JPS6021358A - Tough and hard steel for cold forging - Google Patents

Abstract

PURPOSE:To provide a titled tough and hard steel having an improved cold forging characteristic by specifying the compsn. of a high carbon steel which contains Si and Mn up to the decreased upper limit, contains P, N and O in less amt. and contains S, Al and Cr. CONSTITUTION:A tough and hard steel for cold forging contains 0.40-0.65wt% C, 0.01-0.05% Si, 0.20-0.40% Mn, 0.02-0.03% S, >0.01 and <=0.04% Al and 0.3-0.8% Cr and is limited to <=0.01% P, <=0.005% N and <=0.005% O. Said steel is a carbon steel for machine structural use having improved cold forgeability. The above-mentioned component compsn. is limited to contain essentially P, N and O among Si, Mn, P, N and O which affect adversely deformation resistance, at a low rate, to decrease the upper limit of Si and Mn and to make up the hardenability to be correspondingly deteriorated with C and Cr to improve the cold forgeability. The deformation resistance is thus remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is intended to provide a carbon material for mechanical forging with improved cold forgeability.

In general, strong steels have better wear resistance and transfer fatigue resistance during use, and carbon steels with a resistance of 0.4% or more are treated by tempering to increase the surface hardness and improve the feeling of use. Such a high carbon material has high deformation resistance (indicated by the amount of force required for processing) even when subjected to spheroidizing annealing treatment (hereinafter abbreviated as S and A). Therefore, in the past, cold forging was difficult and hot forging was used. However, hot forging has poor dimensional accuracy and requires a subsequent cutting process. This cutting process requires a large number of man-hours and is very complicated, so cold forging is desired since it has good dimensional accuracy and can greatly reduce the cutting process.

As a result of careful consideration in view of these points, the present inventors found that Si, MntP, N, and O have a more negative effect on deformation resistance than C, and in order to deal with this, low Based on this knowledge, the present invention was able to develop a steel material with significantly improved deformation resistance by making P, low N, and low 01 essential, suppressing the upper limits of Sl and Mn, and supplementing the resulting hardenability fc and cr. The gist of what was done is in weight %, C0.40-0.65%, SiO,
01-0.05%, Mn 0.20-0.40%,
SO, 02-0.03%.

At more than 0.01 and 0.04% or less, CrO, 3 to 0.
Contains 8%, and Po, 01% or less, NO, 005%
The following is a strong steel for cold forging characterized in that the content is limited to 0.005% or less.

The present invention will be explained in detail below. First, the steel targeted in the present invention is a carbon steel for machine rod structure containing 0.40 to 0.65% by weight of C, and the reason why C is specifically limited is because C is an important factor that determines quenching hardness. This is because it is an alloying element, and if it is less than 8.40%, sufficient surface hardness cannot be obtained, so it is set to 0.40% or more. Moreover, if it exceeds 0.65%, quench cracking during quenching tends to occur, so the upper limit was set at 0.65%.

Since St is necessary as a deoxidizing element during steel manufacturing, it has traditionally been set to 0.
It contained 62-0.3%. However, Si is S, A.

The strength increase is large at times, and particularly the deformation resistance at high deformations is greatly increased. Therefore, in order to sufficiently reduce the deformation resistance, the upper limit of i is set at 0.05%, and if it is too small, the B
The presence of some St is necessary because system inclusions may increase and cracks may occur during cold forging, and therefore the lower limit of -
i was set at 0.01%.

Next, Mn completely fixes S as an impurity, which is necessary for preventing surface flaws during hot rolling, and an amount of 0.4 °C is sufficient. In conventional steel, 0.7 to 0.8% of C was added as a relatively inexpensive element useful for ensuring hardenability. but,
Like Si, Mn is a major inhibitor of reducing deformation resistance during high deformation, so from that point of view the upper limit of the Mn content was set at 0.4%.
And so. Note that the deficiency in hardenability caused by setting the upper limit of the M amount to 0.4% is compensated for by Or, which will be described later. on the other hand,
Mn is an impurity SfeM that causes cracking during hot rolling.
It is necessary to add a small amount of nS to fix it and make it harmless, so 0.2% was set as the lower limit.

A low S content is desirable because it promotes work hardening, but the presence of S is necessary to ensure a certain degree of machinability, so the range was set to 0.02 to 0.03%. 0.02
If it is less than 0.03%, sufficient stiffness cannot be obtained, and if it exceeds 0.03%, although the stiffness is satisfactory, work hardening will occur.

Furthermore, since AA is not only effective in deoxidizing, but is also an effective alloying element that fixes Nk and becomes AtN, thereby refining crystal grains, the lower limit is set to exceed 0.01%, while 0.01% is set as the lower limit. 04
%, At203 generated during deoxidation causes cracking during cold forging, so the upper limit (i70.04%) was set.

Next, Cr is added to compensate for the lack of hardenability, and is an excellent element that increases hardenability without significantly increasing the strength of S, A, and steel. In order to suppress the upper limit of Si and Mn in order to lower the deformation resistance, and to compensate for the resulting lack of hardenability by adding Cr, it is essential that the content be 0.3% or more. However, if the amount is large, solid solution hardening will occur.8. A: The upper limit was set at 0.8% because it increases the strength.

Next, one of the features of the present invention is to reduce each of P, N, and O'e, and the reason for this is as follows.

Although P and N are contained as impurities in steel, they are age hardened as the temperature rises during cold forging and cause an increase in deformation resistance, so they are set at 0.01% or less and 0.005% or less, respectively.

0 combines with At+ 81 etc. to form an oxide and causes cracks during cold forging, so the upper limit is o, o o s%.
And so.

Next, the effects of the present invention will be explained in more detail based on examples.

Using steel materials with the chemical composition shown in the table, the load 'f during compression test was investigated by performing spheroidizing annealing treatment, and the surface of the 30φ test material was subjected to induction hardening and tempering tests. The hardness of the position was measured and the results are also shown.

Test material Chemical composition (%) A CSi Mn S AtCr P N 010.3
00.29θ, 830.0220.025-0.018
0.00610. OO&420.440.250.76
0.0100.030-0.0190.00560.0
()4230.460.040.350.0081),
026-0.0170.006B 0.006640.
470,270.750.0550.02B -0,0
150,00290,005550,540,310,
810,008,0,075-0,0160,0080
0,0045G 0.550.250,780.001
0.034-0.0020.00750. (10777
0,560,290,350,0090,0270,3
00,0200,00890,010580,640,
280,810,0160,029-0,0170,0
0770,007090,420,040,330,0
250,0150,420,0020,00280,0
036100,470,020,280,0280,0
300,700,0040,00250,004211
0,540,030,220,0230,0230,6
50,0030,00270,0048120,550
,030,320,02B 0.018 (+,530
．． 0060.00220.0047130.630,0
40.230.0240.0210.310.0050
．． 00320.0033 During Qin compression test Induction hardening/quenching machinability information
Load (1) After hardness Hv) Tool life (drilling length) (σ) 60 530 35 Comparative steel (S30C
)69 620 25 # (S45C)50 420
20 73 620 50 1 (free-cutting steel) 79 690 25 # (S55C) 75 660
15 1 (1) 77 670 25 83 730 25 52 620 45 Invention steel 56 660 40 60 680 35 59 710 35 60 720 35 Hardness table at 3 fins from Qin surface at cutting speed of 40 (m/-h) A1 to A8 are comparative materials, and A9 to A13 are steels of the present invention. First of all, in comparison steel, 51 is a standard material of 8300, and the load during the compression test is relatively low at 60 tons, but the hardness after induction hardening and tempering is 450, which generally has better wear resistance and rolling fatigue resistance. It is lower than the target level of 550, indicating insufficient hardenability. A2 is a standard material of 545C and has a high hardness of 620 after induction hardening and tempering, but the load during the compression test is 69t, which is too high.

A3 was designed to reduce Si and Mn f from normal levels and reduce the load during the compression test, and is low at 50 tons, but the hardness after induction hardening and tempering is low at 420, resulting in insufficient hardenability. A4 is a free-cutting steel with high Si content and has a tool life of 50
Although it is longer than the others at c1n, the load during the compression test is high at 73t. A5 and A6 are 855C materials, and the hardness after induction hardening and Φ tempering is as high as 690,660, improving hardenability, but the load during the compression test was 79t and 75t.
and is extremely high. Furthermore, in the case of A6, S is 0.0
Since the tool life is as low as 01, the tool life is as short as 15 crn.

A7 has a low Mn content and aims to reduce the load during the compression test, but since the St is at a normal level and 0 is high at 1105 pp, the load is 77 t, which is too high.

Company A8 further increases the C content to improve hardenability, and the hardness after induction hardening and tempering is as high as 730, but the load during the compression test is also increased to 83 tons.

On the other hand, all of the steels of the present invention with A9 to flat size 13 fully satisfy the target level of hardness of 550 after induction hardening and φ tempering, and the load during the compression test is 60 or less.
The tool life is similar to that of free-cutting steel.

As mentioned above, the steel of the present invention has sufficient strength after quenching and tempering, improves cold forging properties (deformation resistance), and provides steel that satisfies rigidity, making it extremely useful in industry. Useful.

Claims (1)

[Claims] 11% C0,40-0.65%, SiO,01-
0.05%, Mn0.20-0.40chi, 80.02
~0.03 Excel, At0.01 & 0.04 Chi or less,
Contains CrO, 3 to 0.8 $f, and po, o
itl, below. A strong steel for cold forging which is characterized by being limited to NO.005% or less and NO.00.005% or less.