Quick Information About Stainless Steel, Stainless Steel Welding and It’s Defects

What is Stainless Steel?

Stainless Steel Appearance
Figure 1 Stainless Steel Appearance

Stainless steel is an improved version of steel, which is an alloy of iron and carbon. Variously stainless steel contains chromium so as to protect the steel from corrosion. When chromium is added to steel it  makes a very thin protective surface which is called chromium oxide prevents the metal from rusting. The steel should contain at least 10.5 percent chromium and maximum 1.2% carbon in order to be staniless steel. According to the usage area of steel, it may contain from 10 to 30 percent chroimum.   Also other metals which can be added to stainless steel such as nickel and molybdenum which increases corrosion resistance.

Types Of Stainless Steel

There are lots of different kinds of stainless steel but we can separate them to five main groups.

Ferritic: This type of stainless steel contain chromium between 10,5 and 27 percent and low carbon less than 0,5 percent . It can be formed in room temperature and provides medium level of corrosion resistance. Also it has magnetic feature. The area of usage is mostly in washing machines, kitchen equipments, hot water tanks, automobile frame pieces and exhausts…

Austenitic:  When the nickel added to stainless steel it becomes austenitic. This is the most commonly  used type among the others. It can be formed more easily than ferritic steels and does not have magnetic feature. But if cold forming is applied it can be a little bit magnetic. The usage is generally in industrial piping, housewares, machine and production industry, vessels and architecture.

Duplex: This kind of stainless steel has both ferritic and austenitic feature together. That’s why it is resistant, flexible and strong. They can easily be welded and formed. Genarally used in shipbuilding, petrochemical industry, paper industry and exchangers.

Martenistic: When water is given to austenitich stainless steel in high temperature it becomes martenistic.  Martenistic steel is strong and solid but fragile. The fragileness can be lessened by doing heat threatment and thus it can be more flexible. This type of stainless steel is used in knives, surgery equipments and tribune blades

Precipitation hardening:  It shows both martenistic and austenitic characteristic and made stronger with addition of other metals such as aluminum, copper, molybdenum, niobium.

What is Welding?

Steel Welder
Figure 2 Steel Welder

Welding is an operation that usually combines two or more surfaces. However it is also used in wood and thermoplastics the most common usage area is in metals. Welding operations are separated into two major groups as fusion welding and solid state welding. In fusion welding the parent metal and filler metal are both melted but in solid state welding parent metal doesn’t melt or very small part of it melts and this kind of welding is implemented at lower heat than fusion welding. Lots of methods can be used when in the process of welding such as heat, pressure, electric, friction, ultrasound or laser. It can be operated in open air and also water.  Besides all these, welding is a work that can be dangerous if the person who is operating it doesn’t obey the precautions. Many hazardous situations may occur such as electric shock, exposure of radiation and inhalation of harmful gases

How to Choose The Right Method of Welding?

The welding process that will be operated changes accoring to type of metal and the sizes of surfaces. For some of the metals fusion welding is the best and for others solid state is ideal. In small items fusion welding is common, and for big surfaces solid state is easier. Also you can visit our “6 Methods for Stainless Steel Welding” blog post.

The Welding Methods Which is Used in Steel

In steel welding generally two methods are used. One is inert gas welding which is a type of fusion welding. The necessary heat for this method is provided by burner and burnable gases which is used together. The burner gas is generally oxygen, and the burnable gas maybe hydrogen, acetylene, fuel, methane, propane or air gas. Mostly used burnable gas is acetylene because its flame temperature is higher and inflammation is faster than other gases. The resistance of the surfaces which are made with this type of welding is not very well that’s why it is generally used in repairing and filling works  

The other type of welding in steel is electric arc welding which isone type of solid state welding. The required energy is provided by welding machine. This method is mostly used one in steel constructions and have three subgroups. First type is electrode welding. The electrical current is obtained from welding machine and transmitted to pliers, electrode and workpiece. The electrode gives the welding pieces to the parent metal. This welding method is used at metals thicker than 1,2 mm and wide pieces. Second is submerged arc welding. Essentially it is also electrode welding but only difference is to pour powder while operating it. Thus, the powder protects the weldment from adverse effects of the air and decreases energy consumption. Submerged arc welding provides very strong resistance and can be applied between the thickness from 1,2 to 300 mm. The third kind is inert gas welding. It is also works in the same way with electrode welding but with a special gas which protects the workpiece and electrode. The advantage of this way of welding is to be using in every position and aspect.

WELDING DEFECTS

A person who will operate the welding should have sufficient knowledge and care about the rules. Unless there can be some defects in welding surfaces. Most common ones these:

Splashing

The weldment may have some bubbles after the operation if the surface isn’t clean enough, electric flux density is too high or the arc is taller than necessary

Porosity

Sometimes porosity may occurs because of working with humid electrodes, doing the work too fast, dirty surface, quick drying or lack of gas protection

Lack of Fusion

One of the defects of welding is lack of fusion may occur due to slag ruins, wrong welding bend selection,  fast welding, inadequate electrical flux and voltage.  In conclusion the joining of metals can’t be strong enough because of inadequate melting

Incomplete Penetration

This defect becomes as a result of not melting the metal in full thickness. This may be because of high electrical flux, fast welding, opening inappropriate welding bend, doing zigzag movement with the electrodes. Incomplete penetration reduces the permanent resistance. If force is used to weldment the it may be crashed on welding seam.

Cracks

Cracks may seem on the weldment owing to wrong filler metal selection, to contain too much phospor and sulphur in filler and parent metal , wrong opening of welding bend, quick dry, humidity of the surface

Overflow of Welding Seam

This is mistake that welding spot accumulates on the surface. There isn’t a real joining with this spots and the parent metal. This defect is resulting from wrong hand movements, keeping the electrode in wrong position and using too big electrodes

In every types of welding the quality of theoperation depens of the person who will do it. He should have enough hand skills, choose the right equipments and should do the operatio6n on time.

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