SU1456472A1 - Method of heat treatment of rolled stock - Google Patents

Abstract

The invention relates to heat treatment of rolled products and can be used in the manufacture of high-strength core reinforcement. The purpose of the invention is to increase cold resistance. Example. Steel grade 20GS with a chemical composition (in wt.%): C - 0.18; Si - 1.05; Mp-1.11 was melted in a converter and rolled on a continuous-billet mill to a blank 80x80 mm. The billet was rolled on a mill 250 to a core reinforcement of a periodic profile with a diameter of 16 mm with a rolling end temperature of 1050 ° C. With a rolling end temperature, cyclic cooling was performed before starting the intermediate transformation for 1.0-2.0 s, while cooling from quenching to martensite the surface layer was exposed to a depth of 0 to 15-0.2 R of the rod until the temperature reached 170 ° C on the surface, intermediate warming was conducted to 375 ° C for 0.65, and final warming led to reaching the surface. The number of cycles is 2. The reinforcement is hardened according to this mode, and at –60 ° C 0.63 Shch / m2, b at 900 N / mm2, 0.2 (L 700 N / mm, and according to the prototype method to 0.42 MJ / m2, bGb 550 N / mm G o2 400 N / mm 1 Cp f-crystals, 1 tab.

Description

The invention relates to heat treatment of rolled products and can be used in the manufacture of high-strength core reinforcement.

The purpose of the invention is to increase the worthiness of the hla.

The invention is based on the use of the feature of martensitic transformation to pass more completely with multiple cooling below the temperature Mn than with single cooling.

Example. Experimental melting of steel grade 20GS with chemical composition.

wt.%: C 0.18; Si 1.05; Mp 1.11 you-1 Flat 1 are in the converter, poured

into molds. Ingots from the hot of something. The garden on the blooming and the continuous mill is pierced on the work piece I mm. The billet in mill 250 is rolled to rod reinforcement with a diameter of 16 mm with a rolling end temperature of 1050 ° C. Next, with rolling heating, thermal hardening is carried out according to the modes corresponding to the proposed and known methods (table). MN Z70 with.

J

Yu

The temperature of the surface during cooling in different modes is determined by means of thermocouples and oscillography stamped on the surface of XA rods.

The surface temperature of the rods after the continuous heating during thermal cycling and window temperature. The data presented in the table indicate that the thermally hardened rod reinforcement obtained by the proposed method does not have the necessary requirements.

Armature hardened in mode 4 has a low impact strength at

warming of the surface (temp. Yu-60 C and low resistance to small plastic deformations m (small ratio,.),

The self-tempering behavior is determined using pyrometers of the type Apirs and Smotrich.

The thickness of the martensitic layer is determined by direct measurement on the transverse microfish of the rod after the first cooling cycle. During the second and more cooling cycles, the critical cooling duration is determined experimentally, at which the increase in the thickness of the martensite layer formed during the first cooling cycle does not begin. , and subsequently use this indicator in the hardening mode during cyclic cooling.

The duration of cooling cycles and intermediate warming ups by changing the depth of the intensive cooling sections and the pauses between them, as well as the speed of rolling. The intensity of cooling is controlled by changing the pressure of the water supplied to the cooling chambers,

Full-scale samples of rod reinforcement are strengthened according to the proposed modes and a known method, subjected to mechanical tensile tests to determine the limit of other

G E, and the yield point G ,. or conditional yield strength GO.I Standard samples are subjected to mechanical tests to determine the impact toughness s at

-BOT

The processing modes of the pilot batches, the structural state of the surface layer and the core zone and the mechanical properties of the reinforcement obtained using npejo iaraeMoro and known methods are shown in the table ..

The data presented in the table indicate that the thermally hardened rod fittings obtained by the proposed method provide the required requirements.

The reinforcement, hardened to mode 4, has a low impact strength at

-60 C and low ma resistance

plastic deformations m (small ratio,.),

0.2

The reinforcement, hardened in mode 5, has a low resistance to life and low strength characteristics.

The reinforcement manufactured by a known method has a low cold resistance and an even lower level of strength properties than during hardening according to mode 5.

Thus, rod thermally hardened reinforcement manufactured according to the proposed method acquires, along with high strength characteristics, high cold resistance and high resistance to small plastic deformations.

Claims (2)

Invention Formula 1 o A method of heat treatment of rolled metal, mainly rod reinforcement, using rolling heat, which includes cyclic cooling with surface subcooling at a given depth below the MH point during each cycle with intermediate and final surface warming up and final cooling, characterized in that increase cold resistance, supercooling of the surface is carried out at a depth of 0.15-0.2 R, 45 intercwarming is carried out to Mm + (5-20), and the final otoou  H heating - up to Mj, -b (100-250) С, where R is the radius of rod reinforcement. 2. The method according to p. 1, differs - 50 u and with the fact that cyclic cooling is carried out within 1-2 s with a number of cycles equal to two. Is P § about about sh about cho " “Oh oh