DD141165A2 - THERMOMECHANICAL ADVERTISING TREATMENT METHOD FOR SPRING STACKS FOR IMPROVING MATERIAL PROPERTIES - Google Patents

Abstract

The inventive method can be used in metallurgical operations and operations of the metalworking industry in treatment forged, rolled or drawn by other methods the forming technique plastically formed low-alloyed steel, in particular spring steel, and products derived therefrom. Setting a multi-phase microstructural state can be applied. The Invention pursues the goal, the. technically usable material properties of spring steel beyond the level to improve that in the application of the main patent 135 918 filed method can be achieved and the necessary inevitable Close temporal and spatial coupling of the thermomechanical influence and thermal austenite stabilization in the PS WP C 21 D / 206 599 described invention not required makes. By appropriate management of the thermomechanical process and corresponding tempering treatments becomes an inheritable stable real structure to be formed by compliance certain conditions of re-austenitisation and intermittent Hardening the production of the PS WP C 21 D / 206 599 explained favorable performance enhancing real structure state allows. The invention provides an economically advantageous Technology for complicated parts, based on the factory » Substance property improvement by application of the invention Method for adjusting a multi-phase structure » Condition in low alloy steels with an austenite content of > 7 vol.%,

Description

Field of application of the invention

The invention relates to a technological variant of the so-called high-temperature thermomechanical treatment which is applicable in metallurgical operations and / or enterprises of the metalworking industry. * The process according to the invention relates to the treatment of flat, square and round material of low-alloy steel, in particular spring steel , and products made thereof *

Characteristic of the known technical solutions

The invention relates to a supplementary solution of the heat treatment process for spring steels described in the main patent 135 918 for improving the material properties and the thermomechanical treatment method for spring steels for improving the material properties set forth in the patent WP C21D / 206 599.

The known heat treatment processes for influencing certain processing and / or use properties are described in TGL 21862

The heat treatment process for improving the material properties explained in the main patent Ί35,918 ι is based on the thermal austenite stabilization. As a result, it is possible to set structural states in low-alloyed steels in which the matrix consists of two different phases with cubic «= body-centered or" tetragonal-distorted and cubic " In this way, greatly improved material properties can be achieved compared to conventional tempering on low-alloy steels »According to the invention described in the patent specification WP C21D / 206 539, hot forming and thermal austenite stabilization are linked together to form a uniform technological scheme * In addition to the possible energy - And working time saving leads to the thus adjustable real structure state in a treatment according to Patent Specification WP C21D / 206 599 to a further increase in performance of the spring steels on the level eau of the properties achievable according to the main patent * A deficiency of the technical solution shown in the patent WP C21D / 206 5y9 consists in _? that the hot forming and the thermal Austenitstabilisierung are temporally and spatially closely coupled to adjust the performance-enhancing real structure state ©

The meaningful technological combination of plastic shaping and heat treatment (thermomechanical treatment) and subsequent re-tempering has been known since 1962 as an inheritance scheme of high-temperature thermomechanical treatment for martensitic hardened steels (Stal, Moscow _t ( -1962) 4, p. 346) _e In this case, the steel is transformed above A ₃ , then held for a certain time and then hardened

β »χ» - - - - _

After annealing and possible mechanical processing, the steel is re-tempered. "As a result of this treatment, there is a cause, the mechanical properties of the material are improved over conventional tempering, and approximately reach the values of direct high-temperature thermomechanical treatment."

The technological difficulties of the process are rapid cooling after forming at speeds above the critical cooling rate for hardening, down to temperatures M.M and the risk of retardation upon re-hardening

Object of the invention

The object of the invention is to improve the technically usable properties of low-alloyed steels, in particular spring steels, beyond the level which can be achieved by applying the invention according to main patent 135 918 to spring steels with multi-phase structural states by heat treatment.

At the same time, the possibility should be created not only to adjust the multiphase structure state by direct high-temperature thermomechanical treatment, as described in patent VVP C21Q / 206 599, but also to achieve this after subsequent tempering. The spectrum of products treated in this way can thereby be extended

Explanation of the essence of the invention

The object of the invention is to achieve this by a suitable combination of heat treatment after the forming process to improve the mechanical material property complexes to low-alloy steels, in particular spring steel with more · = phase microstructure states, and the application field of the performance-enhancing real structure states of the notified in Patent WP C21D / 206,599 to expand invention particularly suitable for complex components "According to the invention, this object is achieved in that the spring _s' steels .austenitisiert, then at temperatures above ₀ a * oder.in by a suitable method of hot forming, ZeB" rolling with a cumulative reduction ratio in the last related to both

warns · * -

last transformation steps of & »20 - 60% and a deformation rate f = 1« 10-2 «10 s ^x plastically deformed, then held at these temperatures for up to 60 s and then hardened or» Intermediate stage hardened «Curing can be interrupted and the interstage transformation can also be carried out incompletely, so that thereafter both mar- tensitic, martensitic-bainitic, and bainitic structures can be found, each with or without residual austenite components. Thereafter, the tempering is allowed to start at 650 ° C. After tempering, the parts can be machined using the dicing or forming techniques. Subsequently, the parts are austenitized again. After reaching the austenitizing temperature T., the should not exceed the temperature of the previous transformation, held maximum so long that coarse grain formation of austenite is prevented

The subsequent cooling to a temperature T -> M, where the thermal stabilization of the austenite occurs, must be carried out at a rate which is above the critical cooling rate for curing. The subsequent partial phase transformation of the austenite is controlled so that a multiphase martensite "Austenite", martensite / bainite-austenite or bainite-austenite mixed structure in which the retained austenite content after final tempering at temperatures T < 600 ⁰ C does not fall below a value of 7% by volume "

The inventively treated low alloy steel, in particular spring steel ,, characterized spite of temporal and Bust · = Licher separation aer in the Patentscnrift VVP C21D / 206 high temperature thermo-mechanical and thermal influence described 59Y austenite stabilization over the in the main patent

135 918. The microstructural constituents are finer and more uniformly distributed, which is achievable using the technology cited in the patent specification 125 918 ", by means of increased lattice defect density in the microstructure constituents martensite, martensite / bainite or" bainite and austenite with favorable dislocation arrangement, residual stress and large phase interface density "This microstructure has a positive effect on the technically usable material properties of a

embodiment

According to the invention to be carried out thermornechanische inheritance treatment and recoverable property improvements are 55 SiMn 7 demonstrates the steel "After austenitizing at 950 ⁰ C and Vl / alzung in one pass with a reduction of 40% and a

-1 average strain rate of 12 s was the steel 55 SiMn 7 strength after a holding time at this temperature of 15 s in a 0.4% Aquaplast solution to "quenched to a temperature of ca © 300 ⁰ C and then cooled in air to room temperature "Thereafter, at 220 ⁰ C and 600 ⁰ C per» weils started one hour so that the steel HV30 a 320 at a hardness - 325 kgf / mm is still sufficiently good processing * the re-austenitization at a temperature T. = 900 ⁰ C was carried out at a heating rate of 5 ° C / s with a holding time of the steel after reaching this temperature of 60 s. Thereafter, the thermal austenitization was achieved by quenching in a salt bath with a temperature of 375 C and 120 s holding time Cooling in water continued «The final technological operation was started at 250 ° C _e l h © The mechanical properties of a Re 20% to 35% by volume of the steel 55 SiMn 7 are listed in Table 1 and compared with those which can be achieved after conventional tempering and treatment of the processes filed in Patent Specifications 135 918 and WP C21D / 206 599.

Table H Mechanical material properties of the steel 55 SiMn 7 according to inventive thermo-mechanical inheritance treatment, conventional coating and treatment of the embodiments in the patents Schriften35 913 and VVP C21D / 206 599

Mechanical properties Treatment process «V MPa ^β 0.2 MPa % JL 0 / ^a k K0 / m ² Inventive thermomechanical inheritance treatment for Restaustenit ~ stabilization 1690 C 1460 1420. 1360 * 8th 31 470 Conventional hardening hardnesses of 870 ° in oil, tempering at 500 ° G 1640 1330 6 38 220 Heat treatment according to execution example in patent specification 135 918 1760 1430 8th 36 470 Thermomechanical treatment according to exemplary embodiment in patent specification WP C21D / 206 599 8th 33 480

Claims (4)

E. rf in dun g s a η s pru c h Thermomechanical inheritance treatment processes for spring steels for improving material properties are carried out according to the invention for producing multiphase martensite-austenite, martensite / bainite-austenite or bainite-austenite mixed microstructures and are characterized in that the spring steels are thermoformed at temperatures above A ~ _e the total degree of deformation in the last or the two last forming stages is 20-60 % and the average rate of change of shape is ¹ eee 2 × 10 s ^-1 and the holding time until quenching under A ₃ does not exceed 60 seconds; the quenching is carried out at a rate exceeding the critical rate of cooling for hardening until a temperature T <A. recrystallization excluding austenite below A _{1 s} the austenite transformation is ordered partially or completely in the intermediate or martensite stage by the subsequent two-stage process annealing in the temperature range 150-300 ⁰ C and 500 - formed 650 ⁰ C a ver · »erbungsfähige stable Real structure and a processing with the methods of the Zerteil- and forming is made possible, after re-austenitizing at a temperature T, the temperature of the does not exceed the previous forming and a holding time at which no coarse grain formation of the austenite begins, a Abschrekkung up to a temperature M < T < A. in which the thermal S JL see stabilization of the austenite takes place at a Geschwindigkeitj the above the critical cooling rate for the curing is _e, the following temperature control the setting of the martensitic-austenifischen "martensitic / bainitic-austenitischen- or © bainitic-austenitic mixed structure state allows ^ after the final annealing below 600 ⁰ C a minimum proportion of retained austenite> 7% by volume is guaranteed and the achieved property improvement is achieved by the inventively very well established real structure state of the spring steels * 1, characterized in that instead of the two-stage tempering after the thermo-mechanical influence in the temperature ranges 150-300 ⁰ C and 500-650 ⁰ C in purely martensitic-f martensitic bainitic or bainitic microstructure states without Restaustenitanteile a unique Tempering in the temperature range 500-600 ⁰ C is carried out to produce an inheritable stable real structure » 3 * thermomechanical hereditary treatment method according to item 1 and 2, characterized in that instead of the final annealing, aging can take place at room temperature » 4 "> Thermomechanical hereditary treatment method after Pkt» l and 2, characterized in that the starting process was carried out at a later date at the user