KR102570524B1 - Austenitic stainless steel with improved corrosion resistance and machinability and method for manufacturing the same - Google Patents

Abstract

An austenitic stainless steel with improved corrosion resistance and machinability is disclosed.
The austenitic stainless steel with improved corrosion resistance and machinability according to the present invention contains, by weight, C: 0.05% or less (excluding 0), Si: more than 0 2%, Mn: more than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo: greater than 0 3%, N: 0.15 to 0.25%, B: 0.004 to 0.06%, the balance including Fe and unavoidable impurities.

Description

Austenitic stainless steel with improved corrosion resistance and machinability and manufacturing method thereof

The present invention relates to austenitic stainless steel with improved corrosion resistance and machinability and a method for manufacturing the same, and more particularly, austenitic stainless steel with improved corrosion resistance and machinability that requires machinability and can be used in a corrosive environment such as salt water, and It is about its manufacturing method.

Austenitic stainless steel used for machine parts such as frames, chambers, molds, etc. is manufactured into final shapes through cutting processes such as milling. In order to reduce cutting load during cutting, improve cutting speed, and improve tool life, the machinability of stainless steel materials is required.

As a stainless steel with excellent machinability, a steel type having improved machinability by adding Mn and S to the steel and utilizing a MnS compound, which is a non-metallic inclusion, is widely known. However, since MnS compounds are easily eluted in corrosive environments such as salt water or become the starting point of generating pitting and deteriorate the corrosion resistance of stainless steel, stainless steel using MnS compounds is exposed to corrosive environments and its use is limited in applications requiring corrosion resistance. there is a problem. Accordingly, there is a demand for the development of stainless steel capable of ensuring machinability and corrosion resistance at the same time.

One aspect of the present invention is to provide an austenitic stainless steel with improved corrosion resistance and machinability and a manufacturing method thereof.

Austenitic stainless steel with improved corrosion resistance and machinability according to an embodiment of the present invention, by weight, C: 0.05% or less (excluding 0), Si: more than 0 2%, Mn: more than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo: greater than 0 3%, N: 0.15 to 0.25%, B: 0.004 to 0.06%, including the remainder Fe and unavoidable impurities, BN precipitation More than 10 phases / 100x100μm ² are distributed.

In addition, according to an embodiment of the present invention, 10 MnS precipitated phases / 100x100 μm ² or less may be distributed.

In addition, according to an embodiment of the present invention, 10 MnS precipitated phases having a long axis length of 1 μm or more may be distributed in 10 / 100×100 μm ^{2 or} less.

In addition, according to one embodiment of the present invention, Cu: may further include more than 0 1%.

Also, according to an embodiment of the present invention, the pitting potential may be 300 mV or more.

Method for manufacturing austenitic stainless steel with improved corrosion resistance and machinability according to an embodiment of the present invention, in weight %, C: 0.05% or less (excluding 0), Si: more than 0 2%, Mn: more than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo: greater than 0 3%, N: 0.15 to 0.25%, B: 0.004 to 0.06%, remaining Fe and unavoidable impurities heating at 1,150 to 1,250 ° C. for 1 hour and 30 minutes or more; hot-rolling the heated slab; and holding the rolled material at 1,100 to 1,250° C. for 30 seconds or longer.

The austenitic stainless steel with improved corrosion resistance and machinability according to an embodiment of the present invention can secure both corrosion resistance and machinability.

1A and 1B are photographs showing appearances after hot rolling of Example 7 and Comparative Example 2, respectively.
2a and 2b are photographs of cross sections of stainless steels of Example 7 and Comparative Example 1 observed by SEM, respectively.

This specification does not describe all elements of the embodiments, and general content or overlapping content between the embodiments in the technical field to which the present invention pertains will be omitted.

In addition, when a certain component is said to "include", this means that it may further include other components without excluding other components unless otherwise stated.

Expressions in the singular number include plural expressions unless the context clearly dictates otherwise.

Hereinafter, the present invention will be described in detail.

The following examples are presented to sufficiently convey the spirit of the present invention to those skilled in the art. The present invention may be embodied in other forms without being limited only to the embodiments presented here.

In the present invention, the formation of MnS, which causes deterioration in corrosion resistance, was excluded, so that the MnS precipitate phase was not formed. In addition, it was intended to introduce a BN compound to improve cutting properties by replacing MnS.

However, since the addition of B in excess of the appropriate level causes a problem in which breakage occurs during hot rolling to produce a plate, the inventors of the present invention suppress breakage during hot rolling through various experiments and obtain a level effective for improving machinability. Optimized contents of B, N and other elements for BN formation were found.

Austenitic stainless steel with improved corrosion resistance and machinability according to an embodiment of the present invention, by weight %, C: 0.05% or less (excluding 0), Si: more than 0 2%, Mn: more than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo: greater than 0 3%, N: 0.15 to 0.25%, B: 0.004 to 0.06%, the balance Fe and unavoidable impurities.

In addition, Cu: may further include more than 0 1%.

Hereinafter, the reason for limiting the numerical value of the alloy component element content in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.

The content of C is greater than zero and 0.05%.

C is an austenite forming element and an element that acts as an unavoidable impurity. If the content of C exceeds 0.05%, the corrosion resistance of the welded part may be impaired, so the content of C is limited to 0.05%.

The content of Si is greater than 0 and 2%.

Si is an element that can be added as a deoxidizer and improve corrosion resistance. However, when the Si content exceeds 2%, the toughness may be impaired, so the Si content is limited to 2% or less.

The content of Mn is greater than 0 and 2%.

Mn is an austenite stabilizing element. However, if the Mn content exceeds 2%, corrosion resistance may be impaired, so the Mn content is limited to 2% or less.

The content of S is 0.01% or less.

S is limited to 0.01% or less in order to prevent the formation of MnS to be excluded in the present invention.

The content of Cr is 16 to 22%.

Cr is an element that improves corrosion resistance of austenitic stainless steel. When the Cr content is less than 16%, it is difficult to exhibit the above-mentioned effects, and when the Cr content exceeds 22%, the raw material cost may increase and the toughness may be deteriorated. Therefore, in the present invention, the Cr content is limited to 16 to 22%.

The content of Ni is 9 to 15%.

Ni is an austenite stabilizing element. If the Ni content is less than 9%, the above-mentioned effect is difficult to exhibit, and if the Ni content exceeds 15%, the raw material cost increases. In the present invention, the Ni content is limited to 9 to 15%.

The content of Mo is greater than 0 and 3%.

Mo is an element that improves corrosion resistance. However, when the content of Mo exceeds 3%, it causes an increase in raw material cost. Therefore, in the present invention, the content of Mo is limited to 3%.

The content of B is 0.004 to 0.06%.

B is an element added to secure BN. If the content of B is less than 0.004%, sufficient BN targeted in the present invention cannot be formed, and if the content of B exceeds 0.06%, fracture occurs during hot rolling. Therefore, in the present invention, the content of B is limited to 0.004 to 0.06%.

The content of N is 0.15 to 0.25%.

N is an element added to secure BN. When the B content is less than 0.15%, sufficient BN cannot be formed, and when the B content exceeds 0.25%, the toughness of the steel is deteriorated. Therefore, in the present invention, the N content is limited to 0.15 to 0.25%.

The content of Cu is greater than 0 and 1%.

Cu is an element that improves corrosion resistance and is added as needed in the present invention. However, when the content of Cu exceeds 1%, since hot workability may be deteriorated, the content of Cu is limited to 1% in the present invention.

The balance other than the alloy composition is Fe. The austenitic stainless steel with improved corrosion resistance and machinability of the present invention may contain other impurities that may be included in a typical industrial production process of steel. Since these impurities can be known by anyone having ordinary knowledge in the art to which the present invention belongs, the type and content are not particularly limited in the present invention.

In the austenitic stainless steel according to the present invention, 10 MnS precipitated phases having a major axis size of 1 μm or more are distributed in an arbitrary cross section / 100×100 μm ² or less. At this time, the MnS precipitated phase may include 50 at.% or more of the sum of Mn and S.

In the present invention, since the formation of MnS that causes deterioration of corrosion resistance is suppressed, corrosion resistance can be secured, and the pitting potential of the austenitic stainless steel according to the present invention can be 300 mV or more.

In the austenitic stainless steel according to the present invention, 10/100x100μm ² or more of BN precipitation phases are distributed in any cross section. In this case, the BN precipitated phase may include 50 at.% or more of the sum of B and N. In the present invention, since MnS is replaced with BN, it is possible to secure cutability while suppressing deterioration of corrosion resistance.

Next, a method for manufacturing austenitic stainless steel with improved corrosion resistance and machinability according to an embodiment of the present invention will be described.

The austenitic stainless steel with improved corrosion resistance and machinability according to the present invention can be manufactured by various methods, and the manufacturing method is not particularly limited. However, as an example, it may be manufactured by the following method.

For example, in weight percent, C: 0.05% or less (excluding 0), Si: greater than 0 2%, Mn: greater than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 9% 15%, Mo: greater than 0 3%, N: 0.15 to 0.25%, B: 0.004 to 0.06%, the remainder Fe and unavoidable impurities are heated at 1,150 to 1,250 ° C. for 1 hour and 30 minutes or longer; hot-rolling the heated slab; and holding the rolled material at 1,100 to 1,250° C. for 30 seconds or longer.

At this time, the heating step is a process for forming as many BNs as possible, and may be performed at 1,150 to 1,250 ° C. for 1 hour and 30 minutes or more.

In addition, hot rolling may be performed up to a thickness of 8 mm, but the thickness may vary depending on the use, so it is not limited thereto.

In addition, the maintaining step after hot rolling is a process for forming BN again, and may be performed at 1,100 to 1,250 ° C. for 30 seconds or more.

Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is only for exemplifying the practice of the present invention, and the present invention is not limited by the description of these examples. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

embodiment

An alloy satisfying the alloy composition of Table 1 was melt-cast, and the austenitic stainless steel cast was heated at 1,200° C. for 1 hour and 30 minutes. Thereafter, the heated cast steel was hot rolled to a thickness of 8 mm. Subsequently, the hot-rolled material was maintained at a temperature of 1,150° C. for 30 seconds or more to form a BN precipitated phase, thereby obtaining a hot-rolled material specimen.

division Alloy element (% by weight) C Si Mn S Cr Ni Mo B N Comparative Example 1 0.020 0.6 1.1 0.003 16.2 10.1 2.1 0.000 0.015 Comparative Example 2 0.020 0.6 1.1 0.003 16.2 10.2 2.1 0.031 0.018 Comparative Example 3 0.025 0.4 0.8 0.008 21.3 14.6 0.6 0.012 0.020 Comparative Example 4 0.018 0.6 1.5 0.240 17.4 10.9 2.0 0.001 0.023 Comparative Example 5 0.018 0.6 1.3 0.180 17.5 10.8 2.1 0.001 0.017 Comparative Example 6 0.022 0.4 0.8 - 21.4 9.3 0.6 0.001 0.210 Example 1 0.022 0.4 0.8 0.002 21.1 9.2 0.6 0.013 0.210 Example 2 0.027 0.4 0.8 0.002 21.8 9.3 0.6 0.058 0.200 Example 3 0.025 0.4 0.8 0.008 21.3 14.6 0.6 0.029 0.200 Example 4 0.022 0.4 0.8 0.002 19.2 12.3 0.6 0.004 0.200 Example 5 0.025 0.4 0.8 0.001 19.2 12.3 0.6 0.007 0.200 Example 6 0.024 0.4 0.8 0.003 19.4 12.3 0.6 0.014 0.160 Example 7 0.026 0.4 0.8 0.002 19.3 12.4 0.6 0.020 0.240 Example 8 0.025 0.4 0.8 0.002 19.3 12.3 0.6 0.028 0.200 Example 9 0.048 1.5 1.8 0.001 16.4 12.1 1.5 0.007 0.210 Example 10 0.022 1.8 1.5 0.001 16.3 12.1 2.6 0.008 0.200

For the hot-rolled specimens of Examples 1 to 10 and Comparative Examples 1 to 7, whether or not plate breakage occurred after hot rolling was observed, and the case where breakage occurred was designated as ○, and the case where it did not occur was designated as X in Table 2 below.

division Fracture during hot rolling Comparative Example 1 X Comparative Example 2 ○ Comparative Example 3 ○ Comparative Example 4 X Comparative Example 5 X Comparative Example 6 X Example 1 X Example 2 X Example 3 X Example 4 X Example 5 X Example 6 X Example 7 X Example 8 X Example 9 X Example 10 X

Referring to Table 2, Examples 1 to 10 satisfying the alloy composition of the present invention did not cause fracture during hot rolling. However, in Comparative Example 2, the content of B was satisfactory, but the content of N did not reach the lower limit proposed in the present invention, and thus fracture occurred during hot rolling.

1A and 1B are photographs showing appearances after hot rolling of Example 7 and Comparative Example 2, respectively. Referring to FIG. 1A , it can be confirmed that the appearance of the steel sheet in Example 2 according to the present invention is good without fracture. On the other hand, referring to FIG. 1B, it can be confirmed that Comparative Example 2 had a satisfactory content of B, but the content of N did not reach the lower limit proposed in the present invention, and thus plate breakage occurred during hot rolling.

Although the content of B in Comparative Example 3 was satisfactory, the content of N did not reach the lower limit proposed in the present invention, and fracture occurred during hot rolling.

Subsequently, BN and MnS precipitates were observed for the hot-rolled specimens of Comparative Examples 1 and 4 to 6 and Examples 1 to 10, which were not broken during hot rolling, and corrosion resistance and machinability were evaluated, and are shown in Table 3 below.

For BN and MnS precipitates, the number of MnS precipitates of 1 μm or more per 100x100 μm ² and the number of BN precipitates per 100x100 μm ² were measured by mirror polishing the arbitrary cut surface of the plate, and then the number of BN precipitates was measured using a scanning electron microscope equipped with an energy dispersive spectrometer (EDS). (Scanning Electron Microscope, SEM) was observed, and the number was shown.

Corrosion resistance was evaluated by pitting potential. The pitting potential is measured by immersing a hot-rolled steel specimen in an aqueous solution containing 3.5wt% NaCl, connecting the electrodes, and applying voltage to gradually increase the voltage from the natural potential. The voltage at the point when the current reaches 0.1mA is measured showed up

The machinability was evaluated by measuring the cutting load torque under the conditions of cutting depth of 2 mm, cutting thickness of 5 mm, and end mill rotational speed of 2,000 rpm when cutting using an end mill. However, since the cutting environment may change, the torque of Comparative Example 1 is shown as a reference (100%). Since the maximum value of 1,000 mV is obtained in the experimental method of the present invention, the potential value above that is expressed as 1,000 mV.

division per 100x100μm ²
1μm or more
MnS count per 100x100μm ²
BN count official vanguard
(mV) cutting load
(%) Comparative Example 1 - - 550 100 Comparative Example 4 35 - 2 82 Comparative Example 5 15 - 50 80 Comparative Example 6 - - 1,000 105 Example 1 - 40 1,000 91 Example 2 - 205 1,000 81 Example 3 - 90 1,000 85 Example 4 - 11 1,000 94 Example 5 - 20 651 91 Example 6 - 54 510 90 Example 7 - 88 453 86 Example 8 - 150 329 84 Example 9 - 15 372 92 Example 10 - 21 567 93

Referring to Tables 2 and 3, Examples 1 to 10 satisfying the alloy composition of the present invention do not form MnS precipitates, so the pitting potential is 300 mV or more and corrosion resistance is good, and BN precipitates are cut to 11 or more per 100x100 μm ² It can be confirmed that the load was also lower than that of Comparative Example 1, and the cutting ability was also secured. FIGS. 2A and 2B are SEM photographs of cross sections of stainless steels of Example 7 and Comparative Example 1, respectively. Referring to FIG. 2A , it can be confirmed that in Example 7 according to the present invention, a large amount of BNs to be implemented in the present invention are formed. On the other hand, referring to FIG. 2B , it can be confirmed that Comparative Example 1 did not form BN because conditions for forming BN were not formed. Some visible black areas appear to be oxide rather than BN.

On the other hand, Comparative Example 1 had good corrosion resistance with a pitting potential of 550 mV because MnS was not formed, but BN was not formed because B was not added, and the cutting load was inferior to that of Example.

In Comparative Example 4, MnS was formed and the cutting load was low, but the content of N did not reach the lower limit proposed in the present invention, so sufficient BN was not formed and corrosion resistance was inferior.

In Comparative Example 5, MnS was formed and the cutting load was low, but the content of B and N did not reach the lower limit proposed in the present invention, so sufficient BN was not formed and corrosion resistance was inferior.

Comparative Example 6 had good corrosion resistance with a pitting potential of 1000 mV because MnS was not formed, but the cutting load was inferior because the content of B did not reach the lower limit proposed in the present invention.

The present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible without departing from the concept and scope of the claims described below.

Claims (6)

In weight percent, C: 0.05% or less (excluding 0), Si: greater than 0 2%, Mn: greater than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo : more than 0 3%, N: more than 0.15% and less than 0.25%, B: 0.004 to 0.06%, including the remainder Fe and unavoidable impurities,
10 BN precipitation phases / 100x100μm ² or more are distributed,
An austenitic stainless steel with improved corrosion resistance and machinability, with 10 MnS precipitated phases with a length of 1 μm or more in the long axis distributed less than 10 / 100x100 μm ² . delete delete According to claim 1,
Cu: An austenitic stainless steel with improved corrosion resistance and machinability further containing more than 0 and 1%. According to claim 1,
official position,
Austenitic stainless steel with improved corrosion resistance and machinability over 300mV. In weight %, C: 0.05% or less (excluding 0), Si: greater than 0 2%, Mn: greater than 0 2%, S: 0.01% or less, Cr: 16 to 22%, Ni: 9 to 15%, Mo : more than 0 3%, N: more than 0.15% and not more than 0.25%, B: 0.004 to 0.06%, the remaining Fe and unavoidable impurities are heated at 1,150 to 1,250 ° C. for 1 hour and 30 minutes or more;
hot-rolling the heated slab; and
Austenitic stainless steel manufacturing method with improved corrosion resistance and machinability comprising; maintaining the rolled rolling material at 1,100 to 1,250 ° C for 30 seconds or more.