JPS59157262A - Low alloy soft nitrided steel - Google Patents

Abstract

PURPOSE:To provide a titled soft nitrided steel having excellent soft nitriding properity and high strength, more particularly high internal strength after a soft nitriding treatment in a low alloy soft nitrided steel consisting essentially of C, Cr and Al by incorporating respectively prescribed ratios of V, Ti, Zr, Nb+Ta and S. CONSTITUTION:A low alloy soft nitrided steel consisting essentially, by weight %, of <=0.5% C, <=3% Cr and 0.02-0.5% Al, and incorporated therein with <=3.5% Ni, <=1.5%, <=1.5% Mn, <=1.5% Cu, etc. is prepd. Such soft nitrided steel is incorporated therein with >=1 kind among 0.01-0.5% V, 0.01-0.5% Ti, 0.01- 0.5% Zr, and 0.01-0.5% Nb+Ta and is regulated <=0.010% Si, by which the intended low alloy soft nitrided steel is obtd. A steel blank material, part or product having the above-described characteristics and having fully satisfactory wear resistance and strength is obtd. from such soft nitrided steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-alloy soft-nitriding steel that has excellent soft-nitriding properties and high strength, particularly internal strength, after soft-nitriding treatment.

Traditionally, in office equipment, automobiles, etc., many parts have been used that are made of materials such as carbon steel and alloy steel for machine structures and have been carburized to improve wear resistance and fatigue strength. Carburizing treatment has two drawbacks: (1) high defect rate due to the distortion that occurs during carburizing and quenching; (2) depending on the part, it may be necessary to straighten all parts to remove distortion, which tends to increase costs. There are drawbacks such as.

On the other hand, in contrast to such carburizing and quenching, which causes large heat treatment distortions, there are nitriding treatments and nitrocarburizing treatments, which are surface hardening treatments below the AI transformation point, as heat treatments with small heat treatment strains. This nitriding treatment and soft nitriding treatment is a method in which the material to be treated is heated in NH3 gas and nitrogen is infiltrated into the steel surface to increase surface hardness. Even if a chain or alloy steel is subjected to nitriding or soft nitriding, a sufficient hardened layer depth cannot be obtained, and sufficient strength (fatigue strength and transfer strength) cannot be obtained. It had the disadvantage of being unable to do much. For this reason, various soft-nitriding steels have been developed, but these still have the disadvantage of insufficient strength and soft-nitriding properties.

This invention was made in order to eliminate the above-mentioned conventional drawbacks, and it is a low-alloy alloy that has excellent soft nitriding properties, can obtain a sufficient hardened layer depth, and has high strength, especially internal strength, after soft nitriding. The purpose is to provide soft nitrided steel.

The low-alloy soft nitrided steel according to the present invention has C: 0.5% by weight or less, Cr: 3% by weight or less, and A: 0.02-05% by weight.
is the basic component, and if necessary, Ni: 3.5% by weight or less, Si: 1.5% by weight or less, Mn: 1.5% by weight or less, Cu: 1.5% by weight or less, Mo: 1 .5% by weight
below.

In a low alloy soft nitrided steel containing one or more of the following: W: 1, 5% by weight or less, Co: 1.5% by weight or less, V: 0.01 to 0.5% by weight %, Ti:
Contains one or more of the following: 0.01-0.5ii%, Zr: 0.01-0.5% by weight, Nb+Ta: 0.01-0.5% by weight, S: 0.010% by weight % or less, and if necessary to improve machinability, Fb: 0.01-0.2% by weight, Ca: 00%.
005 to 001% by weight, Se: 0.005 to 0.1% by weight, and more preferably regulated to 0:O, 0O20% by weight or less. There is. The low-alloy soft nitrided steel referred to in this specification naturally includes not only its use as a material for parts, but also the parts and products themselves. In this case, the low alloy steel with the above components is forged into a predetermined part or product shape (for example, roll 2 shaft 1, crank shirt 1, connecting rod, spindle, gear, pin, leaf spring, etc.).

It is formed by cutting, punching, etc., and then subjected to nitrocarburizing using a combination of gas or both to obtain an internal hardness of 200 or higher (Pinker's hardness Hv) after nitrocarburizing. do.

Next, the reason for limiting the composition of the low alloy soft nitrided steel of the present invention will be explained.

C; C is an element necessary to increase the toughness of steel, and is particularly effective in increasing internal hardness and increasing internal strength, but if it is in too much, it will actually reduce toughness and reduce workability. Since it also deteriorates nitriding properties, it is necessary to keep it at 0.5% by weight or less, and it is more desirable to keep it at 0.25% by weight or less especially for applications where press working or cold forging is required.

Cr.

Cr is an element that contributes to improving the soft-nitriding properties of steel, and increases the hardness of the surface by forming nitrides during the soft-nitriding process. However, if too much Cr is present, the effect of improving the soft-nitriding properties becomes saturated and the toughness decreases. Since it causes deterioration, it is necessary to limit the content to 3% by weight or less.

Sentence A: Au is an element that contributes to improving the soft nitriding properties of steel, and forms nitrides through soft nitriding treatment to increase the hardness of the surface. And in order to obtain such an effect, 0,0
It is necessary to contain 2fii% or more, but if it is too large, it reduces the static purity of the steel and deteriorates the toughness, so it is necessary to keep it at 0.5% by weight or less.

Ni, Si, Mn, Cu, Mo, W, Co: Ni, Si
, Mn, Cu, Mo, W, and Co are elements that contribute to improving the strength of steel before treatment and further increasing the internal strength after soft-nitriding treatment, but even if they are added in large amounts, they are not effective. Since increasing the amount cannot be carried out over time and is rather uneconomical, when adding it to steel with the above basic components, Ni: 3.5% by weight or less, Si: 1.5% by weight or less, Mn: 1.5 Weight % or less, Cu: 1.5 weight % or less, Mo: 1.5 weight %
Hereinafter, W: 1.5% by weight or less, C.

: It is preferable to add one or more of these as necessary in an amount of 1.5% by weight or less.

V, Ti, Zr, Nb, Ta: V, Ti, Zr, Nb, and Ta all contribute to improving soft-nitriding properties and shorten the soft-nitriding time required to obtain the initial hardness. V:0. 01-0.5% by weight, Ti
:O, O1-0.5% by weight, Zr: 0.01-0.5i
amount%.

Nb+Ta: 0.01 to 0.5% of heavy hot water contains one or more of these.

S: If the S content is too large, it deteriorates the soft nitriding properties of the steel and reduces the strength, especially the internal strength and pitting strength, so it is regulated to 0.010% or less.

Pb, Ca', Se: Pb, 'Ca, Se' are effective elements for improving the machinability of steel, and are necessary to compensate for the decrease in machinability caused by rust due to regulating the S content. It is good to add it if there is. However, when added in large amounts, it impairs the hot workability of the steel and also deteriorates its strength and toughness, so when adding it,
Pb:O, O1-0.2%, Ca:O', 0O05
-0.01% by weight, Se: 0.005-0.1% by weight
It is preferable to add one or more of these within the following range.

Also, if the content is 0 or too high, the amount of inclusions in the steel will increase,
Since it reduces the strength of the steel, it is more desirable to limit it to 01.0020 Jμ% or less.

By applying nitrocarburizing treatment to low-alloy steel materials or parts with such components, the internal hardness can be reduced to Hv200.
It is possible to obtain soft-nitrided materials or soft-nitrided products (for example, crankshafts, connecting rods, spindles, gears, etc.) with crystal hardness above and high strength.

Steel with the chemical composition shown in Table 1 is melted in an electric furnace, then formed into an ingot, then rolled into a round bar with a diameter of 40 mm, and a part of it is injected with NH3 gas: RX. Soft nitriding was carried out under the conditions of 580°C x 1' and oil cooling for 5 hours in a gas-1:1 atmosphere to investigate the excellent soft nitriding properties, and for 6 parts, 580°C After applying 5"N+cooling, it was processed into a JIS No. 3 test piece and its toughness value was investigated. The results are shown in Table 2.

Table 2 As is clear from the results shown in Tables 1 and 2, the surface hardness of the present invention 1l (No. 1.2, 4, 6.7) is high, and Hv550 is obtained. It can be seen that the distance from the surface layer (DH, 550 (mm)) is large, the internal hardness is large, the internal strength is improved, and the toughness is also excellent. On the other hand, steel No. 83, which has too much S content, has poor soft nitriding properties and toughness, and No. 5 steel and N steel have too much A content and Cr content.
It can be seen that steel No. 7 has excellent soft-nitriding properties but is inferior in toughness.

Further Example 2 Steel 2 having the chemical composition shown in Table 3 was melted in an electric furnace, then formed into an ingot, and then rolled into a round bar with a diameter of 40 mm, and a portion of the steel was made into a test piece for a rotary bending fatigue test. Each specimen was subjected to nitrocarburizing treatment in an atmosphere of NH3 scum: Rx scum - 1:1 under conditions of oil cooling at 580° A fatigue test was conducted using a rotary bending fatigue test (notch shape factor: 1.84) to examine the fatigue strength of the sample. In addition, cutting tests were conducted on other parts of the round bar to examine the rigidity of some steel types. In addition, in this cutting test, Plo.

Feed speed: 0, 2mm/rew, cutting depth +2m
m, cutting speed: The conditions were 150 m/min. The results are shown in Table 4.

Table 4 As is clear from the results shown in Tables 3 and 4, the present invention (Nos. 13 to 20) all have high surface hardness, and the distance pa (DH
v 550 (mm)) is large, internal hardness is large, internal strength is increased, and fatigue limit is also large, showing excellent characteristics. In this case, Pb, Ca
By adding a machinability-improving element selected from , Se, the tool life could be increased, and the decrease in machinability caused by the S content rule could be compensated for. It was also found that when the ○ content is large (NO, 18), the fatigue strength decreases, so it is more desirable to limit the 0 content to 0.0020% by weight. On the other hand, the comparison &'f5 (No, l 1, 12) with a high S content has good machinability, but it is 1Iil! : It was found that the nitriding property was poor, the internal hardness was low, and the fatigue properties were also poor.

As explained above, the present invention provides a low-alloy soft-nitrided steel that has excellent soft-nitriding properties, can obtain sufficient surface hardness and hardened layer depth, and has high strength, especially internal strength, after soft-nitriding treatment. It is possible to obtain a steel material 5 parts or product which has a very excellent effect of being able to obtain 11HtJI wear resistance and strength.

Patent applicant: Daido Steel Co., Ltd. Representative Patent Attorney Shio Koku

Claims (2)

[Claims] (1) C: 0.5% by weight or less, Cr: 3% by weight or less, A
In low-alloy soft nitrided steel whose basic component is u: 0.02 to 0.5% by weight, V: O, O1 to 0-5mE'E%, T
i: 0.01 to 0.5 weight fi%. Zr: 0.01~0.5 Nail amount% Nail view N b 10T a
: A low-alloy soft nitrided steel characterized by containing 0.01 to 0.5% by weight of one type or two or more types per run, and regulated to 0.010% by weight or less of S. (2) In a low-alloy soft nitrided steel whose basic components are C:' 0.5% by weight or less, Cr: 3% by weight or less, and Al: 0.02-05% by weight, V: O, O1-0.5 weight%,
Ti: 0, 01-0.5% by weight, Zr: 0.0
1~0.5ffi amount%, Nb+Ta: 0, 01~
0, 5% by weight of one or more types, and Pb: 0
．． 01-0.2% by weight. Ca: 0, 0005~0, 01 important-%, Se
A low-alloy soft nitrided steel characterized by containing one or more of the following: 0, OQ: 5 to 0.1% by weight, and S: regulated to 0.010% by weight or less.