Experimental application of heat-resistant steel material P91 solid wire

Main products and common welding consumables

Our company is a construction and construction unit, mainly engaged in the construction of chemical petroleum equipment, boilers, tank towers, pipelines and structures. Due to the limitation of construction properties, the commonly used welding methods are mainly electrode arc welding, tungsten argon arc welding, molten gas shield welding, submerged arc welding and gas electric vertical welding, so the welding materials are mainly welding rods and various solid cores. Flux cored wire. The materials involved are also extensive, such as chrome-molybdenum heat-resistant steel, low-temperature steel, stainless steel, nickel alloy, titanium alloy and aluminum alloy. At present, due to the flexible construction and high penetration rate of welding rod arc welding and tungsten argon arc welding in the field, it is the most widely used; and high-efficiency molten gas welding, submerged arc welding and gas electric vertical welding are limited by various conditions. , the application is limited. According to incomplete statistics, the application of welding rods accounts for more than 50% of the total amount of the project, and the molten gas shielded welding wire accounts for less than 30%, and the rest accounts for 20%.

Experimental application of heat-resistant steel material P91 solid wire welding gas shielded gas shielded welding

At present, with the development of construction welding technology, welding methods such as molten gas gas shielded welding and submerged arc welding are gradually applied and popularized at the construction site, such as the application of molten gas shielded welding in alloy pipelines, and the submerged arc transverse welding in tank engineering. In the application, etc.

The martensitic heat-resistant steel material T/P91 has good high-temperature mechanical properties and high-pressure resistance. In petroleum and petrochemical distillation and cracking equipment and refineries, pipes and steel plates of T/P22 grade and T/P5 grade steel are being T. /P91 is replaced by pipes and plates. However, its welding performance is poor, and it is prone to problems such as cold cracking, brittleness of welded joints, softening of HAZ zone, etc. The welding must be strictly in accordance with the technical regulations to obtain a satisfactory welded joint. Therefore, the commonly used welding process is argon arc welding wire bottoming, electrode arc welding filling, and covering surface, and the welding material mainly depends on imports.

P91 materials are mostly thick-walled products, and the low-efficiency process of argon-electric welding is difficult to meet the needs of short-term and fast construction projects in recent years. In response to the characteristics of P91 materials, our company has intensified the research and development of high-efficiency welding processes and materials for P91 material pipelines, such as gas welding and submerged arc welding.

To this end, we tracked the welding consumables manufacturer and conducted a large number of tests on the P91 pipeline solid wire welding gas gas shielded welding. After screening, the experimenter repeatedly performed several welding gas ratio welding tests using the P91MIG solid wire provided by a welding consumables, as shown in the drawing.

First, welding with 100% Ar gas is not possible, the arc drift is severe, and there is almost no melting depth of the molten pool, and the molten pool and the base metal are not well fused.

Second, with 95% Ar + 5% CO2 gas ratio, the arc drift is weakened, but the molten pool has a shallow penetration depth, and the molten iron and the base metal are poorly fused, and the welder is difficult to operate.

Thirdly, with 85% Ar+15% CO2 gas ratio, the arc is basically stable, the weld is well formed, the surface of the weld is less dirt, and the weld is bright. However, the molten pool has a shallow penetration depth, and the molten iron and the base metal are poorly fused. The welder can operate flexibly through the handle, but the welding can not be achieved by automatic welding.

Fourth, it was finally determined that the welding was carried out using a 80% Ar+20% CO2 gas ratio. The arc is basically stable, and the weld is well formed. The molten pool has a moderate penetration depth, and the molten iron and the base metal are well fused, and the welder can handle the operation and the motor welding can be performed.

The focus of the welding process is that the welding layer must be thin, generally ≤ 3mm, pay attention to the two sides to pause, full filling, to ensure good fusion, to avoid the formation of dead angles, resulting in unfused defects. Because it is gas protection, it is necessary to strengthen the wind protection measures to avoid the formation of pores due to the influence of the flowing wind.

At the same time, the welding heat input is strictly controlled, tungsten argon arc welding is ≤15kJ, and gas metal arc welding is ≤30kJ. The temperature between the filling cover layers is controlled within 210~230 °C. After the welding is completed, the temperature is lowered to 120 ° C / 1 h, and the post heat is 350 ° C / 1 h, and heat treatment is performed.

The welding finished test piece joints were evaluated according to the relevant standards, and the results were evaluated. The normal temperature bending, tensile and impact test data were qualified. In order to be prudent, the joints were also subjected to high temperature stretching, high temperature creep and other tests, and the test data also met the specifications. In combination with the test data, 2 parts of the welding process were formed. Based on the successful experience of P91 material gas metal arc welding, we are conducting related tests on pipeline submerged arc welding to meet the company's next P91 material pipe welding requirements.

Some ideas for the future development of welding materials

Modern refining and chemical engineering projects have a large-scale large-scale welding structure, container equipment and pipeline steel structure; large, overweight, super-long, ultra-high, ultra-thick structures continue to emerge, and at the same time need to meet the requirements of high temperature, high pressure, corrosion resistance and other characteristics; The application of materials is diversified: the proportion of alloy materials such as heat-resistant steel, low-temperature steel, stainless steel, duplex steel, and non-ferrous metals is increased and the types are complicated.

The characteristics of the above-mentioned refining and chemical engineering have put forward new and higher requirements for welding consumables and processes. High-efficiency, environmentally friendly, humanized, field-adapted welding processes and research and development of welding materials are imminent.

(1) Steel structure welding efforts to reduce or eliminate the low efficiency, high comprehensive cost of electrode arc welding, gas metal arc welding or melting electrode self-shielded welding is currently the best method to replace electrode arc welding, but the gas shielded welding field The adaptability is poor, the welder's all-position welding is difficult to operate, and it is hoped that the welder's operability can be improved by improving the performance of the welding material. The melting of the self-shielded welding wire can achieve localization and reduce costs, and there will be a large market.

(2) In terms of equipment piping, submerged arc welding without arcing, low pollution, high efficiency and good welder operability during factory prefabrication is undoubtedly the best choice, but now with the emergence of some special materials, such as heat resistant steel P91 Materials, low temperature steel 9% Ni steel materials, the current research and development of submerged arc welding wire and flux in this area has not kept up, affecting the welding application of these materials.

(3) With the demand for deep processing of chemical products, non-ferrous metal materials are widely used, such as titanium alloy, aluminum alloy, nickel alloy, etc., but the welding method and welding materials are relatively simple, such as nickel alloy molten gas shielded welding wire has not been localized. The welding quality of aluminum alloy domestic welding wire is unstable, and the titanium alloy is limited to tungsten argon arc welding. Further research and development of welding materials is needed to improve welding quality and improve welding efficiency.