DE1179971B - Deforming steel in a drawing or pressing die - Google Patents

Description

Deforming steel in a drawing or pressing die The invention relates to a method of continuously deforming hot rolled steels by guiding in bar form through a drawing or pressing die.

It is known to use steels continuously at temperatures above Room temperature, but below the lower transformation temperature to deform, however it was previously assumed that during plastic deformation at elevated temperatures either the tensile strength or the processability of the material decreases. In unexpected It has now been found that in the present process the otherwise customary special Deforming and annealing operations can be omitted and deforming if necessary can be carried out directly after the hot rolling, with steels with mechanical properties that exceed the properties of such steels, those by cold processing or by cold processing with subsequent relaxation or subsequent voltage equalization are established. This method of plastic Deformation at elevated temperatures then brings special and unexpected advantages when this method is applied to steels, their tensile strength decreases the plastic deformation is increased at elevated temperatures. The workability the steels are improved in the present process especially when that Process on steels with a low carbon content or on low-alloy carbon-manganese steels is applied.

The invention therefore consists in the use of the method for continuous deformation of hot rolled steels by guiding them in bar form by means of a drawing or pressing die at temperatures higher than room temperature, but below the lower transformation temperature, on steels that have a) pearlite structure have in a matrix of free ferrite and the b) in processing increased temperature in the area between 300 and 450 ° C result in deformation hardening as well as hardening by some kind of precipitation, whereby the deformation in the drawing or press die between 300 and 450 ° C is made.

The present process produces steels with properties such as so far only by using abnormally high caliber reductions and relaxation, z. According to U.S. Patent 2,320,040 (Landi) considerably in a simplified or economical way. It has been found that due to the temperature and the pressures exerted by the drawing die, Such a reaction in the steel arises that the stress equalization in combination with the development of the described improvements in physical and mechanical Properties occurs.

With regard to the mechanical properties it has been found; ' that it is possible by drawing at elevated temperatures in the defined range is, by applying normal caliber reductions, strength properties, proportionality limits and to achieve a hardness comparable to the corresponding of that Landi patent achieved without subsequent furnace treatment or stress equalization to require. In the case of abnormally high caliber reductions in which the steel is increased to one Temperature is heated, will be greatly improved mechanical properties obtain. This makes it possible to use the more expensive quenched and tempered steels or alloy steels to be replaced by easily accessible non-austenitic steels.

These unexpected and unpredictable results are only achieved on the basis of a) the suitable steel composition, b) the temperature of the plastic deformation and c) the degree of plastic deformation. For example it has been found that when drawing a non-austenitic steel that is within a temperature range of about 300 to 450 ° C is heated with abnormally high caliber reductions, extremely high tensile strength and hardness values obtained if the appropriate temperature for a particular steel composition is applied. When a steel is at a temperature above the specified range is heated, there is a decrease in tensile strength and hardness with a accompanying increase in elasticity.

It was found that according to the invention by suitable temperature control new and unexpected proportionality and yield strengths in steels of the non-austenitic Type can be developed that has a pearlite structure in a matrix of free Has ferrite. Proportionality and yield point run in many relationships parallel to each other. It has been found that by heating the steel to a Temperature within the range of 300 to 450 ° C for superior results the proportionality and yield strength can be achieved and that the heating of the Steel to temperatures above or below the defined range when drawing the Yield or yield point reduced, but at the same time the ductility increased. the Development of such unexpected properties of the yield and proportionality limit seems from the decrease in caliber, the temperature at which the optimal properties can be achieved, and to be dependent on the composition of the steel.

The following examples serve to further illustrate the invention.

Example 1 Steel Composition 0.170 /, Carbon; 0.750 /, manganese, 0.03% phosphorus, 0.04% sulfur, 0.080 /, silicon dioxide, 0.005% nitrogen.

Example 2 Steel Composition: 0.48 "/, carbon, 1.500 / 0 manganese, 0.03% phosphorus, 0.27% sulfur, 0.30% silicon, 0.05% nitrogen.

Procedure Steel bars of the above compositions, made according to normal hot rolling practice to have normal pearlite and ferrite structure, were advanced through a die to give a 19% reduction in area of 15.88 mm round bar stock. A group of rods was drawn with lubricant on the surface, but without prior heating to an elevated temperature. Other bars were drawn through the same die with the same lubricant but heated to various elevated temperatures ranging up to about 566 ° C for drawing. Tensile strength, hardness, proportionality and yield point were each determined. The values are listed in the following tables. Table 1 Tensile strength of various steels, those at different temperatures are drawn with a 19% reduction in cross-section Tensile strength temperature (kg / mm2) drawn steel steel des steel (° C) Example 1 I Example 2 23.9 62.60 94.20 127 62.60 94.90 210 66.80 103.60 293 67.50 105.00 365 71.70 104.30 460 60.50 94.20 557 50.60 85.80 Table 2 Brinell hardness of various steels, those at different temperatures are drawn with a 19% reduction in cross-section Temperature of the Brinell hardness drawn steel I steel I steel (° C) Example 1 Example 2 23.9 174 250 127 183 255 210 197 280 293 205 311 365 200 295 460 191 277 557 140 245 Table 3 Proportionality limits for different steels, those at different temperatures are drawn with a 19% reduction in cross-section Temperature of the proportional limit (kg / mm ') drawn steel steel des steel (° C) Example 1 Example 2 23.9 45.00 43.60 127 45.00 59.80 210 51.30 70.30 293 56.20 75.20 365 62.60 84.40 460 57.00 79.70 557 52.00 70.30 From the above it can be seen that for rods which are drawn with a 19% reduction in cross section within the temperature range of 300 to 450 ° C, the tensile strength properties, the hardness and the proportional limit are at considerably higher values than those which are drawn at temperatures below and are drawn above the range described, and that between temperatures of 300 and 450 ° C a marked improvement in such properties of steels with compositions according to Examples 1 and 2 is achieved.

The improvement in other mechanical and physical properties, combined with the improvements that are ensured in the mechanical properties in the manner described and claimed here, are illustrated in the following table, in which the properties are listed and at the specified caliber decrease and the selected temperature are compared with material properties after cold drawing at room temperature. Table 4 Properties of a steel with different Temperatures with a 19% cross-sectional reduction has been drawn Properties of steel of example 1 23.9 ° C 1 365 ° C Tensile strength (kg / mm2). . . . . . . . 62.60 71.70 Yield or yield point (kg / mmz) .................. 61.90 71.10 Proportional limit (kg / mm ',) .................. 45.00 62.60 Reduction in cross-section (0/0). . 45 57 Elongation at 5.08 cm measuring length (0/0) ....................... 10 12 Rejection value .............. -f-0.29 -0.21 Surface roughness (microinches). 45 15 Brinell hardness ... .... ......... ... 175 I 200 From the above it can be seen that steels which are drawn with a 19% reduction in cross-section at elevated temperature within the range described have significantly improved mechanical and physical properties and reduced recovery values as a result of the present process. Example 3 Steel from Example 2 as 15.88 mm round stock was heated to various temperatures ranging from room temperature from about 23.9 ° C to about 427 ° C in a gas-fired furnace and drawn through a drawing die to produce reductions of 12 To effect 19 and 36%. The tensile strength, hardness and proportional limit values given in Table 5 below clearly show that improvements in strength, proportional limit and hardness occur in each case when the steel is drawn at a temperature within the defined range. Table 5 The table compares the properties of steel in terms of caliber decrease and temperature Caliber decrease drawing temperature 23.9 ° C, i 127 ° CI. 266 ° G. I 365 ° CI 460 ° C Tensile strength (kg / mm2) 12% ........................... 92.10 89.30 97.60 102.00 94.20 190/0 ........................... 94.20 94.90 105.00 104.30 94.20 360/0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 105.00 106.40 112.70-104.30 Brinell hardness 120/0 ........................... 236 246 271 282 236 '- 190/0 ........................... 250 255 311 295 245 36% ........................... 285 283 313 307 277 Proportional limit (kg / mm2) 12% ........................... 48.70 46.90 76.60 71.00 60.50 19% ........................... 43.60 59.80 75.20 84.40 70.30 36% ........................... 54.80 71.70 103.60 95.60 85.80 In the practice of the invention, it has been found possible to achieve previously unattainable combinations of mechanical and physical properties coupled with the development of improved machinability, the size of which depends on the composition of the steel and on the state in which its constituents are during the drawing process are located. Some of the non-austenitic steels appear to be essentially insensitive to the drawing temperature in terms of their machinability characteristics, while substantial improvements in machinability result in steels of a different composition when drawn within a well-defined temperature range so that the metallurgical treatment of the steels is improved and the steel lighter can be adapted to the intended use.

It is difficult to understand the relationship between machinability, composition of the steel, drawing temperature and caliber decrease exactly. From the practical It has been found that in some grades of non-austenitic steels, which contain between 0.10 and 0.50% carbon, the machinability of the steel by drawing at temperatures in the range of 300 to 450 ° C. at such steels result in very substantial and marked improvements the machinability in non-resulfurized, low-sulfur steels with a carbon content between 0.10 and 0.25 0/0 when drawn at temperatures between 300 and 450 ° C will.

Investigations also showed that in the case of non-austenitic Steels containing free ferrite suitable for hardening, such as Strain hardening or precipitation hardening, unexpected improvements in physical properties can be achieved by treatment at temperatures that are able to harden the free ferrite. In steels that have little or no free Having ferrite in their structure, the machinability seems to be essentially different Drawing temperature to be unaffected. On the other hand, non-austenitic steels show which contain substantial amounts of free ferrite, which is an influence of the drawing process is hardened, pronounced Machinability improvements by suitable regulation of the drawing temperature, d. H. at temperatures between 300 and 450`C for non-austenitic steels that have a carbon content that is preferably between 0.10 and 0.20 ° / 0.

By processing the non-austenitic steels at elevated temperatures within the range of 300 to 450 ° C it is not only possible, previously unattainable Strengths, proportional limits and other improvements in mechanical and physical properties to be achieved, but through appropriate choice of Temperature has also been shown to be possible, also making significant improvements to ensure machinability. The improvements to the strength and proportional limit may or may not be obtained with loss of extensibility like them is determined by the processing temperature. By processing at increased Temperatures in the manner described, it is also possible to reduce residual stresses in such a way to reduce low values, as they were previously achieved by the usual drawing processes of the Steel with subsequent stress equalization were achievable. That way is it through the metallurgical process described here in a single step possible to achieve many benefits that previously required multiple steps. Within The pulling temperature range can make up for these unexpected improvements in the To achieve machinability, the applied stress conditions become more prevalent Effect can be brought about, creating compressive forces in the surface part of the drawn Steel occurrence.

Claims (5)

Claims: 1. Application of the process for continuous Deformation of hot rolled steels by guiding them in bar form through a drawing or press die at temperatures higher than room temperature, but below the lower transformation temperature, on steels that have a) pearlite structure in a matrix of free ferrite and b) when processing at elevated temperature in the range between 300 and 450 ° C result in strain hardening as well as by any Harden the precipitation type, with the deformation in the drawing or pressing die between 300 and 450 ° C is made. 2. Application according to claim 1 on steels with a low carbon content of about 0.1 to 0.5%. 3. Application according to claim 1 or 2 on weakly alloyed carbon-manganese steels with a content of further alloy components of together less than about 1%. Considered publications: German Patent Specifications Nos. 359 610, 881673; German patent application p 28695 VIa / 18c (D) (published on February 28, 1952); French Patent No. 767 081; U.S. Patent No. 2,320,040; G. S achs, "Practical Metallkunde", Vol. II, 1934, p.205; P. G oernes, »Introduction to Metallographieu, 7th and 8th edition, Halle 1948, p. 397; H. B orchers, "Metallkunde (11) <4, Goeschen-Volume No. 433, 1952, p. 118; F. R apatz, "The stainless steels", 4th edition, 1951, P. 100; "Material Handbook Steel and Iron", 2nd edition (reprint 1944), sheet T 31 (pp. 1 and 7); D. K. B u 11 e n s, »Steel and its Heat Treatmentr, Vol. 1, 1948, 5th edition, p. 234.