SU874761A1 - Corrosion-resistant weldable steel - Google Patents

Description

(54) CORROSION RESISTANT WELDABLE The invention relates to metallurgy, namely metallurgy of stainless steels used in cryogenic engineering. Known chromium-nickel steels t pas 18-10 have good technological properties with hot and cold deformation, but have low strength (yield strength 6 5 4 25 kgf / mm 1. Closest to the proposed technical essence and the achieved effect is steel of the following chemical composition, you.%: Carbon 0.1-0.2 Chromium 15-17 Manganese 4-10 Nickel 3.5-4.5: Nitrogen 0.035 Molybdenum i 0.5 Copper 2.0 Silicon 1 Iron The Rest 2. Steel is known after quenching has high strength, ductility and toughness at all temperatures. Vacation time, 30 min, causes a sharp decrease in viscosity, especially at cryogenic temperatures., STEEL Workability by pressure was assessed using ASTM R-value, which characterizes the ability of metals to resist thinning or thickening under tension or compression in the sheet plane. It follows from the condition vb ... Vl and Vi - the initial and final width of the sheet; Lp and 11 - the initial and final.: thickness of the sheet. The deformability became better, the closer the value of H approaches. R-2 of known steel is 1.181-1.214 for the hardened and 1.344-1.356 for the tempered condition. The purpose of the invention is to increase the viscosity of the weld with cryogenic plasticity at hot temperatures, water pressure treatment, leading to an extension of the temperature range of application from -253 ° to 700 ° C. The goal is achieved in that steel containing carbon.

chromium, manganese, nickel and iron, additionally contains titanium, zirconium alkynium, boron, rare earth metals in the following ratio of compound HeHtOB, wt.%:

0.01-0.15

Carbon

12-15

Chromium

13-15,5

Manganese

0.5-6.0

Nickel

0.01-0.8

Titanium

0.001-0.3

Zirconium

0.01-0.5,

Alkmini

0,0001-0,005

Bor Rare Earth

metals

0.05-0.1 Remaining Iron As rare-earth metals, mishmetal containing one or more elements of lanthanides can be taken: lanthanum, cerium, praseodymium, neodymium.

Carbon, as an austenitic-forming element, is introduced into the steel in an amount of at least 0.01% to obtain an austenitic structure in the steel. The upper limit on carbon is 0.15% limited to prevent the formation of chromium carbides () in hardened steel, which have a negative effect on the tendency of steel to intergranular corrosion.

The lower limit of 12% for chromium corresponds to the concentration at which the steel has a positive electrochemical potential and is corrosion resistant. The chromium content below 12% leads to a change in the sign of the electrochemical potential and the steel becomes noncorrosive. The upper limit for chromium is 15% limited in order to exclude the formation of a " ferrite " upon heating, which is a brittle phase at low temperatures.

The accepted limits on manganese are due to the need to obtain steel with austenite structure. To do this, with a ratio of components required, at least 13% of manganese is required. The upper limit of 15.5% is due to the fact that, at this concentration of manganese, steel still does not show a strong tendency to work hardening, which leads to embrittlement of steel.

The lower nickel content of 0.8% determines the amount of this element necessary for obtaining service properties at temperatures up to, the upper 6% at temperatures up to j253C.

The lower limit for titanium is 0.01%, which indicates the concentration, beginning with which the positive effect of titanium on reducing the tendency of steel to intergranular corrosion, which consists in the fact that titanium introduced into steel binds carbon to carbide T & C. Due to this, it is difficult to form carbide which reduces the corrosion resistance of the steel by reducing the chromium concentration below the minimum limit in the border areas. The titanium content is higher than 0.8% is impractical, since the excess titanium in the steel of the proposed composition does not take part in the formation of Ti carbide C.

The lower boron limit of 0.0001% indicates the concentration at which the hot ductility of steel improves, the upper limit of 0.005% indicates the content above which boron forms an excess phase and impairs the ductility of the steel at high temperatures.

The lower limits for zirconium (0.001 and aluminum (0.01%) with doping show the smallest content, starting from which these elements increase the strength of steel at + 700 ° C due to the formation of fine and poorly soluble Zf carbide and a thin layer of AljOj oxide which impedes diffusion processes and further oxidation of the metal at high temperatures contributes to the production of finer grains due to the formation of compounds A1N and, which, upon solidification of the ingot, crystallize in the form of submicroscopic dust, which plays the role of barriers to grain growth during subsequent heating, as well as increasing toughness at cryogenic temperatures and improving the cold deformability of steel due to the displacement of excess phases into the body, grains.

The upper limits for zirconium 0.3% and aluminum 0.5% are limited in order to prevent the curd alloying of the solid solution, since the content of zirconium and aluminum is higher than the specified limits due to their limited solubility in austenite can lead to the formation and precipitation of excess phases in intergranular spaces in the form of rough inclusions and cause embrittlement of the metal.

The accepted limit on the amount of lanthanide elements: lanthanum, cerium, praseodymium, neodymium 0.05-0.1% is dictated so that the presence of one or all elements in the specified amounts, due to their high surface activity and affinity for phosphorus and sulfur, inhibits diffusion mobility at the grain boundaries of carbon, chromium, sulfur, phosphorus, and contributes to the displacement of excess phases into the body of the grain.

Experienced smelting steel are given in table ..

Table 2 presents the mechanical properties, the deformability of the base metal and the weld. From the data of Table 2 it follows that the advantages of the proposed steel are mainly manifested in the testing of metal after provoking tempering, simulating thermal conditions after welding. When the work develops cracks (dp) of the base metal of the proposed steel, it is equal to 3.9-6.3 kgcm / cm, while in the known, dp 1, 5-1.6 kgcm / cm. An even greater difference in the values of toughness (Jan and ap at cryogenic temperatures of the proposed and known steels is observed when testing the weld - work, the development of ctp is 3.1-4.3 kgcm / cm and 0.5-0.6 kgcm / cm, respectively. An IpaNM fractal study confirmed that all samples of the proposed steel, tested when destroyed, samples of known steel had completely brittle fracture areas. The advantage of the proposed steel is observed: Also in the study of the deformability of the released condition Rj of the proposed steel differs significantly less than that of the known steel.The use of the proposed steel allows reducing the steel range in the manufacture of chemical engineering and cryogenic engineering, reducing the cost of expensive refrigerant during cooling, as the designs of the proposed steel have a smaller geometric size, reduce weight designs, save the scarcely nickel in the amount of 65 kg per ton of metal. The use of steel is advisable for the manufacture of welded and non-welded structures, working at tempoatures from to almost all areas of engineering.

B10.18 15.1 4.0 6.0 0.025

B20.05 17.1 4.5 10.0 0.030

Not specifically introduced.

0.45 1.2 0, 4 1.8 | The weld was not heat treated. Determined on the base metal after quenching + tempering, 30 min.

Claims (1)

Invention Formula A corrosion-resistant steel to be welded, containing carbon, chromium, nickel, manganese, iron, is characterized in that, in order to increase the toughness of the weld at cryogenic temperatures, ductility under cold working by pressure, it additionally contains titanium, zirconium, aluminum, boron, rare earth metals in the following ratio of components, wt.%: Carbon 0.01-0.15 Chrome 12-15 Manganese 13-15,5 table 2