Комаров Артём о сварке нержавеющей стали (eng) - Артём Комаров
Комаров Артём о сварке нержавеющей стали (eng)

Комаров Артём о сварке нержавеющей стали (eng)

Artem Komarov noted that due to the different properties of stainless steel compared to carbon steel, welding parameters must be different. The solution may be a different filler metal diameter, a change in joint design, or both.

300 series stainless steels are alloyed with chromium and nickel, giving them a predominantly austenitic microstructure. The amount of these alloys gives characteristics different from those of carbon steel.

Austenitic stainless steels have approximately 50% greater thermal expansion and approximately one-third greater thermal conductivity than carbon steel. The combination of higher thermal expansion and lower thermal conductivity makes stainless steels very prone to warping when welded.

Нержавеющая сталь, сварка, Комаров Артем Андреевич

Stainless steel also has approximately four to seven times greater electrical resistivity than carbon steel. This is why the welding parameters of carbon steel do not match well with stainless steel.

A general rule of thumb when welding stainless steel is to use a voltage about one to two volts higher and an amperage about 20% lower than for a comparable carbon steel joint.

Alloying stainless steel also changes the behavior of the molten weld metal compared to carbon steel. The flow of the stainless steel weld pool is slower, which can lead to defects such as lack of fusion or lack of fusion. Typically, when welding stainless steel, the weld joint design requires large bevel angles and an internal hole to accommodate the sluggish weld pool, whereas carbon steel can be welded with a tight fit and smaller bevel angles. These changes in joints allow the weld metal to flow with less restriction and help ensure sufficient penetration.

Another option is to use a smaller diameter filler metal, which will have a higher current density, which will promote deeper penetration at the same welding current. In addition, this will increase the deposition rate of the SAW process in constant current mode.

So why not just increase the amperage when using stainless steel to improve penetration? This is a fair question and usually not a problem. However, with SAW, the heat input is much greater than with manual welding, and there is a highly recommended upper heat input limit. The generally accepted maximum heat input for stainless steels is 50 to 55 kJ/in. Higher heat inputs can degrade the corrosion resistance of the welded product. This should not completely preclude the use of higher heat input procedures, but the use of higher heat inputs requires you to carefully consider the type and grade of stainless steel being welded, as well as the operating conditions required for the finished product.

To solve penetration problems, you can consider changing the connection design, reducing the diameter of the filler metal, or both, summarized Artem Komarov.