JPH06306546A - Free cutting martensitic stainless steel with high hardness - Google Patents

Abstract

PURPOSE:To provide a martensitic stainless steel combining high hardness with machinability. CONSTITUTION:This steel has a composition consisting of, by weight, 0.60-0.80% C, <=0.60% Si, <=1.0% Mn, 10.0-14.0% Cr, <=2.0% Mo, <=0.01% S, further 0.10-0.25% Pb, and the balance Fe with inevitable impurities. Further, one or >=2 components selected from the four groups consisting of one or two kinds among <=0.060% B, <=0.010% Ca, <=1.5% Ni, and <=1.0% Cu and one or >=2 kinds among <=0.5% Ti, <=0.5% Nb, <=1.2% V, and <=1.2% W can be added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a martensitic stainless steel having high hardness and free machinability.

[0002]

2. Description of the Related Art OA equipment and parts for home electric appliances are generally produced in large quantities and handled in large quantities. It is required to have high hardness so that scratches do not occur even if they hit each other during handling. Among such parts, motor shafts, audio guide pins, stepped hole drilling parts, etc. are usually manufactured by machine cutting, and therefore free-cutting property is also required.

Conventionally, SU has been used as a material for components of this type.
S420J2 and SUS440C have been used. However, SUS420J has a hardness of at most HRC in the quenched state.
No. 54, the above requirement (hardness is desired to be 58 or more in HRC) cannot be sufficiently met, and SUS440C shows high hardness of HRC61 when hardened, but it is difficult to cut because of many carbides. Therefore, the emergence of a material having good machinability while maintaining high hardness has been desired.

[0004]

In response to such demands, the object of the present invention is that the machinability is high in the annealed state, the hardness becomes high after quenching, and the corrosion resistance is inferior to the conventionally used materials. To provide free-cutting, high-hardness stainless steel.

[0005]

The free-machining high-hardness martensitic stainless steel of the present invention basically has a C: 0.
60 to 0.80% (weight%, the same below), Si: 0.60
% Or less, Mn: 1.0% or less, Cr: 10.0 to 14.
It has an alloy composition containing 0%, Mo: 2.0% or less, S: 0.01% or less, and Pb: 0.10 to 0.25%, with the balance being Fe and inevitable impurities.

In addition to the above basic alloy composition, one or more of the following four groups of optional additional elements may be further added.

(1) B: 0.060% or less, (2) C
a: 0.010% or less, (3) Ni: 1.5% or less and Cu: 1.0% or less, one or two types, (4) Ti:
One or more of 0.5% or less, Nb: 0.5% or less, V: 1.2% or less, and W: 1.2% or less.

[0008]

The reason why the alloy composition of the free-cutting, high-hardness martensitic stainless steel of the present invention is selected as described above will be described below with reference to the basic composition. C: 0.60 to 0.80% 0.60% or more is required to exert sufficient hardness after heat treatment, while the upper limit of 0.80% is taken into consideration in consideration of deterioration of hot workability. I put it. Si: 0.60% or less From the viewpoint of workability and toughness, addition is limited to within this limit. Mn: 1.0% or less In order to keep hot workability high, 1.0% is the limit. Cr: 10.0 to 14.0% Addition of 10.0% or more is required to obtain desired hardness and corrosion resistance. If added excessively, eutectic carbides are formed, which is not preferable, so the upper limit is 14.0%. Mo: 2.0% or less It is preferable because it improves the corrosion resistance, but if it is added in a large amount, the cost becomes high. From this viewpoint, it is a good idea to add 2.0% or less to this type of material. is there. S: 0.01% or less It is not preferable because it deteriorates hot workability and corrosion resistance.
The amount is reduced to within the above limits.

Pb: 0.10 to 0.25% It is a main component that gives free-cutting property, and has a function of extending spherically in the matrix to extend the tool life.
This effect is obtained by addition of 0.10% or more, while on the other hand, addition of a large amount impairs hot workability, so it is stopped within 0.25%. B: 0.060% or less It has the effect of strengthening the crystal grain boundaries. Addition of an appropriate amount improves the hot workability, but if it is added in a large amount, the hot workability is adversely decreased. Therefore, the above-mentioned 0.06% is the limit. Ca: 0.010% or less The effect of controlling the form of inclusions to improve hot workability and the effect of enhancing machinability can be expected. However, the yield of addition is poor, and even if an attempt is made to add a large amount, the cost becomes high and the effect is saturated.

Since the optional additional elements have the following functions, it is advisable to select and use them properly depending on the use of the material. The reasons for limiting the composition range are as follows. Both Ni: 1.5% or less and Cu: 1.0% or less are useful for improving the corrosion resistance, but addition in excess of the upper limit causes a decrease in strength. Ti: 0.5% or less, Nb: 0.5% or less, V: 1.2%
Below, W: 1.2% or less. All increase the high temperature strength. Ti and Nb impair the workability when added in excess of the above limits. V and W
If added over the limit, the toughness at room temperature will be affected and it will be expensive.

[0011]

EXAMPLE A martensitic stainless steel having the alloy composition shown in Table 1 (unit: weight%, the balance being substantially Fe) was melted, and a 50 kg steel ingot was forged into a 65 mm square bar.

[0012]

[Table 1]

A test piece was cut and collected from the above bar material,
Spheroidizing annealing was performed under the conditions of 0 ° C. × 7 hours → slow cooling (cooling rate of 30 ° C./hr up to 680 ° C.). This annealed material was subjected to a drill life test, a salt spray test and a wet test, and the hardness was measured in the quenched and tempered state.

(Drill life test) Specimen size: height 30 mm x width 60 mm x length 200 mm Drill used: 10 mm diameter SKH9 straight shank drill Feed rate: 0.15 mm / rev Hole depth 20 mm (blind hole) Rating: Cutting speed in the same tool life (VL = 1
000, but based on SUS440F) (Salt spray test) Specimen size: 10 mm diameter x 50 mm length Condition: 35 ° C x 48 hours, 5% NaCl (wet test) Specimen size: 10 mm diameter x 50 mm length Condition: 100% RH, 49 ° C x 96 hours (hardness test) Heat treatment: 1025 ° C x 30 minutes → oil cooling, then 20
Table 2 shows the test results of 0 ° C. × 30 minutes → air cooling.

[0015]

[Table 2]

The criteria for the corrosion resistance test are as follows. There badly slightly spots at all without corrosion wetting being corroded is considerably corroded is A B C D water at all without corrosion little corrosion is little spots have considerable corrosion

[0017]

EFFECTS OF THE INVENTION The martensitic stainless steel of the present invention is easy to cut in the annealed state, hardly shows rust on the cut surface, and has a beautiful finish with a surface roughness higher than that of the conventional steel. Those that have undergone heat treatment exhibit high hardness. (HRC58 or above, HV 6
Most products can meet the demand of 53 or more. ) Corrosion resistance is not inferior to conventional products, and OA equipment used under normal conditions is at a sufficient level as a part of home electric appliances.

Claims (5)

[Claims] 1. C: 0.60 to 0.80% (weight%, the same below), Si: 0.60% or less, Mn: 1.0% or less, Cr: 10.0 to 14.0%, Mo: 2.0% or less, S: 0.01% and Pb: 0.010 to 0.25.
%, A free-cutting high-hardness martensitic stainless steel having an alloy composition with the balance being Fe and inevitable impurities. 2. C: 0.60 to 0.80% (weight%, the same hereinafter), Si: 0.60% or less, Mn: 1.0% or less, Cr: 10.0 to 14.0%, Mo: 2.0% or less, S: 0.01% or less, and Pb: 0.10 to 0.2.
Free-cutting high-hardness martensitic stainless steel having an alloy composition containing 5% and B: 0.060% or less with the balance being Fe and inevitable impurities. 3. C: 0.60 to 0.80% (weight%, the same hereinafter), Si: 0.60% or less, Mn: 1.0% or less, Cr: 10.0 to 14.0%, Mo: 2.0% or less, S: 0.01% or less, and Pb: 0.10 to 0.2.
Free-cutting high-hardness martensitic stainless steel having an alloy composition containing Ca: 0.010% or less in addition to 5%, and the balance being Fe and inevitable impurities. 4. C: 0.60 to 0.80% (weight%, the same applies hereinafter), Si: 0.6% or less, Mn: 1.0% or less,
Cr: 10.0 to 14.0%, Mo: 2.0% or less,
S: 0.01% or less and Pb: 0.010 to 0.25
%, And in addition to B: 0.060% or less and / or Ca: 0.010% or less, Ni: 1.5
% Or less and Cu: 1.0% or less, and a free-cutting high hardness martensitic stainless steel having an alloy composition of the balance of Fe and inevitable impurities. 5. C: 0.60 to 0.80% (weight%, the same applies hereinafter), Si: 0.6% or less, Mn: 1.0% or less,
Cr: 10.0 to 14.0%, Mo: 2.0% or less, further B: 0.060% or less and / or Ca: 0.0.
010% or less, S: 0.01% or less and Pb: 0.1
In addition to 0 to 0.25%, Ti: 0.5% or less, Nb:
Free-cutting high hardness martens having an alloy composition containing 0.5% or less, V: 1.2% or less and W: 1.2% or less, or one or more types, and the balance being Fe and inevitable impurities. Site-based stainless steel.