JP3601749B2 - High strength, free cutting ferritic stainless steel - Google Patents

Description

【００２５】
【表２】

【００２６】
表２に示すように、請求範囲外の比較鋼は、熱間加工性、０．２％耐力、引張強度、被削性、耐食性のいずれかに問題があることがわかる。
【００２７】
【発明の効果】
以上の説明の通り、本発明は、製造性、耐食性の低下を極力抑え、強度を向上させたフェライト系快削ステンレス鋼が提供でき、家電、ＯＡ機器等の電気製品やその他の切削部品で、高い応力を受ける部品等に最適である。[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention can be used for electric appliances such as home appliances and OA equipment and other cutting parts, which are used under high stress.
[0002]
[Prior art]
Conventional ferritic free-cutting stainless steel has excellent machinability, but is not used as a part that receives high stress, because it does not achieve significant improvement in strength and strength due to work hardening and quenching. Was.
[0003]
[Problems to be solved by the invention]
The present invention provides a ferritic free-cutting stainless steel having improved strength while securing conventional manufacturability.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the stainless steel according to the present invention contains, by weight%, C: 0.03% or less, N: 0.05% or less (C + N ≦ 0.060%), and Si: 2.0% or less. , Mn: 2.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Cr: 16.0 to 25.0%, Mo: 1.7 to 3.0%, S: 0.50% or less, Pb: 0.30% or less, Se: 0.30% or less (however, S + Pb + Se ≧ 0.15%), Te: 0.15% or less, Ca: 0.03% or less Nb + Ta: 1.0% or less, Ti: 1.0% or less, V: 1.0% or less, W: 1.0% or less, Al: 1.0% one or more in the following amounts, is contained in a weight percent of 5 times or more of the N, having the composition and the balance Fe, 0.2% proof stress 421MPa or more Wherein the 551MPa or less. (Claim 1)
[0005]
The present invention may further contain one or two kinds of B: 0.001 to 0.02% and Mg: 0.001 to 0.02%. (Claim 2)
[0006]
The reasons for limiting the component range of the present invention will be described.
[0007]
C: 0.03% or less C is a typical solid-solution strengthening element, but it is preferable that C is low because it has a great harm such as lowering of corrosion resistance and room temperature toughness. However, in order to increase the production cost, it is necessary to consider refining technology in order to increase the production cost, and the upper limit is set to 0.03%.
[0008]
N: 0.05% or less N is a typical solid solution strengthening element, but N is desirably low because it has a great harm in lowering corrosion resistance and room temperature toughness. However, in order to increase the production cost, it is necessary to take refining technology into consideration. The sum of C and N is set to C + N ≦ 0.060% due to the above-mentioned problem.
[0009]
Si: 2.0% or less Si is a solid solution strengthening element, and its addition amount may be adjusted as necessary to improve the strength. However, since the addition exceeding 2.0% lowers the hot workability, the upper limit is set to 2.0%.
Mn: 2.0% or less Mn is an element that forms a compound with S and Se and has an auxiliary role of improving machinability. In addition, hot workability is improved to suppress grain boundary segregation of S and Se. However, in the case of stainless steel, Cr forms a compound with S and Se, and the range does not need to be strictly limited in order to suppress grain boundary deflection of S and Se. However, the addition of more than 2.0% lowers the corrosion resistance and promotes the formation of an austenite phase, so the upper limit was made 2.0%.
[0011]
Cu: 1.0% or less Cu contributes to the improvement of corrosion resistance, but is an austenite-forming element and makes the ferrite phase unstable, so the upper limit was made 1.0%.
[0012]
Ni: 1.0% or less Ni contributes to the improvement of corrosion resistance, but is an austenite-forming element and makes the ferrite phase unstable, so the upper limit was made 1.0%.
[0013]
Cr: 16.0 to 25.0%
Cr is an element indispensable for securing corrosion resistance, and it is necessary to add 16.0% or more in order to provide sufficient corrosion resistance. Was set to 15.0% to 25.0%.
[0014]
Mo: 3.0% or less Mo is a solid solution strengthening element and improves the strength. Further, the amount of addition may be adjusted as needed to improve the corrosion resistance. However, since the addition exceeding 3.0% lowers the hot workability, the upper limit is set to 3.0%.
[0015]
S: 0.50% or less S is a free-cutting element and mainly forms (Mn, Cr) S in steel to improve the cutting ability of chips and extend tool life. However, the addition exceeding 0.50% significantly reduces hot workability, so the upper limit is made 0.50%.
[0016]
Pb: 0.30% or less Pb is a free-cutting element, and Pb alone is dispersed in the steel, and the tool life is extended by lubrication between the tool and the chip. However, addition exceeding 0.30% significantly reduces hot workability, so the upper limit is made 0.30%.
[0017]
Se: 0.30% or less Se is a free-cutting element and mainly forms (Mn, Cr) Se in steel to improve the cutting ability of chips and extend tool life. However, addition exceeding 0.30% significantly reduces hot workability, so the upper limit is made 0.30%. If the total amount of S, Pb, and Se is less than 0.15%, sufficient machinability cannot be obtained, so that the sum of S, Pb, and Se is 0.15% or more.
[0018]
Te: 0.15% or less Te spheroidizes sulfides and selenides in S, Se-based free-cutting stainless steel, reduces anisotropy in material strength, and improves workability and machinability. . However, if it exceeds 0.15%, the effect is saturated, so the upper limit is made 0.15%. It is not necessary to add Pb to plain free-cutting stainless steel.
[0019]
Ca: 0.03% or less Ca is an element that improves machinability. However, the addition of a large amount deteriorates the yield due to the formation of oxides, so the upper limit is made 0.03%.
[0020]
Nb + Ta: 1.0% or less, Ti: 1.0% or less, V: 1.0% or less, W: 1.0% or less, Al: 1.0% or less Nb + Ta, Ti, V, W, Al It is a solid solution strengthening element, and the strength is improved by adding one or two or more of them as needed to 1.0% or less. However, since these elements easily form nitrides, the effect is small when added in a small amount, and may be softened in some cases. Therefore, the total amount of these elements must be at least 5 times the weight percentage of nitrogen.
[0021]
B: 0.001 to 0.02%, Mg: 0.001 to 0.02%
B and Mg are elements that improve hot workability. If the effect is less than 0.001%, the effect is small, and if it exceeds 0.02%, the hot workability is adversely affected. Therefore, the range is made 0.001 to 0.02%.
[0022]
【Example】
Next, in order to further clarify the features of the present invention, examples thereof will be described in detail below. After smelting those having the chemical components shown in Table 1 in a 50 kg high frequency induction furnace, they were cast into 50 kg steel ingots, and grease test specimens were collected. Subsequently, the remaining steel piece was forged into a square bar having a side of 60 mm and a round bar having a diameter of 20 mm, and subjected to heat treatment of heating and cooling at 780 ° C. × 4 Hr. Salt spray specimens were collected.
[0023]
Here, in the grease test, a test piece of M6 × 110 l was sampled, heated to a desired temperature in 100 sec, pulled at a rate of 2 in / sec after holding for 60 sec. The hot working was judged to be good when the temperature range where the aperture value was 60% or more at that time was 200 ° C. or more. In the tensile test, a 0.2% proof stress and tensile strength at room temperature were measured using a JIS No. 4 test piece. The drill life test was performed using a φ5 drill (SKH51), without using lubricating oil, and comparing the cutting speed at which the cutting distance at which cutting was impossible to 1000 mm (VL = 1000) with the comparative steel 11 as 1.0. Finally, the salt spray test was performed according to JIS Z2371. Evaluations after the test were evaluated in four stages: A: not corroded, B: slightly corroded, C: corroded, D: general corrosion. Table 2 shows the results.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
As shown in Table 2, it can be seen that the comparative steels outside the claims have problems in any of hot workability, 0.2% proof stress, tensile strength, machinability, and corrosion resistance.
[0027]
【The invention's effect】
As described above, the present invention is capable of providing a ferritic free-cutting stainless steel with improved productivity and suppressed reduction in corrosion resistance as much as possible, and improved electrical strength such as home appliances, OA equipment, and other cutting parts. Ideal for parts that receive high stress.

Claims (2)

In weight percent,
C: 0.03% or less N: 0.05% or less (however, C + N ≦ 0.060%)
Si: 2.0% or less Mn: 2.0% or less Cu: 1.0% or less Ni: 1.0% or less Cr: 16.0 to 25.0%
Mo: containing 1.7 to 3.0%;
Any one or more of S, Pb, Se, Te, and Ca are S: 0.50% or less Pb: 0.30% or less Se: 0.30% or less (however, S + Pb + Se ≧ 0.15%)
Te: 0.15% or less Ca: 0.03% or less
Further, any one or more of Nb + Ta, Ti, V, W, and Al are added to Nb + Ta: 1.0% or less Ti: 1.0% or less V: 1.0% or less W: 1.0% or less Al: High strength, characterized by containing 1.0% or less in an amount of 5% by weight or more of N and containing the balance of Fe , and having a 0.2% proof stress of 421 to 551 MPa. Free cutting ferritic stainless steel. In addition to the component of claim 1, one or two of B and Mg are further added in an amount of B: 0.001 to 0.02%.
Mg: 0.001 to 0.02%
High-strength, free-cutting ferritic stainless steel characterized in that it is contained in an amount of: