Development of technology of welding of steel 08X22H6T

Introduction

The main goal of the course work is to acquire students skills in the practical application of theoretical knowledge obtained during the study of the course "Welding Technology by Melting." During the course work, students must make a choice of economically feasible welding method, type of connection, welding materials, calculate technological parameters of the mode and time standards, select welding equipment and equipment, if necessary, give recommendations on thermal treatment of products, and develop an operating map.

Process features of steel welding of given structural class

Austenitic ferrite steels contain less nickel than austenitic steels, so they are cheaper. They have a fairly high corrosion resistance. Due to the fact that the heat resistance A + F of steels is lower than A, they are used for structures operating at temperatures not higher than 300 C. The strength of steels is at the level of 600700MPa.

Steel 08X22H6T resistant in nitric acid: at 65% of concentration - up to the temperature of 50 With, at 56% to 70 C, at 30% up to the boiling temperature

The main difficulty in welding is the tendency to embrittlement at elevated temperatures. The embrittlement mechanism is slightly different than for ferrite steels, since the two-phase A + F structure is less prone to grain growth.

In A + F steels, embrittlement can be caused by several reasons.

1. Formation of the so-called αphase, which occurs at prolonged holding at elevated temperatures. Phase a is the intermediate structure of the component in the transformation of αα, so it is most characteristic of two-phase A + F structures. It has reduced toughness, which reduces the performance of the weld joint.

Alloying elements have different effects on the intensity of the formation of αphase, shifting the area of ​ ​ its formation towards a lower chromium content. Chromium, nickel and manganese affect similarly. Carbon slows the formation of αphase, shifting the boundary of its region towards a higher Cr content. The occurrence of the β-phase is not associated with the presence of carbides, since it is formed in very pure carbonaceous ferrochromonikel alloys.

In welds, the a-phase falls mainly along the boundaries of columnar crystals or along deformation planes. As a rule, there is no phase around the a-phase, since chromium is involved in its formation, and it dissolves carbon well.

The formation of the a-phase occurs in the temperature range of 650850 C, therefore, when cooling the weld, it is necessary to pass this interval with a maximum speed, reducing the time during which sigmatization occurs. If the structure is used for a long time at high temperatures, it is very difficult to avoid the formation of the [beta] - phase.

It is possible to eliminate the a-phase by short-term periodic heating up to 1000 C. Quenching from temperatures of 10501100 C is also possible, at which complete austenization of the joints is achieved.

It is possible to prevent sigmatization to a certain extent by limiting the content of molybdenum, vanadium, chromium and silicon in the seams.

2. The second reason for the reduction of toughness in the near-joint zone during welding of A + F steels is 475 degree brittleness.

It is caused by chromium α-gland processes without excretion of excess phases. The kinetics of the processes lies in the concentration of chromium atoms at certain nodes of the crystal lattice. As a result of redistribution, micro-volumes are formed, enriched and depleted by chromium. The redistribution of chromium causes distortion of the crystal lattice, an increase in ferrite hardness and a sharp drop in toughness. The most likely manifestation of 475 degree brittleness in steels containing more than 20% ferrite.

The 475 degree brittleness can be eliminated by reheating to several high temperatures (T = 500550 s) followed by rapid cooling.

When welding A + F steels, it is advisable to use welding methods with low linear energies. Welding techniques and modes do not differ from those generally accepted for the entire stainless steel class. Preparation of edges for all welding methods is performed mechanically without thermal heating.

Selecting Welding Materials

For welding of a product we choose the wire of Sv08H19N10 of FBS GOST 224670 having austenitic structure. The use of this wire makes it possible to obtain a seam with an austenite-ferrite structure having high ductility and toughness.

Before welding it is necessary to carefully prepare the welded surfaces (degrease). Welding shall be carried out in a CO2 environment.

Conclusion

As a result of implementation of the term paper the technology of welding of a product from steel 08X22H6T was developed, welding mode parameters are determined, the welding equipment, namely a welding wire of Sv08H19N10FBS are picked up, the automatic welding semiautomatic device of Origo Mig 4004i of Esab is chosen.

Heat treatment is not required for this case.