65Mn Carbon Steel

65Mn Carbon Steel

After heat treatment and cold drawing hardening, the strength is relatively high, and it has certain flexibility and plasticity; Under the same surface state and full quenching condition, the fatigue limit is similar to that of the colorful alloy spring. But the hardenability is very poor, mainly used for smaller size springs, such as pressure regulating spring, force measuring spring, general mechanical round, square coil springs or drawn steel wire for small mechanical springs.

Basic information

Chinese name：Spring steel

Foreign name：Spring steel

brand：65Mn

Standard：GB/T 1222-2007

density：7.85 g/cm³

Characteristics and scope of application:

After heat treatment and cold drawing hardening, the strength is high, with certain toughness and plasticity; In the same surface state and fully quenched condition, the fatigue limit is comparable to that of alloy springs. However, the hardenability is poor, mainly used for smaller size springs, such as pressure regulating spring, force measuring spring, general mechanical round, square coil springs or drawn steel wire for small mechanical springs.

Chemical composition

Carbon C :0.62~0.70

Silicon Si:0.17~0.37

Manganese Mn:0.90~1.20

Sulfur S :≤0.035

P :≤0.035

Chromium Cr:≤0.25

Nickel Ni:≤0.25

Copper Cu:≤0.25

Mechanical property

Tensile strength Rb(MPa):735

Yield strength Rs (MPa):430

Elongation δ10 (%):14~21.5

Section shrinkage (%): not less than 10

GB_T699-1999(high-quality carbon structural steel)

Hardness

Hot rolling hardness :240~270HB

Cold rolling soft hardness :190~220HB

Cold rolling hardness :300~340HB

Heat treatment hardness :38~60H

Heat treatment

Folding heat treatment and specification

Quenching 830℃±20℃, oil cold; Temper 540 ° C ±50 ° C (for special needs,±30 ° C).

Critical point temperature (approximate value)Ac1=726℃, Ac3=765℃, Ar3=741℃, Ar1=689℃, Ms=270℃.

Normalizing specification: Temperature 810±10℃, air cooling.

Quenching, tempering specification: quenching temperature 830±10℃, oil cooling; Tempering temperature 540℃±10℃, water, oil cooling.

Folded delivery condition

Hot-rolled steel is delivered in heat-treated or non-heat-treated condition, and cold-drawn steel is delivered in heat-treated condition. (2.0-16)*1250*C steel/hot coil/hot plate

50Mn (2.0-16)*1250*C Lai-steel/hot coil/hot plate

65Mn (2.0-16)*1010/1250*C steel/hot coil/hot plate

Weight calculation

Plate: length (M)* Width (M)* thickness (mm)* density =KG

Bar: Radius * Radius *3.14* High * Density /1000000=KG

Annealing specification

Traditional cyclic spheroidizing annealing process, annealing temperature 750℃, hold for 2h, furnace cooling to temperature (680±10)℃, hold for 3h, and then furnace cooling to 550℃, air cooling. Low production efficiency, oxidation and decarburization rate of 22%-40%, surface hardness and elasticity can not meet the requirements. New process of incomplete annealing, annealing temperature (740±10)℃, heat preservation for 4h, furnace cooling to 550℃, air cooling. Tensile strength 600-620Mpa, elongation of 53.5%-40%, hardness 209-214HBW metallographic structure of spheroidized pearlite + a small amount of point pearlite, shorten the production cycle, save energy.

New annealing process

Traditional annealing process, annealing temperature 730℃, holding 13h, and then cooling to 650℃, air cooling. New annealing process: annealing temperature (860±10)℃, insulation 45-60min, furnace cooling to (750±10)℃, insulation 3-3.5h, after the furnace cooling to 650-660℃, the oven pile cold or into the insulation pit slow cooling. Metallographic structure meets the requirements: pearlite structure of 2.5-6, with about 4 level as the best, the process improves the efficiency of 80%-100%.

Heat treatment

65Mn low alloy round steel must have high elastic limit and high yield ratio to avoid permanent deformation of spring steel under high load. At the same time, it also requires good hardenability and low decarbonization sensitivity, so that the elastic limit is greatly reduced; And good surface quality, easy to process in hot and cold state and good heat treatment processability.

Heat treatment process of spring thermoforming spring steel formed in hot state. Most of the spring steel formed by this method is a combination of thermoforming and heat treatment, and most of the spiral spring steel is heat treated after thermoforming. The heat treatment method of this spring steel is quenching + moderate temperature tempering, and the structure is tempered trostenite after heat treatment. This kind of structure has high elastic limit and yield limit, and has certain toughness.

Adopt new concepts and methods, and innovate the development of stability control technology. Carefully analyze the formation mechanism of problems such as "rolling break and tail spin" that are most likely to occur in this "0.4 seconds "time, and carry out work from many aspects such as reducing roll damage and reducing tail deviation. After more than 3 years of software program development, tracking test, evaluation, analysis to determine the reasonable process parameters.

65Mn steel plate strength, hardness, elasticity and hardenability are higher than 65 steel, with overheating sensitivity and tempering brittleness tendency, water quenching has a tendency to crack. The machinability of annealed state is reasonable, the cold deformation plasticity is low, and the weldability is poor. Moderately loaded plate springs, coil springs with a diameter of 7-20mm and spring washers. Spring ring. High wear resistance parts, such as grinding machine spindle, spring clamp, precision machine tool screw, cutter, spiral roller bearing sleeve ring, railway rail, etc.