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 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 a maximum of 1.2% carbon in order to be stainless steel. According to the usage area of steel, it may contain from 10 to 30 percent chromium.   Also, other metals 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 into five main groups.

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

Austenitic:  When the nickel is 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 steel and does not have a 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 features together. That’s why it is resistant, flexible, and strong. They can easily be welded and formed. Generally used in shipbuilding, petrochemical industry, paper industry, and exchangers.

Martensitic: When water is given to austenitic stainless steel at high temperature it becomes martensitic.  Martensitic steel is solid but fragile. The fragileness can be lessened by doing heat treatment and thus it can be more flexible. This type of stainless steel is used in knives, surgery equipment, and tribune blades

Precipitation hardening:  It shows both martensitic and austenitic characteristics and is made stronger with the 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 a very small part of it melts and this kind of welding is implemented at a lower heat than fusion welding. Lots of methods can be used when in the process of welding such as heat, pressure, electricity, friction, ultrasound, or laser. It can be operated in the 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 to radiation, and inhalation of harmful gases

How to Choose The Right Method of Welding?

The welding process that will be operated changes according to the 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 a burner and burnable gases which are used together. The burner gas is generally oxygen, and the burnable gas may be 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 is one type of solid-state welding. The required energy is provided by the welding machine. This method is mostly used in steel constructions and has three subgroups. The first type is electrode welding. The electrical current is obtained from the welding machine and transmitted to pliers, electrodes, 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. The second is submerged arc welding. Essentially it is also electrode welding but the 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 also works in the same way with electrode welding but with a special gas that protects the workpiece and electrode. The advantage of this way of welding is to be used 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. The most common ones are these:

Splashing

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

Porosity

Sometimes porosity may occur 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 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 the zigzag movement with the electrodes. Incomplete penetration reduces the permanent resistance. If force is used to weldment it may be crashed on the welding seam.

Cracks

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

Overflow of Welding Seam

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

In every type of welding, the quality of the operation depends on the person who will do it. He should have enough hand skills, choose the right types of equipment, and should do the operation on time.

©[2019] Yena Engineering

Log in with your credentials

Forgot your details?