JPS62202023A - Manufacture of high manganese nonmagnetic steel having high strength and high yield ratio - Google Patents

Abstract

PURPOSE:To manufacture a high Mn nonmagnetic steel having high strength and a high yield ratio by restricting the composition of a steel, hot rolling the steel and cooling it at once at a cooling rate between the air cooling rate and a specified cooling rate. CONSTITUTION:The composition of a steel is composed of, by weight, <1.5% C, <0.8% Si, [-9.26C(%)+19.03]-35% Mn, <0.25% N and the balance Fe with inevitable impurities. The composition may further contain three or less among <5% Cr, <0.5% V, <3% Mo, <0.2% Ti, <0.3% Ni and <0.01% Ca. The steel is heated to 1,000-1,250 deg.C, hot rolled at 700-1,000 deg.C and cooled at once at a cooling rate between the air cooling rate and 100 deg.C/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The present invention relates to a method for producing high strength, high yield ratio, high manganese nonmagnetic steel, which has higher strength and yield ratio through a relatively simple process. It is an object of the present invention to provide a method by which magnetic steel can be produced.

Manufacturing technology for high manganese non-magnetic steel with high strength and high yield ratio for industrial applications.

Conventional technology High Mn nonmagnetic steel has been manufactured in the past, and the conventional manufacturing method involves air cooling after hot rolling, and then reheating to 1000 to 1100°C to remove water dust. A process is needed to suppress the precipitation of carbides, etc.

Problems to be Solved by the Invention The above-mentioned method of water removal inevitably leads to high costs, and also has the problem that the yield strength is low despite the high tensile strength. There is.

"Structure of the invention" Means for solving the problem C: l, 5 at% or less, Si: 0.8 wt%
Below, Mn: 9.26 C(X) +19.03
Wt% or more, 35.0kg [% or less, N: 0
．． 25 wt% or less, S: 0. A steel containing Q3 iyt% or less, with the balance consisting of Fe and unavoidable impurities, is heated at 1000 to 1250°C, and then heated to 700 to 1000°C.
Hot rolling is carried out at
A method for producing a high strength, high yield ratio, high manganese nonmagnetic steel characterized by cooling at a rate of /sec or less, C: 1.5 wt% or less, Si: 0.8 wt%
Below, Mn: -9,26C(X) +19.03 w
t% or more, 35.0wt% or less, N: 0.
Contains 25 wt% or less, S: 0.03 wt% or less, and Cr: 5, Owt% or less V: Q, 5
wt% or less, Nb: 0.3wt% or less, Mo: 3
．． 0wt% or less, Ti: 0.2wt% or less, N
i:3. Oivt% or less, Ca: 0.01 wt% or less, and the remainder is Fe and unavoidable impurities.
A method for producing high strength, high yield ratio, high manganese nonmagnetic steel, which comprises hot rolling at 700 to 1000°C, and then immediately cooling at a rate of not less than air cooling and not more than 100°C/sec.

Effect C: 1.5 wt% or less, Si: 0.8 wt% or less,
Mn knee 9.26 C (1:) +19.03 wt
% or more, 35.0tmt% or less, N: 0.25 wt%
The following contains S: 0.03 wt% or less, and the balance is Fe.
By using steel consisting of Cr:5.
0wt% or less, V: 0.5wt% or less, Nb: 0.3w
t% or less, Mo: 3.0wt% or less, Ti: 0.2wt
% or less, Ni: 3.0 wt% or less, Ca: 0.01 w
By containing three or less types within t% or less, strength increase, yield strength, toughness, and machinability are improved.

Heat to 1000-1250°C, 700-1000°C
By finishing the hot rolling at , a product with favorable properties can be obtained under manufacturing conditions without difficulty, and by cooling after the hot rolling at a cooling rate of 100 ° C / sec or less and higher than the air cooling rate, A stable high-manganese nonmagnetic steel with higher strength, higher yield ratio, and lower magnetic permeability than conventional reheating and water dust can be obtained.

EXAMPLES To further explain the present invention as described above, the inventors of the present invention have conducted repeated studies to solve the problems of the conventional methods as described above, and as a result, in producing high Mn non-magnetic steel, Immediately after rolling, cooling is performed at a cooling rate of 100'C/sec or less, which is higher than the cooling rate when left to cool in the atmosphere, resulting in superior strength and higher yield ratio than when conventional reheated water dust is used. succeeded in obtaining.

That is, the reason for limiting the component composition in the present invention as described above can be explained in terms of -t% (hereinafter simply referred to as %) as follows.

C: 1.50% or less.

C is a strong austenite-forming element and has a significant reinforcing effect, but if it is contained in an amount exceeding 1.50%, grain boundary carbides will be formed due to the effects of welding heat, resulting in a decrease in toughness, so the content should be 1.50% or less. .

St: 0.80% or less.

Si is an element necessary for melting and refining as a deoxidizing element. However, a content exceeding 0.80% promotes the formation of delta ferrite and the like and impairs toughness, so this is set as the upper limit.

Mn: 35% or less.

Mn is an austenite-forming element, an element useful for stabilizing austenite and non-magnetic 6, and increases the solubility of N, which is one of the important strengthening elements. However, if it exceeds 35%, it causes a decrease in strength and deterioration of low-temperature toughness, so the content should be 35% or less.

N: 0.25% or less.

N is one of the important elements for increasing strength. However, if it exceeds 0.25%, the ductility and hot ductility decrease, so this is set as the upper limit.

S: 0.03% or less.

Adding S is effective in improving the machinability of high-Mn steel, which is a difficult-to-cut material, but since this S causes a decrease in ductility, it should be kept at 0.03% or less if machinability is not considered. However, it can be contained up to 0.100% in consideration of improving machinability.

Further, in the present invention, three or less of the following components can be contained.

Cr: 5.00% or less.

Cr is also an important element for increasing strength, but ・5.00%
Exceeding this will result in decreased ductility and increased cost.
The upper limit is 5.00%.

V: 0.50% or less.

(2) is also a very useful element for increasing strength, but excessive addition significantly reduces ductility and toughness, so it should be kept at 0.50% or less.

Nb: 0.30% or less.

Nb is also a useful element for increasing strength, but at 0.30%
If it exceeds this, the ductility and toughness will decrease, so this is set as the upper limit.

Mo: 3.00% or less.

Mo is also a very useful element for increasing strength, but 3.0
Addition of more than 0% reduces ductility and toughness, so 3.00
% or less.

Ti: 0.20% or less.

Ti is also an important element for increasing yield strength by 0.2%;
If it exceeds 20%, the temperature range for carbide precipitation will be expanded, so this should be the upper limit.

Ni: 3.0% or less.

Ni is effective in improving toughness, but excessive addition causes an increase in cost, so the content is set to 3.0% or less.

Ca: 0.0100% or less.

Addition of Ca is effective in improving the machinability of high Mn steel, which is a difficult-to-cut material, and sufficient machinability can be obtained even when the amount added is 0.0100% or less.

However, in the present invention, it is necessary for Mn to satisfy the following formula.

Mn(X) ≧-9,26C(%) +19.03(X
) That is, as mentioned above, both C and Mn are strong austenite stabilizing elements, and as these alloying elements increase, austenite becomes more stable and the magnetic permeability also takes on a stable value. However, when the contents of C and Mn are reduced, austenite becomes unstable, α' fumarunsite is generated, and the magnetic permeability increases. It is known that there is a temperature at which austenite begins to transform into α' fumarunsite.

A1 (χ) + 15Co (χ) - 20 Cry) -10 Cu (χ) - 39 gate n (χ) -5M
o(χ) 17Ni(χ)-35V(χ)-5W(
χ)......■ In order to obtain stable austenite even at low temperatures, the following formula (■) can be obtained from formula I.

=196≧545-361G(χ)+30AJ(Z)
+15Co(A)-20Cr(χ)-10Cu(χ
)-39Mn(χ)-5Mo(χ)17Ni($)
35V(χ)-5W(X)・・・・・・・
・ ・ ・ ■In the present invention, Co and Cu+- are not used together. In addition, Cr, Mo, Ni, and V, which act in the direction of lowering the γ→α′ Ms point (advantageous direction), are set to 0%, and Af, which increases the γ→α′ Ms point, is set to a very high value of 0.04%. Then, the above equation (2) becomes the following equation (2).

Mn ($)≧-9,26C(χ') +19.03
--...III Next, in the present invention, as a manufacturing method, the slab is heated to a temperature of 1000 to 1250'C,
This is in order to sufficiently dissolve carbides etc., and 10
If heating is performed at a temperature below 00° C., a high-Mn nonmagnetic steel with excellent performance cannot be produced even if the subsequent steps are the same as those of the present invention. Moreover, heating at a temperature exceeding 1250°C will reduce hot workability, so the temperature should be 1250°C or lower.

Furthermore, after the above-mentioned heating, the slab is subjected to hot rolling, but in the present invention, the hot rolling end temperature is set at 700 to 1
000℃. In other words, if hot rolling is finished at a temperature below 700°C, carbides will precipitate during rolling and magnetic permeability will increase, whereas hot rolling will be finished at any temperature as long as it does not exceed 1000°C. Although there is almost no difference in mechanical properties and physical properties, a hot rolling end temperature exceeding 1000° C. causes manufacturing difficulties.

In the present invention, immediately after the above-described hot rolling is completed, the material is cooled at a cooling rate of 100° C./see or lower and higher than the air cooling rate. In other words, the upper limit of the cooling rate is set to 100°C/se.
The reason for e is that the current online cooling technology is 100℃/
It is difficult to perform cooling at a cooling rate that exceeds sec, and the reason why we set the lower limit as the cooling rate for air cooling is that carbides, etc. will form in the temperature range around 600°C at a cooling rate lower than that for air cooling. This is because it may precipitate and have an adverse effect on magnetic permeability.

The present invention will be explained below using specific manufacturing examples.

That is, Table 1 below shows the chemical composition of the steels adopted by the present inventors. Steel A-D and steel 0-R have S≦0.1%, steel E
-N is S≦0.3%, steel S, T is S≦0.03
%belongs to.

However, the manufacturing methods for these steels are as shown in Table 2 below, but those with symbols ■~■ and ■~[phase] are based on conventional methods, whereas those with symbols ■~@ and [phase] ] to [phase] are all obtained by the method of the present invention.

However, Table 3 shows steels (A) to (T) that were heated to 1150°C and finished hot rolling at 1000°C, according to the conventional method under manufacturing conditions (■) shown in Table 2, and under manufacturing conditions (■■■). The mechanical properties and magnetic permeability of the steels prepared according to the method of the present invention are shown, and the yield strength, tensile strength, and yield ratio of each steel type are increased compared to those prepared using the conventional method. There is.

In other words, compared to the conventional method, the method of the present invention
0.2% yield strength is 33-35 for 24% Mn system (wire A-D)
kg/m2.7 to 9 kg for 18% Mn system (ME-N)
/m2.15%Mn system (rope 0-R) 12-15kg/m2.
m2.12%Mn system (steel S, T) 12-13kg/m
The yield ratio is 24% Mn-based (A-D
) 30-32%, 18% Mn type (E-N) 4-8%
, 15% Mn system (0-R), 11-16%, 12% Mn
It increased by 10-15% in the system (S, T). Regarding magnetic permeability, both the conventional method and the method of the present invention show stable and low values.

The following Table 4 shows the characteristics of each steel plate manufactured by the conventional method (■) and the present invention method (■■) using the above-mentioned steel A-T with a slab heating temperature of 1150°C and a hot rolling finish temperature of 900°C. A comparison is shown.

Compared to the conventional method, the method of the present invention has a 0.2% yield strength of 2
30 to 34 kgf/w” with 4% Mn system (A-D), 1
7 to 15 kgf/1m” with 8% Mn system (E-N),
12-16 krf/m'' with 15% Mn system (0-R),
The yield ratio increases by 8 to 12 kgf/1m" for the 12% Mn system (S, T). Also, the yield ratio increases for the 24% Mn system (A-D
) is 28-33%, and 18% Mn-based (ENN) is 3-12
%, 15%Mn-based (0-R) 11-16%, 12%M
n(S, T) increases by 8 to 12%, respectively.

In this case as well, both the conventional method and the method of the present invention show low and stable magnetic permeability values.

The following Table 5 shows a comparison of the characteristic values of steel sheets manufactured by conventional method ■ and method ■■00 of steels 0 to T with a slab heating temperature of 1150°C and a hot rolling end temperature of 800°C. It is.

That is, in contrast to the conventional method ■, the method of the present invention ■■ [phase] ■
0.2% yield strength is 30-35 for 24% Mn system (A-D)
kgf/ni”, l 8% Mn system (E to N) 8 to 1
7kgf/mu2.15%Mn system (0-R) 12-2
7kgf/w”, 8 to 11 with 12% Mn system (S, T)
kgf/Tsuru2 each has increased. Also, the yield ratio is 24%M
29-34% for n-based (A-D), 18% Mn-based (E-N
) 4-13%, 15% Mn-based (0-R) 13-27
% and 12% Mn-based (S, T), respectively. Furthermore, in this case as well, both the conventional method and the method of the present invention show stable and low magnetic permeability values.

Furthermore, the following Tables 6, 7, and 8 show cases where the slab heating temperature is 1050°C, and the hot rolling end temperatures are 1000, 900, and 800°C, respectively, but the strength and yield ratio are The increasing tendency is the same as in the case of heating at 1150° C., and the magnetic permeability is also a low and stable value.

"Effects of the Invention" According to the present invention as explained above, special reheating,
It is possible to produce high-Mn nonmagnetic steel with higher strength and yield ratio than the conventional method without water dust, stably, precisely, and at a lower cost, so it is industrially effective. This is a great invention.

Patent applicant: Nippon Kokan Co., Ltd. Inventor: Ono
Thoughtful Matsumoto
Wa Myodo 1
) Hisashi Kawa: H, 75 Agent Patent Attorney Shirakawa -1,”'16: Procedural amendment (voluntary)

Claims (1)

[Claims] 1. C: 1.5 wt% or less, Si: 0.8 wt% or less,
Mn: -9.26C (%)+19.03wt% or more, 3
A steel containing 5.0 wt% or less, N: 0.25 wt% or less, S: 0.03 wt% or less, with the balance consisting of Fe and unavoidable impurities is heated at 1000 to 1250°C, and then heated to 700 to 1000°C.
Hot rolling is carried out at
A method for manufacturing high strength, high yield ratio, and high manganese nonmagnetic steel, characterized by cooling at a rate of less than /sec. 2, C: 1.5 wt% or less, Si: 0.8 wt% or less,
Mn: -9.26C (%)+19.03wt% or more, 3
Contains 5.0 wt% or less, N: 0.25 wt% or less, S: 0.03 wt% or less, and Cr: 5.0 wt% or less, V: 0.5 wt% or less, Nb
: 0.3wt% or less, Mo: 3.0wt% or less, Ti:
0.2wt% or less, Ni: 3.0wt% or less, Ca: 0
．． A steel containing at most 3 of 0.01 wt% or less, with the remainder consisting of Fe and unavoidable impurities, is heated at 1000 to 1250°C, hot rolled at 700 to 1000°C, and then immediately cooled in air or above to 100°C. A method for manufacturing high strength, high yield ratio, and high manganese nonmagnetic steel, characterized by cooling at a rate of less than /sec.