of 800MPa or more.

6. Is copper contained in 304 stainless steel fasteners allowed?

A: According to GB/T3098.6-2014 Fasteners mechanical properties of stainless steel bolts, screws and studs:

The Cu content of A2 material is required to be 0-4%, and the addition of copper is to increase the formability, especially the wire drawing and crack resistance, and the forming of complex shape products can be performed. Its corrosion resistance will not change with the addition of Cu content.