AU679106B2 - Warm forming high strength steel parts - Google Patents

Description

1 WARM FORMING HIGH STRENGTH STEEL PARTS The present invention relates to a method of making high-strength steel parts and the parts produced thereby, and more particularly it relates to a method in which a blank of high-strength steel is warm formed into a desired geometric configuration while maintaining the high-strength properties of the steel blank.

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yp i~ AMENDED SHEET -2i s 7 r J Background of the Invention Steel parts have heretofore been formed using cold forging or hot forging techniques which are well known in the art. In hot forging parts from steel, the I oo c material is initially heated to abou <2000°F)and higher.

At these hot forging temperatures, substantial scale and decarburization of the steel occurs. Since the scale and decarburized surfaces must be removed to obtain the finished part, known hot forging techniques result in the waste of a certain amount of material; furthermore, such techniques are costly due to increased processing steps required to remove the scale and the higher energy consumption because of the high temperatures.

On the other hand, there are drawbacks to cold forming parts as well. Since the part is formed at or about room temperature, the reshaping or forming steps require substantially higher forces. This frequently necessitates a series of cold forning se-eps in which the material is formed into the desired part gradually.

This increases die wear and noise associated with such processes. Furthermore, if the material is worked to a substantial degree over a series of forming stages, the strength of the part is increased and the part must therefore be annealed between successive cold forming operations to relieve internal stress, which adds to the time and cost of such processes.

To avoid the above drawbacks, warm forging may be utilized to form parts from materials at an intermediate r AMENDED SHEET 3 temperature which is high enough to reduce the strength of the material and thereby facilitate forming, and yet is below the hot forging temperature at which scaling and decarburization occurs. One such warm forming method is disclosed in U.S. Pat. No. 3,557,587.

Certain other patents disclose processes which include rolling and extruding steps carried out at "warm" temperatures so as to avoid the drawbacks of decarburization and scaling and/or to impart or improve desired metallurgical and mechanical properties to the steel. See U.S. Pat. Nos. 2,767,836; 2,767,837; 2,880,855; 3,076,361; 3,573,999, and "Warm Working of Steel", Gokyu, et al, translation of the Japanese Institute of Metal, 1968, Volume 9, Supplement, Pages 177-181.

Additionally, there are other known mitlhoi fo: bending or forging steel bars, rods or billets to form a desired product which methods include a warm forming or warm forging step. See U.S. Pat. Nos. 2,953,794; 3,720,087; 3,877_~11; 4,312,210; 4,317,355; 4,608,851 and 4,805,437. No representation is made that any of the above cited references fairly represent the prior art or that such references are the most material references.

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4 U.S. Patent 5094698 describes a method of making high-strength steel parts from blanks of high-strength steel material having a tensile strength of at least 800 N/mm 2 and a yield strength of at least 600 N/mm 2 The blank is warm formed to provide a part of desired geometric configuration. The mechanical properties of the part are substantially the same as the blank without further strengthening processing steps. The high strength steel material comprises, by weight, 0.30 to 0.65% carbon, 0.30 to 2.50% manganzse and up to 0.35% vanadium with the balance being iron.

A method of making a high-strength steel part, in accordance with the invention, comprises providing a blank of high-strength steel material having a tensile strength of at least 800 N/mm 2 (120,000 psi) and a yield strength of at least 600 N/mm 2 (90,000 psi) and warm forming the blank into a part having a specific geometric configuration, whereby the mechanical properties of tensile strength and yield strength of the part are substantially the same as or greater than the blank; wherein,the high-strength steel material comprises, by weight percent:

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carbon 0.30 to 0.65% manganese 0.30 to 2.50% iron balance said part with said mechanical properties of tensile strength and yield strength produced without further jU C 5 strengthening processing steps, characterised in that the steel material further comprises, as a compulsory component, up to 0.35% of aluminum and/or niobium and/or titanium either alone or in a mixture including vanadium.

The present invention is directed to a method of making high-strength steel parts from blanks of highstrength steel material having a tensile strength of at least about 800 N/mm 2 (120,000 psi) and a yield strength of at least about 600 N/mm 2 (90,000 psi).

The method includes warm forming a blank of high-strength steel material whereby the mechanica- properties of tensile strength and yield strength of the part are substantially the same as or greater than the blank and wherein the part, with the desired mechanical properties of tensile strength and yie3d strength, is produced without further strengthening processing steps. High-strength steel parts are produced in accordance with the method of this invention.

The term "blank" as used herein has its usual meaning, a piece of metal to be warm formed into a finished part of desired geometric configuration.

Blanks include such pieces of metal as bar stock a piece of steel long in proportion to its thickness or width). The specific parts and configurations into which the blank is warm formed include various types of headed and upset shanks, cam rollers, nuts, ball joint AMENDED

SHEET

5a casings, torsion bars, axles, cam shafts, spline shafts, steering arms, sway bars, I-beams and other such parts according to this invention.

It is known to use aluminum, niobium, titanium and vanadium as grain refiners in the high temperature heat treatment of steel. An appropriate collective term therefor is accordingly "ferrous grain refiners" and this is employed herein.

The principles of this invention, its objectives and advantages will be further understood with reference to the following detailed description.

Detailed Description of the Invention The method of the present invention is useful for producing a wide variety of high-strength steel parts including ,iarious types of headed and upset shanks, screws, holtL. a rollers, nuts, ball joint casings, torsion bars, axles, cam shafts, spline shafts, steering arms, sway bars, Ibeams and other such parts susceptible to forming by the o warm forging or forming process disclosed herein.

In a preferred embodiment, the metho' of the present invention for making a high-strength steel part includes providing a blank of high-strength steel pMENDED SHEET N oe o o S o o oe material having a tensile strength of at least about 800 N/mm 2 (120,000 psi), and preferably at least about 1000 N/mm 2 (150,000 psi), and a yield strength of at least about 600 N/mm 2 (90,000 psi), and preferably at least about 900 N/mm 2 (130,000 psi). In one form, the high-strength steel material utilized as the blank has been hot reduced and cold drawn to provide the blank having the mechanical properties of tensile strength and yield strength stated above.

The high-strength steel material may be exemplified by the following composition, by weight percent: carbon about 0.30 to about 0.65% manganese about 0.30 to about at least 1 ferrous grain refiner from the group consisting of aluminum, niobium and titanium and mixtures thereof alone or with vanadium, in an effective amount up to about 0.35% iron balance.

In a more preferred form, the high-strength steel material has the following composition, by weight percent: carbon about 0.40 to about 0.55% manganese about 0.30 to about at least 1 ferrous grain refiner from the group consisting of aluminum, niobium and titanium and mixtures thereof alone or with vanadium, in an effective amount up to about 0.20% iron balance.

In a still more preferred form, the high-streuigth. steel material has the following composition, by weight percent: 25 carbon about 0.50 to about 0.55% manganese about 1.20 to about 1.65% at least 1 ferrous grain refiner from the group consisting of aluminum, niobium and titanium and mixtures thereof alone or with vanadium, in an effective amount of about 0.03 to about 0.20% 30 iron balance.

The blank, having a composition and mechanical properties of tensile strength and yield strength as given above, is thereafter warm formed at a temperature of about 150-650'C (300 to about 1200'F) to provide a part having a desired -mometric configuration, whereby the mechanical properties of tensile strength and yield strength of the part are substantially the same as or greater than the blank. The temperature at which the part is formed is related to the chemical composition of the steel material used. The formed part, with the mechanical properties of tensile strength and yield strength given, is produced without any further strengthening processing steps subsequent to the warm forming thereof.

[N:\LIBFF]00665:TCW *095 hi The blank of high-strength steel material having a tensile strength of at least about 800 N/mm 2 (120,000 psi) and a yield strength of at least about 600 N/mm 2 (90,000 psi), which is used as the starting piece in the method of the present invention is produced by any suitable method known in the art. One such method is disclosed in U.S. Pat. No.

3,904,445 to the present inventor, and the specification in its entirety is incorporated herein by reference. The '445 patent discloses a processing sequence to produce a highstrength steel bar stock of the type particularly useful for producing threaded fasteners, including U-bolts. In the deszribed process, the bar stock produced has a fine grained structure between about ASTM No. 5-8. In the disclosed process, a steel, having a chemistry falling within certain disclosed ranges, is subjected to a standard hot reducing operation to within 10%-15% of final gauge. The hot reduced bar stock is then cut or severed into individual lengths for rapid air cooling. Thereafter the individual lengths of hot reduced bar stock are subjected to a cold finishing to final gauge. The final step is a controlled stress relieving step to increase the mechanical strength properties. This stress relieving step comprises heating the lengths of bar stock to between about 260-450°C (500-850'F) for about 1 hour, but may or may not be necessary. Thus, such bar stock, with and without further stress relieving may be used to form the starting blank material of high-strength steel.

The following example illustrates the practice of the present invention to produce an upset shank from high-strength steel bar stock produced in accordance with the method disclosed in U.S. Patent No. 3,904,445 described above. The term "upset shank" refers generally to such structure as wire, rod, bar stock, etc. which has some of its length, typically an end, deformed into some form of a head having a cross-sectional area larger than the cross-sectional area of the balance of its length.

25 Example High-strength steel billet equivalent to grade 8 strength steel, having a diameter of 1.25cm is cut to lengths of approximately 10cm This stock has a tensile strength of at least about 1000 N/mm 2 (150,000 psi) and a yield strength of at least 900 N/mm 2 (130,030 psi) with a ferrite-fine pearlite microstructure and a fine grain 30 structure. The head of the shank is warm formed by forging or heading, one or more times, one end of each bar stock segment with a shaped die using a mechanical forging press applying approximately 150 tons of pressure. The head of the resulting shank is approximately 1cm (8 thick and 2cm (4 wide.

The mechanical properties of tensile strength and yield strength of the finished headed shank part are substantially the same or greater than that originally possessed by the bar stock, and therefore, no further strengthening processing steps are required. The finished headed shank also has enough of the desired mechanical property of ductility originally possessed by the bar stock that the need for further processing steps to improve :toughness can generally be eliminated. However, for certain uses of the Ghank, a stress t.'

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[N:\LIBF100665:TC 8 relieving step may be necessary. For example, in some applications it is not desirable for a shank to break under its head when pulled in tension. It is usually more desirable for the shank to be the weakest section of the part. In such instances, stress relieving improves the toughness of the part such that it breaks in its shank under tensile loading.

Thus, in accordance with other features of this invention, the metbod provides for warm forming a blank into a part whereby the mechanical properties of iensile and yield strengths may be substantially the same as or greater than the blank.

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Claims (9)

1. A method of making a high-strength steel part comprising the steps of: providing a blank of high-strength steel material having a tensile strength of at least 800 N/mm 2 (120,000 psi) and a yield strength of at least 600 N/mm 2 (90,000 psi) and warm forming the blank into a part having a specific geometric configuration, whereby the mechanical properties of tensile strength and yield strength of the part are substantially the same as or greater than the blank; wherein the high-strength steel material comprises, by weight percent: carbon 0.30 to 0.65% manganese 0.30 to 2.50% iron balance said part with said mechanical properties of tensile strength and yield strength lo produced without further strengthening processing steps, characterised in that the steel material further comprises, as a compulsory component, up to 0.35 of aluminum and/or niobium and/or titanium either alone or in a mixture including vanadium.

2. A method as claimed in Claim 1, wherein the high-strength steel material has previously been hot reduced and cold drawn to provide the blank.

3. A method as claimed in either Claim 1 or Claim 2, wherein the blank of high- strength steel material has a tensile strength of at least 1000 N/mm 2 (150,000 psi) and a yield strength of at least 900 N/mm 2 (130,000 psi).

4. A method as claimed in any one of Claims 1 to 3, wherein the high-strength steel material comprises, by weight percent: 20 carbon 0.40 to 0.55 manganese 0.30 to 2.50% aluminum and/or niobium and/or titanium and mixtures thereof alone or with vanadium up to 0.20% iron balance. 25

5. A method as claimed in any one of Claims 1 to 4, wherein the high-strength steel material comprises, by weight percent: carbon 0.50 to 0.55% manganese 1.20 to 1.65% aluminum and/or niobium and/or titanium and mixtures thereof alone or with vanadium 0.03 to 0.20% iron balance.

6. A method as claimed in any one of Claims 1 to 5, wherein the warm forming is carried out at a temperature between 150 to 650'C (300 to 1200'F).

7. A method as claimed in any one of Claims 1 to 6, wherein the part is selected from the group of parts consisting of various types of headed and upset shanks, bolts, .screws, cam rollers, nuts, ball joint casings, torsion bars, axles, cam shafts, spline shafts, ieering arms, sway bars and I-beams. [N:\LIBFR]00665:TCW

8. A method of making a high-strength steel part, which method is substantially as herein described with reference to the Example.

9. A high-strength steel part when produced by the method of any one of Claims 1 to 8. Dated 21 February, 1997 Consolidated Metal Products, Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON o oee *eo ee *e 0 es [N:\LIBFF]00665:TCW INTERNATIONAL SEARCH REPORT ApplEaionNo Intal Applicatin No94/07239 PCT/US 94/07239 LI- I(-S A. CLASSIFICATION OF SUBJECT MATTER IPC 6 C21D7/00 C21D8/00 According to Intemational Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC 6 C21D Documentation searched other than minimum documentation to the cxtert that such documents .er included in the fields searched Electronic data base consulted during the international search (name of data base and, where practical, search terms used) C. DOCUMENTS CONSIDERED TO BE RELEVANT Category" Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. X US,A,5 094 698 GALLAGHER JR) 10 1-9 March 1992 see the whole document X US,A,3 001 897 NACHTMAN) 26 1,7,9 September 1961 see claims 1,2; examples X EP,A,0 093 218 (UGINE ACIERS) 9 November 1,7,9 1983 see page 5; claims 3,8 L. I Further documents are listd in the continuation of box C. Patent family members are listed in annex. Special categories of cited documents: Special categories of cited docun later document published after the intemational filing date Sdocument deng gene state or priority date and not in conflict with the application but A' dcument defining the al state of te art which is not cited to understand the principle or theory underlying the considered to be of particular relevance invention earlier document but published on or after the international document of particular relevance; the claimed invention filing date cannot be considered novel or cannot be considered to document which may throw doubts on priority laim(s) or involve an inventive step when the document is taken alone which is cited to establish the publication date of another document of particular relevance; the claimed invention citation or other special reason (as specified) cannot be considered to involve an inventive step when the document referring to an oral disclosure, use, exhibition or document is combined with one or more other such docu- other means ments, such combination being obvious to a person skilled document published prior to the international filing date but in the art. later than the prionty date claimed document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 24 November 1994 11 Z A Name and mailing address of the ISA Authorized officer European Patent Office, P.B. 5818 PatentiUan 2 NI, 2280 HV Rijswijk Tel. (+31-70) 340-2040, Tx. 31 651 epo nl, Molet, Fac (+31-70) 340-3016 M et Form PCT/ISA/10 (second sheet) (July 1991) page 1 of 2 INTERNATIONAL SEARCH REPORT lntemi. .al Application No IPCT/US 94/07239 C.(ontinuation) DOCUMENT'S CONSIDERED TO BE RELEVANT Category 'Q Ctanon of document, with indication, where appropriate, of the relevant pamagcs I Relevant to claim No. DATABASE WPI Week 7705, Derwent Publications Ltd., London, GB; AN 77-08110 JP,A,51 144 328 (KOBE STEEL) 12 December 1976 see abstract US,A,4 289 548 BUCHER ET AL) September 1981 US,A,3 959 999 FILATOY ET AL) 1 June 1976 DE,A,34 34 743 W DIESEL GMBH) 3 April 1986 WO,A,93 15233 (CONSOLIDATED METAL PRODUCTS) 5 August 1993 see the whole document 1,7,9 1-9 Fonm PCTAISAnICt (continuation of secnd sheet) (July 1992) page 2 of 2 INTERNATINAL SEARCH REPORT nc AApiao N Information on patent faxnily members C/S9/73 ~<US-A-5094698 10-03-92 AU-A- 8300891 26-05-92 CA-A- 2093905 25-04-92 EP-A- 0554257 11-08-93 JP-T- 6501743 24-02-94 WO-A- 9207966 14-05-92 US-A- 5236520 17-08-93 US-A- 5330594 19-07-94 US-A-3001897 NONE '<EP-A-0093218 09-11-83 FR-A- 2525709 28-10-83 CA-A- 1198615 31-12-85 JP-A- 58189358 05-11-83 US-A-4289548 15-09-81 NONE US-A-3959999 01-06-76 FR-A,B 2297918 13-08-76 DE-A-3434743 03-04-86 NONE '40-A-93 15233 05-08-93 AU-B- 3587893 01-09-93 CA-A- 2128019 05-08-93 EP-A- 0624205 17-11-94 Form PCT/ISA/210 (patent tunily annex~) (July 1992)