Stainless steel screw

1.
304 stainless steel screws
Stainless steel screws 304 is a universal anti-rust properties stronger than the 200 series stainless steel. It can be as high as 1000-1200 degrees. 304 stainless steel has excellent corrosion resistance between the can and good resistance to intergranular corrosion.

People often think stainless steel attracted by the magnet, and to verify the authenticity of their advantages and disadvantages, do not attract non-magnetic, that is good, genuine; by magnetic suction, is considered to be counterfeit fake. In fact, this is an extremely one-sided, not practical error identification method. Many types of stainless steel screws, at room temperature by organizational structure can be divided into several categories:
1. Austenitic: The 304,321,316,310; 2. martensitic or ferritic: The 430,420,410 and the like;
Austenitic is non-magnetic or weakly magnetic, martensite or ferrite is magnetic.

Stainless steel is typically used as the decorative sheet tube 304 most of austenitic material, in general, is non-magnetic or weakly magnetic, but the fluctuations caused by smelting or chemical composition different magnetic processing status may occur, but this can not be considered counterfeit or substandard, which is what causes it?
Austenite is the above-mentioned non-magnetic or weakly magnetic, and martensite or ferrite is magnetic, due to improper component segregation during smelting or heat, will cause the martensite and austenitic 304 stainless steel or ferritic body tissue. Thus, with 304 stainless steel will be slightly magnetic.

Further, 304 stainless steel after cold working, the organizational structure will be transformed to martensite, the higher the degree of cold deformation, more martensite transformation, the greater the magnetic steel. As a group number of steel production Φ76 pipe, no magnetic induction, the production Φ9.5 tube. Ling bending deformation to significantly larger number of magnetic induction, production of pipes due to large square and rectangular tube deformation ratio, especially Angular part, more intense magnetic modification more evident.

To completely eliminate the magnetic steel 304 causes, it can be opened to restore stability austenite by solution treatment temperature, whereby a magnetic erasing.
In particular to make he is that the magnetic 304 stainless steel due to the above reasons, stainless steel and other materials, such as 430, magnetic steel is not at the same level, meaning that 304 steel magnetic always shows weak magnetism.

This tells us that if stainless steel with weak magnetic or non-magnetic entirely, should be determined to be 304 or 316; and if the same magnetic steel, showing strong magnetism, because discrimination is not 304 material. Syrup using 304 stainless steel test, after a test to pass, finds all screws are made of 304 stainless steel.

2.
Stainless steel screws and use various types of performance:
302 by machining type for self-tapping screws and bolts.

Type 303 in order to improve the cutting performance, type 303 stainless steel with a small amount of sulfur is added, using a nut bar processing.

304 is suitable for processing by hot upsetting stainless steel screws, for example, specifications of a longer bolt, the bolt of large diameter, they are likely to go beyond the scope of a cold heading process.

305 is suitable for processing a cold heading process using stainless steel screws, for example, cold forming a nut, the cap screws.

Type 309 and Type 310, their high Cr content and Ni content than 18-8 stainless steel, stainless steel screws for high temperature work.
And Type 316 317, which contain the alloying elements Mo, and therefore their high temperature strength and corrosion resistance higher than 18-8 stainless steel.

Type 321 and Type 347, Type 321 alloy elements comprising stable of Ti, type 347 containing Nb, thereby improving the resistance to intergranular corrosion material. Not annealed stainless steel or standard service in the 420 ~ 1013 ℃ suitable for welding.

3.
Stainless steel screws 304 and 316 Contrast:
304 stainless steel is a versatile stainless steel material. Also relatively good high temperature, typically use temperature limit is less than 650 ℃. 304 stainless steel has excellent corrosion resistance between the can and good resistance to intergranular corrosion.
 
316 stainless steel, 18Cr-12Ni-2.5Mo by adding Mo, so the corrosion resistance, atmospheric corrosion resistance and high temperature strength in particular, can be used under severer conditions; hardening excellent (non-magnetic). Model 316 is the second 304, the second of the most widely used of steel, mainly for the food industry and surgical equipment, add molybdenum to obtain a special corrosion-resistant structure. Than the 304 because it has better resistance to chloride corrosion, and thus as "boat
Steel "to use.

4.
The reason stainless steel screws corrosion rust
Characteristics of stainless steel screws is better, there is a strong carry-corrosion, high temperature performance, also has a strong anti-rust performance. But in the harsh environment still rusty. For example, stainless steel screws in very wet conditions, every day the sun and the wind leaching, wind and rain. Over time you, how many students will certainly point rust. For example, some of the acid-base chemistry and contacting, thus producing a chemical reaction. Leading to corrosion rust. There is original is not good stainless steel screws, for example, made of stainless steel SUS201 screws used on marine products, often due soak time, had SUS201 stainless steel screws itself is not very suitable for use in salt strong above the sea. Leading to corrosion rust. In the use of the product above the sea, it is generally recommended to use stainless steel screws SUS316, as 316 stainless steel screws corrosion properties carry more than a bit better.

5.
Fracture Analysis of stainless steel screws
1. raw material quality stainless steel screws are used, good quality stainless steel screws wire. There are a lot of impurities, impurities, resulting in insufficient hardness of stainless steel screws.

2. production of stainless steel screws process issues. For example, stainless steel screws eccentric migraine, as well as production manufacturing operations nowadays overshoot Q and R values ​​of bits designed too small.

3. Customers in the use of stainless steel screws, excessive force. Generally you do the next torsion test to see how much the minimum breaking force, torque can be readjusted.