JPS61170545A - High manganese steel for very low temperature use having superior rust resistance - Google Patents

Abstract

PURPOSE:To provide excellent toughness at very low temp. as well as rust resistance by specifying the amounts of C, Si, Mn, Cr, Ni, N, Al, and Ca as principal components in the high Mn steel. CONSTITUTION:The high Mn steel consists of <=0.20% C, 0.05-2.5% Si, 9-35% Mn, 10-20% Cr, 0.1-8.0% Ni, 0.001-0.50% N, 0.001-0.20% Al, 0.001-0.50% Ca, and the balance Fe with inevitable impurities, to which 0.05-4.0% Mo is incorporated if necessary, and further >=1 kind among Cu, W, Co, Nb, Ti, and V is incorporated by 0.01-4.0% in total in case of Cu, W, and Co and by 0.005-2.0% in total in case of Nb, Ti, and V. Owing to this composition, the high Mn steel for very low temp. use excelling in rust resistance in the wet environment and having superior toughness at the temp. as low as <=about 25K can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a high manganese steel for cryogenic use that has excellent #M properties in wet @ soil conditions and excellent toughness at cryogenic temperatures of 25 or below. .

(Prior Art) Recently, large-scale facilities such as experimental nuclear fusion reactors, two-particle accelerators, and generators using superconducting magnets are being constructed around the world, but the structural materials used in these facilities are Containers of cryogenic liquids such as liquid helium, supporting materials for the H1 conductor, and surrounding structures are cooled to extremely low temperatures in the vicinity of 4. In addition, as the magnet capacity increases, the electromagnetic force also increases, and high strength is also required for rounding, which is used under higher stress than ever before. In addition, such structural materials are sometimes used in contact with a vacuum after being given a metallic luster to the surface as part of a heat insulating structural member, and the 5A surface cannot maintain its metallic luster in order to maintain the vacuum. requested. Therefore, an important property is that the metallic luster does not rust due to dew condensation, freezing, etc. when exposed to the atmosphere or when the atmosphere enters due to vacuum summer deterioration of the equipment, that is, rust resistance. Rust resistance is also one of the properties that cannot be ignored in other applications.

In response to current demands, 8US has a higher N content than usual in order to increase strength and improve toughness at low temperatures.
Cr-N1 such as 304LN +SUB 316LN
Although this steel has extremely good rust resistance, it has the disadvantage that the austenitic structure becomes unstable at extremely low temperatures around 4°C, resulting in a decrease in toughness. It is extremely expensive due to the large number of On the other hand, recently, JP-A-57-2868, JP-A-58-1
As shown in Japanese Patent No. 44418, high Mn austenitic steel containing a large amount of Mm has been developed as a low temperature structural steel, but these have the problem of lacking the rust resistance described above. Recently, high Mn steel has excellent rust resistance in a wet 11Sil environment! #1 in Publication No. 59-104455
9 has been proposed, but this steel has been improved in toughness.

It's not a thing.

(Problems to be Solved by the Invention) The present invention does not rust when exposed to the atmosphere or when condensed, and has excellent toughness even at extremely low temperatures near 4.
-It is intended to be provided at low cost.

(Means for solving the problem) The gist of the present invention is that C0.20% (weight - the same below) or less, Si0.05-2.5%, Mn9-35
%, Cr10-20%, N10.1-8.0%, N0.
001~0.50s, Aj0.001~0.20s, C
a0.001 to 0.020-, and optionally further Mo0.05 to 4.0%, and or Cu #
W * Coe Nb * Tl * Vola There are two or more kinds of f Cu, W, Co K, the total amount of "C" is 0.01 to 4.0%, Nb, TI,
VK-)ite contains a total amount of 0.005 to 2.0%, with the remainder consisting of iron and unavoidable impurities.

First, the reason for limiting the chemical components in the present invention will be described.The mechanical properties described in this article are the properties in 25 below.

C is an extremely effective austenite stabilizing element in steels containing a large amount of Mn and Crt-t).By stabilizing austenite, it improves the toughness at extremely low temperatures below J1725 and has the effect of increasing tensile strength. have However, if the content exceeds 0.2%, the workability deteriorates significantly, and furthermore, when the content exceeds 0.2%, the
Or carbide precipitates in the portion heated to 00 to 800°C, deteriorating rust resistance and reducing toughness. Therefore, the C view was set to be 0.20 or less.

Si is necessary to increase strength, but if it is less than oss, the effect is insufficient and if it exceeds 2.5%, it will destabilize the ostite and reduce toughness, so it is
1.5% Mn stabilizes the austenite phase of steel containing io~zo* Cr and improves strength and toughness at extremely low temperatures, but if it is less than 9%, a sufficient amount of austenite cannot be obtained. , strength and toughness increase as the weight increases, but 3
If it exceeds 5%, it will be difficult to melt the steel, and the amount of Mn alloy added will increase, resulting in a rounding value of 35% or less.

Cr imparts rust resistance and has the effect of stabilizing austenite, but if it is less than 10%, sufficient rust resistance cannot be obtained and rutting occurs when exposed to the atmosphere. If it exceeds 20%, a 7-elite phase will be generated and a sufficient amount of austenite to stabilize toughness will not be obtained, so it is set at 10 to 20%.

N1 has the effect of preventing the transformation of austenite into α' martensite and improving strength and toughness, and can reduce the total amount of M and Nt, which are problems in melting, but if it is less than 0.1%, there is no noticeable effect. I can't get old. On the other hand, since N1 has a smaller strengthening effect than Mn and also reduces the solubility of N, its upper limit was set at 8.01.

Further, Nl is preferably 6,0- or less, which deteriorates rust resistance.

N stabilizes austenite and has a remarkable effect on increasing strength, especially yield strength, at extremely low temperatures. In particular, in the steel of the present invention, Mn and Cr act to increase the dissolution rate of N.
Since it contains a large amount of t-, it is extremely advantageous for increasing strength compared to Cr--Ni thread austenitic stainless steel containing a large amount of N1, which has the effect of reducing N dissolution and obscurity. However, if it is less than 0.001%, such an effect is not observed, and if it exceeds 0.50%, hot workability is poor and cracks occur during rolling.
．． It was set at 50%.

At is a component that improves the hot workability of Mn-Cr-based austenitic steel, further improves the Ca yield, and refines the grains to increase strength, and if it is less than 0.001%, this effect cannot be obtained. On the other hand, if it exceeds 0.20%, the toughness decreases, so it was set to o, ooi ~ 0.20%.

The content of Ca has the effect of significantly improving the cryogenic toughness of around 4 in high Mn, high Cr steel of Mn 9-35% 1CrlO-20%. Figure 1 shows C0.02~0
．． 04%, Sl 0.20~0.30%, Mn22~
26%, 80.003~0.005%eCr
13-16%.

N10.7-3.5%, N0.20-0.259G, A
zo, 0.2 to 4.2 of steel containing 01 to 0.03% M
% proof stress and Charpy impact absorption energy
・These test values are obtained from a tensile test piece (parallel part diameter 7n% r - length 450) from a 30M thick plate solution-treated at 1100℃. And JI No. 84 impact test piece was manufactured and the liquid helium temperature (
4.2K).

As is clear from these results, when the Ca content is 0.001, Charpy*g absorbed energy at 4.2 KK is significantly improved, but when added in a large amount exceeding 0.020, the toughness and ductility decrease. become the cause. Therefore, its content must be o,ooi~0.0201.The effect of Ca becomes greater as the S content decreases, so Si is 0.005.

-The following is desirable.

The present invention further provides Me and/or Cu#W as necessary.
, Co, Nb, TI, '%C)l or more can be contained.

Ultra-low C high Mn-Cr austenitic steel such as the steel of the present invention has a toughness similar to that of Ni-0r austenitic stainless steel in the part heated to 600 to 800°C by stress relief annealing or #coating. The present inventors have found that addition of MO is extremely effective in eliminating this IA phenomenon, which usually occurs due to precipitation. Figure 2 ore, C0,002~0.004%, Si 0.3~
0.5%, Mn22.0-23.0%, So, 003
%, N 0.22-0.23%, Cr 12.
5-13.5%, Ni 2.8-3.3%, At
0.01~0.03%, Ca0.002~0.003
After rolling steel containing % and No. to a thickness of 30 mm, 1
Tensile test pieces (parallel part diameter 7g, r-gear length 45n) and JI84 were prepared from plates solution-treated at 100°C, and then heat-treated at 700°C for 2 hours after the solution treatment for 6 treatments.
A No.-7 Y/L/B equilibrium test piece was prepared and tested at liquid helium temperature (4.2K).The results are shown below. As can be seen from these results, the reduction in rN shock absorption energy due to solution treatment and heating at 700° C. is significantly reduced by the addition of Mo.

Such a Mo effect can be seen when the Mo content exceeds 0.1%, and if it exceeds 4%, a ferrite phase is formed and the toughness decreases, so the Me content was set at 0.05 to 4.0%. At 0.01% or more, Cu e W a Co has the effect of strengthening the same as above for a note and the ground, but when it exceeds 4.0%, the deterioration of the initial pour starts, so the total content of those components is 0
．． Must be O2N2.0%, Nb #T
i.

V has the effect of increasing strength through precipitation hardening and grain refinement. However, the total amount of these elements is 2.0%
If the total amount exceeds 0.005 to 2.0, the toughness will decrease.
It was set to 0%.

The temperature below 25 is used as the cryogenic temperature, which is because most current superconducting magnets are made of liquefied helium (
This is because it was cooled at a temperature of 4.2 K) and liquefied helium was used as the refrigerant for the purpose of testing. The actual operating temperature ranges from the temperature of superfluid liquefied helium (2.1 K) to the temperature of liquefied hydrogen (20.4 K) t.

In addition, as mentioned above, recently, due to the increase in operating stress of equipment due to the increase in magnet capacity, there are cases where a proof stress of 1100 MPa or more is required at the following temperatures.
In that case, it is necessary to increase the N content to 0.20% or more. Traditionally, structural steel used for such purposes is required to be non-magnetic because it is used in strong magnetic field. 4,
It was necessary for the material to be completely austenitic at operating temperatures near 2. However, the steel of the present invention does not necessarily need to be completely non-magnetic in the vicinity of 4.2, and does not prevent the presence of a ferromagnetic ferrite phase in addition to the austenite phase. It is sufficient that the austenite phase is present at 5 Ots or more, and the alloying elements can be increased or decreased or selected within this limit. Of course, it is possible to make a completely austenitic steel at 4.2K, and in this case At is 0.005 to 0.
．． 0896, Dr is 10-18%, Mn is 2
It is desirable that N is 0 to 27% and N is 0.20 to 0.40%. The non-inventive steel is manufactured according to the steps described below. That is, by using a melting furnace such as a converter or an electric furnace, and if necessary, using a vacuum degassing method, a ladle N-line method, a remelting method, etc., the #! mt
After making this into a steel ingot, it is heated to 1000 to 1250°C and forged for 9 minutes, or it is made into a steel billet by continuous casting. After being reheated to 1,000 to 1,250°C depending on the method, or immediately after producing a billet, it is processed by rolling or forging without cooling to a low temperature to produce thick plates, shaped steel, steel bars, wire rods, hot-rolled sheets, etc. Cooling after rolling or ring forming may be done by natural cooling as is usually done, but rapid cooling such as water cooling may also be used to prevent deterioration of toughness and rust resistance due to precipitation of carbonitrides during cooling. good.

The steel of the present invention may be rolled or forged, but in order to further stabilize the rust resistance and toughness, the steel should be heated at 900 to 1150°C.
It is preferable to heat it to a solid solution treatment.

Furthermore, the hot-rolled thin sheet produced in this manner can be cold-rolled by a normal method and heat-treated for recrystallization and solid solution formation at 900 to 1150°C to form a cold-rolled thin sheet. .

In addition, the steel of the present invention can be processed such as cutting, bending, and bath welding without any problems. Maku,? Of course, the present invention can also be used as a default.Next, the present invention will be described with reference to embodiments.

Table 1 shows the chemical composition, mechanical properties, and induction resistance of unexploded #46A and comparative steel.
A thick plate was solution-treated at 1100°C and then water-quenched, and then a test piece of a predetermined size was manufactured and tested.

Is the steel from l to 131 the invention steel or from 14 to 15
This is a comparative steel cutting process. As you can see from this result,
It can be seen that the steel of the present invention is significantly superior in @zero value compared to the comparative steel. In addition, the steel of the present invention shows no rust even when subjected to a 60-day outdoor dew test, and has extremely excellent resistance to corrosion.

Among the comparative steels, 1J410 is a steel that satisfies the composition of the present invention except that it does not contain Ca, steel 11 is SUS 304LN, and 412 is a low C-2596Mn steel.
711 There is te.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a high manganese steel for use at extremely low temperatures with excellent induction resistance and toughness, and therefore the present invention has extremely large industrial benefits.

[Brief explanation of the drawing]

@Figure 1 shows Cajl in steel, 0.2% yield strength, and Charpy*
Figure 2 shows the relationship between M and absorption energy.
It is a figure showing the relationship between the amount of e, 0.2% yield strength, and Charpy@impact absorption energy. Ca (%)

Claims (4)

[Claims] (1) C0.20% or less, Si0.05-2.5%, M
n9-35%, Cr10-20%, Ni0.1-8.0
%, N0.001-0.50%, Al0.001-0.
A cryogenic high manganese steel with excellent rust resistance, containing 20% and 0.001 to 0.020% of Ca, with the remainder consisting of iron and inevitable impurities. (2) C0.20% or less, Si0.05-2.5%, M
n9-35%, Cr10-20%, Ni0.1-8.0
%, N0.001-0.50%, Al0.001-0.
20%, Ca0.001-0.020% and Mo0.
A high manganese steel for cryogenic use with excellent rust resistance, characterized in that it contains 05 to 4.0% and the remainder consists of iron and inevitable impurities. (3) C0.20% or less, Si0.05-2.5%, M
n9-35%, Cr10-20%, Ni0.1-8.0
%, N0.001-0.50%, Al0.001-0.
20%, Ca0.001-0.020%, and further contains one or more of Cu, W, Co, Nb, Ti, and V in a total amount of 0.01-4.0% for Cu, W, and Co. 0
%, Nb, Ti, and V in a total amount of 0.005 to 2.
A high manganese steel for cryogenic use with excellent rust resistance, characterized in that it contains 0% and the remainder consists of iron and unavoidable impurities. (4) C0.20% or less, Si0.05-2.5%, M
n9-35%, Cr10-20%, Ni0.1-8.0
%, N0.001-0.50%, Al0.001-0.
20%, Ca0.001-0.020% and Mo0.
05 to 4.0%, and further contains Cu, W, Co, Nb
, Ti, and V in a total amount of 0.01 to 4.0% for Cu, W, and Co, and 0.005 to 2.0% in total for Nb, Ti, and V. A high manganese steel for cryogenic use with excellent rust resistance, the balance being iron and unavoidable impurities.