How to cope with poor welding performance of high carbon steel

High-carbon steel refers to w (C) higher than 0.6% of carbon steel, which has a greater tendency to harden than medium-carbon steel, and the formation of high-carbon martensite, more sensitive to the formation of cold cracks.

At the same time, the formation of martensitic organisation in the weld heat affected zone, hard and brittle properties, resulting in a significant reduction in the plasticity and toughness of the joints, so the weldability of high-carbon steel is quite poor, must take special welding process to ensure that the performance of the joints.

Therefore, in the welded structure, generally rarely used. High-carbon steel is mainly used for the requirements of high hardness and wear-resistant machine parts, such as shafts, large gears and couplings.

In order to save steel, simplify the processing technology, these machine parts are also often used in welded structures combined.

In the heavy machinery manufacturing, will also encounter high carbon steel parts of the welding problem. In the development of high-carbon steel weldments welding process, should be comprehensively analysed may produce a variety of welding defects, and take corresponding welding process measures.

1 high carbon steel weldability

1.1 Welding method of high-carbon steel is mainly used for high hardness and high wear-resistant structure, so the main welding method is electrode arc welding, brazing and submerged arc welding.

1.2 Welding material high carbon steel welding generally do not require joints and base material strength. Welding electrode arc welding generally choose to go to the sulfur ability, low diffusion hydrogen content of the molten metal, good toughness of low hydrogen type electrode. In the requirements of the weld metal and base metal strength, should be selected with the corresponding level of low-hydrogen electrodes; in the weld metal is not required with the base metal strength, should be selected with a strength level lower than the base material of low-hydrogen electrodes, remember that you can not choose the strength level than the base material of the electrode is high. If the base metal does not allow preheating when welding, in order to prevent cold cracking in the heat-affected zone, austenitic stainless steel electrodes can be used in order to obtain good plasticity, crack-resistant austenitic organisation.

1.3 Bevel preparation in order to limit the mass fraction of carbon in the weld metal, should reduce the fusion ratio, so the weld is generally used U-type or V-type bevel, and pay attention to the bevel and bevel on both sides of the 20mm range of oil, rust and other treatment.

1.4 Preheating using structural steel electrode welding, welding must be preheated, preheating temperature control in 250 ~ 350.

1.5 Interlayer processing multi-layer multi-channel welding, the first weld with a small diameter electrode, small current welding. The workpiece is generally placed in a half-stand welding or the use of welding rod lateral swing, so that the entire heat-affected zone of the base material are heated within a short period of time, in order to obtain the effect of preheating and heat preservation.

1.6 post-welding heat treatment immediately after welding the workpiece into the heating furnace, insulation in 650 for stress relief annealing.

2 high carbon steel welding defects and preventive measures due to high carbon steel hardening tendency is very large, in the welding is prone to hot cracks and cold cracks.

2.1 preventive measures against thermal cracking
1) control the chemical composition of the weld, strict control of sulfur, phosphorus content, and appropriately increase the amount of manganese, in order to improve the weld organization, reduce segregation.
2) control the shape of the weld cross-section, the width and depth ratio should be slightly larger to avoid segregation of the centre of the weld.
3) on the rigidity of large weldments, you should choose the appropriate welding parameters, the appropriate welding sequence and direction.
4) if necessary, take the preheat and slow cold Measures to prevent thermal cracking.
5) Improve the alkalinity of the welding rod or flux to reduce the impurity content in the weld and improve the degree of segregation.

2.2 Cold crack prevention measures
1) preheating before welding and post-welding cooling, not only can reduce the hardness and brittleness of the heat-affected zone, but also accelerate the diffusion of hydrogen in the weld to the outside.
2) Select the appropriate welding measures.
3) The use of appropriate assembly and welding sequence, reduce the constraint stress of the welded joint, improve the stress state of the weldment.
4) Select the appropriate welding materials, welding rod, flux drying, and to do with the use.
5) The use of welding rod, flux, and to do with the use of the weldment.
6) The use of welding rod, flux, and the use of the welding material.
7) The use of welding rod and flux, and to do with the use of the welding material, and to do with the use of the welding material. And do take with the use.

3 high-carbon steel due to higher carbon content, hardenability and poor weldability, welding is prone to produce high-carbon martensitic organisation, easy to produce weld cracks, so in high-carbon steel welding, we must make a reasonable choice of welding process, and take appropriate measures in a timely manner to reduce the emergence of weld cracks, improve the performance of welded joints.