What are the materials with good welding performance? Welding characteristics of common metal materials

Date：2021-12-30 14:08:53 Views：4147

Generally, the weldability of low carbon steel is better than that of other steels. And the lower the carbon content, the better. The higher the carbon content, the worse the weldability. The weldability of alloy steel depends on the different alloy elements added. Generally, the weldability of chromium containing steel is better than that of vanadium containing steel. It is of great help to the level 1 (IC packaging) and level 2 (electronic components assembled to printed circuit board) processes of modern electronic industry, which need high-quality interconnection technology and high-quality and zero defect welding process.

The material with good welding performance also depends on the parent material. Considering that the welding material has excellent performance and wide universality.

1. If the matrix is cast iron, the welding777 cast iron electrode with wide universality and good crack resistance is different from 308 conventional welding gray cast iron and 408 welding ball milled cast iron. This welding777 is suitable for almost all iron castings, including common gray cast iron, ball milled cast iron, cold cast iron, etc.

2. If the parent is carbon steel or alloy steel, whether it is high carbon steel or high alloy steel, it can be welded with a wide range of universal welding rod welding600 welding rod welding material.

3. If the parent is aluminum alloy, no matter what brand it is, such as pure aluminum and 60615052 aluminum alloy, it can be welded with this welding555 aluminum electrode, which has wide universality.

Welding characteristics of common metal materials

1. Welding of carbon steel

(1) Welding of low carbon steel

Low carbon steel has low carbon content and low manganese and silicon content. Under normal circumstances, it will not cause serious structure hardening or quenching structure due to welding. This steel has excellent plasticity and impact toughness, and the plasticity and toughness of its welded joints are also very good. Generally, the welding joint with satisfactory quality can be obtained without preheating and post heating and special process measures. Therefore, low carbon steel has excellent welding performance and is the steel with the best welding performance among all steels.

(2) Welding of medium carbon steel

Medium carbon steel has higher carbon content and its weldability is worse than low carbon steel. When CE is close to the lower limit (0.25%), the weldability is good. With the increase of carbon content, its hardening tendency increases, and it is easy to produce low plastic martensite in the heat affected zone. Cold cracks are easy to occur when the weldment is rigid or the welding materials and process parameters are not selected properly. When the first layer of weld is welded by multi-layer welding, due to the large proportion of base metal fused into the weld, the carbon content, sulfur and phosphorus content are increased, and it is easy to produce hot cracks. In addition, when the carbon content is high, the stomatal sensitivity also increases.

(3) Welding of high carbon steel

High carbon steel with CE greater than 0.6% has high hardenability and is easy to produce hard and brittle high carbon martensite. Cracks are easy to occur in the weld and heat affected zone, which is difficult to weld. Therefore, this kind of steel is generally not used to manufacture welded structures, but used to manufacture high hardness or wear-resistant parts or parts. Most of their welding is the repair of damaged parts. These parts and components shall be annealed before welding to reduce welding cracks, and heat treatment shall be carried out again after welding.

2. Welding of low alloy high strength steel

The carbon content of low alloy high strength steel is generally not more than 0.20%, and the total amount of alloy elements is generally not more than 5%. It is precisely because low-alloy high-strength steel contains a certain amount of alloy elements that its welding performance is different from that of carbon steel. Its welding characteristics are as follows:

(1) Welding crack of welded joint

Cold crack low alloy high strength steel is easy to harden during welding because it contains elements such as C, Mn, V and Nb that strengthen the steel. These hardened structures are very sensitive. Therefore, in the case of high rigidity or high restraint stress, if the welding process is improper, it is easy to produce cold cracks. Moreover, this kind of crack has a certain delay, which is very harmful.

Reheat (SR) crack reheat crack is an intergranular crack in the coarse-grained region near the fusion line of the welded joint during post weld stress relief heat treatment or long-term high-temperature operation. It is generally believed that the formation is due to the solid solution of carbides such as V, Nb, Cr and Mo near HAZ in austenite due to high welding temperature. It is too late to precipitate during post welding cooling, but it is dispersed during PWHT, which strengthens the intracrystal and makes the creep deformation during stress relaxation concentrate on the grain boundary.

Generally, the welded joints of low-alloy high-strength steel are not easy to produce reheat cracks, such as 16MnR, 15MnVR, etc. However, for mn-mo-nb and mn-mo-v low alloy high strength steels, such as 07MnCrMoVR, Nb, V and Mo are the elements that promote the strong sensitivity of reheat cracks. Therefore, during post weld heat treatment, attention should be paid to avoid the sensitive temperature zone of reheat cracks to prevent the occurrence of reheat cracks.

(2) Embrittlement and softening of welded joints

Strain aging embrittlement welded joints need to undergo various cold working (blanking shear, barrel rolling, etc.) before welding, and the steel will produce plastic deformation. If the area is subjected to the thermal action of 200 ~ 450 ℃, strain aging will be caused. Strain aging embrittlement will reduce the plasticity of steel and increase the brittle transition temperature, resulting in brittle fracture of equipment. Post weld heat treatment can eliminate such strain aging of welded structure and restore toughness.

Embrittlement welding of weld and heat affected zone is an uneven heating and cooling process, resulting in the formation of uneven structure. The brittle transition temperature of weld (WM) and heat affected zone (HAZ) is higher than that of base metal, which is the weak link in the joint. Welding linear energy has an important influence on the properties of WM and HAZ of low alloy high strength steel. Low alloy high strength steel is easy to harden, and if the linear energy is too small, HAZ will have martensite induced cracks; If the line energy is too large, the coarse grains of WM and HAZ will cause joint embrittlement. The HAZ embrittlement tendency of low carbon quenched and tempered steel is more serious than that of hot rolled and normalized steel. Therefore, when welding, the linear energy should be limited to a certain range.

Softening of heat affected zone of welded joint due to welding heat, the outside of heat affected zone (HAZ) of low carbon quenched and tempered steel will be heated above tempering temperature, especially in the area near AC1, which will produce softening zone with reduced strength. The microstructure softening of HAZ zone increases with the increase of welding line energy and preheating temperature, but generally, the tensile strength of the softening zone is still higher than the lower limit of the standard value of base metal. Therefore, the softening problem of heat affected zone of this kind of steel will not affect the performance of its joint as long as the process is appropriate.

3. Welding of stainless steel

Stainless steel can be divided into four categories according to its different structure, namely austenitic stainless steel, ferritic stainless steel, martensitic stainless steel and AUSTENITIC FERRITIC duplex stainless steel. The following mainly analyzes the welding characteristics of austenitic stainless steel and bidirectional stainless steel.

(1) Welding of austenitic stainless steel

Austenitic stainless steel is easier to weld than other stainless steels. Phase transformation will not occur at any temperature and is not sensitive to hydrogen embrittlement. Austenitic stainless steel joints also have good plasticity and toughness in the as welded state. The main problems of welding are: welding hot crack, embrittlement, intergranular corrosion and stress corrosion. In addition, due to poor thermal conductivity, large linear expansion coefficient and large welding stress and deformation. During welding, small welding heat input shall be adopted as far as possible, preheating shall not be allowed, and the interlayer temperature shall be reduced. The interlayer temperature shall be controlled below 60 ℃, and the weld joints shall be staggered. Reduce the heat input, do not excessively increase the welding speed, but adapt to reduce the welding current.

(2) Welding of AUSTENITIC FERRITIC duplex stainless steel

AUSTENITIC FERRITIC duplex stainless steel is a duplex stainless steel composed of austenite and ferrite. It combines the advantages of austenitic steel and ferritic steel, so it has the characteristics of high strength, good corrosion resistance and easy welding. At present, there are three types of duplex stainless steel: Cr18, Cr21 and Cr25. The main characteristics of this kind of steel welding are: compared with austenitic stainless steel, it has lower thermal tendency; Compared with pure ferritic stainless steel, it has lower embrittlement tendency after welding, and the ferrite coarsening degree in the welding heat affected zone is also lower, so the weldability is better.

Because this kind of steel has good welding performance, preheating and post heating can not be used during welding. TIG welding should be used for thin plates, and electrode arc welding can be used for medium and heavy plates. During electrode arc welding, special electrodes with similar composition to the base metal or austenitic electrodes with low carbon content should be selected. Nickel base alloy electrode can also be used for Cr25 dual phase steel.

Due to the existence of a large proportion of ferrite in dual phase steel, the inherent embrittlement tendency of ferrite steel, such as brittleness at 475 ℃ σ Phase precipitation embrittlement and coarse grain still exist, which can be alleviated only due to the equilibrium effect of austenite. Attention should still be paid to during welding. When welding dual phase stainless steel without Ni or low Ni, there is a tendency of single-phase ferrite and grain coarsening in the heat affected zone. At this time, pay attention to controlling the welding heat input, and try to use low current, high welding speed, narrow pass welding and multi pass welding to prevent grain coarsening and single-phase ferrite in the heat affected zone. The interlayer temperature should not be too high. It is best to weld the next pass after cooling.

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