Steel for cold forging having good machinability and the method of making the same

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel steel for cold forging having both good formability in cold forging and good machinability. The invention encompasses a preferable method of making the steel for cold forging.
This invention is applicable to various steels such as machine structural carbon steel, manganese steel, chromium steel, molybdenum steel, chromium-molybdenum steel, nickel-chromium steel, nickel-chromium-molybdenum steel, manganese-chromium steel, and nickel-molybdenum steel.
2. State of the Art
Sulfur has been known as an element which deteriorates formability in cold forging of steels. Sulfur in the steel exists as sulfides such as MnS, which are easily extended along the forging direction to become strand-form, and the elongated sulfides are believed to be harmful to the formability in cold forging. Accordingly, conventional production of a steel for cold forging includes a step of desulfurization to form a low-sulfur steel. Low-sulfur steels, however, have relatively low machinability.
We have sought ways of solving the above problem and studied compositions of the steel for cold forging. As a result, we found that, when Te is added to a sulfur-containing steel in an amount where the ratio %Te/%S is at least 0.04, the elongation of the sulfides is remarkably suppressed, and therefore, that the steel has decreased anisotropy in mechanical properties, fairly good formability in cold forging and excellent machinability which is equivalent to, or even better than that of conventional sulfur-containing free cutting steels. Our discovery was disclosed in the U.S. patent application Ser. No. 77,477.
However, there has been further demand for a steel having more highly improved formability in cold forging with sufficient machinability.
SUMMARY OF THE INVENTION
An object of this invention is to provide steels for structural use having both further improved formability in cold forging and machinability.
Another object of the invention is to provide a preferable method of making the above steels.
The present invention is based on our discovery that formability in cold forging of sulfur-containing free cutting steels can be remarkably improved without sacrificing the machinability even at a low sulfur content such as less than 0.04%, if Te is added to the steel so that %Te/%S may be at least 0.04, and if the contents of oxygen and nitrogen are controlled to limited extents.
The invention is further based on our discovery that the formability of the above steels in cold forging can be further improved by choosing a low content of Al to prevent formation of Al.sub.2 O.sub.3 in the steel.

DRAWINGS
FIG. I is a graph showing influence of the ratio %Te/%S on the form of the sulfide particles in the steel.
FIGS. IIA, IIB, IIC, IID and IIE are microscopic photographs showing distribution of the sulfide particles in the steel.

PREFERRED EMBODIMENTS OF THE INVENTION
The steel of this invention for cold forging having good machinability comprises basically: C up to 0.6%, Si up to 0.5%, Mn up to 2.0%, S 0.003 to 0.04% and Te up to 0.03, wherein %Te/%S is at least 0.04, and Al up to 0.04%, and the balance substantially of Fe. Preferably, the oxygen content should be up to 0.0030%, and nitrogen, up to 0.02%.
In the above basic composition, steels of particularly fine crystal grains contain Al 0.01 to 0.04%.
On the other hand, steels of better formability in cold forging contains less than 0.01% of Al.
Roles of the above noted alloying elements and significance of the composition are as follows:
C: up to 0.6%
Carbon is essential for assuring strength to the steel. Carbon content of more than 0.6% affects toughness, which is an important property of a structural material, and formability in cold forging.
Si: up to 0.5%
Silicon is added as a deoxidizing element to steels. It prevents occurrence of surface defects of cast steel. Because an excess amount of Si decreases toughness and hardens the matrix to damage the formability in cold forging, the content should be limited to 0.5%.
Mn: up to 2.0%.
Manganese promotes hardenability, increases strength, and further, forms sulfides, MnS, to arrest hot enbrittlement. However, too much, manganese will reduce machinability, and so, it is used in an amount up to 2.0%.
S: 0.003 to 0.04%
As noted, sulfur improves machinability of the steel, and is necessary to be contained in an amount of usually 0.003% or more to get sufficient machinability-improving effect. In view of lowered formability in cold forging of a large content, the upper limit has been determined to be 0.04%.
Te: up to 0.03%
In a steel containing S up to 0.04%, it is necessary to add a sufficient amount of Te to effectively prevent elongation of sulfides, such as MnS. However, favorable effect of a large content of Te on the improvement of the formability in cold forging is not so high, and thus, the upper limit is determined at 0.03%.
%Te/%S: at least 0.04.
In order to prevent elongation of sulfides, the ratio %Te/%S should be at least 0.04. This is supported by the data of the working examples noted below and shown in FIG. 1.
O: up to 0.0030%
Oxygen is harmful element because it forms oxides, particles of which act as the starting points of inner cracks during cold forging. In order to fully enjoy the effect of Te on improving formability in cold forging, the content of oxygen must be kept at the highest of 0.0030%. In case of particularly high reductions of area, it is preferable to lower the oxygen content as low as 0.0020% or less.
N: up to 0.02%
Nitrogen increases deformation resistance of the steel and decreases formability in cold forging, and therefore, its content should be as low as possible. The upper limit is 0.02% in usual cases, preferably less than 0.015% in case of extremely high reductions of area in cold forging.
Al: up to 0.040%
Aluminum is added as an deoxidizing agent, and is effective in controlling grain size. The effect can be remarkable at a content at 0.01% or higher. If, however, too much is contained, it reduces fluidity of molten steel. The upper limit of 0.040% is determined from this point of view.
On the other hand, aluminum combines with oxygen to form hard Al.sub.2 O.sub.3, particles of which tend to be starting points of inner cracks occurring during cold forging. Alumina also abrades tools at machining of the steel products. From this point of view, a content less than 0.01% is preferable. In case of higher reductions of area in cold forging, it is preferable to decrease the content as low as 0.007% or less.
To the above noted basic composition, the following alloying elements may be added, if desired: One or more of the elements selected from the group of: Ni: up to 4.5%, Cr: up to 3.5% and Mo: up to 1.0%.
The above three elements are useful in the present steel to highten the toughness and anti-temperbility. At a higher contents thereof, the effect of addition is not proportional, and therefore, it is advantageous to add optionally in an amount in the given limits. One or more of the elements selected from the group of: V up to 0.2%, Nb up to 0.1%, Ti up to 0.1%, B up to 0.01% and Zr up to 0.2%.
These elements are useful for improving crystal structure and properties for heat treatment of the steel. In order to maintain the merit of good formability in cold forging due to less elongation of the sulfide particles, the addition amount should be chosen in the above noted limits. It was affirmed by the data of the Examples shown below, that the effect of adding these elements is, available also in cases with the elements of the other group, namely, Ni-group and Pb-group below. One or more of the elements selected from the group of: Pb 0.01 to 0.30%, Se 0.003 to 0.10%, Bi 0.01 to 0.30% and Ca 0.0002 to 0.01%.
These elements are effective for improving machinability. The effect can be obtained at a content higher than the lower limits, and the upper limits are set so that the formability in cold forging of the steel may be kept high.
As noted above, the present invention encompasses a preferable method of making the above described steel for cold forging having good machinability.
The method comprises the steps of:
preparing a molten steel containing adjusted amounts of C, Si, Mn and S, and optionally, the above listed additional element or elements except for those of Pb-group in a furnace or a ladle,
at the time of degassing or after the degassing of the molten steel, or at the time of refining with addition of Al, if performed, agitating the molten steel by introducing non-oxidizing gas thereinto so as to float and separate large particles of non-metallic inclusions into slug, and then
adding predetermined amount of Te, and if necessary, one or more of the elements of the Pb-group to uniformly disperse in the molten steel, followed by conventional casting and hot working.
The present invention will now be illustrated with working examples.
EXAMPLE I
Steels having the compositions indicated in Table I were prepared by adjusting contents of alloying elements other than Te, Bi and Ca in molten steels in an arc-furnace, which molten steels were then poured into a vacuum degassing vessel and degassed.
The degassed molten steel was then poured into a ladle having a porous plug at the bottom, and Al was added in a predetermined amount thereto.
Under agitation of the molten steels by blowing argon gas through porous plug at the bottom of the ladle, Te was added in various amounts corresponding to the contents of S to give ratio %Te/%S of at least 0.04. Then, a certain amounts of Pb, Bi and Ca were added to some batches. If desired, Te, Bi, Pb and Ca could be added to stream of the molten steels during pouring them into the ladle.
The molten steels were cast into 1.3 ton-ingots by bottom pouring. Te, Pb, and Bi could by added to stream of the molten steels to be cast.
The ingots were then hot rolled at a finish rolling temperature of 950.degree. C. to achieve forging ratio of about 100 or higher.
Specimens for various tests were taken from the steel products thus obtained.
TABLE I__________________________________________________________________________Steel % Te/ B,V,Ti, Pb,Se,Mark Run C Si Mn S Te % S O N Al Ni Cr Mo Nb,Zr Bi,Ca L/w__________________________________________________________________________JIS S10C 1 0.10 0.19 0.42 0.025 0.001 0.040 0.0015 0.010 0.035 -- -- -- -- -- 4.1 2 0.09 0.21 0.50 0.034 0.007 0.206 0.0012 0.009 0.030 -- -- -- Zr:0.17 -- 3.6 3 0.11 0.22 0.44 0.031 0.018 0.581 0.0014 0.010 0.034 -- -- -- -- Pb:0.28 3.1 4 0.11 0.20 0.45 0.028 0.019 0.679 0.0025 0.010 0.033 -- -- -- -- Bi:0.29 3.1 5 0.09 0.30 0.48 0.034 0.010 0.294 0.0013 0.009 0.034 -- -- -- Nb:0.07 Ca:0.0032 3.2 6 0.10 0.23 0.44 0.030 0.009 0.300 0.0019 0.009 0.034 -- -- -- Ti:0.09 Pb:0.14 3.1 Ca:0.0015 7* 0.10 0.25 0.47 0.030 -- -- 0.0112 0.010 0.032 -- -- -- -- -- 21.5JIS S55C 8 0.54 0.21 0.71 0.004 0.011 2.750 0.0014 0.008 0.015 -- -- -- -- -- 3.0 9 0.53 0.21 0.69 0.015 0.014 0.933 0.0013 0.009 0.018 -- -- -- B:0.0024 -- 3.1 Ti:0.04 10 0.55 0.20 0.69 0.011 0.005 0.455 0.0013 0.008 0.020 -- -- -- Zr:0.09 -- 3.3 11 0.56 0.19 0.70 0.016 0.002 0.125 0.0010 0.009 0.019 -- -- -- Nb:0.04 -- 3.5 Ti:0.02 12 0.55 0.21 0.81 0.012 0.006 0.500 0.0008 0.008 0.021 -- -- -- -- Pb:0.08 3.1 13 0.56 0.18 0.66 0.007 0.014 2.000 0.0009 0.008 0.015 -- -- -- -- Pb:0.05 3.3 Ca:0.0088 3.3 14 0.54 0.18 0.70 0.008 0.010 1.250 0.0008 0.009 0.018 -- -- -- Zr:0.05 Se:0.095 3.3 Ti:0.07 15 0.55 0.19 0.72 0.008 0.008 1.000 0.0012 0.008 0.016 -- -- -- Nb:0.01 Ca:0.0011 3.2JIS S550 16* 0.56 0.19 0.68 0.013 -- -- 0.0052 0.008 0.014 -- -- -- -- -- 25.1 17* 0.56 0.19 0.77 0.015 -- -- 0.0015 0.009 0.058 -- -- -- B:0.0052 -- 26.3 Ti:0.006JIS SMn21 18 0.20 0.19 1.22 0.009 0.006 0.667 0.0012 0.008 0.025 -- -- -- -- -- 3.2 19 0.21 0.22 1.29 0.008 0.004 0.500 0.0014 0.009 0.031 -- -- -- B:0.0019 -- 3.2 Ti:0.04 Nb:0.05 20 0.19 0.25 1.27 0.011 0.001 0.091 0.0009 0.010 0.028 -- -- -- Ti:0.03 -- 3.9 21 0.19 0.22 1.28 0.015 0.009 0.600 0.0009 0.010 0.028 -- -- -- -- Pb:0.15 3.4 Bi:0.13 22 0.21 0.21 1.25 0.010 0.018 1.800 0.0008 0.007 0.029 -- -- -- V:0.20 Bi:0.10 3.3 Zr:0.10 Se:0.025 23* 0.22 0.23 1.26 0.014 -- -- 0.0048 0.008 0.045 -- -- -- -- -- 23.4 24* 0.21 0.23 1.29 0.015 -- -- 0.0044 0.025 0.035 -- -- -- B:0.0021 -- 23.0 Ti:0.05JIS SCr4 25 0.41 0.20 0.71 0.009 0.002 0.222 0.0011 0.008 0.024 -- 1.02 -- -- -- 3.8 26 0.40 0.19 0.72 0.010 0.008 0.800 0.0013 0.009 0.022 -- 0.91 -- B:0.0032 -- 3.7 Ti:0.04 27 0.39 0.25 0.72 0.029 0.002 0.069 0.0016 0.010 0.023 -- 1.04 -- V:0.12 -- 3.8 28 0.40 0.22 0.69 0.012 0.015 1.25 0.0014 0.009 0.023 -- 1.00 -- Nb:0.06 -- 3.1 29 0.38 0.20 0.70 0.014 0.019 1.357 0.0012 0.009 0.025 -- 0.99 -- -- Pb:0.19 3.1 30 0.39 0.21 0.69 0.013 0.003 0.231 0.0010 0.008 0.025 -- 1.05 -- -- Se:0.059 3.8 31 0.39 0.20 0.73 0.015 0.006 0.400 0.0009 0.007 0.021 -- 1.07 -- -- Bi:0.04 3.3 Ca:0.0093 32 0.41 0.19 0.72 0.010 0.003 0.300 0.0008 0.009 0.019 -- 1.19 -- B:0.0044 Ca:0.0028 3.6 Ti:0.06 33* 0.42 0.23 0.78 0.029 -- -- 0.0015 0.010 .02 -- 1.04 -- -- -- 24.1 34* 0.43 0.21 0.71 0.014 -- -- 0.0041 0.011 0.022 -- 0.92 -- B:0.0044 -- 24.9 Ti:0.06 35* 0.40 0.22 0.75 0.015 -- -- 0.0063 0.015 0.025 -- 1.18 -- V:0.11 -- 22.6JIS SNC2 36 0.29 0.20 0.41 0.025 0.003 0.120 0.0013 0.009 0.025 2.35 0.78 -- -- -- 4.0 37 0.30 0.19 0.42 0.021 0.004 0.190 0.0010 0.008 0.024 2.66 0.76 -- B:0.0049 -- 3.4 38 0.30 0.25 0.40 0.015 0.009 0.600 0.0029 0.007 0.035 2.41 0.77 -- Nb:0.05 -- 3.8 Zr:0.12 39 0.31 0.22 0.48 0.024 0.005 0.208 0.0008 0.008 0.029 2.53 0.69 -- -- Pb:0.05 3.8 Se:0.0 Ca:0.0063 40 0.29 0.30 0.44 0.018 0.008 0.444 0.0009 0.008 0.039 2.49 0.88 -- Ti:0.05 Bi:0.06 3.3 41* 0.34 0.18 0.51 0.027 -- -- 0.0015 0.009 0.019 2.54 0.74 -- -- -- 25.5JIS SNCM25 42 0.41 0.22 0.50 0.020 0.001 0.050 0.0014 0.009 0.035 4.29 0.91 0.20 -- -- 4.5 43 0.15 0.21 0.41 0.015 0.003 0.200 0.0015 0.008 0.032 4.25 0.85 0.25 V:0.01 -- 3.6 Zr:0.06 44 0.16 0.28 0.39 0.012 0.005 0.417 0.0020 0.011 0.028 4.30 0.72 0.23 Nb:0.04 -- 3.5 Ti:0.05 Zr:0.03 45 0.15 0.23 0.41 0.015 0.002 0.133 0.0009 0.010 0.026 4.18 0.79 0.24 -- Pb:0.06 3.9 Se:0.01 Ca:0.0008 46 0.15 0.23 0.40 0.013 0.008 0.615 0.0012 0.009 0.029 4.24 0.86 0.23 B:0.0033 Bi:0.08 3.3 Ti:0.005 Nb:0.04 47* 0.16 0.31 0.43 0.008 -- -- 0.0035 0.024 0.008 4.22 0.88 0.24 -- -- 26.0JIS SCM22 48 0.20 0.21 0.74 0.018 0.019 1.056 0.0014 0.009 0.030 -- 1.05 0.24 -- -- 3.0 49 0.21 0.25 0.72 0.014 0.011 0.786 0.0013 0.008 0.026 -- 1.04 0.18 V:0.04 -- 3.3 50 0.21 0.23 0.73 0.012 0.005 0.417 0.0015 0.009 0.022 -- 1.05 0.29 Nb:0.06 -- 3.2 51 0.20 0.24 0.73 0.015 0.003 0.200 0.0012 0.009 0.027 -- 1.11 0.20 -- Pb:0.17 3.6 52 0.19 0.26 0.72 0.017 0.008 0.471 0.0008 0.010 0.026 -- 1.03 0.19 -- Pb:0.06 3.5 Ca:0.0024 53 0.21 0.26 0.73 0.016 0.002 0.125 0.0009 0.009 0.038 -- 0.98 0.19 -- Ca:0.0040 3.8 54 0.21 0.23 0.78 0.017 0.006 0.353 0.0013 0.009 0.019 -- 1.05 0.22 Nb:0.04 Ca:0.0029 3.4 55 0.20 0.24 0.77 0.034 0.028 0.824 0.0014 0.009 0.023 -- 1.07 0.23 Nb:0.05 Se:0.06 3.6 Ca:0.0015 56* 0.21 0.22 0.74 0.020 -- -- 0.0035 0.010 0.025 -- 1.02 0.22 -- -- 25.4 57* 0.21 0.23 0.75 0.022 -- -- 0.0056 0.010 0.003 -- 1.06 0.21 Nb:0.05 Ca:0.0012 24.9JIS SMnC3 58 0.43 0.23 1.44 0.014 0.002 0.143 0.0012 0.009 0.019 -- 0.52 -- -- -- 4.0 59 0.42 0.25 1.46 0.010 0.003 0.300 0.0014 0.008 0.018 -- 0.55 -- B:0.0021 -- 3.8 Ti:0.04 60 0.42 0.25 1.45 0.009 0.001 0.111 0.0010 0.006 0.016 -- 0.55 -- V:0.05 -- 4.1 Nb:0.07 Ti:0.08 61 0.43 0.24 1.44 0.011 0.005 0.455 0.0012 0.101 0.021 -- 0.55 -- -- Ca:0.0064 3.4 62 0.43 0.25 1.49 0.011 0.002 0.182 0.0026 0.015 0.027 -- 0.54 -- -- Bi:0.03 3.9 Ca:0.0018 63 0.43 0.22 1.41 0.014 0.009 0.643 0.0011 0.008 0.019 -- 0.51 -- Nb:0.04 Pb:0.03 3.5 Bi:0.07 64 0.42 0.26 1.48 0.013 0.015 1.154 0.0014 0.009 0.022 -- 0.58 -- Ti:0.03 Se:0.06 3.3 Zr:0.12 65* 0.44 0.24 1.48 0.018 -- -- 0.0017 0.009 0.021 -- 0.54 -- -- -- 23.6 66* 0.42 0.24 1.44 0.026 -- -- 0.0056 0.010 0.025 -- 0.53 -- B:0.0058 -- 25.1 Ti:0.064032 67 0.33 0.28 0.81 0.036 0.002 0.056 0.0013 0.009 0.021 -- -- 0.25 -- -- 4.4 68 0.32 0.28 0.80 0.029 0.018 0.621 0.0009 0.011 0.025 -- -- 0.26 V:0.02 -- 3.8 Ti:0.03 69 0.33 0.29 0.79 0.038 0.012 0.316 0.0010 0.010 0.019 -- -- 0.25 Zr:0.10 -- 3.8 70 0.31 0.27 0.83 0.034 0.003 0.088 0.0012 0.008 0.020 -- -- 0.25 -- Pb:0.05 4.0 Bi:0.01 Ca:0.0005 71 0.34 0.28 0.82 0.028 0.016 0.571 0.0011 0.009 0.020 -- -- 0.26 Nb:0.22 3.5 72* 0.35 0.27 0.82 0.031 -- -- 0.0015 0.011 0.025 -- -- 0.24 -- -- 22.84621 73 0.20 0.25 0.79 0.030 0.002 0.067 0.0014 0.009 0.025 1.81 -- 0.22 -- -- 4.1 74 0.21 0.27 0.81 0.015 0.005 0.333 0.0014 0.009 0.036 1.82 -- 0.24 B:0.0085 -- 3.7 Ti:0.04 Zr:0.04 75 0.21 0.30 0.83 0.016 0.002 0.125 0.0012 0.008 0.024 1.7 -- 0.26 -- Pb:0.07 4.0 Ca:0.0016 76 0.20 0.28 0.82 0.021 0.009 0.429 0.0013 0.009 0.018 1.85 -- 0.25 -- Ca:0.0038 3.6 77 0.22 0.28 0.82 0.015 0.003 0.222 0.0011 0.009 0.012 1.79 -- 0.24 Zr:0.11 Bi:0.06 3.5 Ca:0.0019 78* 0.20 0.31 0.85 0.039 -- -- 0.0032 0.009 0.051 1.80 -- 0.24 -- -- 24.0__________________________________________________________________________
(1) Form of the sulfides
Inspection was made on the sulfides inclusions in the steel by measuring length(L) and width(W) of 200 particles of the sulfides in a definite field of microscope. Averages of L/W, or aspect ratios, were recorded in Table I. The majority of the sulfide inclusion is MnS.
The relation between %Te/%S ratios and the aspect ratios is shown in FIG. 1.
As seen from FIG. I, %Te/%S ratios larger than 0.04 give aspect ratio of sulfide particles of 5 or less.
Microscopic photographs were taken to record the form of sulfide particles in some of the above specimens after hot rolling (forging ratio:about 170), and shown as FIGS. IIA, IIB, IIC, IID and IIE.
The specimens are of:
______________________________________FIG. Steel Mark Run No.______________________________________IIA S10C 1IIB S10C 2IIC SMn21 18IID S10C 7IIE SMn21 23______________________________________
The photographs show that the sulfides in the steel of this invention are in the form of a spindle, while those in the conventional steels are highly elongated form in rolling direction.
In Tables I and V, the abbreviation "L/W" means the above aspect ratio of a sulfide particle.
Runs with asterisk are control examples.
The numbers of JISs defining composition of the steels in the Tables are as listed below:
______________________________________Steel Marks JIS Number______________________________________S10C, S55C G 4051SMn21, SMnC3 G 4106SCr4 G 4104SNC1, SNC2 G 4102SNCM25 G 4103SCM22, SCM23 G 4105______________________________________
(2) Formability in cold forging
For the purpose of evaluating formability in cold forging of the specimens, test pieces (.phi.:30.times.50 mm) were taken from the specimens. The test pieces were subjected to upset, or cold forging test at 4 different levels of reduction of height, 60%, 65%, 70% and 75%. The upset pieces were then inspected with a microscope at magnifications 20 as to whether the pieces have inner cracks. Percentages of number of pieces which contain a crack among all the pieces at each level (200 pieces per level) are shown in Table II as "Occurrence of inner crack".
The table teaches that the occurrences of inner crack of the present steels are significantly lower than those of the conventional steels. Thus, the steel according to the invention is concluded to have good formability in cold forging.
TABLE II______________________________________ Occurrence of Crack in Cold Forging (%) at variousSteel Reductions of height (%)Mark Run Heat Treatment 60 65 70 75______________________________________JIS S10C 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0.5 4 As Rolled 0 0 0.5 2.5 5 0 0 0 0 6 0 0 0.5 2.0 7* 12.0 41.5 85.0 100JIS S55C 8 0 0 0 12.0 9 0 0 0 7.5 10 0 0 0 5.5 11 Spheroidizing 0 0 0 8.5 Annealing, 12 750.degree. C. F.C. 0 0 0.5 10.5 13 0 0 0 9.0 14 0 0 1.0 11.0 15 0 0 0 6.0 16* Spheroidizing 9.5 35.0 87.0 100 Annealing, 17* 750.degree. C. F.C. 0 29.5 76.5 100JIS SMn21 18 0 0 0 1.0 19 0 0 0 1.5 20 0 0 0.5 21 As Rolled 0 0 0 4.0 22 0 0 0 5.5 23* 11.0 12.5 62.5 97.0 24* 6.5 25.0 75.5 100JIS SCr 4 25 0 0 0 5.5 26 0 0 0 7.0 27 Spheroidizing 0 0 35 15.0 Annealing, 28 770.degree. C. F.C. 0 0 0 6.0 29 0 0 0 16.5 30 0 0 0 8.0 31 0 0 0 7.5 32 0 0 0 6.5 33* Spheroidizing 0 53.0 91.5 100 Annealing, 34* 770.degree. C. F.C. 22.0 35.5 77.5 100 35* 14.5 29.0 78.0 100JIS SNC2 36 0 0 0 0 37 0 0 0 0 38 Annealing, 0 0 0.5 5.0 820.degree. C. F.C. 0 0 0.5 5.0 39 0 0 0 4.0 40 0 0 0 3.5 41* 0 15.5 62.5 100JIS SCM25 42 0 0 0 0 43 As Rolled 0 0 0 0 44 0 0 0 2.0 45 0 0 0 5.5 46 As Rolled 0 0 0 8.0 47* 5.5 7.5 33.0 79.5JIS SCM22 48 0 0 0 0 49 0 0 0 0 50 0 0 0 0 51 0 0 0 6.0 52 As Rolled 0 0 0 1.5 53 0 0 0 0 54 0 0 0 0 55 0 0 0 11.0 56* 14.0 22.0 61.0 98.5 57* 25.0 47.5 75.0 100JIS SMnC3 58 0 0 0 8.5 59 0 0 0 10.0 60 0 0 0 11.0 61 Spheroidizing 0 0 0 7.5 Annealing, 62 750.degree. C. F.C. 0 0 2.5 19.5 63 0 0 0 15.5 64 0 0 0 11.5 65* 0 48.0 86.0 100 66* 35.0 63.5 99.0 1004032 67 0 0 0 11.5 68 0 0 0 15.0 69 Annealing, 0 0 0 10.0 830.degree. C. F.C. 70 0 0 0.5 18.0 71 0 0 1.5 22.0 72* 45.0 82.0 100 1004621 73 0 0 0 0 74 0 0 0 0 75 As Rolled 0 0 0 2.0 76 0 0 0 0 77 0 0 0 3.5 78* 39.5 45.0 100 100______________________________________
(3) Machinability
In order to evaluate machinability of the specimens, they were heat treated and subjected to drilling and lathing tests under the testing conditions shown in Table III.
The test results are given in Table IV.
TABLE III______________________________________Tool life test with Hss twist drillDrill: SKH 9, straight shank drill, 0 (diameter) 5.0mmFeed: 0.10 mm/rev.Depth of hole: 20 mm, (blind hole)Cutting speed: 30 mm/min.Cutting oil: noneCriterion of tool life: Accumulated depth of hole until the drill no longer cutsTool life test with carbide single point toolTool: P10 (-5,--5,5,5,30,0,0.4)Feed: 0.20 mm/rev.Depth of cutting: 2.0 mmCutting speed: 200 mm/min.Cutting oil: noneCriterion of tool life: Accumulated length of cutting time until abrasion of flank reached 0.2 mm.______________________________________
TABLE IV______________________________________ Tool Life Tool Life of ofSteel Heat Hss Twist Carbide singleMark Run Treatment Drill (mm) Point Tool (min.)______________________________________JIS S10C 1 37000 51 2 31200 48 3 96300 55 4 900.degree. C., A.C. 92700 52 5 35800 116 6 56100 120 7* 13000 35JIS S55C 8 360 15 9 320 14 10 300 14 11 300 15 12 540 21 13 850.degree. C., A.C. 460 48 14 520 18 15 340 46 16* 850.degree. C., A.C. 100 10 17* 80 9JIS SMn21 18 3400 21 19 3260 19 20 3280 20 21 880.degree. C., A.C. 6640 31 22 5820 20 23* 1200 13 24* 1140 12JIS SCr4 25 360 35 26 360 34 27 830.degree. C., F.C. 360 30 28 340 35 29 1180 41 30 620 37 31 830.degree. C., F.C. 540 84 32 340 78 33* 120 22 34* 120 22 35* 80 20JIS SNO2 36 560 17 37 560 16 38 850.degree. C., A.C. 480 16 39 700 55 40 660 24 41* 180 10JIS SCM22 42 3220 24 43 850.degree. C., A.C. 2860 23 44 2680 23 45 850.degree. C., A.C. 4900 56 46 4780 31 47 940 15 48 870.degree. C., A.C. 5340 45 49 5060 44 50 5280 45 51 18600 60 52 9260 53 53 5300 91 54 5140 90 55 7760 103 56* 1720 29 57* 1680 40JIS SMnC3 58 300 10 59 280 9 60 300 8 61 870.degree. C., A.C. 320 15 62 420 20 63 960 17 64 600 12 65* 80 5 66* 80 44032 67 420 7 68 400 7 69 830.degree. C., F.C. 400 6 70 1280 32 71 1820 15 72* 120 44621 73 3380 27 74 3140 26 75 5880 66 76 850.degree. C., A.C. 3460 57 77 5440 66 78* 1200 18______________________________________
EXAMPLE II
Preparation of the steels were practiced in accordance with the same procedure as Example I except that the refining with A1 was omitted.
Table V shows the chemical compositions of the prepared steels.
The molten steels were also cast into 1.3 ton ingots, and hot rolled under the same conditions as mentioned above.
Specimens for various tests were taken from the rolled steels thus obtained.
TABLE V__________________________________________________________________________Steel %Te/ B, V, Ti, Pb, Se,Mark Run C Si Mn S Te %S O N Al Ni Cr Mo Nb, Zr Bi, L/W__________________________________________________________________________JIS S10C 1 0.09 0.20 0.44 0.030 0.007 0.233 0.0013 0.009 0.005 -- -- -- -- -- 3.2 2 0.11 0.19 0.49 0.025 0.010 0.400 0.0015 0.010 0.009 -- -- -- Zr: 0.16 -- 4.1 3 0.10 0.20 0.43 0.030 0.002 0.066 0.0025 0.009 0.008 -- -- -- -- Pb: 3.29 4 0.09 0.19 0.50 0.025 0.007 0.280 0.0013 0.010 0.004 -- -- -- -- Bi: 3.28 5 0.11 0.21 0.42 0.034 0.019 0.559 0.0025 0.009 0.001 -- -- -- Nb: 0.08 Ca: 4.1033 6 0.11 0.30 0.48 0.031 0.007 0.226 0.0014 0.010 0.002 -- -- -- Ti: 0.08 Pb: 3.65 Ca: 0.0014 7* 0.10 0.25 0.47 0.030 -- -- 0.0112 0.010 0.032 -- -- -- -- -- 21.5JIS S55C 8 0.56 0.19 0.66 0.011 0.005 0.455 0.0009 0.009 0.001 -- -- -- -- -- 3.2 9 0.55 0.20 0.69 0.010 0.006 0.600 0.0010 0.008 0.003 -- -- -- B: 0.0010 -- 3.0 Ti: 0.05 10 0.56 0.16 0.67 0.004 0.014 3.500 0.0008 0.008 0.004 -- -- -- Zr: 0.05 -- 3.1 11 0.55 0.18 0.83 0.012 0.006 0.500 0.0008 0.008 0.002 -- -- -- Nb: 0.05 -- 3.3 Ti: 0.01 12 0.54 0.22 0.80 0.008 0.002 0.250 0.0014 0.008 0.008 -- -- -- -- Pb: 3.34 13 0.53 0.19 0.71 0.015 0.011 0.733 0.0010 0.009 0.007 -- -- -- -- Pb: 3.34 Ca: 0.0079 14 0.53 0.20 0.81 0.004 0.009 2.250 0.0009 0.009 0.009 -- -- -- Zr: 0.03 Se: 3.474 Ti: 0.08 15 0.53 0.21 0.71 0.016 0.007 0.438 0.0011 0.009 0.006 -- -- -- Nb: 0.03 Ca: 3.0010 16* 0.56 0.19 0.68 0.013 -- -- 0.0052 0.008 0.014 -- -- -- -- -- 25.1 17* 0.56 0.19 0.77 0.015 -- -- 0.0015 0.009 0.058 -- -- -- B: 0.0052 -- 26.3 Ti: 0.006JIS SMn21 18 0.21 0.24 1.28 0.011 0.005 0.455 0.0009 0.010 0.006 -- -- -- -- -- 3.9 19 0.19 0.21 1.22 0.009 0.009 1.000 0.0012 0.010 0.007 -- -- -- B: 0.0020 -- 3.8 Ti: 0.05 Nb: 0.03 20 0.21 0.24 1.28 0.015 0.018 1.200 0.0008 0.007 0.008 -- -- -- Ti: 0.05 -- 3.2 21 0.21 0.25 1.22 0.010 0.006 0.600 0.0012 0.009 0.009 -- -- -- -- Pb: 3.34 Bi: 0.04 22 0.20 0.19 1.29 0.009 0.010 1.100 0.0014 0.010 0.006 -- -- -- V: 0.19 Bi: 3.82 Zr: 0.08 SE: 0.030 23* 0.22 0.23 1.26 0.014 -- -- 0.0048 0.008 0.005 -- -- -- -- -- 23.4 24* 0.21 0.23 1.29 0.015 -- -- 0.0044 0.025 0.005 -- -- -- B: 0.0021 -- 23.0 Ti: 0.05JIS SCr4 25 0.38 0.21 0.70 0.012 0.009 0.750 0.0016 0.009 0.005 -- 1.05 -- -- -- 3.1 26 0.41 0.25 0.69 0.029 0.018 0.621 0.0010 0.010 0.005 -- 0.98 -- B: 0.0030 -- 3.2 Ti: 0.06 27 0.38 0.21 0.69 0.014 0.019 1.357 0.0010 0.008 0.006 -- 1.05 -- V: 0.11 -- 3.2 28 0.38 0.20 0.70 0.013 0.002 0.154 0.0012 0.010 0.008 -- 1.02 -- Nb: 0.05 -- 3.7 29 0.40 0.25 0.69 0.009 0.018 2.000 0.0010 0.008 0.009 -- 0.92 -- -- Pb: 3.80 30 0.41 0.18 0.70 0.028 0.002 0.071 0.0015 0.009 0.003 -- 1.02 -- -- Se: 3.261 31 0.40 0.19 0.73 0.012 0.004 0.333 0.0008 0.008 0.002 -- 1.08 -- -- Bi: 3.53 Ca: 0.0070 32 0.39 0.20 0.73 0.015 0.005 0.333 0.0009 0.007 0.004 -- 1.18 -- B: 0.0043 Ca: 3.4026 Ti: 0.05 33* 0.42 0.23 0.78 0.029 -- -- 0.0015 0.010 0.021 -- 1.04 -- -- -- 24.1 34* 0.43 0.21 0.71 0.014 -- -- 0.0041 0.011 0.022 -- 0.92 -- B: 0.0044 -- 24.9 Ti: 0.06 35* 0.40 0.22 0.75 0.015 -- -- 0.0063 0.015 0.025 -- 1.18 -- V: 0.11 -- 22.6JIS SNC2 36 0.30 0.19 0.48 0.015 0.0009 0.600 0.0029 0.007 0.004 2.55 0.76 -- -- -- 3.8 37 0.29 0.30 0.40 0.025 0.003 0.120 0.0008 0.007 0.005 2.49 0.77 -- B: 0.0050 -- 4.0 38 0.31 0.22 0.44 0.019 0.008 0.421 0.0009 0.009 0.004 2.43 0.69 -- Nb: 0.04 -- 4.0 Zr: 0.11 39 0.30 0.25 0.41 0.020 0.003 0.150 0.0010 0.007 0.003 2.51 0.80 -- -- Pb: 3.96 Se: 0.04 Ca: 0.0066 40 0.28 0.19 0.40 0.019 0.009 0.474 0.0027 0.009 0.004 2.56 0.69 -- Ti: 0.03 Bi: 3.47 41* 0.34 0.18 0.51 0.027 -- -- 0.0015 0.009 0.019 2.54 0.74 -- -- -- 25.5JISSNCM25 42 0.15 0.28 0.44 0.017 0.005 0.294 0.0009 0.008 0.006 4.18 0.85 0.24 -- -- 3.3 43 0.14 0.23 0.50 0.012 0.002 0.167 0.0020 0.011 0.007 4.30 0.72 0.23 V: 0.02 -- 3.5 Zr: 0.05 44 0.14 0.23 0.49 0.020 0.001 0.050 0.0009 0.010 0.003 4.24 0.85 0.20 Nb: 0.05 Pb: 4.44 Ti: 0.06 Se: 0.03 Zr: 0.02 Ca: 0.0009 45 0.14 0.22 0.39 0.013 0.008 0.615 0.0015 0.008 0.005 4.30 0.71 0.20 -- Pb: 4.05 Se: 0.03 46 0.16 0.22 0.50 0.012 0.005 0.417 0.0009 0.010 0.008 4.25 0.87 0.25 B: 0.0029 Ca: 3.5010 Ti: 0.06 Nb: 0.03 47* 0.16 0.31 0.43 0.008 -- -- 0.0035 0.024 0.008 4.22 0.88 0.24 -- -- 26.0JIS SCM22 48 0.19 0.26 0.73 0.014 0.010 0.714 0.0015 0.008 0.009 -- 1.04 0.29 -- -- 3.3 49 0.19 0.26 0.78 0.013 0.005 0.385 0.0015 0.009 0.006 -- 1.11 0.29 V: 0.03 -- 3.0 50 0.20 0.24 0.78 0.018 0.008 0.444 0.0014 0.008 0.007 -- 1.04 0.19 NB: 0.08 -- 3.6 51 0.21 0.26 0.72 0.013 0.002 0.154 0.0008 0.008 0.006 -- 1.05 0.18 -- Pb: 3.68 52 0.21 0.21 0.73 0.033 0.011 0.333 0.0009 0.008 0.005 -- 1.11 0.20 -- Pb: 3.87 Ca: 0.0025 53 0.20 0.21 0.73 0.018 0.008 0.444 0.0008 0.008 0.004 -- 1.10 0.20 -- Ca: 3.0044 54 0.20 0.25 0.76 0.033 0.0027 0.818 0.0012 0.010 0.003 -- 1.07 0.19 Nb: 0.09 Ca: 3.0030 55 0.21 0.25 0.72 0.014 0.027 1.929 0.0015 0.010 0.002 -- 1.11 0.29 Nb: 0.06 Se: 3.37 Ca: 0.0013 56* 0.21 0.22 0.74 0.020 -- -- 0.0035 0.010 0.025 -- 1.02 0.22 -- -- 25.4 57* 0.21 0.23 0.75 0.022 -- -- 0.0056 0.010 0.003 -- 1.06 0.21 Nb: 0.05 Ca: 24.912JIS SMnC3 58 0.44 0.24 1.46 0.009 0.003 0.333 0.0010 0.007 0.007 -- 0.55 -- -- -- 4.1 59 0.40 0.24 1.45 0.009 0.001 0.111 0.0010 0.0010 0.008 -- 0.53 -- B: 0.0022 -- 3.4 Ti: 0.03 60 0.43 0.25 1.44 0.014 0.002 0.143 0.0012 0.007 0.009 -- 0.52 -- V: 0.04 -- 4.0 Nb: 0.08 Ti: 0.10 61 0.42 0.25 1.46 0.009 0.004 0.444 0.0014 0.009 0.006 -- 0.50 -- -- Ca:0.0060 3.9 62 0.42 0.23 1.41 0.013 0.010 0.769 0.0025 0.008 0.005 -- 0.55 -- -- Bi:0.02 3.3 Ca:0.0016 63 0.42 0.26 1.49 0.011 0.005 0.455 0.0019 0.009 0.001 -- 0.52 -- Nb:0.03 Pb:0.04 3.9 Bi:0.10 64 0.43 0.25 1.41 0.011 0.010 0.909 0.0026 0.009 0.002 -- 0.57 -- Ti:0.02 Se:0.10 3.8 Zr:0.13 65* 0.44 0.24 1.48 0.018 -- -- 0.0017 0.009 0.021 -- 0.54 -- -- -- 23.6 66* 0.42 0.24 1.44 0.026 -- -- 0.0056 0.010 0.025 -- 0.53 -- B:0.0058 -- 25.1 Ti:0.06 67 0.34 0.27 0.80 0.029 0.003 0.103 0.0010 0.011 0.009 -- -- 0.26 -- -- 4.0 68 0.31 0.27 0.79 0.034 0.012 0.353 0.0008 0.008 0.008 -- -- 0.25 V:0.03 -- 3.9 Ti:0.04 69 0.30 0.28 0.81 0.037 0.013 0.351 0.0013 0.009 0.009 -- -- 0.24 Zr:0.09 -- 3.9 70 0.33 0.28 0.79 0.028 0.008 0.286 0.0010 0.011 0.006 -- -- 0.24 -- Pb:0.02 4.4 Bi:0.02 Ca:0.0008 71 0.31 0.28 0.80 0.034 0.015 0.441 0.0009 0.011 0.005 -- -- 0.26 Nb:0.02 Pb:0.23 3.8 72* 0.35 0.27 0.82 0.031 -- -- 0.0015 0.011 0.025 -- -- 0.24 -- -- 22.8 73 0.21 0.28 0.82 0.017 0.003 0.176 0.0013 0.008 0.003 1.77 -- 0.25 -- -- 4.0 74 0.22 0.28 0.82 0.030 0.009 0.300 0.0011 0.008 0.009 1.83 -- 0.23 B:0.0086 -- 3.5 Ti:0.03 Zr:0.03 75 0.22 0.24 0.79 0.015 0.007 0.467 0.0013 0.009 0.006 1.84 -- 0.25 -- Pb:0.09 4.1 Ca:0.0016 76 0.21 0.30 0.83 0.030 0.004 0.133 0.0010 0.008 0.008 1.77 -- 0.25 -- Ca:0.0035 3.6 77 0.20 0.30 0.81 0.017 0.007 0.412 0.0012 0.009 0.002 1.78 -- 0.23 Zr:0.10 Bi:0.05 3.5 Ca:0.0020 78* 0.20 0.31 0.85 0.039 -- -- 0.0032 0.009 0.051 1.80 -- 0.24 -- -- 24.0__________________________________________________________________________
(1) Form of sulfide particles
In order to study the form of sulfide particles, the length (L) and width (W) of the particles were measured, and averages of the aspect ratios (L/W) were determined in accordance with the procedure of Example I. The values are shown in Table V.
The relation between the aspect ratios and the %Te/%S has the same tendency as obtained in Example I and shown in FIG. 1, i.e., a %Te/%S larger than 0.04 gives an aspect ratio smaller than 5.
(2) Formability in cold forging
The specimens were subjected to a heat treatment suitable to the steel (some were used as rolled), and test pieces were taken from the specimens. They were tested under the same conditions mentioned in Example I.
Occurrence of inner crack of the steels is shown in Table VI together with the heat treatment conditions. From the Table it is clearly seen that the occurrence of inner crack of the present steels is remarkably smaller than that of the comparative steels, thus showing improved formability in cold forging.
(3) Machinability
Machining tests were conducted using the specimens listed in Table VI under the machining conditions shown in Table III.
The results are given in Table VII.
TABLE VI______________________________________ Occurrence of Crack in Cold Forging (%) at variousSteel Heat Reductions of height (%)Mark Run Treatment 60 65 70 75______________________________________JIS S10C 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0.3 4 As Rolled 0 0 0.3 2.1 5 0 0 0 0 6 0 0 0.3 1.7 7* 12.0 41.5 85.0 100JIS S55C 8 0 0 0 9.0 9 0 0 0 6.1 10 0 0 0 4.7 11 Spheroidizing 0 0 0 7.5 Annealing, 12 750.degree. C.,F.C. 0 0 0.3 9.5 13 0 0 0 7.0 14 0 0 0.7 9.0 15 0 0 0 5.0 16* Spheroidizing 9.5 35.0 87.0 100 Annealing, 17* 750.degree. C.,F.C. 0 29.5 76.5 100JIS SMn21 18 0 0 0 0.7 19 0 0 0 1.1 20 As Rolled 0 0 0 0.2 21 0 0 0 3.7 22 0 0 0 4.7 23* 11.0 12.5 62.5 97.0 24* 6.5 25.0 75.5 100JIS SCr 4 25 0 0 0 4.7 26 Spheroidizing 0 0 0 6.5 Annealing, 27 770.degree. C.,F.C. 0 0 3.5 13.0 28 0 0 0 5.0 29 0 0 0 13.5 30 0 0 0 7.0 31 Spheroidizing 0 0 0 6.1 Annealing, 32 770.degree. C., F. C. 0 0 0 5.1 33* 0 53.0 91.5 100 34* 22.0 35.5 77.5 100 35* 14.5 29.0 78.0 100JIS SNC2 36 Annealing, 0 0 0 0 820.degree. C. FC 37 0 0 0 0 38 0 0 0.3 4.1 39 0 0 0 3.0 40 0 0 0 3.1 41* 0 15.5 62.5 100JIS SNCM25 42 0 0 0 0 43 As Rolled 0 0 0 0 44 0 0 0 1.8 45 As rolled 0 0 0 4.1 46 0 0 0 7.1 47* 5.5 7.5 33.0 79.5JIS SCM 22 48 0 0 0 0 49 0 0 0 0 50 0 0 0 0 51 As Rolled 0 0 0 5.0 52 0 0 0 0.9 53 0 0 0 0 54 0 0 0 0 55 0 0 0 9.0 56* 14.0 22.0 61.0 98.5 57* 25.0 47.5 75.0 100JIS SMnC3 58 0 0 0 6.1 59 0 0 0 9.0 60 0 0 0 10.0 61 Spheroidizing 0 0 0 6.1 Annealing, 62 750.degree. C., F.C. 0 0 2.5 17.1 63 0 0 0 11.5 64 0 0 0 10.5 65* 0 48.0 86.0 100 66* 35.0 63.5 99.0 1004032 67 0 0 0 10.1 68 0 0 0 13.0 69 Annealing, 0 0 0 9.0 830.degree. C., F.C. 70 0 0 0.3 17.0 71 0 0 0.9 20.0 72* 45.0 82.0 100 1004621 73 0 0 0 0 74 0 0 0 0 75 As Rolled 0 0 0 1.7 76 0 0 0 0 77 0 0 0 3.1 78* 39.5 45.0 100 100______________________________________
TABLE VII______________________________________ Tool Life Tool Life of of CarbideSteel Heat Hss Twist single pointMark Run Treatment Drill (mm) Tool (min.)______________________________________JIS S10C 1 39,000 52 2 32,800 50 3 98,100 56 4 900.degree. C., A.C. 93,400 52 5 36,600 122 6 57,000 124 7* 13,000 35JIS S55C 8 380 15 9 340 15 10 300 14 11 850.degree. C., A.C. 320 16 12 540 23 13 480 50 14 560 19 15 360 46 16* 850.degree. C., A.C. 100 10 17* 80 9JIS SMn21 18 3,600 21 19 3,380 20 20 3,360 20 21 880.degree. C., A.C. 6,840 35 22 5,880 21 23* 1,200 13 24* 1,140 12JIS SCr4 25 380 35 26 380 36 27 830.degree. C., F.C. 360 32 28 340 36 29 1,260 43 30 660 37 31 830.degree. C., F.C. 600 85 32 380 80 33* 120 22 34* 120 22 35* 80 20JIS SNC2 36 600 17 37 620 17 38 850.degree. C., A.C. 500 18 39 740 57 40 660 30 41* 180 10JIS SNCM25 42 3,300 26 43 850.degree. C., A.C. 2,980 24 44 2,760 23 45 850.degree. C., A.C. 5,000 58 46 4,980 32 47* 940 15JIS SCM22 48 5,460 45 49 5,180 45 50 5,360 46 51 18,800 60 52 870.degree. C., A.C. 9,400 56 53 5,600 95 54 5,140 92 55 7,820 106 56* 1,720 29 57* 1,680 40JIS SMnC3 58 870.degree. C., F.C. 320 12 59 280 10 60 300 10 61 870.degree. C., F.C. 340 16 62 400 20 63 1,000 18 64 640 14 65* 80 5 66* 80 44032 67 460 9 68 830.degree. C., F.C. 420 8 69 400 8 70 1,320 33 71 1,980 16 72* 120 44621 73 3,380 27 74 3,260 28 75 850.degree. C., A.C. 5,980 68 76 3,500 62 77 5,440 68 78* 1,200 18______________________________________

Number	Name	Date
3152889	Holowaty	Oct 1964
3152890	Holowaty	Oct 1964
3169857	Rathke et al.	Feb 1965
3600158	Molnar et al.	Aug 1971
3634074	Ito et al.	Jan 1972
4032333	Josefsson	Jun 1977

Steel for cold forging having good machinability and the method of making the same

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