JPH062928B2 - Cold drawn free-machining steel bar with sulfur and phosphorus additions with tailored mechanical properties and machinability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a free-cutting cold drawn steel bar with added sulfur and phosphorus, and more particularly, has adjusted chemistry and its yield strength. The present invention relates to a steel bar which is determined not only by the adjusted chemical composition but also by the size of the steel bar after hot rolling and the reduction amount used for drawing the steel bar.

The main purpose of the present invention is in cold drawing free-cutting steel bar,
The mechanical properties of the steel bar, in particular the yield strength, are to provide the steel bar as determined on the basis of the chemical composition of the steel bar and the dimensions, cross section and applied reduction of the steel bar.

Another object of the present invention is to provide a means for adapting the yield strength of a steel bar to a desired working in a cold drawn steel bar when optimizing a component ratio in a chemical composition according to a dimension of the steel bar. It is an object of the present invention to provide a free-cutting cold drawn steel bar in which the amount of carbon is reduced as the amount is adjusted.

Another object of the present invention is to provide a cold drawn free-cutting steel bar,
The properties necessary to improve machinability are to provide a cold drawn free-machining steel bar that is optimized by its chemical composition and the physical properties of the steel bar.

Yet another object of the present invention is the addition of sulfur and phosphorus with excellent machinability provided by optimizing the relationship between steel chemistry conditions, steelmaking conditions, cold drawing conditions, and cutting conditions. It is to provide a free-cutting steel bar.

Still another object of the present invention is cold drawing free-cutting in which the amount and ratio of manganese, sulfur and niobium, and the amount and shape of deformation during cold drawing are adjusted to give optimum machinability. To provide sex steel bars.

Other objects of the invention will be clarified by the following specification and claims.

It is known that certain elements such as sulfur, lead, bismuth, tellurium and selenium are useful in improving the machinability of steel. Machinability is complex and not a well understood property. From the behavior when cutting an alloy with a cutting tool in operations such as single point turning, forming, drilling, reaming, boring, jogging, and thread cutting, the influence of the alloy composition,
There is also a problem in that plastic deformation and cutting mechanics of a metal work piece cannot be easily controlled. There is also a gap from the current knowledge of material behavior between the test results obtained from normal unsteady state tension experiments and the results obtained from cutting force data derived from cutting in the production process.

By modifying the chemical composition and optimizing the size, shape, distribution and chemical composition of inclusions, the brittleness of the chips is increased and the lubricity at the tool / chip interface is increased, allowing free cutting. Attempts to improve the machinability of flexible steel bars have been made by metallurgists for a long time. Furthermore, it is desirable to prevent the formation of abradable particles and microstructures within the steel bar.
For example, bismuth and tellurium (US Pat. No. 4,236,939), lead, bismuth, and tellurium and / or sulfur (US Pat. 4,244,737), tellurium and sulfur (U.S. Pat. No. 4,279,646), varying the amount of one or more elements. However, such a product does not completely meet the needs for improving the machinability of free-cutting steel bars. To improve machinability, much effort has traditionally been put into chemical composition, rather than optimizing chemical composition, reduction or dimensional shrinkage in cold work, and bar steel size and cross section. I came. The present invention is particularly directed to improving machinability by combining the optimum ratio of chemical components, especially manganese, sulfur and niobium, with the cold working amount and the optimum dimensions and optimum cross section of the steel bar. . Therefore, in the present invention, the chemical composition, reduction ratio, size and cross section of the steel bar are
It has been adjusted to be particularly suitable for cutting.

The free-cutting steel bar containing sulfur and phosphorus according to the present invention has
04 wt% to 0.08 wt% carbon; 0.6 wt% to
1.4 wt% manganese; 0.002 wt% to 0.1 wt% silicon; 0.03 wt% to 0.09 wt% phosphorus; 0.25 wt% to 0.50 wt% sulfur; 0.01 wt% to 0.10 wt% niobium; 0.004 wt% to 0.1% by weight of vanadium; the chemical composition is such that the total amount of impurities nickel, chromium, molybdenum and copper is 0.15% by weight and the balance is iron. The ratio of manganese, sulfur and niobium is of particular importance in obtaining steel bars with suitable chemical properties and in predicting the yield strength of such steel bars. Therefore, the ratio of (wt% of manganese) / (wt% of sulfur) is 1.
6 to 4.0, [(wt% of manganese) -1.62 x
The ratio (wt% of sulfur)] / (wt% of niobium) is 2 to 51.

The yield strength of steel bars, and thus their machinability, is determined by the raw material, the dimensions and the draft. The raw materials are hot-rolled coils, hot-rolled rods with diameters up to 5 cm (2 inches), and hot-rolled rods with diameters of at least 5 cm (2 inches), taking into account the type of product obtained from the rolling mill. Can be The raw material, which has been hot rolled to specific dimensions and cut to the appropriate length, is then cold drawn. The reduction rate or dimensional shrinkage rate in cold drawing is also extremely important in determining the yield strength of the final steel bar.

Taking into account the role of various chemical elements in the chemical composition of carbon steel bars up to 0.08% by weight and the influence of these elements on the machinability and behavior of steel bars, work hardening of steel bars undergoing cold drawing and cutting In order to keep the strain hardening and strain hardening low, a low carbon content is an essential condition.
The low carbon content reduces the strength of the steel bar added with sulfur and phosphorus, and in combination with the total amount of each element such as nickel, chromium, molybdenum and steel not exceeding 0.15% by weight, A product having relatively low ductility of chips generated at the tool-workpiece interface and high brittleness can be obtained. If the amount of each element exceeds the above specified amount and the amount of carbon decreases below the above specified amount, it is disadvantageous for the free-cutting product, the ductility of the chips increases, and the brittleness decreases. Further, when the carbon content exceeds 0.08% by weight, the number of abradable particles increases, the possibility of increasing the fracture stress increases, and the surface hardness of the hexagonal cold drawn steel bar increases.

0.6% to 1.4% by weight of manganese The specified amount of manganese is important in forming manganese sulfide (MnS) -based inclusions that affect tool life. Manganese promotes the hardenability and strength of the cold drawn steel bar. The actual manganese specifications in a particular steel bar depend on the diameter of the hot rolled steel bar, the mechanical properties required for the steel bar and the indicated cutting method. The manganese content increases as the size of the steel bar increases, and as the yield strength target increases.

Silicon up to 0.1% by weight Since the amount of abrasive silicates in the final product increases substantially with increasing silicon content, the silicon content is 0.1% by weight.
Need to be limited to.

0.25 wt% to 0.50 wt% Sulfur Sulfur is also required for the formation of manganese sulfide (MnS) -based inclusions that affect tool life. For this reason, the sulfur content should be at least 0.25% by weight. The particular specifications of sulfur for a particular steel bar depend on the steel bar and the dimensions and manganese content. The lowest sulfur content applies when using hot rolled coils as raw material, but 56
The highest sulfur content is required for large diameter cold drawn steel bars with high yield strengths up to kg / mm ² (80 ksi). Excess sulfur increases hot brittleness and reduces ductility, so the upper limit of the sulfur content of the product of the present invention is 0.5% by weight.

0.03 to 0.09 wt% Phosphorus Phosphorus is necessary to improve the smoothness of the finished surface.
However, phosphorus increases work hardening and increases the hardness of the chips produced during cutting. Therefore, in high-strength cold drawn steel bars, it is necessary to reduce the phosphorus content (usually up to 0.09% by weight) which is customarily added to this kind of steel bars for high speed cutting work.

0.01 wt% to 0.10 wt% niobium In the steel bar of the present invention, niobium is an essential element for increasing the strength, adjusting the mechanical properties in the radial direction of the steel bar, and reducing the toughness of the chips. Niobium specifications differ depending on the yield strength and the size of the steel bar. Niobium
It promotes the hardenability of the core of a large diameter cold drawn steel bar and increases the work hardenability. Niobium-containing steel bars can be cold drawn with a small reduction to minimize surface strengthening and substantially strengthen the core. However, when the content is higher than the specified amount, the effect of niobium increases the strength excessively and reduces the tool life.

Vanadium up to 0.1% by weight Vanadium improves mechanical properties such as yield strength, tensile strength and elongation through the core from the surface of steel bars, especially large diameter cold drawn steel bars. If the vanadium content exceeds the specified amount, the machinability of the steel bar deteriorates.

Impurities such as nickel, chromium, molybdenum and copper up to 0.15% by weight
These increase strength and ductility, promote the production of abrasive particles, all of which deteriorate the machinability of the steel bar.
Generally, the elements are harmful to machinability. Therefore,
These impurities should be kept within the specified range.

The ratio (wt% of manganese) / (wt% of sulfur) must be 1.6 to 4.0, and this ratio defines the amount of manganese and FeS inclusions in the solid solution.

The relationship between manganese, sulfur and niobium was defined as [(wt% manganese) -1.62 x (wt% sulfur)] / (wt% niobium), which is the relationship between manganese and niobium in strengthening the product. This is to define the relative contribution of Manganese is a thermodynamic change in the decomposition of austenite.
It affects the strength via cs of austenite decomposition, and niobium reduces the powder size and promotes precipitation hardening. Dimensions of hot rolled products, amount of reduction when squeezing into cold drawn products,
And depending on the required tensile strength of the steel bar in the final application,
The specifications for the ratio vary.

In addition to the listed elements, the machinability is improved by adding one or more of the following elements.

0.03 wt% to 0.35 wt% lead; 0.005 wt% to 0.05 wt% zirconium; 0.05 wt% to 0.25 wt% bismuth; 0.03 wt% to 0.15 wt lead and 0.05 wt% to 0.
15 wt% bismuth; 0.006 wt% to 0.012% nitrogen; 0.05 wt% to 0.25 wt% bismuth and 0.005 wt% to 0.05 wt% tellurium.

Zirconium maximizes machinability by promoting the formation of spherical MnS inclusions, while nitrogen promotes brittleness of the chips, which facilitates the drilling process.

The table below shows the amounts of manganese, sulfur and niobium and hot-rolled raw materials, ie hot-rolled coils, hot-rolled steel bars up to 5 cm (2 inches) in diameter, or at least 5 cm in diameter.
The relationship with a (2 inch) hot rolled steel bar will be described. The table shows the yield strength for a particular product obtained with a particular combination of elements. 42 kg / mm
^As applicable to hot rolled coils, which are about to be processed into cold drawn steel bars having yield strengths in the range of ² (60 ksi) to 56 kg / mm ² (80 ksi), Table 1 shows
The relationship between the yield strength, the weight percentages of manganese, niobium, and sulfur, and the ratio of these three elements is shown. Table 2 shows the manganese, sulfur, and niobium specifications for hot rolled steel bars up to 5 cm (2 inches) and shows the effect of steel bar cross-sectional shrinkage in cold drawing on yield strength. Table 3 shows the same contents as in Table 2 for a hot rolled steel bar having a diameter of at least 5 cm (2 inches). In Tables 1 to 3, each steel commonly contains 0.08% by weight of carbon, 0.03% by weight of phosphorus, 0.003% by weight of silicon and 0.004% by weight of vanadium.

The following are specific examples of products made in accordance with the present invention.

Table 4 shows nine compositions of niobium-containing re-sulfurized and re-phosphorized steels, and Table 5 shows mechanical properties of steels after cold drawing into a predetermined size and shape. is there. Table 5 also includes a steel called 12L14, which is a steel not containing niobium or carbon having the above-mentioned contents specified in the present invention, carbon: 0.10%, manganese: 0.95.
%, Sulfur: 0.32%, phosphorus: 0.08%, silicon: 0.003%
And lead: 0.17%. Table 5 shows the mechanical properties of 12L14 steel having a predetermined size and shape.

As can be seen from Table 5, the prepared chemistry steel bars of the present invention exhibit high yield and tensile strengths without substantially changing elongation and ductility, measured as drawing. . Thus, the mechanical properties of steel bars made in accordance with the present invention are substantially improved over conventional steel bars that do not have niobium, high carbon content, and do not utilize the aforementioned reductions. .

In addition to the steels shown in Tables 4 and 5, Table 6 is provided to show the improved tool life of steels within the parameters of the invention.
Two more types of steel are shown as 10 and 11. It had the following composition: Steel 10-carbon: 0.09%,
Manganese: 0.96%, phosphorus: 0.08%, silicon 0.003%, vanadium 0.004%, sulfur: 0.31% and niobium 0.005
%, Steel 11-carbon: 0.08%, manganese: 0.92%, phosphorus:
0.06%, sulfur: 0.34 Good niobium 0.12%. Steel 10 contained niobium in an amount less than the lower niobium content of 0.01% in the present invention, while Steel 11 contained niobium in an amount exceeding the upper limit of 0.1% niobium of the present invention.

The machinability of steel bars used in conventional threading equipment was measured by mechanically operating the steel bars as a measure of their tool life. Tool life was defined as the elapsed time spent to produce a satisfactory part. Improved tool life maximizes elapsed time, which will reduce cost per unit. Steel with about twice the tool life significantly reduces the user's end product cost.

Table 6 compares the machinability of steels 9, 10 and 11. Three 16 mm (5/8 inch) hexagonal steels were used for the manufacture of radiator fittings. Steel 9 and 10
There is virtually no difference in tool life for the finishing operations of. This is because there is virtually no change in the outer diameter of the work piece during the finishing operation. In rough machining, there is a large change in the outer diameter of the workpiece, and Table 6 shows the increase in tool life when Steel 9 is used in comparison with Steel 10. The results of Steel 11 indicate that the steel having 0.1% or more of niobium specified in the present invention is insufficient as a free-cutting steel.

12 mm round steel 9, 90 and 90 mm (20,000)
Pounds) was used to make the diesel pump nozzle.
Table 6 shows steels 9 and 1 for roughing, finishing or cutting.
It shows that there is no substantial difference in the tool life of 0, but there is a difference in the tool life of about 100% in the drilling operation. Further, Table 6 shows that Steel 11 containing 0.12% of niobium is inferior to Steel 9.

The increase in yield strength and tensile strength in free-cutting steel bars is accompanied by a decrease in elongation and ductility as measured by drawing. The initial shaving operation is performed. For example, optimum yield strength and tensile strength are required to improve surface finish in molding operations. Drilling is enhanced by an increase in ductility, measured as an increase in elongation and drawing.

Steel 12L14 shown in Table 5 exhibits mechanical properties typical of conventional free-cutting steel bars. The yield strength and tensile strength of Steel 12L14 can be increased by high cold drawing, with a substantial reduction in ductility, measured as a reduction in elongation and drawing. A prepared amount of niobium,
The steels of the present invention with low amounts of carbon and increased reduction significantly increase yield strength and tensile strength without a substantial reduction in ductility as indicated by elongation and drawing. Steel bars with increased yield strength and tensile strength, with no reduction in ductility, significantly improve machinability, which requires the ductility required in drills and the increased yield strength required in forming operations. And tensile strength.

Example 18 Hot rolled coil steel containing 0.042% by weight carbon, 0.85% by weight manganese, 0.003% by weight silicon, 0.053% by weight phosphorus, 0.23% by weight sulfur, 0.03% by weight niobium, 0.004% by weight vanadium and 0.311% by weight lead. The total amount of nickel, chromium, molybdenum and copper is up to 0.15% by weight with the balance iron.

The ratio of [(manganese weight%)-1.62 x (sulfur weight%)] / (niobium weight%) is 12.7, and (manganese weight%) /
The ratio (wt% sulfur) is 2.9. The weight percent of sulfur is further determined by multiplying the desired yield strength (ksi) by (0.0042-0.0054).

Example 19 Hot rolled coil steel containing 0.05 wt% carbon, 0.83 wt% manganese, 0.003 wt% silicon, 0.05 wt% phosphorus, 0.30 wt% sulfur, 0.035 wt% niobium, 0.003 wt% vanadium, and 0.12 wt% bismuth. The total amount of nickel, chromium, molybdenum and copper is up to 0.15% by weight with the balance iron.

The ratio of [(manganese weight%)-1.62 x (sulfur weight%)] / (niobium weight%) is 9.83, and (manganese weight%) /
The ratio (wt% sulfur) is 2.8. The weight percent of sulfur is further determined by multiplying the desired yield strength (ksi) by (0.0042-0.0054).

Example 20 Hot rolled coil steel containing 0.04 wt% carbon, 0.83 wt% manganese, 0.008 wt% silicon, 0.048 wt% phosphorus, 0.048 wt% sulfur, 0.35 wt% niobium, 0.04 wt% vanadium, 0.04 wt% lead, 0.1115 wt% bismuth, and 0.10 wt%. The total amount of nickel, chromium, molybdenum and copper is up to 0.15% by weight with the balance iron.

The ratio of [(manganese weight%)-1.62 x (sulfur weight%)] / (niobium weight%) is 6.4, and (manganese weight%) /
The ratio (wt% sulfur) is 2.4. The weight percent of sulfur is further determined by multiplying the desired yield strength (ksi) by (0.0042-0.0054).

An important feature of the present invention is that a steel bar with different machining specifications, different machining performances, different machining compatibility is within the scope of the combination of mechanical and chemical properties disclosed herein by the present invention. It is a choice. Shrinkage in cold drawing also has a substantial effect on yield strength. Yield strength is directly related to the shrinkage in cold drawing, the type of hot rolled material used to make the steel bar, and the manganese, niobium, and sulfur contents.

While the preferred embodiments of this invention have been described, it should be appreciated that many modifications, alterations and alternatives thereto may be made.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Litchiard B. Smith United States. 44035 Ohio, Elia, Washington Avanyu 334 (72) Inventor Litchard El. Thompson United States. 44001 Ohio, Amhurst, Oakhurst Street 709 (56) References JP 62270752 (JP, A)

Claims (8)

[Claims] 1. Carbon (C) is 0.04% by weight to 0.0
8 wt%, manganese (Mn) 0.6 wt% to 1.4 wt%, silicon (Si) 0.002 wt% to 0.1 wt%, phosphorus (P) 0.03 wt% to 0 0.09 wt%, sulfur (S) 0.25 wt% to 0.50 wt%, niobium (Nb) 0.01 wt% to 0.10 wt%, vanadium (V) 0.004 wt% to 0.1 wt%, the total of nickel (Ni), chromium (Cr), molybdenum (Mo) and copper (Cu) which are impurities up to 0.15 wt%, the balance is iron (Fe), %) / (Wt% of sulfur) ratio is 1.6
To 4.0, and the ratio [(wt% manganese) -1.62x (wt% sulfur)] / (wt% niobium) is 2 to 51. Cold drawn free-cutting steel bar added. 2. Carbon (C) 0.04% by weight to 0.0
8 wt%, manganese (Mn) 0.6 wt% to 1.4 wt%, silicon (Si) 0.002 wt% to 0.1 wt%, phosphorus (P) 0.03 wt% to 0 0.09 wt%, sulfur (S) 0.25 wt% to 0.50 wt%, niobium (Nb) 0.01 wt% to 0.10 wt%, vanadium (V) 0.004 wt% to 0.1% by weight, 0.03% by weight to 0.35% by weight of lead, and 0.15% by weight of nickel (Ni), chromium (Cr), molybdenum (Mo) and copper (Cu) which are impurities. The balance is iron (Fe), and the ratio of (wt% of manganese) / (wt% of sulfur) is 1.6.
To 4.0, and the ratio [(wt% manganese) -1.62x (wt% sulfur)] / (wt% niobium) is 2 to 51. Cold drawn free-cutting steel bar added. 3. The cold drawn steel bar according to claim 1, wherein the niobium (Nb) content is 0.01% by weight to 0.06% by weight. 4. The cold drawn steel bar according to claim 1, wherein the niobium (Nb) is more than 0.06% by weight and 0.1% by weight or less. 5. Carbon (C) is 0.04% by weight to 0.0
6 wt%, manganese (Mn) 0.6 wt% to 1.15 wt%, silicon (Si) 0.002 wt% to 0.1 wt%, phosphorus (P) 0.03 wt% to 0 0.06 wt%, sulfur (S) 0.25 wt% to 0.40 wt%, niobium (Nb) 0.01 wt% to 0.07 wt%, vanadium (V) 0.004 wt% to 0.1 wt%, the total of nickel (Ni), chromium (Cr), molybdenum (Mo) and copper (Cu) which are impurities up to 0.15 wt%, the balance is iron (Fe), Wt%) / (wt% of sulfur) is 2.0
To 3.5, the ratio [(wt% manganese) -1.62 x (wt% sulfur)] / (wt% niobium) is 2 to 51, and (wt% sulfur) A cold drawn steel bar according to claim 1 formed from a hot rolled coil steel having a composition of = (0.0042 to 0.0054) x (desired yield strength (ksi)). 6. The cross-sectional shrinkage ratio of cold drawing is 1 of that of a hot rolled bar.
The cold drawn steel bar according to claim 1, which is 5% to 30%. 7. A cross section made of hot-rolled rods up to 5 cm (2 inches) in which carbon (C) is 0.04 wt% to 0.08 wt% and manganese (Mn) is 0.7. Wt% to 1.30 wt%, silicon (Si) 0.002 wt% to 0.1 wt%, phosphorus (P) 0.03 wt% to 0.09 wt%, sulfur (S) 0. 28 wt% to 0.50 wt%, niobium (Nb) 0.02 wt% to 0.08 wt%, vanadium (V) 0.004 wt% to 0.1 wt%, and nickel (Ni) as an impurity. ), Chromium (Cr), molybdenum (Mo) and copper (Cu) total up to 0.15% by weight, the balance iron (Fe), the ratio of (% by weight of manganese) / (% by weight of sulfur) Is 2.0
To 3.2, the ratio [(wt% manganese) -1.62 x (wt% sulfur)] / (wt% niobium) is 4 to 51, and (wt% sulfur) = The cold drawn steel bar according to claim 1, having a composition of (0.0045 to 0.0058) x (desired yield strength (ksi)). 8. A hot rolled bar having a cross section of at least 5 cm (2 inches) and containing 0.04% to 0.08% by weight of carbon (C) and 0.8% by weight of manganese (Mn). To 1.4% by weight, silicon (Si) 0.002% to 0.1% by weight, phosphorus (P) 0.03% to 0.09% by weight, sulfur (S) 0.30% by weight % To 0.50% by weight, niobium (Nb) 0.02% to 0.10% by weight, vanadium (V) 0.004% to 0.1% by weight, nickel (Ni) as an impurity, The sum of chromium (Cr), molybdenum (Mo) and copper (Cu) is up to 0.15% by weight, the balance is iron (Fe), and the ratio of (% by weight of manganese) / (% by weight of sulfur) is 2.0
To 3.5, the ratio [(wt% manganese) -1.62 × (wt% sulfur)] / (wt% niobium) is 5 to 25, and (wt% sulfur) = The cold drawn steel bar according to claim 1, having a composition of (0.0045 to 0.0063) x (desired yield strength (ksi)).