CS230729B1 - Casting steel with carbon coefficient lower than 0,41 suitable to work with at extra low temperatura up to -60c - Google Patents

Description

The invention relates to steel with a carbon equivalent of less than 0.41 for castings intended to operate at very low temperatures up to -60 ° C. The steel is intended especially for castings of spherical closures for gas pipelines.

Castings intended for working at low temperatures are still cast from steels with a carbon content of 0.15 to 0.19% by weight and manganese. 1.00 to 1.40 wt. The steel castings must be upgraded and can only be used up to -40 ° C. Wastes for temperatures up to -55 ° C are cast from steels which additionally contain up to 0.5% w / w silicon and for temperatures up to -60 ° C the steel is alloyed with 3 to 5% by weight of nickel.

Occei na. . castings intended for working at low temperatures are produced in basic arc furnaces by double slag tectaxiology. Usually, the principle of intensive carbon boiling is added to sufficiently degass the bath. After the last addition of iron oxidizing ore at the end of the oxidation, pure boiling is maintained, usually 20-25 minutes. slag and creates a new slag from lime and fluorspar or bauxite. The melt reduction valley is led under a new etruscan, usually with an oxygen activity of 35 to 80 ρρψ. The final deoxidation is usually carried out in a ladle with aluminum and / or aluminum and silicate.

Currently on. castings. Ball valves for transit gas pipelines operating at temperatures up to -60 ° C require an additional liquid carbon dioxide equivalent of less than 0.41. None of the steels used in castings yet at temperatures of -60 ° C are suitable for this condition.

The carbon equivalent is calculated according to the formula:

c _. % c 4. Ж— ♦ JSLijL + YY + № *,. % * * 6 14 5

Ac also requires that the steel for the castings exhibit the following mechanical properties:

strength «M (MPa) 420 to 570 yield strength в. (mp ·) least 355 tatodt ^and 5 («) ' least 25 soužboí OF (56) least 30 notch toughness KCU 3 ⁺² 0 (Jcm ² ) least 80 notch toughness KCU 3-60 (Jcm · ² ) least 50 notch toughness KCV 3 ' ⁶ 0 (Jc.- ² ) least 30

This problem is solved by the steel according to the invention, which is based on the fact that it contains in% by weight:

carbon 0.09 to 0.13 manganese 1.30 ai 1.60 silicon 0.20 to 0.35 titanium 0.005 ai 0.02 aluminium 0.02 to 0.04 chrome tracks to 0.20 nickel tracks ai 0.20 me& tracks ai 0.20 molybdenum tracks al 0.05 phosphorus tracks to 0.015 sulfur tracks ai 0.015

wherein the mutual weight ratio of carbon to manganese content is bound by (% ta) = 6.6. (0.343 - W) - 0.13 /

The carbon black ratio of manganese to carbon monoxide is already ensured during the metallurgical process of steel production.

For steel, the trot limit K # exceeds 355 Ш? _А and the current carbon equivalent value 0 _ekT »· ηίί is greater than 0.41. If they take action,. so that the trot limit Re 'of the steel produced overrides the value. 355. MPa, then reached. Even a notched string at -60 ° C of KCW weighs more than 30 Jcm ² .

H> <dm> The notch toughness at -60 ° C is also sensitive to hydrogen content in steel. If ae. it withdraws not earlier than 6 minutes and at the latest 10 minutes after the last addition of lump oxidic iron ore, or after the blowing of oxygen and okarfity, until carbon boiling is in the bath - to produce a new Etruscan, steel and hydrogen.

The notched value of -60 ° C is also sensitive to the acro-purity of the steel and the grain size. Jeatiižc sb. The oxidation results in a bath temperature at the end of the oxidation within a narrow range of 1580 and 1600 ° C, and not as usual within the wide limits of 1570 to 1620 ° C and at the end of the oxidation ae. it performs very intense aluminum deoxidation so that the oxygen activity in the bath falls below 25 ppm - until now the oxygen activity in the reduction period of the melting usually varies. in the range of 35 and 80 ppm, creating good conditions for floatation of the objects and achieving excellent micro-purity of the steel. At the same time, conditions will be created for minimum burn-off of manganese during alloying and low burn-off of deoxidizing elements at final dssoxldation

Example of the invention:

A charge having a chemical composition in% by weight was charged to a base electric arc furnace with a melting mass of 8 tons:

carbon 0,46; manganese 0,38; phosphorus 0,026; sulfur 0.019; chrome 0,16; nickel 0.11; měů 0,12.

After the batch was melted, the slag was treated with the addition of lime and the oxidation of the carbon was initiated by the addition of kua oxidizing iron ore. Struaka was continuously treated with lime additives. After the carbon content of the bath reached 0.09% by weight, oxidation slag was withdrawn and new slag from lime and bauxite was formed. Upon reaching a carbon content of 0.06% by weight, intense precipitation deoxidation with aluminum (1.9 kg · t ^-1 ) was performed. Oxygen activity decreased from 241ppm to 23ppm. The bath temperature reached 1600 ° C. After precipitation deebxidaei, the bath had the following chemical composition in% by weight:

carbon 0,08; Manganese 0.18; silicon 0.19; phosphorus 0,006; sulfur 0.010; chrome 0,09; nickel 0.11, currency 0.12, aluminum 0.71.

According to the equation (% Mn) = 6.6. (0.343 - (% C) -0.13) the mahganic content was adjusted to the requirement = 0.41 and tapped into the pan at 1610 ° C. Final deoxidation was carried out in a ladle with aluminum (0.2 kg · t ”S, ferrotitanium containing 35% Ti by weight of 1 kg · t ^{1 1} and silicocalcium (3 kg · t ^{1 1} ). % by weight:

carbon 0.11; manganese 1,42; silicon 0.31 *, phosphorus 0.009; sulfur 0.008; chrome 0,09; nickel 0.11; MeS 0.12; aluminum 0.031; titanium 0,02; molybdenum 0.05; C _ekT = 0.36.

Following normalization of the castings, the following mechanical properties were achieved:

strength R m «525 MPa yield strength R * = 369 MPa ductility with - 31? 4 % narrowing of «69,9 % vrubová toughness at 20 ° C KCU 3 * ² ° = 169.8 Jcm ~ ^ vrubová toughness at -60 ° C KCU 3 “ ⁶⁰ * 142.6 Jcm ² vrubová toughness at -60 ° C, notch КСГ ⁶⁰ * 48.2 JcnT ^

Claims (1)

1 · Ос ·! and a carbon equivalent of less than 0,41 for castings for working at very low temperatures up to -60 ° C, characterized in that it contains by weight: carbon 0.09 to 0.13 manganese 1.30 to 1.60 silicon 0.20 to 0.35 titanium 0.005 to 0.62 aluminium 0.02 to 0.04 chrome not more than 0,20 nickel not more than 0,20 mšft not more than 0,20 molybdenum not more than 0,05 phosphorus Not more than 0,015 sulfur Not more than 0,015 wherein the weight ratio of carbon to manganese to each other is given by (% Mn) &gt; 6.6. (0.343 - (5KC) - 0.13).