JPH0472038A - Dead soft austenitic stainless steel - Google Patents

Abstract

PURPOSE:To obtain an extremely soft stainless steel maintaining high corrosion resistance and low in work hardening and tensile strength, in an austenitic stainless steel, by increasing the ratio of Ni/Cr and adding specified elements according to necessary. CONSTITUTION:This is an austenitic stainless steel having a compsn. contg., by weight, <0.05% C, <1.0% Si, <5.0% Mn, 9.0 to 15.0% Ni, 15.0 to 20.0% Cr and <0.04% N and simultaneously satisfying expressions I and IL or having a compsn., in addition to the above components, furthermore contg. one or >=two kinds among <5.0% Cu, <3.0% Mo, <l.5% Al, <0.5% Ti, <0.5% Nb, <0.5% Zr, <0.5% V, <0.03% B and <0.02% rare earth metals and simultaneous satisfying expressions III and IV. The steel has extremely soft properties of <130 hardness in HV and <55kgf/mm<2> tensile strength.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an extremely soft steel sheet that can be used in applications that require higher corrosion resistance in fields where ordinary steel or surface-treated steel sheets are used. This invention relates to austenitic stainless steel that has low work hardening and low tensile strength.

(Conventional technology) Conventionally, it has been used as a material for forming thin sheets such as automobile parts, vessels, interior and exterior panels for building materials, and interior parts.

Plain steel or surface-treated steel sheets are often used from the viewpoint of workability and economic efficiency. Recently, there has been a desire to improve the design and corrosion resistance of the materials used in these materials, and in many fields where ordinary steel or surface-treated steel sheets are used, stainless steel is being used as the material.

However, austenitic stainless steel such as 5IIS304 is harder and more work hardened than low carbon ordinary steel. For example, 1. Common cold-rolled steel sheets and strips (JIS G3141), which are typical materials for forming thin sheets.
The hardness (HV) is 115 or less under standard heat treatment.

Whereas the tensile strength is said to be 28Kgf/■■2 or more.

5US304 has a hardness (HV) of 20 in the solution heat treated state.
It is specified that the tensile strength is 0 or less and 53 kgf/am or more (JIS G4307), and the hardness (IV) of commercially available steel for boat fishing is around 160.

The tensile strength is at a level of around 70Kgf/■-1.

Therefore, although austenitic stainless steel has better corrosion resistance than ordinary steel, it has higher hardness than ordinary cold-rolled steel sheet, and has a higher tensile strength and greater work hardening. Physical characteristics are a major barrier to material change. In fact, when austenitic stainless steel is processed using processing equipment such as a press machine intended for processing soft ordinary steel or surface-treated steel sheets, there are problems such as the inability to obtain a desired shape.

Furthermore, even in fields where stainless steel has traditionally been used, for example, in processing during construction of roofing materials, etc., due to its high hardness and tensile strength.

Currently, it is difficult to process, and materials that are softer and have less work hardening are often desired.

Under these circumstances, an example of conventional austenitic stainless steel that was made softer was the Japanese Patent Publication No. 51-29085.
There is a publication, C: less than 0.02%, Si: 0.1
% and other Mn, P, S, A1. By reducing impurity elements such as Ti, the HV is around 100.

Steel with tensile strength properties of around 50 Kgf/am' has been obtained.

[Problem that the invention seeks to solve]

However, when reducing impurity elements in this way,
From the viewpoint of material properties, hardness decreases due to reduction in solid solution strengthening of the matrix, but decreasing the impurity elements C and N decreases the stability of the austenite phase, increasing work hardening and increasing tensile strength. Problems arise in that the strength increases and the bending workability and spatula drawing workability decrease. Further, if the Si content is lowered to less than 0.1%, the oxygen concentration in the steel will increase, resulting in an increase in nonmetallic inclusions, which will significantly reduce the cleanliness of the steel. In other words, it is difficult to produce soft austenitic stainless steel that has good cleanliness.

[Facts discovered by the inventors]

The present inventors investigated the softening of austenitic stainless steel from the perspective of a decrease in tensile strength as an index of decrease in hardness and work hardening, and investigated the chemical composition of austenitic stainless steel and the mechanical properties of cold-rolled steel strips. We systematically investigated the relationship between physical properties and quantified the relationship between hardness, tensile strength, and components, and obtained the following findings.

(1) In order to reduce the hardness, C+
In addition to reducing impurity elements such as N+St, P+S, AI, and Ti, reducing Cr and increasing Ni, which are essential elements for austenitic stainless steel3.
Furthermore, it is extremely effective to add Cu and Mn.

(2) To lower the tensile strength (work hardening), use Ni
It is extremely effective to increase the amount of copper and add Cu and Mn.

[Structure of the Invention] The present invention is based on the above findings, and is expressed in weight percent.

C; 0.05% or less Si; 1.0% or less Mn; 5.0% or less Ni; 9.0% or more and 15.0% or less Cr; 15.0% or more and 20.0% or less N, 0.
04% or less.

and, in some cases, further.

Cu: 5.0% or less.

Mo; 3.0% or less A　　　　　　　1.5% or less Ti: 0.5% or less.

Nb; 0.5% or less Zr; 0.5% or less V; 0.5% or less B; 0.03% or less REM; Contains any one or two or more of 0.02% or less, the remainder This is an austenitic stainless steel consisting of impurities and Fe that are inevitably mixed in, and the extremely soft austenitic stainless steel is prepared by adjusting these components so that the following formulas (■) and (■) are simultaneously satisfied. .

K=20.5+13. Ox C+0.99x 5i-
1,1X Mn -Ni÷0.4X Cr 0.4X
Cu+117. IX N≦19,5H=27.1+60
．． 9x C+0.26X Si-Ni+0.68x
CrO, 79X Cu+52.6X N≦29-
■ [Function] In the range where the steel has a chemical composition that satisfies both formula (■) and formula 0, it exhibits extremely softness, that is, hardness (
) IV) is 130 or less and the tensile strength is 55Kgf/mm”
The following austenitic stainless steels can be obtained:

The actions and reasons for limiting the content of each component in the steel of the present invention are approximately as follows.

C is an extremely effective austenite-forming element, and increasing the amount added stabilizes the austenite phase, but if it is included in a large amount, it becomes hard due to solid solution strengthening, so it should be kept at 0.05% or less.

St is an effective element as a deoxidizing agent, and from the viewpoint of softness, the lower the value, the better.If added in excess of 1.0%, the hardness and tensile strength will increase, so the upper limit is 1.0%.
%.

Although the hardness and tensile strength of Mn decrease as the amount is increased, even if it is added in an amount exceeding 5.0%, these effects will not increase (the upper limit is set at 5.0%).

Ni is an essential element in austenitic stainless steel, and in order to sufficiently lower the hardness and tensile strength, it is preferable to contain a large amount of Ni, at least 9
．． 0% or more is required. The upper limit number is 15 considering economic efficiency.
%.

From the viewpoint of corrosion resistance, it is preferable to add 15% or more of Cr. However, from the viewpoint of softening, if too large a content is contained, the hardness will increase, so the content should be 20% or less.

N is an extremely effective austenite-forming element, and increasing the amount added stabilizes the austenite phase. However, if the content exceeds 0.04%, hardness increases due to solid solution strengthening and surface quality deteriorates. 0.0 to invite
4% or less.

Cu is an austenite-forming element and is an extremely effective element that reduces hardness and work hardening, and reduces tensile strength. However, if added in excess of 5%, hot workability deteriorates and edge breakage occurs, so the content should be 5% or less.

When the amount of Mo added increases, corrosion resistance is improved.

However, if added in large amounts, the hardness increases, so 3.0
% or less.

A+ is an effective element for deoxidizing during steel manufacturing, especially Ti and Z.
It is added as a deoxidizing agent immediately before adding r to lower the oxygen concentration in molten steel, which is effective for improving and stabilizing the yield of Ti and Zr. However, AI is 1 due to solid solution strengthening.
．． Adding more than 5% increases hardness, so 1.5
% or less.

Ti, Nb, V, and Zr are added for the purpose of making crystal grains finer and preventing roughness after molding.

The effect is saturated even if the amount is added in excess of 0.5%, so the amount should be 0.5% or less.

B is an element that improves hot workability and is effective in preventing hot cracking, but when added in excess of 0.03%, it not only deteriorates hot workability but also reduces intergranular corrosion resistance. The content should be 0.03% or less because it deteriorates the properties.

Like B, REM is an effective element for improving hot workability, but if it is added in an amount exceeding 0.02%, no improvement in the effect can be expected, so it is limited to 0.02% or less.

In addition to the above individual component regulations, in order to obtain an austenitic stainless steel with low hardness, low work hardening, and low tensile strength, it is necessary to
．． It is important to limit the components so that it is 5 or less and the H value according to formula (2) is 29. This point will be concretely illustrated by the test results below.

12 types of steel within the chemical composition range shown in Table 1 (floor 1 to m
12) These steel pieces were hot rolled at an extraction temperature of 1220°C to obtain a hot rolled steel strip having a thickness of 3.8 mm. This hot-rolled steel strip was subjected to hot-rolled plate annealing and pickling at 1100°C x soaking for 1 minute, and then cold-rolled to a thickness of 1.5m.
Intermediate annealing and pickling at 1050℃ x soaking for 1 minute,
Further, it was finish rolled to a temperature of 0.7 mm, finish annealed at 1050°C for 1 minute, and pickled. Samples were taken from each material and their Vickers hardness (MV) and tensile strength (T
S) was investigated. The results are shown in Table 1.

In addition, FIG. 1 shows the relationship between the value and hardness of each sample material.

It can be seen that the hardness increases with increasing value. In order to prevent the hardness from exceeding 130, it is necessary to set the value to 19.5 or less. Furthermore, FIG. 2 shows the relationship between the H value and tensile strength of each sample material. It can be seen that the tensile strength increases as the H value increases. Tensile strength is 55Kgf/am”
In order not to exceed this value, it is necessary to make the H value 29 or less.

[Example] Table 2 shows the invention I (k13 to k23) and comparative steel (k13 to k23).
4 to Nα29) and conventional # (Nα30 to 32), and the values and H values of each sample material calculated from 2 and 3 are also shown.

In the steels of the present invention, those with reduced impurity elements of C, Si, Mn, P, S, and N (steel NQ13), those with further addition of Cu (steel N1114, 15),
Furthermore, Ti.

Added Nb, Zr, A, l (14k16.17
), and increasing each impurity component in consideration of manufacturability,
Those added with Cu (rope devices 8 to 22), and further V,
A steel to which Mo was added (steel No. 23) was used.

The comparative steel contains C, Si, and MnP as well as the steel of the present invention 13.
, S, and N impurity elements, each component satisfies the range specified in the present invention, and the H value does not exceed 19.5 but the H value exceeds 29 (grade 24 and grade 25) and Those in which C, Si, Ni, and N did not satisfy the respective ranges specified in the present invention (Hagane Sosu 26 to 29) were used.

Conventional steel Niha 5tlS304 (fik30), 5tlS
304 straight steel Ha 31 ) and 5US305 (Steel 32) were used.

Austenitic steel containing these components.

Steel strips were melted and hot-rolled from these steel pieces at an extraction temperature of 1220°C to obtain a 3.8ml 11O hot-rolled strip.

This hot steel strip was subjected to hot-rolled board annealing and pickling at 1100°C for 1 minute at soaking temperature, then cold rolled to a thickness of 1.5Il and intermediate annealing and pickling at 1050°C for 1 minute at soaking temperature. Finish rolling to 0.7mm, 1050'c
The hardness and tensile strength of the specimens subjected to final annealing and pickling for 1 minute were investigated. The results are also listed in Table 2.

As seen in the results in Table 2, the present invention al! 113~
All of the steels No. 23 have a hardness (l(V)) of 130 or less and a tensile strength of 55 Kgf/ms" or less, making them extremely soft. In addition, no surface flaws were observed, indicating good manufacturing. It has a sexual nature.

On the other hand, comparative steels 24 and 25 have hardness (HV
) is below 130, but the tensile strength is 55K.
gf/n+m" or higher, indicating large work hardening. Comparison w4Nct26 to 29 are all wires that do not satisfy the requirements of the present invention, but comparison fiNo. 26
Although No. 27 satisfied the hardness of 130 or less, the tensile strength was as high as 60 Kgf/+m'' or more and the work hardening was large.

Comparative jllNa28 and 29 had high hardness and tensile strength, and had not been softened. Conventional 11ii1 30~
All of No. 32 are hard and have high hardness and tensile strength.

〔effect〕

As described above, by adjusting the components of austenitic stainless steel according to the present invention, it has extremely low hardness that cannot be obtained with conventional austenitic stainless steel.
Furthermore, extremely soft austenitic stainless steel with low tensile strength and small work hardening can be obtained without impairing manufacturability. As a result, the steel of the present invention has the following characteristics: 5
It can be used in fields where austenitic stainless steel, represented by US304, is harder than ordinary steel and cannot be used because of its large work hardening and high tensile strength.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the hardness of a cold rolled steel strip and FIG. 2 is a diagram showing the relationship between the tensile strength and H value of a cold rolled steel strip.

Claims (2)

[Claims] (1) In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 5.0% or less, Ni: 9.0% or more and 15.0% or less, Cr: 15.0% 20.0% or less, N: 0.04% or less, the balance is Fe and unavoidably mixed impurities, and the chemical composition satisfies the following formulas [1]' and [2]' at the same time. An extremely soft austenitic stainless steel having a hardness (HV) of 130 or less and a tensile strength of 55 kgf/mm^2 or less. K=20.5+13.0×C+0.99×Si−1.1
×Mn-Ni+0.4×Cr+117.1×N≦19.
5...[1]'H=27.1+60.9×C+0.26
×Si-Ni+0.68×Cr+52.6×N≦29・
・[2]′ (2) In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 5.0% or less, Ni: 9.0% or more and 15.0% or less, Cr: 15.0% 20.0% or less, N: 0.04% or less, Cu: 5.0% or less, Mo: 3.0% or less, Al: 1.5% or less, Ti: 0.5 % or less, Nb: 0.5% or less, Zr: 0.5% or less, V: 0.5% or less, B: 0.03% or less, REM: 0.02% or less, or one of the following. Contains two or more types, the remainder consists of Fe and unavoidably mixed impurities, and the following [1]
and has a chemical composition that satisfies formula [2] at the same time, has a hardness (HV) of 130 or less and a tensile strength of 55 kgf/mm.
Extremely soft austenitic stainless steel of ^2 or less. K=20.5+13.0×C+0.99×Si−1.1
×Mn-Ni+0.4×Cr-0.4×Cu+117.
1×N≦19.5...[1]H=27.1+60.9×
C+0.26×Si-Ni+0.68×Cr-0.79
×Cu+52.6×N≦29...[2]