JPH04168244A - Steel for machine structural use excellent in straightness after cold drawing - Google Patents

Abstract

PURPOSE:To improve the straightness of a steel after cold drawing and straightening and to eliminate its restraightening and terstraightening by adding Al and Ti to a steel for structural use having a specified compsn. and reducing [N] as solid soln. CONSTITUTION:This steel for machine structural use has a compsn. contg., by weight, 0.1 to 0.5% C, <=1.0% Si, <=2.0% Mn, 0.03 to 0.06% SolAl and/or 0.015 to 0.050% Ti, in which total N is regulated to <=0.015 and [N] as solid soln. is regulated to <=0.002 and the balance Fe. At the time of manufacturing parts by machining, [N] as solid soln. is regulated because the higher the bending residual amt. of wire rod recoiled from a coil after cold drawing and straightening before machining the higher its content. As for Al, it is required by the lower limit or above because it fixes N as AlN and regulates [N] as solid soln. to the above value, but in the case of more than the upper limit, it damages the cleanliness of the steel. As for N, it is regulated to prevent the formation of abundant AlN and the deterioration in its fatigue strength thereby. Furthermore, Pb is preferably regulated to <=0.0050.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) The present invention relates to carbon steel that is used as a material for various mechanical structures such as automobiles, industrial machinery, and agricultural machinery. Regarding mechanical structural steels such as low alloy steels and case hardening steels,
In particular, it relates to steel for machine structures that has excellent straightness after cold drawing. (Prior art) When manufacturing parts made of machine structural steel, when manufacturing parts by cutting from rolled steel bars or wire rods, cold drawing is performed before cutting. There are many things to add. Such cold drawing is performed to remove rolling skin (black scale) and to impart good elongation to the steel material to facilitate cutting. (Problems to be Solved by the Invention) Cold-drawn steel materials undergo straightening after being cut to a predetermined length, but conventional steel for machine structures does not have sufficient straightness even after straightening. It may not be possible to obtain a straightened steel material after cold drawing and straightening, as the bending makes centering during cutting difficult. There is a problem in that it may be necessary, and it has been a challenge to solve this problem. (Objective of the Invention) The present invention has been made in view of such conventional problems, and has excellent straightness after cold drawing and straightening, and does not require re-straightening after cold drawing as in conventional The object of the present invention is to provide a steel for machine structures that has excellent straightness after cold drawing without the need for re-straightening.

[Structure of the invention]

(Means for Solving the Problems) The mechanical structural steel having excellent straightness after cold drawing according to the present invention has, in weight percent, C: 0.1 to 0°5%, Si: 1
．． 0% or less, Mn: 2.0% or less, So 1. Al:
0.03-0.06% and/or Ti: 0.01
Contains 5 to 0.050% of Ni, and further contains Ni:
Contains one or more of the following: 5% or less, Cr: 5% or less, Mo: 1% or less, and the total amount N: 0.0
It is characterized in that the solid solution [N]:Q is regulated to 15% or less, Pb:Q is regulated to 0.02% or less, and if necessary, Pb:Q is regulated to 0.050% or less, and the remainder is substantially made of Fe.
The reasons for limiting the basic component composition (weight %) of the mechanical structural steel to which the present invention is applied are as follows. C: 0.1~
0.5% C is desirably contained at 0.1 to 0.5% in machine structural steels such as case hardening steel 9 tough steel, when used after cold drawing. If it is less than 1%, it will not be possible to obtain the necessary strength, and if it is more than 0.5%, it may reduce toughness, cold drawing workability, and machinability, which is not preferable. Si: 1.0% or less Si is used as a deoxidizing agent during steel melting, but 1.0%
Even if the amount is more than 1.0%, the effect will not be improved much, and the toughness and ductility may be deteriorated. Mn: 2.0% or less Mn is an effective element as a deoxidizing agent and desulfurizing agent during steel melting, and is also effective in improving the hardenability of steel. If this happens, the hot workability and machinability of the steel material will be reduced, so it is best to keep it at 2°0% or less. Ni: 5% or less, Cr: 5% or less, Mo: 1% or less Ni, Cr, and Mo are all effective elements for improving the hardenability of steel, so they may be necessary depending on the size of the member, etc. Depending on the situation, one or more of these may be included. However, if too much is added, the machinability will deteriorate or the improvement in properties commensurate with the increase in price may not be obtained, so even if it is added, Ni is 5% or less, Cr is 5% or less, and M is 5% or less. is preferably 1% or less. The basic composition of the mechanical structural steel according to the present invention is as described above, and other alloying elements can also be contained as necessary. In addition, we have investigated how to improve the straightness after cold drawing in such mechanical structural steels, and we have found that one way to do this is to reduce the total amount N to 0.015% or less and It has been found that it is good to keep the solid solution [N amount at 0.002% or less, and to keep Sol and AI at 0.03 to 0.06%. When manufacturing parts made of mechanical structural steel by cutting, bending after cold drawing and straightening is performed on the wire unwound from the coil before cutting. When the relationship between the residual amount and the amount of N in the steel was investigated, it was found that the higher the amount of solid solution [N] in the steel, the greater the amount of residual bending. The presence of a large amount of solid solution [N] in such steel is
If the work hardening of the steel material is increased and the surface is processed during cold drawing, there will be a difference in strength between the center and the surface layer of the steel, and the degree of surface processing will be -like. Therefore, it was presumed that this was the reason why so many bends remained even when straightening was performed after cold drawing. It was also found that in order to prevent such bending from remaining, it is necessary to reduce the amount of solid solution [N] contained in the steel to 0.002% or less. Furthermore, although AI is added to fix N as AIN, it has been found that this AIN does not substantially affect the amount of bending remaining after cold drawing and straightening. Then, N, which is normally contained as an impurity, is fixed as AIN by AI, and also solid solution [N amount is reduced to 0.002
% or less, it is necessary to contain AI by 0.03% or more. However, since an excessive Al content impairs the cleanliness of the steel, it was also recognized that it is better to keep the Al content to 0.06% or less. Then, N is fixed by AI and becomes AIN, but
It has been found that if the total amount N in the steel exceeds 0.015%, a large amount of AIN is formed, which has a negative effect on the fatigue strength of mechanical structural parts, so it is better to keep the total amount N at 0.015% or less. Ta. As described above, one way to improve the straightness after cold drawing is to adjust Sol and AI from 0.03 to 0.0.
0.06%, and the total amount N is 0.015% or less,
Solid solution [It is better to regulate N to 0.002% or less,
Along with this, it has been found that it is even more desirable to restrict Pb in steel to 0.0050% or less. This PB exists in steel and has the effect of preventing carbon in the steel from dissipating into the atmosphere during hot rolling and heat treatment.
Since this PB tends to exist non-uniformly in steel, carbon dissipation also tends to be non-uniform, resulting in non-uniform carbon concentration in the steel and bending after cold drawing and straightening. It was found that the Therefore, in order to have good straightness after cold drawing and to prevent bending from remaining after straightening, p
It has been found that it is more desirable to restrict b to 0.0050% or less. Furthermore, by containing Ti instead of AI, N in the steel is replaced by T.
It has been found that fixing as iN is also good, but for this purpose the Ti content needs to be 0.015% or more. However, since too much Ti impairs the cleanliness of the steel in this case as well, it has been found that even if it is replaced with AI, the Ti content is preferably 0.015 to 0.050%. (Action of the invention) Since the mechanical structural steel according to the present invention has the above-mentioned chemical composition, N in the steel is fixed by the addition of Al and/or Ti, resulting in less solid solution [N]. Therefore, the straightness after cold drawing is good. In addition, by regulating the amount of Pb, the straightness after cold drawing becomes even better, and the amount of bending remaining after straightening is reduced, eliminating the need for re-straightening or re-straightening. becomes. (Example) Steel having the chemical composition shown in Table 1 was melted in a 70 ton electric furnace, made into an ingot, and then bloomed to make a billet. Next, each billet is heated and rolled into a wire rod to a diameter of 1
A 3 mm wire rod was prepared and wound into a coil. Next, while feeding the wire from the coil, a cold drawing process was applied, and after cutting, straightening was performed, and the amount of remaining bending after straightening was measured. Then, the proportion of the 10,000 small rods that were cut and that still had bends was evaluated as the bend remaining rate. The results are also shown in Table 1. As is clear from the results shown in Table 1, the total amount N was 0.
0.015% or less, and Sol and Al from 0.03 to 0.03%.
By fixing N by containing 0.06% or 0.6015 to 0.050% of Ti, the solid solution [N] can be reduced to 0.002%.
In Example Nos. 1 to 9, which were regulated to % or less, cold drawing→
The residual rate of bending after cutting and straightening was all 0.5% or less, and especially in Example No. 4.8.9 in which the amount of PB was regulated to 0.0050% or less, the residual rate of bending was even lower. It had become. On the other hand, Comparative Example No. has low Sol and Al contents and solid solution [N] in the steel exceeds 0.002%,
The bend survival rate of samples 10 to 12 was as high as 2.0%.

【Effect of the invention】

The mechanical structural steel according to the present invention has Sol and Al of 0.0
3~0.06% and/or Ti 0°015~0.
050%, the total amount of N is 0,015% or less, solid solution [N
] to 0.002% or less, and reduce PB to 0 as necessary.
．． 0050% or less, it has excellent straightness after cold drawing, and the amount of bend remaining when straightening after cold working is extremely small, so it cannot be re-straightened or repeated. This has the remarkable effect of eliminating the need for correction. Patent applicant: Daido Steel Co., Ltd.

Claims (8)

[Claims] (1) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Sol. Al: 0.03
~0.06%, total amount N: 0.015% or less, solid solution [N]: 0.002% or less, and the remainder is substantially F
A machine structural steel with excellent straightness after cold drawing. (2) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Sol. Al: 0.03
~0.06%, further Ni: 5% or less, Cr:
5% or less, Mo: 1% or less, total amount N: 0.015% or less, solid solution [
N]: A mechanical structural steel with excellent straightness after cold drawing, characterized in that it is regulated to 0.002% or less, and the remainder is substantially made of Fe. (3) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Sol. Al: 0.03
Contains ~0.06% and total amount N: 0.015%
Below, solid solution [N]: 0.002% or less, Pb: 0.00
A mechanical structural steel with excellent straightness after cold drawing, characterized in that the iron content is regulated to 50% or less, and the remainder is substantially made of Fe. (4) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Sol. Al: 0.03
~0.06%, further Ni: 5% or less, Cr:
5% or less, Mo: 1% or less, total amount N: 0.015% or less, solid solution [
A mechanical structural steel with excellent straightness after cold drawing, characterized in that N]: 0.002% or less, Pb: 0.0050% or less, and the remainder substantially consists of Fe. (5) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Ti: 0.015-0.
050%, total amount N: 0.015% or less, solid solution [N]: 0.002% or less, and the remainder consists essentially of Fe. Machine structural steel with excellent straightness. (6) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Ti: 0.015-0.
050%, further Ni: 5% or less, Cr: 5%
Contains one or more of the following: Mo: 1% or less, total amount N: 0.015% or less, solid solution [N]
: A mechanical structural steel with excellent elongation after cold drawing, characterized in that it is regulated to 0.002% or less and the remainder is substantially made of Fe. (7) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Ti: 0.015-0.
050%, total amount N: 0.015% or less, solid solution [N]: 0.002% or less, Pb: 0.0050
% or less, and the remainder substantially consists of Fe. A steel for mechanical structures having excellent straightness after cold drawing. (8) In weight%, C: 0.1-0.5%, Si: 1.0
% or less, Mn: 2.0% or less, Ti: 0.015-0.
050%, further Ni: 5% or less, Cr: 5%
Contains one or more of the following: Mo: 1% or less, total amount N: 0.015% or less, solid solution [N]
A mechanical structural steel with excellent straightness after cold drawing, characterized in that Pb: 0.002% or less, Pb: 0.0050% or less, and the remainder substantially consists of Fe.