RU2627715C1 - Method of thermomechanical processing microalloy steels - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes heating the workpiece at a rate of 0.01 to 50°C/s to temperatures of Ac₃±15°C, single deforming with a degree of 40-50%, or double deforming of 20-30% with an inter-information pause of not more than 5 s at the temperature of Ac₃±15°C and the deformation rate of 0.1-50 s^-1, cooling.

EFFECT: producing a homogeneous ultrafine-grained ferrite-pearlite structure with a high complex of mechanical properties with a reduction in processing time and energy consumption.

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Description

The invention relates to the field of thermomechanical processing (TMT) of microalloyed steels and can be used in metallurgy and mechanical engineering.

Known methods of thermomechanical processing of steels, allowing to increase the complex of mechanical properties of products [Gulyaev A. Metallurgy. - Ripol Classic, 1986; Bernstein M.L. Thermomechanical processing of metals and alloys. - 1968]. For this, the preform is heated to austenitization temperature, then plastically deformed in a certain temperature range, then quenching and tempering are carried out. However, this method does not guarantee a homogeneous ultrafine-grained ferrite-pearlite metal structure with a high complex of mechanical properties in microalloyed steels, in addition, this method has many technological operations, which makes it very energy-intensive.

The closest selected for the prototype is the method of thermomechanical processing of steel products [RU 2060282 C1 from 05.20.1996]. The method includes the following operations:

- heating at a speed above 50 ° C / s to temperatures from A _c1 to A _s3 + 200 ° C,

- deformation by rolling with a degree of 45-80%,

- for pre-eutectoid steels, the deformation is carried out at a temperature of rolling end above the intercritical interval, and for eutectoid and hypereutectoid steels - above A _r1 ,

- accelerated cooling is carried out to obtain a martensitic structure or decomposition products of austenite,

- vacation products is carried out by single or multiple cyclic high-speed heating.

The disadvantages of the method are: not to obtain a uniform ultrafine-grained ferrite-pearlite metal structure with a high complex of mechanical properties from microalloyed steels, the heating rate of the workpiece above 50 ° C / s is unattainable when heating large slabs during sheet rolling, the degree of deformation above 50% is unattainable during hot rolling of thick sheet on broadband mills, a large number of technological operations leads to large time and energy costs.

A technical problem is the production of microalloyed steels with a homogeneous ultrafine-grained ferrite-pearlite structure with a high complex of mechanical properties while reducing processing time and reducing energy consumption.

To solve the problem, a method for thermomechanical processing of microalloyed steels is proposed, which includes the following operations:

- heating the workpiece at a speed of from 0.01 to 50 ° C / s to temperatures A _s3 ± 15 ° C (A _s3 is the temperature of the end of the transformation of ferrite → austenite);

- a single deformation with a degree of 40-50% or two deformations of 20-30% each with an inter-deformation pause of not more than 5 s at a temperature of A _s3 ± 15 ° C and a strain rate of 0.1-50 s ^-1 ;

- subsequent cooling, for example, in air or in water to room temperature.

Heating a metal at a rate from 0.01 to 50 ° C / s to a temperature of A _c3 ± 15 ° C leads to the formation of a fine austenite grain during the polymorphic transformation ferrite → austenite, and a single deformation with a degree of 40-50% or two deformations of 20- 30% with an inter-deformation pause of not more than 5 s, which is not enough for softening processes to occur, namely at temperature A _s3 ± 15 ° C and a strain rate of 0.1-50 s ^-1 leads to a significant accumulation of strain hardening (elastic energy of defects in the crystal structure ) during plastic deformation account jump modulus of elasticity of iron and steel at a temperature of A _c3 ± 15 ° C, which significantly increases the number of nucleation sites during the phase transformation during cooling, that collectively lead to the formation of microalloyed steels uniform ultrafine ferrite-pearlite structure of the metal with a high complex mechanical properties: yield strength σ _t , temporary resistance σ _in and elongation δ ₅ . The high level of mechanical properties of steels is directly related to their structural state and, like the structure, depends on temperature, degree and strain rate, accumulated deformation. Thus, the combination of distinctive features is necessary and sufficient to solve the problem.

с^-1,

с^-1,

с^-1 соответственно, время паузы между проходами составляло 2 с, 3 с и 5 с соответственно, температура конца прокатки составила Т=900°С. После деформационное охлаждение проводили на воздухе до комнатной температуры. В результате выполненной ТМО в прокатанном металле сформировалась однородная ультрамелкозернистая феррито-перлитная структура со средним размером зерна феррита 5-6 мкм (фиг. 1) и комплексом свойств, соответствующим требованиям по классу прочности 390 согласно ГОСТ 19281-2014 «Прокат повышенной прочности» при значительно более высокой пластичности: σ_т=406 МПа, σ_в=518 МПа, δ₅=35%.Example 1. Thermomechanical processing was carried out on microalloyed steel 17G1S-U. The samples were heated to a temperature of T = 910 ° C at a rate of 0.01 ° C / s, then the metal was deformed by rolling in two passes with a degree of deformation of 20%, 25%, 30% in each and a strain rate

s ^-1

s ^-1

s ^-1, respectively, the pause time between passes was 2 s, 3 s and 5 s, respectively, the temperature of the end of rolling was T = 900 ° C. After deformation cooling was carried out in air to room temperature. As a result of the TMT, a homogeneous ultrafine-grained ferrite-pearlite structure was formed in the rolled metal with an average ferrite grain size of 5-6 μm (Fig. 1) and a set of properties that meet the requirements for strength class 390 according to GOST 19281-2014 “High-strength rolled products” with significantly higher ductility: σ _m = 406 MPa, σ _in = 518 MPa, δ ₅ = 35%.

с^-1,

с^-1,

с^-1 соответственно, время паузы между проходами составило 2 с, 3 с и 5 с соответственно, температура конца прокатки составила Т=905°С. Последеформационное охлаждение проводили на воздухе до комнатной температуры. В результате выполненной ТМО также сформировалась однородная ультрамелкозернистая феррито-перлитная структура металла со средним размером зерна 5-6 мкм (фиг.2) и комплексом свойств, соответствующим требованиям по классу прочности 390 согласно ГОСТ 19281-2014 «Прокат повышенной прочности» при значительно более высокой пластичности: σ_т=418 МПа, σ_в=522 МПа, δ₅=39%.Example 2. Thermomechanical processing was carried out on microalloyed steel 17G1S-U. The samples were heated to a temperature of T = 915 ° C at a rate of 50 ° C / s, then they were deformed by rolling with a degree of deformation ε = 40% and 50% in one pass and a strain rate

s ^-1

s ^-1

s ^-1, respectively, the pause time between passes was 2 s, 3 s and 5 s, respectively, the temperature of the end of rolling was T = 905 ° C. Post-deformation cooling was carried out in air to room temperature. As a result of the TMT, a homogeneous ultrafine-grained ferrite-pearlite metal structure was also formed with an average grain size of 5-6 μm (Fig. 2) and a set of properties meeting the requirements for strength class 390 according to GOST 19281-2014 “High-strength rolled products” at a significantly higher plasticity: σ _m = 418 MPa, σ _in = 522 MPa, δ ₅ = 39%.

Example 3. The processing was carried out as in example 2, however, the sample was heated at a rate of 1 ° C / s, and post-deformation cooling was carried out in water to room temperature to increase the dispersion of the second phase. As a result of the TMT, an ultrafine-grained ferrite-pearlite metal structure was formed with an average grain size of 5 μm (Fig. 3), accelerated cooling led to an increase in the dispersion of the second phase. Mechanical properties of the rolled: σ _m = 418 MPa, σ _in = 601 MPa, δ ₅ = 26%.

Using the example of hot rolling, it was shown that a homogeneous ferrite-pearlite structure with an average ferrite grain size of ~ 5-6 μm and a high complex of mechanical properties was obtained from the initially cast metal structure after carrying out the proposed TMT method. Compared with the prototype in the presented conditions, the average ferrite grain size is formed two times smaller, the level of mechanical properties is 10-15% higher, in addition, the absence of an additional operation in the form of tempering reduces the processing time and energy consumption for production.

Thus, the proposed TMT method forms an ultrafine-grained metal structure, significantly increases the level of mechanical properties of microalloyed steels, reduces time and reduces energy consumption for processing. The indicated TMT method can be used for any metal forming processes, for example, rolling, forging, stamping, drawing, etc., and in particular it can be recommended for use in combined foundry and rolling complexes.

Claims (1)

The method of thermomechanical processing of a workpiece from microalloyed steel, comprising heating the workpiece to an austenitizing temperature and its deformation followed by cooling, characterized in that the workpiece is heated at a rate of from 0.01 to 50 ° C / s to a temperature of Ac ₃ ± 15 ° C, and then, with a strain rate of 0.1-50 s ^-1 , a single deformation with a degree of 40-50% or two deformations of 20-30% with an interdeformation pause of not more than 5 s is performed.

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