Study On The Weldability Of445J2Ultra Ferritic Stainless Steel By Pulsed Current TIG Welding

Ferritic stainless steel has the advantages of resource save and highly cost-effective, because of the containing little or no Nickle. The developing of the ferritic stainless steel posses national strategy meaning, considering the situation that Nickle resource is rare in our country. With the continuously improvement of the component purification, smelting technology, the effectively control of the carbon and nitrogen content in a very low level, the "ultra pure" concept of the ferritic stainless steel has been developed quickly.445J2ultra pure ferritic stainless steel is one kind of ultra pure ferritic stainless steel developed in recent years, which is fabricated by limiting the carbon and nitrogen element content to a very low level and adding the stabilizing elements, such as Mo, Ti, Nb, V and so on.445J2ultra pure ferritic stainless steel exhibits the good machining performance and corrosion resistance performance. The material is suitable for heating equipment, floor heating, solar thermal collectors (coating), power station auxiliary condenser, heater and controlling the central air conditioning, industrial air-conditioning equipment manufacturing tube, and the city power plant for heating to heat water, urban water supply stainless steel pipe and so on.Fusion welding, due to its flexibility, lower production cost and ability to provide strong metallic joint, is widely used for the fabrication and joining of engineering applications. However,445J2ultra pure ferritic stainless steel welding has none phase transformation during the effect of the welding heat circle due to the extremely small amount of austenite forming elements. Therefore, there are two main problems of the ultra pure ferritic stainless steel welding. One is the degradation of joint mechanical performance due to the joint grain growth seriously, the other is the variation of joint corrosion performance due to the welding process. All of these problems affect the service and use of performance of ultra pure ferritic stainless steel and limit its popularization and application.This subject mainly explores the micro structure and properties, and analyzes the solidification and grain growth mechanism of the445J2ultra pure ferritic stainless steel thin plate TIG welding joints with different heat input. And it also studies the micro structure and properties of the pulsed current TIG welding joints, compared to the continuous current TIG welding joint and base metal; and analyzes the pit corrosion mechanism in chloride environment.The different heat input welding technology of TIG welded445J2ultra-pure stainless steel joints was studied. Three heat input combinations were designated as low heat input (16.65J/cm), medium heat input (17.46J/cm) and high heat input (19.50J/cm), respectively. The microstructure and mechanical properties of the joints were analyzed systematically. Tests results show that the average grain size of the joints HAZ are60μm、85μm and130μm, and grain size of joints HAZ are1.71times,2.43times and3.17times respectively as that of base metal. The aspect ratio of the columnar crystal of the joints are4:1,6.5:1and9:1. The solidification and grain growth mechanism of joints were analyzed combined with the alloy composition characteristics of445J2ultra pure ferritic stainless steel.The microstructure, mechanical properties and corrosion properties of pulsed current TIG welded of445J2ultra-pure stainless steel joints were studied. The result shows that the average grain size has been refined. It also shows that the columnar crystal of pulsed current TIG welding joint aspect ratio has decreased and the directional has abated, compared to the continuous current TIG welding joint. Besides, the tensile property, intergranular and pit corrosion resistance properties of the former joint have been improved, in which one joint tensile strength reached94.07%of the base metal and fractured in weld joints. The intergranular and pit corrosion resistance properties of pulsed current joint is better than the continuous current TIG welding joint, and at the same time slight lower than the base metal of445J2ultra ferritic stainless steel.