KR940007276B1 - Making method and product of chain steel - Google Patents

Abstract

The steel comprises 0.17-0.30 wt.% of C, 0.15-0.50 % by weight of Si, 1.2-1.90 wt.% of Mn, not more than 0.030 wt.% of P, not more than 0.030 wt.% of S, not more than 0.30 wt.% of Cu, 0.10-1.0 % by weight of Ni, 0.5-1.30 wt.% of Cr, 0.15-0.70 wt.% of Mo, 0.04-0.10 % by weight of V or 0.02-0.1 wt.% of Nb, and 0.02-0.06 wt.% of Al.

Description

Ultra high strength chain steel and its manufacturing method

The present invention mainly relates to the anchor link platform of oil exploration drilling ships in the Handae region, and relates to the steel for anchor chains of huge marine ships and requires a tensile strength of 90kg / mm ² or more. The present invention relates to an ultra high tensile chain steel that can withstand severe marine weather conditions and has excellent impact resistance and weldability.

Generally, 70kg / mm ² grade is mainly used as high tensile steel, but it has been used only for anchor chains of marine ships in relatively temperate regions. However, as the high tensile strength with improved impact resistance at low temperatures after welding, the demand for lighter ships and oil rigs for continental shelf oil exploration is increasing. In particular, due to the petroleum resource, the chain of petroleum exploration drilling ships in the North Korea (North Sea) is required to have high tensile strength and toughness at low temperatures to withstand harsh and severe marine weather changes. However, the conventional high-strength chain steel has excellent properties in weldability, impact resistance, and bending test, but it cannot withstand large marine structures, cold zones, and harsh conditions, requiring more strength, high toughness, and corrosion resistance.

The present invention solves the problems of the conventional high-strength chain steel, it is stable as evenly hardenability of the welded part and the base material, fine element addition effect to give good weldability, fine grain size forming element addition to impart impact resistance at low temperature It produces carbides and nitrides to prevent strain aging and prevent grain coarsening at high temperatures, and features a precision alloy design that has been a problem in the development of high-grade steel materials. In addition, the application of inclusion control technology and high cleanliness steel control technology suppresses impurities that affect fatigue strength to the maximum. To provide ultra-high tensile chain steel with an emphasis on preventing high tensile strength and low temperature embrittlement, which are different from the conventional high tensile strength steel. It is for.

The steel according to this invention has the following chemical composition (wt%) range.

That is, by weight ratio C 0.17-0.30%, Si 0.15-0.50%, Mn l.2-1.9%, P≤0.030%, S≤0.030%, Cu≤0.30%, Ni 0.10-1.0%, Cr 0.5-1.30%, Mo 0.15-0.70%, V 0.04-0.10% or Nb 0.02-0.1%, Al 0.02-0.06%.

Next, the reason for limitation of chemical composition of this invention steel is demonstrated.

C (carbon) increases the strength, but the required strength cannot be obtained at 0.15% or less, but increases the carbon equivalent (CE) at 0.3% or more to impair weldability, and deteriorates ductility and toughness. have.

Si (silicon) is necessary for deoxidation and increase in strength because steel deoxidation is insufficient at 0.1% or less, but at 0.5% or more, it needs to be 0.5% or less.

Mn (manganese) is a necessary ingredient for deoxidation and strength increase, but if it is less than 1.0%, it is difficult to obtain the required strength, and if it is too large, it increases the carbon equivalent to damage the weldability. Therefore, it is necessary to limit the range of the added ingredient to within 1.90%. .

P (phosphorus) needs to be limited to 0.030% or less since it forms a banded structure during hot rolling, which impairs uniformity of the structure and is difficult to obtain good toughness.

S (sulfur) formed a low-melting emulsion and caused viscous deformation in the rolling direction during rolling to lower toughness and impact value, so the upper limit was 0.030%.

Ni (nickel) has little effect on improving toughness and fatigue strength in small amounts, and it is not economically good because it causes cost increase when a large amount is added, but it is added up to 1.0% to obtain toughness effect at low temperature.

Cu (copper) is effective in improving toughness, but is less effective at 0.1% or less, and is not good because it inhibits moldability at 0.4% or more. Therefore, it is necessary to limit the upper limit to 0.3% or less.

Cr (chromium) is needed to give the required strength and hardenability to steel, but it is less effective at less than 0.3% and damages weldability at large amounts. Therefore, it is necessary to limit it to less than 1.3%. It has the effect of toughness when Mo and heats up C component to some extent because it absorbs C component as stable carbide.

Mo (molybdenum) is effective in obtaining required strength, hardenability, toughness, etc., and it is effective in preventing brittle brittleness, so it is added in the range of 0.15-0.7%. When a large amount is added, it damages weldability and causes cost increase. Therefore, the upper limit was limited to 0.7%.

V (Vanadium) is a strong carbide forming element, which contributes to obtaining fine pearlite by inhibiting precipitation and grain boundary growth at austenite grain boundaries when heated at high temperatures. It has the effect of good quenching and particle refinement, improves bending performance and affects low temperature impact value. However, in the case of welding repair, VN is precipitated and hardened, so brittleness may be required. Therefore, the welding repair needs to be limited to 0.1% or less.

Nb (niobium) is the strongest binding micronized element, which precipitates out of carbide and nitride during hot rolling to minimize the growth of austenite and to suppress the coarsening of the welded area. There is an improvement in low temperature toughness and good weldability, but when excessively added, coarsening Nb carbonitride is formed and the material of steel is deteriorated. Therefore, it is necessary to limit the range of added components to 0.02-0.1%.

Al (aluminum) is required for deoxidation and inhibits the growth of austenite as a nitride (AIN) forming element and refines grains. In addition, at least 0.02% is required to improve toughness, but it is necessary to limit it to within 0.06% because excessive addition increases the transition temperature and reduces the cleanliness of steel.

Next, to obtain the required tensile strength and elongation, section shrinkage rule, and good low temperature impact value, the heat treatment was performed after hot rolling. The heating temperature for the hot working is all the conditions such as the material's hot strength and production volume. However, the excessive increase in the heating temperature reduces the growth inhibition of the austenitic grain growth of carbonitrides, resulting in coarse pearlite upon completion of processing. Therefore, the operating temperature range was selected so that the rolling heating temperature was 1250 ± 25 ° C. and the finish pressing pressure was 925 ± 25 ° C. After quenching at 850-930 ° C., tempering at 600-650 ° C. resulted in ultra high tensile chain steel with significantly increased low temperature impact resistance, weldability, strength, and bendability.

EXAMPLE

After melting and tapping in an electric furnace, degassing and secondary refining were carried out in a ladle, and then injected into a steel ingot to obtain a steel ingot as shown in the first table.

TABLE 1

Chemical composition (wt%)

The steel ingot is heated to 1250 ° C. and hot rolled to a finishing temperature of 930 ° C. before being processed. Yield strength, tensile strength, elongation, cross-sectional shrinkage, material when tempering at 600-650 ℃ to give toughness after heating the quenched steel at 850-910 ℃ in the heat treatment furnace And the low temperature shock absorption energy after welding was very good as in the second table.

[Second Mechanical Property Test Result]

Table 2 shows that tensile strength is much better than that of conventional 70Kg / mm class ² high-strength chain steel and good impact resistance is guaranteed at low temperature without deterioration of impact value. Even when a small amount was added, excellent mechanical properties were obtained and economic effects were also shown. In addition, it can be seen that the substitution of microelements shows almost equivalent mechanical properties in V (vanadium) of samples A and B and Nb (niobium) of samples C and D. In addition, when the ultra-high tensile chain steel according to the present invention had a thickness of 100 mm, a width of 100 mm, and a length of 200 mm, it was bent at 180 ° after welding to obtain a "U" cross-sectional shape.

In addition, the actual high-strength chain steel according to the present invention was manufactured, and a load carrying test and a breaking load test were conducted. The thickness (D) of the chain was 97.0 mm, When the width (W) is 351 mm and the length (L) 590 mm, the chain using the material of the present invention has a load capacity of 752 tons, while the steel of the high tension chain has a load capacity of 477 tons. In addition, the invention of the ultra high tensile chain steel, which has 955 tons of breaking load compared to the existing high tensile chain steel having a breaking load of 682 tons, has about 37% improvement in bearing capacity and 29% in breaking load. .

As described above, the present invention obtains high tensile strength and low temperature impact resistance of ultra high tensile chain steel and at the same time secures high elongation, excellent bendability and high fatigue strength, and thus has a much longer service life than conventional high tensile steel. And excellent materials that maintain life even in harsh conditions.

Claims (2)

C by weight ratio 0.17-0.30%, Si 0.15-0.50%, Mn l.2-1.90%, P≤0.030%, S≤0.030%, Cu≤0.30%, Ni 0,10-1.0%, Cr 0.5-1.30% , Mo 0.15-0.70%, V 0.04-0.10% or Nb 0.02-0.1%, Al 0.02-0.06% of the high tensile chain steel, characterized in that it has a component range. Secondary with a component of claim 1, characterized in that heated to 1250 ± 20 ℃, finish rolling to 925 ± 25 ℃, heat treatment temperature is quenched at 850-930 ℃, tempering at 600-650 ℃ Method of manufacturing high tensile chain steel.